The deltaje complex ofSt. Lloreng del Munt

The deltaje complex ofSt. Lloreng del Munt
(Middle-upper Eocene, SE Catalan basin)
E. MÁasrRo-MÁínEu
Departament de Geologia. Area d’Estratigrafla. Universitat Autónoma de
Barcelona. 08193 Bel/aterra. Spain
ABSTRACT
Ira St. Lloren~ del Munt delta complox, faur dopositional soquoncos
bounded by usaconformities itave beon doscribed, witit titeir main systems
tracts. Titey are named Rellinars sequence, Mura sequonco, Manresa soquonce
asad Poramola sequence. Tito sodimosats whicit cosastitute tite dopositional
sequences are from doltaic origin, asad titeir facies associations itave been
distinguisited from proximally (delta plaisa) to distally (prodelta) for eacit
soquence. Tito delta front sediments of each sequosaco consist of distributary
mouth bars cycles orparasequosacos ranging fromfluvial-daminatodsodiments,
near tite river ¡noutit, to wavo- asad storm-dominated anos, basisaward. Isa
pelitic enviranmosats (usually prodeltaand distal deltafront) titore aro instability
features rosulting fram: (1) difforential weigitt between sands and fines of
titeso sedimosatary esavironments, (2) tite quantity of finos, arad (3) tito cyclic
bottom weigitt of tite storm wavos. Sucit sedimontary instabilities are gullios,
listric sedimentary faults, mudlurnps, ratational slides, asad balis and pillows.
The transgressive systems tracts of eacit dopositional sequence consist of
carbonate sitelf facies sediisaentod isa aroas arad periods of low detriticalsiliciclastic sodimont supply. Tite lowstand systems tract of tite Manresa
soquonco cosasists of great scale instabilities associated to a submarino erosion
(Maestra, 1989), arad isa distal aroas tite sodimentary instabilities form type 111
turbidites (Mutti, 1985). Titis soquence itas probably gat a type 1 boundary
(sensu Vail, 1987). The otiter sequonce bausadarios aro most likoly of type II
(sensa Valí, op.cit.).
Cuadernos de Geología Ibérica N.0 15, 73-102. Madrid, 1991.
Edit. Universidad Complutense.
74
E.
Maestro -Maideu
Key words: Deltaic camplox, Dopositional sequencos, Systems tracts,
Sedimontary isastabilities, Soquenco baundaries, Middle-Upper Eoceno.
RESUMEN
En el complejo deltaico de St. LlarenQ del Munt se itan descrito cuatro
secuencias deposicionales y sus correspondientes cortejos sedimentarias. Las
itemos denominada socuencia de Rollinars, secuencia do Mura, secuoncia de
Manresa y secuesacia de Peramola. Las depósitos que las constituyera son do
origen doltaico, y cada una do estas está formada desde asociaciones do facies
proximales (llanura doltaica) itasta asociaciones do facies distalos (prodelta).
Las facies más desarrolladas corresponden a depósitos de frente doltaico y
están constituidas por barras de desembocadura do canales distributarias, las
cuales se distribuyen desde el dominio fluvial, cerca de la desembocacura,
hasta el dominio del oleaje y do las tormentas, a medida que nos alejamos do
ella. En los ambientes deposicionalos de frente deltaico distal y de prodelta,
tiene lugar un gran número do inestabilidades sisasodimontarias debido
principalmente al peso diferencial de las arenas sobre las pelitas que constituyen
estos ambientes deposicionales, al gran predominio de materiales tisaos y a la
carga cíclica que ejercen las olas do tormenta sobre el fosado marino. Estas
inestabilidades se presentan esa forma de gu!!ies, de fallas sedimentarias
lístricas, de diapiros fangosos, de deslizamientos ratacionalos, y de bolas y
pil!ows. Los cortejos transgresivos de cada secuoncia están formados por
facies de plataforma carbonatada depositadas en áreas y en periodos do escaso
aporto do sedimento detrítico-silicilástico. El cortejo de mar bajo de la
socuencia de Manresa está formado par niveles de inestabilidades a gran
escala relacionados cosa una erosión submarina (Maestro, 1989). El limite de
esta socuoncia probablemente sea de tipo 1 (según Vail, 1987), ya que en áreas
más distales estas inestabilidades dan lugar a turbiditas de tipo III (Mutti,
1985). Las otros límites do secuencia probablemente serían do tipo II (según
Vail, op.cit.).
Palabras clave: Complejo deltaico, Secuencias doposicianales, Cortejos
sedimentarias, Inestabilidades sedimentarias, Límites de secuencia, Eoceno
media-superior.
RESUM
En el complex deltaic do St. Lloreng del Munt s’itan distingit quatre
seqUéncies deposicionals delimitados por discordances, i ots seus corrosponents
prismes sodimontaris. Les item denominat seqíléncia de Rollinars, seqúéncia de
The deltaic comp/ex of St. Lloreng del Munt...
75
Mura, seqiiésacia de Manresa i soqiléncia de Poramola. Els dipésits que los
constitucixon són d’origen deltaic y cada una d’elles está formada des
d associaciosas do facies proximais (plana deltaica) fins a associaciasas do facies
distais (pradelta). Els sodimesats més dosenvolupats corresponon a dipésits de
frant deltaic i estan formats por barres de desembocadura dels casaalsdistributaris,
ets quals es distribueixen do cosatinesat cap a mar, des d’usa domini fluvial fisas a
un daminí do l’accid do les anades de bon tomps y do les tempostes. En ols
ambients doposicionals de frant doltaic distal ide pradelta solesa ocórrer un grasa
nombro d inestabilitats sinsedimontaries dogut al pos diferencial de les sarros
sobre les polites que constitueixon aquests ambients, a la quantitat do sedimesats
fisas y a la cárrega cíclica que sobro el faras exerceixen les onades do tempesta.
Aquestes inostabilitats es presenten esa formade gui!íes, de falles sinsedimosatáries
lístriquos, d’illes do fang, do íliscamesats rotacionalos, y de boles y pi!lows. Els
prismes transgressius de cada seqilésacia ostan formats por facies do plataforma
carbanatadadepositades en ároes y períodos do poc aport de sedimosats detríticosiliciclástics. El prisma de mar baix de la seqilésacia de Manresa está format por
saivolís d’inostabilitats sinsodimesatáries a grasa escala rolaciosaats amb una erosió
submarina (Maestro, 1989), ja que en ároes més distals aquestos inestabilitats
donen lloc a turbidites de tipus III (Mutti, 1985). El límit d’aquesta soqúésacia
probablemesat corrospongui a una discordancia de tipus 1 (segaras Vail, 1987).
La restado límits doscrits probablemont van relacionats amb ]ímits do seqúéncia
de tipus II (sogosas Vail, 1987).
‘
Paraules clau: Camplox doltaic, Soqúéncies deposicionals, Prismes
sedimontaris, Inestabilitats sedimentaries, Límits de seqiléracia, Eacé mitjásuperior.
