Search

A synthesis of deformation patterns within and around the Thaumasia Plateau, Mars, points to a new interpretation for regional deformation and the origin of Valles Marineris and associated outflow channels. The morphology of the Thaumasia Plateau is typical of thin-skinned deformation, akin to a 'mega-slide,' in which extensional deformation in Syria Planum and Noctis Labyrinthus connects via lateral zones of transtension and strike-slip--Claritas Fossae and Valles Marineris--to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the Coprates Rise and Thaumasia Highlands. However, the low regional slope (~1[degrees]) results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the Tharsis volcanic province. Instead, we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and/ or mixtures of salts, ice, and basaltic debris would allow for weak detachments and large-scale gravity spreading. We propose that the generally linear chasmata of Valles Marineris reflect extension, collapse, and excavation along fractures radial to Tharsis, either forming or reactivated as part of one lateral margin of the Thaumasia gravity-spreading system. The other, dextral, lateral margin is a massive splay of extensional faults forming the Claritas Fossae, which resembles a trailing extensional imbricate fan. The compressional mountain belt defined by the Coprates Rise and Thaumasia Highlands forms the toe of the 'mega-slide.' Topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below Syria Planum that could have provided further thermal energy and topographic potential for initiating regional deformation, either intrusively through inflation or extrusively through lava flow and/or ash fall emplacement. Higher heat flow during Noachian time, or geothermal heating due to burial by Tharsis-derived volcanic rocks, would have contributed to flow of salt deposits, as well as formation of groundwater from melting ice and dewatering of hydrous salts. We further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of Echus, Coprates, and Juventae chasmata at relatively uniform source elevations along the northern margin of the 'mega-slide,' where regional groundwater flow would have been directed toward the surface. Our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the Tharsis volcanic province, deformation of the Thaumasia Plateau, and the formation of Valles Marineris and associated outflow channels. Keywords: Mars, salts, sulfates, salt tectonics, Thaumasia, Valles Marineris, gravity spreading, volcanic plume, outflow channels.

Widespread quartz pseudomorphs after evaporitic minerals are interbedded with stromatolites in 2.2 Ga sedimentary rocks in the Yerrida rift basin of Western Australia. These deposits preserve diverse original crystal morphologies that grew displacively either as individuals or as clusters within stromatolitic horizons and associated fine-grained siliciclastic beds. The stromatolites were deposited in shallow-marine, restricted enviroments. Although evaporitic minerals are largely replaced by quartz, their crystal shapes include lenticular, rosette, needle, and nodular forms, suggesting that they formed from calcium sulfate-rich brines. Textures suggest that replacement by quartz occurred during early alteration of the sediments. Original calcium sulfate minerals such as gypsum or anhydrite are indicated by the morphologies of the pseudomorphs; this concept is supported by anhydrite inclusions in the quartz crystals that form the pseudomorphs, and this finding indicates that calcium sulfate existed in Early Proterozoic sedimentary environments.

A revised stratigraphic framework for the Messinian succession of Cyprus is proposed demonstrating that the three-stage model for the Messinian salinity crisis recently established for the Western Mediterranean also applies to the Eastern Mediterranean, at least for its marginal basins. This analysis is based on a multidisciplinary study of the Messinian evaporites and associated deposits exposed in the Polemi, Pissouri, Maroni/Psematismenos and Mesaoria basins. Here, we document for the first time that the base of the unit usually referred to the 'Lower Evaporites' in Cyprus does not actually correspond to the onset of the Messinian salinity crisis. The basal surface of this unit rather corresponds to a regional-scale unconformity, locally associated with an angular discordance, and is related to the erosion and resedimentation of primary evaporites deposited during the first stage of the Messinian salinity crisis. This evidence suggests that the 'Lower Evaporites' of the southern basins of Cyprus actually belong to the second stage of the Messinian salinity crisis; they can be thus ascribed to the Resedimented Lower Gypsum unit that was deposited between 5.6 and 5.5 Ma and is possibly coeval to the halite deposited in the northern Mesaoria basin. Primary, in situ evaporites of the first stage of the Messinian salinity crisis were not preserved in Cyprus basins. Conversely, shallow-water primary evaporites deposited during the third stage of the Messinian salinity crisis are well preserved; these deposits can be regarded as the equivalent of the Upper Gypsum of Sicily. Our study documents that the Messinian stratigraphy shows many similarities between the Western and Eastern Mediterranean marginal basins, implying a common and likely coeval development of the Messinian salinity crisis. This could be reflected also in intermediate and deep-water basins; we infer that the Lower Evaporites seismic unit in the deep Eastern Mediterranean basins could well be mainly composed of clastic evaporites and that its base could correspond to the Messinian erosional surface. [ABSTRACT FROM AUTHOR]

Studies the depositional environments of Upper Miocene evaporite deposits in the Sicilian Basin. Range of evaporitic sedimentary deposits that are developed under a wide variety of hypersaline conditions; Analysis of key issues of interest; Implications on sedimentology.

Studies the depositional environments of Upper Miocene evaporites of Sicily as determined from analysis of intercalated carbonates. Four basic kinds of limestone discovered; Evidence supporting the contention that three of the four kinds of carbonate must have formed close to or above sea level.

Reports that detrital particles were found as a sand-silt layer in a deep-sea Messinian Stage salt deposit in the Mediterranean Basin. Examples of the particles found; Syndepositional reworking of exposed Messinian evaporites.