Petrographic study and geochemical investigation of the evaporites associated with the Germik Formation (Siirt Basin, Turkey)

Evaporites of the Oligocene Germik Formation are represented by massive, laminated, laminated-banded, banded, nodular and/or brecciated nodular and nodular-banded lithofacies in the Siirt-Kurtalan area. Observations of massive and laminated-banded gypsums with undulated-shaped stromatolitic algal mats, corrugated folded structures and clay-carbonate and interlayered marl in laminated gypsum levels are very important in terms of their mechanisms of occurrences. Petrographic and mineralogic examinations of secondary gypsums in the Germik Formation generally display alabastrine and porphyroblastic textures with corroded anhydrite. Structures as satin-spar, chickenwire, enterolithic and minerals as dolomite, calcite and celestite are also observed. Geochemical evaluations of gypsum and anhydrite samples belong to the lithofacies have provided an approach of their original formation and understandings the environmental impacts (such as pH, paleotemperature, paleosalinity, surface-groundwater activity and bacterial activity). Therefore, a number of analyses were conducted on the different samples for major and trace elements and the gypsum-anhydrite samples were analyzed for isotope compositions. Trace elements of these evaporites were found to be in the range of the geochemical values of the depositional environment of shallow marine evaporites. These values show also occasional influx of terrestrial waters to the environment. Moreover, the differences in the isotopic values of the lithofacies identified by the stable isotopic studies indicate the effects of temperature, salinity, biogenic activity and diagenetic processes for the formation of evaporites, under the influence of climate. Geochemical evolution of gypsum and anhydrite lithofacies of the Germik Formation leads up to muddy evaporites indicating that they were deposited in the coastal sabkha or shallow marine environments within effectively developed paleoclimatic conditions, tectonic activities, diagenetic processes and depositional system

Marine Geosciences: A Short, Eclectic, and Weighted Historic Account

Marine geosciences are covering all phenomena and processes related to the formations of shallow shelf seas and of the deep ocean. They draw on modern dynamics of seafloor and sediment formation, marine geophysics and tectonics, volcanology, geochemistry, microbiology, biology, and paleontology of marine organisms. They are of great economic importance because of the wealth of nonliving marine resources

The role of calcification in carbonate compensation

The long-term recovery of the oceans from present and past acidification is possible due to neutralization by the dissolution of biogenic CaCO3 in bottom sediments, that is, carbonate compensation. However, such chemical compensation is unable to account for all features of past acidification events, such as the enhanced accumulation of CaCO3 at deeper depths after acidification. This overdeepening of CaCO3 accumulation led to the idea that an increased supply of alkalinity to the oceans, via amplified weathering of continental rocks, must accompany chemical compensation. Here we discuss an alternative: that changes to calcification, a biological process dependent on environmental conditions, can enhance and modify chemical compensation and account for overdeepening. Using a simplified ocean box model with both constant and variable calcification, we show that even modest drops in calcification can lead to appreciable long-term alkalinity build-up in the oceans and, thus, create overdeepening; we term this latter effect biological compensation. The chemical and biological manifestations of compensation differ in terms of controls, timing and effects, which we illustrate with model results. To better predict oceanic evolution during the Anthropocene and improve the interpretation of the palaeoceanographic record, it is necessary to better understand biological compensation