GENERAL SETTING
Tito deltaic complex of St. Líoreraq del Musat is located isa tite South-oastom
sido of tite Catalan Central Depression (Nortit-eastersa part of tite Ebro basisa),
N of tite Catalan Coastal rangos (Fig. 1). During tite Cenozoic, tite Catalasa
basin was tite foreland basisa of dio surrousading citaisas, tite Pyrenoos isa titeN
asad tite Catalan Coastal Rangos isa tite 5. During part of tite Paloagesae tite
basisa was consaectod to tite opon sea isa dio W. It itad a largo gulf sitapo witicit
was opon to tite isafluosace of tite Atíantio, ¿md closed by dio itigit reliefs. Tite
basin was fillod witit terrigenaus sodimesats witicit formed doltaic complexos
Tito Catatan Coastal Rangos aro an orogosaic citain witit a Paloozoic
basemesat and a Mosozoic cover. Tito Triassic sodimesats represosat tite covor
isa tite studiod area. At first, tite rango was affocted by Hercysaian tectanies asad
aftorwards, durisag tite Paleogeno, by Alpino tectosaic impulsos. Vertical
basomont faults define tite dominant foatures. Titoy aro ariented NEto SW and
76
E. Maestro-Maideu
Hg. l.—General sketch map of the Paleogene deposits in the Catalan region, indicating tho area
of exposition of St. Lloren~ del Munt deltaic camplex.
Fig. 1.—Mapa esquemático general dolos depósitos paleógenos de la región catalana, indicando
el área donde aHora el complejo deltaico de St. Lloren~ del Munt.
ENE to WSW. Titese f’aults are obliquo to tite citain and form an en echeIon
systera (Guimerá, 1984), witit a striko-slip sinistorar sinister-revers movemont
(Anadón eta!., 1979).
During tite Paleocone and lower Eoceno tite Ebro basin was a toctonically
active margin. Clase lo it alluvial faras wore devolapod during Alpino tectonics
arad befare marine conditioras. During the middlo-upporrocene, Ihe basin was
affocted by an important marine transgrossion witicit caused tite developmesat
of fan deltas. Tite saurce area of tite alluvial fans and tite fan deltas wero sited
isa tite Catalanides. Tite Triassic (Muscitolkalk) arad Paleocone cavors bogan
to be oroded during tite lower Eoceno, witereas isa tite middle-upper Eoceno,
tite erosiosa affected tite Triassic (Buntsandstein) cover asad tite Paleozoic
basemesat. Tite sodimentation was conditionod ira tite studied area by tite
WNW-ESE (lower Eoceno) or tite NNW-SSE to N-S (middle-upper Eoceno)
fault diacitrosaic systems.
TIte deltaic complex ofSt. Lloreng del Munt...
77
STRATIGRAPHY
Twa main domaisas can be distinguisitod isa tite margisas of tite Ebro
basin: tite alluvial sediments asad tite doltaic sodiments. Tite alluvial deposits
are sedimented during tite lower ¿md tite uppermost Paleogono. Tito deltaic
doposits are related to tite marine domain of tite basira (middle-upper Eoceno)
arad thoy are describod isa titis article. Titoso doltaic sedimonts constitute tite lower part of a Transgressive-Regressive cycío or a second order cycle (TR
cycles of Vail et al, 1990) Tite upper part of titis cycle cosasists of tite uppermost Eoceno-Oligoceno alluvial facies exposod in tite top of Montserrat
mauntain asad ira tite Catalan areas of tite Ebro basisa. Tite general sectian of tite
Paleogene is:
Paleocene. Farmod by red siltstoraes, witit some sasadstano
asad congiomorato layers, asad abundantMicrocodium. Those doposits itavo a
itigit carbonate cantosat, isacludisag calicite nadules, calcareous crusts asad
lacus-trino-palustrino limestones. These sedimonts líe unconformablo over
tite Meso-zoic substratum. At tite top of tite alluvial facies thero is a condonsed
paleosol ¡ayer sitowing asa important sodimentary broak (Anadón & Marzo,
1986).
Lower Eoceno. Tite baso of tite lower Eoceno sodimorats in tite
Nortit-oastorn (El Far) and Soutit-western (Igualada) extremos of tite
studied area is composed of marine Alveolina limestones. Related to titese
sodimosats, ira tite St.Llorony del Munt-Mosatsorrat area, tite doposits cansist of continental red sandstaraes asad mudstosaos. A reddisit usait, formod by
red marís and sandstosaes overlies tite marino Alveolina limestones, ¿md
brechoid alluvial fasas ovorlay tite red continental doposits latoral lo tite
jimesroraes. Titoso alluvial fasas includo subaerial olistostromes of Triassic
limestones.
Middle Eoceno. During tite middie Eoceno tite first casaglomerato
fasa deltaic unit is doposited ira Sí.Llaron~ del Muní and Montserrat aroas.
Titese areas consistof twa differerat dopositional systems (Fisiter & McGawon,
1967). Tite petralogical cantesat of tite distincí fan deltas is difforosat.
Tito Montserrat depositional systom contaisas cobblos of Mosozoic limostones,
tite St. 1]oreny del Munt depositional systom endioses cobbíes of basement
asad lower Triassic. Reddisit alluvial deposiís constitute tite proximal part of
tite fan deltas, witilo ira tite marine areas a shallow sitelf sotting is doveloped
frontally.
Middlo-Upper Eoceno. Tite deposition of tho middle asad
uppor conglomoratic fasa doltaic units occurs in St. LlorosaG del Munt, farming a titick pradeltaic platform ayer tite Catalan basin. isa tite Montserrat area, a mass flow fan delta front developod by coarsening up massive
conglomerate assembly arad its prodelta is indontod witit tite St. Lloreng
ano.
—
—
—
—
78
E. Maestro-Maideu
ST. LLORENC DEL MUNT DELTAIC COMPLEX
As far as St. Lloren9 del Munt delta is concomed, faur stratigrapitic usaits
are defined (Maestro, 1987, 1989) as depositional sequences isa tite sonso of
Vail (1987). A succossian of proximal deltaic strata asad distal sitelfal strata
form oacb unit, witicit is bound by unconformities isa tite outcrop areas. It is
supposod titat titose baundaries are confarmities in tite central parts of tite
Catalan basisa. Accardirag widi Posamentier eta!. (1988), lowstand systems
tracts (LST) cosasist of delta frorat ¿md prodelta esavironmesats, transgressivo
systems tracís (TST) cosasist of calcareous conglomorates asad carbonate sitolf
facies, ¿md itigitstand systems tracts (HST) consist of proximal alluvial
deposits, delta frorat and pradelta enviroramesats. Titeso depositional sequosaces
(Fig. 2) rango ira age from tite upper Lutetian to tite middlo Priabonian. Tbey
can be assigned to 3.5, 3.6, 4.1 asad 4.2 titird arder cycles of tite Exxon citan
(1-faq eta!., 1987) in basis osa paleosatolagical data (Ferrer, 1971). Titoy aro
namod Rellinars sequence (also defined as lower fan delta isa Maestro, 1987),
Mura sequence (or middle fan delta), Manresa sequonce (or upper fan delta)
¿md Peramola soquence (studied and described isa tite Oliana area, ira Maestra,
1989a, asad comparod isa age with tite St. Lloren~ del Murat area). Isa eacit
sequonco we can distiraguisit tite different systems tracís related ta eustatic
changos. In Maestro (1987), before tite use of tite systems tracts asad agroeing
ta tite terminalogy of tite epocit (Mitcitum eta!., 1977 ¿md Vail eta!., 1977),
tite uraits of marine carbonates witicit overlie tite doltaic citasanelsand bars, arad
dio whito carbonate conglomorates of tite proximal ‘¿roas isa St.Lloron< del
Munt (Fig. 3), itere isacluded isa tite trasasgressive systems tract, were comprisod
into tite itigitstand deposits, and tite titosa-boundaries for oacit sequence
corrosposad to tite maximum flooding surface.
