The controlling parameters on organic matter preservation within the bottom sediments of the northern part of the Persian Gulf

This study revealed that the dissolved oxygen levels, sedimentation rate, biota content, bioturbation and the particle size control the distribution of the total organic carbon (TOO) within the bottom sediments of the northern part of the Persian Gulf (from the Strait of Hormuz to the Khowr-e-Mussa). 525 surface samples (arranged in 19 linear section, as well as some additional samples between them) were taken from shallow to deep water ranging from 10 to 100 m in water depth. Sampling was carried out utilizing Van Veen Grab. All samples were analyzed for biota content (bioturbating organisms), TOO, S-2 (Rock-Eval Pyrolysis), mineralogy and particles size analysis. Composition of samples revealed quartz, feldspar, rock fragments and clay minerals, as well as organic/biogenic components (i.e. bivalves, gastropods, ostracods, bryozoans, benthonic and planktonic foraminifera, echinoderm spines and fish notochords). The organic/biogenic components mainly comprise coarse-grain constituents (gravel to fine-sand size). The mud fraction, total organic carbon (0.6 to 1.48 wt.%) and planktonic foraminifera increase toward the deep parts of the basin (Oxygen minimum zone (OMZ)), whereas the bottom dissolved oxygen level decreases. The OMZ promote organic matter preservation within the muddy sediments. The OMZ are recognized in sediments with low bioturbation (which indicated with decrease in benthonic biota content). The sediments deposited in OMZ are characterized by type II organic matter (marine origin). However, type III organic matter suggests terrestrial organic matter input to the north-western parts of the Persian Gulf. Poor preservation, intense bioturbation and high sedimentation rate prohibited the deposition of organic rich sediments in the shallow parts of the Persian Gulf. Whereas, organic rich sediments are limited to the deeper parts of the Persian Gulf due to low sedimentation rate, high preservation and low bioturbation.