Lower Bajocian ammonites from the stratotype section of the Etropole Formation kept in the Historical Museum in Etropole (Bulgaria)

Abstract

The area of the town of Etropole is famous for the well-preserved Lower Bajocian ammonites, which can be still often found in the nearly located exposures. These ammonites were the source of a number of species that enabled the recognition of the Bajocian in Bulgaria. The ammonite faunas and their host rocks were allocated to a series of stratigraphic horizons that composed the stratotype section designated as the reference standard for the definition and characterization of the Etropole Formation. The latter includes an ammonite spectrum which is composed of both Lower Bajocian species of Northwest European distribution and proper Bulgarian dispersal. It contains rare examples of the ammonite families Graphoceratidae and Sphaeroceratidae, frequent ammonites of the family Sonniniidae, and much more common members of the families Oppeliidae, Otoitidae and Stephanoceratidae that define a biostratigraphic interval from the Hyperlioceras discites to the Stephanoceras humphriesianum zones. This paper deals with the Lower Bajocian ammonite specimens hosted in the collection of the Historical Museum in Etropole (Bulgaria). The best preserved and the most valuable examples of this collection are described and figured. Although not purposefully collected, these ammonites give an excellent impression of the relative abundances of what is common and typical for stratotype section of the Etropole Formation. The study of this collection has triggered the rocks of the Etropole Formation (including the type-section) to be biostratigraphically reassessed, but this will be done elsewhere. Considering that both exposures and the fossil-bearing levels previously known from the Etropole area have now nearly disappeared, the ammonite collection of the Historical Museum in Etropole provides authentic specimens to be viewed. Besides, the collection forms an integral part of the overall heritage of the Etropole region and therefore offers both scientific and educational values.