A4: Depositional systems in a coal-bearing rift basin: Lower Miocene of the Most Basin, Eger Graben

2 days, June 20–21, 2021, Czech Republic; Trip leaders: Mach K.1, Rajchl M.2, Novotný T.1, Matys Grygar T.3, Uličný, D.3 1Severočeské doly a.s., Czech Republic; 2Czech Geological Survey, Czech Republic; 3The Czech Academy of Sciences, Czech Republic
Contact:  mach@sdas.cz 
Price: 190 EUR
Transportation: bus; Participants: Minimum 20, Maximum 30
Departure: Prague, Hotel Diplomat (8:00); Return: Prague, Hotel Diplomat
Includes: field trip guidebook, transportation, accommodation, breakfast, lunch packets, snacks and dinner.
Degree of physical difficulty: intermediate; Hard hats will be provided.
The Most Basin is the largest of basins formed within the Eger Graben, the easternmost part of the European Cenozoic Rift System. Fluvial, deltaic, and lacustrine depositional systems co-existed here between late Oligocene and mid-Miocene with extensive peat swamps, and recorded an interplay of tectonic subsidence, peat compaction, lake-level fluctuations and clastic input. We will examine the depositional processes and discuss their controls in several large opencast coal (lignite) mines and other high-quality outcrops. The highlight of Day 1 will be the seismic-scale exposures of a lacustrine-deltaic system in the Bílina opencast mine. The basin fill is exposed there in a 4 km-long cross-section, in total thickness close to 400 m. Depositional features ranging in scale from bedform through the entire delta system can be studied, together with effects of growth faulting and relationships between clastic deposition and peat-forming swamp growth. Lacustrine strata recording a snapshot of climate evolution during the Miocene Climatic Optimum will be demonstrated as well. On Day 2 the dynamics of an avulsive fluvial system influenced by peat compaction will be demonstrated in another opencast mine, followed by smaller exposures showing, for example, travertine deposits related to faults at the basin margins.
Left: Seismic-scale exposures in the Bílina opencast mine show a major seam overlain by lacustrine and deltaic clastics; Right: Foreset strata of a steep-faced mouth bar bracketed by prodelta and lacustrine deposits; Miocene Bílina Delta, Bílina opencast mine.
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