**SULFUR CYCLING IN GYPSUM DUNES FROM NEW MEXICO -- TERRESTRIAL ANALOGS
TO SULFATE-EOLIAN DEPOSITION AND EARLY DIAGENESIS ON MARS.**
**PRELIMINARY RESULTS.**

A. Szynkiewicz^1^, L.M. Pratt^1^ and M. Glamoclija^1^, ^1^ Indiana
University (Department of Geological Sciences, 1001 East 10^th^ Street,
Bloomington, IN 47405-1405, <aszynkie@indiana.edu>,
<prattl@indiana.edu>, <mglamocl@indiana.edu>).

**Results and discussion:**

SULFUR SOURCE: the main sulfur reservoir for gypsum deposits in the
studied Salt Basins consist mainly of Permian evaporites extending from
Central New Mexico to North Mexico. Dissolution of these Permian
evaporites (average δ^34^S = 11.7 ‰) significantly influences a
high-sulfate content and its δ^34^S value in surface and groundwaters of
that region. A general increase of δ^34^S values in gypsum dunes with
increasing latitude (Fig. 1) evidences that bacterial sulfate reduction
might have controlled the sulfate isotope composition of evaporative
crusts. That process is still common in Estancia and easily recognized
in recent groundwater playa lakes systems (Fig. 1). We propose that the
different latitudinal localizations of Estancia, Tularosa and
Trans-Pecos have involved a diverse microbial community and organic
matter input related to varied climate conditions during last glaciation
in the North America.

+-----------------------------------------------------------------------+
| ![](media/image1.png){width="5.992361111111111in"                     |
| height="4.476388888888889in"}                                         |
|                                                                       |
| Fig. 1. Latitudinal variation in δ^34^S for eolian deposits compared  |
| to δ^34^S of sulfate in recent surface and groundwater system from    |
| Estancia, Tularosa and Trans-Pecos.                                   |
+-----------------------------------------------------------------------+

DUNES FORMATION: A detailed spatial analysis of δ^34^S in dunes taken
from White Sands National Monument and the selected points north of TB
has shown wide and neat variations similar to the source area,
consisting of lakebeds and large selenite crystals exposed in the
southern and western edges of Lake Lucero (Fig. 2). Important
differences in δ^34^S of gypsum dunes from different localities suggest
that they have formed from different evaporative crust during several
eolian episodes due to variation in aridity and the exposure rates of
the source area for surface weathering.

+-----------------------------------------------------------------------+
| ![](media/image2.png){width="5.992361111111111in"                     |
| height="4.502083333333333in"}                                         |
|                                                                       |
| Fig. 2. Variation in δ^34^S value for gypsum eolian deposits and      |
| their source area in White Sands National Monument.                   |
+-----------------------------------------------------------------------+

CLIMATE FINGERPRINT: Good agreement between δD values in gypsum dunes
and δD values of modern precipitation in New Mexico and East Chihuahua
shows that eolian deposits preserve information about hydrogen isotope
composition of water/fluids as a source solution for formation of
evaporative crust from which the dunes may form (Fig. 3).

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| ![](media/image3.png){width="5.992361111111111in"                     |
| height="4.5159722222222225in"}                                        |
|                                                                       |
| Fig. 3. Variation in δD for gypsum eolian deposits from Estancia,     |
| Tularosa (White Sands dunes), Trans-Pecos (Guadalupe dunes) and North |
| Mexico (Cuatro Ciènegas). The ranges of δD for precipitation in New   |
| Mexico and Chihuahua East were taken from Meehan et al. (2004).       |
+-----------------------------------------------------------------------+

MAGMATIC/HYDROTHERMAL SIGNATURE: the sulfur isotope analysis of
individual lenticular gypsum grains and aggregates, carried out along 6
m long profile of lakebeds exposed north of Tularosa, show excursions to
negative values; in Event 1, up to -1.08 ‰, occurred around 30,000 years
ago and Event 2, up to 0.85 ‰, around 20,000 years ago (Fig. 4). Both,
bacterial oxidation and/or magmatic/hydrothermal input may cause the
negative shift in δ^34^S value.

A recent magmatic input of H~2~S may be traced in the northern part of
the Rio Grande Rift. The 3-mile long Sulfur Creek in Valles Caldera is
fed by acid-sulfate hot springs originates from exhalation of H~2~S-rich
gases and differs importantly in δ^34^S(SO~4~) value, from 2.25 to 2.65
‰, compared to other hot springs that preserve the signature of Permian
evaporates dissolution (δ^34^S from 8.87 to 13.14 ‰).

+-----------------------------------------------------------------------+
| ![](media/image4.wmf)                                                 |
|                                                                       |
| Fig. 4. Variation in δ^34^S value for gypsum lake sediments from the  |
| North Tularosa Basin. The range of δ^34^S value for Permian           |
| evaporates was taken from Leslie et al. (1997). Sediment samples and  |
| their age were provided by Bruce Allen working on unrelated project   |
| in the Tularosa Basin.                                                |
+-----------------------------------------------------------------------+

**CONCLUSIONS:** Our preliminary results showing that sulfate eolian
deposits from the Salt Basins associated with the Rio Grande Rift
evolution are competitive places for astrobiologocal constrains, climate
and sulfur studies in order to better understand Martian sulfur cycle
and climate evolution.

**Acknowledgments:** This study was supported by the NASA Astrobiology
Institute team award directed by L.M. Pratt. Sincerest thanks are due to
Bruce Allen for recommending field sites and providing gypsum sediments
from the North Tularosa Basin, to the National Park Service for allowing
access to the White Sands National Monument (WSNM) and Guadalupe
Mountains National Park (GMNP), to David Bustos for field assistance in
WSNM, to Fred Armstrong and Gordon Bell for field assistance in GMNP and
to Marta Kurasiewicz for helping in preparation of some samples for
sulfur isotope analysis.

**References:** \[1\] Fishbaugh K.E. et al. (2006) *LPSC XXXVII,*
Abstract#1642. \[2\] Hynek B.M. (2004) *Nature,* 43*,* 156-159.
\[3\] Knoll G.H. et al. (2005) E*PSL, 240, 179-189*. \[4\] Fishbaugh
K.E. and Head J.W. (2005) *Icarus,* 174, 444-474. \[5\] Olsen et al.
(1987) *Tectonophys, 143, 119-139*. \[6\] Langford R.P. (2003) *Quatern
Internat, 104, 31-39*. \[7\] Allen B.D. (2005) *New Mexico Museum of
Natural History and Science, Bulletin 28, p. 107-114*. \[8\] Allen B.D.
(1991) *New Mexico Bureau of Mines and Mineral Resources 137, 166-171*.
\[9\] Schenk C.J. and Fryberger S.G. (1988) *Sedimen Geol 55, 109-120*.

Leslie et al. (1997) *Sedimentary Geology, 110, 223-235*, Meehan et al.
(2004) *Isotopes in Environmental and Health Studies, 40, 291-300*.