Tite bounding unconformities of tite dopositional sequences are maisaly of
typo 11 (sensu Vail, 1987), except tite uncouformity that separatos Mura
soquesaco from Manresa sequence, witicit is typo 1 limit. The unconformity
corresposads to tite Bartonian-Priaboniarx boundary (-39.4 m.y, sensa Haq et al.,
1987). Great scale instability processes caused tite submarino erosion titat comes
witit tite relativo loworing of tite sea level arad titat induces tite destruction of tite
upper pan of tite doltaic sodiments of Mura sequonce (Fig. 2). It is supposed that
tite eroded deposits generated by titeso processes aro importasat eraougit for
buildisag aturbiditic systom in distal areas of tite Catalan basin. Never tite Ioss titis
systom is nat oxposed, altitaugit type III turbidites (Mutti, 1985) itavo beesa
distinguisited in tite base of tite Manresa sequenco. The otiter depositional
sequences described shaw no signs of submarino erosion, ¿md tite sedimesatary
instabilities are citiefly rolated to tite basinward progradatiosa of dio deltaic
systems during tite lowstand and itigitstand systems tracts. Titey are expased
framproximal (deltaplain) ta distal (distal deltafront andprodolta) onvironmesats.
Tito instabilities are moro frequent isa distal doltaic settings as a result of itaving
a great proportion of pelitic sediments.
TIte deltaic complex of St. Lloren~ del Munt...
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TIte deltai’ comp/ex of St. Lforen~ del Munt...
SI
Rellinars Sequence
Tite first doscribed soquenco consists of proximal deltaic sedimerats of
coraglomeratic compasitiosa, sitowing reduced delta frorat asad prodelta,
deposited isa a lagoanal or sitallow sitelf environment. Basinward titoso
doposits mergo ¡sato a site]f facies. Wititin titis sequonce we can differentiate
lowstand (LST), transgressive (TST) arad itigitstand systems tracts (HST).
LST—A bad exposed prograding doltaic lowormost usaR consists of delta
plain crovasse cauplots, delta front bad doveloped distributary moutit bars and
upper pradolta grey mudstones. Titis lowstasad progradisag complox itas low
thicknoss asad is only representod isa tite Soutit-westom area of St. Llorosa9 del
Munt, near Reltinars village, beneatit tite marine wedge of tite transgressive
deposits.
TST—Ira tite praximal areas a transgressive conglomorato unit can be
distinguished (Fig. 2), showing a higberporcentage of limestone cobbíos titan
tite typical conglomeratos of St. Lloreny del Musat. Tito cosaglomerates are
bigitly cansolidated by carbonato cements, witicit are reflectisag isa a white
calaur. Titese conglomerates rangos basinward to sitelfal carbonate depasits,
witich are anly madorately exposed duo to be covered by tite uppermast
deltaic units.
HST—ln tite proximal arcas, tite itighstand systems tract consists of a
progradational conglomorate association, witicit is woll exposed ira St. Llaren9
del Munt area (Fig. 3). It mergos isata reddisit delta plaira doposits (Fig. 5),
witicit aro praperly developed ira tite Eastersa area. It was deposited in a
íempora]ly floaded¿md plant-rich closed bayenvironmenr, witit cosaglomeratic
citannels arad roddisit sandstonos arad siltstonos of tite intorcitansael aroas. To
tite N and NW tite cosaglomorate deposits pass inta a progradisag delta front
canglamoratic distributmy moutit bars deposits, and to poar oxposed pradelta
enviroraments. Titase deposits are almost cavored by tite sediments of tite
Mura sequence.
Mura sequence
Titis sequence is well oxposed isa tite central and proximal areas of tite St,
Lloreny del Munt ¿md Montserrat delta depasitional systems. Tite lowstand
systems tract (LST) can be recagnized mainly ira tite Montserrat systom.
LST—In tite frontal arcas of tite Montserrat fasa we recognize a pragrading
delta composed of caarsoning-upward distributary moutit bar cyclos whicit
canform tite delta frosal depositional environrnent. Titese deposits rango
basisaward to prodeltaic claystasaes. Isa St. Llareny del Munt osaly tite prodeltaic
esavirorament witit a titick successian of grey mudstosaos arad claystosaes is
exposed. Sucit doposits represesat tite lawstand wedgo progradirag complex
(sensu Vail, 1987).
82
E.
Maestro-Maideu
E
MURA
W
ROCAFORT
VILUMARA
, so
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50
Orn
Fig. 4.—.-E-W evolurion of the facies associalions for tho distinct parasequonces dislinguished
iii the H.S.T. ofMura sq. a- Muía cross section consisís mairdy ofdelta plain facies a.ssociations,
as crevasse lobos, ovorbank deposits and distributary channeis. b- Racafort cross sectian consists
maxnly of distributary channel asad interchannel facies ‘¿esociatioras. c- Poní de Vilumara cross
section consists mainly of distributary mouth bar cycles (channels, fareshore bars anó shareface
deposits) asid prodelta facies associations (grey shales, thin bed turbidites aud anoalgamated
layers with hummocky cross stratification). Tite H.S.T. consists of deltaic coarsening and
thickening upward cycle wiíh a progradational trerad.
Hg. 4.—Evolución E-W de las asociaciones de facies para las diferentes parasecuencias
distinguidas en el H.S.T. do la secuenciado Muía, a- Uorte de Muía. Predominan las asaciactones
de facies de llanura deltaica (lóbulos do crevasse, facies de overb’ank y canales distributarios).
b- Corte de Rocafort. Predominio de las asociaciones de facies de canal distributario y de
intercanal. c- Uorte del Poní de Vilumara. Presenta ciclas de banas de desembocadura de canal
distributario (canales, barras de foreshore y facies do shoreface) y asociaciones de facies de
pradelta (pelitas grises, capas turbidíticas finas y y capas amalgamadas con estratificación
cruzada hummocky). El H.S.T. forma un ciclo deltaica pragradante, estrato- y grano creciente.
