ARTICLE IN PRESS
Continental Shelf Research 23 (2003) 1175–1200
Clay mineralogy and multi-element chemistry of surface
sediments on the Siberian-Arctic shelf: implications
for sediment provenance and grain size sorting
C. Viscosi-Shirleya,*, K. Mammoneb, N. Pisiasa, J. Dymonda
a
College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean Admin. Bldg., Corvallis, OR 97331-5503, USA
b
Hewlett-Packard Company, 1000 NE Circle Blvd., Corvallis, OR 97330, USA
Received 18 July 2002; accepted 3 January 2003
Abstract
Clay mineral and bulk chemical (Si, Al, K, Mg, Sr, La, Ce, Nd) analyses of terrigenous surface sediments on the
Siberian-Arctic shelf indicate that there are five regions with distinct, or endmember, sedimentary compositions. The
formation of these geochemical endmembers is controlled by sediment provenance and grain size sorting. (1) The shale
endmember (Al, K and REE rich sediment) is eroded from fine-grained marine sedimentary rocks of the Verkhoyansk
Mountains and Kolyma-Omolon superterrain, and discharged to the shelf by the Lena, Yana, Indigirka and Kolyma
Rivers. (2) The basalt endmember (Mg rich) originates from NE Siberia’s Okhotsk-Chukotsk volcanic belt and Bering
Strait inflow, and is prevalent in Chukchi Sea Sediments. Concentrations of the volcanically derived clay mineral
smectite are elevated in Chukchi fine-fraction sediments, corroborating the conclusion that Chukchi sediments are
volcanic in origin. (3) The mature sandstone endmember (Si rich) is found proximal to Wrangel Island and sections of
the Chukchi Sea’s Siberian coast and is derived from the sedimentary Chukotka terrain that comprises these
landmasses. (4) The immature sandstone endmember (Sr rich) is abundant in the New Siberian Island region and
reflects inputs from sedimentary rocks that comprise the islands. (5) The immature sandstone endmember is also
prevalent in the western Laptev Sea, where it is eroded from sedimentary deposits blanketing the Siberian platform that
are compositionally similar to those on the New Siberian Islands. Western Laptev can be distinguished from New
Siberian Island region sediments by their comparatively elevated smectite concentrations and the presence of the basalt
endmember, which indicate Siberian platform flood basalts are also a source of western Laptev sediments. In certain
locations grain size sorting noticeably affects shelf sediment chemistry. (1) Erosion of fines by currents and sediment ice
rafting contributes to the formation of the coarse-grained sandstone endmembers. (2) Bathymetrically controlled grain
size sorting, in which fines preferentially accumulate offshore in deeper, less energetic water, helps distribute the finegrained shale and basalt endmembers. An important implication of these results is that the observed sedimentary
geochemical endmembers provide new markers of sediment provenance, which can be used to track sediment transport,
ice-rafted debris dispersal or the movement of particle-reactive contaminants.
r 2003 Elsevier Ltd. All rights reserved.
Keywords: Clay minerals; Sediment chemistry; Sediment composition; Sediment sorting; Shelf sedimentation; Provenance; Arctic;
Siberia and Alaska; Chukchi Sea; East Siberian Sea; Laptev Sea (65 N–78 N,110 E–160 W)
*Corresponding author.
E-mail address: [email protected] (C. Viscosi-Shirley).
0278-4343/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0278-4343(03)00091-8
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1. Introduction
Knowledge of the Arctic Ocean’s modern
sedimentary processes is essential to evaluating
the potential ramifications of environmental
disruption in the Arctic. Models suggest that
the Arctic will respond sensitively to and amplify
the effects of global climate change (Walsh, 1991).
Understanding modern Arctic sedimentary
processes is a necessary prerequisite for paleoceanographic reconstructions of environmental
change that may ultimately help us define the
role of the Arctic in the global climate system
(Imbrie et al., 1992; Stein and Korolev, 1994). On
a more local scale, industrialization threatens
Arctic continental shelves with a number of
particle-reactive contaminants. Studying Arcticshelf sediment sources and transport pathways
enables us to predict the fate of these contaminants, which may be transported throughout the
Arctic bound to ice rafted or current borne
sediments (Macdonald and Bewers, 1996; Pfirman
et al., 1997). Additionally, the identification of
unique sediment types on the Arctic shelf can be
used to monitor changes in production locations
and drift patterns of turbid sea ice (Pfirman et al.,
1990; Nurnberg
.
et al., 1994; Reimnitz et al., 1994;
Dethleff et al., 2000).
Making up over one-third of the total Arcticshelf area (Silverberg, 1972; Holmes, 1975; Macdonald et al., 1998), the Arctic Ocean’s Siberian
continental shelf is a region influenced by both
anthropogenic and natural environmental change
(Naidu and Mowatt, 1983; Macdonald and
Bewers, 1996). While numerous investigations
have characterized modern Siberian-shelf clay
and heavy mineral distributions (Silverberg,
1972; Naugler et al., 1974; Naidu et al., 1982;
Nurnberg
.
et al., 1994; Bischof and Darby, 1997;
Behrends et al., 1999; Rossak et al., 1999; Wahsner
et al., 1999), much less is known of the multielement chemistry of surface sediments in this
region (Schoster et al., 2000). In this study, we
determine the surface sediment chemistry of an
extensive collection of sediment cores taken from
the Chukchi, East Siberian and Laptev Seas (Figs.
1a and 1b) by the US Coast Guard in the 1960’s,
as well as presenting new clay mineral data for
these areas. Our results are compared with those of
previous investigations of Siberian shelf sediment
composition. We provide the new clay mineral
data to allow direct comparison of the geochemical with clay mineral results. A primary objective
of this study is to assess the usefulness of sediment
chemistry in distinguishing detrital material from
different locations on the shelf. Surface sediment
composition is controlled both by sediment
provenance and physical processes that sort
sediment by grain size, since different sized grains
are often different mineralogies. Thus, another
main goal of this study is to evaluate the roles of
sediment provenance and grain size sorting in
determining various chemical/clay mineralogical
signatures evident in shelf sediments. In a companion paper (Viscosi-Shirley et al., 2003) we use this
information to estimate sediment source strength,
determine sediment transport pathways/accumulation patterns, and investigate the relationship
between sediment distribution and various sediment transport agents.
2. Conceptual approach and background
The Siberian shelf is characterized by extreme
geographic and temporal variability in factors that
control sediment dispersal, including input from
rivers, coastal erosion, current intensity and
direction, and sea ice formation and movement
(Barnett, 1991; Coachman and Shigaev, 1992;
Dmitrenko et al., 1995; Hass and Antonow,
1995; Timokhov, 1994; Lisitzin, 1996; Pavlov
et al., 1996; Weingartner et al., 1998a, b; Kassens
et al., 1999). A number of different geologic
terrains comprise the landmasses that supply
sediment to the shelf (Parfenov, 1992; Stone et al.,
1992; Bogdanov and Tilman, 1993; Fujita et al.,
1997). As a result of these different factors we
anticipate that Siberian shelf surface sediments,
which are known to have distinct clay mineral
trends, also have obvious chemical gradients and
that sediment composition is influenced both by
provenance and grain size sorting. This study seeks
to understand the roles of these factors in
determining shelf sediment composition by comparing spatial variability in terrigenous sediment
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1177
(a)
(b)
Fig. 1. (a) Arctic Ocean and marginal seas. (b) Siberian-shelf surface-sediment sample location () and geology map.
composition with geographic gradients in regional
geology, shelf bathymetry and physical oceanography. We characterize the composition of
Siberian-shelf terrigenous surface sediments using
clay mineral and bulk chemical (Si, Al, K, Mg, Sr,
La, Ce, Nd) analyses. These elements are present
in biogenic as well as terrigenous material (Turekian and Wedephol, 1961; Martin and Knauer,
1973; Chester, 1990). However, concentrations of
Siberian-shelf sedimentary biogenic matter are
generally low (Mammone, 1998). Consequently,
with the exception of Si, the distributions of these
elements are primarily controlled by spatial
gradients in the lithogenic fraction. To ensure that
our Si data describe the composition of the
lithogenic fraction, we subtract biogenic Si from
total Si concentrations. To correct for dilution of
terrigenous by biogenic material we express the
chemical data on a biogenic free basis. Bathymetric data are shown in Fig. 1b. Geologic and
physical oceanographic data are taken from
published literature, reviewed below.
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2.1. Geologic terrains and sediment inputs
The Siberian hinterland consists of distinct
geologic terrains. From west to east, these terrains
include the: (1) Siberian platform, (2) Verkhoyansk Mountains, (3) Kolyma-Omolon superterrain, (4) Okhotsk-Chukotsk volcanic belt, and
(5) Chukotka terrain (Fig. 1b). Unless otherwise
noted, the following brief description of the
terrains is taken from Parfenov (1992), Stone
et al. (1992), Bogdanov and Tilman (1993),
Dylevskiy (1995), Fujita et al. (1997), and Huh
et al. (1998). Central-Russia’s Precambrian Siberian platform consists of basement rock blanketed
by extensive sedimentary deposits (UNESCO,
1976) and one the largest flood basalts in the
world (Sharma et al., 1992). East of the platform
lies the Verkhoyansk Mountains, uplifted and
deformed Devonian sediments that grade eastward
from shelf clastic sequences to deep-water shale
deposits. East of the foldbelt is the KolymaOmolon superterrain, accretionary terrain that is
chiefly an amalgamation of continental fragments
and island arc material bracketed by remnants of
fore and back arc basins. South and east of the
superterrain, extensive volcanic activity occurred
along what was the late Cretaceous active margin
forming the Okhotsk-Chukotsk volcanic belt. The
composition of the Okhotsk-Chukotsk volcanic
belt is zoned laterally in northeast Siberia, with
acidic to intermediate rocks predominating in the
west and intermediate to basic rocks in the east.
Lying north of the volcanic belt, the Chukotka
terrain consists primarily of sedimentary rock
(Fujita and Cook, 1990; Harbert et al., 1990).
