Kathleen C. Benison

Modern and Ancient Extremely Acid Saline Deposits: Terrestrial Analogs for Martian Environments?

Extremely acid (pH <1) saline lakes and groundwaters existed in the mid-Permian of the mid-continent of North America. Modern counterparts have been found in acid saline lake systems throughout southern Australia. We compare and contrast the Permian Opeche Shale of North Dakota and Nippewalla Group of Kansas to modern Australian salt lakes in southern Western Australia and in northwest Victoria. With the exception of some minor variations in pH, evaporite mineralogy, and water geochemistry, the Permian and modern systems are similar and characterized by: (1) ephemeral saline continental playas hosted by red siliciclastic sediments, (2) evaporite minerals, including abundant sulfates, (3) Al-Fe-Si-rich waters with low pH values, (4) acidophilic microbes, and (5) paucity of carbonates. The composition of these terrestrial systems is strikingly similar to compositional data returned from the martian surface. Specifically, both Earth and martian systems have high amounts of iron oxides and sulfates, and little, if any, carbonates. We propose that the modern and ancient terrestrial acid saline environments may be good analogs for possible environments on Mars.

Extremely acid Permian lakes and ground waters in North America

Evaporites hosted by red beds (red shales and sandstones), some 275–265 million years old, extend over a large area of the North American mid-continent. They were deposited in non-marine saline lakes, pans and mud-flats, settings that are typically assumed to have been alkaline. Here we use laser Raman microprobe analyses of fluid inclusions trapped in halites from these Permian deposits to argue for the existence of highly acidic (pH <1) lakes and ground waters. These extremely acidic systems may have extended over an area of 200,000 km2. Modern analogues of such systems may be natural acid lake and groundwater systems (pH ∼2–4) in southern Australia. Both the ancient and modern acid systems are characterized by closed drainage, arid climate, low acid-neutralizing capacity, and the oxidation of minerals such as pyrite to generate acidity. The discovery of widespread ancient acid lake and groundwater systems demands a re-evaluation of reconstructions of surface conditions of the past, and further investigations of the geochemistry and ecology of acid systems in general.

Sedimentology of Ancient Saline Pans: An Example from the Permian Opeche Shale, Williston Basin, North Dakota, U.S.A.

ABSTRACT The mid-Permian Opeche Shale of North Dakota consists of bedded evaporites and red-bed siliciclastics. Detailed core and petrographic study has documented sedimentary and early diagenetic features in order to develop a depositional model, and to refine paleoclimatic data and paleogeographic setting for the late Paleozoic of the U.S. midcontinent. Lithologies and sedimentary features indicate lacustrine, distal alluvial, and minor eolian deposition, subaerial exposure, and soil formation. Bedded halites consisting of chevron and cumulate crystals, dissolution surfaces and pipes, and mudcracked microcrystalline salt crusts were deposited in a saline pan dominated by flooding, evaporative concentration, and desiccation. Bedded halites containing chevron and cumulate crystals but lacking any dissolution or desiccation features formed in perennial saline lakes. Chaotic halite, composed of red mudstone and siltstone with displacive halite crystals, represents saline mudflat deposits. Red mudstone and siltstone with little or no displacive halite but with abundant cracks and root features suggest deposition in a dry mudflat. Red-bed sandstones and conglomerates, composed of poorly sorted, subrounded quartz grains cemented with halite indicate distal alluvial deposition with possible transport by ephemeral streams, sheet floods, and debris flows. Most deposition took place in halite-dominated shallow perennial and ephemeral saline lakes surrounded by saline and dry mudflats. Evaporation, desiccation, flooding, and wind played significant roles in this environment. Therefore, the Opeche evaporites and red beds are representative of an ancient saline pan system. An inland playa setting is favored as a depositional model for the Opeche Shale. The abundance of soil features and halite dominance, as well as lack of nearshore carbonates and lack of restricted marine fossils, suggest a closed-basin nonmarine setting for the mid Permian of the U.S. midcontinent.

Molecular analysis of the microbial communities of Mars analog lakes in Western Australia.

Unique, shallow interdune lakes and groundwaters with extremely low pH and high salinity exist in Australia, along with nearby lakes that possess higher pH values. These acidic hypersaline environments are possibly the best modern terrestrial analogues for past martian environments. However, no previous microbiological analyses of these lakes have been conducted. During the Australian winter of 2005, water samples were taken from several hypersaline lakes located in southern Western Australia that possessed acidic to slightly alkaline pH. These samples were subjected to molecular analysis to identify bacterial communities. DNA extraction and polymerase chain reaction (PCR) amplification of the 16S rRNA gene sequences, by using universal bacterial primers, were also performed on the samples. Extracted DNA was amplified with 1070 forward and 1392 GC-clamped reverse primers and analyzed by using denaturant gradient gel electrophoresis (DGGE). In addition, libraries were developed from DNA retrieved from four lakes, including a marginal marine neutral lake, an inland neutral lake, and two inland acid lakes, and selected clones with distinct operational taxonomic units were sequenced. The DGGE profiles and clone sequence data indicate that there are distinct, abundant, and diverse microbial populations in these Australian hypersaline environments, especially the acidic ones. These results are significant for two reasons: (1) they provide the first microbiological survey of natural acid saline lakes and (2) they hint at the possibility that there could have been a diverse microbial population in acidic hypersaline environments on Mars.