TST—In the praximal cosaglomoratio aroas of St. Lloren9 del Munt, a
secorad carbonate conglomeratic usait is identified, similar to tite witite
canglomerato unit describod for tite TST of tite Rollinaes sequenco. In tite
intermodiato parts of tite basin, tite TST cosasists of main minar retrogressive,
metrio to decamotric, carbonato marine cyclos witich can be idontified
overlayirag tite LST. Titis urait basisaward intorfisagers witit coralgal patcit reefs
growing on tite wedge of coraglomerates (Fig. 9).
The deltaic complex ofSt, Lloren~ del Munt...
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Tire deltaic comp/ex of St. Lloi’enc del Muat...
85
HST—Tite bigbstand systems tract in tite proximal areas consists of a
progradational conglomeratic sequence (Fig. 2). Tito N and HE reddisit delta
plain deposits (Figs. 4. 6) dovolop to tite NW sitallowing and coarsenisag up
distributary moutit bar sequences (Figs. 4, 7), witit a canglomeratic bedsot ira
tite uppermost part. Titeso deltaic soquencos mergo into wave- and stormreworkod distal deltaic facies, witit hummocky crass stratification. isa tite
sitoroface environmonts, on-laping reefal limestones develop ayer tite
paleotapograpity of tite moutit bar cyclos. Fine prodelta doposits built tite
distal deltaic platform. Near tite faulted area of tite Llobregat river, affocting
tite upper part of tite pradelta and tite lower part of tite delta front onvironmonts,
we fisad somo doformatianal features sucb as gullios, rotational sudes arad
mudlumps, induced by differential woigitt arad fault mox’oments. Tite HST of
tite Mura soquence itas a progradational basinward trosad. Ira its delta front
dopositianal osavironment wo itave distinguisited, at loast, eleven distributary
moutit bar cycles or parasequences
Manresa sequence
Tite erosivo unconformity that baunós tite Manresa soquosaco from Mura
soquence is cloarly marked isa tite marino aroas by kilometric seale sedimentary
instabilitios titat pravo tite erosion occurred isa tite uppermost pail of tite HST
deposits of Murasoquenco (Fig. 11). In tite continental areas wo rocognize an
erosivo surface.
Fig. 6—A- Thick tabular canglornerate body in between delta plain depasits (red sandstones,
mudstones and conglamerates), exposed in Rellinars-Castellbell road, and representing a majar
distributary channel in the delta plain environnient. B- Delta plain deposits in TerrassaNavarcíes road (Mora sequence). Red, rhin sandstane beds (crevasse splays depasits) alternate
with red mudstones of overbank origin, forming subaerial, partially floaded levee deposits,
laterally to principal distributary channels. C- Delta plain deposits in the St. Lloren9 SavailUaldors road (Mora soguence). Reddisb coarse-saridstone heds hayo erosivo bases and are
aflected by rootlets. They reprosent crovasso deposits. At top there isa channel of graveis, with
high erosivo base. ‘¡‘bose deposits are related to interdistributary areas and fonsa a rumor mouth
bar/cmvasso couplet.
Fig. 6.—A- Cuerpo tabularpotonto do conglomerados situadoentre depósitos do llanura deltaica
(areniscas, pelitas y conglomerados rojos), que afloran en la carretera de Rellinars a Castefibelí,
y representan un canal distributario mayor en ambiente de llanura deltaica. 3- Depósitos de
llanura deltaica in la carretera de Terrassa a Navarcíes (secuencia de Muía). Las finas capas de
arenisca roja (depósitos de crevasse splays) alternan con pelitas rojas, típicas de zonas de
averbank, fornando paste do depósitos de leveo subaéroa, parcialmente inundada, y lateral a los
canales distributarios principales. U- Depósitos de llanura deltaica en la carretera de St. Lloren
9
SavalI-Calders (secuencia de Mura). Las capas rojas de areniscas groseras presentan bases
erosivas y están afectadas porraices. Representan depósitos do crovasse. A tocho ahora un canal
de gravas con una base fuertemente erosiva. En conjunto representan depósitos de aseas
interdistributarias y forman una barra de desembocadura menor/asociación de lóbulos de
cfOV¿5550.
E. Maestro-Maidea
86
¿0<
Si,
25
20
Ob
15
Da
c
10
6
5
A
—Fe
O
TIte deltaic comp/ex of St. LlorenQ del Munt...
87
LST—Tite deepest deposits idosatifiod isa tite deltaic complex, witicit may
be fonsad isa tite LST of Manresa sequenco, are grey sitales asad silts titat
cosatain citannol sitape sandstosae bed sets isatowretod as type III turbiditos
(Mutti, 1985). Thaso slope doposits rango landward to pradelta and delta front
prograding facies. Titese typical deltaic facies itave 10w titickness. Tite total
of diese sodimosats reprosesats tite lowstand wedge progradisag complex (Vail,
1987). Tite sedimontary isastabilities (Fig. 11) aro pali of LST asad distally
titoy produce tite type III turbiditos ana poritaps a turbiditie systom.
TST—In tite continental arcas tite TST cosasists of a titird witite canglomoratic unit. Isa tite marine areas twa calcareous wedges osalapping tite LST
deltaic sediments can be identified. isa tite transition from continental to
Fig. 7—Complete distributary inouth bar cycle ar parasequonce (Mura sequence) in El Pont de
Vilumara, with tite four deltaic facies described in tite text. The boundary with tite provious
parasequence is faund in te ferruginized top of a conglamerate-to-veiy coarse’sand bed (O)
which ropresonts the distributary channelfacies of tite lower deltaic cycle. A- Facies 1: thin bed
turbidites, with erosivo base, including faunal fragments, altemating with grey mudstanes, asad
related to distal shareface. B- Facies 2: linsen ea wavy etratification level, including grey
mudstones, thin beds witit ripple trains asad thick sandstane bods with hummocky cross
stratification, representing shoreface stonn deposits. U- Facies 3: medium to coarse sandstone
beds altcmating with microconglomerate or vorycoarse sandstonos, witb moderate ea high anglo
cross planar stratification, typical from foresitore megaripples. The first sandstone bed shows
pillow structures. D - Facies 4: represents tite distributary channel. Da- lower distributary:
conglomerate bed (pebblo to microconglomerate) with sasad matrix, planar to asymptotical cross
stratiftcation, asad some wavo ripples. Represents tite base alto distributary, in storm-reworked
fareshoro environment, fanning xnegaripples with lateral migration. Db- Iipper distributary:
thick conglomerate beds (eabble to pebble) with trougit cross stratiftcation, typical fram fluvial
processes and, minority, moderato to high anglo planar cross stratification, typical from tite
upper foroshoro mogaripplos. Tho masIs and te calcarenitic debris (Sh) which overlies tite
conglonieratos form tite baso of an uppermost parasequence.
