Upper Ordovician through lowermost Silurian stratigraphy and facies of the Borenshult-1 core, Östergötland, Sweden
2010
Noor, Amir
The Ordovician is an important period in the Phanerozoic, with remarkable faunal turnovers, several major carbon isotope excursions, and shifting climate. The strata of this time period not only re-veal these events but also provide useful information about the palaeoclimate and sea-level. The Boren-shult-1 core form Östergötland, southern Sweden constitutes a complete succession of the upper Middle Ordovician through lowermost Silurian. This study describes the sedimentary rocks, fossil fauna and de-positional environment of these strata. The observations of the study are based upon cut and polished core slabs and thin sections photograph. Sedimentary data and a generalized facies model are used to reconstruct the depositional environment and changing bathymetry. The ~71 m thick succession is com-prised of eight formations. The bioclast composition reflects normal cool-water ecological assemblages with the exception of Favosites tabulate corals in the middle Freberga Formation, and ooids in the Loka Formation, indicating tropical climate. On the basis of the facies model of Harris et al. (2004), the strata represent 51% of mixed facies, 32% grain-supported facies and 12% mud-supported facies. Based on the sedimentary data, carbon isotopic values, stratigraphy and the faunal information, four major regressions and four transgressions of the sea-level are recorded.
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