ATOLL RESEARCH BULLETIN No. 50 Geology of Kapingamarangi

Transcription

ATOLL RESEARCH BULLETIN
No. 50
Geology of Kapingamarangi Atoll,
Caroline Islands
by
Edriin D. PIcKee
THE PACIFIC SCIENCE BOARD
National Academy of Sciences--Natianal.Research Council
Washiii&ton,. D. C.
June 30, 1956
Page
.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknovledgriients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A t o l l fra~nework. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Geology of the islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Character of i s l a x i s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lagoon beaches and bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sear.iard beaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
R a g a r t and rampart wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Migration of islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Problem of Xapingamararigi e a c h r o c lr. . . . . . . . . . . . . . . . . . .
Petrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parent materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A l t e r a t i o n processes ..................................
Eelation of s o i l t o posi-ti03 on is:.and . . . . . . . . . . . . . . . .
DevelopneilL of p11osphor.i-ie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generai f e a t u r e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Objectives of investigatioi? . . . . . . . . . . . . . . . . . . . . . . . . . . .
Methods of si;udy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Depth t o ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Variations i n water l e v e l . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
La!: i n r i s e and f a l l of g ~ o u n d7.iater . . . . . . . . . . . . . . . . . . .
Relative permeability of seaj.riier~tarymateri.als . . . . . . . .
E f f e c t s of i s l a n d s i z e on leiis . . . . . . . . . . . . . . . . . . . . . . . .
Quali-ty of t h e ground water . . . . . . . . . . . . . . . . . . . . . . . . . . .
Near-shore currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sedimenta-tion i n the lagoon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Geology of t h e patch r e e f s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References c i ted
,
..........................................
.
.
3li.
5.
6.
Figure 1
2
.
7
8.
9
1.0
.
.
11
Geologic map of Torongahai I s l a n d . . . . . . . . . . . . . .
Geologic map of Ringwtoru and Rikwnanu Islands . .
Geolagic map of Nunalrita I s l a n d . . . . . . . . . . . . . . . . .
Geologic map of Werua I s l a n d . . . . . . . . . . . . . . . . . . .
Geologic map of Taringa I s l a n d . . . . . . . . . . . . . . . . .
Geologic Map, of' Matiro 1sl.arld . . . . . . . . . . . . . . . . . .
Geologic map of Matulietuke Island . . . . . . . . . . . . . .
Geologic map of Hare I s l a n d . . . . . . . . . . . . . . . . . . . .
Geologic map of P m a t a h a t i I s l a n d . . . . . . . . . . . . . .
Geologic ma2 of Natukerekere Island . . . . . . . . . . . .
E r o f i l e s of lagoon beaches and d i s t r i b u t i o n of
beach sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1
Page
Figure 1 2 ,
'Iypical s o i l profi.les i n t e s t pl.ts on Ringui;oru
end k'umatahat,i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13. Typical s o i l p r o f i l e s i n t e s t p i t s on Riirvmanu,
Pwakahi and Tokmgo 1sl.aniis . . . . . . . . . . . . . . . . .
1.4. Lithology and water l e v e i s i n wells on 'l'aringa
Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15. Lithclogy and water l e y e l s i n wells on Werua
Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6s. Tide and well. f l u c t u a t i o n s , Taringa Island, June
23-24, 1954.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16b. Tide and weli fluctutitions, , Taringa Island, J u l y
30-31, 1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16c. Tide and well f l u c t u a t i o n s , Taringa Island, Aug.
20-21, 19jk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17a. Tide and .*r,ell ,fluc,tuations, hTerua Isl.ar.d, J-me
23-%!$, 1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
l.7b. Tide arid well f l c c i x a t i o n s , Werua Island, J u l y
30-3i, 1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
172. 'I'icle and well f l u c t u a t i o n s , Werua Island, Aug.
20-21, 1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
:1.8a. Tide tiad :re].:. fluctutitions, Hukuniu arid. ParaIrahi
IsleLs, July 30-31, 1954 . . . . . . . . . . . . . . . . . . . . . .
18b. Tide and well f l u c t u a t i o n s , Xuiruniu and Parakahi
I s l e t s , Auk:. 20-21, 1951: . . . . . . . . . . . . . . . . . . . . . .
Near-shore
currerits of two soutlie:rn, ixo e a s t e r n
19
ana one nort;?ern i s l a n d s of KapYngarnarar.gi . . . .
20. Near-shore currents of two e a s t e r n and two
norther;l i s l a i ~ d sof Kapingmarangi . . . . . . . . . . . .
21. Sections across lagoon, v e r - t i c a l exagzeration
approximately X30 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22. Offshore p r o f i i e s , eas.t and south sections of
a t o l l arid d i s t r i b u t i o n of bottom sedjments . . . .
23,. P r o f i l e s of Ivianin patch reef . . . . . . . . . . . . . . . . . . . .
24. lso~oathicl i n e s of Kapingamarangi Ato1.l comgiled
from data on U, S. Navy Hydrographic Cha,r-t 6042
25. Relative proportions of p r i n c l p a l t y ~ e sof
sediment a t 5-root depth i n t e r v a l s a s determined
by sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F i e i d sketches of patch r e e f s showing d i s t - i b u t i o n
of sediments and c o r a l s ........................
lac
1.8d
22a
22b
,
Table 1. C h a r a c t e r i s t i c s of lagoon beaches . . . . . . . . . . . . . . . . .
2. D i s t r i b u t i o n and c h a r a c t e r i s t i c s of ramparts and
rampart wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 . Mineral composition of Kapingamarangi sediments
a s determined by X-ray d i f f r a c t i o n pa-tterns . . . . .
4. Elements i n Kapingamarangi s o i l s determined by
semiquantitative spectrographic method . . . . . . . . . .
26a
26b
2 6 ~
26d
26e
26r
26g
26h
28a
28'0
30a
3Ob
3Oc
306
Table
5.
6.
7.
8.
9.
10.
Runice analyses; elements determined by semiqua.ntj.ta-Live syec'irogra;~hic method . . . . . . . . . . . . .
Percentages of a p a t i t e a s deterinined by X-yay
d i f f r a c t i o n analyses ...........................
h a l ~ p e sof' %rater. samples fro^:! t e s t w l l s and
comparative d a t a for normal s e a water . . . . . . . . . .
Depth ( i n f e e t ) of :.agoon f l o o r surro~.urdir~gMmirl
patch reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Some c h a r a c t e r i s t i c coi-a1 assemblages on KzplngalnarangiAtol1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thickness ( i n inches) of sand accumulations on
patch reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page
-.-1%
21
27
311.
35
35
Kapingamaraiigi A t o l l i s located a t .the southerrmost end of t h e Caroline
.roup of i s l m d s , s l i g h t l y rimre than 1' north of t h e i$quatf>i.. It i s about
k10 miles s0xthcas.t of T n k and 350 mlles novth of I?a'uaul i m New Bribain.
This i s o l a t e d a t o l l s u r r o m d s a lagoon al>out 6 miZes across fzom e x - l ; t o x e s t
and s l i g h t l y l e s s ffora n w t h t o south. It i s inhabited by 1125Po!.ynesians
(19511), mos-t of vhom l i v e on Timhou and Werua i s l a n d s on t h e e a s t e r n s i d e .
~ ~ t been
D E . G R ~ ~ofS geographic s e t t i n g , cl.ima:te, and general e : i v i x - o ~ : ~ ehilve
treatec?. H. J . %icws o w i l l not be iacluried h w e .
This report on t h e gectlogy of Ihpingamar'angi A t o l l covers prelimi.riary
resul", f f r ~ i lf i e l d investiga%ioi:s conciuc'ted during l a t e J w e , J
, and AUg u s t of 1954 and l z i ~ o r a t o l yexamination of specimens made d u r i ? ? -the
~
winter
of 1951!-1955. Much a t t e n t i o n has been devsted t o s t u i i e s of t h e islands, with
s p e c i a l emphasis oil t h e c l a s s i f i c a t i c n of sedimeuts an& sedimentary rocks, t h e
occurrence %,id. behavior of grouiXl ::ater, and. t h e distribu-tion of s o i l s . Det a i l e d s t u 6 i . c ~a l s o were made of -t;ile processes of seiliinen-tation t h a t curreiltly
a r e q e r a t i n g bot;h oa t h e reef &id i n t h e lagoon. These s-Ludies incl.uded t h e
making of deta5.3.ed aina,lyses of beach aad bar s t r ~ c t u r e s ,t h e recor::stru.ction
of reef acd offshore p r o f i l e s , and t h e sysi,ema-ti2 sampling of t h e lagoon f l o o r .
Termiiiology m e d i n t h i s r e p o r t f o l i o > ~ s ,i n general, t h a t reconumnded by
Trace:? and othe;s (1995) i n t h e i r receiit p a i e r t l - i l e d "Conspicuous f e a t u r e s
of organic ~ e e f s". The terra " a t o l l " i s useu f o r t h e peri;3lieral reef arid
everythiiig ~ r i t h i iit.
~
The upper surface of t h e p e r i p h e r a l r e e f , except where
covered by i s l a n d s , i s r e f e n e d t o as t h e reef f l a t . Small r e e f s within t h e
lagoon, i c d i a r i t i s t h a t heve been ca1l.ed patch r e e f s , small t a b l e
r e e f s , reef knolls ma reef pinriacles, a r e discussed under the ger.ei-al designation of patch r e e f . Dense growths of staghorn o r branchinl: c o r a l s a r e r e f e r r e d t o a s t1iic;rets. Other terms for geomorphic and organic f e a t u r e s a r e
expl.ained i n t h e t e x t wherever t h c i r meaning is not apparent.
The geokogical iilvestigation described i n t h i s repa?t ms conducted a s
p a r t of a p r o j e c t of Vne P a c i f i c 'Science B0ar.d of t h e NzrLiona!. Hesearch Counc i l and ?!as supported 'oy funds from t h e Office of' Naval Research through i t s
contrac-t Wronr-29104 ('NR ,388 001) with t h e PJaational Acade~~y
of S c i m c e s . The
U. S. Navy Depa.rtment aild t h e ~ M i l i i a r yA i r Transport Service furnished t r a n s p o r t a t i o n t o aiid from t h e a t o l l and t h e Navy Department a s s i s t e a g r e a t l f by
supplying many items of equipment. The C i v i l Administi,ative s t a f f of t h e
T r u s t T e r r i t o r y of the P a c i f i c Islands was h e l p f u l i n milily vays
.
Many thanks a r e due Harold Coolidge, Lenore Smi:th,and Ercestine Akers
of t h e P a c i f i c Science Board f o r t h e help t,hat they renaered. t h e p a r t y . App r e c i a t i o n i s a l s o e,upressed t o iienneth P. &lory of t h e Bishop hiuseurn i n
Honolulu f o r h i s b r i e f i n g s on t h e a t o l l and i t s inhabitan-& and f o r personal
introduction t o i t s peop2.e. Preston Cloud and Joshla Tracey of the U. S.
Geological Survey \,rere both extremely h e l n f u l with sugges-tioils f o r t h e work
and with t h e loan of scj.enti.fic equi-gme;i,t.
My associates in the field. pazty were Cadet Iiand, Robert R. EIarry, Id.
Jar1 Newhouse, W i l l i a m Niering, and H. J. Wierls, a l l of whom cortributed i n
various ways totrard the developmer-t of t h i s report. The base maps of t h e
i s l a d s prepared by Wiens were e s p e c i a l i y important i n carrying out a genl o g i c a l nrogram arrd the a s s i s t a x e of Niering i n soil. s t u d i e s arid t i d e recording i s g r a t e f u l l y ackrrowledged. I<api.ilgans who served f a i t h f u l l y a s
a s s i s t a n t s throughout the s m i e r were Tai'tos i n t e r p r e t e r , and Aisea, Exsol,
and Turibureti, boatmeii and t e s t - p i t diggers.
,
I n the study of collections and samples of materials, I have been a s s i s t e d by a nurilber of s p e c i a l i s t s , a d it i s with pl.easuz-e tha.t I ackno:~rledge
Che following cooperation:
--
Coral i d e n t i f i c a t i o n
John W. Wells, Cornell U!liversity.
Foraminifera i d e n t i f i c a t i c ~ n Ruth Todd, U. S. Geological Survey.
Analyses of water from wells arid. lagoon
john Hem, U. S. Geological
Survey.
X-ray 'diffraction i d e i l t i f i c a t i s n of mirierals
A. J. Gude 111, U. S.
Geological Survey.
Analyses of elements i n s o i l s -- P. R. Barnett, U. S. Geological
Survey.
--
--
--
For c r i t i c a l reading of - h e manuscript and many helpful su~;gestioi.ls,
t h e w r i t e r i s indebted 'GG G. D. Robinsoil of the U. S. Geological Survey,
John Chronic of t'ne University of Colors~do, and Halka P, Chronic.
THE ATOLL ~.UEI.JORK
The peripheral reef of Kapiiigamararrgi A t o l l ( f i g . 24) e n c i r c l e s ail oval
lagoon, almost cormple-tely s e p , r a t i n g i t s waters, especially a t times of lo%!
t i d e , from those of the surrounding sea. The only major breaks a r e r e l a t i v s l y
narrow passes on the south s i d e where channels nearly 20 f e e t deep permit
strong currents t o flow i n and out continuously. This peripheral reef includes what has a p t l y been termed t h e "frame" of the reef complex o r reef
e r m t h of organisms, especially
mass, arid i s a l a t t i c e constructed -through the -;
corals and c o r a l l i n e algae. A s s t a t e d by Cloud ili)52a, p. 2128), these organisms "serve t o holc! i t b h e reef7 together, and the frame they b u i l d is
a t r a p f o r c l a s t i c o r chenicallg pyecipitated sediments."
--
nearly 4,000 f e e t
The surface of the peripheral reef i s widest
across
near t h e northernmost s e c t o r , although it i s almost a s wide i n the
extreme western p a r t ( f i g . 24). On the sov.thern arc, west of the main
passes, t h e surface i s no wider than 1,000 f e e t . Tfie 33 islands d i s t r i b u t e d
along t h e e a s t e r n half of t h e reef a.pgear a s very low mounds t h a t r i s e
s l i g h t l y above t h e general f l a t top along i t s lagoonmrd margin. They alone
--
stand above the l e v e l of high-tide waters. El.sewhere along ?he a t o l l , especia,l?.y on t h e southwectern, western, and nor'cnwestem s e c i o r s , t h e reef
surface i s d.iride4 i n t o a seavard slope anu a lagoolivai-d. slope by a lovr b u t
d e f i n i t e c r e s t . Bokh s?.opes a,re extreneiy geii+~Lei n most ~ l a c e s . The:. a?:e
r e f e r r e d t o i n t h i s paper a s the outer reef f i a t , a n d the i m e r reef f l a t .
The essential1.y f l a t top of ?:early a l l the outer park and sone of t h e
inner p a r t of t h e reef fc~rmsa p i t t e d rock pavemen-t. Over wide areas t h i s
surface contains no organisms now contributing appreciably t o grcwth of the
r e e f . To the contrary, i - t appears t o be s o l e l y the resu-lt of the wearing
d o ~ i l ,by waves and currents, of c o r a l mmsses t h a t once stood. higher than the
present surface. Eviderlce from Okinawa obtained by MacNeiL (1950) indicates
t h a t s i m i l a r surfaces there a r e t h e r e s u l t of recent wave o r solution planat i o n . Other siniilar reef f l a t s reported from many islands of tile :Pz.cific
suggest, a s sLated by various geologists, t h a t t h i s wiciespread f e a t u r e i s the
e f f e c t of a recent lowering of sea l e v e l irith r e s u l t a n t death of a l l corals
back from t h e reef eGge, fol.lmred by a be.veling of higher p a r t s of t h e reef
structure.
The present surface of t h e reef f l a t appears t o r e s u l t from an essent i a l l y s t a t i c position of the sea f o r a time sufficieiit t o develop a general
evenness of planation and a condition of near s t e r i l i t y over wide a r e a s .
Boodlea cover extensive areas of the
Today, small l i v i n g algae of the genus ----.
rock surface; mollusks and other marine anima2.s con@;regateal-ound and under
limestone boula.ers and cora.1 heads t h a t a r e strewn over. tiie rock surface
debris-washed across from the seaward s i d e . Brl-ctle stars., e e l s , and marine
worms i n h a b i t cracks and c a v i t i e s t h a t extend down i n t o t h e rock mass. Liv-'
ing corals and c o r a l l i n e algae, howver, a r e l a r g e l y r e s - t r i c t e d t o the seaward margins 01the reef and, where isl.a!lds a r e absen-t, t o wa.tei-s of' t h e
inner reef a r e a bordering the lagoon e d ~ e .
--
C l a s t i c sediments a r e r e l a t i v e l y . s c a x e over much of t h e present reeff l a t surface, but a r e p ~ o g r e s s i v e l ymilo:-&! abundaat toward t h e ' i m e r margins
of the reef where they fokm a veneer t n a t covers a framework of coral. The
small amount of f r a g e n t a l rraterial on the outer s i d e of t h e reef' f i a t cons i s t s l a r g e l y of c o ~ a an&
l
c o r a l l i n e a l g a l de'bris, up t o and including
boulder size,, strewn over the surface, and of e l a s t i c p a r t i c l e s from mollmk
s h e l l s and echinoid spines, concentrated i n pockets and c r a c k s . Foraminifera
of t h e genus Calcarina t h a t a r e reported a s common on t h e reef f l a t s of m.@njj
Pacific a t o l l s a r e absent here; few Foraxinifera o f any type occur on t h e '
seawardparts of t h e a t o l l . The t e s t s of t h e s e arlimals accumulatein quantit i e s s u f f i c i e n t t o ' forin 'deposits.d f lime sand o:~lx bn the i s l a n d 1-agoon
beaches and on the inner p a r t s of -the a t o l l . A s poi.nted out by Sollas (1904,
p. 6, 7 ) however, such l i n e sands u l t i m a t e l y fill many of t h e i n t e r s t i c e s
i n the framework limestone mass, and they develop i n t o extensive deposits on
the inner s i d e of the ''retaining
wall"
of c o r a l and a l g a l s t r u c t u r e s .
.
.
.
Attempts were made a t ~ a ~ i n ~ a m a r taon determine
~i
the l i t h o l o g i c chara c t e r and s t r u c t u r a ~f'e a t u r e s of the framework limestone through s t u d i e s of
material exposed i n cracks belo7.1 t h e pavement and of l a r g e aoulders washed
up from seaward exposures. The investj.gatio13 was hamered b~the extreme
a i d by a genezal i.ack of na.tural
d i f f i c u l t y of digging i n t o the reef
breaks elcpocing sections, b u t from a s e r i e s of samples some genera1.Lzations
can be made. I n ma,n:r spec?.rr.e?~s,the reef rock appears aphanitic, but i n
others the r e l i c t s t r u c t u r e s of corals a r e c l e a r l y preserved.
The framework limestone a s a whole seems t o be very cavernous, although
small masses and hand specimens c ~ ~ m l o n lhave
y
a r e l a t i v e l y low apparent
porosity. Cavernous structuxe, observed i n near-surface e:xavations, probably extends t o considerable depths. This i s inaicated by t h e behavior of
t h e fresh-water lens on various islands, i n ~ h i c ha l l p a r t s of the lens r i s e
simultaneously and with a simil.ar t i d a l l a c (2escribed under "Ground water").
It a l s o i s suggested by evidence from the C r i l l holes a t Funafvti ( ~ o l l a s ,
1904, p . 6) and a t Eniwetok Atoll a add e t a l . , 1953, p., 2259). Oil the
o-ther hand, some of vhat o r i g i n a l l y were c a v i t i e s appear t o have been f i l l e d
with c l a s t i c sediment. This f e a t u r e has been noted by Neweli (1954, p . 1 0 )
i n reference t o reef blocks from the outer edge of the reef f l a t a t Raroia.
