Ancient Lake Research Articles

Gillnets selectivity and effectivity for controlling invasive fish species in Lake Matano, South Sulawesi

Lake Matano is one of the ancient lakes in East Luwu Regency, South Sulawesi, which has uniqueness and high endemicity for freshwater fishes. The presence of invasive alien fishes there can threaten the existence of endemic fishes. This study aimed to investigate the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the population of invasive alien fishes in Lake Matano, South Sulawesi. Sampling was conducted in May, October, November 2015 and February, July, November 2016 using monofilament experimental gillnets with various mesh sizes (0.75, 1.0, 1.5, 2.0, 2.5, 3.0 inches) and yarn thickness (D = 0.15, 0.20, 0.25 mm). The mesh size of 1.5, 2.0, and 2.5 inches could catch flowerhorn cichlid as the dominant and invasive alien fish with little chance to catch native fishes in Lake Matano. The selectivity factor (SF) for the mesh size of 1.5, 2.0, and 2.5 inches was 3.02. The average catch size of flowerhorn cichlid captured by the mesh size of 1.5. 2.0, and 2.5 inches were 11.5, 15.3, and 19.2 cm, respectively. The yarn diameter did not significantly affect flowerhorn cichlid capture (P <0.05). However, the mesh size of 1.5 inches was significantly different (P>0.05) to other mesh sizes. For effectiveness, gillnet was better to operate in littoral areas of lakes, especially in the location associated with the sand substrate with macrophytes. The operation of the gillnet in Lake Matano needs to be regulated in terms of location and setting time to minimize the capture of fish species other than flowerhorn cichlid.

A Mars helicopter preps for launch: The first drone to fly on another planet will hitch a ride on NASA's Perseverance rover - [News

If ever there was life on Mars, NASA's Perseverance rover should be able to find signs of it. The rover, scheduled to launch from Kennedy Space Center, in Florida, in late July or early August, is designed to drill through rocks in an ancient lake bed and examine them for biosignatures, extract oxygen from the atmosphere, and collect soil samples that might someday be returned to Earth.

Microsatellite design for species delimitation and insights into ploidy for the Lake Baikal Cladophoraceae species flock

ABSTRACT Ancient lakes are centres of adaptive radiation and speciation. The Cladophoraceae endemic to ancient Lake Baikal is a morphologically diverse group nested within Rhizoclonium that may represent a case of sympatric speciation. Recent research using ribosomal DNA markers indicates that these taxa form a monophyletic group but was not able to resolve boundaries between all of the investigated morphospecies due to very low genetic diversity. For this reason, a population genetics approach using more variable markers was investigated. In this study, we developed a set of microsatellites (SSRs) using high-throughput sequencing (HTS) data obtained from three morphospecies of Cladophoraceae from Lake Baikal. To increase amplification rate of the microsatellites across taxa, we performed an in silico cross-validation step comparing the microsatellites retrieved from three HTS datasets and tested the most promising loci on 14 of the mostly endemic morphospecies. We obtained 11 SSRs that cross-amplified among morphospecies, eight SSRs in 12 taxa and three in only four taxa. Our results showed that most loci had more than two alleles, but also displayed variation between and within morphospecies. These results indicate that this group may have gone through polyploidisation. Polyploid systems require a different approach from standard population genetic analyses. We produced ‘allelic phenotypes’ (presence/absence matrices) to analyse genetic diversity. We showed that similarity indices mostly grouped morphospecies, suggesting that this scoring method will be useful in species delimitation, but further work is needed to elucidate the speciation process in this algal species flock in Lake Baikal.

Noteworthy Four Ancient Lakes in Gujarat

There are many ancient lakes in India. State of most today is poor today. They are filled up over a period by earth/garbage under pretext of “development” by people/authorities. This paper is describing 4 of those in Gujarat. They have been in existence since centuries and have been in often in religious/folk references. Munsar lake at Viramgam is big lake and does get fully filled up during rains while dries up later. It has religious-social-literature connection. Sahastraling Lake in Patan corresponds to very important and outstanding era in history of Gujarat. Said lake is one of few monuments built contemporary to it e.g. Raniki Vaav which is world heritage site. Kundvav at Kapadvanj is similarly important but ignored lake. Surprisingly it has intricately carved stone Toran which has remained unique tradition in Gujarat. Malav Talav at Dholaka has similar lake again with famous king Siddhraj Jaysinh. All 4 lakes stated herewith has remained in constant historical significance and carries potential to go at national tourist map also provided they get due attention.

