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Glaucony formation during warm phases of Earth history: new insight from Upper Cretaceous greensand giants

Massive and (geologically) fast shallow-marine glaucony formation was a widespread phenomenon during the Cretaceous greenhouse world that has no recent analogue. Based on several integrated case studies from different basins around the Mid-European Island, we intend to better understand the geochemical and depositional constraints on Late Cretaceous glaucony formation. X-ray diffraction analyses showed that the abundant green grains and matrix of all sites definitely constitute glauconitic minerals with high-order, 1M-type layer stacking. Inorganic geochemical analyses, normalized to Al and compared to average shale (AS), demonstrate that most element/Al ratios of greensand deposits are higher than AS values, including the chemical index of alteration (CIX). These observations suggest an intense chemical weathering of the exposed hinterlands, resulting in a continuous supply of essential elements required for glaucony authigenesis in nearshore settings under variably reducing and/or oxidizing redox conditions, associated with somewhat increased palaeo-productivities. The leaching of palaeosols and swampy coastal low-/wetlands during major transgressions related to eustatic Late Cretaceous sea-level rises was an important process for trace metal and nutrient mobilization. Furthermore, the significant influx of terrestrial organic matter from the densely vegetated continents suggests a significant impact of plant-decay-related potassium to glaucony maturation. In a nutshell, our new integrated data provide novel insights into the anactualistic formative processes of authigenic glauconitic minerals during greenhouse phases of Earth history.

Details

Author
Markus Wilmsen1, Niklas Metzner1, Udita Bansal2, Philipp Böning3
Institutionen
1Senckenberg Naturhistorische Sammlungen Dresden, Germany; 2Department of Applied Geology, Indian Institute of Technology, Indian School of Mines, Dhanbad, Jharkhand, India; 3Institut für Chemie und Biologie des Meeres (ICBM), Universität Oldenburg, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/nv2p-4554