Miąższość i zasięg osadów albu w obszarze lubelskim

Abstract

Przedstawiono wyniki pracy nad odtworzeniem regionalnego rozkładu miąższości piaszczystych osadów albu środkowego i górnego w obszarze występowania karbonu lubelskiego. Głównym rezultatem jest mapa miąższości osadów albu w skali 1:200 000 obejmująca obszar Lubelskiego Zagłębia Węglowego. Praca została oparta na reinterpretacji pomiarów karotażowych z 442 otworów wiertniczych. Wykorzystano również i porównano z danymi geofizycznymi rezultaty rdzeniowania interesującego odcinka profilu ze 104 otworów. Autorzy prezentują tezę o związku miąższości transgresywnych osadów kredy dolnej, reprezentowanych w tym obszarze przez osady albu, z blokową budową podłoża krystalicznego i pokrywy paleozoicznej. Zaobserwowano wpływ aktywności tektonicznej elementów bretońskich i asturyjskich w kredzie dolnej, wyrażający się kontrastem miąższości osadów albu oraz jej szybkimi zmianami w strefach głównych dyslokacji podłoża.THICKNESS AND EXTENT OF ALBIAN DEPOSITS IN THE LUBLIN REGION Albian deposits are present almost in the whole area of the Lublin Coal Basin. They are represented by weakly cohesive or non-cohesive sands with glauconite and phosphorites. The layer, from 0 to over 30 m thick in the Lublin region, is usually saturated with water which represents a hazard and makes construction of coal mines very difficult. Petrophysical features of Albian deposits make possible easy separation of that layer and Jurassic and Upper Cretaceous carbonate rocks. The properties were used in mapping distribution of thickness of the Albian on the basis of interpretation of well logs for all the borehole columns in the Lublin Coal Basin. The results of well log interpretation were subsequently compared with sections of the Albian, established on the basis of core material. It appeared that the well log interpretation is sufficiently accurate to reconstruct regional changes in thickness of the Albian. Thickness of Albian deposits depends on deep structure of Precambrian and Paleozoic basement in this area. It is mainly determined by subsidence of individual tectonic blocks in time of sedimentation of the Albian. Two sedimentary regions may be delineated in northern part of the coal basin, situated in elevated part of the East-European Platform. North-western region is situated in area of Paleozoic (Bretonian) Łuków Horst. This area was subjected to subsidence in the Albian, which resulted in origin of a series of sandy sediments up to 36.5 m thick. The other region, Włodawa Depression, is situated SE of the Łuków Horst, being separated from it by the Hanna Fault. The Albian is relatively thin there (2 to 6 m thick) which indicates that this block was fairly stable in the Albian. Albian deposits are lacking in area of Hercynian structures of the Kumów Horst and Terebin Depression, situated south-east of the Włodawa Depression. Eastern boundary of these deposits coincides with a fault separating the Lublin Trough and elevated part of the Platform. The Platform sockle was subjected to strong uplift in the Albian along with Hercynian blocks of the Paleozoic cover. The Albian appears more differentiated in thickness in western part of the coal basin. The thickness reflects there some rows of NW - SE oriented Paleozoic horsts and depressional structures. The structures were acting independently from one another in time of deposition of the Albian. The Stoczek - Dorohucza Depression, one of the major tectonic elements in this part of the coal basin, was stable at that time. In turn, some other elements such as Żyrzyn, Abramów, Świdnik and Trawniki horsts, are characterized by highly differentiated thickness of these rocks. High rate of subsidence in the Albian is also typical of areas belonging to the Radom - Kraśnik Elevation, situated SW of the Lublin Coal Basin.