This is an accretionary terrain that rifted from
Canada during the opening of the Arctic basin and
forms much of the shelf basement, outcropping on
sections of the Chukchi Sea’s Siberian coast and
Wrangel Island. Although the New Siberian
Islands’ relationship to the Chukotka terrain is
unresolved, these islands are likewise composed of
sedimentary rock with a lithology similar to that of
the Chukotka terrain. Alaska also supplies sediment to the Siberian shelf since it borders the
Chukchi Sea and contiguous Bering Sea, which is a
potential source of water and sediment for parts of
the study area (Fig. 1a). Geologic provinces in
Alaska are compositionally similar to those in NE
Siberia (Harbert et al., 1990; Deming et al., 1996).
Sediments from these landmasses are introduced
to the continental shelf by coastal erosion and
river discharge. Rivers draining to the Laptev Sea
and their sediment yields in 106 tons/yr include the
Khatanga (1.4), Anabar (0.4), Olenek (1.1), Lena
(17.6) and Yana (3.1) (Fig. 1b) (Gordeev et al.,
1996; Lisitzin, 1996). The Lena River has the
largest sediment yield of any river along the
Siberian and northern European coast (Gordeev
et al., 1996). The Indigirka and Kolyma Rivers
discharge 13.7 106 and 16.1 106 tons sediment/
yr, respectively, into the East Siberian Sea. Coastal
erosion also appears to be a significant source of
sediment (Timokhov, 1994). In the Laptev Sea
alone, Rachold et al. (2000) estimated sediment
input by coastal erosion is 58.4 106 tons/yr. Are
(1999) calculated that retreat of an 85 km segment
of Laptev coastline, less than one-tenth of this
sea’s total coastline, supplies 3.4 106 tons of
sediment to the shelf annually.
2.2. Physical environment
Knowledge of current and ice flow regimes is
critical to understanding sedimentation patterns
on the Siberian shelf. Although Siberian shelf
currents can fluctuate substantially, waters in the
Laptev and East Siberian Seas typically flow in
cyclonic gyres (Dmitrenko, 1995; Hass and Antonow, 1995; Timokhov, 1994; Pavlov et al., 1996).
On the Chukchi shelf there is net northward flow
with water entering the region through Bering
Strait (Coachman and Shigaev, 1992; Roach et al.,
1995; Weingartner et al., 1998a). Alongshore, the
Siberian coastal current generally flows east from
the Laptev, to the East Siberian and finally into
the Chukchi Sea (Pavlov et al., 1996; Munchow
et al., 1998), where it turns north-northeast to join
the cross shelf flow (Coachman and Shigaev,
1992).
Ice covers much of the shelf from roughly
September to May (Barnett, 1991; Pavlov et al.,
1996). Fast ice grows to a width of 10–15 km in the
Chukchi Sea, 250–500 km in the East Siberian Sea
and 500 km in the Laptev Sea (Barnett, 1991).
Seaward of the fast ice, drifting sea ice forms and
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typically moves onshore in the Chukchi and East
Siberian Seas, making these seas ice bound. In
the Laptev Sea, this drifting ice moves offshore
creating a polynya in which new ice continuously
forms and is advected basinward. Conditions
in the polynya, i.e. open, shallow and sometimes
turbulent water, are primed for fine-grained
bottom sediments to be resuspended, entrained
by sea ice and exported from the shelf (Pfirman
et al., 1990; Dethleff et al., 1993; Nurnberg
.
et al., 1994; Reimnitz et al., 1994; Eicken et al.,
1997). This entrainment process, known as
suspension freezing, is argued to be an important sediment entrainment mechanism on the
shelf. Sediment entrained by this mechanism
appears to be relatively fine grained compared
with bottom sediment from its region of origin,
suggesting this process preferentially removes
fines from areas of active suspension freezing
(Nurnberg
.
et al., 1994).
3. Methods
3.1. Sediment sample clay mineral and chemical
analyses
In this study, we sampled 81 sediment cores
collected on the Siberian shelf by the US Coast
Guard research vessels Northwind and Burton
Island between 1962 and 1964 (Fig. 1b). Samples
were taken from within the top B0–5 cm of the
cores. This interval represents sedimentation during roughly the past decade to several centuries
given observed sedimentation rates (Kulikov et al.,
1970; Huh et al., 1997; Johnson-Pyrtle, 1999;
Bauch et al., 2001; Stein and Fahl, 2000). To
avoid contamination from the core liner, each
sample’s outer edge was trimmed off and discarded. To avoid cross contamination between
samples, sampling equipment was rinsed with
ethanol and distilled water and dried subsequent
to sampling each core. After being dried overnight
in a 60 C oven and gently disaggregated, two splits
were taken from each sample, one for clay mineral
and a second for chemical analysis.
Sample preparation for clay mineral analysis
followed the technique of Glasmann and Simon-
1179
son (1985). Organic material was removed by
treating the samples with H2O2 (Mammone, 1998).
Two size fractions (o2 and 2–20 mm) were
separated by centrifugation, Mg-saturated, and
smeared on slides to prepare oriented grain
mounts. Clay mineral measurements were made
with a Scintag DMC-105 X-ray Diffractometer
(XRD) using CuKa radiation. Peak areas were
estimated from glycolated XRD traces using the
( smectite, 10 A
( illite, 7 A
( chlorite plus kaolinite
17 A
( peak between
peaks. We partitioned the 7 A
chlorite and kaolinite based on the relative
( chlorite and 3.58 A
( kaolinite
intensity of the 3.54 A
peaks (Biscaye, 1964). Semi-quantitative estimates
of clay mineral percentages were calculated following Biscaye (1965). This calculation was made only
for the o2 mm size fraction as specified by
Biscaye’s method, which assumes that clay minerals constitute 100% of the sample, an assumption
that is generally reasonable for the o2 mm size
fraction.
Major element (Si, Al, K, Mg) concentrations in
the sediment samples were measured on a PerkinElmer 5000 Atomic Absorption Spectrophotometer (AAS), and minor element (Sr, La, Ce,
Nd) concentrations on a Fisons VG Plasma Quad
2+ Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Prior to analysis, the samples
were dissolved in nitric and hydrofluoric acids
(method modified from that of Robbins et al.,
1984) and neutralized with boric acid. ICP-MS
samples were diluted 40 times with 1% double
distilled nitric acid containing Be, In, Bi and, for
25 of the 81 samples, Re internal standards. We
diluted splits of the samples analyzed by the AAS
1–20 times and added cesium chloride to control
ionization effects. For both ICP-MS and AAS
analyses, elemental concentrations were determined by calibrating the instrument response to
prepared standard solutions.
To assess the accuracy of our elemental data we
analyzed four rock and sediment reference standards and compared the results with accepted
compositions for these materials. These standards
included a North Pacific sediment that has been
analyzed in house numerous times and the US
Geological Survey rocks AGV-1 (andesite), BCR3 (basalt) and MRG-1 (gabbro). Sediment samples
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1180
were analyzed in sets of B20 and the standards
accompanied each run. Each time a standard was
analyzed the accuracy of a particular element was
estimated as
½elementaccepted
½elementaccepted
accuracyelement ¼
for standard
for standard
½elementmeasured in standard
½elementaccepted for standard
!
100:
Major and minor element concentrations are
accurate to within 76% and 714%, respectively.
To determine the precision of our sample
digestion and analytical techniques splits of several
samples were analyzed. For each sample we
calculated the precision with which we are able
to measure an element as
precisionelement
standard deviation ½element
100:
¼
average ½element
Major element analyses are precise to within
73%, and minor element analyses to within
79%.
Throughout the study area, the amount of
biogenic material (opal, CaCO3 and organic
carbon) in shelf surface sediments varies from 1.4
to 16.4 wt% (Mammone, 1998). To correct for
dilution of terrigenous material by biogenic matter
we present the elemental data on an organic-free
basis where
½elementorganic
free
¼ ½elementmeasured ð100=ð100
% biogenic opal % CaCO3
ð2:5 % organic carbonÞÞÞ:
Organic carbon contents are multiplied by 2.5 to
estimate organic matter concentrations. Biogenic
opal, CaCO3 and organic carbon data for the
samples were provided by Mammone (1998), and
are reported elsewhere. Prior to making this
correction, we calculated lithogenic Si concentrations by subtracting biogenic Si from total Si
concentrations. Like Si, Sr may be present in
biogenic material (CaCO3) in significant amounts
(Chester, 1990). However, it was not necessary to
correct total Sr concentrations for the presence of
biogenic Sr since on the Siberian shelf CaCO3
concentrations are generally low, p1 wt% (Naugler, 1967; Logvinenko and Ogorodnikov, 1983;
Nolting et al., 1996; Mammone, 1998). Sedimentary concentrations of organic material,
which may contain Al, K and Mg (Martin
and Knauer, 1973) and REEs (Turekian and
Wedephol, 1961), are similarly low enough
(Mammone, 1998) that the distributions of these
elements are controlled by spatial variability in the
lithogenic fraction.
3.2. Geochemical data analysis
The geochemical data were evaluated using
. et al.,
a combination of scatter plots (Bostrom
1973; Heath and Dymond, 1977) and Q-mode
factor analysis (Klovan and Imbrie, 1971; Klovan
and Miesch, 1976). The factor analysis did
not include the clay mineral data, as these data
are semi-quantitative estimates and represent
compositional trends in the o2 mm size fraction
only. Q-mode factor analysis describes a
multivariate data set in terms of a few endmember
samples, or factors, that account for most of
the variability in the data set. Given an n by m
data matrix Xnm ; where n is the number of
samples and m is the number of variables, the
technique first transforms Xnm into a row
normalized matrix Unm ; in which the row sum
of squares is equal to one. Factor analysis then
uses matrix algebra to solve for matrices that
satisfy the equation
Unm ¼ Bnf Ff m þ Enm ;
where Bnf is the factor loading matrix, Ff m is the
factor score matrix, Enm is the error matrix and f
is the number of factors. The factor score matrix
defines factor compositions, describing the importance of each original variable in every factor. The
factor loading matrix indicates the contribution
each factor makes to every sample, and can be
used to map factor distributions. These matrices
must meet the conditions that the factor compositions described by the F matrix are orthogonal and
the sample representations described by the B
matrix preserve the original relationships between
samples.
