Mioceński poziom buliminowy w rejonie Pilzno – Dębica

Abstract

THE MIOCENE BULIMINA HORIZON IN THE REGION PILZNO - DĘBICA

Summary

In the marine Miocene deposits the bulimina forms occur fairly often, however, in single specimens only. A greater number of these forms forces certain research workers to distinguish bulimina horizon or to stress their rich occurrence in an assemblage. A huge amassement of these forms has recently been observed in the deposits encountered by the bore holes made in the region Pilzno – Dębica (Fig. 1). In this region, the whole cycle of Miocene deposits can be subdivided into the following microfaunistic horizons: in the Lower Sarmatian - anomalinoides horizon (7), infra-anomalinoides horizon (6), bulimina horizon (5); in the Upper Tortonian - dendrophrya horizon (4), globigerina horizon (3); in the Lower Tortonian – horizon of chemical deposits (2) and candorbulina-uwigerina horizon (1). In the bore holes where no chemical deposits were encountered, the Miocene begins with the dendrophrya horizon. The bulimina horizon has been ascertained to occur in two bore holes: Pilzno 9 and Dębica 2. In the remaining bore holes the horizon has not been encountered, the dendrophrya horizon being immediately overlain by the infra-anomalinoides horizon (Fig. 2). The bulimina horizon begins with a fairly abundant specimens of Bulimina elongata and single specimens of Bulimina aculeata, Dendrophrya sp., Streblus beccari and Globigerina bulloides. Towards the top the specimens of Dendrophrya sp. disappear giving way to the abundant Bulimina elongata and fairly abundant Bulimina aculeata. Accompanying fauna is represented by fairly rich Eponides omnivagus and Quinqueloculina akneriana. Towards the top the accompanying fauna gradually impoverishes, and the bulimina horizon is almost completely represented by very abundant specimens of Bulimina elongata. At the top of the horizon the fauna becomes poor and dwarfish, and faunistic elements of the infra-anomalinoides horizon appear. The bulimina horizon is not characterized by a sharp boundary. However, a gradual transition from the dendrophrya horizon at the bottom to the infra-anomalinoides horizon at the top can here be observed. Definition of the stratigraphical position of the bulimina horizon is fairly difficult. It results from the microfaunistic observations and from correlations made on the basis of microfaunistic assemblages and BSE loggings that in the remaining bore holes the lower part of the infra-anomalinoides horizon corresponds to the bulimina horizon under consideration. This is also proved by a great thickness (400 m) of the bulimina horizon observed where a reduction of infra-anomalinoides horizon appears. Stratigraphically, it belongs to the Lower Sarmatian. Distribution of the bulimina horizon in the region Pilzno-Dębica seems to be fairly restricted. It results from the data so far obtained that the horizon in study occurs, in the area discussed, in the form of large lenses stretching in an ENE - WSW direction.