The reef-buildiag organisms thai; contribute c h i e f l y t o the framework
linestone, a s judged by the forms currentiy growing a l m g t h e eastern seaward margin of the a t o i l , a r e very l a r g e l y corals but include soce nasues
of the c o r a l l i n e a l g z -Porolithon
onimdes. The corals a r e represented by
.-many species ( t a b l e 9 ) ; t h e most cmimon belong t o the genus Acropora, except
along the inner margin, where microatoils of P o r i t e s l u t e % a r e dominant.
Suggestion t h a t much of the limestone beneath the presenb reef f l a t i s composed of a comparable assemblage i s found i n -th- mineral content of s e l e c t e d
samples examined by X-ray d i f f r a c t i o n met!nods,~7 A l l specimens t e s t e d show
--
I./.
-
Analyses by A. J. Gude 111, U. S. Geological Survey.
90 percent o r more aragonite, which percentage probably r e f l e c t s the proport i o n of coral, thouzh a small atnoun-t of aragonice roc$ be due t o irl-terstiti 1
deposits of c l a s t i c s h e l l s . Five t o 1 0 percent of high-magnesium calcite-27
2/ Iiigh-magnesium c a l c i t e , a s opposed t o low-magnesium o r norrial c a l .+.
c i t e , i s discussed by Chave (1954, p . 267). Iie points out t h a t c a l c i t e of
alga!. s t r u c t u r e s contains more than 1 0 percent magnesium carbonate, whereas
t h a t i n mollusks and c e r t a i n ot'ner organisms contains l e s s than 2 percent.
i n some specimens suggests the amount of a l g a l contribution. A lack of normal c a l c i t e i n a l l samples indicates Vnat t h e common reef-dwelling Forami n i f e r a of the genus Amphistegina were not included i n the samples examined.
Unfortunately, no data a r e yet a v a i l a b l e on t h e l i t h o l o g y or s t r u c t u r e
of the Kapingamarangi reef a t appreciable depths below t h e pavement; of t h e
reef f l a t . Judging from records of v e l l s d r i l l e d on other a t o l l s (F'airbridge,
1950, p, 384), however, one might expect t o f i n d zones of c l a s t i c ma-terials
representative of v a f i o u s depths and einvironments, a l t e r n a t i n g v i t h zones of
reef-forming corals and algae s i m i l a r t o those on the surface today. N.1 such
changes a t depth appear t o be r e l a t e d t o times of advance and r e t r e a t of t h e
a c t i v e l y growing framework corals and c o r a l ~ i n ealgae and probably were cont r o l l e d by r e l a t i v e changes of sea, l e w l and s t i l l - s t a n d s . Both t h e upward
and the l a t e r a l deoe1oprnen.t of t h e lj-mestone framework a r e a record of tectonic and clima-tic events.
GEOLOGY OF T I a ISTAWS
Character
of the islands.-. Thirty--three islands a r e d i s t r i b u t e d along
---...tne arc -that forms the eastern, rrindviard peripheral reef of Kapingmarangi
A t o l l . The l a r g e s t i s IIare Island, vhich i s more than a mile long and 600
f e e t vide, and the s1:iallest i s Matukerekere Island, vknj.ch i s about 130 f e e t
long and supports b u t a s i n g l e mature t r e e . Sou~eof -i;hese islands a r e
composite, having a t t a i n e d t h e i r presen-t s i z e s by the combining of two or
more small islands through processes of sediaentation. Other islands probab1.y represent various stages of diminution through p a r t i a l destruction o r
dissection r e s u l t i n g from cyclonic storms.
The o r i g i n of islands perched on oceanic a-tolls i s a problem about which
man has speculated f o r a long time. Some e a r l y views on t h i s subJect a r e
recorded i n the l o g of Captain Cook (LI-ojd, 1949, p. 266) under the 6at.e of
April 17, 1777:
"There a r e d i f f e r e n t op;nions amongst ingenious t h e o r i s t s , coi?cerning
the formation of such low islands as ~ a l m e r s t o n ' s Some w i l l have it, t h a t ,
i n remote times, t,hese l i . t t l e separ'ate heads' or i s l e t s were joined, arid
formed one contiliued arid more elevated trac-t of land, which t h e sea, i n the
revolution of ages, has washed away, leaving only the hi;;her grounds; which,
i n time, also, w i l l , according t o t h i s theory, share the same f a t e . Another
conjecture i s , t h a t they havebeen thrown up by earthquakes, and a r e t h e
e f f e c t of i n t e r n a l convulsions of t h e globe. A t h i r d opirioii, and which
appears t o me a s the most probable dne, maiiltains t h a t they a r e formed from
shoals, o r coral banks, and of consequence increasing."
.
I11 order systema-tically t o accumulate data r e l a t i v e t o the islands on
Ka.pingamarani$. Atoll, geologic maps were prepared during t h e suumer of 1954
f o r a l l of t h e l a r g e r and some of t h e smaller ones ( f i g s . 1 t o 1 0 ) . IsLand
maps on a s c a l e of ore inch ecpals 100 f e e t , compi!.ed and surveyed by H. J .
Wiens, furnished bases t o work on. The d i s t r i b u t i o n of materials was p l o t t e d
according t o the classifica.i;ion discussed i n the section of t h i s report on
"l?etroiogy." Dips i n sedimentary s t r a t a were recorded on t h e maps.
Analysis of the
maps indicates t h a t Xapineamarangi islailds
a r e forrned of three p r i n c i p a l c l a s s e s of material: ( 1 ) sedimentary rocks
formed through t h e cemensation of clas'cic p a r t i c l e s and organic remains,
( 2 ) unconsolidated sediments of beaches and bars, and ( 3 ) s u r f i c i a l deposits
forming the ramparts, rampart wash, and s o i l s ( n o t mapped) t h a t g a r t l y
cover and mask the other two. On t h e basis of the d i s t r i b u t i o n and s t r u c t u r e
of these three classes of material, much of the i s l a n d h i s t o r y may be i n t e r preted.
Sedimentary rocks.- Beds of sedimentary rock r i s e above t h e reef f l a t s
along t h e seaward margins of a l l t h e l a r g e islands and many of t h e small ones,
and they crop out l o c a l l y within many islands. Because i n most places the
c l a s t i c p a r t i c 2 . e ~of which they a r e formed a r e c l e a r l y d.iscernib1.e and because t h e i r s t r a t i f i c a t i o n cownonly i s prominent a f t e r weathe~ingthese
rocks, f o r the most p a r t , a r e r e a d i l y distinguishable from t h e reef rock on
vhich they re&.
I s o l a t e d pedestals and undercut bl.ocks formed. of s i m i l a r
c l a s t i c rock stand on the reef f l a t considerable distances seaward fmm some
islands
reimants of e a r l i e r island. masses. Conspicuous illus-brations a r e
on the f l a t s e a s t of Werua Island. Likewise, r e l i c t pla.tforms o f s t r a t i f i e d
c l a s t i c rock, mrn t o a low l e v e l .through planation but stand-ing above t h e
coral rock of the reef f l a t , extenir 11.00f e e t northeastward from T'orongahai
Island.
--
Evidence furnished by t h e d i s t r i b u t i o n of erosional remimts of s t r a t i f i e d rock suggests t h a t the seaward shores of a l l Kapin~aroarangiislands
have been retreating: f o r a considerable time. Similar evidence on Raroia,
iwdicating r e e f - f l a t extension a t t h e expense of islacds, has keen noted by
Kevell (1954, p . 1 4 ) . A second feaLure t h a t tends t o support t h i s concept
i s the o r i e n t a t i o n of cross-s+,ra';ification along shore-line exposures of
i s l a n d rock. On many islands, of which Werua i s an excellent i l l u s t r a t i o n
( f i g . h ) , the s-brats i n rocks t h a t form t h e seaward coast dip exclusively
lagoomard over lorig s t r e t c h e s i n t h e same manner and degree a s s t r a t a i n tihe
modern lagoon beaches. This f a c t suggests t h a t s t r a t a i n the two places were
developed i n a s i m i l a r manner and., therefore, t h a t t h e deposits forming these
rocks accumulated a t a time when the lagoon pargin was i n t h e present posit i o n of the seaward shore. S t i l l further evidence of i s l a n d r e t r e a t i s
presence of the mineral a p a t i t e i n c o a s t a l s t r a t i f i e d rock on Nunakita and
Ringutoru Islands i n wave-washed a r e a s beyond the present l i m i t s of t r e e s ,
This l o c a t i o n indicates t h a t phosphorite must have developed a t some time i n
the p a s t vhen these l o c a l i t i e s were t h e i n t e r i o r s of islznds and vhen guano
from b i r d s was accumulating nearby.
The present d i s t r i b u t i o n of s t r a t i f i e d rock indicates not only a former,
more sear,rard posi-tion of the islands b u t a l s o a higher surTace l e v e l . S t r a t i f i e d rocks on various islaads, especialiy prominent on Rikumanu a l d
Ringutoru, stand 4 t o 5 l'eet above t h e present high-tide l e v e l . These rocks
a r e formed of c l a s t i c p a r t i c l e s and. a r e c r o s s - s t r a t i f i e d ; they tippear t o be
leaclled and p a r t l y phosphatiz,ed. Rocks having a similar high-level p o s i t i o n
i n many a t o l l s of the Pacific have been recorded avid and Sweet, 1904, p .
67-66; Ladd e t a l . , 1950, p. 413) and a r e generally considered t o represent
deposits r e s i d u a l from a time twhen, owing t o e u s t a t i c changes, sea l e v e l was
higher than a t present.
Lagoon -.beaches and bars.- Larse p a r t s of most of the present i s l a n d s ,
lagoonward sides, a r e composed of unconsolidated. c l a s t i c materials and foraminifera: sands. Such sediments a r e accumul a t i n g today on t h e bars o r horns projecting i n t o the lagoon from both er:ds
of each i s l a n d and along the incurving beaches between these bars ( f i g s . 1
t o 1 0 ) . Test p i t s an& .wells on various islands indicate t h a t s i m i l a r unconsolickted materials extend dcr~rnwardi n many places a t l e a s t as f a r a s lowwater l e v e l , 3 o r 4 f e e t below the surface. Sedimentary s'zuctures,
especially s t r a t i f i c a t i o n , f u r t h e r show t h a t t'nese sediments were deposited
l a r g e l y a s beaches, dipping lagoor?ward, and a s b a r s .
inclu-~
a i- r t u a 1 . 1 ~
a l l of-he
'
EXPLANATION
0
Beach or bar sand
Aphanitic to granular limestone
p
z
J
a
Beoch or bar rubble
Rampart boulders
Corol rubble con lomerate
Rampart rubble
Limestone boulder canglomerote
Wash rubble
a*
Puraka pit
d oO
Strike and dip of beds
*
a
House
Fxa
FIGURE I. - GEOLOGIC MAP OF TORONGHAI ISLAND
0
500 Feet
RIKUMANU
FIGURE 2.- GEOLOGIC MAP OF
0
RINGUTORU AND RIKUMANU ISLANDS
500 Feet
EXPLANATION
rn
Rampart boulders
i':,.i,.q
.
Romport rubble
DJ
Wash rubble
Beach or bar sand
Beach or bar rubble
m
m
Coral rubble conglomerate
Limestone boulder conglomerate
m
Aphanitic to granular limestone
a
Purako nit
0
House
FIGURE 3- GEOLOGIC MAP OF NUNAKITA ISLAND
0
I
I
I
,
I
500 Feet
EXPLANATION
Beach or bor sand
Rampart boulders
Beach or bar rubble
R a m ~ o r trubble
m
100.0 1
E
Y
s
Wash rubble
a
m
rn
Puroka pit
1~2"
Aphanitic to gronular limestone
C]
House
FIGURE 4. -GEOLOGIC MAP OF WERUA ISLAND
0
I
I
I
I
I
500 Feet
EXPLANATION
Beach or bar sand
Rampart boulders
Beach or bar rubble
Rampart rubble
Wash rubble
pq
m
Q
Puroka pit
9 O
a
House
1
S t r i k e and dip of beds
FIGURE 5.-GEOLOGIC MAP OF TARINGA ISLAND
0
5 0 0 Feet
EXPLANATION
Rampart rubble
r
J
Beach or bar sand
Beach or bar rubble
FIGURE 6 --GEOLOGIC
MAP OF MATIRO ISLAND
500 Feet
0
I
I
I
I
I
EXPLANATION
limestone
Strike ond dip of beds
FIGURE 7.-GEOLOGIC MAP OF MATUKETUKE ISLAND
0
500 Feet
FlGU RE 8
.-
GEOLOGIC MAP OF HARE ISLAND
0
500 Feet
w
1954
EXPLANATION
Beach or bar sand
Wl
B e a c h or bar rubble
m
Carol rubble conglomerate
m
Rampart boulders
Rampart rubble
rn
Wash rubble
,so
Limestone boulder conglomemte
0
House
1
E 9.-GEOLOGIC
MAP OF PUMATAHATI ISLAND
FIGURE 10.- GEOLOGIC MAP OF MATUKEREKERE ISLAND
50
100 Feet
I . 2
0
Beaches and b a s on a l l of the major islands were n ~ ~ p e dand
, details
of t h e i r struc-Lure were recorded from trenches dug a t r i g h t angles t o t h e
strand on Taringa, Pemkahi, IuIatiro, l%matahati, and Singutom Islands. Res u l t s of these stild.ies must at1ai.t d.escription and axtPysis a t a l a t e r date,
but some s a l i e n t features a r e shown on t h r e e i y p i c a l b e d l profil-es ( f i g .
11). The f o r e s e t beds of. the beaches dip from h0 t o 11' lagoonward, except
f o r s h o r t distances immediately below beach c r e s t s , whei.e many dip as much a s
15' t o 20' ( t a b l e I ) . Backshore beaches commonly a r e h o r i z o ~ ~ k a but
l , sGme
dip inland 3' or 4'.
No evidence t h a t any of t h e lagoon beaches a r e being
converted i n t o beach i'ock covld be found, and beach deposits encountered i n
t e s t holes on t h e lagoon sides of many islands 'were unconsolidated.
Lagoon beach d.eposits vary i n composition from time t o time and from
place t o place 8,ccording t o e f f e c t i v e wave conditions. Four p r i n c i p a l comp o n e i ~ ka r e recogrized, and these are normally s u f f i c i e n t l y well s o r t e d t h a t
they a r e s e p r a t e d i n t o p a r a l l e l bands along t h e beaches.. The components
a r e ( 1 ) lime sand canposed l a r g e l y of an orange, ovoid-shaped foraminifer
(&iphistegina nadagascariensis),
vi-th l e s s e r mounts of a v h i t e , disc-shaped
,
f o i a ? l i n i f---.--.~ ~ r g i ~ . ov~e-.or treab r a l i s ) ; ( 2 ) white coquiina sand composed l a r g e l y
of cotminuted pieces of she11;73T-gray coral rub'ole, worn and washed, up t o
1 - l / 2 o r 2 inches long; (4) pieces of gray ol. black pumice averaging from
1/4 t o 1/2 inch i n diameter but some a s much. a s 5 inches, worn and rounded
except where broken along f r e s h f r a c t u r e s .
..
The s o r t i n g of beach ma,terials according t o weight and s p e c i f i c g r a v i t y
r e s u l t s inpumice being concentra-bed on the backshore and t h e &her t h r e e
types of sedininen-t on foreshore beaches. The orange f o r m i n i f e r a l s3nds today domirate the foreshore surfaces of most lagoon b e a c h e s , b u t on Fumatah a t i and par.ts of Ha:z Island, c o r a l rubble covers the su.rface because of
s p e c i a l conditions responsibie f o r s'cro~?gwave action. Test trenches show
t h a t a t vario,us times the beaches of a l l the islarlds have-heen covered by
deposits of rubble, but most of these beaches were l a t e r buried by sand a s
they b u i l t forward under conditions of normal wave action. Island horns
o r bars t h a t a r e ilOW building ou'c i n t o the lagoon commonly c o n s i s t i n p a r t
f c o r a l rubble, t h e d i s t r i b u t i o a of each
of foraminifera1 sand and i n p a r t o
ma-berial depending oil conditions of l o c e l current aad wwe strength.
-Island
Parakahi
Matiro
hatahati
Ringutoru
Torongahai
------
-1
---
Table 1.--Characteristics of lagoon beaches
.
. .-.Angle of dip
toward lagoon
.
--.-(degrees) Width, iow t i d e
ores shore
/subcrest s l ~ p e ~ B a c k s h o rslopel
e
-
T---
~10'~e
- lo
20
26
4-9
1
Unconsolidated deposits of beach and bar t h a t form major p a r t s of some
islands on Kapingamarangi furnish evidence t h a t sedimeatation has cause&
the layoonward sides of -these islands t o b u i l d forward ad; an appreciable
b u t i~ndetermiiiedr a t e . Beach .trenches show t h e r e c e i ~ ta c c . a i ~ ~ l a i i oofn backshore deposits over e a r l i e r foreshvre sediments; t e s t p i t s near -the shore
ex2ose humus l a y e r s mixing with backshore deposits; w e l l s i n 'die i n t e r i o r
bring t o view sequences of 7-agoon1,~ard-dippingforaminifera1 sands of foi.mer
beaches. Most conspicuous of a l l features furnishing evidence or) beach m i gration i s t h e presence of r e l i c t zones of pumice, located back from the
margins of; some beaches and marking the baclishore a c c u m u l a t i o ~ ~ofs e a r l i e r. . .
periods ,g
-.1/ Similar bands of punice on Addu Atoll have been reported by Sewell
(19-93G P. 77).
Whether t h i s agsradational process i s a s rapid a s o r more rapid than
t h e ra-t,e of i s l a n d destruction oil t h e seaward s i d e i s not knobm. Presumably
the r a t e of wearing back of land has decreased i n proportion t o t h e distance
from the reef firon'; during t h e current still.-stand of t h e sea. Although t h e
present reef f l a t i s r e l a t i v e l y wide i n most places, t h e r e i s ample evidence
t h a t erosive forces of the sea a r e s t i l l vei-y e f f e c t i v e on many of Yne islands. On the other hand, t h e r a t e of i s l a n d building through sedinienta,tion
majr be retarded a s t h e shore moves forward i n t o c o n t i m a l l y g r e a t e r depths
of the lagoon, requiring g r e a t e r amounts of sediment t o b u i l d up the bottom.
Seaward
beaches.- Beaches a r e ? e l a t i v e l y scarce on t h e seawo-d
Kapingamarangi islands; furthermore they a r e small and short-lived.
sides of
Most
of them a r e perched on t h e bevelled surfaces of s t r a t i f i e d i s l a n d rock a t
various distances above low-tide l e v e l . As i:idicated on t h e geologic maps
(P.:..
&s. pto l o ) , few of them a r e continuous f o r long distances along the
shores. It i s doubtful t h a t any of -these beaches make permaneit co!itrr;.out i o n s t o the growth of t h e islands.
The seavard.beaches d i f f e r from t h e beaches on t h e lagoon sides of
islands not only i n being more patchy and f a r l e s s extensive, but a l s o i n
composition and color. They a r e foymed l a r g e l y from c o m i m t e d s h e l l s of
mollusks and a r e white, i n contrast t o .the orange lagoon beaches, r,rhich a r e
mostly composed of Foraminifera. A small beach a t the seaward end of ;)ungupungu Island ( f i g . 6) forms a coquina composed almost e n t i r e l y of unbroken
s h e l l s of a small pelecmod of the genus Trigonocardia,
-Ranparts and rampart wash.- Accumulations of c l a s t i c debris consisting
l a r g e l y of c o r a l rubble, c o r a l heads, add limestone bloclcs a r e deposited
on tne borders of most islands, abovk wave-cut benches and beach c r e s t s , by
occasional violent s-torms. The deposits a r e c l a s s i f i e d as boulder rzmnparts
and rubble ramparts,' according t o t h e i r c o n s t i t u e ~ ~ t so,r a s rampart wash
where the debris has been spread out a s a sheet below and beyond the iinland
p a r t of the rampart ridge.