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see Appendix A for clay mineral percentages at
individual sample locations). Illite is generally the
most abundant clay mineral in shelf sediments
(Laptev Sea-eastward increase from 35% to 63%;
East Siberian Sea—mean 62%, SD 2%; Chukchi
Sea—mean 51%, SD 4%). Chlorite is also fairly
4. Results
4.1. Clay mineralogy
We find that the clay minerals exhibit distinct
trends in Siberian shelf surface sediments (Fig. 2;
75
°
1181
(a) Illite %
Laptev
Sea
70
°
67
New
Siberian Ils.
61
Chukchi Sea
E. Siberian Sea
Wrangel I.
65
°
56
60
°
gS
Yana R.
tr.
Indigirka R.
12
0°
40
°
180
°
140°
75
°
160°
150°
51
45
0°
-17
Kolyma R.
130
-1
0°
rin
11
Be
Lena R.
35
170°
(b) Chlorite %
28
Laptev
Sea
70
°
New
Siberian Ils.
25
Chukchi Sea
E. Siberian Sea
23
Wrangel I.
65
°
60
°
gS
Yana R.
0°
-17
Kolyma R.
130
19
tr.
Indigirka R.
12
0°
16
°
180
°
140°
75
°
160°
150°
21
-1
0°
rin
11
Be
Lena R.
14
170°
(c) Smectite %
Khatanga R.
39
Laptev
Sea
70
°
New
Siberian Ils.
33
Chukchi Sea
E. Siberian Sea
28
Wrangel I.
65
°
Yana R.
80°
°
1
140°
°
60
0°
-17
Kolyma R.
130
150°
17
tr.
Indigirka R.
12
0°
160°
23
-1
gS
rin
0°
11
Be
Lena R.
11
6
170°
Fig. 2. Siberian-shelf surface-sediment clay mineralogy for the o2 mm size fraction: (a) illite %, (b) chlorite % and (c) smectite %.
Kaolinite is not shown since its concentrations exhibit the least spatial variability.
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common (Laptev Sea-eastward increase from 14%
to 25%; both East Siberian and Chukchi Seas—
mean 23%, SD 2%). Smectite exhibits the steepest
concentration gradients, with maximum concentrations in the western Laptev Sea and elevated
values in the Chukchi Sea (Laptev Sea-eastward
decrease from 39% to 7%; East Siberian Sea—
mean 9%, SD 2%; Chukchi Sea—mean 20%, SD
4%). Kaolinite concentrations are low throughout
shelf surface sediments (mean 7%, SD 2%). We
compare our clay mineral results with those of
previous publications investigating shelf clay
mineral distributions in Section 5.
4.2. Multi-element chemistry
Elemental concentrations (Si, Al, K, Mg, Sr, La,
Ce, Nd) also exhibit significant spatial variability
in Siberian shelf surface sediments (see Appendix
B for elemental concentrations at individual
sample locations). To simplify interpretation of
our multivariate chemical data set, we look for
regional variability in sediment composition using
scatter plots of single and multiple element ratios
.
as suggested elsewhere (Bostrom
et al., 1973;
Heath and Dymond, 1977). In this type of plot,
if the data points form a linear array, the
endpoints of the array define unique compositions,
while points along the array can be explained as
various mixtures of the two endmember compositions. Plotting the major element data as Si/Al vs.
Mg/K (Fig. 3a) we find that Siberian shelf surface
sediments have at least four endmember compositions. These are found in the (1) eastern Laptev
and East Siberian Seas, (2) Chukchi Sea, (3)
Wrangel Island region, and (4) western Laptev
Sea and New Siberian Island region. Consistent
with the major element data, in plots of the minor
element data these regions again exhibit endmember compositions (Figs. 4a and 4b). Since
sedimentary REE (La, Ce, Nd) concentrations are
positively correlated (La vs. Ce, R2 ¼ 0:88; La vs.
Nd, R2 ¼ 0:89; Ce vs. Nd, R2 ¼ 0:92), we present
only the Ce data here. Note that only three of
the four endmembers evident in the major
element data are needed to describe Ce’s distribution (all but the western Laptev/New Siberian
Island region endmember). A different three
are required to characterize Sr’s distribution (all
but the Chukchi Sea endmember). This analysis
emphasizes the importance of using multi-element
data to distinguish shelf sediment compositional
trends.
Factor analysis provides an additional means of
simplifying the geochemical data (Klovan and
Imbrie, 1971; Klovan and Miesch, 1976). With this
analysis, we find that we can describe 99.8% of the
variability in the multi-element data set with four
factors. The first three factors account for roughly
31%, 36% and 32% of the data, respectively.
While the fourth factor is much less important,
explaining approximately 1% of the data, it is
geologically reasonable to include this factor, as
seen in Section 5. Fig. 5 shows scores, or
compositions, for the four factors; Fig. 6 illustrates
their loadings, or distributions.
There are very few published shelf-sediment
geochemical data with which to compare our
results. Nolting et al. (1996) characterized the
multi-element chemistry (Si, Al, Mg) of Laptev Sea
bulk surface-sediment samples, and mean total
elemental concentrations reported by these
authors (not presented on an organic-free basis)
are within 13% of comparable means calculated
with our own data. Schoster et al. (2000) report
mean K/Al ratios for the eastern Laptev (0.33) and
western Laptev (0.31) that are similar to our
estimated mean for the entire Laptev (0.32).
5. Discussion
5.1. Clay mineralogy: evidence for sediment source
and transport
In polar regions, where physical weathering
dominates, sedimentary clay mineral assemblages
reflect source rock compositions and can be used
to identify inputs from specific geologic terrains
and transport pathways of sediments. Numerous
investigations show that this is true for modern
sediments in the Arctic Ocean. Here we present
new clay mineral data and compare our results
with those of Silverberg (1972), Naidu et al. (1982,
1995), Nurnberg
.
et al. (1994), Rossak et al. (1999),
Wahsner et al. (1999), and Dethleff et al. (2000).
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1
0.9
Chukchi Sea
0.8
0.7
Mg/K
0.6
E. Laptev Sea
& E. Siberian Sea
0.5
Wrangel I. Region
0.4
0.3
0.2
W. Laptev Sea
& New Siberian I. Region
0.1
0
0
1
2
3
4
5
(a)
6
7
8
9
10
Si/Al
1
Basalt (ref. 2)
0.9
0.8
0.7
Sandstone (ref. 3)
Mg/K
0.6
Sandstone (ref. 1)
Shale (from top
down, refs. 1, 5, 2)
0.5
0.4
0.3
0.2
Sandstone (ref. 4)
0.1
0
0
3
6
(b)
9
12
15
Si/Al
Fig. 3. Siberian-shelf surface-sediment major element data plotted as Si/Al vs. Mg/K (Chukchi Sea, filled circles; East Siberian Sea,
open circles; Laptev Sea, crosses; Wrangel Isl. region, triangles; New Siberian Isl. region, squares). (a) Four extreme, or endmember,
compositions are evident in shelf sediments. Samples within the data set are selected as proxies for these endmembers (apices of
enclosed field). Mixing of the endmember proxies produces compositions encompassed by the enclosed field. (b) To help determine the
origin of these sedimentary endmember compositions we compare them with the chemistry of potential sediment source rocks (stars)
and find they may represent lithogenic material eroded from basalt, shale and two different types of sandstone (ref. 1, Turekian and
Wedephol, 1961; ref. 2, -Taylor and McLennan, 1985; ref 3, American Geological Institute (AGI), 1989; ref 4, Cullers, 1995; ref 5,
Gromet et al., 1984).
Methodological differences exist between several
of these studies and undoubtedly create some
scatter in the data. We find that our data agree
with previous results within the B20% accuracy
typical for clay mineral results based on different
analytical techniques (Pfirman et al., 1997). The
trends evident in our data, as presented in the
results and discussed below, are quite similar to
those previously described.
The clay minerals illite and chlorite are generally
abundant at high latitudes, supplied by physical
weathering of metasedimentary and plutonic rocks
(Chamley, 1989). These rock types are prevalent in
Siberia and Alaska (Parfenov, 1992; Stone et al.,
1992; Bogdanov and Tilman, 1993; Fujita et al.,
1997). Consistent with these conditions, o2 mm
bottom sediments of rivers discharging into the
East Siberian and Chukchi Seas are >59% illite
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C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1184
100
Shale
90
E. Laptev Sea &
E. Siberian Sea
80
Shale ref. 2
Ce ppm
70
Sandstone ref. 4
60
50
Basalt ref. 1
Basalt
Chukchi Sea
Sandstone-mature
40
Wrangel I. Region
30
0
1
2
3
4
(a)
5
6
7
8
9
Si/Al
300
Sandstone-immature
W. Laptev Sea &
New Siberian I. Region
250
Shale ref. 2
Sr ppm
200
Shale
150
E. Laptev Sea &
E. Siberian Sea
Sandstone ref. 4
Sandstone-mature
Wrangel I. Region
100
50
0
0
1
2
3
(b)
4
5
6
7
8
9
Si/Al
Fig. 4. Siberian-shelf surface-sediment Si/Al ratios vs. (a) Ce concentrations and (b) Sr concentrations (Chukchi Sea, filled circles; East
Siberian Sea, open circles; Laptev Sea, crosses; Wrangel Isl. region, triangles; New Siberian Isl. region, squares). The chemistries of
potential source rocks (stars, refs. as in Fig. 3) are included for comparison with the sedimentary data. Ce distributions indicate the
presence of three sedimentary endmember compositions, which may represent lithogenic material derived from shale, basalt and
mature sandstone sources. Sr distributions indicate the presence of three sedimentary endmember compositions, which may represent
lithogenic material derived from shale and two types of sandstone sources. Samples selected from within the data set to represent the
endmember compositions (apices of the enclosed field) are identical to those in Fig. 3. Mixing the endmember proxies produces
compositions encompassed by the enclosed field.
and >21% chlorite (Naidu et al., 1982). Our data,
as well as that of previous studies (Silverberg,
1972; Rossak et al., 1999; Wahsner et al., 1999),
indicate that illite is abundant and chlorite is
fairly common in shelf surface sediments. Illite
and chlorite on average account for more
than 50% and 20% of the o2 mm size fraction,
respectively (Fig. 2). The distribution of
these minerals is fairly uniform, with a low evident
in western Laptev sediments where there are
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1185
Fig. 5. Factor scores, or compositions, for the four factors identified by Q-Mode factor analysis of Siberian-shelf surface-sediment
geochemical data.
significant inputs of terrigenous material from
basaltic rocks (this study; Rossak et al., 1999;
Wahsner et al., 1999).
