Analogue Sites for Mars Missions (2011)
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THE GYPSUMVILLE – LAKE ST. MARTIN IMPACT STRUCTURE: SHOCKED
CARBONATES, INTRACRATER EVAPORITES, AND CRYPTOENDOLITHS. E. A.
Cloutis1, G. Berard1, P. Mann1, and J. Stromberg1. 1Department of Geography,
University of Winnipeg, 515 Portage Ave., Winnipeg, MB, Canada R3B 2E9,
e.cloutis@uwinnipeg.ca.
Introduction: The Lake St. Martin (LSM) impact structure is an ~40 km impact
structure approximately 200 Ma in age located in central Manitoba, Canada [1-4]. The
impact occurred in ~200-400 m of Ordovician and Devonian sandstones, shales, and
carbonates overlying Archaean-aged granite [1]. Outcrops are sparse in the area, but
include uplifted, unshocked granites, shocked granites and pseudotachylites of the
central uplift, and intracrater red beds and gypsum/anhydrite deposits exposed by open
pit mining operations.
The red beds include a wide variety of poorly sorted clasts including impact melts and
shocked granites, and shock-melted carbonates. An open pit gypsum mine in the area
(Gypsumville) has exposed a continuous ~5 km long section of gypsum/anhydrite
deposits, of up to 15 m vertical exposure (Fig. 1). Exploratory drilling in the area
indicates that these beds range in thickness up to at least 30 m [3, 5].
The Ca-sulfates in the area consist largely of gypsum and anhydrite, with minor
glauberite [3, 5], and occasional interbedded clays. Grain sizes and bed morphologies
are highly variable, ranging from multi-cm selenite crystals to cryptocrystalline,
saccharoid-textured dense layers. The gypsum beds grade laterally and abruptly into
poorly sorted red beds that contain a variety of clasts, including gypsum, impact melt,
shocked granite, and impact-melted carbonates (Fig. 2).
This site provides an accessible example of intracrater evaporites. Exposed gypsum
faces exhibit a variety of weathering textures (Fig. 3), drag folds due to the movement of
glacial ice [6], and cryptoendoliths located at depth (>1-2 cm) in gypsum boulders (Fig.
4) [7]. This site has some similarities to Columbus crater on Mars, which exhibits
interbedded gypsum-phyllosilicates with complex folding [8].
Mission Description: Gypsum-bearing terrains are not included in the four candidate
MSL landing sites. However, Eberswalde, Gale, and Holden craters will all sample
presumed intracrater sediments. Gypsum-bearing terrains may be targets for future
(Mars 2018) campaigns. The LSM site can be used to:
1. determine how well mineralogically-unique clasts in red bed (poorly sorted clastic
sediments) deposits can be distinguished;
2. determine whether shocked and unshocked carbonates are spectrally
distinguishable;
3. determine how and whether cryptoendoliths can be detected in sulfate-rich
environments.
Science Merit Related to Mission Objectives: The LSM site provides access to
intracrater sediments and evaporites, impact melts, different shocked and unshocked
Analogue Sites for Mars Missions (2011)
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lithologies (carbonates, granites), and gypsum-hosted cryptoendoliths. Exposures of
these materials are all located within 20 km of each other at LSM. The age of the impact
is ~200 Ma; the age of the intracrater deposits is less well known, but likely immediately
post-dates the impact [1-5]. Results from previous and ongoing work are helping to
better define its various Mars-relevant characteristics. Available imagery for the site is
limited to Landsat and aerial photographs.
Given the presence of microbial activity at the site and the diversity of rock types and
terrains, it is relevant to the exploration goals of determining if life ever arose on Mars
(MEPAG Goal I; Objectives A and B), the history of climate on Mars (Goal II; Objectives
B and C), and evolution of the surface (Goal III, Objective A)
[http://marsoweb.nas.nasa.gov/landingsites/].
Most Important Question Answered by Site: This analogue site can help us address
the conditions necessary for cryptoendoliths survival in Ca-sulfate deposits and how
their detection can best be undertaken.
Logistic and Environmental Constraints: The LSM site is located ~2 hours by road
from Winnipeg, MB by paved road. Access to various sites within the area is largely by
an all-weather gravel road. The majority of the sites are located on Crown land and no
permits are required for site access. Mined areas and bedrock exposures are free of
vegetation.
Standard Information Required for Analogue Sites: A regional map, and images
from the gypsum and red bed quarries, and cryptoendolith-bearing gypsum boulders are
shown below.
Table 1: Table of characteristics of Lake St. Martin analogue site.
Site Name
Lake St. Martin Impact Structure
Center Coordinates
51° 46’ 13”N 98° 38’ 06” W
Elevation
258 m
Areal Extent
~40 km by 40 km
Prime Science Questions
Detection of cryptoendoliths
Characteristics of intracrater evaporite deposits,
shocked/unshocked carbonates
Distance from nearest road
0 – 2 km
Environmental
Max temp: 18°C. Min temp: -18°C.
characteristics
Precipitation: 53 cm. Vegetation coverage: None in
areas of interest
Previous studies at site
References 1-7 (see below)
Primary Landing Site Target
Columbus crater
References: [1] Grieve R.A.F. (2006) In: Impact Structures in Canada; Geo. Assoc.
Canada. [2] Currie K.L. (1970) Nature, 226, 839-841. [3] Bannatyne B.B. (1959)
Gypsum-Anhydrite Deposits of Manitoba. MB Dept. Mines Natur. Res. Publ. 58-2. [4]
Simonds C.H. and McGee P.E. (1979) Proc. 10th LPSC, 2493-2518. [5] McCabe H.R.
and Bannatyne B.B. (1970) Lake St. Martin Crypto-Explosion Crater and Geology of the
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Surrounding Area. MB Dept. Mines Natur. Res. Geol. Pap 3/70. [6] Wardlaw N.C. et al.
(1969) Cdn. J. Earth Sci., 6, 577-593. [7] Stromberg J. et al. (2011) LPSC, 42, abstract
#2170. [8] Wray J.J et al. (2009) LPSC, 40, abstract #1896.
Figure 1. Upper left: geological map of Lake St. Martin impact structure (from ref. 5).
Upper right: slab of red bed deposit. Lower left: wall of gypsum quarry with minor iron
oxide staining. Lower right: broken surface of gypsum boulder showing cryptodendolith
layers (blue-green). Rock is ~20 cm across and original exposed surface is to the upper
right (arrows).