Present d i s t r i b u t i o n of these s u r f i c i a l deposits, shown on the geologic
maps of the islands ( f i g s . 1 t o lo), gives some indication of the directions
Main crest
Foreshore
7
Backshore
I Crest
-
Foreshore ----
Crest
~
&,ckshore
-Foreshore
....-....7
--------?
Subcrest
0
'
x
X
0
0 -
.. 20 .,.
. ',.
...).
,
0
0 . J
EXPLANATION
Farominiferal sand (orange)
Clastic shell sand (white)
Coral rubble
Pumice gravel
-
FIGURE I I. -PROFILES OF LAGOON BEACHES AND
DISTRIBUTION OF BEACH SEDIMENT
0
5 fl
iLllli
.
of approach and the i n t e n s i t i e s of recent storms. Large islands along t h e
Torongahai, Ringutoa~, and hJunaltita -- all. have
northern a r c of the a t o l l
large ramparts on both eastern a;id western shores. The widest a r e on t h e
western s i d e s and i n these the l a r g e s t blocks ( 3 b inches i: diameter on
Torongahai) a r e concentrated near t h e ilol.thern ends ( t a b l e 2 ) .
--
--
--
have ramparts
Islands of the eastern arc
Werua, Matiro, and Hare
on t h e i r eastern seaward siLes, b u t these ramparts a r e forlred mostly of f i n e
rubble w i t h very small areas of boulders. Individual bloclis a r e on t h e
average much Smal.Ler than on northern is1and.s ( t a b l e 2 ) . On -the southern arc,
a t Puniatahati Island, large ramparts :have been formed or1 both seaward and
lagooiiward shoses. The rampart t o seavard consis-ts l a r g e l y of boulders; t h a t
on the lagoon s i d e of coral rubble oidy. The unique development on t h i s
i s l a a d of a lagoon-facing rampart mus;t b e : a t t r i b u t e d t o a f e t c h s u f f i c i e n t l y
g r e a t t o allow e a s t e r l y storms i n -the 18ggon.to reach high intensity-.
Rampart wash, a s indicated on most of t h e : maps ( f i g s . 1 -to l o ) , extends
inland from the ranparts f o r distances as much a s 250 f e e t , forming a surf a c e covering of coi-a1 ~ X b b l e . Because ranpart wash ha.s developed l a r g e l y
ou t h e seaward sides of islands, it r e s t s on bedrock i n manjr places, on s o i l
j.11 others.
Apparently it i s t h e r e s u l t of vatem washing a p u t ' of the
gravels and other small constituents of t h e rampart beyond i t s c r e s t . On
t h e northern islands especially, rampart .wash covers extensive areas back
from the seaward margins.
.
Migration
of is?.a,nd.s - I n preceding sections of %!]ispaper, geological
----e v i d e k e has been c i t e d showing t h a t the seaward sides of islands a r e curr e n t l y being eroded back so t h a t t h e c a t e r reef f l a t i s becoming wider a t the
expense of island s t r a t i f i e d rock, and t h a t the lagoon sides of lslands a r e
constantly growing through accumulation and deposition of beach and. b a r sediments. The t o t a l e f f e c t , therefore, i s t h a t of i s l a n d migrakion across the
r e e f , from seaward t o lagoonward s i d e . So long a s sea l e v e l remains r e l a t i v e l y s t a b l e with respect t o t h e a t o l l , t h i s process may be expected t o continue, though increasing distance from the, reef f r o n t causes the e f f e c t i v e
c u t t i n g power of iqaves t o aecreaie, &d the advance, of the lagoon shore i n t o
progressively deeper ria-ters requires more and more sedimen'cary material t o
b u i l d up a comparable amount of beachjfront. J. I. Tracey (written comunic a t i o n j July 1355) suggests t h a t s o l u t i o n of. rock i s more e f f e c t i v e than
abrasion by waves i n the r e t r e a t o f islands and t h a t wide r e e f s favor r a p i d
solution. He a l s o suggests t h a t wide r e e f s may favor rapid sedimentation
as they probably provide more sediment. Thus, it i s not !mom uhe'chei- o r
not these islands migrate a t a progressively slower r a t e .
I n addition t o t h e evidence of i s l a ~ l dmigration already given, many
b i o l o g i c a l f e a t u r e s support
the t h e s i s . One of the chief among these i s t h e
-undefiiiiing of t r e e s
especially coconut palms
by waves 01; the s e a m r d
shores. Mmv such t r e e s a r e t i l t e d o r have f a l l e n outward from zhe i s lands, The Kapingans a r e aware of t h e effectiveness of t h i s process and on
both Touhou and Werua Islands have constructed stone embankments along t h e
southeast coasts t o p r o t e c t the land. Evidence of the recent growth of
lagoon shores i s found on several islands where successive l i n e s of c e r t a i n
shore-fringing species of t r e e s a r e now standing i n the i n t e r i o r s , marking
the s i t e s of former shore l i n e s . Detailed studies of the r e l a t i o n s of
--
--
island m&ration t o g l a n t l i f e were niade by William Eiering duriiig the siunmer of 1954, and r e s u l t s nave iiecn reported by him.
On ICapingamara,ni;i Atoll., isl.and mizratior appears t o have been, i n
general., grea-test f o r the n6rther.n islands a n t leas's f o r tlie :;oYcherr?. This
i s indicated not ori?y by a greate;. width of outer reef f l a t i n the emf-Lh than
i n the south, b u t al.so by t h e e x t e ~ t o vhich b e i e l i e d relllranl-,s of s'matif i e d bedrock extend outvard from the seaward coasts of Toi-on:~&hai,Fingutoru,
Nunakita, aiid lderua Islai?ds ( f i g s . 1, 2, 3, and 4). I n c o n t r a s t , Hare Island,
or. t h e soutlierii par% of t h e ai;oll, appeers t o have been r e l a t i v e l y s t a b l e ;
it shows l i t t l e evidence of shore recessio?? on fhe seaward s i d e and does not
appear t o be building out rapidly lagooiivard. 11Its adjacent outer reef f l a t
L/ I t s lagoon beach probably i s t h e t y ~ eof t:?at a t A r i ~ o A t o l ldescribed
by We& (1.951, p . 5 ) a s I I degrading." Much of i t s surface i s covered b y rubb l e c ~ n c e n t ~ a t e sthe
, sand having been removed, and several coconut palrns
growins near i t a r e p a r t l y underniined.
-.
--.---
i s coi~iparativelynarrov.
debris aa6 'oclr fragments, cemen-ted by c a l c i ~ mcarbonate, I t varies g r e a t l y
i n texture and i n degree of cenientzbion, some being ex'creuiely f r i a b l e , some
well cemented and dense. M L I C ~of it i s s b r a t i f i e d o r c r o s s - s t r a t i f i e d i and.
it has a l l t h e charac,te-istics normally a t t r i b u t e & t o beachrock. Details of
i t s origin a r e not e n t i r e l y c l e a r , however, despite t h e numerous suggestions
cancerning t h e o r i e i n of beachrock t h a t have been offered i n the many publications on t h i s subject.
Because modern beachrock i s limited t o t r o p i c a l seas, i t s r e l a t i o n t o
e develops excl.usively
warm waters apgears t c be beyond question. B e c a ~ ~ sit
i n the i.ntertida1 zone, i t s r e l a t i o n t o the r i s e and f a l l of t i d e s seems
equally d-efinite. Other fac.tors
those responsible f o r i t s l o c a l i z a t i o n
oi c e r t a i n beac&es o r p a r t s of beaches
a r e l e s s c l e a r . basic rerpi?:ements
i n the development of beachrock have i-ecently been summarized by Gizsburg
(1953, p. 88) a s ( 1 ) high temperature, ( 2 ) rapid r a t e of beach draiiiage between high t i d e s , and (3) a permai?eixx of beach deposits s u f f i c i e n t t o allow
t h e cementation process t o operate. The l o c a l i z a t i o n of b e a c h r ~ c ki s com.only
explained a s due t o the p r e c i p i t a t i o n oii calcium carboaate from s e a irater a s
a resul-t of heating and evtiporation. The probable inportacce of blue-green
aigae a s agents t h a t bind sand grains toge-bher u n t i l they can be cemented has
been su.ggested by Cloud (1952b, p . 28) and others.
--
--
As a r e s u l t of observations on vszious Pacific a t o l l s , a diiver&ence of
conclusions has 'been reached concernin;; the areas i n which beachrock i s curr e n t l y developing. Ladd and others (1950, p . U ) s t a t e t h a t on Bikini Moll.
"beachrock may be fornied bekween t h e reef f l a - t and t h e beach." These &u-thors
r e f e r t o the Fresh look of the rock a?d the o r i g i n a l color of organ5.c i n c h sions as evidence t h a t l i t h i f i c a t i o n i s going on today, bu-b a l s o point out
t h a t exposed p a r t s of t h e beachrock are beins eroded. Regardin:: Onotoa Atoll,
Cloud (1952?o, p. 28) describes "bonded limesand," which he consi6ers t o be
incipient beachrock, forming on l a g o ~ nbeaches, i n t i d e pools, and i n spray
pools, and s t a t e s t h a t it was not fot~qcl021 t h i s a t o l l anywhere c;n the seaward
Table 2.--Distribut-ion
vBoulc e r r a n p a r t
Island
Torongahai
Location
'
Width
(feet)
S i z e of bovJders
(inches) -
Eal
t
..
$o
Rikumanu
II North shore
! Wss~shore
/I
E a s t shore
!
--
surface
I
-A
I
i
P a r t of west
shore
Sout:l.west
1 30-200
1 23-72
end borders
e s s t raxpart
South p a r t of
e a s t and west
sii0:-es
Nortk end
borders e a s t
r a m p a r t
24
South. s liore
East shore
Borders e a s t
ranpar t
6-24
East shore
6-12
East shore
Southeastsh
24
6-10
6-12
/
-
100
18-2b
22-1'20
31-68
12-36
6-8
I
South p a r t
of e a s t and
west shores
28-32
115-164
18-77
21-54
Rampart wash
Location
Mid t h
______/I____'
36
I
Ringutoru
Rubble rampart
'id t h
Location
feet)
I
/i West
shore
East s h o r e
i
of ramparts and r a ~ p a r - twash
z
Nunakita
I
West shore
E a s t shore
wema
Soutk%east
silo rE
Matiro
Southeast
1i
j
57-120
-
/
I
I
E a s t end
I Northeast
I
I
Puniatahati
South s h o r e
/
42-67
33-100
/
6-12
North shore
--rampart
West end
borders
I
30-1 00
beach. Concerning Raroia Atoll, Newel1 (1954, p. 32) says t h a t beachrock i s
quite r a r e along lagoon shores, b u t t h a t it appears t o be forming i n "moats"
i n the island interiors
behind lagoon shore ridges and, especially, back
of seaward ramparts. This i s probably the Cay Sandstone of B r i t i s h and
Australian geologists.
--
Most of the beachrock exposed a t Kapingamarangi A t o l l todtiy apgears t o
be r e l a t i v e l y old; This is suggested by ( 1 ) the presence of t y p i c a l beds
preserved a s r e l i c t deposits standing above present high-tide l e v e l on seve r a l islands, ( 2 ) the bevelled remnants of t y p i c a l beachrock extending seaward a few hundreii f e e t , across t h e reef f l a t , from the present i s l a n d shores,
and ( 3 ) evidence of replacement of calcium carbonate by a p a t i t e i n s t r a t a
both i n the i n t e r i o r s and on the shores of several islands.
Although considerable evidence indicates t h a t a c t i v e erosion dominates
the seaward shores of most Kapingamaraiigi islands today, t h e r e i s reason t o
believe t h a t , l o c a l l y a t l e a s t , some lime p r e c i p i t a t i o n i s going on contemporaneously. On the reef f l a t near t h e shore,of Parakahi Island a rectangle
of boulders placed there by man a t an unkaom date has been firmly welded i n
place through cementation. On t h e e a s t shore of Tirakavme Island, a 3-foot
block of s t r a t i f i e d limestone from an ancien-k outcrop of beachrock i s now
standing on end, incorporated i n t h e present middle beachrock layer. How
recently t h i s development took place i s not known, b u t it c l e a r l y shows a
second stage i n beachrock development. Such i l l u s t r a t i o n s of recent, though
l o c a l , p r e c i p i t a t i o n of calcium carbonate on the seaward shores of islands
a r e supported by records from other a t o l l s . . These include t h e record of a
fragment of green glass from a Japanese f i s h n e t f l o a t , embedded i n beachrock
deposits a t Bikini a add e t a l . , 1950, p. 416) and the r e p o r t of a firmly
bonded gravelly sand containing brass c a r t r i d g e s h e l l s on t h e seaward shore
a t Tarawa (cloud, 1952b, p.
a).
.
,
On Kapingamarangi Atoll no development of beachrock on t h e lagoon shores
of t h e islands could be detected. Although a l a r g e number of t e s t trenches
were dug across the beaches of various islands and most of the beaches were
examined i n connection with mapping o r the islands, without exception they
were found t o be e n t i r e l y of normal unconsolidated deposits of sand and gravel. Likewise, no c l e a r evidence of beachrocls development vas found i n the
i s l a n d i n t e r i o r s , f o r "moa.is" t h a t a r e periodically flooded by s e a >rater a s
described by Nevell (1954) f o r Raroia do not occur a t Fapingamarahgi. Thus,
if beachrock i s forming today i n appreciable amounts on t h e islands o f % pingamarangi, i - t must be on the seaward sides. Most of t h e rocks on these
sides, however, appear t o be wearing away rapidly, s o it i s doubtful t h a t '
beachroclr development i s extensive t h e r e a t present.
'
The theory t h a t bea,chrock may develop by the worls of ground water t h a t
dissolves calcium carbonate from lime sand and p r e c i p i t a t e s it a s it seeps
through t h e beach a t low t i d e was proposed many years ago (Field, 1920, p.
215). Considerable evidence opposed t o t h i s idea has since been presented
by Daly (1924, p. 138) and others. On t h e islands a t Kapingarnarangi, it
c l e a r l y cannot apply because ( 1 ) i n t e r t i d a l sedimei~tson t h e lagoonward margins of islands a r e not l i t h i f i e d , ( 2 ) bedrock on the seaward s i d e r i s e s
above high-tide l e v e l and extends inland a considerable distance, and ( 3 ) no
c o r r e l a t i o n between the water l e v e l s and i s l a n d bedrock can be detected i n
t h e s e r i e s of wells across Taringa and CJerua Islands ( f i g s . lb. and 1 5 ) .
Sedimentary material t k a t foms the a t o l l of Kapingamerangi i s , with
few exceptions, comgosed of calcium carbonate. P a r t of i t i s uiiccmolida%ed accmulatioiis of c l a s t i c p a r t i c l e s . The r e ~ a i n d e r , r e f e r r e d t o a s
sedimentary rock, i s l i t h i f i e d m a t e - i s 1 developed through cenient,ation of
these c l a s t i c sediments and froin the reef-building processes of co-als, a l gae, and other orgauisms. For pwposes of studying and mapping, p r i n c i p a l
v a r i e t i e s of sedirneiit and sedimen.tary rock have been c i a s s i f i e d l n t o e a s i l y
reccgni.zable types, based primarily on t e x t u r e wad secondarily on the major
contributing ~ r g ~ i s m
o rs rock inp;redi?nts.
Sediments.Unconsolid.ated materials a r e separated i n t o t h r e e groups
--.-according t o p a r t i c l e s i z e , folloving ';he Wentworth c l a s s i f i c a t i o n of
d e t r i t a l sediraeints. These groups a r e (1) lime gravel, i n which par.ti:les
a r e g r e a t e r than 2 mm i n diameter, ( 2 ) lime sand, i n which they a r e between
1/16 and 2 mm, and (3) lime mud, i n which they a r e l e s s tinan 1/16 mm. Dep o s i t s of a l l t h r e e of these gr.oups form significan-t p a r t s of tine a t o l l ,
3;ld e8ch accumulates i n c h a r a c t e r i s t i c situations,. as w i l l be described
l a t e r . 20th Lime grsvel and lime sand a r e concentrated on the reef f l a t s ,
l o c a l l y forming deposi-ts from which the islands a r e b u i l t . They a l s o cover
mnch of t h e l a g o m f l o o r . Lime muds, on the other hand, a r e confined l a r g e l y
t o the deepest p a r t s of the lagoon.
<
Two p r i n c i p a l v a r i e t i e s of lime gravel a r e recognized: One i s r e f e r r e d
t o as boulder gravel, f o r it contains angular blocks of reef rock, rounded
c o r a l heads, o r masses of c o r a l l i n e a.lgae which a r e of boulder ( > l o - i n c h )
s i z e . The other i s formed almost exclusively of c o r a l d b l e , derived l a r g e l y
k.orn broken fragaen-cs of Acropora
o r elk-horn c o r a l ranging from about 1/2
--t o 2-i/2 inches i n length. Although many mixtures o r intermediate stages
between these v a r i e t i e s of grave.': e x i s t , t h e importance of recogxizing them
a s separate types i s t h a t t h e boul3er gravel lndicaies the a c t i o n of viol e n t storms awl accompanying l a r g e waves, whereas the much smaller coral
rubb1.e i s t r a m p o r t e a a l s o by normal waves and currents, and so i s being
deposited' almost coatinuously.
Lime sands of Ihpinganarangi A t o l l vary according t o the oi-gailisms o r
combinations of orgar!isma Trom which they have been derived. Those of the
beeches and shc.llow offshorre wxters a r e com~osedl a r g e l y of t h e small
orange foraminifer Ar;;;?hj.sl-egina
msdagasca~iensis
..._-----w-_-_- 1 the white ',?heel-shaped
foraminifer Mar.rginop~:r.: v x t e b m X s ) o r botll, Some 'Jeaches contaii; a high
percentage of white i-'rafperr'cs of molluslr s h e l l s ; elsewhere beach sands
l o c a l l y consist of t i n y , un;7xolrerr pelecypod s h e l l s forming coquinas. Some
shallov-water 1.irne sands, espec-ially on the tops of patch r e e f s , include
l a r z e amounts of t j . 1 1 ~cc,rnl frag!iients; and i n waters more than 80 f e e t deep,
sands a r e formed a.Lmst ex-l~isive;.. of f r a m e n t s of 8a!.iz1eda. (cal.cereous
,~
green algae) o r of t h e hemis:>heri.cai pale-olive foraminifer Pmghistegina
lessonii .
.,
~
~~
-
~-
P m i c e i s abw-&ant on -C?ebackshore beaches of mast islands. Muck of
i t i s of granule o r small-pebble s i z e , but a few fragments a r e a s much a s 6
inches i n di.m.ie'ter. Most cf -the pumice i s l i g h t gray; some i s black. Large
specimetis conunonly a r e well roun2ed. This material i s s o concentrated on
some backshores a s t o form e s s e n t i a l l j pure pumice l a y e r s .
Lime muds include ( l j some small depgsits of s i l t (1/16-1/256 ma) derived from s h e l l s o r ot!~er organic s t r i ~ c - t a r e sand ( 2 ) extensive deposits of
very f i n e pale-olive oozes v l ~ i c ha r e s-ticlry when wet, The s i l t s develop
l a r g e l y a t moderate depths i n lagom channels o r other plcces where t h e r e
a r e curren-ts strong enough t o gather and transport them. The calcareous
oozes form only i n the deepest p a r t s of the lagoon bottom. They a r e composed mostly of clay-sized payticles of calcium carbonate but include perhaps 10 percent of Foraminifera, l a r g e l y of very small species not fouiid i n
t h e shallower waters (discussed under "Sedimentation i n the l.agoon" ) . This
calcareous ooze has high p l a s t i c i t y and c o n t a i m a slimy residue of organic
matter conspicuous f o r i t s f e t i d odor 1.7hen wet.