How ancient is Lake Lugu (Yunnan, China)? The gastropods’ viewpoint with focus on Radix (Lymnaeidae)

Lake Lugu has been termed an “ancient lake” in several publications. Ancient lakes, such as Baikal or Tanganyika have in common an age of several million years and an outstanding biodiversity and rate of endemism. Lake Lugu’s age is unknown, however, and has been inferred from the presumed Pliocene increased tectonic activity on the Yunnan-Guizhou Plateau. The lake was thus considered to be of tectonic origin, but supporting studies do not exist. Here we report and describe seven endemic species. The endemic gastropod Gyraulus luguhuensis exhibits an aberrant pseudo-dextral shell morphology, which is predominantly known from undisputed ancient lakes. To better understand the origin of the lake and of its biodiversity, we present a preliminary geological study, which shows that Lake Lugu is a tectonic-solution lake. During a survey of the aquatic habitats up to 21 gastropod morphospecies could be differentiated macro-morphologically. An aberrant neritid-like Radix was genetically studied for the first time. The genetic data suggest that Lugu-Radix, typical and neritid shell shapes, constitute a clade, comprising four possibly endemic evolutionary lineages, which potentially represent four different species. The molecular-clock approach indicates a Late Pliocene to Early Pleistocene origin of the clade, which we consider the minimum age of Lake Lugu. Our study reveals that the biodiversity in general and that of gastropods in particular is significantly higher than previously known. Against this background and considering the co-occurrence of aberrant Gyraulus and Radix with an evolutionary history of more than two million years, Lugu is putatively an ancient lake.

Evolutionary History and Diversity of Unionoid Mussels (Mollusca: Bivalvia) in the Japanese Archipelago

The evolutionary history and diversity of unionoid mussels in East Asia need to be clarified and would shed light on the formation process of the unique fauna of Japan. Unionoid mussels (Mollusca: Bivalvia) are unique models for understanding the process by which organisms have diversified before and after the formation of the Japanese archipelago. Unionoid mussels have poor dispersal ability, so it is thought that they would have been strongly influenced by the archipelago’s formation. Therefore, the speciation and diversification processes of mussels before and after the archipelago’s formation were investigated by analyzing the nuclear and mitochondrial DNA of a wide range of species, particularly those inhabiting East Asia. The evolutionary history and divergence time of these mussels were examined. Unionoid mussels were found to have higher endemicity than other freshwater organisms. Although most of the endemic unionoid mussels of Japan are likely to have diverged before the formation of the Japanese archipelago, some other Japanese unionoid mussel species, including species endemic to Lake Biwa, an ancient lake in Japan, potentially diverged after the Japanese archipelago began to separate from the continent. This suggest that adaptation to the unique habitat of the ancient lake has caused diversification in the mussels endemic to it.

Microorganisms of Lake Baikal-the deepest and most ancient lake on Earth.

Lake Baikal (Russia) is the largest (by volume) and deepest lake on Earth. The lake remains relatively pristine due to the low population density around its basin. Being very distant from any marine water body but having a remarkable number of similarities to oceans (depth, oxygen content, oligotrophy) provides a unique model of pelagic microbiota that is submitted to marine-like conditions minus the salt content of the water. It is also a model of lakes located at high latitudes and submitted to yearly ice cover (from January to April). The analysis by different approaches has indeed provided a view of the microbiota of this lake. It contains novel microbes that are closely related to marine groups not known to be present in freshwater like Chloroflexi or Pelagibacter. The deep water mass contains large communities of chemolithotrophs that use ammonia generated in the photic zone or methane from the sediments. KEY POINTS: • The chemical composition and limnic features of the deepest lake on Earth determine the vital activity of microorganisms. • The diversity, ecology, and role of individual taxa of microorganisms were studied using cultivation and molecular methods. • Data of large metagenomic datasets in the epipelagic and bathypelagic layers of the water column in southern Baikal were discussed.