A Martian analog in Kansas: Comparing Martian strata with Permian acid saline lake deposits

An important result of the Mars Exploration Rover’s (MER) mission has been the images of sedimentary structures and diagenetic features in the Burns Formation at Meridiani Planum. Bedding, cross-bedding, ripple marks, mud cracks, displacive evaporite crystal molds, and hematite concretions are contained in these Martian strata. Together, these features are evidence of past saline groundwater and ephemeral shallow surface waters on Mars. Geochemical analyses of these Martian outcrops have established the presence of sulfates, iron oxides, and jarosite, which strongly suggests that these waters were also acidic. The same assemblage of sedimentary structures and diagenetic features is found in the salt-bearing terrestrial red sandstones and shales of the middle Permian (ca. 270 Ma) Nippewalla Group of Kansas, which were deposited in and around acid saline ephemeral lakes. These striking sedimentological and mineralogical similarities make these Permian red beds and evaporites the best-known terrestrial analog for the Martian sedimentary rocks at Meridiani Planum.

Extremely high temperatures and paleoclimate trends recorded in Permian ephemeral lake halite

Although the late Paleozoic deglaciation is arguably one of the best deep-time analogs for current and predicted climate change, quantitative paleotemperature data from this interval are generally lacking. We reconstruct extreme paleoweather conditions and paleoclimate changes from Permian Nippewalla Group (probably uppermost Leonardian/Kungurian; North America) ephemeral lake halite by using fluid inclusion homogenization temperatures to directly measure the water temperature when the halite precipitated; in these depositional settings, this is an excellent air temperature proxy. Extremely high temperatures, to 73 °C, and large diurnal temperature ranges are evidenced in the lower Nippewalla Group, suggesting conditions more extreme than anywhere on Earth today. In contrast, the upper Nippewalla Group was cooler; maximum temperature was 43 °C and diurnal temperature ranges were smaller, though even these conditions are similar to modern extremely hot environments. Comparison to prior studies suggests that these results may be indicative of regional patterns. This study represents the first pre-Quaternary high-resolution quantitative data set of extreme paleoweather and possible paleoclimate trends from fluid inclusions in halite, and provides new insight into climate change during the late Paleozoic deglaciation.

Recognizing acid lakes and groundwaters in the rock record

Abstract Permian red beds and evaporites in the midcontinent of the United States were formed and altered under the influence of extremely acidic (some with pH

Permian surface water temperatures from Nippewalla Group halite, Kansas

Primary fluid inclusions in evaporite minerals may yield significant data on local paleoclimates. This method requires initial nucleation of vapor bubbles in all liquid inclusions, followed by measurement of the temperatures at which these inclusions homogenize to liquid. This paper presents surface water paleotemperatures from primary, originally all liquid fluid inclusions in middle Permian Nippewalla Group halite from southwestern Kansas.One phase aqueous primary fluid inclusions in Nippewalla Group halite were cooled in order to nucleate vapor bubbles. Their homogenization temperatures range from 32°C to 46°C and are relatively consistent along individual chevron and cornet growth bands. These data fall within the same range as modern evaporative surface waters, suggesting that this Permian environment was relatively similar to its modern counterparts.Reproducible, consistent homogenization temperatures indicate fluid inclusions have not been altered by thermal reequilibration and that this method for determining surface water paleotemperatures is valid. The future application of this method to numerous ancient evaporites may result in a wealth of quantitative local paleoclimate data.

Could microorganisms be preserved in Mars gypsum? Insights from terrestrial examples

Could the abundant sulfate salts on Mars contain microfossils and/or viable microorganisms? Here we report a variety of microorganisms trapped both as solid inclusions and as potentially viable halophilic and acidophilic prokaryotes and eukaryotes within fluid inclusions in Mars-analog gypsum. We have documented pennate diatoms, green algae, and prokaryotes in gypsum precipitated from acid (pH 1.8–4.6) saline (5%–28% total dissolved solids) waters at Salars Gorbea and Ignorado in an active volcanic terrain in the high Andes (4000+ m) of northern Chile. These salars are strikingly similar in geology and geochemistry to Mars. We propose that this discovery should serve as a model for fossilization of possible life on Mars and may inform methodologies used in future missions to Mars. Furthermore, the potential long-term viability of microorganisms within fluid inclusions in gypsum suggests the possibility of a living, yet isolated and likely dormant, microbiological community on Mars today.

Acidophilic Halophilic Microorganisms in Fluid Inclusions in Halite from Lake Magic, Western Australia

Lake Magic is one of the most extreme of hundreds of ephemeral acid-saline lakes in southern Western Australia. It has pH as low as 1.7, salinity as high as 32% total dissolved solids, temperatures ranging from 0°C to 50°C, and an unusually complex aqueous composition. Optical petrography, UV-vis petrography, and laser Raman spectrometry were used to detect microorganisms and organic compounds within primary fluid inclusions in modern bedded halite from Lake Magic. Rare prokaryotes appear as 1-3 μm, bright cocci that fluoresce green with UV-vis illumination. Dimpled, 5-7 μm yellow spherules that fluoresce blue with UV-vis illumination are interpreted as Dunaliella algae. Yellow-orange beta-carotene crystals, globules, and coatings are characterized by orange-red fluorescence and three distinct Raman peaks. Because acid saline lakes are good Mars analogues, the documentation of prokaryotes, eukaryotes, and organic compounds preserved in the halite here has implications for the search for life on Mars. Missions to Mars should incorporate such in situ optical and chemical examination of martian evaporites for possible microorganisms and/or organic compounds in fluid inclusions.