The m i n e r d composition of Kapingamarangi sediments a s determined
-- 1/ Analyses by A.
-
-11
J. Gude 111, U. S. Gedogical Survey.
with X-ray diffractorneter patterns shows wide v a r i a t i o n depending upon the
type of organism t h a t dominates any p a r t i c u l a r samp1.e ( t a b l e 3 ) . It i s s i g n i f i c a n t t h a t t h e two comon species of shallow-water Foraminifera a r e composed of essential.ly pure c a l c i t e , and t h e common foraminifer 'oe1.o~ depths of
100 f e e t , $nphis.tegina les~or&, i s of nearly pure calciLe. I n c o x t r a s t ,
corals including Acropola and other cornon genera a r e v i r t u a l l y pure aragonite except f o r a 1 i t t I . e c a l c i t e i n t h e i r 'dead" i n t e r i o r portions. Corall i n e algae of the genus Porolithon,
----..- .- which grow i n ab~nbanceon the a l g a l
ridge of the outer reef, appear t o be formed cf c a l c i t e having a spacel a t t i c e d i f f e p e n t frcm t h a t of normal c a l c i t e and i n t e r p r e t e d by Gude a s
r e s u l t i n g from high magnesium content. Green algae of the genus l l $ i m s % ,
rihich form important coritributions -GO Lagoon sediment b e h w 80 f e e t , contain
about 98 percent aragonit? together with small. amounts of c a l c i t e . The bottom calcareous oozes a r e about three-fourths aragonite and orie-fourth c a l cite.
---
Sedinentary rocks.- Carbonate rocks of various types form the outer
-----..r e e f , p a r t s of the islands on the outer reef, and patch r e e f s within t h e
lagoon. Four mappable v a r j e t i e s of these rocks a r e recognized, based on
texture and s-tructure. These a r e ( 1 ) coral and c o r a l l i n e a l g a l limestone,
( 2 ) aphanitic t o s t r a t i f i e d e l a s t i c limestone, ( 3 ) c o r a l rubble limestone,
and ( 4 ) boulder conglomeratic limestone. The f i r s t and second types canno-t
everywhere be distinguished because of r e c r y s t a l l i z a t i o n and other modifications r e s u l t i n g from secondary processes; t h e t h i r d and fourth, i n many
places, grade from one i n t o t h e other. Nevertheless, an attempt t o recognize and map these types must be mad.e 2.f the processes developing t h e a t o l l
a r e t o be understood.
Limestone from corals and c o r a l l i n e algae forms the framework of t h e
outer reef and of t h e patch r e e f s and c m be seen developing today wherever
contributing organisms a r e growing, especially along the outer margins of
the r e e f s . The rock developed from t h e s e organisms forms the pavement on
the present bevelled reef surface. It i s d i f f i c u l t t o examine i n section,
however, because of i t s extreme r e s i s t a n c e t o breakage and because of t h e
s c a r c i t y of exposed n a t u r a l cuts i n t o it. Samples from immediately below
the pavement surface commonly sho\~r e l i c t s t r u c t u r e s of organisms, a s might
be expected, b u t many appear aphanitic a s a r e s u l t of secondary processes
a c t i n g on the calcium carbonate. Although hand specimens comiiiiollly appear
t o be low i n porosity, the rock mass i s cavernous and c o n ~ a i n smany cracks,
some of which a r e f i l l e d with c l a s t i c debris.
Aphanitic t o s t r a t i f i e d & a s t i c limestone forms an appreciable p a r t Of
the bedrock on a l l islands and occurs i n many places on t h e reef f l a t s a s
pedestals and r a i s e d ridges considere? t o be r e l i c t s of former i s l m d s . Where
the rock i s aphanitic, l i t t l e can be determined concerning i t s origin. Where
planes of s t r a t i f i c a t i o n remain o r a r e etched out on weathered surfacss and
c h a r a c t e r i s t i c s of grain a r e preserved, however, the h i s t o r y of the rock can
r e a d i l y be determined. Dips of c r o s s - s t r a t a and other c h a r a c t e r i s t i c s show
close s i m i l a r i t y t o f e a t u r e s of t h e unconsolidated deposi-ts of i s l a n d beaches
Boulder conglomeratic limestone and coral. rubble limestone a r e major
consrituents of most islands on Kapiiigamarangi A t o l l and form conspicuous
ledges and shelves along many of the seaward shores. The limestones a r e
easy t o recognize because t h e gravel within the lime matrix normally weathers
i n t o prominence and, i n some places, i s extremely conspicuous because of
color contrasts. Boulder limestone includes angular blocks of reef limestone, rounded c o r a l heads, and masses of c o r a l l i n e algae of many s i z e s and
shapes similar t o those i n modern boulder ramparts. The c o r a l rub'ole limestone i s formed e n t i r e l y of small rubble i n a lime matrix. These c l a s t i c
limestones a r e distinguished i n mapping, a s a r e t h e i r n o n l i t h i f i e d equival e n t s , because of the d i f f e r e n t origins t h a t they imply.
The varied mineralogy of d i f f e r e n t limestones on t h e a t o l l doubtless i s
i n p a r t due t o secondary processes of r e c r y s t a l l i z a t i o n and replacement.
Many of t h e differences, however, a r e d i r e c t l y a t t r i b u t a b l e t o dirfei-ences
i n the source materials. Foraminifera of which some rocks a r e composed a r e
c a l c i t i c , corals i n other rocks a r e aragonitic, and a l g a l deposits i n s t i l l
others a r e high i n magnesium ( t a b l e 3). Therefore, fundamental genetic d i f ferences may account f o r t h e d i f f e r e n t compositions of many of these youthf u l limestones.
On a few islands phosphorite r a t h e r than limestone l o c a l l y forms s t r a t i f i e d rock. Phosphorite, presumably developed from the guano of s e a b i r d s
through replacement of calcium carbonate, occurs on p a r t s of Fumatahati,
Nunakita, and possibly a few other islands. It i s an earthy, light-colored
rock resembling Lhe l o c a l limestone i n texture and s t r u c t u r e , b u t commonly
l i g h t e r i n weight o5ring t o high porosity. Mineral s t u d i e s by Gude 'with X-ray
d i f f r a c t i o n patterns show t h a t i n some specimens the e n t i r e rock i s composed
of a variety of a p a t i t e .
Table 3.- Mineral composii;ion of Kapin@marangi sedimeiits a s dibermined by
X-ray d i f f r a c t i o n p a t t e r n s
. .
*Calcite A i s i n t e r p r e t e d a s normal c a l c i t e ; c a l c i t e B a s magnesian
calcite.
-15-
SOILS
Genera.1 statement. - S o i l s of Kapinganiarangi Atoll a r e necessnrily
j.our,g: the islands oil wlij.ch they occur a r e of recent origiri. Most of the
s o i l p r o f i l e s a r e cl.assed as A-C p r o f i l e s and consist of materiais l i t t l e
a l t e r e d from t h e parent rock o r sediment, cove'ed by o r mixed with varying
aniour~tsof dark humus. The s o i l s show few fea4tures of well-developed horizons such a s norma.l.ly r e s u l t from long periods of deccmposit,ion of varied
source maberials
.
Kapinganarangi s o i l s cliaracteris-tical1:r a r e well drained and a l k a l i n e ,
They a r e l a r g e l y mechanizal mix:ures of organic material and gravel., sand,
o r f i n e calcium carbonate p a r t i c l e s . They vary from dark bro;m t o gray a d
creamy white, accordiag t o the proportions of various consti-tuents. S o i l
p r o f i l e s a l l have dark layers a t the top and light-colored bedded rock o r
sediment below, buc some layers axe separated by t r a n s i t i o n zones of in'Lermediate color aad composition, vhereas others a r e marked b;, abrupt change.
I n order t o obta.in q u a n t i t a t i v e Cata on the s o i l s of [email protected]
Atoll, s o i l p r o f i l e s were measured and samples f o r mialjrsis were c o l l e c t e d
from e i g h t wells, dug i n connection iiith ground-vater s t ~ d i e s ,and f'rom e i g h t
t e s t p i t s . These p r o f i l e s were d i s ~ r i b u t e d o nseven islands a s follows:
Wema 3, Taringa 3, Parakahi 1, Pumatahati 3, Ringutoru 3, Tokongo 1, Rilrumanu 1. Conclusions r e s u l t i n g from s t u d i e s of the s o i l p r o f i l e s and of the
anal.yses of samples c o n s t i t u t e -the basis f o r most of the following discussion on s o i l s .
Parent materials of s o i l s . - The s i m p l i c i t y of s o i l s on the i s l a a d s of
Kapingamarangi stems, f o r the most p a r t , from the f a c t t h a t they a r e formed
aln1os.t e a t i r k l y from- only two b a s i c ingredients
( 1 ) parent; r k k or sediment composed of calcium (and some magnesiunl) carbonate, and ( 2 ) humus from
vegetable matter. The carbonate material varies considerably i n physical
form. Much of it i s limestone which makes up a l l the bedrock; tke r e s t of
it occurs a s unconsolidated sediment inc'uding gravel, lime sand, and lime
mud. Large c l a s t i c fragments include blocks broken from the reef, c o r a l
heads, and masses of c o r a i l i n e algae. Small gravel i s almost en-tirely c o r a l
ru6hle. Lime sand consists of s h e l l fragments and t e s t s of Foraminifera,
with l o c a l contributions of t h e alga &limeda and other organisms. The lime
mud appears t o 'be p r i n c i p a l l y from t h e decomposition of s t r a t i f i e d rock o r
of limestone blocks. A l l these c l a s t i c .materials mixed with 'numus a r e r e l a t i v e l y l i t t l e decomposed even though they a r e i n an area of prevailing warm,
h w i d climate. This iudicates t h a t t h e s o i l i s very youthful.
--
Variations i n the s o i l s of Kapingamarangi a r e i n p a r t due t o differences
i n the amount of o r i g i n a l contamination and i n downward f i l t r a t i o n of vegeLabie carbon i n t o the calcareous host matecials.
High perraeabil.ity of much
of the sediment, allowing r a i n water t o e n t e r readily, t h e penetration of
roots as fourrd i n most t e s t p i t s , and t h e work of various animals a l l cont r i b u t e i n varying degrees t o domiriard xixing. I n some places a " t r a n s i tion" zone ( A ~horizon) i n which small percentages of carbonaceous matter
a r e mixed with c o r a l rubble o r l i m e sand has develoged below the normal zone
of incorporated organic rua.tler (.A,,horizon) t o a distance of' 1.2 t o 3.5 inches.
I n other places no " t r a n s i t i o h " zone i s present.
Appreciable variations iil the chemi.cal character of t h e i s l a n d s o i l s
( t a b l e 4) were not detected in the present study. I n general, the youthfulness of the parent limestone vLrtually precludes the p o s s i b i l i t y t h a t any
a'gpreciable concentrations of rioucarbonate miiierals have &evelope6 throvgh
leaching o r decomposi.tion. On the other hand, l o c a l addi-Lions t o t h e soil.
may consist of puiiinice, b i r d guano, s h e l l s of crustaceans and echihoids, o r
skeletons o? f i s h ; the overflovs of s e a water possibly have a f f e c t e d the s o i l
i n some places. Bacisshore beaches composed l a r g e l y or e n t i r e l y of pumice
( t a b l e 5 ) a r e present on the lagoon s i d e s of sevcral islands, and some pwnice
has been found i n t e s t p i t s , but i t s influence on vegetation i n general i s
not kno+m. Bird gu.ano has contribu-ted t o t h e l o c a l development of phospha;tic
s o i l on some islazlds, especially Pumataha'ti, where a c c o r d k g t o ::a.tive reports
many f r i g a t e birds formerly roosted. S a l t s from sea water and s e a spray t h a t
l o c a l l y make s o i l s high3.y s a l i n e have not ]..eft any conspicuous record of s a i c
c r u s t s , probably because evapora.tion i s low a s compared with coiitribu-Lions of
fresh water; the s a l t s d.o .lot seem t o have a f f e c t e d l.nfge a.reas.
.-
Alteration processes
Factors conspi.cuous in bringing about t h e a,lterat i o n both of s o i l s a i l d 7 f the p a r e r t materials of s o i l s on Kapingamarangi
Atoll include' %hose t h a t remove substances, those t h a t add substances, and
those t h a t mix substances. I n the f i r s t category, one of t h e most important
f a c t o r s appears t o be rain. Showers on t h e i c l a s d s normal1.y a r e s h o r t b u t
violent, and permeable sxrfaces allow most of the l a t e r t o e n t e r r e a d i l y
with a fl.ushi.og e f f e c t t h a t prob3bly accounts f o r the gelera1 lack of s a l i n e
residues. Also s i g n i f i z a n t i s the abuidant evidence of solution work i n
limestone beds, probably l a r g e l y the r e s u l t of carbonic a c i d from p i a n t s ,
which enables t h e migrating waters t o dissolve car6ona6,es.
A t the low lev-el,s i n the centers of some islands, especially where p i t s
f o r growing puraka 1 have been excavated by the natives, ground water reaches
--.
-.-
-1/
A p l a n t with a tuberous, starchy root, r e l a t e d t o the t a r o .
the s o i l l e v e l and, l o c a l l y , appears a t t i e surface of the grounu. Where
t h i s occurs, normal oxidation of organic matter i s retarded o r stopped by t h e
water &d black mucks develop. The fresh-water lens, moving up and down i n
response t o t i d a l fluctuations, appareiitly has a considerable solvent e f f e c t
on calcium carbonate i n the s o i l wherever it comes within range, as shown by
the calcium bicarbonatecoiltent of water samples from the wells.
Extraneous b u t s i g n i f i c a n t elemenk i n t h e s o i l include nitrogen, added
by legumes and some t m e s of algae. Calcium carbonate introauced through
evaporat,ion does not seem t o be important, f o r no caliches such a s occur i n
a r i d o r semiarid regions were observed, and f r e s h v a t e r above the water t a b l e
aspears t o be removing r a t h e r than conkributing calcium carbonate.
A process t h a t i s especially important i n the forming of s o i l s through
the mixing of..materials i s the burrowilg of c e r t a i n animals. Especially
,.
conspicuous are: holes r e s u l t i n g from the a c t i v i t i e s of la.nd crabs. Systemand e f f e c t s of these animals on several.
a t i c studies of the di~trib?!~tioni
isle.!ids were made by ~ i l l i G nNlering of the 1954 P a c i f i c Science Boaud p a r t y .
Probably a l s o in~portantthough l e s s apparent a r e -the borings of e a r t h worms;
observations 05 the d i s t r i b u t i o n of ihese were a l s o made by Niering. The eff e c t s of roots i n peiletrating qiid breaking U ~ J s o i l mate?ials vere see3 i n the
sides of a l l v e 1 . l ~aid t e s t pits. Roots a r e e f f e c t i v e only i n tile vpper 1 o r
2 f e e t of s o i l and sand, however, fo;. t h e i r abundance and s i z e diminish rapi d l y with depth. Oaly a few were observed as deep a s 4 f e e t .
of s o-.-i l t o -p
n .--on
Because seaward and ls$;oo:ltiard
. ositio
- island.islands on Kapinxamaran?i
P.toll
d i f f e r corisiderab:L:ji i n age,
- - . the
stage of s o i l development oil each s i d e liiceriise i s varied. On l a r s e and
medium-sized islands the seaward sides a r e composed l a r g e l y of 1il;;es.tone bedroclc,.believed t o be r e l i c t f r o m a e p o s i t s of a f o r a e r and higher stage of sea
level, overlain i n most places by rubble. In con+,rast, the lagoon s i d e s of
these islands a r e formed of r e l a t i v e l y recent beach and bar deposits such a s
a r e developing today along t h e lagoon shores.
parts
-
Relation
-of most
Excavations representative of 'the seaward and lagoonward s i d e s and the
centers of i s l a c d s demonstrate tire d:iffe?er;ces ip t h e i r s o i l p r o f i l e s . Wells
and p i t s . l o c a t e 6 approximately 100 f e e t from the lagoon beaches of Ringutoru,
Taringa and Werua Islands show s o i l lajrers of 24-, 2- and 5-inch thickness,
respectively ( f i g s . 12, 1 4 and 1 5 ) . S o i l layers measured near t h e centers of
the same islands a r e 8, 11 and l j inches thick, and on t h e seaward sides 8,
1 4 aild 32 inches. Small islands l i k e Rikunanu and Tokongo, composed l a r g e l y
of bedrock from an e a r l i e r stage of sea l e v e l , probably correspond i n a.ge t o
t h e seaward portions of t h e l a r g e r islands. Commensurate w i t h t h i s age,
~~O
s o i l layers of 29 ;inches on Rikumanu, and 18 and 7 inches on T O ~ O I were
noted i n t e s t p i t s ..(f i g . 13).
,
Buried p r o f i l e s occur 'on the seaward s i d e s of a t l e a s t three: islands and
may be expected on others i n corresaondirig p o s i t i o n s . On Ringutor:u,-,Taringa,
and Werua ( ~ i ~ 12,
s . 14. and 15) t h e s o i l p r o f i l e s include a r e l a t i v e l y t h i n
upper layer of dark-brown s o i l , separated from a lower, much thicicei, s o i l by
9 t o 24 inches of light-gray sediment, iilcl.uding sand, c o r a l rubble, and
small amounts of humus. This light-colored l a y e r is i n t e r p r e t e d as representing an interruption i n the s o i l development process, during which t,ilne
waters deposited e l a s t i c sediments. It i s postulated t h a t t h i s deposition
was a r e s u l t of sheet wash a t a time of storm a c t i v i t y . Much sand and son;e
rubble, but no' very coarse inaterials, a r e included. Judging from t h e appreciable thickness of t h e overlying layer of s o i l (4-9 inches), which i s
comparable t o t h a t of the e n t i r e s o i l layer on the other s i d e of the island,
and from the f a c t t h a t buried p r o f i l e s have r1o.t been found on t h e lagoon
sides of any islands, a period longer than t h a t required f o r development of
the present, lagoon s i d e i s considered probable-for t h i s interruption i n s o i l
formation. Thus, although the buried p r o f i l e may be t h e r e s u l t of some r e cent storm, more l i k e l y it dates back .to the time of an e a r l i e r sea-stand.
..
Extremely youthful s o i l occurs l o c a l l y where two islands have, within
h i s t o r i c times, become joined through sedimentation r e s u l t i n g from causeway
Table 4.- Elements in Kapingamarangi soils determined by semiquantitative spectrographic method.
Analyses by Paul Barnett, U. S. Geological Survey. Elements reported by percent ranges.
Depth
(inches) Si
.01
4
.02
.002
20
.cq
.O1
31
.02
Well
~ e r u a#5
Werua
6
'nierua #5
Taringa #2
5
Taringa #2
20
39
Taringa #2
< .Ol
c.01
<.01
<,01
Taringa #2
55
Taringa #3
2
"01
Taringa $3
8
'.O1
< .01
Tzringa #3
18
c.01
Al
Fe
.02 .1
.05
2
.002 .005
.oo5 .ole
-01 0
0
-05
'02 .05
-05
.05
.5
1.0
P
Mn
.002
.005
.0002
.ow5
.0002
.OW5
5
Ca
)lo
e5
c.005
.oo5
10
0
0
>10
0
0
>10
; : :1
Mg
.1
.2
.5
1.0
.5
1.0
Not
found
.002
(.005
..0-05
.002 .001
.a05 -002 <.005
-002 .005 <.oo5
.005 .OlO
.002 .002
-005 .OO5 "Oo5 -002 -001
.005 ,002 <.0°5
'01 <.005
.02 .02
.002 .002.005 .005 c.005
Taringa #3
34
The folloving elements
Sensitivity limit
.00005
.0001
.OOO~
.001
.003
.005
.01
-03
Ti
Not
found
Not
found
Not
found
>lo
l.O
.1
2
.2
.5
.2
.j
.5
Na
.2
.5
2
.5
.2
B
.001
.002
-001
.002
,001
.5 .002
.2 .QOl
.5 .002
.2 -001
.5 .OO2
,2 .001
-5 .002
.2 -001
.5 .002
2 .oo1
.5 .002
.2 $002
'5 .>O>
.0002
.0005
.0005
.0010
'
>lo
1.0
.2
O
>lo
0
-5
.5
O
2
5
>lo
> 10
1.0
,
C
.
re
'5
.2
O
>lo 1.0
were also looked for but not found:
Elements
.5
.0005
.0010
‘
0
ng
Be, Yb
Co, Ge, Ni, Pd
Bi, Ga, In, Mo,
A , ~t
Cd, Er, Gd, Ir,
Li, Nd, Sb; Sm,
Te, Zn
As, Ce, D , Hf,
K
K?
