Orbital forcing and abrupt events in a continental weathering proxy from central Europe (Most Basin, Czech Republic, 17.7-15.9 Ma) recorded beginning of the Miocene Climatic Optimum

摘要

We describe orbital forcing in siliciclastic lacustrine sediments, deposited in central Europe (ca. 50.5 degrees N and 13.5 degrees E, the Most Basin, the Czech Republic) between similar to 17.7 and similar to 15.9 Ma, i.e., before the Miocene climatic optimum (MCO) and in its early stage. Chemical element analysis combined with magneto- and cyclostratigraphy produced a consistent stratigraphy for the studied basin fill. The palaeoenvironmental record is mainly based on variations of the chemical weathering intensity in the lake catchment (normalised potassium concentration K/Al or K/Ti). The Most Basin sedimentary profile is specific by relatively high deposition rates (typically 20 cm/kyr, sampling density corresponded to temporal resolution of 1-2 kyr) and sensitivity to a regional continental climate. For age control, we used the ATNTS2012 for younger sediments and an alternative age of the onset of C5Dn chron and the end of C5Dr.1r short chron. In the earliest studied interval, the chemical weathering intensity in the catchment was controlled by precession, while between 17.5 and 17.15 Ma, short eccentricity was mainly driving chemical weathering intensity. After 17.05 Ma, i.e., just before the onset of the MCO, and in the period of persistent high eccentricity between 16.95 and 16.7 Ma, chemical weathering intensity reached its precession-controlled maxima. In the subsequent period of the persistent low eccentricity at 16.65 Ma, the orbital signal nearly vanished in the Most Basin. Abrupt but temporary environmental change occurred in the interval between 16.5 and 16.35 Ma (polarity chron C5Cn.2n), within two cycles of high eccentricity. Its trigger is uncertain but it might have been local or regional. The obtained composite record was compared with marine delta C-13 and delta O-18 data, showing certain global control of the Most Basin deposits. The Most Basin record thus shows climatic events of the pre-MCO and early MCO period in terrestrial settings of Cen