Crandallite-rich beds of the Libkovice Member, Most Basin, Czech Republic: climatic extremes or paleogeographic changes at the onset of the Miocene Climatic Optimum?

Abstract

We describe the occurrence and possible origin of rare beds 1–10cm thick and containing 20–70% of crandallite, a Ca-Al phosphate enriched in Sr and Ba, found within otherwise monotonous clay-rich lacustrine sediments of the Most Basin in the Central-European Neogene Ohře Rift system. The beds were formed at ca. 17.31, 17.06, and 16.88Ma, while the entire suite of monotonous clays of the Libkovice Member was deposited between 17.46 and 16.65Ma. Trace-element and organic geochemistry, Ar-Ar geochronology and C-O-Sr isotope systematics are used to infer their source and processes leading to their formation. The most enigmatic aspect of the formation of the crandallite beds is the removal of a huge amount of phosphorus from its biogenic cycle in the lacustrine system, which was otherwise stable for ca. 0.8My. Formation of detritus-poor crandallite beds could result from some exceptional environmental disruptions that hindered transport of fine clastic material to the basin floor. Silicic volcanic activity in the area of the Pannonian Basin could have triggered this disruption. Crandallite could provide evidence of long-lasting droughts and acidification of the exogenic environment, as they are roughly coeval with the onset of the Miocene Climatic Optimum at ca. 17.0Ma.

Sample preparation and chromatographic separation for Sr, Nd, and Pb isotope analysis in geological, environmental, and archaeological samples

“…The three-column separation procedure using BioRad Sr and Ln resin columns was successfully employed in the isotopic study of plutonic and volcanic rocks (Walther et al 2016;Mysliveček et al 2018;Janoušek et al 2020;Casas-García et al 2021;Mach et al 2021;Janoušek et al 2022) as well as loess samples (Waroszewski et al 2021).…”

New ichthyofauna from the Holešice and Libkovice members in the western part of Most Basin (Early Miocene), the Czech Republic

“…Above this are deposited very similar clays of the Libkovice Member, intercalated by at least 3 thin layers of phosphate sediment. These are called "crandallite bearing horizons", and each layer has volcanogenic material at its base (Mach et al 2021). These horizons help with stratigraphic ranking in the Libkovice Member.…”