Condensation and phosphatization of the Middle and Upper Ordovician limestones on the Malopolska Block (Poland): Response to paleoceanographic conditions

The growth fault activity in the late Middle Ordovician resulted in the establishment of a horst-like submarine paleohigh in the northern Malopolska Block. This topographic submarine swell was the site of carbonate deposition characterized by a low overall net sediment accumulation rate. The sedimentary and ecological conditions on this paleohigh were controlled by a paleocurrent that flowed along the northern margin of the Malopolska Block, however seasonal intense storms associated with the mid-latitude location of this “terrane” cannot be excluded. The paleocurrent induced (seasonal?) upwelling of nutrient-rich waters from deeper parts of the current system that shifted onto the paleohigh and caused phosphatization of the sediment. The winnowing and reworking of sediment, together with slow carbonate production by a temperate-water biota and relatively long periods of omission, resulted in low accumulation rates and sediment condensation. The cessation of the paleocurrent and associated phosphatization coincides with changes in the oceanic circulation system due to the Late Ordovician collision of Avalonia with Baltica and gradual closure of the Tornquist Sea.