Paleoenvironmental and stratigraphic investigations of the foraminiferal fauna from the Karpatian (Lower Miocene) Garab Schlier Formation of the Matraverebely-122 (Mv-122) borehole (North Hungary)

摘要

The Garab Schlier Formation is composed of gray sand, silt clay and clay marl, deposited in an open marine environment. The aims of this study were to reconstruct its paleoenvironmental features and to propose a hypostratotype of the Garab Schlier Formation. Eighty-seven samples from the Mv-122 borehole (between 177.0-698.0 m) provided a dataset for detailed qualitative and quantitative analysis. The benthic and planktonic foraminiferal fauna were studied together. The associations indicated three different environments in the section. The lower part of the section records deposition in a normal marine, cool, outer shelf environment. Later on conditions changed to an upper bathyal, normal salinity, cool environment without permanent currents. Assemblages from the upper part of the section suggest that the water depth decreased and an inner shelf, normal salinity sea is inferred, with fluvial influence and open marine connections. The age of the sediment is Late Karpatian (Latest Burdigalian) as indicated by the M4b Planktonic Foraminifera Zone. The middle part of the studied section (337.0-664.0 m) is proposed here as the hypostratotype of the Garab Schlier Formation.