MEGAFLORAL PERTURBATION ACROSS THE ENNA MARINE ZONE IN THE UPPER SILESIAN BASIN ATTESTS TO LATE MISSISSIPPIAN (SERPUKHOVIAN ) DEGLACIATION AND CLIMATE CHANGE

The Late Mississippian (Serpukhovian) megafloral record of the Upper Silesian Basin, Czech Republic, occurs in a sequence of 51 genetic cycles wherein thick marine intervals mark the boundaries between members of the Ostrava Formation. A significant vegetational change occurs in the Late Serpukhovian across the Enna Marine Group, marking the boundary between the Hrsuov and Jaklovec Members. Extinctions impact all plant clades, affecting taxa that were centered in mineral-substrate soils. Taxa centered in wetlands were unaffected. Similar vegetational responses are not identified elsewhere although thick marine zones (e.g., Barbora Marine Group) also developed during the Serpukhovian.

Proximal to distal sedimentological and petrophysical (Γ-ray log) trends in the Enna and Barbora Groups indicate different mechanisms were responsible for generation of accommodation space in these two intervals. The Enna Marine Group (Hrusov-Jaklovec boundary) records at least 4, possibly 6 or more, genetic sequences, each equal in duration to that recognized for individual 100 ka cyclothems in the coalfield. Discrete Maximum Flooding Surfaces (MFS) with associated condensed sections and well-preserved macrofaunas are prominent in distal areas of this marine group, and identified using gamma-ray log responses. In contrast, the petrophysical expression of distal regions of the Barbora Marine Group (Jaklovec-Poruba boundary) shows no such strong positive gamma-log excursions that can be interpreted as MFSs. Rather, a succession is preserved that may be equal in duration to 2 cyclothems. The Barbora Marine Zone is interpreted to represent sedimentation in a glacial-interglacial cyclothemic framework. In contrast, the Enna Marine Zone interval represents accumulation under continued eustatic sea-level rise in response to southern hemisphere deglaciation and global warming.

Late Mississippian vegetational response to paleoequatorial climate change is interpreted to represent a shift towards greater seasonality with an increased number of dry months (monsoonal rainfall pattern?) resulting in statistically significant extinction/ extirpation several million years prior to the onset of maximum glaciation and sea-level drawdown at the Mississippian-Pennsylvanian boundary.