Lower Ordovician glauconite-bearing facies in the Holy Cross Mountains and their equivalents on the Małopolska Block (SE Poland): depositional environments and the relationship with eustatic changes in Baltica

Abstract

Glauconite-bearing siliciclastic lithofacies are widely distributed throughout the Lower Ordovician (upper Tremadocian– Floian) sedimentary record of Poland. They form a diachronous horizon composed of glauconitic sandstones that locally rest on a basal conglomerate, which occur on the Małopolska Block (including the southern Holy Cross Mountains) and the East European Platform. The Lower Ordovician facies architecture in the Holy Cross Mountains can be roughly correlated with the sea-level changes reconstructed in Baltoscandia, though the local tectonics contributed to some notable differences. The Lower Ordovician glauconitic interval reflects a major change of depositional environment on the Baltica and Małopolska shelves characterised by favourable conditions for stratigraphic and sedimentary condensation. It corresponds to a transgressive and early highstand depositional system encompassing the upper Tremadocian to lower Floian interval in the Holy Cross Mountains. On the East European Platform, an extremely condensed glauconitic horizon is associated with the Floian, although its basal conglomerates may be related to the latest Tremadocian. A low accumulation rate, including periods of sediment starvation, facilitated early diagenetic precipitation of a siliceous phase in tuffitic muds, resulting in bedded and nodular cherts in the upper Tremadocian of the southern Holy Cross Mountains.