Kaolinite develops under hot humid conditions
and is abundant in the tropics (Chamley, 1989),
though it is found in polar sedimentary deposits
that formed under a warmer/wetter climate in the
geologic past. A classic example of the this
situation are the ancient kaolinite-bearing paleosols and shales of northern Alaska and Canada,
which supply kaolinite rich sediments to the
Beaufort shelf and Canada Basin (Fig. 1a) (Naidu
et al., 1971; Darby, 1975). Siberian soils, in
contrast, contain very little kaolinite (Darby,
1975), and clays discharged by the Indigirka and
Kolyma Rivers into the East Siberian Sea are
o10% kaolinite (Naidu et al., 1982). Siberian
shelf surface sediments have low kaolinite concentrations, with slightly elevated values in the
western Laptev Sea compared with other parts of
the shelf (maximum values 11%, this study) (this
study; Rossak et al., 1999; Wahsner et al., 1999).
The source of this kaolinite is erosion of kaolinitebearing detrital rocks of the Siberian platform
(Rossak et al., 1999).
Smectite is a good indicator of sediment derived
from volcanic sources (Chamley, 1989). Its strong
concentration gradients in Siberian shelf sediments
are well documented (this study; Silverberg, 1972;
Rossak et al., 1999; Wahsner et al., 1999; Schoster
et al., 2000). Smectite concentrations are greatest
(X33%) in the western Laptev Sea, where they
exceed values in the eastern Laptev and East
Siberian Seas by up to a factor of five (Fig. 2). The
source of this smectite is the extensive flood basalts
blanketing much of the Siberian platform (Fig. 1b)
(Rossak et al., 1999; Wahsner et al., 1999; Schoster
et al., 2000). These flood basalts outcrop extensively in the Khatanga River basin, and the
Khatanga River appears to be a main conduit
for delivering smectite to the shelf. Khatanga
River suspended particulate material has been
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C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1186
Factor 1 - Shale
75
˚
Laptev
Sea
70
˚
Factor 2 - Sandstone
Laptev
Sea
New
Siberian Ils.
E. Siberian Sea
New
Siberian Ils.
E. Siberian Sea
Chukchi Sea
Wrangel I.
65
˚
Indigirka R.
˚
60
-1
Yana R.
Indigirka R.
0˚
Kolyma R.
Kolyma R.
-17
130
˚
tr
gS
rin
Be
0˚
11
Yana R.
0˚
Lena R.
tr
gS
rin
Be
Lena R.
12
Chukchi Sea
Wrangel I.
˚
180
140˚
0.37
0.43
150˚
0.48
170˚
160˚
0.53
0.59
0.66
0.70
0.46
0.51
Factor 3 - Basalt
Laptev
Sea
0.55
0.60
0.65
Laptev
Sea
New
Siberian Ils.
E. Siberian Sea
E. Siberian Sea
Yana R.
0.57
0.62
Kolyma R.
0.66
0.71
-0.12 -0.08 -0.03
0.01
0.05
0.09
tr
0.53
Chukotka
Peninsula
Indigirka R.
Kolyma R.
gS
rin
tr
gS
Indigirka R.
Be
Lena R.
rin
Yana R.
Chukchi Sea
Wrangel I.
Be
Lena R.
0.48
0.75
New
Siberian Ils.
Chukchi Sea
Wrangel I.
0.43
0.70
Factor 4 - Mature &
Immature Sandstone
0.13
Fig. 6. Factor loadings, or abundances, for the four factors identified by Q-Mode factor analysis of Siberian-shelf surface-sediment
geochemical data. High positive loadings indicate elements with high positive scores (see Fig. 5) are abundant. Negative loadings
indicate a depletion of elements with high positive scores and abundance of elements with negative scores. Black lines show the location
for the Lena and Yana Rivers submarine channels. The Indigirka and Kolyma Rivers’ lack clearly defined channels.
observed to contain 83% smectite (o6 mm size
fraction) (Dethleff et al., 2000). Smectite concentrations over 60% have been documented near the
mouth of the Khatanga River (Wahsner et al.,
1999), and are seen to decrease with increasing
distance from the rivermouth (this study; Silverberg, 1972; Rossak et al., 1999; Wahsner et al.,
1999; Schoster et al., 2000).
Chukchi sediments also contain significant
amounts of smectite, up to 28% (Fig. 2). Based
on regional trends in geology, ocean currents, and
sedimentary smectite distributions, Naidu et al.
(1982, 1995) and Naidu and Mowatt (1983)
concluded that Chukchi smectite is derived from
Siberian and Alaskan volcanic rocks, discharged
to the Bering Sea and transported northward
through the Bering Strait into the Chukchi Sea
(Fig. 1a). We suggest that in addition physical
erosion of Chukotka Peninsula highlands, comprised largely of the Okhotsk-Chukotsk volcanic
belt (Fig. 1b) (Parfenov, 1992; Bogdanov and
Tilman, 1993), may supply smectite directly to the
Chukchi Sea via runoff. Naidu et al. (1982) cite a
coastward decrease in smectite concentrations as
evidence against a local supply. However, smectite
is typically found primarily in the o2 mm size
fraction (R. Glasmann, pers. comm.) In energetic
environments smectite concentrations may increase offshore from smectite sources due to
differential sorting, or the preferential accumulation of fines in quieter offshore waters (Chamley,
1989). Siberian shelf grain size data (Mammone,
1998) indicate fine-fraction percentages increase
offshore in the Chukchi Sea, suggesting differential sorting may control smectite’s distribution
here.
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Knowledge of shelf clay mineral distributions
can be used to determine sediment sources and
transport pathways on regional and basinwide
scales (Darby, 1975; Naidu et al., 1982; Nurnberg
.
et al., 1994; Stein et al., 1994; Pfirman et al., 1997;
Rossak et al., 1999; Wahsner et al., 1999; Dethleff
et al., 2000) and to characterize Arctic paleoenvironments (Muller
.
and Stein, 2000). For example, in
the Laptev Sea the relatively high smectite content
of Khatanga River suspended particulate material
has been used to track dispersal of Khatanga River
sediments offshore and eastward (Rossak et al.,
1999). On the basis of smectite’s prevalence in
Laptev and Kara Sea sediments, these regions
have been identified as important sources of
central Arctic ice-rafted debris (Nurnberg
.
et al.,
1994; Pfirman et al., 1997; Dethleff et al., 2000). In
contrast, smectite’s absence in central Arctic surface sediments suggests supply by sea ice makes a
minor contribution to modern sediments in the
Arctic basin (Stein et al., 1994; Wahsner et al.,
1999). As will be seen below, even greater
differentiation of Siberian shelf sediment types is
possible on the basis of a combination of clay
mineral and geochemical data.
5.2. Geochemical endmember compositions:
implications for sediment provenance and grain size
sorting
The geochemical data indicate there are four
endmember compositions in Siberian shelf surface
sediments. To test whether mixtures of these four
endmember compositions can adequately describe
the variability evident in sediment chemistry,
samples from within the data set were selected as
representative of the endmembers (Figs. 3a, 4a and
4b). We based our choices on a review of a number
of elemental scatter plots, in which we found these
samples to consistently have the most extreme or
close to the most extreme compositions. Mixing
the samples selected as proxies for the endmembers
produces the compositions encompassed by the
enclosed fields (Figs. 3a and 4). All our samples lie
within or close to these fields, indicating the
four endmember model accounts fairly well for
the observed range of Siberian shelf sediment
chemistry.
1187
To help determine the origin of these endmember compositions, we compare them with the
chemistry of potential sediment source rocks.
Since there are few direct measurements of
Siberian rock chemistry, we use published data
for the average compositions of rock types
prevalent in Siberia: basalt, relatively coarsegrained sedimentary rock, and shale. Fig. 3b
includes several composites of each rock type to
illustrate that even given the chemical variability
exhibited by a single rock type their major element
chemistry is easily distinguishable. Basalt has the
highest Mg/K ratio; coarse-grained sedimentary
rock, or sandstone, has the greatest Si/Al ratio;
and shale characteristically has both low Si/Al and
Mg/K ratios. Comparing the major and minor
element chemistry of the sedimentary endmembers
with that of these rock types (Figs. 3 and 4), we
find that Chukchi sediments have elevated Mg/K
ratios and low Ce concentrations consistent with
inputs from a basalt bearing source. Low Si/Al
and Mg/K ratios and high Ce concentrations
suggest a shale source for eastern Laptev sediments. Both the endmember evident by Wrangel
Island and that by the New Siberian Islands have
elevated Si/Al ratios, consistent with sandstone
sources. There are differences between these two
endmembers. Sediments near Wrangel Island are
relatively Si rich and Al, K, Ce and Sr poor
compared with those near the New Siberian
Islands. This result implies that in contrast to
New Siberian Island region sediments, those near
Wrangel Island region have a more mature
sandstone source, characterized by a greater
abundance of stable minerals (such as quartz)
and fewer weatherable mobile materials (such as
aluminosilicates and oxides).