ON NIGHTTIME VERTICAL MIGRATIONS OF AMPHIPODS IN LAKE LADOGA

Daily vertical migrations (DVM) of amphipods is a widespread phenomenon both in rivers and lakes, and in seas. The leader among freshwater bodies in terms of the number of amphipod species and the intensity of DVM is the ancient Lake Baikal. Lake Ladoga is also inhabited by several species of these crustaceans, and some of them are invaders from Lake Baikal. Therefore, the aim of this study was to check whether amphipods in Lake Ladoga perform nighttime vertical migrations. To test this assumption, we used a combination of video equipment (a video system consisting of a metal frame, a GoPro 4 video camera, 3 lighting elements, and an iButton temperature logger), a plankton net, and a bottom grab. Co-application of these methods did detect vertical nighttime migrations in amphipods in Lake Ladoga, but their intensity was extremely low and they were observed only in invasive species from Lake Baikal, Gmelinoides fasciatus and Micruropus possolskii . A comparison of depth-specific intensities of vertical nighttime migrations revealed no significant variation. In addition to amphipods, the nighttime migrants community in Lake Ladoga includes representatives of such groups as fish, chironomids, water bugs, opossum shrimps, and predatory cladocera Leptodora kindtii (Focke, 1844) .

Clumped isotope constraints on changes in latest Pleistocene hydroclimate in the northwestern Great Basin: Lake Surprise, California

AbstractDuring the Last Glacial Maximum (LGM) and subsequent deglaciation, the Great Basin in the southwestern United States was covered by numerous extensive closed-basin lakes, in stark contrast with the predominately arid climate observed today. This transition from lakes in the Late Pleistocene to modern aridity implies large changes in the regional water balance. Whether these changes were driven by increased precipitation rates due to changes in atmospheric dynamics, decreased evaporation rates resulting from temperature depression and summer insolation changes, or some combination of the two remains uncertain. The factors contributing to these large-scale changes in hydroclimate are critical to resolve, given that this region is poised to undergo future anthropogenic-forced climate changes with large uncertainties in model simulations for the 21st century. Furthermore, there are ambiguous constraints on the magnitude and even the sign of changes in key hydroclimate variables between the Last Glacial Maximum and the present day in both proxy reconstructions and climate model analyses of the region. Here we report thermodynamically derived estimates of changes in temperature, precipitation, and evaporation rates, as well as the isotopic composition of lake water, using clumped isotope data from an ancient lake in the northwestern Great Basin, Lake Surprise (California). Compared to modern climate, mean annual air temperature at Lake Surprise was 4.7 °C lower during the Last Glacial Maximum, with decreased evaporation rates and similar precipitation rates to modern. During the mid-deglacial period, the growth of Lake Surprise implied that the lake hydrologic budget briefly departed from steady state. Our reconstructions indicate that this growth took place rapidly, while the subsequent lake regression took place over several thousand years. Using models for precipitation and evaporation constrained from clumped isotope results, we determine that the disappearance of Lake Surprise coincided with a moderate increase in lake temperature, along with increasing evaporation rates outpacing increasing precipitation rates. Concomitant analysis of proxy data and climate model simulations for the Last Glacial Maximum are used to provide a robust means to understand past climate change, and by extension, predict how current hydroclimates may respond to expected future climate forcings. We suggest that an expansion of this analysis to more basins across a larger spatial scale could provide valuable insight into proposed climate forcings, and aid in climate model process depiction. Ultimately, our analysis highlights the importance of temperature-driven evaporation as a mechanism for lake growth and retreat in this region.

Earthquake-induced liquefaction features in a late Quaternary fine-grained lacustrine succession (Fucino Lake, Italy): Implications for microzonation studies

The Fucino lacustrine basin in central Italy is a large flat area mostly devoted to agriculture, with urbanization along the perimeter of the ancient lake. In 1915 a strong earthquake struck the area (Mw 7.0), producing large damages and geological effects, including surface faulting, ground failures and liquefaction. A channel excavated in the lacustrine sediments exposed ground failure, with dykes of fine-grained sediment that we interpret as the result of earthquake-induced liquefaction. We present the results of a multidisciplinary work aimed at characterizing in detail the geology of the buried stratigraphic succession, its susceptibility to liquefaction and the likely source of the fine-grained liquefied material. The succession down to 20 m deep is formed by fine-grained sediments younger than ~170–180 kyrs (mostly Late Pleistocene - Holocene), prevailingly silt or silt-clay mixtures.The geological field analysis indicates that the dykes are filled by prevailing silt, liquefied and transported by upward-directed flow of short duration, as for earthquake-induced liquefaction. Tilting and lateral spreading accompanied the process. The overall liquefaction potential derived from the “simplified methods” is high. Correlations of X-Ray Powder Diffraction mineralogy of samples from drilling cores with those from dykes allowed us to identify the most likely source layer filling dykes, corresponding to a silt layer at 7–8 m depths. This layer and the dykes lack illite and montmorillonite clay particles.These results contribute to improve studies of liquefactions in sediments that differ from typical liquefiable loose sands. They have also implications for microzonation studies. Most samples show grain-size curves that do not fit within the field of potentially liquefiable soils, suggesting that criteria based on grain-size can be poorly significant in seismic microzonation studies of recent (Late Pleistocene-Holocene) lacustrine, fine-grained successions.

