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Goldschmidt2015 Abstracts
Combined analysis of Uranium series
nuclides and in situ Beryllium in a
weathering profile located in the
Strengbach catchment (Vosges massif,
France)
JULIEN ACKERER1, F.CHABAUX1, J.VAN DER WOERD3,
E.KALI3, E.PELT1, M.C.PIERRET1, D.VIVILLE1, R.WYNS2
2
AND P.NEGREL
1
Laboratoire d’Hydrologie et de Géochimie de Strasbourg
(University of Strasbourg, 1 rue Bleissig, 67084 Strasbourg
cedex, France).
2
Bureau de Recherches Géologiques et Minières (3 Avenue
Claude Guillemin, 45100 Orléans, France).
3
Institut de Physique du Globe de Strasbourg (University of
Strasbourg, 5 rue René Descartes, 67084 Strasbourg cedex,
France).
Recent studies underline the potential of U series nuclides
to quantify the regolith production rate in weathering profiles
(Chabaux et al, 2013; Dosseto et al, 2011; Dequincey et al,
2002). However, the quantification of regolith production rate
in climatic temperate context encountered a certain number of
limitations when analyzing only superficial samples in the first
meter of soil (Rihs et al, 2011). In this work, we propose to
combine the analysis of Uranium-Thorium-Radium isotopes
with the cosmogenic in situ Beryllium in a weathering profile
extending from the top soil to the granitic fractured bedrock at
2 m depth to better estimate both production and denudation
rate of regolith. The data confirm that the Uranium series
isotopes in the surface of the profile are difficult to interpret in
term of weathering rate, while the disequilibria in the deeper
weathered bedrock show a smooth trend. The consistency
between the calculated regolith production and denudation
rates suggests therefore that in such a temperate context, the
long-term mass balance of soil developed on granitic bedrock
would be close to a steady state.
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11
Goldschmidt2015 Abstracts
Weathering of continent-scale
volcanic ash deposit: Geochemical
and climatic implications
C. F. ARAGÓN-TOBAR1, Y. GODDÉRIS2, S. OPFERGELT1
1
AND P. DELMELLE
1
Earth & Life Institute, Université catholique Louvain,
Belgium (*correspondance: [email protected],
[email protected],
[email protected])
2
Géosicence Environnement Toulouse (GET), CNRSUniversité de Toulouse III, Observatoire Midi-Pyrénées,
Toulouse, France ([email protected])
Continental weathering of silicate rocks is an essential
component of global geochemical cycles. Previous studies
have shown that weathering of basaltic rocks emplaced during
Large Igneous Provinces events accounts for a significant
portion of the total continental silicate weathering flux and
atmospheric CO2 withdrawal. In contrast, little is known about
the short- and long-term influence on weathering flux and CO2
consumption of extensive continental ash deposits, blanketing
areas of up to several millions of km2, which can be emplaced
by Plinian volcanic supereruptions.
Here we apply the geochemical box model WITCH [1] to
simulate mineral dissolution/precipitation in a modern-day
continent-sized ash deposit. The model results are then used to
estimate the weathering fluxes and the comsumption of
atmospheric CO2. Our case study is based on the modeled ash
deposit from the 0.64 Ma eruptions of Yellowstone volcano,
USA, covering much of North America. The temperature and
drainage conditions required in the weathering calculations are
derived from a glocal climate model. The simulations are run
for one, 100 and 1000 years. The main findings of our original
study will be presented.
[1] Godderis, François, Probst, Schott, Moncoulon (2006),
Geochimica et Cosmochimica Acta 70, 1128-1147.
101
101
Goldschmidt2015 Abstracts
Contribution of minor minerals to the
U-Th-Ra budget of Gandak River
sediments.
C. BOSIA1, F. CHABAUX1, C. FRANCE-LANORD2, E. PELT1,
E. DELOULE2, P. STILLE1 AND J. LAVÉ2
1
LHyGES, EOST, Université de Strasbourg et CNRS, 1 Rue
Blessig, 67084 Strasbourg Cedex, France.
(*correspondence: [email protected])
2
Centre de Recherches Pétrographiques et Géochimiques
(CRPG), UPR 2300, CNRS-Université de Lorraine, 15
Rue de Notre Dame des Pauvres, 54501 Vandoeuvre les
Nancy, Cedex, France.
Transfer time of sediments in alluvial plains may be
constrained by analyzing the variations of the U-series
disequilibria in river sediments along the stream. However,
previous estimates obtained for bank sediments of Himalayan
rivers (1,2) can be questioned by recent 10Be and Sr-Nd
isotope studies (3,4), which yield much lower transfer times
than those estimated by U-series approach. The recent study
performed on bank sediments from the Gandak River (Bosia et
al, GES 10-Paris) confirms the occurrence of significant 238U230
Th-226Ra disequilibria in river sediments, with no simple
upstream-downstream variation, but with a clear decrease of
the U/Th and 230Th/232Th ratios. The correlations observed
between (238U/232Th) activity and Ti/Th ratios as well as
between (230Th/238U) and (Nd, Ce, La, Sm)/Th ratios suggest
that minor mineral phases, such as Ti-bearing minerals, REEbearing minerals (in particular monazite and xenotime) and
zircon are likely to control a significant part of the U-Th-Ra
budget in these sediments. To test this assumption and quantify
the real contribution of such minor minerals to the U-Th-Ra
budget of the Himalayan sediments, we have undertaken a
detailed analysis of the U-Th-Ra concentrations and isotopic
compositions in the Gandak sediments, similarly to the
approach developed in (5). Our results clearly demonstrate that
budgets of U and Th but also of Ra in river sediments of the
Gandak River are significantly influenced by such primary
minor phases, especially monazite and zircon, and by clay
fractions. The data therefore demonstrate that the relative
abundances of U-series nuclides in these sediments do not only
depend on their chemical evolution during their transfer within
the plain and on the duration of the transfer, but also on the
mechanical transformation of the sediments mineralogical
composition. Both processes have therefore to be taken into
account for interpreting the variation of U-series
disequilibrium in river sediments to recover sound estimations
of the transfer time of sediments along the Gandak River.
[1] Granet et al., 2010, GCA, 74 (10): 2851-2865 ; [2] Granet
et al., 2007, EPSL., 261 (3-4): 389-406; [3] Lupker et al., 2012,
EPSL., 333-334: 146-156; [4] Garçon et al. , 2014, Chemical
Geology 364, 45-55.
348
348
Goldschmidt2015 Abstracts
Pre-Jurassic weathering and erosion
studied on Andøya, northern Norway
M. BRÖNNER12*, A. E. CRNE3, H. RUESLÅTTEN4 AND
O. OLESEN1
1
Geologcal Survey of Norway, 7040 Trondheim, Norway
(*[email protected])
2
Department of Petroleum Engineering & Applied Geophysics,
NTNU, Trondheim, Norway
3
Exploro Geoservices, Trondheim, Norway
([email protected])
4
HakonGeo, Trondheim, Norway
Introduction
Remains of old regoliths onshore Norway are sparse due to
several glaciations during the Quaternary. Remnants of the
Mesozoic cover and potential thick packages of altered
basement rocks were eroded and today's landscape with steep
deep valleys and fjords was formed.