The similarity of the four endmembers evident
in Siberian shelf surface sediments to shale, basalt,
mature sandstone and immature sandstone implies
that the endmembers are likely derived from these
four rock types and provenance may be the
primary control on spatial trends in shelf sediment
chemistry. As sediments rich in the various endmembers are transported throughout the shelf and
mixed they could form samples whose chemistry
can be modeled as combinations of the four
endmember compositions. However, transport
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explain variations in shelf sediment chemistry.
Unlike some other mathematical tools that look at
relationships between samples, factor analysis also
allows us to create detailed maps of factor
distributions in shelf sediments and thereby facilitates determining controls on endmember formation. The factor analysis indicates that four factors
are needed to account for most of the variability in
the elemental data. The factors are by definition
orthogonal, or perpendicular. To determine if
these four factors correspond to the four endmembers identified in the scatter plots, we
compare factor compositions (scores, Fig. 5) and
distributions (loadings, Fig. 6) with the characteristics of the scatter plot endmembers (Figs. 3 and
4). Factor 1 appears to correspond to the shale
endmember, as both are most prominent in the
eastern Laptev Sea and characterized by the
highest Al, K and REE scores/concentrations in
shelf sediments. Factor 3 is equivalent to the basalt
endmember, both of which predominate in the
Chukchi Sea and have the highest observed Mg
score/concentration. The two sandstone endmembers (immature and mature) are represented
primarily by factor 2, which has relatively high Si
and low Al, K, Mg and REE scores and is
abundant in the western Laptev, New Siberian
Island and Wrangel Island regions. Factor 4
differentiates the chemistry of sediments in these
processes sort sediment by grain size and may
influence sediment composition, since different
grain sizes can represent different mineralogies.
Thus, an alternate explanation for the endmember
compositions is that they represent materials
derived from various sediment sources whose
compositions have been modified by grain size
sorting subsequent to discharge on the shelf. Shelfsediment grain size data from Mammone (1998)
(Fig. 7), who worked with splits of many of our
samples, support this idea. Samples representing
the two endmembers apparently derived from
sandstone sources are coarse grained, with mean
Fo5, and those representing the shale and basalt
endmembers are fine grained, with mean F>6.5.
So, while erosion of sandstone source rocks may
have produced the coarse-textured Si-rich sandstone endmembers, for example, these endmembers could also reflect removal of fine particles by
grain size sorting.
In order to clarify the roles of provenance and
grain size sorting in controlling endmember formation, we consider the factor analysis results.
Factor analysis is a powerful tool in this case. By
defining endmember samples (factors) that account for most of the variability in the geochemical data, factor analysis enables us to test our
interpretation of the scatter plots, specifically that
four endmember compositions are needed to
Si/Al
2
3
4
5
6
7
8
9
Mean Φ (without >14 phi)
2
3
Sandstone-immature
4
Sandstone-mature
5
6
7
8
Basalt
Shale
9
Fig. 7. Siberian-shelf surface-sediment Si/Al ratios plotted vs. grain size data expressed as mean F: Labeled samples are those selected
from within the data set to represent the four endmembers evident in the sedimentary geochemical data. The shale and basalt
endmembers are fine grained, with mean F>6.5. The two end-members apparently derived from sandstone sources are relatively
coarse grained, with mean F>5. Grain size data from Mammone (1998).
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regions into two separate endmembers. In the
scatter plots, the two sandstone endmembers are
distinguished mainly by the fact that the immature
sandstone endmember contains 94% more Sr than
the mature sandstone endmember, while the latter
has 12% more Si than the former. Factor 4 has
high positive Sr and negative Si scores. Positive
factor loadings indicate elements with positive
scores are abundant and those with negative scores
are depleted, while negative loadings indicate the
opposite is true. Thus, factor 4’s relatively high
positive loading in the western Laptev and New
Siberian Island regions indicates sediments here
are comparatively enriched in Sr and depleted in
Si, consistent with the immature sandstone endmember’s composition and distribution. Sediments
near Wrangel Island are negatively loaded with
factor 4 and are therefore comparatively Sr poor
and Si rich, consistent with the mature sandstone
endmember’s characteristics. Overall the factor
analysis confirms the presence of the four geochemical endmember compositions identified in
scatter plots. Factors 1 and 3 correspond, respectively, to the shale and basalt endmembers. A
combination of positive factor 2 and positive
factor 4 loadings represent the immature sandstone endmember, while positive factor 2 and
negative factor 4 loadings describe the mature
sandstone endmember.
Comparing factor compositions and distributions with geographic gradients in regional geology, we find there is a clear correspondence
between factor characteristics and geologic trends.
Factor 1, whose composition implies a shale
provenance, is most prevalent offshore from the
Lena, Yana, Indigirka and Kolyma Rivers suggesting it is discharged by these rivers (Fig. 6).
Factor 1 loadings increase with proximity to the
mouth of the Yana River and to the Lena River
delta’s eastern branches, which supply >84% of
the Lena’s total water outflow (Le! tolle et al.,
1993). Adjacent to the Indigirka and Kolyma
River mouths, factor 1 loadings increase offshore,
a feature that will be discussed in detail below.
Consistent with a riverine source for the shale
endmember, these rivers’ drainage basins encompass extensive shale deposits found in the Verkhoyansk Mountains and Kolyma-Omolon
1189
superterrain (Fig. 1b) (Parfenov, 1992; Stone
et al., 1992; Bogdanov and Tilman, 1993; Fujita
et al., 1997). Additionally, available data characterizing the chemistry of the Lena River’s
suspended sediment load indicates that it is similar
to that of shale (Rachold, 1999). Lena River
suspended particulate material typically has a Mg/
Al ratio of 0.16–0.19 (Nolting et al., 1996; Gordeev
and Shevchenko, 1995; Rachold, 1995), and its
average K/Al ratio is estimated as B0.30 (Rachold, 1995) to 0.35 (Gordeev and Shevchenko,
1995). The shale endmember likewise has Mg/Al
and K/Al ratios of 0.1770.01 and 0.3070.03,
respectively.
Factor 3, whose composition suggests a basalt
source, dominates in the Chukchi Sea (Fig. 6).
This result corroborates the clay mineral data,
which indicated there are elevated concentrations
of the volcanically derived clay mineral smectite in
Chukchi sediments (Fig. 2). As described in the
previous section, potential sources of volcanic
material in this region include erosion of NE
Siberia’s Okhotsk-Chukotsk volcanic belt and, as
suggested by Naidu et al. (1982, 1995), influxes
from the Bering Strait of lithogenic material
derived from volcanigenic terrains bordering the
Bering Sea (Fig. 1a).
The mature sandstone endmember is found near
Wrangel Island and along sections of the Chukchi
Sea’s Siberian coast (Fig. 6, modeled as a mixture
of positive factor 2 and negative factor 4 loadings).
Rocks in these regions are composed of Chukotka
terrain, which consists primarily of relatively
coarse-grained sedimentary rock (Fig. 1b) (Fujita
and Cook, 1990; Harbert et al., 1990; Parfenov,
1992; Bogdanov and Tilman, 1993), and thus are a
likely source of the mature sandstone endmember.
The immature sandstone endmember is found in
the western Laptev Sea and New Siberian Island
region (Fig. 6, represented by positive factor 2 and
positive factor 4 loadings). Extensive sedimentary
formations of similar lithology overly much of the
Siberian platform and the New Siberian Islands
(Fig. 1b) (Parfenov, 1992) and erosion of these
formations probably produces the immature sandstone endmember.
Although the chemistries of western Laptev and
New Siberian Island bulk sediments are generally
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similar, there are subtle differences in their
compositions. As discussed earlier, unlike New
Siberian Island region sediments, western Laptev
sediments in the o2 mm size fraction are comparatively rich in smectite (Fig. 2). The presence of
volcanic detritus in the western Laptev Sea
indicates that, in addition to inputs from the
sedimentary formations blanketing the Siberian
platform, Siberian platform flood basalts are a
sediment source for this region (Fig. 1b). Consistent with this observation, western Laptev bulk
sediments have somewhat elevated factor 3, or
basalt endmember, loadings (Fig. 6).
In addition to provenance, various sediment
transport processes (currents and ice rafting) affect
endmember distribution, as discussed in detail in a
companion paper (Viscosi-Shirley et al., 2003).
Here we focus on the role of such physical
processes in controlling endmember formation
and spatial trends in sediment chemistry through
grain size sorting. Samples rich in the sandstone
endmembers are also coarse grained (Fig. 7). So
while these endmembers most likely originate from
the relatively coarse-grained sedimentary rocks
found on nearby landmasses, they may reflect
post-depositional reworking and removal of fines
as well. The sandstone endmembers are most
prevalent in the western Laptev Sea, New Siberian
Island region and south of Wrangel Island (Fig. 6).
Wintertime ice cover in these areas is broken by
polynyas. A large persistent polynya is found in
the Laptev Sea. South of Wrangel Island, a small
intermittent polynya is produced by strong northerly winds (Barnett, 1991). These polynyas allow
greater opportunity for waves and currents to
resuspend and remove fine particles. The Laptev
polynya also provides ideal conditions for the
formation of turbid sea ice and its export from the
shelf. The western Laptev is known to be an
important source of ice-rafted debris for the
central Arctic (Nurnberg
.
et al., 1994) and in the
eastern Laptev ice-rafted debris export is highest
adjacent to the New Siberian Islands (Dethleff,
1995). Since sea ice appears to preferentially
entrain fine sediment (Nurnberg
.
et al., 1994),
sediment ice rafting may further contribute to the
coarse character of bottom sediments in these
regions.
The shale and basalt endmembers also reflect a
combination of provenance and grain size sorting.
Similarity of the shale endmember’s composition
to the geochemistry of Siberian rocks and riverborne particles indicates it originates from Siberian shale deposits and discharges to the shelf via
the Lena, Yana, Indigirka and Kolyma Rivers.
