Biostratigraphy and paleoecology of Upper Paleocene to Lower Oligocene deposits in Southeast of the Hajiabad Area (Zagros Basin, SW Iran)

摘要

This study deals with foraminiferal biostratigraphy and paleoecological interpretations for the Late Paleocene to the Early Oligocene carbonate sequence in the Zagros Basin, the Hajiabad Area, SW Iran. This sequence could be divided into three parts, basal fossil-less strata have related to Sachun Formation base on their stratigraphical position, the middle part involves dolomitic to dolomitic limestone of Jahrum Formation, and the upper part consists of the Lower Asmari Formation. In general, the bulk of the section consists of marine deposits, and it is possible to divide them in to several parts base on benthic foraminiferal biozones. The Late Paleocene to the Early Eocene (the Lower Jahrum Formation) has been distinguished by the Miscellanea, Kathina, Alveolina, Fallotella, Lokhartia, Orbitolites, and small rotalids Assemblage Zone. The Middle Eocene (the Middle Jahrum Formation) has been characterized by the Somalina Total Range Zone and the Nummulites-Alveolina Assemblage Zone. The Late Eocene (the Upper Jahrum Formation) has been distinguished by the Chapmanina, Pllatispira, Baccullogypsinoides Assemblage zone, and the outcrop of the Asmari Formation belongs to the Early Oligocene Base on the Nummulites vascus, Nummulites fichteli Assemblage Zone. Clustering content benthic foraminifera in the studied section base on their morphology, coiling, feeding habits, and habitats lead to identification of 15 distinct assemblages with similar ecological niches. Paleoecological reconstructions base on benthic foraminiferal communities indicate that five major ecological habitats include tidal flat and shore, restricted shelf, nonrestricted shelf, oligotrophic shelf, and open marine.