Palynomorphs’ response to sea-level fluctuations: a case study from Late Cretaceous – Paleocene, Gurpi Formation, SW Iran

Statistical studies on Palynology contents of Late Cretaceous to Paleocene age Gurpi Formation in a surface section in Zagros Basin,SW Iran indicate changes in abundance, species diversity, ratio of Spiniferites to Cyclonephelium (S/C), palynological marine index(PMI) values and organic facies. These palynological variations clearly reflect fluctuations in relative sea-level and depositionalenvironment and can be used for recognition and differentiation of systems tracts and key horizons such as flooding surfaces andsequence boundaries. Dramatic increase in PMI, dinoflagellate species diversity and S/C ratio associated with sedimentary faciesparameters indicate a marine transgressive systems tract while, a reduced species diversity, lower S/C ratio and PMI value along withincrease in abundance of phytoclasts and degraded land-plant materials are characteristics of marine regression. The variation trends ofthe palynological parameters when consecutive indicate a complete cycle of relative sea-level change. Abundance of Spiniferites,Achomosphaera, Areoligera, and Cleistosphaeridium species and presence of peridiniacean dinoflagellate cysts show a warm Tethyan,upper bathyal to middle shelf environment of deposition for the Gurpi Formation. The nine depositional sequences identified here canbe correlated to the global third-order sea-level cycles. The main regional sequence surfaces like K180 (maximum flooding surface) inthe Late Cretaceous sequences (68Ma) in northeast of Arabian Plate are recognizable here.