Sediments rich in the shale endmember contain up
to 99% fines (Mammone, 1998). In the Laptev
Sea, both shale endmember abundances and the
percentage of fines increase proximal the Lena and
Yana River deltas (Fig. 6) (Mammone, 1998), as
expected given the endmember’s provenance. In
contrast, East Siberian Sea shale endmember and
clay concentrations are somewhat elevated adjacent to the Indigirka and Kolyma River mouths
but increase offshore. Shelf bathymetric data show
that submarine channels lie off of the Lena and
Yana Rivers (Fig. 1b), whereas there is a broad
shallow shoal immediately offshore from the
Indigirka and Kolyma Rivers with deeper water
seaward of the shoal. These observations suggest
that fine-grained shale-endmember rich sediment
discharged from the Indigirka and Kolyma Rivers
preferentially accumulates offshore in deeper,
more quiescent water. In the Chukchi Sea, both
shale and basalt endmember distributions reflect
bathymetrically controlled grain size sorting. Like
the shale endmember, the basalt endmember is
quite fine grained (up to 96% clay and silt)
(Mammone, 1998). Abundances of both these
endmembers in the Chukchi Sea generally increase
offshore as water depths increase and peak in
the western Chukchi’s Hope Sea Valley (Figs. 6
and 1b).
5.3. Independent evidence of Siberian-shelf modern
sedimentary processes
Mainly on the basis of geochemical data with
supplemental information from clay mineral analyses, we have defined five compositional regimes
in shelf sediments whose presence reflects a
combination of provenance and grain size sorting.
These include: (1) shale-endmember rich eastern
Laptev and East Siberian sediments; (2) smectite
and basalt-endmember bearing Chukchi sediments; (3) mature sandstone endmember rich
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sediments found near Wrangel Island; (4) western
Laptev; and (5) New Siberian Island region
sediments, both dominated by the immature
sandstone endmember, yet distinguished by the
former’s comparatively high smectite content and
basalt endmember loadings (Figs. 2 and 6). We
compared our clay mineral results with those of
previous publications above. In addition, there are
extant studies of shelf sedimentation based primarily on heavy mineral and petrographic data
(Silverberg, 1972; Naugler et al., 1974; Stein and
Korolev, 1994; Bischof and Darby, 1997; Behrends
et al., 1999; Schoster et al., 2000). Our geochemical
and clay mineral results are consistent with the
findings of these investigations. In the Laptev Sea,
our observation that the chemistry/provenance of
western sediments (basalt endmember/Siberian
platform basalt) differs from that of eastern
sediments (shale endmember/Lena and Yana
Rivers) is consistent with trends in (1) heavy
mineral data (Silverberg, 1972; Naugler et al.,
1974; Stein and Korolev, 1994; Behrends et al.,
1999; Schoster et al., 2000), (2) sediment petrography and Fe oxide composition (Bischof and
Darby; 1997) and (3) a suite of geochemical data
that, with the exception of K; differs from the one
considered here (Schoster et al., 2000). Sediments
south of the New Siberian Islands are rich in the
immature sandstone endmember due to inputs
from sedimentary rocks and possible removal of
fines by erosional processes. Heavy mineral data
similarly indicate sediments in this region have a
unique signature that may reflect winnowing of
sediments (Stein and Korolev, 1994). East Siberian
sediments originate from the Indigirka and Kolyma Rivers and are geochemically similar to eastern
Laptev sediments, with distinct local inputs from
the Wrangel Island region. This pattern is also
evident in the heavy mineral data (Silverberg,
1972; Naugler et al., 1974). The Kolyma River’s
drainage basin intersects with the Okhotsk-Chukotsk volcanic highlands and sediments offshore
from this river have somewhat elevated basalt
endmember concentrations. In the absence of
Chukchi samples, in which we observe peak basalt
endmember abundances, Silverberg (1972), Naugler et al. (1974), and Bischof and Darby (1997)
identify sediments off the Kolyma River as an
1191
endmember sediment type. Bischof and Darby
(1997) are also able to distinguish sediments off the
Indigirka River as compositionally distinct. Some
of our samples from this region lie just outside the
mixing field described by the geochemical endmembers (Figs. 3 and 4), suggesting their composition may reflect subtle but unique features of
source rocks within the Indigirka River drainage
basin.
6. Conclusions and implications
Investigating the compositional trends in Arcticshelf surface sediments and the processes controlling these trends is critical to addressing a number
of important research questions. Comparisons
between the make up of shelf sediments and icerafted debris reveal the production locations and
drift patterns of turbid Arctic sea ice (Pfirman
et al., 1990; Nurnberg
.
et al., 1994; Reimnitz et al.,
1994; Eicken et al., 1997; Dethleff et al., 2000).
Compositional signatures unique to particular
parts of the shelf are useful in predicting the fate
and transport pathways of particle-reactive contaminants (Macdonald and Bewers, 1996). Knowledge of modern sedimentology also provides a
necessary baseline for interpreting the record of
paleoenvironmental change recorded in Arctic
sediment stratigraphy (Bischof and Darby, 1997;
Muller
.
and Stein, 2000).
While numerous works have described modern
clay and heavy mineral distributions in Siberian
Arctic-shelf sediments (Silverberg, 1972; Naugler
et al., 1974; Naidu et al., 1982; Nurnberg
.
et al.,
1994; Bischof and Darby, 1997; Behrends et al.,
1999; Rossak et al., 1999; Wahsner et al., 1999),
much less is known of their multi-element chemistry (Schoster et al., 2000). In this study, we
characterize the chemistry of Siberian shelf surface
sediments, as well as providing new clay mineral
data for the region. We identify five regions with
distinct, endmember sedimentary compositions
(Figs. 2 and 6). The formation of these endmembers is controlled by a combination of
sediment provenance and grain size sorting. (1)
The shale endmember (characterized by high
concentrations of Al, K and REEs) is abundant
ARTICLE IN PRESS
1192
C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
in the eastern Laptev Sea off the Lena and Yana
Rivers and in the East Siberian Sea off the
Indigirka and Kolyma Rivers. This endmember
is derived from the fine-grained sedimentary rocks
of the Verkhoyansk mountains and KolymaOmolon superterrain that lie within these rivers’
drainage basins. (2) Prevalent in Chukchi sediments, the basalt endmember (high Mg) is supplied
by erosion of NE Siberia’s Okhotsk-Chukotsk
volcanic belt. Bering Strait inflow is also a source
of volcanic material originating from volcanigenic
terrains bordering the Bering Sea and advected
northward into the Chukchi Sea (Fig. 1a) (Naidu
et al., 1982, 1995). Concentrations of the volcanically derived clay mineral smectite are elevated in
Chukchi fine-fraction sediments, corroborating
our conclusion that these sediments have a
volcanic origin. (3) The mature sandstone endmember (high Si) is found proximal to Wrangel
Island and sections of the Chukchi Sea’s Siberian
coast, and originates from the sedimentary Chukotka terrain that comprises these landmasses. (4)
The immature sandstone endmember (high Sr) is
concentrated in the New Siberian Island region,
reflecting inputs from the sedimentary rocks that
constitute these islands. (5) This endmember is also
abundant in the western Laptev Sea, where it is
derived from sedimentary deposits blanketing the
Siberian platform that are compositionally similar
to those found on the New Siberian Islands.
However, western Laptev sediments can be distinguished from those in the New Siberian Island
region by their comparatively elevated smectite
concentrations and the presence of the basalt
endmember, which indicate the Siberian platform
flood basalts are also a source of western Laptev
lithogenic material. In certain locations physical
processes that sort sediment by grain size noticeably influence sediment chemistry as well. Erosion
of fines by currents and sediment ice rafting
contributes to the formation of the coarse-grained
sandstone endmembers. Bathymetrically controlled grain size sorting, in which fines preferentially accumulate offshore in deeper, less energetic
water, helps distribute the fine-grained shale and
basalt endmembers.
An important implication of these results is that
the combination of geochemical and clay mineral
data allow differentiation of more sediment types
than do the clay mineral data alone. While the clay
mineral signatures of western Laptev and East
Siberian sediments are unique, with the highest
smectite and illite concentrations on the Arctic
shelf (Rossak et al., 1999; Wahsner et al., 1999),
similar clay mineral assemblages are found in
sediments from the eastern Laptev, Chukchi, New
Siberian Island and Wrangel Island regions.
However, sediments from these areas can be
distinguished on the basis of their chemical
composition. Thus, the observed sedimentary
geochemical endmembers provide new markers
of sediment provenance, which can be used to
track sediment transport, ice-rafted debris dispersal, or the movement of particle-reactive contaminants. In a companion paper (Viscosi-Shirley et al.,
2003), we use this information to estimate sediment source strength on the Siberian Arctic shelf,
determine the dominant sediment pathways/accumulation patterns, and examine the role of various
sediment transport agents in controlling these
dispersal patterns. In closing, we hope this study
of Siberian-shelf surface-sediment compositional
trends and the factors regulating these trends will
facilitate new and ongoing investigations of the
Arctic Ocean, illuminating this unique frontier and
its place in the world ocean.
Acknowledgements
Bobbi Conard, Chi Meredith and Andy Ungerer
gave valuable input regarding sample analysis and
data processing. Reed Glasmann provided advice
on XRD analysis and the use of his laboratory.
Gary Klinkhammer answered numerous questions
about sediment chemistry. Ian Walsh supplied
editorial and interpretive suggestions. Chris Guay
provided a file that was modified to create Fig. 1a.
