Akademik Veri Yönetim Sistemi
SEDIMENTOLOGY, cilt.66, sa.7, ss.2627-2660, 2019 (SCI-Expanded)
Ancient evaporite deposits are geological archives of depositional environments characterized by a long-term negative precipitation balance and bear evidence for global ocean element mass balance calculations. Here, Cretaceous selenite pseudomorphs from western Anatolia ('Rosetta Marble') - characterized by their exceptional morphological preservation - and their 'marine' geochemical signatures are described and interpreted in a process-oriented context. These rocks recorded Late Cretaceous high-pressure/low-temperature, subduction-related metamorphism with peak conditions of 1 center dot 0 to 1 center dot 2 GPa and 300 to 400 degrees C. Metre-scale, rock-forming radiating rods, now present as fibrous calcite marble, clearly point to selenitic gypsum as the precursor mineral. Stratigraphic successions are recorded along a reconstructed proximal to distal transect. The cyclical alternation of selenite beds and radiolarian ribbon-bedded cherts in the distal portions are interpreted as a two type of seawater system. During arid intervals, shallow marine brines cascaded downward into basinal settings and induced precipitation. During more humid times, upwelling-induced radiolarian blooms caused the deposition of radiolarite facies. Interestingly, there is no comparable depositional setting known from the Cenozoic world. Meta-selenite geochemical data (delta C-13, delta O-18 and Sr-87/Sr-86) plot within the range of reconstructed middle Cretaceous seawater signatures. Possible sources for the C-13-enriched (mean 2 center dot 2 parts per thousand) values include methanogenesis, gas hydrates and cold seep fluid exhalation. Spatially resolved component-specific analysis of a rock slab displays isotopic variances between meta-selenite crystals (mean delta C-13 2 center dot 2 parts per thousand) and host matrix (mean delta C-13 1 center dot 3 parts per thousand). The Cretaceous evaporite-pseudomorphs of Anatolia represent a basin wide event coeval with the Aptian evaporites of the Proto-Atlantic and the pseudomorphs share many attributes, including lateral distribution of 600 km and stratigraphic thickness of 1 center dot 5 to 2 center dot 0 km, with the evaporites formed during the younger Messinian salinity crisis. The Rosetta Marble of Anatolia may represent the best-preserved selenite pseudomorphs worldwide and have a clear potential to act as a template for the study of meta-selenite in deep time.