A small Mesozoic basin has been preserved onshore on the
island Andøya, Northern Norway, and earlier studies suggest
that Mesozoic sedimentary rocks are resting on deeply
weathered bedrock. At the southern boundary of the basin a
kaolinite-rich horizon is outcropping, sandwiched between the
basement and the overlying Early Jurassic siliciclastic rocks.
The present study aims an improved understanding of i)
old weathering processes in Norway; and ii) assess whether
weathered basement is preserved underneath Mesozoic
sedimentary rocks on a regional scale. We investigated the
mineralogy and geochemistry of the outcropping weathering
profiles, focusing on the transition zone between mildly
weathered basement and overlying sedimentary rocks from
three well cores in the basin.
Results
Our results show a 18-m-thick transition zone consisting
mostly of kaolinite and quartz. Quartz grains are angular
indicating short transport. An abundance of clay minerals in
the transition zone (65-92 wt%) in comparison to underlying
mildly weathered basement rocks (11-36 wt%) and overlying
sedimentary rocks (8-13 wt%) suggests that a zone of deeply
altered basement rocks existed prior to the deposition of the
sedimentary rocks. A kaolinite-rich horizon of comparable
thickness to the one observed at the surface is absent in all drill
holes onshore Andøya. Deeply weathered basement rocks may
therefore have developed only locally, or it may have been a
regional development, that was only locally preserved. The
latter can be explained by local erosion during development of
the basin, when parts of the regolith were close to sea level
and exposed to waves and tidal changes.
398
398
Goldschmidt2015 Abstracts
The magnesium isotopic composition
of planktonic foraminifera
ANGELA R. DIAL1, S. MISRA2, W. M. LANDING1 AND
V. J. M. SALTERS1
1
Florida State University; NHMFL – Geochemistry;
Tallahassee, FL, USA; ([email protected])
2
Uni. of Cambridge; Dept. of Earth Sciences; Cambridge, UK
Global climate is strongly influenced by the atmospheric
concentration of the greenhouse gas CO2. The weathering of
continental rocks consumes CO2 as well as transports cations
to the oceans, playing a critical role in both seawater chemistry
and climate. Magnesium, a major component of continental
silicate minerals, is homogeneous in both concentration and
isotopic composition. Seawater Mg isotopic composition
δ26MgSW (-0.82‰) reflects a balance between continental
weathering driven input, via rivers (δ26MgRiver ~ -1.09‰) and
groundwaters, and removal by high-temperature hydrothermal
oceanic crust alteration (Δδ26MgSW–HT ~ 0.0‰), dolomite
formation, and authigenic alumino-silicate clay formation
during low-temperature alteration of the oceanic crust. Since
the oceanic residence time of Mg is significantly longer than
the oceanic mixing time, variations in Mg isotopic composition
of seawater (δ26MgSW) recorded by marine calcites reflect a
global picture that is driven by an imbalance between the
source and sink [1-3]. Preliminary work [2] [3] has highlighted
the potential of planktonic foraminifera as an archive of
δ26MgSW despite a temperature effect on the Mg concentration
in the CaCO3 shell. The limiting factor in the published Mg
isotope work has been the choice of foraminifera species and
of the sample cleaning method to minimize post depositional
alterations. The present study investigates the Mg isotopic
composition of planktonic foraminiera as a potential proxy for
δ26MgSW [1-4]. We analyzed 48 core-top planktonic
foraminifera (covering 10 species) with an average of δ26Mg =
-4.63±0.57‰ (2σ) (Fig. 1). Our study demonstrates that there
is limited species-specific variability and that the fractionation
of Mg during calcification of inorganic calcite is not only
smaller, but is also less variable than that of foraminiferal
calcite (∆26MgCalcite-Solution = 2.13±0.24‰ [5]; ∆26MgForam-Seawater =
-3.81±0.57‰). In addition, we observe that the δ26Mg of
foraminifera cleaned with and without the reductive cleaning
step is consistent (Fig. 1), suggesting that the Mg isotopic
composition of high-Mg calcite bands which are preferentially
dissolved during reductive cleaning (hydrazine + citric acid), is
of similar composition as low-Mg bands.
Figure 1: δ26Mg (‰) of 48 coretop planktonic foraminifera
cleaned with Reductive cleaning
(blue diamonds, n=28) and
without it (red, n=20). The data set
is compared to other planktonic
foram values open diamonds [2]
and open circles [4].
[1] Broecker & Peng (1982)
Lamont-Doherty Geol. Obs.,
Palisades, NY. [2] Pogge von
Strandmann (2008) Geochem. Geophys. Geosyst., 9, Q12015,
doi:10.1029/2008GC002209. [3] Pogge von Strandmann et al.
(2014) Biogeosciences. 11, 5155-5168. [4] Wombacher et al.
(2011) Geochim. Cosmochim. Acta. 75, 5797–5818. [5]
Saulnier et al. (2012) Geochim. Cosmochim. Acta. 91, 75-91.
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Goldschmidt2015 Abstracts
Ca sources for pedogenic carbonate
nodules in a silicate watershed (FarNorth Cameroun)
F. DIETRICH1*, N. DIAZ1, P. DESCHAMPS2,
B. NGOUNOU NGATCHA3, D. SEBAG4 AND
E.P. VERRECCHIA1
1
Earth Surface Dynamics Institute, Lausanne University,
Switzerland (*correspondence: [email protected])
2
CEREGE, Aix-Marseille University-CNRS-IRD, France
([email protected])
3
Earth Science Department, Ngaoundere University, Cameroon
([email protected])
4
Laboratoire M2C, Université de Rouen, France / IRD, LMI
PICASS’EAU, Ngaoundéré, Cameroun
([email protected])
Unexpected pedogenic carbonate nodules are observed in
clayey-loamy soils of a silicate watershed (Far-North
Cameroon). Occurrence of such pedogenic carbonates is
enigmatic in this semi-arid area. 87Sr/86Sr and ε(Nd) have been
used to trace Ca and parent material that comprise nodules and
soils [1] [2].
According to 87Sr/86Sr signatures of carbonate nodules
(0.711200 ± 484 on average, n=10), their Ca source is mainly
attributed to local granite plagioclases that show similar
isotopic compositions. The quantity of nodules accumulated at
the surface reach 17 kg/m2. One kilogram of nodules contains
280g ± 25 g of Ca (n=10), whereas one kilogram of granite
contains 8 g of Ca. Due to this budget, and despite the huge
amount of available granite, some specific processes are
needed to retain and concentrate Ca in this acidic geosystem.
The mean values of 87Sr/86Sr and ε(Nd) of clay-loamy soils
(0.719646 ± 75 and -11.68 ± 0.23, n=4, on average and
respectively) are close to the signature of the average Saharian
dust (0.7179 and -12.0, respectively [3]). The clayey-loamy
soils and the presence of smectites provide good conditions for
Ca concentration.
Albeit processes responsible for pedogenic carbonate
formation remain elusive, the Ca source of North Cameroon
nodules seems to be local, excluding any major allochthonous
sources, contrary to the observations from other sites [4].
However, the aeolian part in the clayey-loamy soil plays a key
role in the Ca conservation in this acidic geosystem.
[1] Capo et al (1998) Geoderma 82 197-225. [2] Borg et
Banner (1996) GCA 60 4193-4206. [3] Pelt et al (2013)
Chemical Geology 341 147-157. [4] Chiquet et al (1999) GCA
63 311-323.
