Hypersaline Deposits Research Articles

Trace fossils of hypersaline environment and its implication in identifying tidal inundation boundary in Great Rann of Kachchh, Western India

Extreme hypersaline environments are known to be challenging ecosystems for the survival of organisms. These extreme environments are characterized by high evaporation, resulting in a drastic reduction in the ichnological and bioturbational diversity. Moreover, such environments are poorly understood on account of limited documentation in rock records. The Great Rann of Kachchh forms an exclusive salt-encrusted geomorphic facet and is India’s most extensive exposure to hypersaline deposits. The area is inundated by tidal ingress from the Arabian Sea during the monsoon, followed by an evaporative period. Moreover, tidal ingress in the Rann of Kachchh and its effect on the ecology ispoorly documented. Ichnological investigations of the hypersaline Great Rann of Kachchh revealed four recurring trace fossils, Arenicolites, Palaeophycus, Polykladichnus, and Skolithos, with annelids, and crustaceans as the most likely producers. Furthermore, the existence of their juvenile forms is indicated by the presence of small and tiny subsurface burrows. Hence, in the present research, we used ichnology to document the limit and mechanism of tidal ingress to demarcate the tidal inundation boundary up to the east of Khadir Island. We propose a hypothesis identifying the tidal inundation limit by larval recruits burrows and present an ichnological model for a hypersaline environment.

Molecular preservation in halite‐ and perchlorate‐rich hypersaline subsurface deposits in the Salar Grande basin (Atacama Desert, Chile): Implications for the search for molecular biomarkers on Mars

AbstractSimilarities between the Atacama Desert (Chile) and Mars include extreme aridity, highly oxidizing chemistry, and intense ultraviolet radiation that promoted the photochemical production of perchlorates and nitrates. Concentration of these ions under hyperarid conditions led to the formation of nitrate‐ and perchlorate‐bearing deposits in ephemeral lakes, followed by later deposition of chlorides and sulfates. At some locations, such as the Salar Grande, hypersaline deposits have remained unaltered for millions of years. We conducted a drilling campaign in deposits of the Salar to characterize the preservation state of biological molecules. A 5 m deep discontinuous core was recovered and subjected to multitechnique analysis including the antibody microarray‐based biosensor LDChip300 and the SOLID (Signs Of Life Detector) instrument, complemented by geophysical, mineralogical, geochemical, and molecular analysis. We identified two units based on the mineralogy: the upper one, from the surface to ~320 cm depth characterized by a predominance of halite and anhydrite, and the lower one, from 320 to 520 cm, with a drop in halite and anhydrite and an enrichment in nitrate and perchlorate. Organic compounds including biomolecules were detected in association with the different depositional and mineralogical units, demonstrating the high capacity for molecular preservation. Hypersaline environments preserve biomolecules over geologically significant timescales; therefore, salt‐bearing materials should be high‐priority targets for the search for evidence of life on Mars.

Study of Hypersaline Deposits and Analysis of Their Signature in Airborne and Spaceborne SAR Data: Example of Death Valley, California

Field measurements of dielectric properties of hypersaline deposits were realized over an arid site located in Death Valley, CA. The dielectric constant of salt and water mixtures is usually high but can show large variations, depending on the considered salt. We confirmed values observed on the field with laboratory measurements and used these results to model both the amplitude and phase behaviors of the synthetic aperture radar (SAR) signal at C- and L-bands. Our analytical simulations allow reproducing specific copolar signatures observed in both Airborne SAR (AIRSAR) and Spaceborne Imaging Radar (SIR-C) data, corresponding to the saltpan of the Cottonball Basin. More precisely, the main objective of the present paper is to understand the influence of soil salinity as a function of soil moisture on the dielectric constant of soils and then on the backscattering coefficients recorded by airborne and spaceborne SAR systems. We also propose the copolarized backscattering ratio and phase difference as indicators of moistened and salt-affected soils. More precisely, we show that these copolar indicators should allow monitoring of the seasonal variations of the dielectric properties of saline deposits at both C- and L-bands. Because of the frequency dependence of the ionic conductivity, we also show that L-band SAR systems should be efficient tools for detecting both soil moisture and salinity, while C-band SAR systems are more suitable for the monitoring of soil moisture only. Through the study of terrestrial evaporitic environments by means of spaceborne SAR systems, our results could also be of great interest for defining future planetary missions, particularly for the exploration of Mars.

