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rsta.royalsocietypublishing.org
Research
Cite this article: Bishop JL, Englert PAJ, Patel
S, Tirsch D, Roy AJ, Koeberl C, Böttger U, Hanke
F, Jaumann R. 2014 Mineralogical analyses of
surface sediments in the Antarctic Dry Valleys:
coordinated analyses of Raman spectra,
reflectance spectra and elemental
abundances. Phil. Trans. R. Soc. A 372:
20140198.
http://dx.doi.org/10.1098/rsta.2014.0198
One contribution of 14 to a Theme Issue
‘Raman spectroscopy meets extremophiles on
Earth and Mars: studies for successful search
of life’.
Subject Areas:
geology, geochemistry, biogeochemistry,
astrobiology, solar system
Keywords:
Antarctic Dry Valleys, sediments, Raman
spectra, reflectance spectra, chemistry
Author for correspondence:
Janice L. Bishop
e-mail: [email protected]
Electronic supplementary material is available
at http://dx.doi.org/10.1098/rsta.2014.0198 or
via http://rsta.royalsocietypublishing.org.
Mineralogical analyses of
surface sediments in the
Antarctic Dry Valleys:
coordinated analyses of Raman
spectra, reflectance spectra
and elemental abundances
Janice L. Bishop1,2 , Peter A. J. Englert3 , Shital Patel1,4 ,
Daniela Tirsch5 , Alex J. Roy6 , Christian Koeberl7,8 ,
Ute Böttger5 , Franziska Hanke5,9 and Ralf Jaumann5
1 Carl Sagan Center, SETI Institute, 189 Bernardo Avenue, Mountain
View, CA, USA
2 NASA Ames Research Center, Moffett Field, CA, USA
3 Hawaii Institute of Geophysics and Planetology, University of
Hawaii at Mânoa, HI, USA
4 Department of Chemistry, San Jose State University, San Jose,
CA, USA
5 German Aerospace Center (DLR), Berlin, Germany
6 Department of Land and Natural Resources, Honolulu, HI, USA
7 Department of Lithospheric Research, University of Vienna,
Althanstrasse 14, 1090 Vienna, Austria
8 Natural History Museum, Burgring 7, 1010 Vienna, Austria
9 Technische Universität Berlin, Berlin, Germany
Surface sediments at Lakes Fryxell, Vanda and
Brownworth in the Antarctic Dry Valleys (ADV)
were investigated as analogues for the cold, dry
environment on Mars. Sediments were sampled from
regions surrounding the lakes and from the ice
cover on top of the lakes. The ADV sediments were
studied using Raman spectra of individual grains and
reflectance spectra of bulk particulate samples and
compared with previous analyses of subsurface and
lakebottom sediments. Elemental abundances were
coordinated with the spectral data in order to assess
trends in sediment alteration. The surface sediments
in this study were compared with lakebottom
sediments (Bishop JL et al. 2003 Int. J. Astrobiol.
2014 The Author(s) Published by the Royal Society. All rights reserved.
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The objective of this study is to investigate surface sediments in the Antarctic Dry Valleys (ADV)
region (figure 1) with a focus on Wright and Taylor Valleys. The overall goal of this project is to
identify and interpret weathering and soil formation processes on Mars through comparison with
the composition and weathering status of systematically studied Mars analogue soils [1–3]. We
seek to identify signatures of physical and chemical alteration in these sediments, and, further,
to apply these data to Mars and determine if there are short-term and long-term liquid-waterbased chemical alteration indicators embedded in current Mars chemical and physical data. The
extremely cold, arid ADV environment provides one of the best analogues for the surface of Mars
today. For this reason, ADV soils and sediments have long been under study [2,4–7].
The data presented here will be useful for comparison with orbital and landed datasets
from Mars. Raman spectrometers have been proposed for use on Martian rovers [8,9] and
Raman data from cold, dry analogue sites will be supportive of data interpretation for a future
Raman spectrometer at Mars. Visible/near-infrared (VNIR) reflectance spectra presented here are
comparable to the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra
[10], and analyses of these samples will assist in characterizing sediments from orbit on Mars.
Similarly, mid-IR region spectra are related to data collected by the Mars Global Surveyor Thermal
Emission Spectrometer instrument [11]. The X-ray diffraction (XRD) data presented are similar to
data collected by the Chemistry and Mineralogy (CheMin) instrument [12] on the Mars Science
Laboratory (MSL) rover. Elemental abundances were acquired at Mars by the Mars Odyssey
Gamma Ray Spectrometer (MOGRS) [13,14] and the Mars Exploration Rovers (MER) [15,16], and
the elemental analyses presented here will assist in interpreting these data.
(a) Antarctic Dry Valleys
Pioneering work by Claridge [17], followed by the suggestion that the ADVs are the best
terrestrial approximation of contemporary Mars [18–20] encouraged other studies of ADV
soils and sediments as potential analogues for Martian surface material [1,2,6,7,21–36]. Gibson
and co-workers [2,30] provided an early precedence for this kind of study, applying multiple
dimensions of analysis to several samples in an 80 cm depth profile from Prospect Mesa, Wright
Valley. That study links analyses to soil formation processes in the ADV and on Mars. Data
evaluated encompass adsorbed water, and petrography from fine- and coarse-grained fractions
of representative sample aliquots, and mineralogical and chemical composition, water soluble
ions, plus total carbon, sulfur and sulfates from bulk samples. Minerals were analysed in detail,
including identification of zeolites, clays and sulfates. Geochemical analyses performed on soil
samples from the pit found the permanently frozen zone at a depth of approximately 40 cm [2],
consistent with subxerous regions in the dry valleys where soils may be exposed to liquid water for
short periods of time [31,37]. Gibson et al. [2] noted elevated salt concentrations approximately 2–
4 cm below the surface, which have been attributed to subsurface migration of brines [38] owing
to the presence of thin films of liquid water at temperatures much below freezing [39].
.........................................................
1. Introduction
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rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
2, 273–287 (doi:10.1017/S1473550403001654)) and samples from soil pits (Englert P et al. 2013
In European Planetary Science Congress, abstract no. 96; Englert P et al. 2014 In 45th Lunar
and Planetary Science Conf., abstract no. 1707). Feldspar, quartz and pyroxene are common
minerals found in all the sediments. Minor abundances of carbonate, chlorite, actinolite and
allophane are also found in the surface sediments, and are similar to minerals found in greater
abundance in the lakebottom sediments. Surface sediment formation is dominated by physical
processes; a few centimetres below the surface chemical alteration sets in, whereas lakebottom
sediments experience biomineralization. Characterizing the mineralogical variations in these
samples provides insights into the alteration processes occurring in the ADV and supports
understanding alteration in the cold and dry environment on Mars.
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162° E
163° E
study
location
(a)
164° E
165° E
166° E
167° E
(b) 77°15¢ S
77°15¢ S
77°45¢ S
77°30¢ S
78° S
77°45¢ S
161° E
162° E
0
163° E
5 10
0 5 10
164° E
20 miles
165° E
166° E
20 km
(c)
Figure 1. Images of ADV study sites: (a) overview indicating location of ADV in Antarctica, (b) ADV region showing Taylor and
Wright Valleys and (c) locations of Lakes Brownworth, Fryxell and Vanda. (Online version in colour.)
Another interesting feature of the ADV region is the presence of perennially ice-covered lakes
that host active biosystems in these extreme habitats [4–6,26]. Organisms exist in microbial mats in
the lakebottom sediments below both oxic (oxygen-rich) and anoxic (oxygen-poor) waters in these
lakes. Lake Hoare in the Taylor Valley has received abundant attention owing to the 3–5 m thick
year-round ice cover and algal mats growing in both oxic and anoxic regions of the lakebottom
[33,40–43]. The water temperature in Lake Hoare varies from 0.0◦ C to 0.8◦ C [44], whereas the
mean annual air temperature above the ice is typically −18◦ C [45].
Coordinated reflectance spectroscopy and geochemical analyses of lakebottom sediments
from the Dry Valleys have enabled identification of minerals formed in this environment
and characterization of microbial activity [24,25]. Those studies analysed numerous sediments
.........................................................