737
737
Goldschmidt2015 Abstracts
Weathering regime recorded by
boron isotopes in grain size fractions
of soil and river sediments
C. ERCOLANI12, D. LEMARCHAND*, A. VOINOT1,
C. BOSIA AND A. DOSSETO2
1
LHyGeS-EOST, University of Strasbourg, Strasbourg, France,
*[email protected]
2
Wollongong Isotope Geochronology Laboratory, School of
Earth and Environmental Sciences, University of
Wollongong, NSW, Australia
The relationships between tectonic, erosion and climate
control the transport and transformation of the sediments and
can be schematically summarized as the competition between
erosion and weathering rates. Generally, these processes are
determined by chemical, and sometimes isotopic, mass budgets
from river waters, soils and/or sediments. However, the
chemical heterogenity of the parent material, even at the
weathering profile scale, often hampers accurate determination
of the weathering rates.
In the present study, we explore whether B isotopes (δ11B)
in soils and river sediments can record the mechanisms and
forcing parameters of the weathering reactions. The key idea is
based on the observation that cogenetic silicate minerals have
very similar δ11B signatures and that isotopic fractionation only
occurs during precipitation of secondary products [1]. Thus,
we anticipate that the δ11B in coarse minerals reflects the
source of sediments whereas the δ11B in clay fractions is
controlled by the weathering regime. Following this model, we
compare the δ11B in different grain size fractions (bulk sample,
clay-sized
and
coarse
fractions)
from
various
geomorphological settings: forest soils, supended sediments
from Himalayan rivers and paleochannel sediments from
southest Australia.
In forest soils or suspended sediments from active river
channels, constant δ11B values in the coarse fractions indicate a
petrographically unique source for the particles. By contrast,
the δ11B in coarse fractions of sediments from Australian
paleochannels (deposition ages: 0-100 kyr) display evidence of
slow but regular variations that can be interpreted either as a
change of the sources supplying the sediments or postdepositional weathering. In all systems, δ11B in clay fractions
significantly differ from those in the coarse ones. Comparison
of the δ11B variations between coarse and clay fractions with
major and trace data could help determining the conditions and
intensity of the weathering reactions.
[1] Lemarchand, D., et al. (2012) Geochim Cosmochim Ac 98,
78–93.
837
837
Goldschmidt2015 Abstracts
Behaviour of lithium isotopes during
estuarine mixing of ice melt from the
Greenland Ice Sheet and offshore
waters
D. M. FRIES*1, R. H. JAMES1, M. J. HOPWOOD2,
D. P. CONNELLY3, D. A. H. TEAGLE1
1
Ocean and Earth Science, National Oceanography
Centre, Southampton SO14 3ZH, UK.
(*[email protected])
2
GEOMAR Helmholtz Centre for Ocean Research Kiel,
24148 Kiel, Germany
3
Marine Geoscience, National Oceanography Centre,
Southampton, SO14 3ZH, UK
Continental weathering and transport of dissolved elements
from rivers to the ocean are major processes regulating
atmospheric CO2 and thus act to moderate climate. During
glacial-interglacial cycles, changes in weathering processes
due to changes in ice melt (fresh water runoff), rock exposure
and temperature may affect the chemical composition of river
water and the concentration of suspended particulate matter, as
well as chemical weathering rates. For these reasons, improved
knowledge of glacial weathering processes is essential.
The lithium isotopic composition (δ7Li) of river water is only
affected by the formation of secondary mineral phases. It is
independent of catchment lithology and unaffected by
biological processes. Thus, river water δ7Li is an excellent
tracer of weathering processes and, as the δ7Li of foraminifera
records the Li isotopic composition of seawater, information
from the marine sedimentary record can potentially be used to
assess past changes in weathering processes.
During mixing between river water and sea water, changes in
the chemical and isotopic composition of some elements can
occur, modifying the signal delivered to the ocean. To assess
the effects of estuarine mixing on Li and Li isotopes, in a
glacial system, we have analysed a series of water samples
from Godthåbsfjorden (64° N, 51° W), West Greenland.
Samples were taken along a section from the inner parts of the
fjord, close to the Greendland Ice Sheet, to the offshore parts
close to Fyllas Banke [1], in both summer and winter. We will
present Li and Li isotope data, together with analyses of other
key parameters (major cations and anions, salinity,
chlorophyll, dissolved oxygen, temperature, turbidity), and use
these information to determine whether Li behaves as a
conservative or non-conservative element in this glacial
estuarine environment. We will evaluate the importance of
estuarine mixing in determining the Li and Li isotopic
signature of the weathering flux delivered to the ocean from
glacial weathering systems.
[1] Arendt K.E. et al. (2010) Mar. Ecol. Prog. Ser. 401, 49-62.
951
951
Goldschmidt2015 Abstracts
Intense weathering and
geochemical dispersion in a Tertiary
palaeochannel system: the DeGrussa
Cu-Au deposit marker, Australia
IGNACIO GONZALEZ-ALVAREZ1*, WALID SALAMA1,
MONICA LEGRAS1, PAUL HILLIARD2 AND
RICHARD BECKLEY2
1*
CSIRO, Mineral Resources Flagship, Perth, Western
Australia; [email protected]
2
Sandfire Resources Ltd., West Perth, 6005, Western Australia
Ore deposits are localized geochemical oddities having
unusually high concentrations of one or more ‘trace’ elements
(Ni, Co, Cu, Au, Cr, Sc, Nb, REE, HFSE). They can be seen as
exceptional geochemical markers for decoding complex
element dispersion due to successive weathering events over
long time periods. The DeGrussa Cu-Au deposit is hosted in
Proterozoic turbidites, mafic basalts and intrusive dolerites,
and is located in the Naracoota Formation in the Bryah Basin,
on the margin of a Tertiary palaeochannel system. The clayrich palaeochannel sediments have mean Chemical Index of
Alteration (CIA) values of ~95, with low absolute contents of
Sr, Ca, K, Mg and Na, and high concentrations of Al2O3 (mean
~22wt%) and CIA-Eu/Eu* covariation of extreme values. This
is interpreted as the result of exceptionally intense postdepositional weathering and/or deposition of already
weathered sediments. Strikingly, Cr (~370ppm), Ni (~60ppm),
V (~350ppm) and Sc (~35ppm) are widely enriched in the
sedimentary cover as well as in the fresh sedimentary
basement rocks (turbidites, siltstones) compared to Upper
Continental Crust (UCC) averages of ~70, ~35, ~100 and
~15ppm respectively. These elements are significantly
depleted in the ore. Copper, Ag, In, As and Se are enriched
throughout the sedimentary cover relative to UCC.
Sedimentary units above the Tertiary channel package have
higher anomalous concentrations of As (mean ~8-12ppm) and
Mo (~1.2-1.3ppm), compared to ~5 ppm As and ~1.0 ppm Mo
in the channel clays. Covariation of CIA-Eu/Eu*, CIA-ΣREE
and Sr-Eu/Eu* could be indicative of a large catchment area.
However, the pervasive metal enrichment of the sedimentary
cover reflects a drainage system with a restricted catchment
with sediment provenance linked to the area of the local
mineral system or to the Proterozoic basement rocks enriched
in Cu, Ag, Cr, Ni, V and Sc. The relative significance of
overprinting by vertical chemical dispersion from fresh
basement rocks versus mechanical dispersion due to
sedimentary dynamics remains uncertain.
