Late Albian calcareous dinocysts and calcitarchs record linked to environmental changes during the final phase of OAE 1d – a case study from the Tatra Mountains, Central Western Carpathians

Abstract

Calcareous dinocysts and calcitarchs have been investigated for the first time within the Upper Albian limestone and marl succession of the Zabijak Formation from the High-Tatric Unit in the Tatra Mountains (Central Western Carpathians), related to the Oceanic Anoxic Event 1d (OAE 1d). Four groups of morphotaxa of calcareous dinocysts have been distinguished. They totally dominate the assemblages, and belong to the pithonellids. They are represented by Pithonella sphaerica (Kaufmann in Heer) and P. ovalis (Kaufmann in Heer), which dominate, as well as P. trejoi Bonet and P. lamellata Keupp in Keupp and Kienel, which are less abundant. Two other morphotaxa, Colomisphaera gigantea (Borza) and Cadosina oraviensis Borza, occur sporadically in the assemblages. Both forms represent the calcitarch group, which assembled calcispheres of unknown taxonomic affinity. The calcareous dinocyst and calcitarch diversity is low to moderate, compared to the general species richness known from Late Albian assemblages in other Western Tethyan sections. This is interpreted as a result of nutrient input fluctuations due to changes in the circulation pattern of surface and intermediate waters. The changes in the P. sphaerica/P. ovalis ratio along the Upper Albian section are here correlated with short-term (third-order) sea level fluctuations including transgressive and regressive events and a highstand. Pelletization processes might have influenced cyst abundance on the sea floor, especially during periods with oligotrophic surface waters