Oxygen as a factor controlling palynological record: An example from the Cenomanian–Turonian transition in the Rybie section, Polish Carpathians

Palynology constitutes a useful tool for biostratigraphical and palaeoenvironmental analyses and is commonly used in academic and applied research. However, the palynological signal can be significantly influenced by both, intra- and post-depositional oxidizing processes. To estimate the dependence of the palynological record on the oxygen level near the sediment-water interface, the palynofacies have been analysed from shale and marlstone of the Cenomanian-Turonian (C-T) transition in the Rybie section (Carpathians, Poland) and correlated to previously obtained ichnological record and interpretation. The results show abrupt and intense palynofacies fluctuations from samples rich in organic matter to almost barren. Only the short, middle to upper Cenomanian interval yields well preserved and diversified organic-walled dinoflagellate cysts. The whole section reflects palaeoenvironmental fluctuations within a deep-water basin, including: mesotrophic conditions and environment deterioration (interval 1); extreme oligotrophic conditions (hyperoligotrophy) influencing oxydation of organic matter (interval 2); reduction of oxygen content, enhanced organic productivity, increased production of organic carbon and deposition of amorphous organic matter (Bonarelli Level comprising the Late Cenomanian Oceanic Anoxic Event OAE-2); rapid increase in oxygenation above the Bonarelli Level (interval 3). The hyperoligotrophy recorded within the interval 2 is likely associated with the Plenus Cold Event and coeval enhanced oxygenation of bottom waters prior to the OAE-2. The results yield the enhanced environmental fluctuations near the C–T transition and emphasise the sensibility of palynological record to near-bottom oxygen content.