Beginning of the Miocene Climatic Optimum in Central Europe in sediment archive of the Most Basin, Czech Republic

 

Authors: Matys Grygar T, Mach K, Koubová M, Martinez M, Hron K, Fačevicová K

Published in: Bulletin of Geosciences, volume 96, issue 1; pages: 61 - 81; Received 17 April 2020; Accepted in revised form 20 October 2020; Online 13 December 2020

Keywords: lacustrine sediments, stratigraphy, orbital forcing, weathering proxies, geomagnetic reversals,

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Abstract

The Most Basin (Czech Republic) offers an extraordinarily detailed archive of the continental environment in Central Europe (ca. 50° N) in the period around the beginning of the Miocene Climatic Optimum. The sediments were studied by magneto-, chemo-, and cyclostratigraphy. Novel proxies for chemical weathering intensity were derived from K/Al concentration ratios and Mg/Al concentration ratios corrected for autochthonous carbonate content using an isometric log-ratio methodology and robust regression (RR). The correction confirmed that the association of chemical weathering maxima (lows in K/Al or Mg/Al) with eccentricity, obliquity, or precession maxima were affected by sediment grain size to only a minor degree. The orbital control allowed for the refinement of a magnetic-polarity-based depth-age model to unprecedented resolution. The timing of the basin development after the peat swamp flooding was confirmed; it started in the C5Dr.2r subchron, intensified in the C5Dn.1n subchron over several tens of kyr, and spread over the entire basin in the early part of C5Dr.1r. The expression of orbital cycles in weathering proxies changed abruptly near 17.07 and 16.90 Ma, in close temporal proximity to two step-like changes in global marine δ18O records between 17.2 and 16.9 Ma. The sensitivity of weathering intensity in the Most Basin to orbital forcing decreased coevally with the initial floods of the Columbia River Basalt Group and disruptions of the global δ13C record near the C5Dr/C5Dn reversal at around 16.6 Ma. Ratios K/Al and Mg/Al, either raw or carbonate corrected, can be recommended for the study of continental basin sediments.