Fig. 7—Ciclo comploto de barra de desembocadura de distributario (secuenciado Mura) en el
Pont de Vilumara, con las cuatro facies doltaicas descritas en el texto. El límite con la
parasequencia precedente se encuentra en el techo ferruginizado do una capa de conglomerados
y areniscas groseras (D) que representan las facies do canal distributario del ciclo inferior. AFacies 1: capas turbidíticas fizas, con base erosiva y que incluye fragmentos de fauna, alternando
con peliras grises. Pertenecen al shoreface distal. B- Facies 2: nivel dcon estratificación linsento-wavy, donde se incluyen pelitas grises, capas finas de arenisca formando trenes de ripples,
y capas de arenisca más potentes con estratificación cruzada itummocky, representando
depósitos de tormenta de sitoreface. U- Facies 3: capas de areniscas medias a groseras que
alternan con areniscas muy groseras y microconglamerados, presentando estratificación cruzada
planar de ángulo moderado a alto, típica de los megaripples do foreshore. La primera capa de
arenisca presenta estructuras pillow. D- Facies 4: representa el canal distributario. Dadistributario inferior: capa de conglomerados con matriz do arenisca, estratificación cruzada
planar a asintótica, y algunos wave ripples. Representa la base del distriburario, en un ambiente
de foreshore retrabajado parlas tormentas; donde so forman megaripples con migración l’ateral.
Db- Distributario superior: capas potentes deconglomerados con estratificación cruzada trough,
típica de procesos fluviales y minoritariamente, estratificación cruzada planar de ángulo
moderado a alto, típica de los megaripples del foreshore superior. Las margas y el debris
calcarenftico (Sh) que aparecen sobre los últimos conglomerados constituyen la base de una
nueva parasecuencia.
The deltaic comp/ex of St. Lloreng del Munt...
89
marino aroas some patcit roefs facies are dopasited overlaying calcareous
conglomerate beds.
HST—As isa tite previous sequonco, isa tite praximal areas, tite HST
cansists of a progradatianal titick conglomeratic sequonce (Fig. 2). Tito
roddish delta plain oraviranments are sited in tite NF of tite fan. Tito delta front
deposits corasist of several sitallawing. coarsesaing up distributary moutit bar
sequonces (Figs. Sc, d, e) pragrading over tite Pradelta environments. Reefal
Fig. 8.—A- Facies 2 and 3 ofa distributary mouth barsequonce in tl,e Mura-Rocafort raed (Mure
sequence). The sandstono and gravel beds have tractive plane-parallel laminations, showing
lateral migration of tite megaripplos. Vertical burrows of Ophiomorpha are usual, B- Facies 3
of a mouth bar cycle (Mura-Rocafart road. Mura sequence) C- Complete sequence of a
distrihutary mouth bar cycle, which ropt’eserus facies 2,3 and 4 aL top (St. Pee outcrop. Manresa
sequence) D- Facies 2 and 3 of a deltaic cycle (St. Pan. Manresa sequence) E- Extensivo vision
showing tite MW accretion of Che deltaic bars (SL. Pau. Manresa sequence)
Fig. 8.—A- Facies 2 y 3 de una secuencia de barra de desembocadura de distributario en la
carretera entre Muray Rocafart (secuenciade Mura). Las capas de arenisca y de gravas presentan
láminas tractivas plano-paralelas, observándose la migración lateral de los megaripplos. Son
frecuentes los buri-ows verticales de Ophiamorpha. B- Facies 3 de un ciclo de barras de
desembocadura (carretera de Mura a Rocafort. Secuenciado Mura) C- Secuencia casi completa
de un ciclo do barras distributarias do desembocadura, presentando las facies 2, 3 y 4
(Afloramiento de St. Pan. Secuencia de Manresa) D- Facies 2 y 3 de un ciclo deltaico (St. Pau.
Secuencia de Manresa) E- Visión extensa mostrando la acreción hacia el 14W de las barras
deltaicas (St. Pan. Secuencia de Manresa).
90
E. Maestro -Maideu
limestosaes or titeir storm destroyed calcaresaitic equivalesat sediments form
titetopmost deposits oftite HST. They deposited witen tite deltaic sedimesatatiosa
was Iowered due to tite cammutatiosa of tite basin in the studiod area. In somo
cases tbey represesat tite late itigitstand systems tract (Vail, 1987).
Peramola sequence
Titis sequence, defined in tite NW Catalan basin (Otiasaaaroa), is correlated
ta St. Llaresag del Musat area isa base of faraminifera and nannaplasactan datisag
(Caus, 1971, Ferrer, 1971). It ropresonts tite Iatest doltaic deposits isa dio
studied complex, asad it is woll exposed isa tite N area (Navarcles-Calders). At
prosent, only a rough subdivision into systems tract is possible. Tite sequence
consists isa sitelf margisas systems tract, trasasgrossive systems tract asad
progradisag low titickness itigitst¿md systems tract (Fig. 2).
FACIES ASSOCIATIONS
Tite facies associations will be described fram maisa proximal to distal
environments whore they aro depositod. Tbey suppart tite facies arrangernesat
inside each depasitional soquenco, indistinctly.
Al!uvial cone
Tite ‘¿fluvial cone consists of clast- or matrix-supported conglomerate
assaciations, witit isaclined or subitorizosatal disperse stratification asad erosivo
bases. Proximal asad distal cono facies cara be distinguisited.
Proximal Cone
Tito proximal cono includes massivo conglomoratos with boulders (up to
1 m thick), disperso stratification asad planar internal erasiosa surfaces. Sorne
massive levols itave no stratificatiora. witit mass flow or debris f’low depasits,
asad laterally pass to searce reddisit floodplaisa sasadstonos. Otitorconglomeratie
facies itave horizontal to obliquo stratification, with roactivation surfaces arad
wititout grading. Titey reprosent longitudinal bars whicb graw accardisag to
tite polarity of tite depasitional system. Tite matrix is coarse sarad to
microconglomerate. Titere are quartz, schists, liditos arad siates cobbles.
supplied by tite eroded Hercynian basement of tite Catalan Coastal Rangos,
arad conglomerate, red sandstones ¿md limestosaes cobitíes titat itavo a Triassic
arad Paleocene cover origisa. Titey reprosesat altogetiter tite proximal facies of
an alluvial fan.
TIte de/taic comp/ex of St. Lloren~ del Munt...
91
Distal cone
Massive conglomerates disposed isa sharp base tabular badies interlayered
witit reddisit mudstasaes and sandstosaes of ovorbank origisa. Titese doposits
itave abundasat roatlets, paleosoils are cammasa. Tite conglomoratic bodios
sitowisag a citansael sitape itavo low lateral porsistence. Tite stratification is
horizontal, witit imbricate cobblos, represesating longitudinal bars witit tite
main polarity of tite alluvial-deltáic systom, higit anglo planar or ablique,
representisag transverso bars, asad isa sorne cases titoro are poiní bar structuros.
Some low scale sandstone bars or sitoots are fausad botweesa tite conglomeratic
bodies. Tite maisa cosaglamerate units develop to misaorbraidodtoasaastamasisag
channeis latorally. As a whole, titoy represesat a braided or an anastomosing
fluvio-alluvial system.
Delta plain
Titree maisa typos of delta plain depasits can be fourad. Titese doposits itavo
a lateral continuity fram tite distal cono.
