Sedimentary record of subaerial volcanic activity in the basal Ordovician shoal-marine deposits: The Třenice formation of the Prague Basin, Bohemian Massif, Czech Republic

Abstract

The basal Ordovician Třenice Formation represents an initial member of the preserved infill of the Prague Basin. Volcanic admixture in sediments preserved in the south-western part of the basin suggests subaerial volcanic activity during the deposition of the Třenice Formation. Three principal lithofacies associations were defined within sedimentary record of the Třenice Formation based on petrography and observed sedimentary structures: i) graded conglomerates, ii) lithic sandstones and iii) volcanigenic deposits. The studied sediments were mostly deposited as subtidal sand dunes, locally interbedded with volcaniclastic rocks. They are considered deposits of a marine lower shoreface influenced by ebb-tide currents. Volcaniclastic intercalations are interpreted as deposits of debris flows and turbidity currents that redeposited volcaniclastic material derived from subaerial Křivoklát-Rokycany and Strašice volcanic complexes.