Tracing the Origin of Planktonic Protists in an Ancient Lake.

Ancient lakes are among the most interesting models for evolution studies because their biodiversity is the result of a complex combination of migration and speciation. Here, we investigate the origin of single celled planktonic eukaryotes from the oldest lake in the world—Lake Baikal (Russia). By using 18S rDNA metabarcoding, we recovered 1414 Operational Taxonomic Units (OTUs) belonging to protists populating surface waters (1–50 m) and representing pico/nano-sized cells. The recovered communities resembled other lacustrine freshwater assemblages found elsewhere, especially the taxonomically unclassified protists. However, our results suggest that a fraction of Baikal protists could belong to glacial relicts and have close relationships with marine/brackish species. Moreover, our results suggest that rapid radiation may have occurred among some protist taxa, partially mirroring what was already shown for multicellular organisms in Lake Baikal. We found 16% of the OTUs belonging to potential species flocks in Stramenopiles, Alveolata, Opisthokonta, Archaeplastida, Rhizaria, and Hacrobia. Putative flocks predominated in Chrysophytes, which are highly diverse in Lake Baikal. Also, the 18S rDNA of a number of species (7% of the total) differed >10% from other known sequences. These taxa as well as those belonging to the flocks may be endemic to Lake Baikal. Overall, our study points to novel diversity of planktonic protists in Lake Baikal, some of which may have emerged in situ after evolutionary diversification.

Platebaikalia - a new monoraphid diatom genus from ancient Lake Baikal with comments on the genus Platessa

A new monoraphid diatom genus, Platebaikalia gen. nov., was described based on a detailed morphological investigation using light and scanning electron microscopy. Previously Platessa elegans Kulikovskiy et Lange-Bertalot was described from ancient Lake Baikal, and this species serves as the generitype for the newly-described genus. Platebaikalia elegans is a rare taxon found in the deeper parts of Lake Baikal. Platebaikalia elegans is characterized by having multiseriate striae on the raphe valves with biseriate striae on the rapheless valves, though in some specimens a short third row of areolae may be present in some striae. Morphology of striae is helpful to distinguish the genus Platebaikalia from Platessa and other monoraphid genera. Other morphological features that differentiate our new genus from other monoraphid taxa are discussed. We review the morphological data on Platessa species, and based on these data can recognize eight groups of taxa in the genus. Our analysis shows that Platessa as currently circumscribed may contain groups of species that are quite different from one another morphologically, and possibly includes taxa that could be recognized as different at the genus level. A few new combinations are suggested when taxa from the genus Platessa transferred to genera Psammothidium and Planothidium. Some problems of taxonomy of monoraphid taxa are discussed and we believe that taxonomy of this group of diatoms is in need of special attention in future.

Hydrocarbon accumulation patterns of salt crust covered biogenic gas reservoirs in the Sanhu Depression, Qaidam Basin

Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin, where the largest domestic biogenic gas production base has been built up. In recent years, however, the exploration of biogenic gas there encounters a variety of difficulties, such as the identification of true and false seismic abnormality, the determination of micro-relief structure and the identification and description of lithologic traps, which are the bottlenecks restricting its exploration breakthrough. In this paper, hydrocarbon accumulation patterns of biogenic gas were studied. Then, based on fine structure interpretation results, combined with laboratory experiments, the sealing capacity, distribution range, formation time and genesis of salt crust were discussed, and the salt crust covered hydrocarbon accumulation pattern of biogenic gas was put forward. Finally, combined with the conditions of source rocks and reservoirs, the exploration prospect of salt crust covered biogenic gas reservoirs was predicted. And the following research results were obtained. First, the Quaternary in the Sanhu Depression is composed of sandstone–mudstone interbeds of shore-shallow lake facies, with superior conditions of source rocks and reservoirs. Many source–reservoir–caprock assemblages are vertically formed. The biogenic gas has the characteristics of dynamic hydrocarbon accumulation, i.e., continuous migration, accumulation, diffusion and re-accumulation. Second, under the effect of Himalayan movement, the climate changes frequently and the salinity of the ancient lake is zoned in the Sanhu Depression. A freshwater area is formed at the inlet of the river in the south and a brine area is formed in the north. Under the influence of evaporation, the phreatic water in the north is salinized continuously, and a set of extensively distributed salt crust with steady thickness and a strong sealing capacity is formed at the eastern part of Lingjian fault. Third, the biogenic gas generated by dark mudstone of lacustrine facies in the depression center migrates laterally and vertically to Lingjian fault zone and gets accumulated under the sealing of salt crust. In conclusion, high-quality source rocks and reservoirs and the salt crust with a strong sealing capacity in the Sanhu Depression constitute a good spatial–temporal configuration relationship of source rocks, reservoirs and cap rocks, so salt crust covered biogenic gas reservoirs can be formed to provide abundant natural gas resources with a broad exploration prospect.

