Abstract
Interpretations of sea-level changes over geological time are mainly based on analyses of sediments deposited within stable platforms. One of the criteria for recognizing these changes is the composition of skeleton-bearing protists living in environments close to the shoreline and on the continental shelf. It can be assumed that the source of information about sea-level changes may also be found in assemblages of microfossils redeposited from the shelf to the marginal ocean basin. With such an assumption, this article presents an interpretation of changes in marine plankton communities (radiolarians and planktonic foraminifera), which during late Albian–middle Cenomanian were redeposited with carbonate mud by gravity currents from the peri-Tethyan shelf to the northern, marginal Silesian Basin of the Western Tethys. Planktonic biota identified in sediments deposited by gravity flows and those found in hemipelagic shales separating them, indicate that their composition may be correlated with eustatic changes in the sea level from the late Albian (KAl8) to middle Cenomanian (KCe3).
Highlights
The late Albian through middle Cenomanian period is characterized by a stepwise sea level rise that led to one of the highest sea levels recorded in the history of the Earth [1]
The uppermost part of this unit passes gradually into the lower part of the Barnasiówka Radiolarian Shale Formation (BRSF) which differs from Mikuszowice Chert Beds (MCB) by the lack of chert layers
Referring to contemporary plankton communities and those known from the Cretaceous strata, the radiolarian and planktonic foraminiferal fluctuations could correspond to the chemistry and physical properties of the water column and nutrient availability, partly associated with sea-level changes, especially in a marginal part of the basins (e.g., [4,58])
Summary
The late Albian through middle Cenomanian period is characterized by a stepwise sea level rise that led to one of the highest sea levels recorded in the history of the Earth [1]. A majority of modern polycystine radiolarians inhabit nutrient-rich surface waters, and are known to be abundant in sediments that accumulated under eutrophic waters, such as those characteristics of upwelling areas, while others being symbiont-bearing live in oligotrophic environments [17] These environmental and sedimentary processes were important for the distribution of biotic constituents in epicontinental seas along the West European Platform as well as on the European peri-Tethyan shelves during the late Albian to Cenomanian. Such processes played an important role in mass-deposition into the deep Outer Carpathian basins, spreading out along the southern margin of the European Platform, where biogenic particles were transported by turbidity currents from sediments under shallower water depths and mixed to lithologically different types of deep-water deposits (e.g., [18]).
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