1073
1073
Goldschmidt2015 Abstracts
Ocean acidification causes element
release from the sediments of
Changjiang (Yangtze River) estuary
Y. W. GUO* AND S. Y. YANG
State Key Laboratory of Marine Geology, Tongji University,
Shanghai 200092, China
(*correspondence: [email protected])
The Changjiang (Yangtze River) is the largest river in
China, which plays a critical role in terrestrial material cycle
and ecosystem health of the East China Sea. In recent years,
the Changjiang delivered a huge amount of nutrients into the
estuarine and coastal areas, resulting in the deterioration of
marine environment such as the occurrences of red tide and
hypoxia off the estuary. How the estuarine and shelf sediments
that are originally weathered from the land respond to the rapid
changes of oceanic environment may significantly influence
the material cycle and biogeochemical process in the East
China Sea and the West Pacific.
In this contribution, an experimental study was carried out
to examine the release rates of major elements (Ca, K, Mg, Mn
and Fe) from the surface sediments in the Changjiang Estuary,
aiming to explore the element release behavior and mechanism
in terms of ocean acidification. Under the wide pH ranges of
simulated seawater from 4.0 to 8.0, the release fluxes of Ca, K,
Mg, Mn and Fe from four sediment samples increase rapidly
while the sediments reacting with the solution, and then show
different variations. The dissolution rates of the elements
decrease with the simulated seawater pH increasing from 4.0 to
7.0, but increase while the pH increasing from 7.0 to 8.0.
Furthermore, Ca, K and Mg have relatively higher dissolution
rates than Mn and Fe. The different release rates of these
elements are closely related to the original mineral
composition of the studied sediments and the reaction kinetics.
Overall, although the release rates of the elements are
relatively slow, the enhancing ocean acidification could cause
significant release of major elements from naturally-weathered
terrigenous sediments into the ambient marine environment,
which has to be considered carefully in the future studies on
global environmental change and ocean chemistry.
Acknowledgements: This work was supported by NSFC
research fund (Grant No: 41225020, 41376049).
1128
1128
Goldschmidt2015 Abstracts
Features of geochemistry and
mineralogy of the modern river
sedimentogenesis
V. V. IVANCHENKO, M. V. BELITSKAYA AND
A. S. ILYINA1
1
National Academy of Sciences of Ukraine, Kiev,
[email protected]
The river system transports huge masses of minerals from
the continents in the sea basins. In the modern era river
hydrodynamics, chemical and mineral composition of
sediments has changed substantially.
The authors examined more than 100 samples of alluvium
in the major industrial regions of Ukraine. Purpose of work determine the mechanism of interaction of natural and
anthropogenic factors in the formation of precipitation. Used
chemical, spectral and mineralogical analysis, electron
microscopy, microprobe analysis, new methods of separation
of natural and technogenic ores.
Established a joint accumulation of heavy elements of
natural and industrial origin As a result of the separation of
sediment produced in the laboratory ore concentrate. A feature
of modern river sediments is mobilization of trace chemical
elements and extensive development of authigenic minerals.
Euhedral crystals, brushes, crusts, concretions and spherulites
of the microscopic dimensions are typical for them. Authigenic
minerals are represented by carbonates, sulfides, oxides and
silicates. Hexahedrons, octahedrons and dodecahedrons of
authigenic pyrite formed in the basal horizons of alluvium.
There they accompany the particles of gold and may be used as
indicators for his search.
[1] Chugunov & Ivanchenko (2014), Patent of Ukraine. Bul. 7,
105092.
1395
1395
Goldschmidt2015 Abstracts
Chemical characteristics of heavy
metal concentration of riverbank
sediment by river flow from the Hii
river, Shimane prefecture, southwest
Japan – a preliminary study.
ISAMU KYOMEN1* TETSUYA SAKAI2 WAN LI1 AND
ICHIRO MATSUMOTO1
1
Faculty of Education, Shimane University, Matsue, Japan.
[email protected] (corrspondence)
2
Department of Geoscience, Interdisciplinary Faculty of
Science and Engineering, Shimane University, Matsue,
Japan.
Heavy metal concentrations pattern of riverbank sediment
by river flow of Hii river were measured at the small area
(sand bank in the river water) (20m*35m in size), Izumo city,
Shimane prefecture, southwest Japan. Sediment samples were
collected at about 150 points at the small area. The interval of
the samples were about 1-2m each.
Analyzed elements are mainly Ca, Ti, Mn, Fe, Co, Zn, and
Cr by portable (handheld) XRF. We also check the mineral
compositions and grading analysis of each samples.
The mineral and chemical concentration patterns on the
river bank became clear by this preliminary study.
We are going to study these results in details further and to
perform the environmental and geological assessment to the
Hii river.
[1] Takayasu, K (2001): Tatara-syobou (press), pp184. [2]
Matsumoto, I (2009): Laguna, 16, 53-62. [3] Matsumoto,
Komatsu and Kamei et al. (2008): Memories of Faculty of
Education, Shimane Univ, 42, 97-105. [4] Matsumoto, I.,
Hoffman D., Wolfe J. and Ishiga H. (2010): Texas Journal of
science, 62, 223-236.
1736
1736
Goldschmidt2015 Abstracts
Extrapolating regolith geochemical
data for regional analysis of the
critical layer using ASTER remote
sensing data
HETA LAMPINEN1*, CARSTEN LAUKAMP2,
SANDRA OCCHIPINTI1 AND SCOTT HALLEY3
1
CET, University of Western Australia, Australia
(*correspondance: [email protected])
2
CSIRO, Mineral Resources Flagship, Kensington, Western
Australia
3
Mineral Mapping Pty Ltd, Rossmoyne, Western Australia
The mineralogical composition of the critical layer
extracted from VNIR-SWIR reflectance spectra was
investigated to establish a link between remote sensing ASTER
geoscience products [1] and regolith geochemistry, for the
purpose of mapping regolith landforms and mineral footprints
potentially related to base metal mineralisation. Advantages of
remotely detecting patterns of hydrothermal fluid flow from
the cover where the alteration signal is diluted by weathering,
and often distorted by transported cover, would be vast. To
unravel these connections a regional study (60*110 km) was
conducted in the Edmund Basin of the Capricorn Orogen in
Western Australia, in an area around Abra basemetal
mineralisation.
Analysis of the data suggests the regolith geochemistry
reflects the underlying lithology and correlates with the VNIRSWIR data. The critical layer over basement granites and the
overlying Edmund depositional packages 1 and 3 have high
SiO2% in contrast to dolerites and Edmund depositional
package 4 where silica content is relatively low. Analysis of
reflectance spectra using 2200 nm wavelength depth for Alclay and 2160 nm wavelength depth for kaolinite feature
extraction, combined with 2200 nm wavelength location,
suggests that Al-rich clays are kaolinite, which are poorly
ordered for most of the dataset, resembling transported
material, but that there are occurrences of inferred white micas
and other minerals that could relate to insitu regolith and
subsequently, the bed rock signature. Compositional
differences of Al-­‐clays is also supported by K radiometric
images, that indicate K-­‐bearing minerals where reflectance
spectroscopic data suggest the presence of white micas. The
ASTER AlOH Group composition shows moderate correlation
with sample geochemistry Al2O3% as well as with reflectance
spectra Al-clay composition detected by the change in 2200
nm wavelength position.
