Paleotemperature, oxygen and symbiotic relationships of Asmari Formation deposits based on large benthic foraminifers
Authors
1
Geology Department, Earth Sciences Faculty, Lorestan University, Khoram Abad, Iran
2
Department of Geology, Faculty of Science, Lorestan University, Khorramabad, Iran
Abstract
In the present study, a stratigraphic section was selected to study the paleotemperature, oxygen, and symbiotic relationships of the Oligocene-Miocene Asmari Formation deposits in the northwest of Rostam County (Izeh Zone). The thickness of the Asmari Formation in this section is 291 meters, which is mainly composed of thin, medium, and thick-layered limestones and thin shale-marl interlayers, and the Pabdeh Formation is gradually and continuously located at its lower boundary. Sampling of this section was carried out systematically with sampling intervals of one meter. In this study, 280 microscopic thin sections of the Asmari Formation were studied. In this stratigraphic section, the abundant presence of large hyaline benthic foraminifera with elongated, thin-walled shells such as Eulpidina, Operculina, Spiroclypeus, and Heterostegina from the distal part of the middle ramp at the base of the Asmari Formation is indicative of tropical and subtropical regions. The abundance of surface-living foraminifera relative to endophytic foraminifera indicates an oxygenated environment. The complex internal morphology of the bodies of large benthic foraminifera is due to the presence of symbiotic algae in the bodies of these organisms, such that the symbiotic need for light affects the shape of the shell and the arrangement of cells. Miliolids are non-symbiotic and can live at shallow depths with high salinities, while Archaias have symbiotic algae and live at greater depths than miliolids.
Keywords
