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

Abstract

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