Stoykova, K. ; Ivanov, M.

2004 Calcareous nannofossils and sequence stratigraphy of the Cretaceous/Tertiary transition in Bulgaria.

Published in: Journal of Nannoplankton Research, volume 26, part 1, pages 47-62.

DOI: https://doi.org/10.58998/jnr2231

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Abstract:
Five Cretaceous/Tertiary transitional sections were examined for calcareous nannofossil content and analysed in terms of sequence stratigraphy. Sections for study were selected in order to represent a variety of depositional environments. Calcareous nannofossils were examined in order to provide a detailed biostratigraphy. This study is restricted to sediments from the Upper Maastrichtian (nannofossil biozones CC25-26) and the Lower Danian (biozones NP1-2). Three basic depositional environments were recognised: 1) a shallow-water environment, represented by carbonate-dominated sediments; 2) a hemipelagic environment represented by marly limestone sediments deposited on the shelf margin and the upper slope; and 3) a deep-water environment consisting of flysch-type turbidite sequences. Specific lithologies and calcareous nannofossil occurrences characterise each depositional setting. In terms of sequence stratigraphy, three third-order depositional sequences were identified, two in the Upper Maastrichtian (Ma3 and Ma4) and one in the Lower Danian (Da1). These are described herein and their boundaries are calibrated with the calcareous nannofossil biozonations.