Eocene dinoflagellate cysts from the Sołokija Graben (Roztocze, SE Poland)

Abstract

The Sołokija Graben is a tectonic structure in Roztocze, the south-eastern Poland, unique by its infill with the Eocene marine strata. The over 40 metres thick sandy succession is the only well-dated palaeontologically trace of Eocene marine transgression at Roztocze being virtually the only remains of the Eocene epicontinental sea in this part of Poland: the surrounding area is devoid of coeval marine strata, which were eroded. This makes the Sołokija Graben succession crucial for the palaeogeography reconstruction of the south-eastern Poland during Eocene as well as the tectonic history of this region. For its precise age determination, the over 30-m-thick succession of loamy sands that fill the Sołokija Graben in a borehole at Leliszka and a 4-m-thick one at Łaszczówka were sampled for dinoflagellate cysts. Samples from Łaszczówka are barren, whereas the ones from Leliszka contain rich and taxonomically diverse assemblages. Their biostratigraphical interpretation confirms previous results suggesting the Bartonian age of the most of the Sołokija Graben succession; the postulated Priabonian age of its non-calcareous part was documented in its uppermost part only. Palynological record allows reconstruction of sedimentary setting of the Leliszka succession. Basal part of the Bartonian was deposited in a shallow but relatively vast marine basin characterized by normal salinity and high energetic hydrodynamic conditions. Subsequently, marine basin underwent gradual shallowing and temporal cease of sedimentation. During the late Bartonian basin became brackish. A short-lasting early Priabonian marine basin was characterized by shallow marine conditions; it became brackish during its final stage. Comparison with neighbouring Eocene deposits of the epicontinental and Carpathian basins shows that the marine basin at Roztocze was presumably connected with both during Bartonian, and separated from the Carpathian one during early Priabonian. Factors controlling seaways pattern of the Roztocze basin were either eustatics and substratum tectonic movements, the former dominating during Bartonian, and interfingering with uplift of the Meta-Carpathian Swell during early Priabonian.