Stratygrafia osadów dolnokredowych okolic Sompolna

Abstract

STRATIGRAPHY OF LOWER CRETACEOUS SEDIMENTS OF THE REGION OF SOMPOLNOIn the Mogilno-Łódź syneclinorium, in the region of Sompolno (approximately 30 km. NW of Kłodawa), both the Department of Lowland Geology and the Department of Iron Ore Deposits of the Geological Institute undertook a number of drilling which, among other strata, pierced sediments of the Lower Cretaceous. Unfortunately, almost the entire series of these sediments proved to be devoid of index fossils. On the other hand, relatively numerous ammonites were found in bore-holes sunk in the region of Rogoźno; these bore-holes were investigated by s. Marek (1960). The detailed lithological sections indicate the feasibility of correlating both these regions, situated relatively far from each other (some 100 km.); they also enabled the author to distinguish in the Sompolno region, on the basis of the ammonite fauna found in the region of Rogoźno, the Infra-Valanginian, the Valanginian and the Lower Hauterivian. In both correlated regions, the higher stages Jack index fossiIs.The author bases stratigraphy of the Upper Hauterivian on its microfauna and on glauconite as index of marine sedimentation. These deposits indicate here a shallow shelf sea, disclosing a marked lithological variableness in the individual sections; this fact makes correlation difficult, especially correlation with the more silty deposits of that same age found in the region of Rogoźno.In the region of Sompolno, as shown in bore-hole Pagórki, the Hauterivian marine deposits pass directly into sandy deposits with glauconite of the Middle Albian. Fresh-water deposits of the Barremian, Aptian and Lower Albian are lacking. In other bore-holes of the Sompolno region, no glauconite was found in the Middle Albian distinguished by the author. However, the identity of succession in sedimentation, the inconsiderable distance from Pagórki, as well as their position in the center of the sedimentation basin existing at that time (S. Cieślińs.ki, 1959), - all these features imply the appurtence of these sediments to the Middle Albian too. On top of the sandy sediments of the Middle Albian already lie Upper Albian marls with Aucellina gryphaeoides (S o w.).In the region of Sompolno, the thicknesses of the successive stages of the Lower Cretaceous are as follows: the Infra-Valanginian - 27 m., the Valanginian - 80 m., the Hauterlvian - 132 m., the Albian - 110 m.