The first mayfly from the Lower Cretaceous of southern England (Insecta: Ephemerida= Ephemeroptera)

The first mayfly from the British Cretaceous, Durlophlebia radleyi gen. et sp. nov., is described on the basis of a subimaginal hind wing from the Berriasian Purbeck Limestone Group of Dorset, UK. Its presence in hypersaline deposits in the Lulworth Formation indicates that there were also fresher water bodies in the region at that time.

Isotopically heavy carbon in the C 21 to C 25 regular isoprenoids in halite-rich deposits from the Sdom Formation, Dead Sea Basin, Israel

A series of Miocene/Pliocene halite deposits (with extremely low organic carbon contents) from the Sdom Formation (Dead Sea Basin, Israel) have been studied. Distributions and δ 13C contents of biomarkers have been determined using GC–MS and irm-GCMS analyses, respectively. The hydrocarbon fractions consist mainly of pristane, phytane and C 21 to C 25 regular isoprenoids. The predominance of C 21+ regular isoprenoids in the Dead Sea halites and other hypersaline deposits indicate that these components could be derived from ether-bound membrane lipids of halophilic archaea. The lack of intact ether-bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis. Their δ 13C contents are enriched in 13C, by up to 7‰, compared to the biomarkers of presumed phytoplanktonic origin (i.e. steranes and hopanes) within the same sediment sample, in agreement with a source other than algae and cyanobacteria, thus, tentatively assigned as halophilic archaea. Based on biomarker distributions, δ 13C contents and mineral compositions, these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine. Continual evaporation and deposition of the higher salts (i.e. carnallites) are favourable conditions for the growth of halophilic archaeal communities.

Reefs and Reef Environments: ABSTRACT

Reefs are considered as largely unbedded or obscurely bedded, massive structures which are composed of solid, organically bound, in situ organisms, and which were at least potentially wave-resistant structures that rose topographically above the surrounding depositional surface. Reefs are somewhat unusual and quantitatively minor features in the geologic record, but they have received considerable attention because of their economic importance, biologic uniqueness, or distinctive facies relations. Any model for recognition of reefs in the geologic record must allow for considerable variation in relief, size, shape, biologic composition, and facies relations. They are associated commonly with normal marine environments, but the associated complex may span from freshwater to hypersaline deposits or from euxinic to well-oxygenated conditions. Relief and shape depend on several factors, principally the comparative rate of subsidence and growth, direction of prevailing currents, structural relation, and organic composition. Size and shape commonly are discernible, but demonstration of depositional relief is difficult in many places. Textures of single outcrops, hand specimens, or thin sections, may be diagnostic of at least potential if the massive, bound relations of organisms are apparent, but commonly additional criteria are necessary. Recognition of biologic and lithologic facies relations are critical in investigation of and associated environments in the geologic record. The term reef has been applied loosely to several structures by different workers. Locally, it has been used for merely a faunal association, even though the organisms are present as loose, discrete fragments and the rocks in which they occur are evenly bedded in moderately thin layers. The term also has been applied to carbonate lenses in noncarbonate sequences, even though these lenses are of bedded, unbound detritus, oolites, or crinoid columnals. It also has been applied to sheetlike deposits of in situ corals or algal crusts or other reef-associated organisms even though the deposit is widespread, thin, and with no demonstrable topographic expression. Massive tumbled blocks also have been considered to be reefs, particularly if the blocks are abundantly fossiliferous and occur n distinctly more thinly bedded rocks. The term reef also has been applied to large carbonate structures which may be truly of origin at their margins, but which are composed mainly of bedded, clastic debris. End_of_Article - Last_Page 738------------