77°30¢ S
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
Antarctica
77° S
3
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Quantitative approaches using major element weathering indices such as the chemical index of
alteration (CIA) have been used to assess the effects of physical versus chemical weathering in
pedogenesis [46–48]. CIA values can be used to assess weathering processes [49,50] by comparing
source rock material CIAs with those of soils. The CIA is based on mobility of the major elements
Al, Ca, Na and K. Fresh basalts have a CIA of about 30–45, whereas completely weathered
kaolinite has a CIA of 100.
K and Th abundances are important chemical parameters for provenance and weathering in
soils and K/Th ratios are a useful indicator for alteration profiles. K and Th data are available for
the ADV granitoids [51] and Ferrar dolerites [52] and provide unaltered baseline values for our
sediment dataset.
2. Methods
(a) Samples
Sediment samples were collected in 2004 by scooping material from the surface in multiple
locations around Lakes Fryxell, Vanda and Brownworth (FVB) and a few locations on top of the
lakes. Maps of sample collection sites are provided in figure 2. Samples were sealed at the field
site and returned to the laboratory for study. A list of the samples is provided in table 1. For each
sample, ground aliquots were prepared of a portion of the material by gently crushing the grains
and dry sieving the crushed product until all of the crushed material passed through a less than
125 µm sieve. Samples were ground and sieved iteratively in order to avoid over-grinding the
softer grains.
Through analysis of these samples, we seek to determine whether chemical alteration or
microbial activity is taking place at the surface near the lakes of the ADV. We used XRD, Raman
spectroscopy and reflectance spectroscopy to identify and characterize the mineralogy of these
sediments. We used VNIR reflectance spectra to characterize chlorophyll bands in the sediments
and to identify CH vibrations owing to organic material. Elemental trends are coordinated with
the observed mineralogy and ratios of selected elements are used for assessing the degree of
alteration in the sediments.
(b) X-ray diffraction
XRD was run on the particulate less than 125 µm size fraction of each sample using the Terra
X-ray diffraction and X-ray fluorescence instrument (Olympus Corporation) [53]. Base mineral
concentrations were then analysed using JADE, which is pattern processing, identification and
.........................................................
(b) Characterizing soil alteration through elemental abundances
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retrieved from oxic and anoxic zones in Lake Hoare. Calcite and organic matter were abundant in
oxic region lakebottom sediments [24]. Spectroscopic parameters were developed to discriminate
the organic C and calcite in these sediments, as the features for these groups both occur in the
3.3–3.5 µm spectral region. The mineralogy of the Lake Hoare sediments is dominated by quartz,
feldspar and pyroxene [24], consistent with the rocks and soils from the ADV region [37].
Another study involving Raman and reflectance spectra of coarse sediment grains from Lake
Hoare more closely identified the types of minerals present [1]. The presence of biogenic pyrite,
chlorophyll-like spectral absorptions and organic C in that study correlated well with the S
isotope compositions in anoxic sediments, and microbial activity was found to be much higher
in the anoxic than oxic sediments. Raman analyses of sediment grains showed the presence of
chalcedony together with quartz in some sediments [27]. Raman analyses of feldspar grains in that
study found spectra consistent with a range of compositions, including sanidine, albite, oligoclase
and labradorite, and found pyroxene grains corresponding to orthopyroxene and clinopyroxene.
Selected magnetic grains were found to contain titanomagnetite [1,27].
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(a)
5
LFR-4(E)
LFR-3(E)
LFR-6(ss)
LFR-1(E)
LFR-9(ss)
LFR-7(ss)
LFR-2(E)
Lake Fryxell (lower Taylor Valley)
(b)
LVA-5(ss)
LVA-6(ss)
LVA-4(E)
LVA-7(ss)
LVA-3(E)
LVA-9(E)
LVA-2(E)
LVA-1(E)
LFR-8(ss)
Lake Vanda (upper Wright Valley)
(c)
LBR-4(E)
LBR-3(ss)
LBR-2(ss)
LBR-1(ss)
blue ice area; no
samples collected
Lake Brownworth (lower Wright Valley)
Figure 2. Views of lakes showing locations of sediment sampling sites: (a) Lake Fryxell, (b) Lake Vanda and (c) Lake Brownworth
(image credit: Will Hine/ TVNZ). Samples were collected from the ice surface as ‘surface samples’ (SS) and along the ‘edge’ (E)
of each lake. (Online version in colour.)
quantification software (Materials Data, Inc.), to determine specific minerals present in processed
samples. The XRD unit is similar to the CheMin instrument on the MSL rover [12]. The instrument
provides for both quick survey and quantitative analyses of sample suites.
(c) Raman spectroscopy
Raman spectra were collected on multiple grains of the original sample material for one sample
from each lake region. These spectra were measured with a Witec Alpha 300 Raman spectrometer
.........................................................
LFR-5(E)
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LFR-10(ss)
LFR-8(ss)
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Table 1. List of samples studied.
6
lake name
Lake Fryxell
sediment location
SS, sediment on surface of ice covering lake
JB651
LFR-1
Lake Fryxell
E, sediment at edge of lake
JB652
LFR-2
Lake Fryxell
E, sediment at edge of lake
JB653
LFR-3
Lake Fryxell
E, sediment at edge of lake
JB654
LFR-4
Lake Fryxell
E, sediment at edge of lake
JB655
LFR-5
Lake Fryxell
E, sediment at edge of lake
JB656
LFR-6
Lake Fryxell
SS, sediment on surface of ice covering lake
JB657
LFR-7
Lake Fryxell
SS, sediment on surface of ice covering lake
JB658
LFR-8
Lake Fryxell
SS, sediment on surface of ice covering lake
JB659
LFR-9
Lake Fryxell
SS, sediment on surface of ice covering lake
JB660
LFR-10
Lake Fryxell
SS, sediment on surface of ice covering lake
JB661
LVA-1
Lake Vanda
E, sediment at edge of lake
JB662
LVA-2
Lake Vanda
E, sediment at edge of lake
JB663
LVA-3
Lake Vanda
E, sediment at edge of lake
JB664
LVA-4
Lake Vanda
E, sediment at edge of lake
JB665
LVA-5
Lake Vanda
SS, sediment on surface of ice covering lake
JB666
LVA-6
Lake Vanda
SS, sediment on surface of ice covering lake
JB667
LVA-7
Lake Vanda
SS, sediment on surface of ice covering lake
JB668
LVA-8
Lake Vanda
SS, sediment on surface of ice covering lake
JB669
LVA-9
Lake Vanda
E, sediment at edge of lake
JB670
LBR-1
Lake Brownworth
SS, sediment on surface of ice covering lake
JB671
LBR-2
Lake Brownworth
SS, sediment on surface of ice covering lake
JB672
LBR-3
Lake Brownworth
SS, sediment on surface of ice covering lake
JB673
LBR-4
Lake Brownworth
E, sediment at edge of lake
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under ambient air of a spot approximately 1.5 µm in diameter using a confocal microscope
as in [54]. The excitation wavelength was 532 nm, the laser power ranged between 0.5 and
3 mW, and a 600 lines mm−1 grating was used. The spectral resolution was about 4–5 cm−1
across the range 100–3800 cm−1 . Raman spectra were measured at several spots on the grains
in order to characterize as many minerals present as possible. Confocal Raman microscopy [55]
was used in order to view the surface of the mineral grains at the specific sites where spectra
were collected.
(d) Reflectance spectroscopy
Reflectance spectra were measured on the particulate less than 125 µm size fraction for each
sample from 0.3 to 50 µm as in past studies [1,25]. The spectra are a composite of bidirectional
spectra collected under ambient conditions at 5 nm spectral resolution from 0.3 to 1.3 µm relative
to Halon and biconical Fourier transform IR spectra collected under a dehydrated environment
at 4 cm−1 spectral resolution from 1 to 50 µm relative to a rough gold surface.
.........................................................
lake id
LFR-A
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
sample id
JB650
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(e) Elemental analyses
The XRD data contribute semi-quantitative mineralogical trends (figure 3) and provide
confirmation of the minerals detected using Raman and reflectance spectroscopy. The Raman
and reflectance spectra of Lake Fryxell sediments are presented in figures 4 and 5, respectively;
the Raman and reflectance spectra of Lake Vanda sediments are presented in figures 6 and 7,
respectively; and the Raman and reflectance spectra of Lake Brownworth are presented in
figures 8 and 9, respectively.