Conglomerate channeis
Tito conglomorato citarmels ropresosat tite minar distributaries isa tite delta
plain. Titey sitow witit great evidonce a citasanel morpitology asad titoy aro
interlayered with roddisb mudstosaes asad sandstones. Isa tite channeis it is
passible to distisaguish a finisag upward cyclo of meandering citasanol
abasadonment (Fig. 5) constituted by a Iower usait of cosaglomorates, witit
sand-matrix and trougit cross stratificatiosa, associated witit longitudinal asad
transverso bars, andan uppor unit of gravelly sandstosae bars with trougit cross
stratifieation, indicatisag tite gradually flow docrease, when rootlets hayo no
dostroy tite stratificatiosa. Ciraisa-sizo dimisaisites from tite centre to tite margins
of tite citasasael. Tite pobitíes are rounded. Higit anglo planar crass stratificatiosa
arad gravolly point bars are developod.
Major distributary channeis
Tite major distributary channels (Fig. 6A) sitow tite samo facies arrangemesat of tite massive alluvial cono casaglamoratos, but witit a itigiter
roundnoss rato. Titus thoy cosasist of cosaglomorates disposed in tabular
bodies. Tite stratificatiasa into tite distributarios is itorizosatal, witit imbricate
cobbles, represosating longitudinal bars witicit rofloct tite maisa polarity of tite
systom, but they alsa sitow itigh anglo planar or abliquo stratification,
reprosonting transverso bars.
92
E, Maestro-Maideu
Overbank deposits
Titey are formed by interlayerisag of reddisit siltstones asad sandstones
(Fig. 6B). Titese massive sasad beds (up to 20 cm thick) aro sedimentod by
turbiditic flows and titey itave erosivo bases, disperso gradisag and rootlets. Isa
sorne casos we usad sasadstano beds witit climbisag ripples.
Crevasse depos¡ts
Tite crevasse deposits corasist of coarse grained sandstono layers (up to 70
cm thick) witit erosivo bases, grading and disperso gravels. Tite top of tite
Iayers consists of paleosoils witit mudcracks and raotlots. Durirag periodical
floods cryptalgal lamiraites formed. Some citanneis of tite braidod stylo,
showing a complex intemal goometry arad a long latoral persistence, are tite
semiporpotual crevasse charaneis wbicit form caarsening and titickening up
crevasse lobos, witit dio canglomoratic channo] at tite top (Ng. 6C). Ira sorno
cases bioturbation has destioyod ah sedimentary stnictures.
Delta front distributary mouth bars
This esavironmont iracludes tite sedimonts deposited between the strand
lino arad tite sitorefaco. They are arrasaged ira coarsoning and titickening
upward cyclos of distributary moutit bars. We can distinguisit praximal arad
distal disti-ibutary mouth bars. Proximal moutit bar deposits are mainly
sedimonted ira poriads of fair woatiter rogime due to fluvial arad wave
processes. Distal moutit bars are reworkod by storm waves. Sands due to tite
wave induced cyclic weight in tite marine bottom aro eroded from tite delta
frorat (destructivo storm facies, Gabaldón, 1989) asad rosedimoratod ira tite
prodelta environment as amalgamated layers witit itummocky cross
stratification (constructivo storm facies, Gabaldón, op.cit.).
Tite St. Lloreng delta frosat contairas faur main delta front facies arrasaged
in metric to decamotric caarsesaing upward sequences (Figs. ‘7, 8). From base
to top we recograize:
Facies 1
Titis facies lies at tite baso of tite delta frasat cyclos. It is formed by
bioturbated, fine grained titin bed turbidites, with erosivo base, horizontal and
vertical burrows arad iracluding faunal fragments (Ng. 7A). Titose sandstorae
layers altemate witb grey mudstones. We firad somo proximal storm sand
layers, alineated pebitie layers asad faunaldebris. Tite exwironmentofdoposition
is tite sitoreface, witere tite bioturbation is more importasat titan tite rising of
The deltak’ comp/ex of St. Lloren~ del Munt...
93
tite sedimontary structures. Titase titin bods lay ayer tite prodelta rnudstonos
or tite sitelf limestonos. Tito baundary botweosa dio sitorefaco beds ¿md tito
prodelta/sitelf mudstonos can be isa tite fair woatiter waves base (Reinock &
Singit, 1972).
Facies 2
Titis facies is cosastitutod by usadulatisag, medium graisaed sandstosae beds,
witit parallel tractive laminations forming wave mogaripples, usasen to wavy
stratified sandstosaos, titin beds witit ripplo trairas arad thick sandstone beds
witit iturnmocky cross stratification, witicit are ombedded isa grey mudstonos
(Fig. iB, SA, C, D). Tite esavironrnosats of deposition aro tite forositoro and tite
higiter palis of tite sitareface baes. Tite mogaripples mayo to lasad isa tite fair
weather regime poriods. Tito beds witit hummocky stratification reprosesat tite
sitorefaco storni doposits. Seaward, titese deposits are progressively reworkod
by tite starm waves.
Facies 3
Titis facies is compased of modium to coarse grained sasadstosaos, witit
somo microcosaglamerates asad vory coarso sandstorae beds. Tite titicksaess of
tite bods rango fram 20 cm to 1 m, sitowing a moderato to itigit anglo crass
planar stratificatiosa of forositore megaripples andparallol tractivo laminations,
witicit is typical of sitare zonos (Fig. JC, 8). These deposits aro formod of
sodimonts brougbt by tite river in front of its mouth. As bappens witb Facies
2, tite foreshore bars aro reworkod it>’ storni wavos, seaward.
Facies
4
Facies 4 cosasists of’ cosaglamerate and very coarse sands, typically with
traugit cross stratification, arranged isa citannel sitapo bods. Channeis ma>’
erado tite sandstano bars of Facies 3. Isa sorne cases oblique cross stratification,
witit lasadward or basinward accretiosa, is developed at tite base of the citansael.
Wo can distisaguisit upper distributar>’ citannels asad lower distributary anos
(Ng. 70). Tite latter consist of conglomerate beds (pobble to
microconglornorato) witit sand matrix, planar to asymptotical cross
stratification, ¿md some wavo ripplos, witicit reprosent tite baso of tite
distributary citasarael, in a foresitaro environmont, forming mogaripples witit
lateral migratiosa. Uppor distributary citasanols cansist of titick casaglomerate
beds (cobitlo to pobble) witit trougit crass stratificatiosa, typical of fluvial
proeesses asad to lesserextond moderato to 11gb anglo planarcross stratification,
94
E. Maestro-Moiden
.1
‘Sil’
-
¿‘4
Fig. 9.—A- Calcareous conglomerate body of the TST of the Mura sequence. The calcareous
content increase towards tIlo top of tl-ie unit. Overlaying the conglomerates a coralline-algal
patcb reef is exposed. B- Detail of the top of [Ile previous calcareous conglomerate body.
Hg. 9.—A- Cuerpo de conglomeradas calcáreos del TST de la secuencia de Mura. El contenido
en calcárea aumenta hacia el techo de la unidad. Solapandolos conglomerados existe un patc/z
reefcoralino’algal. II- Detalle de la parle superior del cuerpo conglomerásico anterior.
