Controls on Cyclic Formation of Quaternary Early Diagenetic Dolomite

The origin of sedimentary dolomite and the factors that control its formation within the geological record remain speculative. In most models, dolomite formation is linked to evaporative conditions, high water temperature, increasing Mg/Ca ratio, increasing alkalinity, and high amounts of biomass. Here we challenge these archetypal views, by documenting a case example of Quaternary dolomite which formed in Lake Van at constantly low temperature (<4°C) and without direct control of the latter conditions. Dolomite occurs within highstand sediments related to suborbital climate variability (Dansgaard‐Oeschger cycles). We propose that dolomite precipitation is a product of a microbially influenced process, triggered by ecological stress, resulting from reventilation of the water‐sediment interface. Independently from the validity of this hypothesis, our results call for a reevaluation of the paleoenvironmental conditions often invoked for early diagenetic dolomite‐rich intervals within sedimentary sequences and for caution when interpreting time series of subrecent lacustrine carbonates

Similarities and differences in the dolomitization history of two coeval Middle Triassic carbonate platforms, Balaton Highland, Hungary

Dolomitization of platform carbonates is commonly the result of multiphase processes. Documentation of the complex dolomitization history is difficult if completely dolomitized sections are studied. Two Middle Anisian sections representing two coeval carbonate platforms were investigated and compared in the present study. Both sections are made up of meter-scale peritidal–lagoonal cycles with significant pedogenic overprint. One of the sections contains non-dolomitized, partially dolomitized, and completely dolomitized intervals, whereas the other is completely dolomitized. Based on investigations of the partially dolomitized section, penecontemporaneous dolomite formation and/or very early post-depositional dolomitization were identified in various lithofacies types. In shallow subtidal facies, porphyrotopic dolomite was found preferentially in microbial micritic fabrics. Microbially induced dolomite precipitation and/or progressive replacement of carbonate sediments could be interpreted for stromatolites. Cryptocrystalline to very finely crystalline dolomite, probably of pedogenic origin, was encountered in paleosoil horizons. Fabric-destructive dolomite commonly found below these horizons was likely formed via reflux of evaporated seawater. As a result of the different paleogeographic settings of the two platforms, their shallow-burial conditions were significantly different. One of the studied sections was located at the basinward platform margin where pervasive fabric-retentive dolomitization took place in a shallow-burial setting, probably via thermal convection. In contrast, in the area of the other, smaller platform shallow-water carbonates were covered by basinal deposits, preventing fluid circulation and accordingly pervasive shallow-burial dolomitization. In the intermediate to deep burial zone, recrystallization of partially dolomitized limestone and occlusion of newly opened fractures and pores by coarsely crystalline dolomite took place

Synthetic topography from the decameter to the centimeter scale on Mars for scientific and rover operations of the ESA-Roscosmos ExoMars mission

The ESA-Roscosmos ExoMars platform and rover mission will have complex interactions with the martian surface. In order to plan and perform landing, roving and scientific operations, the morphological characteristics of the terrain surrounding the rover need to be characterized from the decameter to the centimeter spatial scale. The smallest possible features currently identifiable are typically >0.75 m in size, corresponding to three times the ground sampling resolution of the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO). We have developed a synthetic topography with a ground sampling resolution of 0.01 m by integrating 1) a modeled topography of small-scale topographic features (e.g., rocks) into 2) a 0.25 m resolution digital elevation model (DTM) built by applying stereo and shape-from-shading techniques to HiRISE data. The modeled topography of small-scale topographic features is based on the extrapolation of the abundance and spatial distribution pattern of geological features measurable in HiRISE data. We determined that the cumulative fractional area covered by relief, i.e., float blocks and ridged outcrops, over the entire Oxia Planum landing site spans the range 0-30% with a mean abundance of relief of 7 +/- 5%. The synthetic topography can be used for highly realistic environment simulations and rover drive planning. Artificial rover camera images produced with the synthetic topography incorporate orbital-based geomorphological units and can be used for improved planning and analyses of actual rover images

Coastal uplift rate at Matanzas (Cuba) inferred from MIS5e phreatic overgrowths on speleothems

Many morphological elements in Cuba's landscape (e.g. marine terraces, tidal notches) demonstrate that coastal uplift has taken place, but the rate at which this occurs is not known. Carbonate phreatic overgrowths on speleothems have been found in a cave in Central North Cuba, ~1\ua0km from the present coastline at 16\ua0m asl. They form exceptional and unique mushroom-shaped speleothems and balconies decorating the walls of the rooms. These phreatic overgrowths on speleothems (POS) formed at the oscillating air\u2013water interface in sea-level controlled anchialine lakes. U/Th dating of these overgrowths suggests ages that are compatible with the Marine Isotope Stage 5e (i.e. 130\u2013115\ua0ka). These POS have fixed this sea-level highstand and demonstrate that this part of Cuba has been subjected to a much lower uplift rate than previously reported, that is, less than 0.1\ua0mm/year since the last interglacial

ExoFiT: ExoMars-Like Field Trials – a Mission Simulation.

International audienceHere, we focus on the ExoMars-Like Field Trial (ExoFiT), a series of realistic mission simulations based on the ESA ExoMars rover mission slated to be launched in 2020. The mission will carry a suite of instruments to carry out its mission objectives focused on geological and exobiological researc