Spectroscopy data presented in this paper are available in the electronic supplementary
material. Raman spectra from figures 4, 6 and 8 are provided in table S1 and reflectance spectra
from figures 5, 7 and 9 are provided in table S2.
(a) X-ray diffraction
The XRD data indicate that the composition of all samples is dominated by quartz, feldspar
and pyroxene. Representative XRD scans illustrate distinct mineral distribution patterns for each
of the lake environments, although the general mineralogical composition is very similar for
all samples (figure 3a). A quantitative mineral assessment (figure 3b) shows that Lake Fryxell
sediments are dominated by albite, whereas the Lake Brownworth sediments are rich in albite
and Na- and Ca-bearing feldspars. The major mineral component for Lake Vanda samples is
quartz followed by feldspars and pyroxene. The average quartz content of the Lake Brownworth
samples is lower than that of Lake Vanda samples, but exceeds the Lake Fryxell average and all
of the individual sample quartz abundances. The samples collected from the ice cover at both
Lakes Fryxell and Vanda tend to have higher quartz components than those collected along the
perimeter of the lakes. The feldspar and pyroxene abundances do not show notable differences
between lakeshore and on-ice samples.
(b) Raman spectroscopy
Raman spectra are dominated by quartz, feldspar and pyroxene signatures, whereas a few spots
were consistent with aluminosilicates and amorphous material. The Raman peak positions are
given in table 5 for selected spectra of individual grains shown in figures 4, 6 and 8. The Raman
signatures of feldspar-rich grains are, in general, more characteristic of albite (NaAlSi3 O8 ) and
oligoclase (Na,Ca)[Al(Si,Al)Si2 O8 ] and less consistent with Ca-rich anorthite or K-rich microcline
or sanidine. Typically, a strong doublet is observed near 510 and 480 cm−1 and additional peaks
or combinations of peaks occur near 290 and 190 cm−1 . Raman spectrum 1 of a feldspar-rich grain
in the Lake Brownworth sediment JB671 (figure 8) also contains peaks at 1086, 995, 949, 817 and
777 cm−1 and its spectrum closely resembles that of albite. Raman spectrum 4 of a feldspar grain
in the Lake Fryxell sediment JB651 contains a broad peak shape near 252–288 cm−1 and a peak at
160 cm−1 that are consistent with a small amount of sanidine (K-feldspar) in this grain together
with Na/Ca-rich feldspar.
.........................................................
3. Results
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
Major elements were measured for the particulate less than 125 µm size fraction of each sample
by ACME laboratories. Additional minor and trace element abundances, including those of the
rare earth elements, were measured by instrumental neutron activation analysis (INAA) at the
Department of Lithospheric Research, University of Vienna, Austria. Details on instrumentation,
accuracy and precision of this method are described by Koeberl and co-workers [56,57]. There
was excellent agreement for the elements measured by both techniques and an average was
used, where applicable, for the elemental abundance data presented in tables 2–4. Elemental
abundances and ratios of selected elements of these surface sediments were compared with data
from Martian meteorites and Mars as in prior studies [58].
7
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Table 2. Elemental abundances. Lake Fryxell.
8
LFR-1
JB651
LFR-2
JB652
LFR-3
JB653
LFR-4
JB654
LFR-5
JB655
LFR-6
JB656
LFR-7
JB657
LFR-8
JB658
LFR-9
JB659
LFR-10
JB660
C (wt%)
1.1
0.17
0.22
0.23
0.19
0.12
0.28
0.29
0.76
0.72
0.56
TOC (wt%)
0.96
0.07
0.09
0.03
0.06
0.07
0.26
0.28
0.75
0.71
0.49
TIC (wt%)
0.14
0.1
0.13
0.2
0.13
0.05
0.02
0.01
0.01
0.01
0.07
Na (wt%)
2.00
2.42
2.27
2.27
2.26
2.16
1.92
1.87
2.01
1.96
2.09
Mg (wt%)
2.65
4.35
3.76
3.00
3.29
4.24
3.53
3.50
3.11
3.15
3.81
Al (wt%)
7.01
6.93
7.17
7.51
7.39
6.84
6.67
6.68
7.02
7.04
6.93
Si (wt%)
27.89
25.36
26.03
27.78
26.96
26.86
29.24
29.28
28.82
28.47
26.93
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P (wt%)
0.08
0.18
0.15
0.11
0.11
0.12
0.05
0.05
0.06
0.07
0.12
S TOT (wt%)
0.57
0.03
0.05
0.04
0.04
0.03
0.03
0.02
0.02
0.04
0.04
S SO4 (wt%)
0.196
0.013
0.027
0.020
0.023
0.017
0.017
0.010
0.010
0.020
0.017
K (wt%)
2.05
1.84
2.10
1.76
1.94
1.72
1.84
1.70
1.81
1.80
2.01
Ca (wt%)
3.89
4.89
4.84
4.36
4.69
4.70
4.24
4.3
4.13
4.24
4.72
Sc
15.75
19.48
20.53
14.76
17.68
22.07
22.90
22.40
20.50
19.38
19.18
Ti (wt%)
0.46
1.04
0.84
0.58
0.65
0.70
0.34
0.38
0.38
0.41
0.69
Cr
129
245
236
145
173
248
202
192
174
169
211
Mn (wt%)
0.070
0.116
0.108
0.077
0.093
0.108
0.085
0.085
0.077
0.077
0.101
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Fe (wt%)
3.89
6.29
5.82
4.09
4.76
5.67
4.32
4.40
4.11
4.16
5.08
Co
20.0
34.1
31.3
21.2
23.9
32.9
27.4
25.7
24.2
23.6
31.6
Ni
58.27
128.40
90.13
70.57
87.75
102.65
74.13
73.04
59.43
73.58
107.67
Zn
66.6
98.2
95.6
65.5
74.4
92.4
70.9
71
69
70.4
92
Ga
2
9
9
22
3
7
6
3
2
3
10
As
1.32
1.43
1.10
1.09
1.34
0.61
1.72
<0.8
0.53
0.6
1.25
Se
1.27
<0.9
<0.9
0.75
0.98
1.04
0.29
0.89
0.8
1.07
<1.3
Br
1.7
0.6
0.6
0.6
0.6
0.6
0.7
0.6
0.9
1.2
1.0
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Rb
84.5
66.6
74.1
85.8
73.5
66.1
70.2
72.7
74.1
76.2
75.8
Sr
342
512
463
451
422
396
312
285
307
322
251
Y
18
27
25
19
24
24
18
19
19
20
22
Zr
172
388
312
214
241
297
169
217
176
159
268
Nb
23
55
41
31
29
28
11
11
16
20
35
Sb
0.14
0.15
0.12
0.15
0.13
0.09
0.03
<0.1
<0.1
0.06
<0.3
Cs
1.77
1.39
1.54
1.66
1.48
1.38
1.28
1.28
1.32
1.39
1.38
Ba
341
323
338
373
345
311
315
325
328
345
346
La
25.5
48.4
42.1
30.0
32.2
41.7
23.5
29.1
28.9
31.0
33.5
Ce
47.5
90
79.4
55.4
60.9
76.9
44.2
55.2
54.4
57.1
60.8
Nd
20.3
38.5
35.4
25.3
27.8
33.4
17.2
24.0
19.6
21.3
25.4
Sm
4.30
7.51
6.69
4.95
5.54
6.24
3.85
4.27
4.05
4.81
5.87
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
(Continued.)
.........................................................
LFR-A
JB650
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
elements
(ppm)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 2. (Continued.)
