Vyzkum paleomagnetickeho zaznamu v sedimentech v nadlozi hlavni uhelne sloje mostecke panve (spodni miocen)

Current paleomagnetic investigations in the Most Basin are unique among the recent studies as the number of explored localities and samples, and use of up-to-date equipment concerns. Extensive lacustrine and fluvio-deltaic deposits overlying the Main Coal Seam (Most Formation, Lower Miocene) are the subject of the research. This article summarises the main results of investigations in magnetostratigraphy and rock magnetism in context with other related disciplines since 2014.

So far, magnetostratigraphic analysis has been carried out on the following boreholes 70–380 m deep from both central and marginal parts of the basin: SP269 (Spořice), HK591, HK772 and HK930 (the former Hrdlovka village), HD50 (Háj u Duchcova), A24 (Srbice u Teplic), ZU5A (Chabařovice), LB432 (the former Libkovice village), OS17 (Osek), DO565 (Droužkovice), AL505 (the former Albrechtice village), DU7 (Dubí u Teplic), JU2183 (the former Jenišův Újezd village), MR93 (Mariánské Radčice), ZL70 (Litvínov-Záluží), and RL8 (the former Růžodol village).

In terms of magnetostratigraphy, we demonstrate that a local lake was present in the Bílina area from the end of paleomagnetic chron C5Dr.2r through chron C5Dr.1n to the beginning of the C5Dr.1r chrons (Holešice Member). The progradation of the Bílina Delta took place during the end of C5Dr.2r and its rapid development occurred mainly during the C5Dr.1n subchron. The coalescence of small local lakes began in the C5Dr.2r subchron and early in the C5Dr.1r chron culminated in the formation of a large basin-wide lake. Substantial changes occurred at the Holešice/Libkovice boundary near the C5Dr.1r/C5Dn reversal when hydrology of the basin-wide lake changed. The sediments of the Libkovice Member were deposited over a period of ca. 1.0 million years during C5Dn, C5Cr, and C5Cn.3n chrons. The beginning of the Miocene Climatic Optimum is also dated to this period. In the Lom Member sediments, geomagnetic polarity was not measurable; the C5Cn.2r/C5Cn.2n reversal was thus not recovered, and most of C5Cn.2n was missing in the record. The youngest lithostratigraphic unit in which geomagnetic polarity has been measured is the Osek Member with sediments of the second basin-wide lake. Here, the Most Basin record ends at C5Cn.1n chron in the uppermost part of the Burdigalian. This comprehensive magnetostratigraphic framework allows for chronological understanding for the basin evolution from small isolated lakes to a major basin-wide system, terminating about 15.9 million years ago.

Note that, in magnetostratigraphic studies, identification of sedimentary magnetic carriers is crucial for ensuring the reliability of paleomagnetic records. However, our understanding of this issue remained limited until the recent study of the RL8 core. The findings indicate that the magnetic carriers in the studied section consist of a mixture of diagenetic greigite and biogenic magnetite, implying that the paleomagnetic age is younger than the sediment itself. This discovery should be considered in the chronostratigraphic framework of the Most Basin. Yet, the character of magnetic carriers in the cores from different parts of the basin remains an open question.

The objective of this multidisciplinary research of the Most Basin is not only to make the stratigraphic scale significantly more accurate, but also to acquire better knowledge of paleogeography and environmental changes during Miocene. Výzkum paleomagnetického záznamu v sedimentech v nadloží hlavní uhelné sloje mostecké pánve (spodní miocén) Investigation of the paleomagnetic record of sediments overlying the Main Coal Seam in the Most Basin (Lower Miocene).

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