Investigation of shallow-water carbonate distributions related to the QomFormation in distant sections of the type area, southeast of Kerman, Iran: insight to calcareous nannofossils

Calcareous nannofossils are essential for age dating and studying environmental changes. These microscopic (1–20µm) calcitic cell-wall fossils coverings are abundant in most post-Paleozoic marine sedimentary rocks, providing a continuous stratigraphic record of biotic change. This study aims to document the stratigraphic occurrence of calcareous nannofossils at the wide-spread shallow marine carbonates of related to the Qom Formation in the Nargesan, Band, and Qaleh-Gabri sections, southeast of Kerman province (East of Central Iran Basin). Samples were collected at 50-100cm intervals from the marly parts of the section to basal part of the Upper Red Formation. To preserve the small-sized coccoliths, samples were processed using simple smear slide method. The prepared slides were examined with an Olympus BX53 light microscope using cross-polarized light at a magnification 1500-2000X. Gypsum and Quartz plates were used to identify various species. In this study employed the standard calcareous nannofossil zonation by Martini 1971 for the Oligocene sediments. The studied interval ranges from the Lowest Appearance (LA) of Sphenolithus ciperoensis species to the Highest Appearance (HA) of the Sphenolithus distentus, corresponding to the NP24 zone defined by Martini 1971. The calcareous nannofossil assemblages exhibit moderate diversity and frequency, with moderately to well-preserved nannofossil specimens observed, such as: Sphenolithus ciperoensis, Sphenolithus conicus, Sphenolithus moriformis, Zygrhablithus bijugatus bijugatus, Helicosphaera recta, Helicosphaera euphratis, Reticulofenestra bisecta, Reticulofenestra dictyoda, Reticulofenestra minuta, Cyclicargolithus floridanus, Cyclicargolithus abisectus, Coccolithus pelagicus, Braarudosphaera bigelowii, etc. According to the above-mentioned calcareous nannofossil assemblages, the age of late Rupelian can be assigned for the studied samples from the surface sections. Furthermore, the high-resolution study of calcareous nannofossils indicates a significant decrease in the abundance and diversity of Oligocene nannofossils, mirroring trends observed at other low and middle latitudes sites. This record of calcareous nannofossils and bioevents provides valuable insights into the paleoenvironments of thatperiod. This research marks the first report of nannofossils from shallow-water carbonates (related to the Qom Formation) from Jiroft-Kerman area.

References

Martini, E. (1971) Standard Tertiary and Quaternary Calcareous Nannoplankton Zonation. Proceedings of the 2nd Planktonic Conference, Roma, 1970, 739-785.