The middle Cretaceous was a period of extreme climate changes and repeated perturbations of the global carbon cycle, which resulted in widespread deposition of organic carbon-rich sediments. High atmospheric pCO2 has been invoked as the main cause of middle Cretaceous super greenhouse Oceanic Anoxic Events (OAEs) and biocalcification crises. Most of what we know about climate and global change in the middle Cretaceous was derived from the study of geochemical proxies and biotic change in deep-water sequences. Comparatively much less is known from shallow-water carbonate systems, although they are an important part of the global carbon cycle and are very sensitive to oceanographic and climatic forcing. Larger foraminifers were among the most conspicuous carbonate producers in the late Cenomanian carbonate platforms. They were almost completely wiped out by extinction during the late Cenomanian OAE (about 94-93.5 million years ago). Parente et al. show how the pattern of extinction parallels the ecological succession along a gradient of increasing nutrient input predicted by model studies and observed in field studies of nutrient-polluted habitats of larger foraminifers. Correlation by high-resolution carbon-isotope stratigraphy shows that extinction on shallow-water platforms is contemporaneous with an episode of thermal instability in the open ocean. They suggest that enhanced water mass mixing delivered high-nutrient loads to the oligotrophic surface waters of the subtropical Tethys, triggering the stepwise extinction of larger foraminifers and the drowning of many carbonate platforms.
Anhydrite-bearing andesite and dacite as a source for sulfur in magmatic-hydrothermal mineral deposits
Isabelle Chambefort et al., CODES, ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia. Pages 719-722. NSF funding received.
Magmatic anhydrite from andesites and dacites o
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Geological Society of America