[1] Cudahy T., Caccetta M., Hewson R., et al. (2012). Satellite
ASTER Geoscience Map of Australia. v1. (DOI.
10.4225/08/51400D6F7B335).
1757
1757
Goldschmidt2015 Abstracts
Evanescent weathering surface
evidenced by 234U/238U activity ratios?
R. XUE1, A. J. WEST2, L. LI1, C.-F. YOU3 AND G. LI1
1
Department of Earth Sciences, Nanjing University, Nanjing
210046, China ([email protected])
2
Department of Earth Sciences, University of Southern
California, Los Angeles, California 90089, USA
3
Earth Dynamic System Research Center, National Cheng
Kung University, Tainan 70101, Taiwan
Direct α-recoil and preferential dissolution of 234U from the
damaged lattice make (234U/238U) a potential rate-meter for
mineral dissolution that is normalized to α-recoil scale of
~30 nm [1]. Here we present mathematical model and
laboratorial experiments showing that the (234U/238U) of
weathering solution is functions of surface age, dissolution
rate, and dissolution preference (p) of the 234U sites (Fig. 1A).
For a given rock type with fixed p value, the (234U/238U) is
approximately a monotonic function of dissolution depth if
dissolution rate is higher than 10-9 mm/yr (Fig. 1B). The
(234U/238U) value of basaltic catchments [2-7], which is mostly
higher than 1.2, indicating dissolution depth of less than
0.2 µm (Fig. 1B), and thus implying an evanescent weathering
surface of about twenty years given a weathering rate of
~10-2 mm/ky [8]. Accumulation of leached layers and
secondary precipitates may inhibit deep dissolution.
Interestingly, the depth of mineral dissolution, as proxied by
riverine (234U/238U), correlates well with weathering
temperature.
234
3
U dissolution preference, p = 2
A
Dissolution rate = 10-11 mm/yr
-1
10
0
(234U/238U)
4
(234U/238U)
r
/y
102
104
Surface age (yr)
p = 10
m
r
/y
m
m
p=5
p=3
-9
2
100
m
3
10
4
r
/y
m
m
r
/y
m
m
1
10-2
-7
-4
10
10
2
106
108
B
p=2
p = 1.5
(234U/238U)=1.2
1
10-6
10-7
10-5
10-4
10-3
10-2
Weathering depth (mm, = surface age × dissolutoin rate)
[1] Vigier, et al., 2001, EPSL, 193, 549; [2] Riotte et al. 2003,
Chem. Geol. 202, 365; [3] Vigier et al., 2005, Chem. Geol.
219, 69; [4] Vigier et al., 2006, EPSL. 249, 258; [5] Pogge von
Strandmann et al., 2006, EPSL, 251, 134; [6] Pogge von
Strandmann et al., 2010, Chem. Geol., 270, 227; [7] Bagard et
al., 2011, GCA, 75, 3335; [8] Navarre-Sitchler, et al., 2007,
EPSL, 261, 321.
3482
3482
Goldschmidt2015 Abstracts
Exploring time-dependent
geomagnetic and atmospheric effects
on cosmogenic nuclide productionrate scaling
NATHANIEL LIFTON1
1
Department of Earth, Atmospheric, and Planetary Sciences
and Department of Physics and Astronomy, Purdue
University, West Lafayette, Indiana, 47907 USA,
[email protected]
The scaling implications of two recent time-dependent
spherical harmonic geomagnetic models spanning the
Holocene are explored using a recently published cosmogenic
nuclide (CN) production-rate scaling model [1] termed the
LSD model. [2] and [3] updated earlier paleomagnetic models,
now covering 0-10 ka. Time-integrated scaling predictions
using the new models and LSD differ significantly from those
using 1) the earlier models, and 2) another recent timedependent spherical harmonic geomagnetic model from
0-14 ka [4].
In addition, the effects of a time-dependent atmospheric
model (SynTraCE-21, e.g., [5]) on LSD scaling predictions are
evaluated from 0-21 ka. Given the dominance of altitudinal
over latitudinal (geomagnetic) scaling effects on CN
production, incorporating such transient global simulations of
atmospheric structure into scaling frameworks may contribute
to improved understanding of long-term production rate
variations and their implications for surficial process studies.
[1] Lifton et al., 2014 EPSL 386, 149–160 [2] Korte and
Constable (2011, Phys. Earth. Planet. Int. 188, 247–259 [3]
Korte et al. (2011, EPSL 312, 497–505 [4] Pavón-Carrasco et
al. (2014, EPSL 388, 98–109 [5] Liu et al., 2009, Science 325,
310–314
1861
1861
Goldschmidt2015 Abstracts
Mobility indices for the evaluation of
metal contamination in soils affected
by mining activities
M. J. MARTÍNEZ-SÁNCHEZ1, C. PÉREZ-SIRVENT1,
M. L. GARCÍA-LORENZO2 AND
M. HERNÁNDEZ-CÓRDOBA3
1
Department of Agricultural Chemistry, Geology and
Pedology, . International Campus of Excellence “Campus
Mare Nostrum”, University of Murcia, Murcia, (Spain).
[email protected]
2
Department of Petrology and Geochemistry. Faculty of
Geology, Complutense University of Madrid, Madrid
(Spain)
3
Department of Analytical Chemistry. International Campus of
Excellence “Campus Mare Nostrum”, University of
Murcia, Murcia, (Spain).
This work presents a methodology to assess the
environmental potential risk of soils when submitted to
different conditions. The potentially toxic elements (PTEs)
behaviour was evaluated by single chemical extractions in
order to simulate four conditions: PTEs leaching under actual
rainfall conditions; acid mine drainage; an anoxic and an oxic
environment. Soil pollution assessment was carried out using
the contamination factor (CF) and the pollution load index
(PLI) for total contents and indicators of mobility were
established for each extraction: natural mobility indicator
(NMI), acid mine drainage mobility indicator (AMI), oxic
mobility indicator (OMI) and anoxic mobility indicator
(ANMI).
The total PTEs content in samples was high, and this
content decreased when the distance of the sampling site to the
source of contamination increased. The results obtained after
the extractions suggested that the highest PTEs content were
extracted in the acidic medium. These results allow to suggest
that acid mine drainage in the studied area is an important
problem, especially in samples located close to the
contamination sources, where soils could act as secondary
contamination sources if they receive acidic waters. In
addition, the complexing-medium results suggest that if in
sediments close to contamination sources a change from
oxidant to reducing conditions takes place, PTEs mobilisation
could be an important issue.
The most reactive materials under oxic conditions are, in
the study area, the most modern. The proposed indices may
constitute a first attempt to define areas with high potential
environmental risk, where urgent action is needed. In addition,
the proposed methodology could be a valuable tool to prioritise
these interventions.
2031
2031
Goldschmidt2015 Abstracts
Strontium isotopic signatures of the
streams and lakes on James Ross
Island, Antarctica
J.MÍKOVÁ1* AND V. ERBAN1
1
Czech Geological Survey, Geologická 6, 152 00 Prague 5, CZ
(*correspondence: [email protected])
The Antarctic Peninsula region as the the fastest warming
site in the Southern Hemisphere experience not only
accelerating retreat of glaciers but also the rate of rock
weathering. In order to understand processes of chemical
weathering we are using strontium isotopes (87Sr/86Sr).
