Kreda górna i paleocen dolny okolic Lublina

Abstract

Przedstawiono korelację geofizyczną osadów węglanowych górnokredowego cyklu sedymentacyjnego z okolicy Lublina. Do podziału geofizycznego stosowanego w tym regionie dla utworów kredy górnej wprowadzono kompleks geofizyczny VI - skorelowany z osadami paleocenu dolnego. Na podstawie pomiarów geofizyki wiertniczej wydzielono w okolicy Lublina osady górnego albu, wszystkich pięter górnej kredy i dolnego paleocenu oraz omówiono ich litologię i stratygrafię. W wyniku przeprowadzonej analizy zrewidowano profil kredy z głębokiego wiercenia w Lublinie, opracowanego przez Z. Sujkowskiego (1931) i W. Pożaryskiego (1938). THE UPPER CRETACEOUS AND LOWER PALEOCENE IN THE VICINITIES OF LUBLINIn the vicinities of Lublin, Upper Cretaceous and Lower Paleocene rocks were penetrated by numerous deep drillings but usually without coring (Fig. 1). Therefore, lithological-geophysical correlations of the strata in individual borehole columns were made in order to establish uniform lithostratigraphic subdivision. The correlations were based on well-logs and a scheme worked out by the Authoress (A. Krassowska, 1981a). Two cross-sections show the correlations: one running along the strike of strata (Lublin IG 2 - Lublin SUJK - Lublin IG 1, Fig. 2), and the other, running normal to the strike (Zemborzyce 2 - Lublin SUlK - Świdnik 5, 6, Fig. 3). The analyses were made taking into account scarce lithological and biostratigraphic data for individual stages, mainly from the boreholes Lublin IG 2 and (for the Maastrichtian) Trawniki SW 2 (Fig. 4).The analyses showed that the well log data are well correlable (when their quality is appropriate). The correlations appeared useful for subdivision of the Cretaceous. It appeared possible to establish a more precise geophysical subdivision. The geophysical complex IIB was further subdivided into three horizons, and a new geophysical complex VI (correlatable with the Lower Paleocene) was differentiated. Figure 5 presents characteristics of the geophysical units. The marker value of the complex IV, fully cored in the drilling Lublin IG 2, is emphasized. The complex comprises marls with microfauna indicative of upper part of the Campanian and lower part of the Lower Maastrichtian.The studies showed that the Upper Cretaceous is represented by all the five geophysical complexes (including the complex VD - the uppermost Upper Maastrichtian, and, locally, the complex VI – Lower Paleocene) in the vicinities of Lublin.The correlations made also possible mainly stratigraphic revision of the Cretaceous section of a deep drilling made in the Lublin area in the years 1926 -1927 (Z. Sujkowski, 1931; W. Pożaryski, 1938, 1956), still treated as the reference one. Position of boundaries of lower stages of the Cretaceous in this section remained unchanged whereas boundaries of the upper ones drawn lower than hitherto accepted (Fig. 4). Moreover, the lithology of the sequence was modified. This is especially the case of the Maastrichtian, shown to comprise marls, chalk, and opokas.The correlations showed the presence of the Upper Albian in the vicinities of Lublin (but not in all the boreholes), Upper Cretaceous from the Cenomanian to the uppermost Maastrichtian (locally missing due to erosion) and, in some places, Lower Paleocene (Montian). The Montian with microfaunistic record is known from the drilling Lublin IG 2.The paper also presents lithological-stratigraphie-thickness characteristics of individual stages of the Cretaceous and Lower Paleocene (Figs. 2 - 5). The studies showed the changes in thickness of individual stages of the Upper Cretaceous to be minor and mainly marked along the axis of subsidence of the Lublin Basin. The changes are fairly large in the case of younger strata (Santonian Maastrichtian) in direction transversal to the axis as the strata are thinning out from the south-west to north-east.