Persian Gulf Holocene sedimentary environment based on two cores in shallow part of Bandar Abbas and Bushehr

Sedimentology of Persian Gulf have been studied by various researchers, however, no detail Holocenesedimentary environments study has been made in the northern part of the Persian Gulf. The main purposeof this research is to investigate the environment changes during Holocene by mineralogy, sedimentconstituents and organic matter in the two cores from northern part of the Persian Gulf up to ۱۵ meters.Sedimentary environments that are distinguished by recognizing shallow marine and intertidal zonesettings, beach, flood plain environment causing by sea level changes. In this research, two undisturbedcores, ۱۰ and ۱۵ meters were taken from shallow water of Persian Gulf near Bandar-Abbas and Bushehr bydrilling method. Thirty five sub samples were picked for mineralogical and geochemical studies, grain sizeand, geochemical and ۱۵ selected samples from foraminifera for C۱۴-AMS dating. Morphoscopy ofsamples were performed using Olympus microscope. Total Organic Carbon (TOC) and S۲ (PyrolysisHydrocarbon Yield) were measured by type VI Rock-Eval pyrolysis. According to Folk's classification,more than ۵۰% of all samples are in the mud-size (silt and clay-size) range. The components of the marinesediments can be subdivided into two main groups, namely, detrital and organic/biogenic components.Recently, Organic/biogenic particles in the shallow and coastal areas mainly comprises shells of benthonicorganisms such as bivalves, gastropods and benthonic foraminifers. In the deeper parts of the Persian Gulf,these particles comprise benthonic and planktonic organisms. In general, planktonic fauna were moreabundant in the deeper regions of the Persian Gulf. Non-skeletal components, such as ooids were alsoobserved in the shallow areas. Detrital particles mainly comprise quartz, mica, feldspars, clay minerals,clastic carbonate and carbonate-non carbonate rock-fragments. Meanwhile, fragments of halite, dolomiteand gypsum have been observed in deposits. In general, XRD and EDS results indicate the presence of clayminerals (chlorite, kaolinite, smectite, palygorskite, illite), quartz, feldspar, calcite, dolomite, aragonite,hematite, mica, halite and gypsum. These results indicate that carbonate components (calcite) are moreabundant than detrital components (quartz, feldspar and mica). According to mineralogical results, thenorthern part of the Persian Gulf can be considered the relatively calcite rich sedimentary basin and quartzpoor. It should be noted that the mineralogical results of fluvial deposits also indicate the abundance ofcalcite and quartz minerals compared to other sedimentary components. Based on the current conditionsof sediments in different regions of the sea, the old sediments of the cores were interpreted.Flood plainsediments in the cores are red in color and indicate a period of low seawater and seawater regression. Asthe sea level rises, the sediments of the floodplain change to coastal sediments and then to gray marinesediments. As the sea level fall, the sedimentary environment and associated sediments change inversely.The sedimentological data indicate that the sediments collected in both cores document several finingupward parasequences. Based on sedimentological evidence, in the two cores, we could distinguish fivesignificant depositional phases during the last ۱۰,۰۰۰ years. The potential of small mountain river systemsfor paleoenvironmental reconstructions in drylands – an example from the Binaloud Mountains innortheastern Iran.