History, mass loss, structure, and dynamic behavior of the Antarctic Ice Sheet.

Antarctica contains most of Earth's fresh water stored in two large ice sheets. The more stable East Antarctic Ice Sheet is larger and older, rests on higher topography, and hides entire mountain ranges and ancient lakes. The less stable West Antarctic Ice Sheet is smaller and younger and was formed on what was once a shallow sea. Recent observations made with several independent satellite measurements demonstrate that several regions of Antarctica are losing mass, flowing faster, and retreating where ice is exposed to warm ocean waters. The Antarctic contribution to sea level rise has reached ~8 millimeters since 1992. In the future, if warming ocean waters and increased surface meltwater trigger faster ice flow, sea level rise will accelerate.

Freshwater biogeography in Wallacea: The case of sphaeriid bivalves in the Malili lake system (Sulawesi, Indonesia)

Ancient lakes are renowned as freshwater hotspots of biodiversity and endemism. However, some of these water bodies are poorly studied with the minute pill clams in the genus Pisidium (family Sphaeriidae) being particularly overlooked. The Malili lake system is located on Sulawesi, which is the largest and possibly biologically most diverse Indonesian island within the biodiversity hotspot region of Wallacea. This lake system consists of 5 interconnected lakes that harbour a unique freshwater fauna including 42 mostly endemic mollusc species described to date. The only bivalves recognized in this lake system have been in the widespread genus Corbicula. We present new insights into the sphaeriid biodiversity of the ancient Malili lakes and provide the first fossil-calibrated phylogeny for this family to discuss the biogeographical history of the Wallacean Pisidium fauna including the dating of speciation events. Both morphological and molecular data suggest that the Malili lake system is inhabited by at least three Pisidium species, two of which are potentially endemic to these lakes. This diversity is probably derived from a single colonization event from the Oriental region. The fossil-calibrated phylogeny further indicates that intra-island diversification occurred well after the island was fully formed. Our study improves understanding of the overall sphaeriid biodiversity in Indonesia as well as the endemic fauna of the ancient lakes.

UNUSUAL FOSSILIFEROUS CONCRETIONS FROM LACUSTRINE DEPOSITS IN THE LOWER JURASSIC MOENAVE FORMATION IN ST. GEORGE, UTAH, USA: IMPLICATIONS FOR ANCIENT FISH MASS MORTALITIES

ABSTRACT Two types of unusual concretions with similar biotic contents but markedly different shapes and distributions were found in close stratigraphic proximity within the Lower Jurassic Whitmore Point Member of the Moenave Formation in St. George, Utah. Both types of concretions formed in lacustrine sediments and contain abundant ganoid fish scales, numerous ostracode carapaces, and apparent rip-up clasts. Elongate, cylindrical concretions developed in parallel and regularly spaced rows in one horizon, and comparatively flat and irregularly shaped and distributed concretions formed in an overlying layer only a few centimeters above. Microprobe and Raman analyses of concretion samples reveal abundant hematite in both concretions as well as groundmass minerals dominated by silica in the cylindrical concretions and dolomite in the flat concretions. The abundance of fish skeletal debris in concretions from two consecutive horizons may suggest recurring fish mass mortality in ancient Lake Dixie, the large lake that occupied the St. George area during the Early Jurassic. We propose a model for the formation of the concretions based on their shapes, distributions, and chemistry. In this model, accumulations of disarticulated fish debris were colonized and consolidated by microbial mats and shaped by oscillatory flow (in the case of the cylindrical concretions) or lack thereof (in the case of the flat concretions). Then, after burial, groundwater chemistry and possibly the metabolic activities of microorganisms led to the precipitation of minerals around and within the masses of fish material. Finally, diagenetic alteration changed the mineral makeups of the cylindrical and flat concretions into what they are today.