Sampling on the James Ross Island was performed during
the 2011 and 2012 field campaigns with respect to bedrock
lithology, consisting of two main geological domains
(palagonitized basalts and Mesozoic sediments).
Data for water samples from Torrent Valley and Brandy
Bay (Phormidium Lake and Monolith Lake basins) fall within
two isotopically distinct groups. Samples from Torrent Valley
have less radiogenic 87Sr/86Sr ratios than samples from Brandy
Bay. In Torrent Valley the 87Sr/86Sr ratios of the stream profile
from the glacier to the sea shore become less radiogenic with
increasing distance from the glacier. Torrent Valley is
dominated by volcanic rocks and the isotopic composition of
waters is close to their previously published isotopic data
(0.7033 ± 0.0002), thus implying major contribution of
volcanic source of the Sr in the water.
Water samples collected within Phormidium Lake basin
have 87Sr/86Sr ratios close to marine sediments (0.7085 ±
0.0006) which are in good agreement with the geological
situation on site. There are significant isotopic variations in the
stream data. Some of the small streams entering Phormidium
Lake are more radiogenic and some are less radiogenic than
the waters of the lake itself. The 87Sr/86Sr ratio of the
Phormidium Lake lies on the mixing line between the stream
waters. Data for Monolith Lake basin show 87Sr/86Sr ratios as a
mixture between marine sediments and volcanic rocks as
volcaniclastic breccias are quite abundant at this site. Our
results imply that key factor affecting chemical composition of
water and nutrient availability is lithology of bedrock and the
sea spray contribution is not significant, even in the close
proximity to the sea shore. Use of Sr isotopes can discern the
proportions of geological materials undergoing chemical
weathering at James Ross Island.
This study was supported by the Czech Ministry of
Environment (project No. SPII1A9/23/07), by the Czech
Geological Survey, and by scientific infrastructure of the
Czech Antarctic Station ‘‘J.G. Mendel’’.
2128
2128
Goldschmidt2015 Abstracts
Rates and trends in in situ chemical
weathering in a tropical soil, Basse
Terre Island, Guadeloupe
MURPHY, MARIAH1, SAK, PETER B.1, MA, LIN2,
GAILLARDET, JEROME3, DANIEL, CHRIS G.4 AND
BRANTLEY AND SUSAN L.5
1
Dickinson College, Carlisle, PA 17013 USA
University of Texas at El Paso, El Paso, TX 79968 USA
3
Institut de Physique du Globe de Paris, Paris, France
4
Bucknell University, Lewisburg , PA 17837 USA
5
Pennsylvania State University, University Park, PA, USA
2
We present chemical and U-series isotope analyses of an
oriented weathering clast collected from the B horizon of
weathered Quaternary volcanoclastic debris flow on Basse
Terre Island, Guadeloupe. The sample consists of an
unweathered andesitic core overlain by a weathering rind, an
indurated crust that separates the rind from the overlying soil
matrix. U/Th disequilibria dating indicate that rind age
increases away from the core-rind boundary to a maximum of
66 ka. This translates to a rind-advance rate of 0.2 mm yr-1,
broadly consistent with rind advance rates calculated
elsewhere on Basse Terre Island. The overlying indurated
crust is 72 ka and the enveloping ~ 270 ka matrix material.
Elemental variations are constrained by a bulk ICP-AES
vertical transect spanning from the core to the overlying soil
matrix and parallel electron microprobe transections. The
hierarchy of elemental loss across the core-rind boundary
varies in the order Sr ≈ Ca > Mg ≈ Na ≈ Mn > Al > K ≈ Ba ≈
Si > P > Ti. The <1000 μm wide reaction front at the rind-soil
interface is marked by an indurated horizon with Fe and Mn
enrichment, followed by the enrichment of Mn, Ba, Al, Mg
and K in the soil.
Unlike previously studied clasts, the preservation of the
rind-soil interface permits characterization of weathering
reactions between the weathering core, the rind, and the
surrounding soil matrix, shedding insights into communication
between the enveloping weathering rind and host regolith.
2223
2223
Goldschmidt2015 Abstracts
226
Ra/238U disequilibrium as a
weathering index in heavy mineralsenriched beach sand sediments
A. PAPADOPOULOS1*, A. KORONEOS1, G. CHRISTOFIDES1
2
AND S. STOULOS
1
Department of Mineralogy, Petrology, Economic Geology,
Aristotle University of Thessaloniki, 54124, Thessaloniki,
Greece (*correspondence: [email protected],
[email protected], [email protected])
2
Laboratory of Nuclear Physics, Aristotle University of
Thessaloniki, 54124 Thessaloniki, Greece,
[email protected]
Weathering indices can be used to quantify weathering of
sediments at various stages of weathering and provide a better
understanding of element mobility during weathering. For
these reasons, various weathering indices are proposed in
literature. 37 samples from Kavala and 30 from Sithonia beach
sands, all of them being the weathering products of the local
granitic plutons are studied for their secular disequilibrium in
238
U-series (226Ra/238U ratios) and the results are compared to
those of the weathering indices already in use worldwide. The
parental rocks of the beach sand sediments were in radioactive
secular equilibrium concerning 226Ra/238U [1].
Results of 226Ra/238U radioactive disequilibrium are quite
similar to those given by Weathering Index of Parker (WIP)
and Product of Weathering Index (PWI), especially for the
well/very well sorted sands and the heavy minerals-enriched
sands of Kavala. Therefore it could be used as a relatively
sensitive weathering index in sediments, considering however
the mineralogical composition and sediment sorting.
[1] Papadopoulos et al. 2013. Radioactive secular equilibrium
in 238Uand 232Th series in granitoids from Greece. Appl Radiat
Isotopes 75, 95–104
2394
2394
Goldschmidt2015 Abstracts
Geochemical characterisation of
topsoils, surface waters and
efflorescences in a historic-metal
mining area in SE, Spain
C. PÉREZ-SIRVENT1, C. HERNÁNDEZ-PÉREZ1,
M. L. GARCÍA-LORENZO2, M. J. MARTÍNEZ-SÁNCHEZ
3
AND M. HERNÁNDEZ CÓRDOBA
1
Department of Agricultural Chemistry, Geology and
Pedology, . International Campus of Excellence “Campus
Mare Nostrum”, University of Murcia, Murcia, (Spain).
[email protected]
2
Department of Petrology and Geochemistry. Faculty of
Geology, Complutense University of Madrid, Madrid
(Spain)
3
Department of Analytical Chemistry. International Campus of
Excellence “Campus Mare Nostrum”, University of
Murcia, Murcia, (Spain).
Acid mine drainage (AMD) from sulphide-rich wastedumps exposed to weathering processes is an important focus
of environmental impact, generally due to their low pH, high
salinity and high potentially toxic element (PTE) content. The
present study represents a contribution to the knowledge of the
mineralogy and geochemistry of the solid phases and surface
waters formed in the AMD setting of the Sierra Minera (SE,
Spain) and their environmental significance. In addition, the
exposure of the population to arsenic and the associated risk
were assessed.
