Zarys stratygrafii kredy dolnej niecki brzeżnej

Abstract

OUTLINE OF THE LOWER CRETACEOUS STRATIGRAPHY IN THE MARGINAL TROUGHSummaryLower Cretaceous deposits are best developed in the marginal  trough. Here, they attain their maximum  thickness that, in the area of the Warsaw basin (Fig. 1), which is a portion of the central part of the Lower Cretaceous basin in the Polish Lowland area, amounts to 500–600 metres. Towards the Pomeranian trough, Lublin trough, and East-European platform, a gradual decrease in thickness of the deposits can be observed, as well as greater and greater sedimentary and erosional gaps and facial changes are noted.To the south-easternmost occurrence area of the Extra-Carpathian Neocomian deposits belong those from the region of Lubaczów situated in front of  the Alpine massif within a foredeep .Ammonite fauna is restricted to the Berriasian, Valanginian and Hauterivian. It points to a connection between the Lower Cretaceous lowland basin, the boreal basin and the Mediterranean basin. The fauna does evidence certain relations with the basin of the Central Russia platform, as well.The Berriasian deposits (Figs. 2, 3, 5) of the marginal trough are developed in brackish-marine facies (Warsaw basin), and in marine facies. The basin gradually widened and deepened, beginning with the first marine ingressions in the freshwater Purbeckian basin, and tending with the type sedimentary marine environment that disclosed ammonite fauna represented for example by Euthymiceras sp.Lower Valanginian deposits (Figs 2, 3, 5) are a continuation of the Berriasian marine sedimentary cycle. They are characterized by a scarce fauna with Platytenticeras and Polyptychites (Tabl. I, Fig. 11).Middle Valanginian deposits (Figs. 2, 3, 6), lacking index fauna, are related to the period of a distinct shallowing of sedimentary basin. They consist here mainly of arenaceous series.At the Upper Valanginian time (Figs. 2–4, 7), a new (Necomian transgression took place. This sub-stage is evidenced by the ammonite fauna of the genera Dichotomites (Tabl. II, Figs. 12–14), Leopoldia (Tabl. III, Figs. 19, 20) and Neocomites (Tabl. II, Fig. 18).Among the Neocomian formations, the Lower Hauterivian deposits (Figs. 2–4, 8) are most wide-spread, Ammonite fauna is represented here by the species of the genera Endemoceras (Tabl. II, Figs. 16, 17), Leopoldia (Tabl. II, Fig. 21) and Neocrasrpedites (Tabl. I, Fig. 15).Upper Hauterivian has been distinguished tentatively. In the lower part of this sub-stage a distinct shallowing of the basin took place, followed probably by a disruption in the connection with the Mediterranean basin. The upper part of the sequence shows a recurrence to the marne regime.The Barremian – Middle Albian (Figs. 2–4, 10) are represented by arenaceous deposits of a shallow shelf sea, resting transgressively on the Neocomian formations.