9
LFR-1
JB651
2.13
LFR-2
JB652
1.89
LFR-3
JB653
1.40
LFR-4
JB654
1.47
LFR-5
JB655
1.67
LFR-6
JB656
1.10
LFR-7
JB657
1.16
LFR-8
JB658
1.19
LFR-9
JB659
1.23
LFR-10
JB660
1.57
Gd
4.26
6.32
5.99
4.06
5.29
4.48
4.01
4.58
3.98
4.78
4.35
Tb
0.59
1.02
0.90
0.67
0.76
0.85
0.60
0.64
0.61
0.69
0.84
Tm
0.22
0.45
0.39
0.28
0.34
0.38
0.28
0.27
0.27
0.26
0.36
Yb
1.46
2.52
2.28
1.60
1.88
2.12
1.78
1.85
1.72
1.69
2.12
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
Lu
0.23
0.36
0.34
0.24
0.29
0.34
0.27
0.29
0.28
0.27
0.30
Hf
3.04
7.48
6.03
4.29
5.16
6.42
3.41
4.78
4.08
3.12
5.02
Ta
1.6
4.29
3.17
2.47
2.13
2.44
0.98
1.07
1.06
1.35
2.88
Ir (ppb)
<1.2
<1.4
<1.4
<1.2
<1.5
<1.3
<1.4
<1.4
<1.4
<1.4
<1.5
Au (ppb)
4.6
0.3
0.2
0.3
<0.3
0.8
0.9
<0.3
<0.3
<0.3
<2.3
Th
6.40
8.58
7.56
6.40
6.48
7.62
5.52
6.33
7.01
7.47
11.0
U
1.59
1.97
1.79
1.67
1.55
1.51
0.86
1.02
0.76
1.29
1.65
K/Th
3199
2141
2771
2744
2996
2259
3337
2691
2589
2406
1833
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
Raman spectra of the pyroxene-rich grains in most of the sediments are more consistent with
monoclinic clinopyroxene (or pigeonite) than orthopyroxene with peaks at 1016, 667–670, 390–
391, 326 and 130–136 cm−1 . The quartz grains exhibit Raman peaks near 466–470, 207–209 and
130–133 cm−1 . Spectrum 3 of Lake Vanda sediment JB669 contains not only a mixture of feldspar
and quartz and is dominated by feldspar peaks but also contains weak peaks or shoulders
attributed to quartz near 467, 211 and 126 cm−1 . The Raman spectrum 2 of an aluminosilicatebearing grain in the Lake Brownworth sediment JB671 has peaks at 1040, 990–1030, 679, 667,
547 and 198 cm−1 attributed to chlorite. The Fe2+ endmember chamosite has peaks at 1031,
667, 544 and 198 cm−1 , whereas the Mg-rich endmember clinochlore has peaks at 1037, 670,
547 and 201 cm−1 . The grain likely contains an intermediate Fe2+ Mg chlorite as well as some
orthopyroxene contributing to the weak and broad band from 990 to 1030 cm−1 and the sharp
peak at 679 cm−1 .
(c) Reflectance spectroscopy
Most VNIR spectra are dominated by strong electronic absorption bands characteristic of Fe2+ in
pyroxene. These are observed near 0.94 and 1.94 µm in spectra of most Lake Fryxell samples
(figure 5a) and are attributed to Fe2+ -rich pyroxene based on band centre correlations with
pyroxene chemistry [59]. These band centres are observed at slightly longer wavelengths, near
0.95 and 1.98 µm, in spectra of the Lake Vanda (figure 7a) and Lake Brownworth (figure 9a)
sediments, implying a small shift towards lower Fe in the pyroxene [59].
Chlorophyll bands are observed at 0.67 µm (figure 5a) for samples JB650 and JB660 collected
from the ice surface above Lake Fryxell. These samples also exhibit the strongest aliphatic CH
stretches at 3.3–3.5 µm owing to the presence of organic material. Weak chlorophyll and CH bands
are observed for Lake Fryxell samples JB656–JB659, but there is no evidence of chlorophyll or CH
bands in Lake Vanda or Lake Brownworth samples.
Spectra of Lake Fryxell samples JB650–JB654 and JB660 include bands characteristic of calcite
near 2.3, 2.5, 3.4 and 4 µm (figure 5a,c). Carbonate bands are not observed in spectra of the
Lake Vanda and Lake Brownworth samples. The CH and carbonate bands overlap near 3.4 µm;
however, they have distinctive triplet signatures and the 3.42 µm band is stronger for aliphatic
.........................................................
LFR-A
JB650
1.17
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
elements
(ppm)
Eu
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 3. Elemental abundances. Lake Vanda.
10
LVA-2
JB662
0.08
LVA-3
JB663
0.04
LVA-4
JB664
0.04
LVA-5
JB665
0.05
LVA-6
JB666
0.04
LVA-7
JB667
0.05
LVA-8
JB668
0.04
LVA-9
JB669
0.14
TOC (wt%)
0.03
0.08
0.04
0.03
0.04
0.04
0.05
0.05
0.07
TIC (wt%)
0
0
0
0.01
0.01
0
0
0
0.07
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
Na (wt%)
1.19
1.77
0.97
1.00
1.15
1.19
1.13
1.37
1.35
Mg (wt%)
2.4
3.35
4.36
4.13
2.41
1.88
1.87
1.68
2.92
Al (wt%)
4.4
6.36
4.12
4.23
4.88
4.55
4.61
4.63
5.42
Si (wt%)
34.77
29.23
29.23
30.06
34.12
35.74
35.49
35.95
31.37
P (wt%)
0.03
0.03
0.03
0.03
0.02
0.02
0.02
0.02
0.03
S TOT (wt%)
0.02
0.08
0.03
0.02
0.02
0.02
0.02
0.01
0.01
S SO4 (wt%)
0.010
0.060
0.010
0.010
0.010
0.010
0.010
0.000
0.000
K (wt%)
1.10
1.54
0.73
0.87
1.01
1.12
0.99
1.08
1.00
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
Ca (wt%)
3.24
4.54
4.69
4.51
3.54
3.15
3.11
2.84
4.67
Sc
19.77
27.21
37.38
34.64
19.89
16.82
16.12
14.87
27.61
Ti (wt%)
0.19
0.35
0.95
0.81
0.20
0.16
0.15
0.14
0.34
Cr
140
172
239
231
122
98
98
97
142
Mn (wt%)
0.062
0.093
0.147
0.132
0.070
0.054
0.054
0.046
0.085
Fe (wt%)
3.19
4.67
7.73
6.89
3.25
2.85
2.57
2.44
4.62
Co
19.3
27.4
40.7
36.6
20.1
18.3
15.6
15.8
28.4
Ni
46.39
64.54
84.25
74.24
50.83
35.14
33.58
32.87
60.43
Zn
58
93
146
132
60
56
42
43
96
Ga
1.8
3
5.3
9.4
1.6
3.4
1.2
1.8
8.8
As
<1.0
<1.4
<1.5
<2.1
<1.2
<1.3
<1.4
<1.1
0.52
Se
<1.1
<1.4
<1.9
<1.6
<1.1
<1.1
<1.3
<0.9
<1.4
Br
0.4
0.4
0.4
0.5
0.3
0.5
0.6
0.5
0.5
Rb
42.5
58.5
43.8
40.0
44.9
48.0
37.5
47.5
53.2
Sr
81
126
83
73
69
80
72
96
88
Y
14
17
24
20
13
11
11
10
16
Zr
100
186
346
201
104
102
85
111
198
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
Nb
5
6
10
13
8
5
5
6
7
Sb
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
Cs
1.15
1.26
1.10
1.16
1.14
1.23
0.88
1.24
1.38
Ba
201
306
163
157
179
207
180
226
211
La
14.5
23
35.3
19.1
12.7
14.6
12.4
13.3
21.0
Ce
25.6
40.3
61.4
34.1
23.3
25.2
22
23.8
37.4
Nd
9.03
15.7
21.4
14.4
9.48
9.34
8.50
8.28
13.4
Sm
2.23
3.18
4.80
3.29
2.12
2.25
1.79
2.04
3.26
Eu
0.59
0.79
0.76
0.64
0.59
0.66
0.53
0.66
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
0.77
..........................................................................................................................................................................................................
(Continued.)
.........................................................
LVA-1
JB661
0.03
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
elements
(ppm)
C (wt%)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 3. (Continued.)
