Stratigraphic position and sedimentary features of the Tertiary Uppermost Fluvial Member in the Kleszczów Graben, central Poland
Abstract
Pozycja stratygraficzna i cechy sedymentologiczne trzeciorzędowej najwyższej serii fluwialnej w rowie Kleszczowa, Polska środkowa
The Uppermost Fluvial Member of the Neogene sequence of the Kleszczów Graben represents a thick sand body which was deposited by a "threshold" river, with some characteristics of sinuous rivers, though with no point bars and limited overbank deposition. Dominating lithofacies are very large-scale troughs, up to 6 m deep and 25 m wide. These troughs represent palaeochannels, which have been filled with large- and medium-scale cross bedded sands and less common thin and discontinuous fine sands, clayey-silt or peat/organic mud and clay lenses. The sandy material comes mainly from the redeposition of the underlying older Neogene deposits, and locally from Jurassic sands from the graben margins. The age of the member is late Middle Miocene to Upper Pliocene, and pollen analysis has indicated thermophilous forest (late Middle Miocene) at the lower and middle parts of the series and relatively cooler conditions, though still with forest (late Pliocene) in the uppermost part of the series. Formation of the Uppermost Fluvial Member was tectonically controlled. At first it is because of the unexpected sedimentary environment and formation of a sand body despite dense vegetation cover. On the other hand, the Uppermost Fluvial Member represents the lower part of the youngest sedimentary mega-cycle of the Neogene sequence in the Kleszczów Graben, which is interpreted as entirely tectonically controlled sedimentary sequence.
The Uppermost Fluvial Member of the Neogene sequence of the Kleszczów Graben represents a thick sand body which was deposited by a "threshold" river, with some characteristics of sinuous rivers, though with no point bars and limited overbank deposition. Dominating lithofacies are very large-scale troughs, up to 6 m deep and 25 m wide. These troughs represent palaeochannels, which have been filled with large- and medium-scale cross bedded sands and less common thin and discontinuous fine sands, clayey-silt or peat/organic mud and clay lenses. The sandy material comes mainly from the redeposition of the underlying older Neogene deposits, and locally from Jurassic sands from the graben margins. The age of the member is late Middle Miocene to Upper Pliocene, and pollen analysis has indicated thermophilous forest (late Middle Miocene) at the lower and middle parts of the series and relatively cooler conditions, though still with forest (late Pliocene) in the uppermost part of the series. Formation of the Uppermost Fluvial Member was tectonically controlled. At first it is because of the unexpected sedimentary environment and formation of a sand body despite dense vegetation cover. On the other hand, the Uppermost Fluvial Member represents the lower part of the youngest sedimentary mega-cycle of the Neogene sequence in the Kleszczów Graben, which is interpreted as entirely tectonically controlled sedimentary sequence.