A comparison of benthic meiofaunal communities in the oldest European lake

The comparison of isolated stable habitats, that share major ecological parameters and organism groups, generates valuable knowledge about ecology and evolution. In this study we want to identify the most suitable habitat and organisms for comparisons. For this, we needed to study the effects of seasonality, habitat variability and diversity. Therefore, we studied the benthic meiofaunal communities in the sediment and hard substrates of Lake Ohrid’s littoral and profundal sediments as well as littoral rotifers collected monthly and seasonally between 2000 and 2010. Our results showed that, among the over two million meiobenthic organisms per square meter, nematodes dominated the profundal (mean proportion: 91%) and littoral (mean proportion: 87%) sediments; whereas, rotifers were the most abundant group in littoral periphyton (mean proportion: 64%). The community composition was very typical of each habitat-type, homogeneous in the profundal and more heterogenous in the littoral. Rotifer communities were only significantly less diverse and abundant in winter. Thus, a comparison of ancient lake nematodes living in the deep profundal is potentially quite valuable. However, littoral communities are less stable in terms of seasonality and heterogeneity.

The Blue Forest of Ancient Lake Gosiute: Sweetwater County, Wyoming

The Blue Forest of Ancient Lake Gosiute: Sweetwater County, Wyoming

Reconstructing the palaeoenvironment at the early Mesolithic site of Lake Duvensee: Ground-penetrating radar and geoarchaeology for 3D facies mapping

We investigate the landscape development of the early Mesolithic hunter-gatherer sites of Duvensee (10000–6500 cal. BCE). Based on ground-penetrating radar (GPR) and geoarchaeological drillings, we present for the first time a three-dimensional (3D) reconstruction of the palaeoenvironment of 63 ha covering subarea of the former lake during the Mesolithic. The archaeological aims were (1) to detect the location of former islands possibly hosting hunter-gatherer settlements and (2) to reconstruct the ancient landscape development for understanding prehistoric land use. The research in Duvensee lasts almost 100 years, providing vivid illustrations of early Mesolithic life. Clusters of Mesolithic camps have been found located on small sand hills that formed islands in the prehistoric lake. For this environment, we present depth maps of the three most important sedimentary facies interfaces of the ancient Lake Duvensee. Interface1 represents the transition between coarse organic sediments (peat and coarse detritus gyttja) and fine-grained organic sediments (fine detritus gyttja, calcareous gyttja), Interface2 represents the transition to the underlying clayish-loamy sediments, and Interface3 marks the top of the basal sand deposits at the lake bottom. From Interface3, we identified the location and extent of five former islands with Mesolithic camps. Stratigraphic information from the corings enabled us to create a 3D model of the spatio-temporal development of the Duvensee bog. The locations of the islands and their estimated dive-up times agree with the spatio-temporal pattern of the previous archaeological finds. The model shows where hunter-gatherers could settle and move from one island to another following the shorelines of the overgrowing lake. The 3D stratigraphic model provides growth and shrinking rates of the island and lake areas in the Mesolithic, and volumes of organic and non-organic deposited lake sediments. Besides, it provides a basis for a sustainable groundwater management needed for heritage preservation.

Grain Size Variations in the Murray Formation: Stratigraphic Evidence for Changing Depositional Environments in Gale Crater, Mars

AbstractThe lowermost exposure of the Murray formation in Gale crater, Mars, was interpreted as sediment deposited in an ancient lake based on data collected by the Curiosity rover. Constraining the stratigraphic extent and duration of this environment has important implications for the paleohydrology of Gale. Insights into early Martian environments and paleofluid flow velocity can be obtained from grain size in rocks. Visual inspection of grain size is not always available for rocks investigated at field sites on Mars due to limited image coverage. But grain sizes can also be estimated from the Gini Index Mean Score, a grain‐size proxy that uses point‐to‐point chemical variations in ChemCam Laser Induced Breakdown Spectroscopy data. New Gini Index Mean Score results indicate that the Murray formation is dominated by mudstones with grains smaller than the spatial resolution of all rover cameras. Intervals of fine to coarse sandstone also are present, some of which are verified using observations of grain size and sedimentary structures in associated images. Overall, results demonstrate that most of the Murray consists of mudstone, suggesting settling of grains from suspension in low energy depositional environments such as lakes. Some of the mudstones contain desiccation cracks indicating periods of drying with a lowering of lake water level. However, beds and lenses of cross‐bedded sandstones are common at specific intervals, suggesting episodes of fluvial and possibly eolian deposition. The persistence of lacustrine deposits interspersed with fluvial deposits suggests that liquid water was sustained on the Martian surface for tens of thousands to millions of years.