Nb, Sn,
V, Y, Zr
La, Os, Re, Rh, Xu
T1, W
a
Th, U
.5
Ba
.01
.02
.0005
.001
.002
.005
,002
-005
Cr
.0005
.001
.a02
.0005
.om2
.0005
.W2
.0005
.a05 .om1
.0010 .0002
.0005 .0001
.0010 .0002
.0005 .0005
.0010 .0010
.ooo5 .ooo1
.0010 -0002
.0005
.OOlO
m i COP .go05
.002 -005 .0010
.00l .coo5 .0001
,002 .0010 .0002
.
Pb
Sr
Cu
.OOl .a02 .5
.002 .OW5 1.0
.0001 Not
-5
.a02 found1.0
.coo2 -0002 .5
.COO5 .0005 1.0
.0005
.2
,0010
5
.0005
.5
O 1.0
.0010
.0002
.5
O
1-0
.0005
.0002
*5
O 1.0
.0005
.0005
O 1:;
.OOlO
.0002
.5
.0005
0 1.0
05
.0010
.0005
.5
O
I,O
.0010
0
Table 5.- Pumice analyses; elements determined by semiquantitative
spectrographic method. Analyses by Paul Barnett, U. S.
Geological Survey. Elements reported by percent ranges.
Gray pumice
lement*
Black pumice
Hare Island
Gray pumice
Element*
Black pumice
Haze Island
1
Si
.0001-.
0002
A].
.001-.002
Fe
.ooo5-.oolo
Ti
.oo5- .ole
Mn
.001-.002
Ca
.005-.010
Mg
.005- .OlO
Na
.0002--0005
K
.OoO5-.0010
B
-02-05
Ba
.001-.002
Be
.005-.010
Ce
.ooo5-.o010
Co
.02-.05
q h e following elements were looked for but not found: Ag, As, Au, Bi,
Cd, Dy, Er, Gd, Ge, Hf, Hg, In, I i N 0 , P Pd, Pt, Re, Rh,
Ru, Sb, Sm, Sn, Ta, Te, Th, T1, U, W, Zn.
RlNGUTORU ISLAND
(105 ft from lagoon)
(132 ft. fra
W end
N. Of center
~eo)
1 end
EXPLANATION
.....
.....
m
.....
......
Humus
. ._:
.....
.....
......
. .....
....
.....
......
C0rOl rubble
J- /
.....
._...,
......
_ ...
. . .
.....
.......
...
.-....
Lime sand
Q3
Limestone
Scale
PUMATAHATI ISLAND
(16'2 f t from sea; 2 3 0 ft. from lagoon)
W. center
Center
E. center
P. 0'
....
...
.....
......
.....
.....
0..
....
. . ..
. .. . .
..
. 0.
....
_
u
FIGURE 12- TYPICAL SOIL PROFILES 1N TEST PITS ON RINGUTORU AND PUMATAHATI ISLANDS
RIKUMANU
PARAKAHI
40 f t from shore. 136 ft. from lagoon shore
EXPLANATION
Humus
m
Limestone f ragments
Coral rubble
p
LJ
L i m e sand
IT3
Limestone
TOKONGO
100 f t S.logoon.
6 0 ft. S. lagoon
FIGURE 13.- TYPICAL SOIL PROFILES IN TEST PITS ON RI KUMANU,
PARAKAHI AND TOKONGO ISLANDS
construction. Several i l l u s t r a t ~ . o n s of t h i s process, i n various stages of
development, axe irnom; and the natives a r e fu3.ly awa!ce of the poss;'oil.S.tles
of increasing the s i z e of t h e i r islands by t h i s method. Oile of the b e s t examples of sedimen-ta,tion r e s u l t i n g from the process i s near the south end. of
Hare Island, where a small i s l e t has been attached and completely incorporated i n t o the main i s l a n d ( f i g . 8 ) . Eemaiits of a stone causeway about
15.0 f e e t long a r e s t i l l v i s i b l e i n t h e middle of t h e a r e a though sediments
have accurnul.ated t o a considezable height on both sides of it. Seaward from
the causeway an area about 300 f e e t Ion,? has been e n t i r e l y f i l l e d i n by
n a t u r a l processes, l o c a l l y wi-th sand and elsewhere with mixed sand acd rabble
S o i l has not yet developed. On the lagoon s i d e sand aad rubS2.e have been
p i l e d up on the shoreward p a r t , leaving a iiepressed area inland toward the
causeway; t h i s low area i s swampy and already has accumultited some black
s t i c k y mud.
According t o s o i l ncmenclatwe used on okhe; a t o l l s of the Pacj.fic (stone
1951, p. 19-37), most of t h e s o i l a t Kapingamarar~giprobab1.y should be classed
a s belonging t o the "Shioya s o i l s e r i e s . " This i s e s p e c i a l l y t r u e where the
s o i l has developed i n the very young seaiments on t h e lz,goon sides of islands.
I n some ?laces on the older, seaward p a r t s of islands, development has gone
beyonu the Shioya stage and greater, more concen4Lrated a.ccumulations of organic material have r e s u l t e d i n a darker s o i l which p e ~ h t i pshould be assigned
t o t h e "Amo s o i l s e r i e s . " I n these two s o i l types there i s g r e a t t e x t u r a l
v a r i a t i o n both v e r t i c a l l y and l a t e r a l l y . Such variations, a s shown i n t e s t
p i t s ( f i g s . 1 2 t o 1 5 ) , include orgarlic materials t h a t a r e r e l a t i v e l y pure and
others t h a t a r e mixed with lime sand, coral rubole, o r limestone blocks.
Because nearly a l l the s o i l s a r e developed on surfaces a o n e the water ,table
t h a t allow r a i n water t o pass thruugh rapidly and t h a t a r e conducive t o
r e l a t i v e d r y n ~ s s ,mangrove swamps do not e x i s t and muck o r peat is scarce.
Only puralra pl.'is end a few bomb c r a t e r s where water a c c ~ ~ u l a t egermanen-tiy
s
have an enviroment favorable t o these s o i l s .
Many i l l u s t r a t i o n s of c o r r e l a t i o n s between p l a n t indicators and types
of s o i l and sediment a r e apparent on Kapingamarangi. The constant associat i o n of Scaevola with sandy beaches and'of -Guettarda with coarse rubble ramp a r t s o r with smal.1 i s l e t s covered by rubble a r e examples. This subject has
been studied i n d e t a i l by William Niering and w i l l be described by him.
DEVELOPMENT OF PHOSPHORITE
Phosphatic s o i l s and rock phosphate o r phosphorite occur a t numerous
places on various i s i a n a s of Kapingamarangi Atoll. The s o i l s appear t o be
very s i m i l a r t o ather s o i l s t h a t a r e composed of lime sand and humus, b u t
X-ray d i f f r a c t i o n t e s t s show t h a t mineralogically they contain a p a t i t e i n
addition t o c a l c i t e and aragonite and t h a t a few samples c o n s i s t of a p a t i t e
only. The phosphorite o r rock phosphate resembles i n t e x t u r e and s t r u c t u r e
the limestone from which i t developed, but commonly it i s very l i g h t i n
weight owing t o high porosity. I n many places it i s various shades of brown,
and i n general has a powdery, earthy appearance.
The ori.gin of t h e phosphorite from t h e & i n o of b i r d s i s a t t r i b u t e d t o
p h o ~ p h o r i ~ a t i oof
n s a l t s i n t h e guano,. inyolving reactions with f o r m i n i f e r a l
o r coral. limestone. According t o Aso ' ( 1 9 5 3 ; p . ' 1 9 ) t h e p r i n c i p a l components
of t h i s t n e , of phosphate normally a r e secolaary ca1:iurc p?.ios:,i~ate, CaXFO4;
t e r t i a r y calcium phcs:~haiaSe, CajP2U~;,,and cakciuii carhona-te: present i n varying r a t i o s . ':il:us, the phcspha~epLcbabl$ r e p r e s e n t s a s.'.a7;e intemediat,e
t k e coaversion taking
betveen f r e s h glans and t e r t i a r y : calciuii
place under t h e ind..uence of orga:iic a c i d and carb5nic 6 c i d gac. The e a s e
with which c a ~ . c i u m , c a r b o n a t e i sdissolved by phos~hatic'so:l.utionsi s a s i g n i f i c a n t f a c t o r i n t h i s process (.!so, 1953, p . , 17'):
.
.
.
.
The d i s t r i b u t i o n of ph3sphati.c s o i l s and .p$osph;>r:itc a t Kapingamarangi
t o have a sigrnifi2nd t h e concen~;.ati:on.,of these .p-ociucts ( t a b r
can-t relatioiiship co tk:.e h i s t o r y of i s l a n d dev.elq!n,?:~;. i!.t F;iii.a-taha-Li
Island, t e s t p i t 1 r e a r the i s l a n d c e n t e r shows cqj>l.e-te phos:>horiza:tion of
1.imestone i n both : s o i l and s t r a t i f i e d r o c k 50 a depth of 2 f e e t o r more
( t a b l e 6 ) . Test p i t 2, f a r t h e r east on 'the s&e island, shows o11l.y a l i t t l e
a p a t i t e , pcesent, and tha:t i s n e a r t h e surface. Nevertheless, t h e f a c t t h a t
surface s o i l i s ar'fected. i n b o t h -places sug:;ests recent development. High
concentration i n t k e c e n t r a l a r e a is expectable; f o r . t h. i s island. i s reported
by t h e na-Lives t o hkve been the r o o s t i n g place of i&rge iiumbei-s of f r i g a t e
b i r d s f o r man; year;.
..
'
Varying concen.trationsof. phosphatxic s o i l a r e recognized on s e v e r a l
:islands: o t h e r than P u i a t a h a t i . These i r l c l u d e T a r i ~ g a( t a b l e 6) and ld'iJerua
he
( t a b l e 4) and probably others f o r which analyses have n o t been made.
l c c a l i z a t i o n of a p a t i t e n e a r t h e s o i l surfaces on these i s l a n d s sugxests
t h a t i t s development may be r e l a t i v e l y recent. Phosphorite comprising t h e
s t r a t i f i e d rock o n s e v e r a l o t h e r i s l a n d s , however, c l e a r l y i s o f c o n s i d e r a b l e
age, i . e . , formed before t h e i.slands. had migrated t o t h e i r pyesenc d o s i t i o n s
On Ringutoru and Rilrmanu, f q r instance, high-level r e m a n t s ' of s t r a t i f i e d
rock considered t o antedate t h e l a t e s t f a l l i n sea. l e v e l , and stand.ine; above
areas of s o i l on t h e i s l a n d margins, a r e highly phosphorized. On Hare,
Iuunalrita, and Ri1:-umanu, s t r a t i f i e d rock t h a t today i s on t h e seaward shores,
beyond t h e ou.ter f r i n g e o f vege-Lation, and i s p e r i o d i c a l l y covered by hight i d e waters, likewise i s h i g h i n a p a t i t e ( t a b l e 6): .These deposits a r g i n t e r p r e t e d as rel'icts from a time when they were i n i s l a n d i n t e r i o r s , such
a s t h e f r i g a t e b i r d s i n h a b i t today, and when b i r d s i n numbers frequented t h e
areas.
..
. .
. .
G R O r n kITEX
.
..
,.
.
General features.;- The p r e s e x e on most small i s l a n d s of f r e s h o r bracki s h gFound water f l o a t i n g on t h e r e l a t i v e l y heavy s a l t riater within i s l a n d
rocks and t h e l e n s shape normally assumed by s - ~ c hbodies of f r e s h water have
long been r e c o g ~ i z e dby. hydzologists. . The riame "Ghyben-Herzberg l e n s " comm o n l y i s used i n r e f e r r i n g t o t h e s e lenses of. f r e s h water ( s t e a r n s and
Vaksvik, 1935, p. 237-:239.).
.
. .
~
Nost of t h e i s l a n d s on. Kapingamarangi
.
A.boll contain ground water of
varying degrees of freshness. On t h e l a r g e r i s l a x i s t h i s water i s potable
of a y a t i t e a s de-termined by X-1-ay d i f f r a c t i o n analyses.
Data from .Janies Gude, U. 8 . Geological Survey.
6.- Percentages
.e
\ p a t i be
3ercent;
Com~ents
-..---R e l i c t bedrock.,
50
fii!;torT-
Stra+igzapMc
--Position
High-level rermant
Rikumanu
High-level remnant
75
R e l i c t bedxocls.
Rilwanu
S t r a t i f i e d shore deposits
20
R e l i c t bedrock.
ilrumanu
40
RelicC bedrock.
unakita
30
% r a t i f i e d shore deposits
20
Soil, top
100
P i t 1, near
i.sland center.
IPuma-tahati
Upper bedrock
100
P i t 1, near
i s l a n d center.
Fmatahati
Lower bedrock
LOO
P i t 1, near
i s l a n d center.
Pumatahati
Top s o i l
2
P i t 2, eastern
interior.
IPumatahati
Transi-tion s o i l
2
P i t 2, e a s t e r n
interior.
Pumatahati
Unconsolidated
0
P i t 2, ea.stern
interior.
Taringa
Top s o i l
50
Well 2, near
island center.
Taringa
Transition s o i l
0
Well 2, near
island center.
Taringa
Coral rubble
0
Well 2, near
island center.
Island
I
I
Llt
ahat i
i
and of s u f f i c i e n t quarltity f o r domes-tic use. The natives have dug wells penet r a t i n g it i n a number of places, bwt i n general they p r e f e r c i s t e r n water
f o r drinking. This i s fortunate, f o r the wells near the places of habitation
a r e zpt t o be polluted. I n t h e v i l l a g e on Touhou, water from the community
well i s used l a r g e l y f o r washing purlsoses; much of it i s c a r r i e d i n buckets
t o bath houses b u t some i s used i n the immediate v i c i n i t y .
Because of drouths the supply of c i s t e r n rmter becomes low from time t o
time and l o c a l l y is'exhausted. A t such times t h e ground water of the islands
constitutes an impor-tant supplementary supply of potable water.. Factors t h a t
control the location, quality, and amount of t h i s water a r e similar t o those
t h a t have been described i n connection with the ground water of other a t o l l s
(COX, 1951; Arnon, 1954), b u t d i s t i n c t i v e f e a t i r e s of climate, lithology, and
t e ? r a i n a r e responsible f o r l o c a l variations and make d e s i r a b l e an analysis
of the l o c a l water problems.
Objectives
of investigation.Ground-'water s t u d i e s on Kapingamarangi
-.
-k t o l l , made p e r i o d i c a l l y during June, July a d August of 1954, wei-e conducted
Taringa, Werua, ~ a r a l i a h i ,and Hukuniu. These islands were
on four islands
selected p a r t l y because of a c c e s s i b i l i t y b u t l a r g e l y because they were considered representative of the p r i n c i p a l i s l a n d types. Taringa i s an example
of a moderately long b u t narrow (600 f.t.) i s l a n d with s t r a t i f i e d rock forming
the seaward shore and sand beaches the lagoon shore. Werua i s similar b u t
considerably wider (1000 f t ) and with more v a r i a t i o n i n topographic character
r e s u l t i n g from l a r g e r s i z e . Parakahi i s a small i s l a n d (400 f t x 300 f t )
the surface of which i s formed e n t i r e l y of ulconsolidated sediments. Hukuniu
i s a very small i s l a n d (250 f t x 150 f t ) i n which s t r a t i f i e d rock forms a l l
of the shores and a l s o the surface, except f o r a t h i n mantle of humus i n
the i n t e r i o r .
--
The p r i n c i p a l objectives of the ground-water investigation were t o obtain
data on ( 1 ) t h e depth t o water i n various p a r t s of t h e islands, 2
the amount
of change i n water l e v e l a s compared with t i d a l changes i n adjoining s e a and
lagoon, (3) the amount of l a g between t h e extremes of t i d e and the corresponding changes represented i n well levels, ( 4 ) tine e f f e c t s of permeability
i n d i f f e r e n t types of rock and i n unconsolidated sediment, ( 5 ) t h e variat i o n s i n ground-water lenses resul-Ling from differences i n s i z e of islands,
and ( 6 ) t h e q u a l i t y of the water r e s u l t i n g from various s i t u a t i o n s . A l l
these features have a close r e l a t i o n s h i p t o the a v a i l a b i l i t y and usefulness
of ground-water on Kapiugamarangi.
--
Methods of study.- A s e r i e s of e i g h t wells
t h r e e on each of t h e l a r g e
i s l a z d s and one on each of the small islands
were dug by native labor t o
a depth below .the lowest l e v e l of the water t a b l e f o r each a r e a involved.
Records were made of t h e types of sediment penetrated ( f i g s . 1 4 and 1 5 ) and
a s t a f f gage was i n s t a l l e d i n each well f o r measuring water f l u c t u a t i o n s .
Three times during t h e summer hourly reaaings were made f o r 24-hour periods
t o obtain i'rom t h i s s e r i e s of wells r e l a t i v e measurements of t h e times and
extent of water f l u c t u a t i o i ~ s . Some water samples were analyzed i n t h e f i e l d
f o r s a l i n i t y and pH. Others, representative of a l l the wells, were brought
back t o the U. S. Geological Survey i n Denver, where analyses were made by
John D. Hem.
--
EXPLANATION
rn
Coral rubble
a
3.Seaward side
Limestone
Calcareous mud
Sand: Forminifera
and/or shell fragments
I. Lagoon side
.....
-_
- I -
-
''
0
0
0
'July 30-31
- -Aug 20-21
- June 23-24
0
FIGURE 14- LITHOLOGY AND WATER LEVELS IN WELLS ON TARINGA ISLAND
Rfl
JzEy
a
Coral rubble
6 Seaward side
Limestone
Colcoreous mud
,.
Sand: Forminifera
and/or shell fragments
5 inches
Logoon side
5 lslond middle
-Aug. 20-21
"July 30-31
High
woter
levels
Low
woter
level
-
--
FIGURE 15- LITHOLOGY AND WATER LEVELS IN WELLS ON WERUA ISLAND
The v e l l s on both Tari.nga and Werna Islarids were dug i n e row across tile
islands from west (lagoon shore) t o e a s t (seaward s h t r e ) a.nd alao~ztu~idvay
along t h e lenqkh (noi.th.south di;nension) of each island. Locations of weils
a r e shom 011 maps ( f i g s . 4 and 5 ) . The spacing of the t h r e e w e l & . r e l a t i ~ e
t o the coasts on these islarlds was a s f o l l o m :
7Jel.L 2 t o- well. 3 We1.l 3 t o sea
1 Well
1 t o well 2
Lagoon t o well
--
ST---
I--
68 st..
Tarlnga
rt
2;
Ii
\
160 f t
125 f t
The s i n g l e wells OQ the two small islands were dug near t h e c e n t e r s .
cations were a s foll3ws:
l~aralcahi
/
From lagoon
(w) s i d e
-
-..
