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Authors = Stefan Lӧhr

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19 pages, 25672 KiB  
Article
Revisiting Glauconite Geochronology: Lessons Learned from In Situ Radiometric Dating of a Glauconite-Rich Cretaceous Shelfal Sequence
by Esther Scheiblhofer, Ulrike Moser, Stefan Lӧhr, Markus Wilmsen, Juraj Farkaš, Daniela Gallhofer, Alice Matsdotter Bäckström, Thomas Zack and Andre Baldermann
Minerals 2022, 12(7), 818; https://doi.org/10.3390/min12070818 - 27 Jun 2022
Cited by 24 | Viewed by 5469
Abstract
The scarcity of well-preserved and directly dateable sedimentary sequences is a major impediment to inferring the Earth’s paleo-environmental evolution. The authigenic mineral glauconite can potentially provide absolute stratigraphic ages for sedimentary sequences and constraints on paleo-depositional conditions. This requires improved approaches for measuring [...] Read more.
The scarcity of well-preserved and directly dateable sedimentary sequences is a major impediment to inferring the Earth’s paleo-environmental evolution. The authigenic mineral glauconite can potentially provide absolute stratigraphic ages for sedimentary sequences and constraints on paleo-depositional conditions. This requires improved approaches for measuring and interpreting glauconite formation ages. Here, glauconite from a Cretaceous shelfal sequence (Langenstein, northern Germany) was characterized using petrographical, geochemical (EMP), andmineralogical (XRD) screening methods before in situ Rb-Sr dating via LA-ICP-MS/MS. The obtained glauconite ages (~101 to 97 Ma) partly overlap with the depositional age of the Langenstein sequence (±3 Ma), but without the expected stratigraphic age progression, which we attribute to detrital and diagenetic illitic phase impurities inside the glauconites. Using a novel age deconvolution approach, which combines the new Rb-Sr dataset with published K-Ar ages, we recalculate the glauconite bulk ages to obtain stratigraphically significant ‘pure’ glauconite ages (~100 to 96 Ma). Thus, our results show that pristine ages can be preserved in mineralogically complex glauconite grains even under burial diagenetic conditions (T < 65 °C; <1500 m depth), confirming that glauconite could be a suitable archive for paleo-environmental reconstructions and direct sediment dating. Full article
(This article belongs to the Special Issue Formation and Evolution of Glauconite. New Scale Approach)
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