Sedimentary environment and tectonic controls of the Snochowice Beds (Lower Jurassic, western margin of the Holy Cross Mountains, Poland)

Abstract

The Snochowice Beds represent the lowermost part of the Lower Jurassic succession in the western part of the Mesozoic margin of the Holy Cross Mountains (Central Poland). This thick, gravelly has a different lithological character to other Lower Jurassic sandy and fine-grained deposits. Eight lithofacies have been distinguished, mainly gravelly and sandy, grouped into four genetic associations: M – massive gravels, interpreted as clast-rich debris flow deposits, G – horizontally to cross-stratified gravels, interpreted as gravelly bars and bedforms, S – cross-stratified and massive sandstones, interpreted as sandy bars and bedforms and F – massive mudstones and claystones, generally fine-grained deposits, interpreted as overbank deposits. Analysis of depositional geometry and lithofacies successions allowed reconstruction of the sedimentary environment: landforms of alluvial fan type, formed mainly by braided river processes and rarely by sediment gravity flows. A decrease in the thickness and content of gravelly lithofacies towards the north and north-east is documented. Analysis of transport directions has revealed that the clastic material was transported toward the north and north-east, perpendicular to the main faults fringing the basin. Depositional geometry facies and palaeocurrent patterns of the Snochowice Beds indicate that sedimentation was controlled by tectonic activity