136 f t
2
From sea
(z) side
----
t
r
.
F r m north si&e
145 f t
1
'
Lo-
From south s i d e
--
-.
The riells on Tal3nga and hlerua Islands ranged i n depth from b f e e t 2
inches $0 7 f e e t 1 inch, dependiug on t h e depLh .!LO grour?d-water a t i t s lowe s t stage. The t ~ i odeepest wells were those adjacent -to t h e seaward coast.
They weye not located on boulder ramparts but OIL lower ground inl.and from
the ramparts.
These wells were t h e most d i f f i c u l t t o dig, f o r s t r a t i f i e d
rock vas encoun-te~edi n each a l i t t l e more tinan halfway devil.
Depth
t o p,round .-water.- As s t a t e d i n the Ghjbec-Herz'uerg p r i n c i p l e , the
-hi&est p c r t of the fresh-water. l e n s within the rocks of most small islands
i s sonev7hat higher than sea l e v e l adjacent t o tne island. Because t h e r a t i o
of fresh- t o salt-water density t h a t controls t h i s lens i s approximately
40/41, it follov~st h a t t h e elevation of f r e s h water above sea level. i s s l i g h t
on islands t h e s i z e of those on Kapingaxarangi. CO:~ (1351, p . 22) and Arnow
(1.954, p. 3) show t h a t an average height of at-oi~ta foot i s -to be expected
on the islands tinat they examined i n d i f f e r e n t p a r t s of the Marshall group.
Equipment was not adequate t o measure t h e elevation of ground-water
lenses with respect t o sea l e v e l a t Kapingamarangi, It seems s a f e t o assume,
however, t h a t t h e elevation on any of those islands does not exceed 10 t o
1 2 inches and i n most places i s f a r l e s s . Thus, the water l e v e l on those
islands may be regarded as roughly equal t o sea l e v e l , and the depth t o water
i n any well i s approximately equal t o the elevation above sea l e v e l of the
surface a t t h e well s i t e . Because t h e lagoon margins of islands commonly
a r e s1ie;ktly higher than the i s l a n d centers and because t h e seaward
margins a r e considerably higher than t h e lagoon margins, t h e depth t o ground
water normally i s g r e a t e s t near the seaward margins of t h e islands and l e a s t
near the centers. Figures 14 and 15, using low-vater l e v e l a s a datum plane
(not allowing f o r the increase i n elevation i n the i s l a n d center t h a t r e s u l t s
from t h e l e n s e f f e c t of t h e f r e s h water body), show t h e following depths t o
the h-ighest recorded water l e v e l :
Lagaon s i d e
1---
Middle i s land
-
43 inches
I
~erua
1
@ inches
/
Seaward s i d e
43 inches
\~'-~K'T~CZZ---.~
29 inches
I
66
inches
1
The f i g u r e s i n t h e preceding t a b l e probably a r e r e p r e s e n t a t i v e of de2-ths
required t o reach t h e u p x r l i m i t s of water on a l l -the l a r g e r isl.a.nds a t
Kapingamxrangi, but t o reach t h e l e v e l of permanent water (I&-water l e v e l )
an a d d i t i o n a l 8 t o 12 i m h e s i s required. Further, i f wells a r e t o be used
f o r domestic purposes, allowailces must be ~ m d ef o r normal drawdown, f o r
lowering due t o peri0d.s of l i t t l e recharge and f o r adeq~~.aLe
storage, s o add i t i o n a i depth is necessary. The d.ep-th should riot be g r e a t e r than necessary
t o achieve t h e e,bove o'bjectives, however, o r s e l t - w a t e r contamination of t h e
wells may occur.
On the veiy small i s l a n d s a t Kapingamarangi, t h e water t a b l e cmnonly
i s c l o s e r t o t h e surface tnan on Taringa and Werua. This i s due t o loiier
topography. Hovever, the amouut of f r e s h ilater ( i f p r e s e n t a t a l l on these
small i s l a n d s ) normally i s much l e s s and tine degree of s a l i n i t y higher than
on islands with l a r g e recharge s u r f a c e s , . a s shown by t h e wells on Parairahi
and Hukuniu I s l a n d s .
Variations i n water l ev e l . - Fluctuations i n water l e v e l i n i s l a n d s l i k e
those of Kapinganarangi A t o l l a r e p r i n c i p a l l y of two types. I n one t h e
changes a r e g r a d u a l a n d a r e t h e r e ' s u l t of.:increases o r decreases i n tine
amount of recharge; i n t h e other t h e movement i s observable from hour t o
hour and r e s u l t s frorn r i s i n g and f a l l i n g tides' t h a t cause t h e s a l t water
under the f r e s h water l e n s t o go up o r down. Fluctuations due t o gain o r
l o s s i n recharge were not detected duriflg t h e p e r i o d spent OJ Kapingamarangi
Atoll, though doubtless such changes were coiitinuous1.y a f f e c t i n g -the water
l e v e l s of a l l i s l a n d s , e s p e c i a l l y t h e very small ones. On t h e other hand,
s i g n i f i c a n t a a t a were obtained on t h e e f f e c t s of t i d e on ground-vater l e v e l s
a
p
.
Figures l l i and 15 show t h e t o t a l r i s e and f a l l of water l e v e l s i n t h e
wells on Taringa and Werua Islands, respectively, a s shown by r e a d b g s taken
oa Jilrie 28, J u l y 30, and August 20. Tile low-vater l e v e l f o r each well, a s
measured with respect t o t h e well bottom, r;ia$ e s s e n t i a l i y t h e same f o r t h e
'three dates. The high-water-levels, however, show ma.riced differences, esp e c i a l l y on Taringa, and these differences a r e d i r e c t l y r e l a t e d -Lo t i d a i
f l u c t u a t i o n s a s indicated by t i d e records. The amount of r i s e i n t h e two
wells located i n i s l a n d centers is s l i g h t l y t o moderately l e s s tha;n t h a t of
t h e r , ~ e l l son t h e corresponding i s l a n d margins, This d i f f e r e n c e v.ncloubtedly
resuLts frorn incomglete readjustment of t h e fresh-water l e n s , due t o i n creased f r i c t i o n from distance of t r a v e i , during t h e s h o r t i n t e r v a l s between
t i d a l changes. It supports t h e p r i n c i p l e , pointed out, f o r example, by Cox
(1951, p. 1 , t h a t f l u c t u a t i o n s i n t h e water t a b l e of small i s l a n d s a r e
inversely proportional t o distance from t h e coast.
-
Lag i n r i s-.-e.- and f a l l of ground water.- The elapsed time between a t t a i n -.--ment of high
- o r low s t a g e by- %he t i d e i n waters adiacent t o an i s l a n d and tine
attainment of a corresponding high o r low l e v e l by t h e ground waters i n the
i s l a n d i s variable according t o the s i z e of the island, the permeability of
rock o r sediment invol.ved., and other l e s s e r f a c t o r s . I n any eveiit, t h i s
elapsed time i s represented by a d e f i n i t e lag, vhich on Taringa Island was 3
t o 4. hours and on Werua 4 t o 5 hours ( f i g s . 16a, 16b, 2.62, 17a, -17b, 1 7 ~ ) .
On the sma'll i s l a n d of Hukwiiu, however, there w a s vir-Luaily no 3.ag between
t h e time of high t i d e and high-water l e v e l ( f i g . 18a and 18b). This i s int e r p r e t e d a s pyinlarily the r e s u l t of high permeability, a s w i i l be discussed
l a t e r , r a t h e r -than merely the small s i z e of the island.
-
Analysis of the charts showing t i d e and w e l l f l u c t u a t i o n s ( f i g s . ' 6 , 17,
1%) shows t h a t the lagoon t i d a l variation i s consistent1.y g r e a t e r than t h e
v a r i a t i o n on the seaward s i d e of the islands, b u t t h a t i n t h e areas studied,
t h e high and lor? t i d e s a r r i v e i n b o t h places a t about t h e same time. Water
l e v e l s i n the wells on each island. 1i.kewise show differences in. amount of
fluctuation, but on each i s l a n d they reach t h e i r peaks a t approximaLely the
same time. Tnese data Suggest t h a t differences i n permeability as riel1 a s
i n distances from the shore and i n t i d a l f l u c t u a t i o n a t t h e shore a r e respons i b l e f o r differences i n tne mount of r i s e and f a l l of t h e water 'cable i n
any p a r t i c u l a r p a r t of an island. Thus, i n these small i s l a n d s the freshwater lens a c t s a s a u n i t insofar a s t h e time of r i s e and f a l l i s concerned..
Relative
of sedimentary n1ateriais.An asymmetry i n t h e
----.--nerrneability
---.-permeability of a t o l l islands has been' indicated i n the work of wmerous
geololjis.ts (COX,1951, p. 19). I n most islands t h e lagoon shores a r e composed of beach sands, wheream t h e sea,%rardshores a r e comp~sedof s t r a v i f i e d
rocks, boulder ramparts, o r both. The fine-grained sedinient of the lagoon
s i d e i s f a r l e s s permeable than the coarse d e t r i t a l fragments of Lne ramp a r t or the cavernous limestone t h a t constitutes much of t h e s t r a t i f i e d rock.
Fluctuations i n water t a b l e on a t o l l islands appear t o be proportional t o
the perrneabili-ty of the sediment o r rock through which the water moves.
"-
On the islands of Taringa and Werua the seavard coasts a r e formed of
s t r a t i f i e d rock up t o and above high-tide l e v e l and of narrow boulder ramp a r t s above the rock. The rampal-'ts a r e not s i g n i f i c a n t i n s o f a r a s the
movements of the f r e s h v a t e r lenses a r e concerned, f o r , a s i l l u s t r a t e d i n
well p r o r i l e s , a l l of t h e ground-water movement on t h i s s i d e of the islands
i s within the s t r a t i f i e d rocks. Fbrthermore, water from wells on the seaward s i d e i s d e f i n i t e l y brackish, mostly not potable, which suggests t h a t
it enters through open c a v i t i e s o r cracks with Pree c i r c u l a t i o n r a t h e r than
by the slow percolation t h a t c o n s t i t u t e s intergranular movement i n t h e sanas.
I n contrast, ground water on t h e lagoon s i d e s of these i s l a n d s is f r e s h and
drinkable almost t o the beaches.
Parakahi and Hukuniu i l l u s t r a t e the e f f e c t s of permeability on the
ground water of very small islands. Well l e v e l s on Parakahi show approximately the same l a g behind t i d e fluctuazions a s represented i n wells of t h e
l a r g e r islands. The water, which i s potable, murj't enter through sand dep o s i t s from any d i r e c t i o n . I n contrast, water l e v e l i n t h e well on Hulruniu
Island, which i s formed al.most e n t i r e l y df s t r a t i f i e d rock, reaches i t s high
and low points e s s e n t i a l l y a t the same 'times t h a t high arid lo~,rt i d e s a r r i v e .
Furthernore, the s a l i n i t y .of t h e water i n t h i s w e l 1 . i ~c l o s e -to -that of sea
water
again sugg,estingeasy access through l a r g e ' channels,
--
,
.. .
--
-
of i s-. l a n d .s i z..e-on
l e n s . - . Observation w e i l s i n the centers of the
.Effects
-..
ti10 very small islands
Parakahi (1400 fi; r: 300 f t ) and HuBuniu (250 f-t x
--
150 f t )
suggest t h a t , on these islands a t lea&, permeabiliLy of t h e rock
o r sediment, r a t h e r than s i z e of t h e island, controls the amount of wa-terl e v e l r i s e and f a l l . 'Figure 18 show t h a t o n Parakahi .the r i s e i s comparable
t o t h a t of x e l l s dug i n similar sediments on the l a r g e r islands, whereas on
IIukuniu, where. cavernous, s t r a t i f i e d rock i s involved, the r i s e i s donsiderably g r e a t e r , even approaching i n amount the corresponding t o t a l r i s e of the
. .
tide.
. .
.
.
The r e a l significance of i s l a n d s i z e i n regard t o the fresh-watsr problem i s whether o r not a lens can develop and, if developed, can b e k i n t a i n e d
i n a par-t5culs.r 'area. Because continued operation of a l e n s dep'enls i n
l a r g e measure on the amount of recharge, a s i z a b l e surface are8 f o r catching
p r e c i p i t a t i o n a ; . i d a s u f f i c i e n t amount of p r e c i p i t a t i o n a r e b a s i c . I n consideririg how small An i s l a n d may maintain a fresh-water lens, Parakahi
Island, i n a region of on1.y moderate r a i n f a l l , : i s noteworthy f o r having a
lens of fresh, potable water. Hukuniu., which i s s t i l l smalier, has highly
s a l i n e water but t h i s may be due a s much t o contamination from free circulatioi? through open channels i n limestone as t o small s i z e of the i s l a n d ,
Thus, only a rough q u a l i t a t i v e measure of t h e minimumsize requirement, furnished by t h e exaniple 'of Parakahi, i s available f o r .&pirigamarangi Atoll..
..
Quality of the
ground water. - Water samples .collected on August 20,
--.--195h,?rom each of the e i g h t t e s t wells and analyzed by the U. S. Geological
Survey a r e s~wmarizedi n t a b l e 7
Data presented in t a b l e 7 i l l u s t r a t e that:well waters froid Taringa and
Wema Islands a r e progressively higher i n chemical coinponeni;s, toEa1 haruness, and percent sodium from the lagoonsrard t o t h e seaward s i d e of each
island. This trend almost c e r t a i n l y i s r e l a t e d t o t h e amount of mixing w i t h
. s e a water i n each place and probably r e s u l t s from differences i n permeability
of i s l a n d sediments and rocks. The cavernous nature of rock beds on t h e seaward sides apparently allows r e l a t i v e l y g r e a t e r mixing than i s possible i n
the intergranular spaces of sands on t h e lagoo!mard s i d e s .
--
--
Cchparison of water from t h e tr.10 small islands
~a.raliahiand Hukuniu
show d i f f e r e r i c e s s i m i i a r t o those n o t e d from one s i d e t o the other of t h e
large islands, b u t contrasts a r e g r e a t e r . These con-crasts apparently a l s o
r e s u l t f ~ o mvariations i n permeability and i n degree of mingling with sea
water. . iJat,er. from the Parakahi well i l l u s t r a t e s r e l a t i v e l y poor m i x i n j ; t h a t
i n t h e Yukun&u well has nearly the coriiposition of sea watei-.
The hardness of the well waters of '&2ingamarangi A t o l l undo&tedly ref l e c t s c o n t r i b u t i c ~ sof calciun and magnesium fromlimestone and lime sand.
The hardness increases across Taringa and Werua from lagoon t o sea, r e f l e c t ing an increase i n the degree of mixing of ground >rater with s e a water.
-m -a -a
3 3 %
PM
FIGURE 16b
-.-.-
TIDE AND WELL F L U C T U A T I O N S , TARINGA
JULY 3 0 - 3 1 , 1 9 5 4
Tide on s e a w a r d s h o r e
T i d e on l a g o o n shore
----
-
-
ISLAND
Well #I, L a g o o n s i d e
Well #2, C e n t e r o f i s l a n d
Well #3, S e a w a r d side
FIGURE 16c
T I D E AND W E L L F L U C T U A T I O N S , TARINGA
AUG. 20-21, 1954
T i d e on s e a w a r d s h o r e
T i d e on l a g o o n s h o r e
ISLAND
Well # 1 , L a g o o n s i d e
# 2 , C e n t e r of i s l a n d
----- Well
.. ..-..Well
#3, S e a w o r d side
iches
10
12
4
2
6
8
10
AM.
FIGURE 170-.
T I D E AND W E L L F L U C T U A T I O N S ,
JUNE 23-24,
Tide
----T i d e
on s e a w o r d s h o r e
on - l a g o o n s h o r e
WERUA
ISLAND
1954
W
e
l
l #4, L a g o o n s i d e
#5, C e n t e r of i s l a n d
---- Well
12
iches
FIGURE 17b
TIDE AND W E L L F L U C T U A T I O N S ,
WERUA
JULY 30-31, 1954
T i d e on l a g o o n s h o r e
-----
ISLAND
W e l l #4, L a g o o n side
Well #5, C e n t e r of i s l a n d
Well #6. S e o w o r d side
.. . . ...
iches
30
FIGURE 17c
-- -Tide
-- - -Tide
TIDE AND WELL FLUCTUATIONS, WERUA
AUG. 20-21, 1 9 5 4
on
on
seaward shore
lagoon shore
-Well
......
ISLAND
#4, Lagoon side
Well # 5 , Center of island
.Well # 6 , Seaward side
nches
A.M.
FIGURE 180-. TIDE AND WELL FLUCTUATIONS, HUKUNIU AND PARAKAHI ISLETS
JULY 30-31, 1954
---Tide
on s e a w a r d shore
----Tide
on
lagoon shore
Well # 7 , Po r o k o h i
.. . .... Well # 8 , Hukuniu
iches
i? M.
A.M.
FIGURE 18b
TIDE AND WELL FLUCTUATIONS, HUKUNIU AND PARAKAHI ISLETS
AUG. 2 0 - 2 1 ,
-----.
Tide on logoon s h o r e
1954
- d e l l
.--...Well
#7, Porakahi
# 8, Hukuniu
Table 7.- Analyses of water samples from test wells a ~ d
comparative data for normal sea water.
(~rialysesby U. S. Geological.Survey)
Taringa
-
-.
Werua
j Paraltahi ! Hukuniu
Normal
sea
water
:hemica1 components (pPm
..
Calciun (ca)
Magnesium (mg)
Sodium (?$a)
Potassium (K)
Sulfate (SO&)
chloride (~1)
?hysical characteristics
Hardness (ppm)
Percent sodium*
*Fercentage of sodium among the principal cations (sodium, potassium, calcium, and
magnesium), all expressed as chemical equivalents.
These rela.tionsbi:ps a r e i l l u s t r a t e d by the f a c t t h a t calcium i s much hi&er
than magnesium i n the near-l.a,goon sainples, r e f l e c t i n g s o l u t i o n of c a l c i m
caybona-Le and rel.ative3.y l i b t l e mixing w i t h sea crate?, :.~t~ereas
c a l c i m exceccis nia.gr;esium on1.j moderately i n -the near-sen smpl.es, r e f l e c t i n g mixing
til:Lh sea water, r.rhi.c:i has a proportlorlately h:i.yher mag~.iesi~m
con-tent.
The hardness of water from wells on the Lagoon sides and i n t h e islarid
ce!-kers ranges Se.b.;eeii 300 and 70s pgm, so t,he:i a r e inuch higher than f o r s o f t
waters ( < 50-60 p:pm) as recognized i n the United S t a t e s . These i.iakeel.s would
require "water soi'-ter?erst' f o r dc:ynest-ic use i n &ueyice. They a r e s i m i l a r i'ci
q i s l i - t y t o waters from the noi-thern ivlazshall 1sland.s recorded by l::rno>i (l95li,
P 7).
Water samples from t e s t wells on Tminga and Werua 1sla:lds were checked
a t various times during the sm!ein f o r PH arid ten@erature. The PH readings
rziiged from about '1.0 t o '7.5, alid those from the r e l a t i v e l y brackish waters
of wells on the seaward s i d e were corisisteintly high, apparectly ref'lec-Ling
a sl-ight alisaline increase from s e a :.:ater mixing. Temperahire readings f o r
alL v e i l v a t f r s were 2-1.5' t o 28O C (81.5O-ti3O F) i n the ea.ily morning, but
the) couunonly rose loo r 2O C during tile warmer p a r t of the d.ay.