TIte deltaic conzplex of St. Lloren~ del Munt...
95
typical of tite upper foresitoro megaripples. Tite titickness of titeso beds is
strongly roduced basinward. They can be intorpreted as braided arad meandering
fluviatilo chasaneis whicit have fusactiosaed as delta distributaries, supplying
sands asad conglomorates fram tite alluvial cono to tite delta front.
SHELF
Two main typos of doposits can be fausad isa tite sitolf onvirosament: marts
arad Jimestosaes. Titose marís aro argiflaceous or ca]carenitic, asad they contesat
ricit faunas (Nummulites, molluscs, ecitinoids, carais, etc), witile tite limestonos
consists of grainstones or baundstones (reefs or patcit roofs) (Fig. 9). Titere
is also some carbonato debris flow layers that onlap tite proximal doltaic
sediments. isa titose proximal airas calcarcoas debris inciudo some pebblos
(Ng. 75it). asad in prodelta onvirosamorats, tite same layers itavo a calcarenitic
cosatesat.
Prodelta
Prodelta deposits are exposed ira tite Western asad Nortit-westem arcas of
tite studiod zane. Wo can distisaguisit twa types of deposits (Fig. 10).
—
Grey mudstosaes (silts or sitalos), witicit farm tite main prodelta
platform. Titey are fall-out depasits. Some titin bed turbiditos may be
iraterlayerod.
Units of sandstosae bods doposited during major stonsas, witicit sitow
humniocky cross stratificatian. Tite beds hayo a tractivo parallel or low
undulating laminations, and Iheir thicksaess is up to 40 cm. Tite top of tite
layers sitow curresat ripples. Erosivo bases, calcaresaitic layors can be
isatorboddod.
Tite síape deposits cosasist of titisa bod turbidites sitowing a citannel sitapo
witicit are iraterlayerod wititin grey mudstones. Titey aro isaterpreted as type III
turbidites (sensu Mutti, 1985).
Dest¿-uc’tive de/tajefeatures
Tito ratos of deposition in tite continental sitelf where St. Lloresa9 del Munt
rivor delta developod were elevated, witb mucit fine sedimont supplied.
Isacidesatalí>’, gravity induced, subaqueaus, sysadepositional mass movemesats
were gesaeratod, asad so, importarat changos taok placo ira tite deltaic platfarm.
Tito river supplied mudstonos are rapidly dissominatod, buildisag a prodoltaic
96
E.
Maestro-Maidea
lo
a
a
a
a
—
~-
a
o
SN
~
vi
m
O yo u
Hg. lO.—Parasequence of Mura soquence showing prodelta facies assocíatíons. From base Co
top, it cansistsof calcareousmarí, thin bod turbidites alternating with grey shale. asad a Chick body
of arnalgamated sandstone layors (np toSO cm) with hummocky cross stratification. (Marganell
section).
Fig. 1 0—Parasecuencia de la secuencia de Mura mostrando asociaciones de facies de prodelta.
De baso a techo distinguimos: margas calcáreas, capas turbidíticas finas entro arcillas grises y
finalmente un cuerpo potente de capas amalgamadas de arenisca con estratificación cruzada
ttumtnocky. (Serie de Marganell~.
platform. Titis fast depositian produces a higit sedimentar>’ woigbt of tite
coarse sediments averlayirag subconsolidated, water- and organic mattor-ricit
mudstonos of tite prodelta síape. A great volumo of sedimentar>’ gases are
formed from tite degraded organic matter, witich contribute to increase tite
water poro pressuro. Isa tite offshare areas, multiple winter storms arad
iturricanes are generatod, causisag a wave isaducod cyclic weigitt isa tite marine
bottom, which also cosatributes ta incroase tite pare pressuro. Tite sedimeratary
processos involved isa tite pradolta platform aro produced cosatomporaneously
TIte de/taic comp/ex of St. Lloren~ del Munt...
97
with tite basement fault movemesat near tite Llobregat river faultisag area.
Many law scale instabilities, usualí>’ pillaw asad balI structures, are faund
evorywitere alosag tite marine areas, from tite delta plain to tite prodelta.
Twa difforent scale of sedimesatary instabilities can be distisaguisited isa tite
doltaic complex of St. Lloreng del Munt. Qn tite ono hand, tite great scale
instabitity processos witicit originated tite submarino orasiosa durisag tite
relativo Iowstand asad inducod tite erosion of tite upper pali of tite preceding
soquonce. On tite otitor hand. minar scalo sedimentar>’ instabilities are
specifically related ta dio pragradatian of tite deltaic systems. Titey are visible
from proximal environments (delta plaira, delta frant) to distal enviranments
(dista] delta front asad prodelta), where diere is a high propoliion of fines
(Fig.l 1).
N
Ng. 11 .—Block diagram showing the sedimentary instabilities (Mura sequence) in front of
Che distributary channel mouth. a-distributary channel, b- delta front deposits, c- prodelta
deposits, d- shell deposits, o- gully of tije Cardoner river, f- gully lobos, g- niudlurnps of El
Pont de Vilumara and, h-patch reef. LST of Mura sequence consists mainly of b and c depasits,
TST, in d and c deposits and HST, in a, b, c and it. Tite base ofManresa sequence is represented
by Che instability erosional features (e and f).
Hg. II .~Bloque diagrama mostrando las inestabilidades sedimentarias (secuencia de
Mura) frontales a la desembocadura del canal distributario. a- canal distributaria. b- depósitos
de frente deltaico, c- depósitos de prodelta, d- depósitos de plataforma, e- gully del rio
Cardoner, f- lóbulos de gully, g- mudlumps de El Pant de Vilumara y, h- patcIt reef El LST
de la secuenciado Mura está formado por facies b y c, el TST, por facies c y d, y el HST por
facies a, b, c y h. La base de la secuencia de Manresa está representada por los fenómenos de
inestabilidad erosivos (e y f).
98
E. Maestro-Maideu
Proximal delta front
Tite fast deposition of tite coarsor sodimerats of tite distributar>’ mautit bars
ayer tite pelitic sedimonts, provokes tite instability of tite mudstones witicit
riso as diapiric intrusiosas (mudlump) titrougit tite deltaic bodies. Titase pelitic
movements localí>’ produce great subsidenco isa tite sandstone bars. Near El
Pont do Vilumara (Mura sequence) titore is an up to 8 m pelitic iratrusion
titrougit a deltaic sandbody, forming a largo pillow (Fig. 12A). Ira tite samo
stratigrapitic level usastable mudstones sitow signs of dowraward sliding, liko
slumping arad mass flows. Tite most usual features aro small scale balis asad
pillows. Tite origin of diese structures results from minar mud intrusioras in
the lowost palis of tite doltaic bars combisaed witit tite sliding of tite sands ayer
tite instabilizing mudstones. Distalí>’ fram tite river mautit, tite delta front
sedimerats can be affected by small listric faulis retragrading up from tite
upper prodelta. They provoke intraformational unconformities witit¡n tite
doltaic bars.
