Środowiska sedymentacyjne dolnego liasu północnego obrzeżenia Gór Świętokrzyskich

Grzegorz Pieńkowski



The paper presents results of complex sedimentological analysis of the Lower Lias at northern margin of the Holy Cross Mts, carried out on the basis of material from drillings and outcrops. Sedimentary paleoenvironments were interpreted with reference to analysis of cyclic character of sedimentation, based on detailed studies of lithological, sedimentological, mineralogical and geochemical features. There were identified cycles of continental environments (mainly those of meandering or, sometimes, braided rivers, with grain size decreasing upwards) and cycles of nearshore zones of brackish reservoir (reversed progradational coastal cycles, reversed barrier-lagoon cycles and similar deltaic ones).
Sedimentary modes for individual series were reconstructed taking into account frequency of occurrence of the cycles and results of measurements of transport directions and spatial analysis of the environments in outcrops. Trace fossils appeared highly useful in reconstructing sedimentary environments. Domichnia were found to be much more common in sediments of barriers and sandy coasts than in coarse-grained sediments of deltas. It is also worth to note that in comparison with fine-grained sediments of open reservoir, fine-grained lagoonal ones practically display Fodinichnia trace fossils only.
In the Holy Cross Mts, the Lower Lias is tripartite. Its lowermost, Zagaje series displays a succession of continental environments with steadily decreasing energy of river water. The Skłoby and Przysucha ore-bearing series represent a sequence beginning with rapid transgression in the Lias alpha 1 and ending with regressive sediments of basal part of the Ostrowiec series. The next transgression has taken place in the Lias alpha 3. In this region, the Lower Lias displays interfinging of the associations: coal-bearing (continental as well as deltaic and lagoon-barrier environments, mainly of the Zagaje and Przysucha series) and quartz sands (littoral environments of a closed brackish reservoir - mainly Skłoby and Ostrowiec series).

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