:,later from >rells on t!ie lagoon margins of islands i s ::enerally more
potable than t h a t from other p a r t s and is e a s l e r t o reach by d i ~ g i n g , p r ~ ~ b ably a l l wells thus s i t u a t e d w i l l f u r n i s h water of &oad q u a l i t y which, i f
protected from pollution, can be used t o advarrtage by the Kapingans. The
U. S. Public Health Service recomuiends 250 ppm of s u l f a t e ( ~ 0 : ~and
) tine same
amoun-t of chloride ( ~ 1 )a s upper i i m i t s f o r water used i n n o r m 1 domestic
cons~ur~ption,
although water considerably higher i n these componeilts may be
used without apparent harm by people who have become adjusted t o it. Water
fro= t h e i s l a n d centers i s moderately good, b u t t h a t on t h e seaward s i d e s i s
too brackish t o be acceptable.
NEAR-SHORE
cams
Currents moving along t h e shores of t h e Kapingamarangi islan(ls a r e , i n
p a r t , normal longshore currents generated by waves and, i n p a r t , t h e r e s u l t s
of t i d e s . They contribute t o the r?orlc of erosion and deposition; a l s o they
a r e s i g n i f i c a n t i n maintaining v e n t i l a t i o n within the lagoon, introducing
and c i r c u l a t i n g new sea water with each r i s e i n t i d e . The t i d e r i s e s 5 t o 13
inches higher within t h e lagoon than it does on tine seaward sid.es of the i s lands ( f i g s . 16, 17, and 18), probably because the passes between islands
form c o n s t r i c t i o n s t h a t l i m i t the movements of water entering and leaving
the lagoon.
I n order t o obtain s p e c i f i c d a t a on t h e movemelits of near-shore currents,
records were tabulated on the d i r e c t i o n and r e l a t i v e r a t e s of ri:ovemen-t wi-th
ihina-.
respect t o nine islands ( f i g s . 19 and 20). TPxee of these islands
k i t a , Torongahai and R i n ~ x t o r u a r e i n the northern s e c t i o n of the a t o l l ,
on the eastern side, facing the
four --. Werua, Natiro, Hare, and Taringa
dominant wind direction, and two
;Pumatahaa-tiand Matukerekere -.- or1 the
southern a r c . To observe currents, fluorescein dye, which pro&uces an orange
color r e a d i l y observable even a t a distance, was poured i n the water. Movements recorded a t times of both r i s i n g and f a l l i n g t i d e s were p l o t t e d f o r
contrast.
--
--
--
--
LAGOON
Lowerfng
tide
LAGOON
--.
LAGOON
300 ft.
-O
&.
LAGOON
-O
300 ft.
300 ft.
LAGOON
?
'.
LAGOON
..
PUMATAHATI
MATUKEREKERE
-
Lowering fide
Lowering tide
0
400 fl.
,
'
FIGURE IS.-NEAR-SHORE CURRENTS OF 2 SOUTHERN,
2 EASTERN AND I NORTHERN ISLANDS OF
KAPINGAMARANGI
cuuseway
4 .
i
LAGOON
:,
!
'
*---/,
\
\-.
WERUA
W n g tide
.1
,
...,
......
. ..,
rr
causeway
/
.
TORONGAHAI
Rising fide
FIGURE 20.- NEAR -SHORE CURRENTS OF 2 EASTERN
AND 2 NORTHERN ISLANDS OF KAPINGAMARANGI
The r e s u l t s o f observations on near-shore currevts a s swwarized i n
f i g u r e s 19 and 2 0 s h o t ~t h a t on the seaward sides of most islands t i d a l curr e n t s normally move i n opposite directions from a cen-tral point. During
r i s i n g t i d e s , however, longshore currents may develo:, w i t ? s u f f i c i e n t
s t r e n g t h t o d i r e c t a l l movement i n one direction. The maps a l s o sho>~t h a t
on the concave lagoon sides, near the sand beaches, vhich a r e protected by
horns o r bars a t the i s l a n d extremities, movement of currents i s extremely
small a t most times and has no dominant direction.
The most s i g n i f i c a n t current movements adjacent .'to isl.antls a r e those
passing along the s i d e s between islands. These a r e e s p e c i a l l y e f f e c t i v e duri n g r i s i n g t i d e s . Such curreilts consistently t r a v e l t o ~ i a r dt h e lagoon, movi n g e l a s t i c s e d h e n t s and building rubble and sand bars out i n t o the lagoon
from the e n d s o f each island. Furthermore, between the bars of adjacent islands these curren-ts pro6uce submerged d e l t a s t h a t protrude well out i n t o
t h e lagoon. The d e l t a s a r e prominent i n airplane photographs and a r e conspicuaus even from a boat; normally they a r e compbsei? dominantly of c o r a l
rubble i n t h e i r headward p a r t s and of foimniuiferal sand i n deeper i , ~ a t e r s
beyond.
Because bare reef f l a t s and l i t t l e sandoccur seaward of the Kapingamarangi islands,
r e l a t i v e l y l i t t l e sediment has accumulated on t h i s s i d e . .
I/
-
This i s i!?c o n t r a s t t o t h e conditions on Nu!moro and c e r t a i n other
a t o l l z where Foraminifera ( -~ a l c a r i n a fl i v e i n abundarcce on Cne reef f l a t
outside the islands arid form extensive sand deposits.
-
-----
shores a t and below sea l e v e l a r e l a r g e l y of s t r a t i f i e d rock, whic'n shows t h e
e f f e c t s of pla;lation as should be expected from knotm current 'trends. Tb.e
few lime sands t h a t wash i n t o t h i s a r e a normally do not remain but a r e moved
along by currents and waves through t h e g a p between i s h 3 d s and thence i n t o
t h e lagoon. Even c o r a l rubble from t h e reef edge, which i s ictroduced i n
considerable amounts, appears t o be t r a n s i t o r y w i t h respect t o most seaward
shores. Only the ramparts of, boulders o r rubble t h a t stand a'oove high-tide
l e v e l and a r e formed by: t h e waves of occasional l a r g e s t o r m form s i g n i f. i. cant deposits on seaward p a r t s o f t h e islands.
I n the near-shore waters on. the lagoon sides of i s l a n d s , protected from
t h e 13revalent e a s t e r l y winds by t h e i s l a n d s themselves a n d from t i d a l curr e n t s by the horns o r bars a t i s l a r $ d ' e x ~ r 6 i i t i e s , the, normal, extremely weak
and variable currents seem incapable e i t h e r of depositing o r of removing
sediments of the beach. Most of these beaches a r e of foraminifera1 sand and
t h e species represented appear t o l i v e i n t h e s h a l l o w waters nearby,.but
t h e i r accumulation and t h a t of c o r a l r&oble a s fou,nd a t Hare and some other
islands probably r e s u l t fkom the, occasional reversals i n wind direction,.
which bring waves f ~ o &
west t o e a s t ' across the lagoon. These wind reversals
r e s u l t i n a considerable p i i i n g up of water andsediment a g a i n s t lagoon
shores of t h e islands.
The i s l a n d of. w a t a h a t i , on t h e southern rim of t h e a t o l l and near t h e
v e s t e r n end of i t s islands, i s unique i n t h a t i t s lagoon beach i s formed a l most e n t i r e l y of c o r a l rubble r a t h e r than sand and i n t h a t it has a welldeveloped rubble rampart on the lagoon s i d e ( f i g . 9). Both of these feat u r e s can be explained only a s t h e r e s u l t s of t h e a c t i o n of l a r g e waves
'
'
"
''
caused by strong winds. Furthermore, the winds must have come from e a s t t o
west across the la6oo11, f o r the source of rubble on the rampari; and t h e
g r e a t e s t conceii-txtion of rubble on t h e beach a r e a t the eastern end. Such
feal;ures developed on t h i s island. and not on others probably because of I t s
f a r westerly position on the southern r e e f .
SEDIMElKT!ATION I N THE LAGOOB
The lagoon a-t K a p i n g ~ a ~ a n gcovers
i
an area of about 15.5 square miles
and has maximum dimensiow of 5 by 6 n a u t i c a l miles ( ~ u g e n t , 1946, p. 755).
Although it i s roughl.~c i r c u l a r i n plan, i t s symme-try i s f a r from p e r f e c t
because of an almost s t r a i g h t southwestern s i d e . P r o f i l e s of t h e lagcon
bottom, disregarding the many i r r e g u l a r i t i e s caused by patch r e e f s t h a t r i s e
from i-t, a r e those of a shallow basin ( f i g . 21). Even. with the g r e a t l y exaggerated v e r t i c a l s c a l e used i n t h e s e c t i o n s , the slope apnears gentle,
and sections of near-shore areas ( f i g . 22) and of Manin knoll ( f i g . 23),
made with t h e same v e r t i c a l and horizontal scales, demonstra'ce t h e lowangled slopes on which sediraeri-i;s a r e accumulating.
The deepest par-ts of the lagoon, i n the north-central and east-cen-tzal.
areas ( f i g . 2 ) a r e recorded as 4.3 fathoms on U. S. Navy Hjdrogmphic Off i c e Chart 5042. The g r e a t e s t depth measured by t h e writ,er i n more %hail
200 soundings was :!O fathoms (2b0 f e e t ) ; however, t h i s depth was reacheii
i n a t l e a s t f i v e places, suggesting a r e l a t i v e l y f i a t bottom. Beeawe of
the s l i g h t l y a s p m e t r i c a l d i s t r i b u t i o n of t h e deepest areas, resul.tiiig i n
gent1.e slopes on the south and wes-t sides of t h e lagoon, Nugent (1946, p .
756) postulated t h a t Kapingatnarangi "is apparently t i l t e d t o the nor+;heast."
This f e a t u r e of d i s t r i b u t i o n can b e equally well explained i n other Trays,
however, and the r e l a t i v e narrowness of t h e southwest a r c of the a t o l l a s
compared t o t h e northeastern arc argues against t h e postulate.
I n order t o obtain a d e t a i l e d record of bottom sediments i n t h e lagoon,
samp1.e~were col.lected systematically along many l i n e s forming a modified
g r i d p a t t e r n . Both grab samplers and bottom drags were employed durinz t h e
vork, and i n r e l a t i v e l y shal.10~waters samp3.e~were obtained by diving.
Approximately 250 samples, representative of e s s e n t i a l l j a l l par-ts of t h e
lagoon, were collected. Time has n o t y e t permitted study of these sani$.es
except i n a general way, so d e t a i l s regarding t h e i r c h a r a c t e r i s t i c s , d i s tribwtion, and s i g n i f i c a x e must await publication a t a l a t e r date. Only
a generalized statement can be made a t t h i s time.
A r e l a t i o n s h i p between type of sediment and depth of water ( f i g . 25)
i s apparent i n t h e lagoon a t Kapingamaran&i. Of seven p r i n c i p a l tyjjes of
sediment t h a t a r e recognized, s i x a r e r e s t r i c t e d t o r e l a t i v e l y narrow l i m i t s
i n depth, forming a s e r i e s of bands e n c i r c l i n g t h e deepest p a r t s of t h e
lagoon. The seventh type of sedimen-t i s a white s i l t , ap;3arently formed
of comminuted s h e l l s , corals, and other debris; i t i s d i s t r i b ~ ~ t eal.ong
d.
%t~.e
paths of s t r o n z bottom currents a t depths ranging from a few ree-t down t o
at l e a s t 200 f e e t . The other sediments and tiieir general ranges a r e a s
f ollorrs :
3
LL
0
2I
(L
F
0
Z
e
I
2
4
5*
5I
3
3
,$?
4
I
a
/
NORTH-SOUTH SECTION
2
W
".
,<
=
t"
Z
0
W
D.
i:
9
I
Y
w
::::
W
e
"
i
NORTH-SOUTH SECTION
FIGURE 21.- SECTION ACROSS KAPINGAMARANGI LAGOON
/ VEM/CAL EXAGGERAVON APPROX/MATEL Y X30)
I Nautical mile (6080 Feet1
- O
r 40 Fathoms (240 Feet;
~ + m r r .. , ,_
,
.,
........... Low lid8 /eve/
Y
-"
3 0
____-
V
,,
... -
- - ........... -.
FROM MATiRO BEACH WESTWARD
/,
.-
Low tide level
.
.
. -
.
O O O O O O O O D O O O O o O ~ l l
FROM MATIRO-MATUKETUKE PASS (N)
WESTWARD
....
FROM MATIRO-MATUKETUKE
PASS ( S ) WESTWARD
____..__~
-___. ..
--
Low lids leod
FROM S.W. REEF (WEST OF TIUTUA KNOLL) NORTHWARD
EXPLANATION
Ezg
F14
Coroi rubble
Microatolls
Foiominiferai sand
Branch corals
FIGURE 22- OFF-SHORE PROFILES IN EAST AND SOUTH SECTIONS OF
ATOLL AND DISTRIBUTION OF BOTTOM SEDIMENTS
0
50 Feet
u
Verf,coi ond horizonto1 scole
WEST-EAST PROFILE
-
NORTHWEST-SOUTHEAST PROFILE
NORTH-SOUTH PROFILE
NORTHEAST-SOUTHWEST PROFILE
FIGURE 23.- PROFILES OF MANlN PATCH REEF
0
50
100 Feet
u
Verhcol ond hormntol rcole
EXPLANATION
Depth
in
feef
Z
u
FIGURE 25.-RELATIVE PROPORTIONS OF PRINCIPAL TYPES
OF SEDIMENT AT 5-FOOT DEPTH INTERVALS
AS DETERMINED BY SAMPLING
-
tegina
1. Sand dominantly of Foraminifera fhphis -- madagascariensis
..
dlOrbigny, Marginopixa
vei'tebraiis
S
l
a
i
n
v
i
l l e , and Elphidirun
. -- - ---..c r a t i c u la t w . ( ~ = c T t e ar:d
l
~:;ollr/
(50 f e e t ; mostly 0-25
-.
feet.
2 . Sand dominantly of c l a s t i c shell. frabments
10-50 f e e t ; mostly
25-50 f e e t .
-
--
--
--
3.
Coarse debris, l a r g e l y of dead branch corals, acclmiulated between
30-105 f e e t .
and below t h i c k e t s of livir-g c o r a l s
--
Accumlations
<patchx).
5.
-
macroloba fragzents
of Halimeda -
--
90-160 f e e t
F o ~ a m i n i f e r a lsand (Amphistegina Lessonii d10rbigny) &I--120-210
L'eet.
-
I/ Chief mino:r faunal elements a r e .-Iieterostegina
suborbicularis
dlOrbigny
-., -and G e r c u l --i n a -----anmoroides (Gronovius); others associa,tsd a r e Spiroloculina
comiwis ?&rmz~i and To&&, .
Cibicides
lobatulus
(walker and 3a"ob),and
.- - .- . -. -Planorbulinella l a r v a t a (Parker ant! Jonesj. I d e n t i f i e d by M. W;h Todd.
-
-
----
6 . Calcareous mud (coiltains aragonite needles a.nd ab0u.i; i O percent of
small Foraminifera)
--
150-240 f e e t .
Sedimentary b e l t s within the lagoon appear t o represent, f o r t i e most
p a r t , t,he normal h a b i t a t s of the various orgaxisms invoiv.d, f o r a l a r g e proportion of samples show l i t t l e of t h e mixing tha-t would be expected if crganisms had been trarsported by currents i n t o pockets of accumulation. Orange
foraminifera1 sand of near-shore areas ( b e l t I) grades outvard and downward
i n t o white c l a s t i c sand of b e l t 2. Likewise, t h e r e i s gradation betveen the
Halimeda
macroloba sand of b e l t 4 an6 h e Amphistegina
i e s s..--o n i i sand of b e l t
---5 . Corals, especially branching types t h a t cover the boiAorn surface mainly
between depths of 30 and 90 f e e t , form an e f f e c t i v e b a r r i e r i n most p a r t s of
the lagoon betveen the sediments above and below these depths. Fragments
of brolien coral, many of them large, cover most of t h e lagooil f l o o r be.hreen
the l i v i n g corals.
The calcareous mud which covers most of the lagoon bottom a t d e p t h belor? 34 fathoms (204 f e e t ) , but which has been obtained from si;a4;ions a s
shallow a s 25 fathoms (150 f e e t ) , i s p a l e o l i v e green and very p l a s t i c anq
s t i c k y when wet. Mineral analyses made with X-ray d i f f r a c t i o n p a t t e r n s :/
show t h a t much of t h i s mud i s aragonite, but it contains a small proportion
- -2/
-
Analyses by A. J. Gude 117, U. S. Geological Survey.
of c a l c i t e . The c a l c i t e probably i s a t t r i b u t a b l e t o t h e Foraminifera included. These form only a small percentage of the mud but a r e represented
by a r i c h fauna including man$ genera and species. I n a s i n g l e sample from a
depth of 36 fathoms, Ruth Todd of t h e U. S. Geological Survey noted 39 spec i e s . She reports the following a s crude estimates of the percentage of t h e
. . .
t o t a l foraminifera1 fauna:
................
Todd; ; . :
........
----
Cibicides 1oba.tulus (walker and Ja.cob)
.
A
Spiroloculina comunis Cuslmian .. and
-----comp!.ana.ta
-Virgulina
.--.
2 . .
Percent
--
20
20
10
Eg,ger
). . . . . . . . . . . . . . . . . .
a -agglutinans dtOrbigny
-T e x t u l m i.
12
I
f o l i a c e a Heron-Allen and ~ a r l a c d )
-T. -.-Amphistegina .mada?;asoariensis d'orbigny ) . . . . . . . . . . . . . . .
-----,-
-A.
10
)
sp. (small, f l a t worm)
1
"The remaining 28% is.cotnposed of gbout 32 a d d i t i o n a l species among
which one species e a c h o f Tretompha+$-,
Globigerina, C ~ & o ~ g p o r e t A aL,o=st%=
and OperculLna make up t h e - b u l l ; (perhaps a s much a s 15 c r 20% of
the whole fauna). The Globiger*~ i.s a planktonic form arid t h e T~zouip:n&l>.si s a n , a t t a c h e d form with a plankt,oriic s t a g e . Cc~mbalopoiettaand Cibe.ci.d.es
may be attached, b u t a r e not n e c e s s a r i l y al'rrays attached. ( U l t h e others a r e
benthonic forms, s o f a r a s imor.rn."
The o r i g i n of t h e calcareous mud i s n o t known, and d e t a i l e d s t u d i e s of
it have not y e t been made. Evidence a t hand, however, suggests & a t t h e mud
i s not derived primarily from t h e r e s i d u e of sediments occurring a t higher
l e v e l s . Although i t s composition i s p r i n c i p a l l y aragoni,Le, it i s l a r g e l y
surrouiided by a bel-t of Amphistegina --l e s s o n i i with a composiLion of normal
c a l c i t e . If t h e a r a g o n i t e were eerived from e i t h e r c o r a l o r s h e l l debris of
shallower depths, t h e difficult;. of explaining how i t bypassed the surroundirig c a l c i t e b e l t i s encountered. On t h e o t h e r hand, t h e presence of some
aragonite needles suggests t h e p o s s i b i l i t y t h a t it formed a s a chemical precipitate.
..
The o v e r a l l pa-ttern formed by b e l t s of sed.imentation i n t h e lagoon a t
Ihpingamarangi i s , of course, much complicated by t h e many pa.tch r e e f s that
r i s e above t h e f l o o r . Each o f t h e s e has sediments on i t s top and s i d e s of
v a r i e t i e s i n keeping with the general depth ranges, except t h a t where slopes
a r e e s p e c i a l l y s t e e p t h e lower l i m i t s of various sedimentary types exlend
deeper than otherwise. Further complications i n t h e p a t t e r n of se2imen-kary
b e l t s a r e caused by bottom currerlts i n c e r t a i n a r e a s . Tile white s i l t s
c h a r a c t e r i s t i c of these current z o n e s a r e e s p e c i a l l y well developed i n and
near the ma.in pass on t h e south, i n a broad a r e a bordering t h e sou-th s i d e of
t h e a t o l l and within a mile of it, and .in narrow zones bordering t h e ves-i;erri
and northern a r c s . The east-trending deposits of current-'cramported s i l t s
a r e prominerit i n a i r p l a n e photographs of t h e southern p a r t of t h e l a ~ o o n .