Some instabilities can be found isa tite sitallow delta frorat, witere tite
distributary moutit bars aro sitoaled ira bay aroas. Ira titis envirosament,
mudstones are not as thick as seawards. Titose snudstones are autocittonous
ba>’ doposits, arad sorne of titom are river-supplied. Due ta tite little titicknoss
of tite pelitie sediments, tite instabilitios formed itere are less impartant. Tito
prevailisag structures are pillows asad balís, up to 3 m, witicit affect tite wliole
low titicksaess distributary bar ira tite surroundirags of Talamanca village.
Laterally to tite pillaws, ira tite same levol, tite doltaic sasadbody sitows sigsas
of sitifting ayer tite underlaying mudstones.
Distal delta front
In tite Marganell-Castellgalf area, titore are blocks of saradstones titat itave
fallen down. Tite>’ are great distributar>’ moutit bar or distal bar fragments
Hg. 12.—A- Mudluswp: diapiric intrusion of prodelia grey mudstones in througha deltaic body,
El Pant do Vilumara, showing a pillaw shape. B- Rotational peripheral sUde, in MarganelJ
road, formed by a kilometrical delta front block which has slided over a listric bedding fault. CGully of the Cardoner river (railway outcrop). Metric sandstone blocks (in the right) on the
irregular surface of Che bottom of a gully, and posterior infilling of Che gully dopression by grey
mudstones and thin bedded storm sand layers.
Fig. 12.—A-Muldlump: intrusión diapírica de pelitas de prodelta que atraviesan un cuerpo
deltaico, cercado El Pont de Vilumara, mostrando forma de pillow de grandesdimensiones. BDeslizamiento rotacional periférico, en [a carretera de Marganelí, formado por un bloque
kilométrico de materiales de frente deltaico deslizados sobre una falla sedimentaria lístrica. CGal/y del río Cardoner (afloramiento de la vía del tren). Bloques métricos de arenisca (en la
derecha) sobre la superficie irregular del fondo de un gully, así como el relleno posterior de la
depresión del gal/y por perlitas grises y capas de tempestitas.
loo
E. Mae.vt,-o-Maideu
slided ara tite cancavos bodded sitoar planes to tite prodelta mudstones (Fig.
1 2B). Titeso are interpreted as rotational faults isa distal palis of tite delta frant
(Colemara, 1981). Sometimos tite mass movements of tite usaderlayisag prodelta
mudstanes are cosatomporasaoous witit tite delta front slides, isaduced by
intense storm wave action asad by degasing due to tite itigit organic matter
contont, isa tite small dopressions of tite distal delta frasat asad upper prodelta.
Prodelta
Tite mudflow gullies asad tite related depositional lobos are tite most usual
deformational features of tite upper prodolta, isa deptits from -7 to -100 m,
extoriding radially from eacit of tite distributaries (Calomasa, 1981).
Titero is exposed ara irregular blocky bottom itummocky depression, with
sandstorao blacks up to 7 m (Fig. 12C). lacate botween Castelígalí and
Manresa. Tite gully depressiora, largor titan lOO m, is filled witit thin bedded
storm turbidites maulded on tite irregular, stepped bottom paleomorpitalagy.
Titese doposits sitaw intraformational unconformities. Tite bottom blocks (up
to 1 m) are formed of titin sandstono layers witicit usually exceed very few cm,
intorbeddod witit mudstanes. Landward from tite gulí>’ doprossion, a succession
of listric, rotational faults resulting from retrogressiosa upslape, inforred tite
growtit of tite deprossion asad producod a stopped platform. Basinward, asad
because of tite dawnslope emptying of tite gulí>’ depression, citaotic sediments,
like mudflaws, debris flows including metric sasadstarae balís, slumps and
slurry flows, occur. Titey are pan of tite proximal areas of tite gulí>’ lobo. More
distal sedimosais cansist of mudflows asad muddy debris flows witit a citasanel
sitape base betweon tite prodelta asad tite síape mudstones.
CONCLUSIONS
isa St. Llorong del Musat delta complox, four depositional sequonces
baunded by usaconformitios itavo boesa doscribod, witit titeir maisa systems
tracts, namely Rellinaes sequesace, Mura sequonce, Manresa sequonce asad
Peramola sequerace. Tito described deposits hayo mainly a deltaic origira, arad
titeir facies associatiaras itave beora distinguisitod from proximal to distal ira
eacit sequerace.
Tite deltaic esaviroramesats sitow titree differesat facies associatiosas: (1)
delta plain associatians: maisa and minar distributary citannels, crevasses or
crevasse lobos, overbasak arad levee facies; (2) delta frosat assaciatians:
distributar>’ mouth bars, formirag titickerairag, caarsening arad sitallowirag
upward cycles. Titese bars can be fluvial-dominated noar tite river moutit, arad
storm and wavo daminatod offsitare; asad titen tite bars witit planar cross
stratificatiara are trasasfornied ta bars witit itummacky crass stratificatiora.
The deltaic comp/ex of St. L/orenc del Munt...
101
Storm reworkisag ispresont also, neartite sitorelino, isa dio proximal distributary
mautli bar. Lastly, (3) prodolta associatioras, witicit isacludos tite finest
deposits, mainly silts and sitales, asad starm sasad layers.
Ira politic esavironmosats sedimentar>’ instabilities usually cause foatures
sucit as gullios. listric sedimentar>’ faults, mudlumps, rotatianal sUdes, baUs
asad pillaws. Tito maisa factors coratrallisag titis instabilitios are tite differential
woigitt betwoon sarads arad finos, tite quantity of finos, arad tite cyclic bottom
weigitt of tite storm waves. Sedimentar>’ isastabilitios appear from tite delta
plain to tite prodelta. but tite most impartasat features take placo isa tite doepost
onvironmerats, sucit as pradelta asad upper síape.
A majar instability level is forarad ira tite bousadary of Mura arad Manresa
sequences, arad is related to tite submarino erasiosa isa a type 1 soquerace
bauradary (sensu Vail, 1987). Tite odier usaconformitios are described as type
II baundaries.
Tito sitolf facies associations are restricted ira spaco asad ira timo. Isa spaco,
isa areas of low siliciclastic sodiment supply, at tite base of many deltaic
parasequesaces or distributary moutit bar cycles, arad ira time, related maisal>’ to
transgressivo systems tracts.
ACKNOWLEDGEMENTS
1 wauld liko to titank Dr. Cristino J. Dabrio for tite facilities given to realizo
titis articlo, Dr. Joan Roselí, for supervising tite scieratific work, Dr. Sergio
Robles lar praviding sodimentological asad stratigrapbical ideas asad Dr.
Citristiara Botzler arad Gloria Roitues, for roviewisag tite Englisit version.
Titis work has been partialí>’ suppoliod by tite D.G.I.C.Y.T., projoct nY
PS88-0021.
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Manuscript received: 22 April 1991
Revision accepted: 10 May /991