Understanding palaeoenvironmental constraints on glaucony formation – insights from Late Cretaceous greensand giants

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Green authigenic marine clays developed in Earth history from the late Palaeoproterozoic to the Recent with an accumulation maximum centered on the Cretaceous Period. This project aims at understanding the environmental parameters which controlled the massive formation of green marine clay minerals during the (early) Late Cretaceous (Cenomanian to Coniacian) and their accumulation to thick, widespread sequences of greensands ("greensand giants") characterising nearshore settings in many basins worldwide. The integrated approach combines stratigraphical, sedimentological, mineralogical and geochemical analyses with the Cretaceous palaeoenvironmental/-geographical context. Regionally tied to and based on well-dated sections around the Mid-European Island, the project also challenges the geological principle of uniformitarianism positing that "the present is the key to the past": the massive, very widespread formation and accumulation of glaucony-dominated greensands in nearshore settings is not matched by data from recent depositional systems. These observations suggest that the presence is not always the key to the past and we suggest that the widespread shallow-marine green marine clay formation during Cretaceous times was basically controlled by the (physico-)chemical properties of the riverine flux from the low-lying, deeply weathered continents. The main goals of the project can thus be summarised as follows:1) to investigate stratigraphical, sedimentological and palaeogeographical conditions of greensand giants around the Mid-European Island;2) to obtain quantitative data on the rock-forming green grains (morphology, colour, abundance, mineralogy, geochemistry);3) to characterise and understand the geochemical environment of shallow-marine Late Cretaceous greensand formation;4) to test the hypothesis that widespread shallow-marine glaucony formation during the (early) Late Cretaceous is related to the deep weathering of the continents and the chemical properties of the fluvial run-off.Although the application is regionally based on sections from Germany, it deals with a global phenomenon of considerable importance that can be narrowed down and tackled well in the proposed study area: the integrated analysis and comparison of different settings around the Mid-European Island will provide clues for the formation conditions of Late Cretaceous greensand giants.