The problem of 37by b e l t s of sedimen-t comparable t o those i n ICapingm!arangi lagoon a r e nut recognized i n other a t o l l s merits consideration. A
l i k e l y answer i s found i n comparative depths: mosi; o t h e r lagoons t h a t have
.
.
.
.
been sampled a r e shal!;.oyer thah the one a i ' I b p i n g m a r e n g i . Available des c r i p t i o n s i n d i c a t e tnaf b e l t s co~-res_noi~c?ii~g
t o those of t h e rel.alive3.y
shallow waters do occur, i . , the b e l t s of near-shore f o r a m i u i f e r a l sand,
of c l a s t i c sand, and of c o r a l d e b r i s . At Raroia, i n t h e deeper p a r t s (2025 fa-thorns), Ner.~ell(1954, p. . 25). r e p o r t s , a l a c k of bo-mom mud but records
This 'dht:ibution paral3.els c l o s e l y t h a t
some accumulatioris of Hal.i.meda.
--.-f o r correspoi.ding depths a t Kapingamarmgi . .
-
.
GECLOGY OF
TI% PATCH REEFS
The evenness of t h e bowl-shaped basin chat contains t h e lagoon a t Kapingamarailgi i s disrupted i n many places by patch r e e f s t h a t r i s e as moulds from
: i t s s i d e s and floor.. Many of these r e e f s a r e s u b c i r c u l a r i n plan, b u t others
a r e linea?, and s t i l l others very i r r e & a r .
They range i n s i z e from low
: k n o l l s or pinnacles a few dozen f e e t c.cross and 10 o r 20 f e e t high t o wide
platforms t h a t a r e 1.00 f e e t high o r more. Among t h e l a r g e s t i s Sokoro, vhose
'tab i s 2,900 f e e t long and 700 fee-t vide, aiid Tokope;, which has an upper
surface approximately 1,1100 f e e t by 900 f e e t ( f i g . 20).
.
.
The t o t a l number of pa-tch r e e f s i s no-ci"imown, but 20 of those i.isted
a r e more than 500 f e e t long.. Available mapsshoy aoproximately '75 of a l l
s i z e s , y e t even -this number probably i s far from'Lhe t o k a l , f o r :nany very
sma1.l ones and others t h a t 60 n o t reach th&'sul.fa&ea r e noi: included. Cou~ltigg oT patch r e e f s i s f V t h e r co,pfus&d &caVs& sane r e e f s tha-t appear sepa r a t e a t the surface a r e c o i e c t e d a t 'diallor< 'dep$hs. Of t h e az?roximately
I 5 inciicated on maps, 35 are ' i n w a t e s deeper ,than 60'f e e t , including some
of t h e very l a r g e o m s t h a t . r i s e from t?ne deepest pakis of t h e lagoon. The
o t h e r 40 pa-tch r e e f s shown on. t h e niaps , r ~ ' m o ~ , tsmall
ly
imd occur i n shoal
waters bordering t h e i k i e r garGih. o f . The 'a;toll; ,especfally along i t s northern
. .
. .
, ..
and western s i d e s .
:
-
~.
. .
.
Nearly a l l t h e patch reefs. a:t :~b,billgmfl&ran~i
'have f l a t tops a t o r
s l i g h t l y above ].ow-tide.. l e v e l , &.viilg t o each ix3ul.a t h e i@pea;.ance of. a
mesa r i s i n g up through
. . t h e lagoop. Only on & few of t h e s.dbmeimged'.reefs
do top surfaces appea? t o b e . soniqhat Poun~ledand i r r e g u l a r . F l a t tops :are
c h a r a c t e r i s t i c a l l y developed and m a h t a i n e d i n most patch r e e f s 'because t h e
ulx~ardgrowth of orgariisms is c o n t r o i l e d b y t i d e l e v e l s and t h e s u r f a c e . i s
continually being bevelled by w a v e ' a c t i o n , The s i d e s a r e steep, i n general,
an4 commonly slope off a t angles of 30" Lo Cboo'.'
hey have t h e appearance of
being f a r s t e e p e r than t h i s ' and l o c a l l y seem' t o l b e nearly v e r t i c a l , butmeasurements show t h a t m ~ s - vt i s u a l estimates a r e high.
.
,
. .
..
The general shape of Manin k n o l l i n t h e n o r t h e a s t . e m ' ~ a r tof t h e lagoon
wa:; determined from soundings ( t a b l e 8). This p&h r e e f probably i s t y p i c a l of most a t Kapingamarangi. P r o f i l e s ( f i g . 23) silo>: t h a t i t s southwest
s i d e , i n i t s s t e e p e s t p a r t , slo$es dor.m a t about 50' within a v e r t i c a l d i s tance of h0 t o 50 fee-L, and t h a t t h e i ~ o ~ t h w e s it d e has a slope of about
40°. These a r e extremes, and o t h e r s i d e s of t h e reef have more g e n t l e
slopes, including t h e southeastern s e c t o r , which extends a s a s l i g h t l y submerge3 promontory o r ridge f a r out i n t o t h e lagooil.
Table 8.- Depth ( i n f e e t ) of lagoon f l o o r ,surrounding Manin patch reef
Distance ( i n f t )
outward from
reef margin
- -- .-- -- -. -
Directior
r--
1 4 5 ~ ~8 '0 ' ~
..
--
..-
2
2
30
18
60
-96
.s4
, 54.
1
80
PO2
n b
i
I
I
--.
-
*Along submarine ridge, 128 f e e t outward from 2-foot margin.
The d i s t r i b u t i o n and o r i e n t a t i o n of patch r e e f s i n the lagoon seem t o
r e f l e c t i n l a r g e measure the trends o f currents and waves. A c l u s t e r of
patch reefs, some of them large, near the s h i p ' s pass on t h e south s i d e of
the a t o l l probably i s d i r e c t l y r e l a t e d t o the strong currents t h a t maintain
good c i r c u l a t i o n i n t h a t area. The many small patch reefs immediately ins i d e t h e northwestern and western a r c s of t h e a t o l l apparently developed i n
response t o waves of maximum f e t c h before t h e dominant winds. Likewise a
general northwestward l i n e a t i o n of many r e e f s i n t h e lagoon center probably
r e f l e c t s t h i s dominant wave d i r e c t i o n . The f a c t t h a t many of the patch
r e e f s a r e subcircular r a t h e r than elongate i s believed t o be due t o the
r e l a t i v e quietness of lagoon waters., allowing nearly equal growth i n a l l
directions, a s suggested by Cloud (1952a, p. 2140).
A l l of t h e patch reefs i n deep water, and many of those i n shallow, r i s e
from p a r t s of t h e iagoon bottom t h a t a r e covered with extensive deposits of
foraminifera1 sand and calcareous mud. The patch reefs themselves, however,
a r e l a r g e l y mantled with growing c o r a l s . Dense t h i c k e t s o r f o r e s t s of t h e
yellow, branching Porites andrewsi cover most of t h e sides, and both microa t o l l s and smaller c o r a l h e a d ~ ~ r e p r e s e n t i nnumerous
g
species, cover extensive areas on the f l a t tops, e s p e c i a l l y along the margins. Typical c o r a l
assemblages from three Kapingamarangi patch r e e f s , i d e n t i f i e d by J. W.. ldells,
a r e l i s t e d i n t a b l e 9. The l i s t served t o i n d i c a t e the p r i n c i p a l forms,
though others contribute t o t h e r e e f s a l s o . A comparison of these lists
with those of Wells (1954, p . 390-393) f o r the Marshall Islends shows t h a t
a l l of t h e genera and a l l b u t two of the species of Kapingamarangi occur
a l s o i n t h e Marshall Islands.
Table
9.-
Some c h a r a c t e r i s t i c c o r a l asscliiblages on Kapil~~amarangi
Atoll,
determiried by Z. W. Weils
1.. b5i l k
s
Im" ". $ 0
k aJ
ikd ~i
k u
o
c-i
ii
i6 b .
r(
i
z4
o 6o1
i1
$2
;
4
l;da :o. .rn /
lu
[in
.- -- .----.
--+
Psammocnra
n. l e.-.r; s t r a s z i. v.d. Horst
I
j S e r i a t o p o r a h y s t r l x Dana
1
/
-..
P o c l l l o p o r a d a m' c o r n i s ( ~ i n n a e u s )
x
i
!
daGe3FFFil-1
I
1
. - I
.L
i
i
i
/
'
~
Wells -i
p r o l i"---.f e r a ~ r u e g g e m a i ' i!
.
i
v e r r i l l i Vaurrhan
!
--'--
--
f < a s o ~Dana
l-u t e e M.
F@vJ~ p&l&Lda -(Dana)
E.
&
H.
i
k
i
,
!
t1
-.-
i
I'
,-I
8~
~ jrr\ b /
.
!
,
0
.
,
I
X
The s u r f a c e s of piitch reefs, whe?e not covered with l i v i n g c o r a l s , a r e
eit.her occupied by a c c m u l a t i o n s of c l a s t i c and foraminifera1 sailds o r a.re
barren areas of dead c o r a l . The proportion of each i s extremely \rar:iable
from reef t o r e e f . The amoun'; of dead c o r a l a r e a seems t o depend, i n l a r g e
ineasure, on t h e elevation of t h e reef top with resx~ectt o low-tide l e v e l .
Tolrohui and T h a n , f o r example, a r e 1mol.ls aitii top surfaces 2 t o 3 f e e t
lower t1la.n those of most a s s o c i a t e d patch r e e f s ( f i g . 26) and as a r e s u l t
have no extensive areas of' barren, 6.ead c o r a l . Their surfaces a r e l a r g e l y
covered with well-formed c o r a l s . Few of t h e massive types of c o r a l have
dead centers o r form microa.tolls, and many of t h e yellow, branching P o r i t e s ,
which on other 1moll.s grow only on t h e margins and s i d e s , a r e well developed
even near t h e centers of these r e e f s . In c o n t r a s t , on Sokoro sad Tiwawe
k n o l l s , both of which sttiild w e l l above l o w t i d e l e v e l , ex-bensive areas of
dead, bevelled c o r a l occur i n t h e centers, and microatolls a r e conunon along
the tops ( f i g . 26).
Lime sand i h a t accumulates on t h e upper.sides i n d tops of most patch
r e e f s i s s i m i l a r t o t h a t accumula-tin6 a t corresponding depths o f f t h e lagoon
beaches and lagoon reef margins of t h e a t o l l . This sand c o n s i s t s l a r g e l y of
s l i e l l s arid c o r a l s . Some sand coriiains moderate amounts of l o c a l l y derived
Halimeda opuntia fragments. From f i e l d sketches of 10 r e p r e s e n t a t i v e pa-tch
reef-ig.
2b), t h e c i l a r a c t e r i s t i c d i s t r i b u t i o n of sand i s apparer~t. In
general, sand is concentrated i n t h e centers and on t h e norbheastern margins,
belaw which it cormonly covers slopes down t o depths of 20 fee-t o r more.
The thickness of sand accumulations on most patch r e e f s does not appear t o
be g r e a t ( t a b l e l o ) , and on some, where c o r a l growth i s e s p e c i a l l y h x u r i a n t , sand i s confined Lo small pockets. In c o n t r a s t , Sokoro, Tokopel,
and a few other knolls contai:l s u f f i c i e n t sand t o form b a r s of appreciable
s i z e t h a t r i s e well above low-tide l e v e l .
.
.
.
.
h i b 1 . e 10.- Thickness ( i n inches) of sand accumulations on patch r e e f s
I
..
~.
..
...-.
.
S
W Area
Patch Reef
- I
E Margin
Center
/
!
j
1i
1
.
,.
...........-..
6
Tisu
i
%tamtong
Sokoro
!
Why
entirely
thickets
wl-th tine
I
i
.. i
11
-
...............................
I
1
I
II
I
5
7
lo
!I
Ii
i
5
lj
.....
.i.
sand t h a t extends over t h e rims of t h e lmolls i s confined almost
t o t h e northeastern slopes i s not known. On o t h e r s i d e s , where
of branching c o r a l s a r e absent, t h e slopes normally are covered
debris of dead c o r a l branches i n s t e a d of sand.
As s t a t e d by Ladd and o t h e r s (1950, p. b2l.), " t h e age, o r i g i n and
i n t e r n a l c o n s t l t u t i o n of t h e k n o l l s i s not known, as no s t r u c t u r e of this
I
1
1i
..
!
i
i
I
EXPLANATION
n
rn
Microatolls
Dead coral pavement
Sand surface
Branch corals
Spherical coral heads
HAKAROPURAP
Diameter 500 ft.
TIWAWE
I200 ft x 800f1.
TOKOPEL
1400 ft. w 90011.
MATAMATONG
1000 ft. x 800 ft
TlSU
Diameter 500 ft
TOKOLARA
Length 500 ft
THOKOMOTU
Diameter 500 f1.
SOKORO
2900 f f x 700fl
TOKOHUI
3 0 0 ft.
FIGURE 26.-FIELD SKETCHES OF PATCH REEFS SHOWING
DISTRIBUTION OF SEDIMENTS AND CORALS
t o e has ever been d r i l l e d . " Those w r i t e r s suggest t h a t -the p t c h r e e f s filayhave developed through sporadic cora:L growth t h a t was i r i i t i a t e d during a
p a r t of t h e Pleis-Locene e ~ o c h ,when s e a >.eve1 was much lover than now. Such
avail.db1e c o n c e r ~ i n g
an hypothesis iiould f i t very well tine mcager kno:.led;:e
t h e shape of t h e lagoon basin, t h e extensive bot"com saiids arid r;uds t h a t a r e
helping t o f i l l it, and t h e patch r e e f s t.hat r i s e t o 10.7-tide l e v e l within
Che lagooii. Fu~thermore, t h e bevelled. surfaces of dead coi,al, ba.ck from
tine a c t i v e l y y-owing rims on ;nos t of t h e high knolls, s t r o n g l j s u g g e s t t h a t
l i k e the o u . k r reef of' t h e ato1.l they were higher than a t p r b e r i i not f a r
back i n h i s t o r y and ha,ve been 'truncated because of a receut drop i n sea l e v e l .
From ?>hatmay be observed of t h e i r simple s h a j e and s t r u c t u r e , it seeins
probable t h a t t h e s e patch r e e f s a r e s i a i l a r i n a l l e s s e n t i a l res2ects t o
t h e bioherins t h a t have been described fr-om many ancient deposits, especial1.y
those of S i l u r i a n and Devoxian age ( ~ h r o c l r ,1939).
RE>TRFfi?CES CITED
Arnox, Ted, 195it, Die hg-krology of t h e northern K a r s t a l l Islands:
Research Bull. 30, 7 p. ;
.. . .
Atoll
Aso, Yavata, 1-953, A yrel.iminaly study of t h e p r o p e r t i z s and forr(iatioi1 of
phosphate deposits on Tolwbei Island; r e p o r t , Sou-;;'? Sea Developmmt.
aJ B r . , U. S.
Company, Pe<xu%cy 193': l'ranslation, M i l i t a r y Goolos-i
Geo1. Survey, Tokyo, 19 p.
Chave, K. E . , 19:'+, Aspects ol' t h e biochemistry of magnes%um. 1. Calcareous rnarine organisms: Jour. Geology, v. 62, no. 3 , p. 266-233.
Cloud, ?. E., Jr., 1952a, F'acies r e l a t i o n s h i p s of' organic r e e f s : Am. kssoc.
Petroleum Geologists Bull., v. 36, no. l k , p . 2125-2149.
, l952b, Preliminary r e p o r t on geology and marine environ-.-----ments of' Onotos Atoll, G i l b e r t Islands: A t o l l R e s e a x h Bull. 12, 73 p.
Cox, D. C . , 1951, T'ne hydrology of Arno Atoll, Marshall Islands:
Research Bull. 8, 29 p.
D a l ~ ,R . A . , 1924, The geology of American Samoa:
ton k b . 340, p . 93-143.
Atoll
Carne@ie I n s t . ilashing-
Davici, T. W., anG Sweet, G . , lgOh-, The geology of li'unafu2;i: Royal Soc.
London, Nept. of Coral Keef Corm.,
A t o l l of I'unafwii, sec. 5,
p. 6 1 - 2 4 .
Fairbridge, R. W., 1953, Recent and Pleistocene c o r a l r e e f s of Australia:
Jour. Geology, v. 58, .no. 4, p. 330-401,
Fiela, R . M., 1920, Origin of t h e "Beach Xock" ( ~ o ~ u i i l a t) Loggerhead. Keyi
Tortugas: Geol. Soc. America B u l l . , v. 31, no. 1, _u. 215.
Ginsburg, R, N., 1953, Beachrock i n south Florida:
Petrology, v. 23, no. 2, p. 85-92.
Jour. Sedimentary
Ladd, H. S., Tracey, J. I . , Wells, J, F., and Ekery, I:. O . , 1950, Organic
grow-th and sedimentatAon on iin a t o l l : Sour. Ge(Goyj, v. 58, no- '.I,
p , 410-495.
Ladd,
H. S., Ingerson, E a r l , Tomsend, R . C . , Russell, I.la.rtj.n, aild St,ephenAm.
son, H. K., 1953, Drill-ing on Eniwntok PLu11, Miirsxiail Is!.anr;s:
Assoc. Petroleum Geolo<is"u Bull., v. 3,1;s. 0
p. 225.r-2260.
Llogd, Christcpiier, lg&J3 The voyaces of Captain James Cook r m 3 t:ie world,
s e l e c t e d from h i s journals: London, Cresset Press, 384 9.
MacNeil., F. S . , i950, Planation oC r e c e n t reef fla-ts on OXinawa:
Ari.erica Bull., v. 61, no. 11., p. 1307-1308.
Newell, N. D., 1954, Reef's and sedlneztary processes of Ilal-oia:
search Bull. 36, 35 p.
Geol. SOC.
A t o l l Ne-
Nugent, L. E., Jr., 1945, Coral r e e f s i n t!le G i l b e r t , Marshall and. Caroline
Islands: Geol, Soc. America Bull,, v. 57, :lo. 8, p. 735-790.
Shrock, R . R . , 1939, Wisccnsin S i l u r i a n bioilerms (organic r e e f s ) :
Soc. America Bull., v, 50, no. 4, p . $29-562.
Geol.
Sewe1.1, R . B. S . , 3.936, .b accoun-t of Adau k t o l l : E r i - t i s h Kus. Nst. History,
The Johr, Murray Ex@.
1931-34, S c i . Rep-ts., v . 1, no. 3 and 55, p .
63-95.
S o l l a s , W. J., 1904, Xarrative of t h e expedition i n j.896: Royal Sac. London,
Re3.l: of Coral Reef Comfi., The A t o l l of Funafuti, sec. 1 p 1-28.
Stearns, H. T., an6 Vaksvik, K. N., 1935, Geology and ground-.rater' resources
of' -the is]-and cf Oahu, Hawaii: Hawaii Dept. of Public Lsnds, Div.
Iiyckograpily, Bull. I., 479 p .
Stone, E . L., J r . , 1951, The s o i l s of A x o A t o l l , Marshall I s l a n d s :
Research E u l l . 5, p . 1-55.
Atoll
Tracey, J. I , , Emery, K. O . , and Cloud, P. E., Jr., 1955, Conspicuous feat u r e s of organic r e e f s : A t o l l Research E u l l . 46, 3 p .
Wells, J. W . , 1951, The c o r a l r e e f s of Arno A t o l l , Marshall. Islands: A t o l l
Research Bull. 9, 1 4 p .
-- 1954, Recent c o r a l s of t h e Marshall Islands: U, S. Geol.
Survey Prof. Paper 269-1, p 385-486.
,
.

ATOLL RESEARCH BULLETIN No. 50 Geology of Kapingamarangi

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