11
LVA-2
JB662
3.34
LVA-3
JB663
3.86
LVA-4
JB664
2.86
LVA-5
JB665
2.28
LVA-6
JB666
2.27
LVA-7
JB667
1.54
LVA-8
JB668
2.11
LVA-9
JB669
3.56
Tb
0.38
0.52
0.77
0.48
0.35
0.36
0.29
0.32
0.54
Tm
0.17
0.24
0.36
0.29
0.17
0.16
0.14
0.15
0.25
Yb
1.25
1.59
2.42
2.07
1.21
1.21
1.01
1.09
1.78
Lu
0.20
0.27
0.40
0.34
0.20
0.20
0.17
0.17
0.31
Hf
2.15
3.71
9.02
5.26
2.30
2.26
2.2
2.10
4.58
Ta
0.39
0.59
1.31
0.92
0.32
0.36
0.24
0.29
0.53
Ir (ppb)
<1.2
<1.4
<2
<1.6
<1.2
<1.1
<1.3
<0.9
<1.4
Au (ppb)
<1.5
<2.0
<2.1
2.0
<1.6
<1.7
<1.9
<1.6
<1.9
Th
5.66
8.85
13.9
7.52
6.49
6.12
5.01
7.37
9.93
U
0.65
0.80
1.33
1.02
0.75
0.92
0.53
0.68
0.97
K/Th
1941
1745
522
1157
1563
1835
1968
1469
1003
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
CH absorptions, and the 3.36 and 3.48 µm bands are stronger for calcite [25]. The carbonate band
position at 3.98 µm is characteristic of calcite, as found previously for lakebottom sediments [25].
OH combination stretching plus bending bands in the range 2.19–2.34 µm characteristic of
aluminosilicates are observed in many samples (figures 5c, 7c and 9c). These features are often
weak and the relative band strengths vary indicating differing abundances of the OH-bearing
components. The 2.34 µm band is generally owing to Fe2+ –OH species and is strongest in
spectra of sample JB671 from Lake Brownworth, but is present in all four Lake Brownworth
spectra. This feature is also clearly detected in spectra of sample JB657 from Lake Fryxell and
samples JB667 and JB668 from Lake Vanda. A weak band near 2.34 µm is present in most of
the sediment spectra. For occurrences of a stronger band at 2.34 µm, a weak band near 2.25 µm
is also present, which is consistent with a chlorite mineral [60]. This band occurs at 2.36 µm in
spectra of chamosite and at 2.33 µm in spectra of clinochlore [61], so our samples likely have
an intermediate composition chlorite mineral. In spectra from the Lake Fryxell region, a weak
doublet near 2.33 and 2.38 µm is more consistent with actinolite spectra [62] as observed in some
lakebottom spectra [7]. An additional weak feature near 2.19 µm is present in spectra of most
samples and is attributed to the presence of allophane as in a past study [7]. Features owing to
H2 O in these samples are present near 1.4, 1.9, 2.9–3.1 and 6.1 µm. The H2 O band near 1.9 µm is
often correlated with the OH bands near 2.2–2.4 µm and could be due to the allophane or another
hydrated component.
The mid-IR spectral region exhibits strong bands consistent with quartz near 1215, 1160, 1080,
805, 785, 550, 495 and 375 cm−1 for most sediments (figures 5b, 7b and 9b). These are particularly
strong in the Lake Vanda and Lake Brownworth spectra. The Christiansen feature (reflectance
minimum) shifts from near 1330–1340 cm−1 for the Lake Vanda spectra to approximately 1310–
1330 cm−1 for the Lake Brownworth spectra and to approximately 1280–1310 cm−1 for the
Lake Fryxell samples, which indicates a shift from more quartz-dominated sediments to more
intermediate or basaltic materials [63,64]. The Christiansen feature is observed at approximately
1350 cm−1 for quartz, approximately 1300 cm−1 for albite, approximately 1235 cm−1 for anorthite
and approximately 1175 cm−1 for augite [63]. The Lake Fryxell spectra also include a peak near
885 cm−1 that is consistent with pyroxenes such as enstatite and broadened features from 450 to
600 cm−1 under the sharp quartz peaks at 550 and 495 cm−1 that are characteristic of pyroxenes
such as augite and enstatite [63]. Carbonate features are difficult to detect in the mid-IR region
.........................................................
LVA-1
JB661
2.24
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
elements
(ppm)
Gd
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 4. Elemental abundances. Lake Brownworth.
12
LBR-2
JB671
0.06
LBR-3
JB672
0.09
LBR-4
JB673
0.09
TOC (wt%)
0.08
0.06
0.09
0.08
TIC (wt%)
0.01
0
0
0.01
Na (wt%)
2.00
2.41
2.01
1.61
Mg (wt%)
1.89
1.56
1.89
2.64
Al (wt%)
6.68
7.19
6.82
6.32
Si (wt%)
32.35
31.92
32.37
31.51
P (wt%)
0.03
0.03
0.03
0.03
S TOT (wt%)
0.01
0.01
0.03
0.05
S SO4 (wt%)
0.010
0.000
0.017
0.027
K (wt%)
1.87
2.80
2.01
1.52
Ca (wt%)
3.36
3.07
3.30
4.08
Sc
14.40
12.58
14.52
20.41
Ti (wt%)
0.17
0.17
0.17
0.24
Cr
107
84
100
147
Mn (wt%)
0.054
0.046
0.046
0.070
Fe (wt%)
2.64
2.64
2.61
3.50
Co
15.6
14.2
15.6
20.6
Ni
39.76
30.26
37.03
50.46
Zn
49
55
45.0
56.3
Ga
4.8
3.9
4
2
As
<1.8
<1.9
<1
<0.6
Se
<1
<1
<0.7
0.98
Br
0.4
0.5
0.5
0.4
Rb
89.2
114
78.8
62.5
Sr
151
170
259
202
Y
13
15
13
17
Zr
131
152
107
105
Nb
6
6
5
8
Sb
0.05
< 0.2
< 0.1
< 0.1
Cs
1.43
1.90
1.33
1.24
Ba
399
485
348
280
La
18.3
20.6
13.7
19.2
Ce
32.9
35.5
25.4
34.5
Nd
12.6
13.8
10.9
13
Sm
2.82
3.18
2.28
3.02
Eu
0.81
0.96
0.82
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
0.78
..........................................................................................................................................................................................................
(Continued.)
.........................................................
LBR-1
JB670
0.09
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
elements
(ppm)
C (wt%)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 4. (Continued.)
13
LBR-2
JB671
3.19
LBR-3
JB672
2.48
LBR-4
JB673
3.6
Tb
0.42
0.46
0.36
0.49
Tm
0.18
0.25
0.19
0.22
Yb
1.14
1.52
1.14
1.48
Lu
0.19
0.22
0.19
0.23
Hf
2.54
3.10
2.37
2.57
Ta
0.50
0.60
0.42
0.60
Ir (ppb)
<1.0
<1.0
<1.1
<1.2
Au (ppb)
6.3
<1.9
0.6
<0.2
Th
8.80
8.88
3.95
5.88
U
0.89
0.96
0.64
0.95
K/Th
2123
3154
5077
2576
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
owing to multiple overlapping bands, but weak bands are observed near 1530 cm−1 in spectra of
JB650 and JB656–JB660 from Lake Fryxell that are attributed to calcite.
(d) Elemental analyses
The samples from FVB collected for this study show distinct major and minor elemental
abundance patterns indicating that each lake environment may represent different soil formation
and weathering conditions. For example, K/Th ratios in the sample suite range from 522
to 5077 (tables 2–4), and are below 3000 for all but three samples, with Lake Vanda soils
clearly distinguished by ratios systematically below 2000. K/Th ratios are useful in providing
information on soil provenance and for comparison of ADV soil data and processes to
Mars findings. Individual element abundances can provide clues on compounds they may be
associated with as is the case for carbon and sulfur. Major and minor element abundances are used
in geochemical indices to obtain information on weathering- or liquid-water-related processes.
Trace elements were measured and are provided in tables 2–4, but not discussed in detail.