A total of ten topsoils and surface waters and
11 efflorescences affected to varying degrees by mining
activities were studied. The total PTE content (As, Cd, Cu, Fe,
Pb and Zn) was determined. In addition, the mineralogical
composition of solid samples was determined by X-ray
diffraction and some efflorescences were also analysed using a
scanning electron microscopy-energy dispersive X-ray
spectrometer. Finally, an arsenic-intake risk assessment was
carried out, both as regards carcinogenic and non-carcinogenic
effects and considering the total and the bioaccesible As
content.
The study area is heavily polluted as a result of historical
mining and processing activities, during which time great
amounts of wastes were produced, characterised by a high PTE
content, acidic pH and minerals resulting from supergene
alteration, including soluble metal-salts, mainly sulphates,
iron-hydroxysulphates and iron-oxyhydroxides, all of which
form ochreous precipitates. Topsoil samples showed risk
values and hazard quotients higher than the reference levels,
particularly for children. In the efflorescences these values
were lower but still unacceptable.
2459
2459
Goldschmidt2015 Abstracts
Precipitation dependent erosion rates
along the western Peruvian margin
REGINA REBER*1, CAMILLE LITTY1, ANDREA MADELLA1,
NAKI AKÇAR1, ROMAIN DELUNEL1 AND
FRITZ SCHLUNEGGER1
1
University of Bern, Institute of Geological Sciences,
Baltzerstrasse 1+3, CH-3012 Bern
*correspondence: [email protected]
The Western Andean margin of Peru is characterized by
large precipitation gradients from nearly tropical conditions in
northern Peru to an arid/semiarid climate near the political
border with Chile. Although these climate gradients have been
illustrated, a possible erosional response has to be thoroughly
explored. Here, we measure erosion rates in different river
catchments along the western Peruvian margin with the scope
to explore possible decencies to today’s precipitation pattern.
To this extent, we sampled river-born sand in active stream
beds from about 30-40 catchments along the Peruvian margin
between 5° S to 20° S latitude. These bedload samples will be
used to measure 10Be-based catchment-averaged denudation
rates. In addition to the N-S decreasing trend of rainfall
amount, the catchments reveal different morphometric
properties (relief, hypsometry, slopes, size etc.), which
potentially influences the pattern of erosion rates. Despite of
these differences, they all share the same trend of downstream
decreasing precipitation rates from their sources on the
Altiplano to the Pacific coast, and they are all affected by the
along-strike N-S decreasing trend in the rainfall amount. We
thus expect to be capable to disentangle between these intrinsic
and extrinsic driving forces.
2598
2598
Goldschmidt2015 Abstracts
Particulate riverine inputs of metals
and their isotopes to the oceans
B. N. REVELS1*, J. D. RICKLI1 AND D. VANCE1
1
Institute for Geochemistry and Petrology, Department of
Earth Sciences, ETH Zürich, Switzerland
([email protected])
A sound constraint on global sources and sinks of trace
metals (e.g., Fe, Cu, Zn, Mo, Ni) and their isotopes is of
utmost importance in understanding the oceanic mass balance
of these elements, and how they affect global biogeochemical
cycling. Traditionally, research on the riverine source of
transition metals has focused on the dissolved load, as this is
the most obvious contribution to the dissolved load of the
oceans. However, early and recent work has shown clearly
that: (a) the particulate phase dominates the riverine load for
most transition metals and; (b) for many of the transition
metals a large fraction of this particulate load is chemically
labile, enabling the particulate phase to interact with the
dissolved phase as both a source and a sink. Here we document
the application of sequential leaching methods to riverine
particulates to further understanding of the potential influence
of riverine particulate phases on seawater.
Initial results from Rhine River samples suggest that our
methods are successful in leaching specific particulate
fractions (exchangeable, organic, carbonate, FeMn and
residual silicates) that are isotopically distinct and
reproducible. In addition, isotopic analyses of Cu, Zn and Fe
suggest that, for this river, the isotopic composition of the
dissolved load is, to first order, closely related to the rocks in
the source region and not modified by the weathering process
(e.g. incongruent weathering) or extraction of distinct isotopic
signatures into secondary phases during riverine transport.
We will present the results of leaching experiments on
artificial sample composites to confirm the reliability of the
leaching techniques.
2621
2621
Goldschmidt2015 Abstracts
Annual lamination in a recent
speleothem from Zoolithencave
(Bavaria, Germany)
DANA F. C. RIECHELMANN1, KLAUS PETER JOCHUM2,
RIK TJALLINGII34, JENS FOHLMEISTER5,
DETLEV K. RICHTER6, GEERT-JAN BRUMMER4 AND
DENIS SCHOLZ1
1
Johannes Gutenberg-University Mainz, Institute for
Geosciences, Mainz, Germany, ([email protected],
[email protected])
2
Max Planck Institute for Chemistry, Department of
Biogeochemistry, Mainz, Germany, ([email protected])
3
GFZ German Research Centre for Geosciences, Section
Climate Dynamics and Landscape Evolution, Potsdam,
Germany, ([email protected])
4
NIOZ-Royal Netherlands Institute for Sea Research,
Department of Marine Geology and Chemical
Oceanography, ‘t Horntje (Texel), The Netherlands, Geert([email protected])
5
Ruprecht-Karls University Heidelberg, Institute for
Environmental Physics, Heidelberg, Germany,
([email protected])
6
Ruhr-University Bochum, Institute for Geology, Mineralogy
and Geophysics, Bochum, Germany,
([email protected])
A stalagmite from Zoolithencave (Bavaria, Germany) was
analysed for visible, elemental and UV-luminescent
lamination. The visible lamination was determined on thin
sections, and lamina thickness was measured with the software
analySIS pro (Olympus). The elemental concentration was
measured by LA-ICPMS (Element 2, ThermoFinnigan,
213 nm Nd:YAG Laser, NewWave) and UV SpectralLuminescence Scanning (UV-SLS) of the stalagmite. Its age is
constrained by 14C-dating of a charcoal piece deposited below
the stalagmite and detection of the radiocarbon bomb peak.
The dating results show that this stalagmite grew in
approximately during the last 200 years, and the age model
was improved by lamina counting. The preliminary results
show that all three types of annual lamination (visible,
elemental and UV-SLS) occur in this stalagmite. The
concentration of Mg, Sr and Ba reflects the annual variability
with higher values in the brighter than in the dark layers. The
concentration of P can be used as an indicator for soil activity,
which increases in the darker layers. These darker layers are
induced by humid acids from the soil above the cave.
Therefore, P was compared with the G/B ratio of the UV-SLS,
which is as well an indicator for humic acids originating from
the soil.
2637
2637
Goldschmidt2015 Abstracts
Metal(loid)s and radioactive metallic
elements in the clay-sized fraction of
soils used for agriculture in Brava
island (Cape Verde)
ROSA MARQUES12, M. I. PRUDÊNCIO1, M. I. DIAS1,
FERNANDO ROCHA23, J. C. WAERENBORGH1 AND
J. MADEIRA4
1
C2TN, Instituto Superior Técnico, Universidade de Lisboa,
EN10 (km 139.7), 2695-066 Bobadela, Portugal
2
GeoBioTec – GeoBiociências, GeoTecnologias e
GeoEngenharias (Foundation for Science and Technology)
3
Dep. de Geociências – Univ. Aveiro, Campus Univ. Santiago,
3810–193 Aveiro, Portugal, [email protected]
4
Instituto Dom Luiz, Faculdade de Ciências, Universidade de
Lisboa., Lisboa, Portugal
Brava is a small volcanic island of the Cape Verde
archipelago with an older basement composed of a submarine
volcanic sequence (nephelinitic/ankaramitic hyaloclastites and
pillow lavas) and an intrusive complex (alkaline–carbonatite)
that is unconformably covered by younger sub-aerial volcanic
deposits (dominated by phonolitic magmatism). Sediments
also occur. Intrusive and extrusive carbonatites increase the
imbalance of elements in the parent materials that can impact
on the health of plants and animals growing in or on the soils.
