The Cretaceous/Paleogene (K/Pg) boundary in the Mezdra and Lyutidol syncline, Vratza District (West-Fore Balkan, Bulgaria)

Abstract

This paper discusses the unjustified assignment (based on calcareous nannofossils) of a large portion of the Maastrichtian strata in the Mezdra and Lyutidol synclines (West Fore Balkan, Bulgaria) to the Paleogene. The co-occurrence of Paleocene nannofossils, reported by some authors, and Maastrichtian macrofossil taxa in these sections indicates diachronism in the appearance of macro- and nannofossils across the K/Pg boundary. Thus, this boundary cannot be precisely localized except if the Maastrichtian fossils are assumed to have been redeposited, but there is no evidence of resedimentation. Maastrichtian macrofossils are found not only within the range of the Paleogene nannofossil zones, but also in sections overlying them in the Kajlâka Formation where new Maastrichtian macrofossil taxa, such as the echinoid Hemipneustes striatoradiatus (LESKE), appear and some inoceramid and cephalopod taxa range into this unit. These facts shed doubt over the applicability of nannofossils in determining the K/Pg boundary where this has already been firmly documented by macrofauna.