MARS ANALOG SOILS IN THE ATACAMA DESERT, CHILE. B. Sutter1, J. Owen2, and R. Amundson2.
1
SETI Institute, MS 245-3 NASA Ames, Moffett Field, CA 94035, bsutter@mail.arc.nasa.gov 2 Div. Ecosystem
Sci., UC Berkeley, Berkeley, CA 94720.
0
50
Soil Depth (cm)
Introduction: The Atacama Desert of
northern Chile is one of the driest deserts on Earth
where precipitation levels occur on the order of 2-3
mm decade-1-[1]. Soils in the hyperaird Atacama
accumulate salts (e.g., sulfates, chloride) in
concentrations detected on Mars. The Atacama
climate is relatively wetter than Mars, yet the
transient nature of aqueous activity in the Atacama
may mimic transient aqueous activity (e.g.,
percolating snow melt) that may have existed on a
paleo-Mars. The objective of this work is to assess
the amounts and distributions of sulfate, chloride,
nitrate, and carbonate bearing Atacama soils. Results
from this work will be used to assist the
understanding of formation of salty soils on Mars.
Materials and Methods: Three soils were
sampled in the arid core of the Atacama Desert; one
near Cerro Buenos Aires (24o43.7´S; 69o42´W) and
two others near the abandoned mining town of
Catalina (25o12.7´S; 69o.41.9´W). The Catalina soils
occurred at the top (Catalina Summit) and the base of
the same hill (Catalina Base). The Buenos Aires soil
occurs at the top of a small hill, as well. Soil
sampling depths ranged from 40 to 400 cm. All soils
developed on basalt lava flows. Eolian inputs may
also supply parent material. Total chemical analyses
of soils along with mineralogical identification by Xray diffraction were conducted on all soils.
Results and Discussion: Basalt mineralogy
consisted of plagioclase feldspar and pyroxene
(augite). A minor amount of quartz was present and
is likely of hydrothermal origin. All soils have high
levels of sulfate mostly as gypsum (up to 20 wt% S)
(Fig. 1). Atacama S concentration at the surface is
relatively low, increases to a maximum, and then
decreases with depth (Fig. 1). A similar S distribution
occurs at Endurance crater where S concentration is ~
3  10  7 wt.% S along the surface  Tennessee
 Mackenzie transect, respectively [2]. Similarities
of S distributions between Atacama soils and
Endurance crater suggest pedogenic redistribution of
deposited S in Mars soils may be a viable hypothesis.
Unlike the other soils, the Catalina Base soil
possesses significant amounts of anhydrite (CaSO4),
thenardite (Na2SO4), glauberite [Na2Ca(SO4)], blodite
[Na2Mg(SO4)2•4H2O] and has the highest levels of
nitrate (1.6 wt%) and chlorine (0.5 wt%) relative to
the other soils (0.01 wt% Cl and NO3). Receiving
material from the summit and slope, the Catalina
Base soil is deeper (~400cm) than the Catalina
Summit soil (~40cm). Accumulation of nitrate,
100
150
Catalina Sum
200
Catalina Bas e
250
Buenos Aires
300
350
400
0
10
20
t. % S
Fig. 1. Sulfur concentrationw(wt.
% S) versus depth
(cm).
chloride and Na-sulfate salts in the Catalina Base soil
may be the result of mass wasting and leaching
processes. A thicker soil would have the additional
effect of inhibiting subsequent aqueous activity from
leaching these salts from the profile.
The Buenos Aires soil resides at the top of a
small hill, but is 130 cm deep. The concentrations of
chloride and nitrate are much less than the Catalina
Base soil and no Na-sulfate was detected. The
Buenos Aires soil has the highest carbonate
concentration (1.1 wt% CO3) relative to the other
soils (<0.55 wt% CO3). The lack of Na-sulfates, low
NO3 and Cl and higher CO3 concentrations suggests
that the Buenos Aires soil is exposed to more
aqueous activity than the Catalina soils.
Alternatively, the carbonates may not be authigenic,
but eolian derived. However, if carbonate had an
eolian origin, then carbonate would be expected to
occur at Catalina. Soil micromorphological
investigations will assess the origin of the carbonate
material. The phyllosilicate mineralogy is being
examined to determine if phyllosilicates are
authigenic or eolian derived, as well.
Atacama soils possess salts that occur at
levels found on Mars. Pedogenic processes may
explain S distributions as function of depth on Mars.
Mass wasting processes on Mars may concentrate
salts (e.g., chlorides, nitrates, sodium sulfates) at the
bases of Martian hills. The Atacama carbonate
concentrations are below the detection limit of
instruments deployed to Mars. If the levels of
aqueous activity in the Atacama are similar to paleoMars levels, then carbonate may be present, albeit
below the detection limits of current Mars
instrumentation.
References: [1] Ericksen, GE (1981) Geo. Surv. Pro.
Paper 1188. [2] Clark, BC (2005) EPSL 240,73