Brava is characterised by an irregular plateau between 300 and
976 m above sea level, with numerous closed depressions
corresponding to recent phreato-magmatic craters. Soils are
incipient mainly due to a semi-arid climate. Cultivated land is
mostly found in soils developed on phonolitic pyroclasts at the
plateau area around Nova Sintra village, where a higher index
of moisture occurs, together with soils developed on sediments
particularly in fluvial valleys.
A geochemical, mineralogical and iron speciation study of
topsoils developed on phonolitic pyroclasts and on sediments
is reported, aiming at assessing metal(loid)s behavior,
including radioactive elements, and the mineralogical
assemblage. Whole samples and the clay-sized fractions were
analyzed by neutron activation analysis, X-ray diffraction and
Mössbauer spectroscopy.
A general enrichment of the chemical elements studied in
the clay-sized fraction of soils is observed, with exception of
Fe and Cr suggesting their occurrence in coarser particles of
iron oxides; a significant enrichment of Sb occurs in the claysized fraction of the plateau soils particularly those close to
fault zones. Radioactive elements tend to be concentrated in
the fine particles, except in soils developed in sediments with a
significant contribution from extrusive carbonatites and from
the alkaline–carbonatite complex. Illite, mixed-layered
minerals and kaolinite were the main clay minerals identified
in the studied topsoils. Chlorite also occurs in trace amounts.
Approximately 85% and 75% of the total Fe is in the Fe3+
oxidation state in soils developed on sediments and phonolitic
pyroclasts, respectively. Hematite is virtually the only Fe oxide
present in soils of sediments, while maghemite is more
abundant than hematite in soils developed on pyroclasts.
2018
2018
Goldschmidt2015 Abstracts
Sodium-titanium ratios in tsunami
deposits from the Sendai plain, the
Pacific coast of northeastern Japan
T. WATANABE1*, N. HOSODA1, N. TSUCHIYA1,
S. YAMASAKI1, F. W. NARA2, T. NAKAMURA2 AND
TOHOKU UNIVERSITY TSUNAMI RESEARCH GROUP
1
Tohoku University, Sendai 980-5879, Japan
(*correspondence: [email protected])
2
Nagoya University, Nagoya 464-8602, Japan
The Sendai plain, northeastern Japan, had severe damages
by tsunami after the 2011 off the Pacific coast of Tohoku
Earthquake (Mw=9.0). After tsunami invasion, these areas had
been covered by huge amount of tsunami deposits [1]. The
tsunami deposits contained gravel, sand, mud (silt and clay),
and microfossils. On the other hand, past tsunami deposits (for
example, Jogan tsunami deposits, ~1000 years ago) can be
found from outcrops and boring core samples as visible sandy
event layers [2] [3]. The past tsunami deposits in strata are
useful indicator to assess possible tsunami invasion area [4].
However, discrimination of past tsunami deposits is still
uncertain because muddy tsunami sediments were mixed with
land soil. Therefore, geochemical techniques were applied for
discrimination of the deposits in this study.
In this study, we performed radiocarbon dating of plant
residues, tephra dating and geochemical measurements for
continuous soil sediments (HS2-7) from Sendai plain, the
Pacific coast of northeastern Japan, taken by handy-geoslicer
(Fukken co. ltd.). The soil sediments are 84–183 cm in length,
and composed of cultivated surface soils, peaty clay, silt and
fine-medium sands. The HS2–HS7 was sub-sampled at 1 cm
intervals, and measured for chemical component by EDXRF
on the discrete samples. Beside, plant residues were picked up
from the samples for radiocarbon dating. In addition,
geochemical discrimination of tsunami deposits using Na/Ti
atomic ratios were adopted to HS2-HS7 sediment samples.
These samples were taken from coastal side (HS2, 3, 4, 7) and
inland side (HS5, 6). For the HS7 samples (coastal side), Na/Ti
and Si/Al atomic ratios in sandy layers were relative high (up
to ~30 and ~7 respectively) in comparison to those of peaty
clay layers. On the other hand, relative low Na/Ti atomic ratios
in sandy layers (~5-7) were observed for HS6 (inland side).
Therefore, these results indicate that Na/Ti could be proxy of
past tsunami invasion.
[1] Kuwatani et al. (2014) Sci. Rep. 4, 7077. [2] Chague-Goff
et al. (2012) Sediment. Geol. 282, 65-77. [3] Sawai et al.
(2012) GRL 39, L21309. [4] Sugawara et al. (2012) Sediment.
Geol. 282, 14-26.
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Goldschmidt2015 Abstracts
Silicon isotopic sytemematics of
different weathering profiles, Deccan
Traps, India
M. WILLE1*, M. G. BABECHUK2, M. WIDDOWSON3,
B. S. KAMBER2 AND R. SCHOENBERG1
1
Department of Geosciences, University of Tübingen,
Germany (*correspondence: [email protected])
2
Department of Geology, Trinity College Dublin, Ireland
3
Department of Geography, Environment and Earth Sciences,
University of Hull, UK
Chemical weathering of Earth’s upper crust cycles most
key elements in response to tectonic activity, and climatic and
environmental conditions such as soil water residence times,
and pH and Eh. Accordingly, different surface weathering
regimes around our planet place fundamental controls upon the
supply of element to the oceans and associated biosphere. Of
the key major elements, Si has particular importance.
Globally, basalt is one of the most widespread and
compositionally uniform rock types, accordingly continental
flood basalt successions provides a useful natural laboratory
for weathering fluxes. Here, we compare two weathering
profiles of differing chemical maturity developed upon basalt
of the Deccan Volcanic Province, India. We present new Si
isotopic data in combination with major and trace element
information. High rates of chemical weathering during the
Paleogene led to extreme basalt alteration characterising the
Bidar profile, with iron-rich lateritic horizons displaying high
loss of Si compared to the unweathered protolith. By contrast,
the Quaternary age Chhindwara profile displays a much lower
degree of chemical alteration, with only small changes in Si
concentrations during chemical weathering.
Importantly, the bulk sample Si isotopic variations are
relatively small in both weathering profiles. Si isotopic
variation associated with increasing kaolinisation is not
observed but, crucially, increasing Fe/Al ratios are associated
lighter Si isotopic values. The correlation of ∆30/28Si(soil-protolith)
with Si/Fe with indicates that formation of iron oxides may
control Si isotopic varations in both profiles. Further, lower Eh
and pH conditions appear to have caused Fe2+ migration and
iron oxide precipitation associated with Si adsorption at a
restricted paleo-water table level in the Bidar profile By
contrast, the entire Chindwarra profile was oxic, leading to in
situ formation of iron oxides associated with Si adsorption.
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