Carbon and sulfur abundances were measured for all samples in order to evaluate the potential
of biogenic material present. Both total organic carbon and total inorganic carbon are presented
in tables 2–4. Sulfur was measured as sulfate (S SO4 ) and total sulfur (S TOT) and both values are
given in tables 2–4. The carbon abundance patterns for each of the lake areas are different with
Lake Fryxell showing exceptionally high abundances between 0.1 and 1.1 wt%, followed by Lake
Brownworth close to 0.1 wt%, and Lake Vanda below 0.1 wt% apart from two samples (figure 10).
Most significant, however, is that the majority of Lake Fryxell samples have an organic carbon
component between 0.1 and 0.96 wt% (absolute). Organic carbon abundance is generally lower
in samples from the other two lake regions. Lake Fryxell samples with significant organic carbon
components are JB650 and JB656–JB660 collected on top of the lake ice, with JB650 having the
highest total carbon and the highest organic carbon abundance. Inorganic carbon abundances
tend to be elevated in the sediments collected along the edges of the lakes with the highest
abundances present in samples JB650–JB655 and JB660 from Lake Fryxell and sample JB669 from
Lake Vanda. Inorganic carbon is below 0.02 wt% for the remaining samples from Lakes Fryxell
and Vanda and for all of the Lake Brownworth samples.
Sulfur abundance in all lake surface samples does not exceed 0.1 wt% except for JB650
(Fryxell) whose total sulfur abundance is 0.57 wt% (figure 11). In addition, sample JB650’s sulfate
.........................................................
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JB670
2.81
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elements
(ppm)
Gd
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(a)
14
normalized counts
Lake Vanda
Lake Brownworth
Lake Fryxell
600
400
200
0
10
(b)
60
Lake Fryxell
20
30
scattering angle, 2q
Lake Vanda
40
50
quartz
albite
50
augite
Ca-rich feldspars
others
Lake
Brownworth
abundance (%)
40
30
20
10
JB
6
JB 50
6
JB 51
65
JB 2
6
JB 53
65
JB 4
6
JB 55
65
JB 6
6
JB 57
65
JB 8
6
JB 59
66
JB 0
6
JB 61
66
JB 2
6
JB 63
66
JB 4
6
JB 65
66
JB 6
6
JB 67
66
JB 8
6
JB 69
67
JB 0
6
JB 71
6
JB 72
67
3
0
sample number
Figure 3. XRD data of <125 µm size fractions of sediments in the study. Peaks are observed for quartz, feldspar and pyroxene
in all samples, but the relative abundances vary. (a) Representative XRD scans from each lake environment and (b) relative
abundance in weight percentage of major mineral components from each sample. (Online version in colour.)
contributes less than 0.2 wt% (absolute) to total sulfur, leaving more than 0.3 wt% (absolute) to be
accounted for by other sulfur compounds. For most samples, however, sulfate and other sulfur
compound contributions to total sulfur are balanced. Low surface sulfate abundance is a normal
aspect of ADV soils, although sulfate is generally enriched in subsurface soil strata.
Important chemical parameters for provenance and weathering are K and Th abundances.
Figure 12 shows K/Th ratios and K abundances (ppm) for ADV lake surface sediments, their
potential source rocks, ADV granitoids and Ferrar dolerite [46,68], MOGRS average regional and
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1000
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(a)
(b)
15
1-feldspar
2
100 µm
(c)
2-pyroxene
1000
3
3-quartz
100 µm
500
(d)
4-feldspar
0
800
700
600
500
400
300
wavenumber (cm–1)
200
4
100
100 µm
Figure 4. (a) Raman spectra of mineral grains in sample 1 from Lake Fryxell (JB651), (b) image of grains 1–3, (c) image of grains
2–3 and (d) image of grain 4. Spectra are offset for clarity and lines mark key features in Raman spectra. (Online version in
colour.)
(a)
(b)
5
6
wavelength (µm)
7 8
15
10
25
JB650
JB651
JB652
JB653
JB654
JB655
JB656
JB657
JB658
JB659
JB660
0.2
reflectance
reflectance
0.4
50
(c)
0.1
0.2
carb
1.8
1
2.0
2.2
2.4
2.6
2
3
wavelength (µm)
4
2000
1600
800
1200
wavenumber (cm–1)
400
Figure 5. Reflectance spectra of the <125 µm size fraction of Lake Fryxell samples. (a) VNIR spectra from 0.35 to 5 µm showing
features owing to pyroxene, carbonate and aluminosilicates. (b) Mid-IR spectra from 5 to 50 µm showing features owing to
quartz, feldspar, pyroxene and carbonate. (c) NIR inset from 1.8 to 2.5 µm showing a H2 O band at 1.92 µm, OH features at 2.19,
2.25 and 2.34 µm, and carbonate bands near 2.3 and 2.5 µm. (Online version in colour.)
global surface areas [13] and Martian (SNC) meteorites [67]. For the purpose of comparison, K/Th
is normalized to bulk planet ratios of 2900 for Earth and 5300 for Mars, following Taylor et al. [13].
Normalized K/Th ratios for the FVB surface sediments have only a slightly wider spread, but
higher K abundances, as expected, than those for Mars. To first order, different proportions of the
source materials can explain the K/Th versus K pattern for ADV lakes: a high K/Th and high
K component, ADV granitoids, and a relatively low K/Th and K abundance component, local
Ferrar dolerite.
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Raman intensity
2000
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(a) 1500
(b)
1-feldspar
Raman intensity
+
100 µm
(c)
3
3-feldspar
500
100 µm
(d)
4-pyroxene
+
0
1200
1000
800
600
wavenumber (cm–1)
200
400
4
100 µm
Figure 6. (a) Raman spectra of mineral grains in sample 9 from Lake Vanda (JB669), (b) image of grains 1 and 2, (c) image of
grain 3, and (d) image of grain 4. Spectra are offset for clarity and lines mark key features in Raman spectra. (Online version in
colour.)
(b)
5
6
reflectance
0.6
wavelength (µm)
7 8
15
10
25 50
BKR1JB661
BKR1JB662
BKR1JB663
BKR1JB664
BKR1JB665
BKR1JB666
BKR1JB667
BKR1JB668
BKR1JB669
0.4
0.2
reflectance
(a)
(c)
0.1
0.2
1.8
2.0
1
2.2
2.4
2.6
3
2
wavelength (µm)
4
2000
1600
800
1200
wavenumber (cm–1)
400
Figure 7. Reflectance spectra of the <125 µm size fraction of Lake Vanda samples. (a) VNIR spectra from 0.35 to 5 µm showing
features owing to pyroxene, carbonate and aluminosilicates. (b) Mid-IR spectra from 5 to 50 µm showing features owing to
quartz, feldspar, pyroxene and carbonate. (c) NIR inset from 1.8 to 2.5 µm showing a broad H2 O band centred at 1.94 µm and
OH features at 2.19, 2.25 and 2.34 µm. (Online version in colour.)
4. Discussion
(a) Mineralogical trends
Quartz is identified in all ADV sediments in the XRD, Raman and mid-IR data and has the highest
abundance for the Lake Vanda samples and lowest abundance for the Lake Fryxell samples.
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1
1000
16
+
2
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(a) 1000
(b)
17
+
Raman intensity
1
100 µm
600
2-clay
(c)
3-pyroxene
400
+
3
100 µm
200
(d)
4-quartz
+
0
1200
1000
4
200
800
600
400
wavenumber (cm–1)
100 µm
Figure 8. (a) Raman spectra of mineral grains in sample 2 from Lake Brownworth (JB671), (b) image of grains 1–2, (c) image
of grain 3 and (d) image of grain 4. Spectra are offset for clarity and lines mark key features in Raman spectra. (Online version
in colour.)
(a)
(b)
5
6
25
50
0.3
JB670
JB671
JB672
JB673
0.2
0.4
(c)
0.60
reflectance
reflectance
0.6
wavelength (µm)
7 8
15
10
0.1
0.56
0.2
0.52
1.8
2.0
1
2.2
2.4
2.6
2
3
wavelength (µm)
4
2000
1600
800
1200
wavenumber (cm–1)
400
Figure 9. Reflectance spectra of the <125 µm size fraction of Lake Brownworth samples. (a) VNIR spectra from 0.35 to 5 µm
showing features owing to pyroxene and aluminosilicates. (b) Mid-IR spectra from 5 to 50 µm showing features owing to quartz,
feldspar and pyroxene. (c) NIR insert from 1.8 to 2.5 µm showing a very broad H2 O band centred at 1.92 µm with a shoulder
extending past 2.1 µm and OH features at 2.19, 2.25 and 2.34 µm. (Online version in colour.)