This work was funded by the Office of Naval
Research (grant N00014-9410982 and Augmentation Award for Science and Engineering Research
Training N00014-9311170 (N. Pisias)). Additional
support came from a College of Oceanic and
Atmospheric Sciences Dean’s Scholarship and an
Oregon State University Supplemental Oregon
ARTICLE IN PRESS
C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1193
Table 1
Clay mineral percentages
Sample ID
Latitude
Longitude
Illite (%)a
Chlorite (%)
Smectite (%)
Kaolinite (%)
BI64-17
NW362-62
NW362-70
NW63-14
NW63-18
NW63-19
NW63-21
NW63-25
NW63-26
NW63-27
NW63-28
NW63-29
NW63-32
NW63-34
NW63-37
NW63-39
NW63-40
NW63-41
NW63-42
NW63-44
NW63-46
NW63-50
NW63-51
NW63-52
NW63-54
NW63-57
NW63-60
NW63-64
NW63-67
NW63-77
NW63-80
NW63-82
NW63-87
NW63-88
NW63-94
NW63-95
NW63-97
NW63-99
NW63-101
NW63-103
NW63-107
NW63-115
NW63-118
NW63-119
NW63-122
NW63-125
NW63-128
NW63-130
NW63-134
NW63-136
NW63-139
NW63-141
NW63-143
72.40
69.00
68.50
67.47
68.60
68.13
67.58
68.72
68.93
69.15
69.42
69.89
69.80
69.32
69.75
70.18
70.43
70.63
69.63
69.20
70.45
71.42
71.57
71.38
70.72
70.09
70.83
71.17
71.92
72.40
73.07
73.47
73.33
73.03
74.33
74.44
74.50
74.50
74.00
73.50
72.50
73.00
73.75
72.80
71.50
72.25
73.03
73.57
74.77
75.25
76.02
76.42
76.43
157.50
176.00
170.98
170.37
171.60
172.40
173.41
174.83
174.25
173.78
173.25
174.44
176.65
177.58
179.80
179.57
179.25
179.00
171.00
172.00
175.00
174.95
170.00
169.99
170.00
165.00
165.07
159.95
160.03
155.23
155.37
155.40
149.67
149.63
143.73
142.72
140.43
138.00
138.03
138.00
137.67
134.17
133.88
133.00
130.92
131.00
131.17
131.42
134.48
134.50
134.55
133.50
129.88
65
49
44
48
50
53
52
54
48
47
54
49
57
44
50
52
55
56
55
51
62
63
67
61
63
59
61
58
64
64
64
62
62
63
56
61
57
59
61
63
62
54
53
56
59
57
53
52
54
53
53
50
46
19
24
23
26
25
24
19
28
25
27
21
23
24
24
22
20
22
22
20
22
21
23
23
24
23
28
24
27
24
23
21
25
22
24
27
23
25
23
23
23
24
20
20
21
22
22
20
21
20
20
20
21
15
12
26
28
23
19
17
23
13
20
19
21
22
14
24
21
23
19
15
19
20
13
11
6
12
10
9
11
10
7
7
10
6
9
8
8
9
10
10
9
7
8
15
18
14
10
10
17
19
16
18
19
18
28
4
2
5
4
5
7
6
6
7
7
4
6
6
7
7
6
4
7
6
7
3
4
4
3
4
4
4
5
5
6
5
7
7
6
8
8
8
9
7
7
6
10
10
9
9
11
10
8
10
9
8
11
11
ARTICLE IN PRESS
C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1194
Table 1 (continued)
Sample ID
Latitude
NW63-146
NW63-148
NW63-149
NW63-151
NW63-153
NW63-157
NW63-160
NW63-161
NW63-166
NW63-188
NW63-193
NW63-197
75.57
75.08
74.79
74.53
74.53
75.18
75.72
76.03
75.50
74.93
73.93
71.65
a
Longitude
129.82
129.78
129.77
128.38
125.93
124.33
124.37
125.97
120.00
127.30
128.28
157.00
Illite (%)a
Chlorite (%)
Smectite (%)
Kaolinite (%)
49
48
48
49
47
45
44
41
35
44
52
64
17
18
21
17
17
15
14
15
16
17
19
21
24
24
25
27
26
32
32
34
39
30
20
9
9
9
6
7
10
9
10
10
10
9
9
5
Percentages calculated based on Biscaye (1965).
Table 2
Siberian-shelf surface-sediment multi-element chemistry
Sample name
Part A: measured
BI64-10
BI64-11
BI64-17
BI64-31
BI64-34
BI64-38
BI64-48avg
BI64-52
BI64-53
BI64-55
BI64-59
NW362-62avg
NW362-70
NW362-72
NW362-77
NW362-78
NW362-79
NW362-80
NW63-14
NW63-18
NW63-19
NW63-21avg
NW63-25
NW63-26
NW63-27
NW63-28
NW63-29
NW63-32
NW63-34
NW63-37
NW63-39
NW63-40
Latitude
Longitude
Al
(wt%)
K
(wt%)
elemental concentrations in bulk sediment samples
74.62
160.00
8.4
2.7
74.35
160.00
8.6
2.7
72.40
157.50
7.2
2.0
70.63
167.50
7.2
2.0
70.05
165.00
7.9
2.1
71.27
170.00
7.6
2.4
70.92
175.00
6.7
2.0
71.12
177.50
5.4
1.6
70.77
177.50
4.4
1.4
70.00
177.50
6.7
2.3
70.78
163.50
6.8
2.1
69.00
176.00
6.5
1.9
68.50
170.98
6.2
1.6
68.48
169.02
6.1
1.5
68.02
169.03
5.9
1.6
68.03
170.00
5.6
1.5
68.03
171.00
6.0
1.6
68.03
172.07
6.0
1.7
67.47
170.37
5.9
1.6
68.60
171.60
6.3
1.5
68.13
172.40
6.2
1.7
67.58
173.41
5.7
2.2
68.72
174.83
6.5
1.9
68.93
174.25
6.4
1.9
69.15
173.78
6.4
1.8
69.42
173.25
6.4
1.8
69.89
174.44
6.4
1.8
69.80
176.65
6.5
1.9
69.32
177.58
4.3
1.6
69.75
179.98
6.0
2.1
70.18
179.57
5.1
1.6
70.43
179.25
5.1
1.5
Mg
(wt%)
Si
(wt%)
Sr88
(ppm)
La139
(ppm)
Ce140
(ppm)
Nd146
(ppm)
1.2
1.2
0.7
0.8
0.9
1.2
1.0
0.8
0.5
0.9
0.7
1.3
1.2
1.3
1.1
1.1
1.2
1.2
1.1
1.2
1.4
0.6
1.4
1.5
1.5
1.4
1.4
1.3
0.6
0.8
0.7
0.8
28
28
33
31
30
28
31
34
36
32
33
29
32
31
31
31
29
29
31
30
30
34
28
28
28
30
29
29
37
31
35
35
148
150
189
183
172
162
157
133
137
172
181
146
192
192
193
203
187
175
182
169
177
166
158
162
158
174
165
160
133
163
148
148
30
28
30
27
29
25
26
23
20
29
29
23
23
22
22
21
22
21
21
23
22
24
23
22
22
23
22
22
19
26
22
21
87
66
69
59
66
59
59
53
47
64
69
44
45
45
44
41
44
42
42
45
45
46
43
44
44
46
42
44
40
50
44
48
30
26
29
28
27
26
25
21
19
29
29
20
21
23
19
18
20
18
19
21
21
20
20
20
20
21
20
21
16
22
20
21
ARTICLE IN PRESS
C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1195
Table 2 (continued)
Sample name
Latitude
Longitude
Al
(wt%)
K
(wt%)
Mg
(wt%)
Si
(wt%)
Sr88
(ppm)
La139
(ppm)
Ce140
(ppm)
Nd146
(ppm)
NW63-41
NW63-42
NW63-44
NW63-46
NW63-50
NW63-52
NW63-54
NW63-57
NW63-60
NW63-64
NW63-67
NW63-74
NW63-77
NW63-80
NW63-82
NW63-87
NW63-88
NW63-94
NW63-95
NW63-97
NW63-98
NW63-99
NW63-101
NW63-103
NW63-107
NW63-112
NW63-115
NW63-118
NW63-119
NW63-122
NW63-125
NW63-130
NW63-134
NW63-136
NW63-139
NW63-141
NW63-143
NW63-146
NW63-148
NW63-149
NW63-151
NW63-153
NW63-157
NW63-160
NW63-161
NW63-166
NW63-188
NW63-193
NW63-197
70.63
69.63
69.20
70.45
71.42
71.38
70.72
70.09
70.83
71.17
71.92
72.75
72.40
73.07
73.47
73.33
73.03
74.33
74.44
74.50
74.32
74.50
74.00
73.50
72.50
72.25
73.00
73.75
72.80
71.50
72.25
73.57
74.77
75.25
76.02
76.42
76.43
75.57
75.08
74.79
74.53
74.53
75.18
75.72
76.03
75.50
74.93
73.93
71.65
179.00
171.00
172.00
175.00
174.95
169.99
170.00
165.00
165.07
159.95
160.03
155.03
155.23
155.37
155.40
149.67
149.63
143.73
142.72
140.43
138.97
138.00
138.03
138.00
137.67
134.42
134.17
133.88
133.00
130.92
131.00
131.42
134.48
134.50
134.55
133.50
129.88
129.82
129.78
129.77
128.38
125.93
124.33
124.37
125.97
120.00
127.30
128.28
157.00
4.9
6.3
6.5
6.8
6.9
7.9
7.7
8.2
7.1
8.2
7.5
7.9
7.9
8.8
8.9
7.0
6.4
5.8
5.9
7.8
7.2
6.9
8.1
8.2
8.5
7.0
6.8
7.3
8.9
8.7
8.2
8.0
6.9
7.1
8.0
8.3
7.5
8.0
8.0
7.9
7.7
6.3
6.9
7.5
6.7