XRD results indicate feldspar abundance is highest in the Lake Fryxell samples and lowest in
the Lake Vanda samples. Raman spectra of feldspar grains are consistent with albite and Naand Ca-rich feldspars. VNIR spectra indicate an Fe-rich pyroxene, whereas the Raman data
indicate a monoclinic clinopyroxene form in most cases, with less orthopyroxene. XRD data are
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1-feldspar
800
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Table 5. Raman bands.
18
−1
peak positions (cm )
1-feldspar (albite + Na/Ca-feldspar)
511
2-pyroxene
670
482
293
252
209
192
175
..........................................................................................................................................................................
390
326
..........................................................................................................................................................................
3-quartz
466
209
131
..........................................................................................................................................................................
4-feldspar (albite + Na/Ca-feldspar +
517
479
455
288
278
252
197
179
160
some K-spar)
..........................................................................................................................................................................................................
LVA-9 (JB669)
1-feldspar (albite + Na/Ca-feldspar)
511
2-quartz
467
482
409
292
267
195
183
174
..........................................................................................................................................................................
409
357
268
207
133
..........................................................................................................................................................................
3-feldspar (albite + Na/Ca-feldspar +
509
483
467
406
280
211
199
182
126
quartz)
..........................................................................................................................................................................
4-clinopyroxene
1016
667
391
326
136
1-feldspar
1086
995
949
817
777
..........................................................................................................................................................................................................
LBR-2 (JB671)
513
483
..........................................................................................................................................................................
(albite + Na/Ca-feldspar)
391
2-chlorite (+orthopyroxene)
1040
324
290
207
189
167
..........................................................................................................................................................................
∼ 1000
679
667
391
667
547
198
..........................................................................................................................................................................
3- clinopyroxene
1016
326
130
..........................................................................................................................................................................
4- quartz
470
207
130
..........................................................................................................................................................................................................
consistent with augite (figure 3b) or could be attributed to a combination of two pyroxenes as
found previously for lakebottom sediments [7]. Pigeonite (Fe-rich monoclinic pyroxene) could be
present along with augite in order to produce the bulk Fe-rich pyroxene signature observed in
the VNIR spectra. NIR and Raman data are consistent with a minor amount of chlorite, especially
in the Lake Brownworth samples. The spectral features from both datasets fall in between the
peak positions for chamosite (Fe2+ -rich) and clinochlore (Mg-rich) suggesting that the chlorite is
an Fe2+ /Mg-chlorite. NIR spectra of the Lake Fryxell samples are also consistent with a small
presence of actinolite. The NIR and mid-IR carbonate features present in spectra of the samples
collected around Lake Fryxell are characteristic of calcite. The weak NIR bands at 1.92 and
2.19 µm in spectra of most of the samples are attributed to a small amount of the amorphous
aluminosilicate allophane, which is an indicator of immature volcanic soils [69].
The weak NIR calcite bands are in line with inorganic carbon concentrations between 0.1
and 0.2 wt%. The highest inorganic C levels are found in the lakeshore sediment samples from
Lake Fryxell (JB651–JB655) and also the surface sediments JB650 and JB660. The wt% inorganic C
follows the trend: JB653 > JB650 > JB652, JB654 > JB651 > JB660 > JB655. The 3.98 µm calcite band
is strongest in spectra of samples JB650–JB654 and JB660, which is consistent with the elemental
trends. A calcite band is also observed in the Lake Vanda sediment JB669 spectrum (figure 7a)
corresponding to 0.07 wt% inorganic C (table 3). The rest of the Lake Vanda sediments and all of
the Lake Brownworth sediments have very low inorganic C levels (less than 0.02 wt%) and do not
exhibit calcite spectral features.
(b) Organic material
The highest organic C levels are found in the sediment samples collected from the surface of
the ice from Lake Fryxell. The wt% organic C follows the trend: JB650 > JB658 > JB659 > JB660 >
JB657 > JB656. The CH-stretching bands at 3.3–3.5 µm (figure 5a) follow this same trend, and
the chlorophyll bands are strongest for samples JB650, JB660 and JB658. This suggests that
the organic C is largely present as saturated hydrocarbons and that photosynthetic microbes
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sample
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1.2
19
C total
Lake Fryxell
TIC
abundance (%)
0.8
0.6
0.4
0.2
Lake Vanda
Lake
Brownworth
JB
6
JB 50
6
JB 51
65
JB 2
6
JB 53
65
JB 4
6
JB 55
65
JB 6
6
JB 57
65
JB 8
6
JB 59
6
JB 60
66
JB 1
6
JB 62
66
JB 3
6
JB 64
66
JB 5
6
JB 66
66
JB 7
6
JB 68
6
JB 69
67
JB 0
6
JB 71
6
JB 72
67
3
0
sample number
Figure 10. Weight percentage abundance of total carbon (C total), total organic carbon (TOC), and total inorganic carbon (TIC)
in the FVB sediments. Carbon abundance patterns are different for each lake. Lake Fryxell samples show the highest organic
carbon abundance. (Online version in colour.)
0.6
Lake Fryxell
0.5
S total
S SO4
S other
abundance (%)
0.4
0.3
0.2
0.1
Lake Vanda
Lake
Brownworth
JB
6
JB 50
6
JB 51
65
JB 2
6
JB 53
65
JB 4
6
JB 55
65
JB 6
6
JB 57
65
JB 8
6
JB 59
6
JB 60
66
JB 1
6
JB 62
66
JB 3
6
JB 64
66
JB 5
6
JB 66
66
JB 7
6
JB 68
6
JB 69
67
JB 0
6
JB 71
6
JB 72
67
3
0
sample number
Figure 11. Weight percentage abundance of sulfur in the FVB sediments. The S values are divided into total sulfur (S total),
sulfate (S SO4 ) and S present in other compounds (S other). Sulfur and/or sulfate abundance is low as expected for the ADV
samples in this study, except for JB650 (Lake Fryxell). (Online version in colour.)
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20
4
2
0
103
2
3
4
5
6 7 8 9
104
K (ppm)
2
3
4
5
6
Figure 12. K/Th ratios and K abundances (ppm) for ADV lake and surface sediments (circles, tables 2–4 and [24]) and their
source rocks (triangles, [51,65,66]) and nearby soils (squares, [65]), MOGRS regional averages (diamonds, [13]) and Martian
(SNC) meteorites (diamonds, [67]). K/Th is normalized to bulk planet ratios of 2900 for Earth and 5300 for Mars, following Taylor
et al. [13]. (Online version in colour.)
are present in some but not all of these environments. Spectral features owing to chlorophyll
have been observed previously in the lakebottom mats in both the oxic and anoxic regions of
Lake Hoare [25,70]. Neither a chlorophyll band nor clear CH vibrations were observed for the
lakeshore sediments from Lake Fryxell, nor the sediments from Lakes Vanda and Brownworth,
which correlates well with the low organic C values for these samples. Weak CH vibrations were
observed for samples with organic C approaching 0.1 wt%.
(c) Trends in elemental abundances
K/Th and Al/Ti ratios indicate local sources such as the Ferrar dolerite and ADV granitoids as
the provenance of our sediments. Typical terrestrial weathering conditions fractionate (mobile)
K from Th, creating a trend to lower K/Th as a function of weathering grade. Normalized
K/Th ratios for several surface sediments studied exhibit a range of 0–2 and high K abundances
(figure 12). The lower K/Th ratios (table 3) for the Lake Vanda sediments are correlated with a
higher quartz content, whereas the slightly elevated K/Th ratios (table 2) for the Lake Fryxell
sediments are correlated with more feldspar, clays and calcite. ADV granitoids exhibit an even
wider range of normalized K/Th ratios (approx. 0–8) and higher K abundances, whereas ADV
Ferrar dolerites exhibit normalized K/Th ratios on a par with our sediments but much lower K
abundances. These data are consistent with a preference of physical over chemical weathering
processes for our sediments. Additional K/Th values are provided for comparison with Martian
meteorites [67] and Martian orbital data [13], which both represent lower K abundances than
our sediments, but a similar spread in normalized K/Th ratios. Interestingly, the K abundances
of lakebottom sediments from the ADV are similar to those of our surface sediments and the
normalized K/Th ratios cluster similarly, but some K/Th ratios are elevated for the lakebottom
sediments (figure 12).