6.5
7.3
8.3
8.0
1.4
1.7
1.7
2.0
2.0
2.4
2.2
2.2
2.0
2.2
2.0
2.2
2.3
2.6
2.7
2.1
2.0
2.0
2.1
2.3
2.3
2.2
2.3
2.4
2.5
2.4
2.3
2.3
2.7
2.6
2.5
2.6
2.3
2.4
2.6
2.7
2.5
2.7
2.6
2.5
2.5
2.4
2.5
2.4
2.4
2.3
2.5
2.5
2.2
0.7
1.4
1.4
1.0
1.2
1.2
1.1
0.9
0.7
0.9
0.8
0.8
0.9
1.2
1.3
0.06
0.5
0.4
0.5
1.0
0.8
0.7
1.1
1.1
1.2
0.8
0.7
1.1
1.5
1.4
1.4
1.3
0.8
0.9
1.4
1.5
1.3
1.5
1.5
1.6
1.5
0.6
1.0
1.3
1.2
1.0
1.4
1.6
0.9
36
31
30
31
30
28
30
29
34
31
31
32
31
28
28
34
34
35
35
26
32
33
29
29
29
32
33
30
26
28
28
28
33
32
28
27
30
27
28
28
28
34
31
29
31
33
29
26
30
134
177
175
177
151
147
161
165
193
175
272
194
172
188
169
230
227
190
199
209
223
227
172
159
145
203
238
217
139
145
180
183
248
231
171
162
219
161
180
172
193
273
222
219
219
253
222
177
172
23
22
24
27
25
25
28
28
26
30
36
35
28
35
35
35
35
27
25
37
35
34
32
33
32
30
31
36
39
38
36
37
32
36
34
34
39
34
35
36
35
29
32
33
32
27
35
38
33
45
45
46
59
54
58
67
65
59
70
79
82
61
83
85
79
82
57
52
90
70
72
70
71
72
68
67
77
86
81
75
78
68
78
73
74
72
77
77
78
75
61
69
74
70
57
74
80
75
20
21
23
26
24
24
28
27
24
29
33
34
26
36
33
32
32
23
22
35
30
29
29
31
30
27
28
34
36
34
29
32
28
32
29
30
30
32
32
32
31
24
29
29
28
23
30
32
32
Part B: biogenic free elemental concentrationsa
BI64-10
74.62
160.00
8.8
BI64-11
74.35
160.00
9.0
2.8
2.8
1.3
1.3
28
29
155
157
32
29
92
69
31
27
ARTICLE IN PRESS
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1196
Table 2 (continued)
Sample name
Latitude
Longitude
Al
(wt%)
K
(wt%)
Mg
(wt%)
Si
(wt%)
Sr88
(ppm)
La139
(ppm)
Ce140
(ppm)
Nd146
(ppm)
BI64-17
BI64-31
BI64-34
BI64-38
BI64-48avg
BI64-52
BI64-53
BI64-55
BI64-59
NW362-62avg
NW362-70
NW362-72
NW362-77
NW362-78
NW362-79
NW362-80
NW63-14
NW63-18
NW63-19
NW63-21avg
NW63-25
NW63-26
NW63-27
NW63-28
NW63-29
NW63-32
NW63-34
NW63-37
NW63-39
NW63-40
NW63-41
NW63-42
NW63-44
NW63-46
NW63-50
NW63-52
NW63-54
NW63-57
NW63-60
NW63-64
NW63-67
NW63-74
NW63-77
NW63-80
NW63-82
NW63-87
NW63-88
NW63-94
NW63-95
NW63-97
NW63-98
NW63-99
NW63-101
72.40
70.63
70.05
71.27
70.92
71.12
70.77
70.00
70.78
69.00
68.50
68.48
68.02
68.03
68.03
68.03
67.47
68.60
68.13
67.58
68.72
68.93
69.15
69.42
69.89
69.80
69.32
69.75
70.18
70.43
70.63
69.63
69.20
70.45
71.42
71.38
70.72
70.09
70.83
71.17
71.92
72.75
72.40
73.07
73.47
73.33
73.03
74.33
74.44
74.50
74.32
74.50
74.00
157.50
167.50
165.00
170.00
175.00
177.50
177.50
177.50
163.50
176.00
170.98
169.02
169.03
170.00
171.00
172.07
170.37
171.60
172.40
173.41
174.83
174.25
173.78
173.25
174.44
176.65
177.58
179.98
179.57
179.25
179.00
171.00
172.00
175.00
174.95
169.99
170.00
165.00
165.07
159.95
160.03
155.03
155.23
155.37
155.40
149.67
149.63
143.73
142.72
140.43
138.97
138.00
138.03
7.4
7.6
8.3
8.5
7.5
6.2
4.7
7.4
7.0
8.1
7.1
6.7
6.8
6.3
7.0
7.1
6.7
7.3
7.3
6.0
7.7
7.6
7.6
7.4
7.5
7.8
4.6
6.6
5.4
5.6
5.1
7.1
7.5
7.6
7.9
8.1
8.3
8.6
7.3
8.5
7.8
8.2
8.2
9.1
9.3
7.1
6.6
6.0
6.1
8.1
7.4
7.1
8.4
2.1
2.2
2.2
2.7
2.3
1.7
1.5
2.5
2.1
2.3
1.8
1.7
1.8
1.7
1.9
2.0
1.8
1.8
2.0
2.3
2.3
2.2
2.1
2.1
2.1
2.2
1.8
2.3
1.7
1.6
1.5
1.9
2.0
2.3
2.4
2.4
2.4
2.3
2.1
2.3
2.1
2.3
2.4
2.7
2.8
2.1
2.1
2.1
2.2
2.4
2.4
2.3
2.4
0.7
0.8
0.9
1.4
1.2
0.8
0.6
1.0
0.7
1.7
1.4
1.4
1.3
1.2
1.4
1.5
1.3
1.4
1.6
0.7
1.7
1.8
1.7
1.6
1.7
1.6
0.6
0.9
0.8
0.9
0.7
1.5
1.6
1.2
1.4
1.3
1.1
1.0
0.7
0.9
0.8
0.9
1.0
1.2
1.3
0.7
0.6
0.5
0.5
1.0
0.8
0.8
1.1
33
32
30
28
31
35
37
32
34
29
33
32
32
32
30
29
31
30
31
34
28
28
28
31
30
29
38
31
35
35
36
31
30
31
30
28
30
30
34
31
32
32
32
29
28
34
35
36
36
27
33
34
30
195
194
180
182
178
144
146
191
187
182
219
213
222
227
218
208
208
197
208
175
189
194
187
201
194
191
145
180
160
162
141
198
202
197
174
151
173
173
198
181
283
201
178
195
175
235
232
197
204
217
230
233
179
31
29
30
29
30
25
21
33
29
28
26
25
25
23
26
25
24
26
26
25
28
26
26
27
26
27
21
28
24
22
24
25
27
31
29
26
30
29
27
32
37
36
29
36
36
36
36
28
25
39
36
35
34
71
63
69
67
66
57
49
72
71
55
51
50
50
46
51
50
48
52
52
48
52
53
52
53
50
53
43
55
47
53
47
51
53
66
63
59
72
68
60
73
82
85
63
86
88
80
84
59
53
93
72
74
73
30
29
29
29
29
23
20
32
30
25
24
25
22
20
23
22
22
24
24
21
24
24
23
24
23
25
18
24
22
22
21
24
26
28
28
25
30
28
24
30
35
35
27
27
34
33
33
23
23
37
31
30
30
ARTICLE IN PRESS
C. Viscosi-Shirley et al. / Continental Shelf Research 23 (2003) 1175–1200
1197
Table 2 (continued)
Sample name
Latitude
NW63-103
NW63-107
NW63-112
NW63-115
NW63-118
NW63-119
NW63-122
NW63-125
NW63-130
NW63-134
NW63-136
NW63-139
NW63-141
NW63-143
NW63-146
NW63-148
NW63-149
NW63-151
NW63-153
NW63-157
NW63-160
NW63-161
NW63-166
NW63-188
NW63-193
NW63-197
73.50
72.50
72.25
73.00
73.75
72.80
71.50
72.25
73.57
74.77
75.25
76.02
76.42
76.43
75.57
75.08
74.79
74.53
74.53
75.18
75.72
76.03
75.50
74.93
73.93
71.65
Longitude
138.00
137.67
134.42
134.17
133.88
133.00
130.92
131.00
131.42
134.48
134.50
134.55
133.50
129.88
129.82
129.78
129.77
128.38
125.93
124.33
124.37
125.97
120.00
127.30
128.28
157.00
Al
(wt%)
K
(wt%)
Mg
(wt%)
Si
(wt%)
Sr88
(ppm)
La139
(ppm)
Ce140
(ppm)
Nd146
(ppm)
8.6
9.0
7.3
7.0
7.6
9.5
9.3
8.6
8.3
7.1
7.3
8.3
8.7
7.7
8.4
8.4
8.3
8.1
6.5
7.2
7.8
6.9
6.7
7.6
8.9
8.3
2.5
2.6
2.5
2.3
2.4
2.9
2.8
2.6
2.7
2.4
2.5
2.7
2.8
2.6
2.8
2.7
2.7
2.6
2.5
2.6
2.5
2.4
2.3
2.6
2.7
2.3
1.2
1.2
0.8
0.7
1.1
1.7
1.5
1.5
1.3
0.8
0.9
1.4
1.5
1.3
1.5
1.6
1.6
1.6
0.7
1.1
1.3
1.3
1.0
1.4
1.7
0.9
30
30
33
33
32
27
29
29
29
33
33
28
28
30
28
29
29
29
34
32
29
32
33
30
27
30
167
153
212
244
227
148
154
191
192
254
238
179
169
226
169
190
181
204
281
232
228
226
262
232
189
178
34
34
31
32
37
42
40
38
38
33
37
36
36
41
36
37
38
37
30
33
34
33
28
36
40
34
74
76
71
69
81
92
86
80
82
70
80
76
77
75
81
81
82
79
63
72
77
72
59
77
85
78
32
32
28
29
36
38
37
31
34
29
33
31
32
31
34
34
34
32
25
31
30
29
24
31
35
33
a
Biogenic free elemental concentration=measured elemental concentration in bulk sediment sample 100/(100–% opal–%
CaCO32.5 % organic carbon). Prior to making this correction we calculate Si lithogenic=Si measuredSi biogenic. Biogenic data
from Mammone (1998).
Laurels Graduate Scholarship awarded to C.
Viscosi-Shirley.
Appendix A
See Table 1.
Appendix B
See Table 2.
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