.........................................................
6
Lake Hoare bottom sediments, Taylor V. [T.] (Bishop et al. [24])
Lakes Fryxell [T], Vanda and Brownworth, Wright V.
Barton Peninsula soils (Lee et al. [65])
MOGRS global and regional avarages (Taylor et al. [13])
selected Martian meteorites (Lodders [67])
Antarctic Dry Valley granitoids/basement (Allibone et al. [51])
Antarctic Dry Valley Ferrar dolerites (e.g. Morrison et al. [66])
Barton Peninsula source rocks (Lee et al. [65])
Hawaii basalt reference suite (Basaltic Volcanism Study Project 1981)
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K/Th normalized to K/Th = 2900 (Earth)
or to K/Th = 5300 (Mars)
8
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80
50
40
ADV source rock averages
basement
lower beacon
Ferrar dolerite
McMurdo volcanic group
Lashley formation
30
CIA
48.7
64.6
42.4
33.9 and 43
63.7
(Al2O3/TiO2)molar
17.6
18.6
15.0
2.8 and 8.7
18.8
20
10
20
30
(Al2O3 /TiO2)molar
40
50
60
Figure 13. Chemical index of alteration (CIA) versus molar oxide ratio of Al/Ti for sediments from FVB. For comparison potential
source rock data (triangles, [51,65,66]) and Lake Hoare bottom sediment data (circles, [24]), a Prospect Mesa Core (circles, [2])
and Barton Peninsula soils data (squares, [65]) are included. V, valley; Is., island. ADV source rock average geochemistry (box,
lower right) is adapted from Roser & Pyne [68] and Krissek & Kyle [46]. (Online version in colour.)
The CIA can be used to assess weathering processes in ADV soils and sediments [46,47,49,50]
by comparing CIAs of source rock material with those of soils and sediments. The CIA is based
on the mobility of the major elements Al, Ca, Na and K. Fresh basalts have a CIA of about 30–
45, while completely weathered clays such as kaolinite have a CIA of 100. The CIA values are
compared with molar Al2 O3 /TiO2 ratios for our surface sediments (figure 13) together with data
from other sediments, soils and source rocks from the region. The CIAs for our sediments from
FVB are low, especially for samples higher in sulfate. Our results for ADV surface sediments
show that mixing of source materials is dominating the alteration process, while leaving open
the option of isochemical weathering. Some of the classical molecular major element weathering
and pedogenesis ratios and indices can be applied to the ADV samples, as well as to Martian
rock and soil data from the MER, but only a few of these can be applied to Martian orbital
MOGRS data. Sheldon & Tabor [47] provide a summary of quantitative methods addressing
weathering, including the application of Al/Si and Ti/Al molar ratios. The CIA values for the
surface sediments in this study are similar to those of lakebottom sediments and soil pits from
previous studies (figure 13), but are distinct from the CIA values of the Barton Peninsula soils
from King George Island, West Antarctica [65]. This is consistent with more limited chemical
weathering in the arid environment of the ADV samples compared with those from the less arid
environment of the Barton Peninsula.
5. Implications for Mars
This study evaluates several techniques for characterization of minerals, organic material and
evidence of microbial activity in ADV sediments as potential analogues for the cold, arid
environment on Mars. Here, we seek to determine if chemical alteration or microbial activity
is taking place in the sediments near the lakes and on top of the ice cover in the ADV. We
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70
chemical index of alteration (CIA)
21
Lake Hoare bottom sediments - Taylor V. (Bishop et al. [24])
Lakes Fryxell - Taylor V., Vanda and Brownworth - Wright V. (Englert et al. [29])
Prospect Mesa Core - Wright V. (Gibson et al. [2])
Barton Peninsula soils - King George ls. (Lee et al. [65])
Antarctic Dry Valley granitoids/basement (Allibone et al. [51])
Antarctic Dry Valley Ferrar dolerite (e.g. Morrison et al. [66])
Barton Peninsula source rocks - King George ls. (Lee et al. [65])
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and Life’ that partially enabled these analyses. Thanks are due to Brandy Anglen who collected sample LFRA and to W. Hine who provided the image of Lake Brownworth. We are grateful to D. Mader (University of
Vienna) for assistance with the INAA work, and to the staff of the Atominstitut (Vienna) for the irradiations.
We also thank T. Hiroi at Brown University’s RELAB for assistance with the reflectance spectra used in the
study and J. W. Garcia and G. J. Taylor of the Hawaii Institute of Geophysics and Planetology for support of
the XRD work.
References
1. Bishop JL, Anglen BL, Pratt LM, Edwards HGM, Des Marais DJ, Doran PT. 2003 A
spectroscopy and isotope study of sediments from the Antarctic Dry Valleys as analogs for
potential paleolakes on Mars. Int. J. Astrobiol. 2, 273–287. (doi:10.1017/S1473550403001654)
2. Gibson EK, Wentworth SJ, McKay DS. 1983 Chemical weathering and diagenesis of a cold
desert soil from Wright Valley, Antarctica: an analog of Martian weathering processes.
J. Geophys. Res. 88, A912–A928. (doi:10.1029/JB088iS02p0A912)
3. Flamini E, Ori GG, di Pippo S, Osinski GR. 2009 Exploring Mars and its terrestrial analogues.
Planet. Space Sci. 57, 509. (doi:10.1016/j.pss.2009.02.004)
.........................................................
Acknowledgements. We are grateful to the Helmholz Foundation and the research alliance ‘Planetary Evolution
22
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20140198
used XRD, Raman spectroscopy and reflectance spectroscopy to identify and characterize the
mineralogy of these sediments. We used VNIR reflectance spectra to characterize chlorophyll
bands in the sediments and to identify CH vibrations owing to organic material. Elemental trends
are coordinated with the observed mineralogy and ratios of selected elements were used for
assessing the degree of alteration in the sediments.
Previous studies of lakebottom sediments have shown that biologic activity was responsible
for sulfide formation [1] and that photosynthetic pigments were present in organic mats
[25,70]. Raman spectra of these lakebottom sediments revealed the presence of pyrite deposits
approximately 5 µm in diameter on quartz grains. These were not observed in this study of
surface sediments on top of and at the edges of ADV lakes, although photosynthetic pigments
and elevated organic carbon levels were observed in sediments collected from the ice surface on
top of the lakes.
We have used both normalized K/Th ratios and the CIA approach to evaluate the relationships
between the ADV sediments, soils and rocks with rocks and soils from Gusev Crater and
Meridiani on Mars. Taylor et al. [13] investigated terrestrial and MOGRS abundances of K and
Th and the relation to terrestrial CIAs for neutral and acidic environments, including submarine
and hydrothermal alteration conditions, in order to assess general regional and global weathering
on Mars. MOGRS K/Th ratios vary from 0.64 to 1.66. The SNC meteorite K/Th ratio range is
somewhat lower. MOGRS K abundance data form a cluster at about 3000 ppm [13]. SNC meteorite
K abundance data are very low and overlap with the MOGRS range only in a few instances.
Based on the ADV provenance model, a major contribution to Mars soil development processes
could be explained by mixing of several basic source materials. However, the counterpart to
the role that ADV granitoids play for FVB samples, a component with relatively high K/Th
ratios and K abundances, is missing on Mars. The small spread of K/Th ratios across the Mars
surface observed by MOGRS can be explained by igneous processes and physical weathering
and does not require the presence of aqueous alteration to explain the observed variations. The
CIAs of Martian rocks and soils are low, similar to the ADV data, indicating that little chemical
weathering or predominantly isochemical weathering has taken place, probably in an acidic and
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measure trace elements. Finding new elemental relationships that work in analogues and can be
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extent of water-based alteration derived from indicators in the Martian surface.
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