Stable Isotopic and Trace Elemental Composition of Mollusks From the “Inland Sea” Lagoon and Channel System, Southeastern Qatar

Abstract

The Kor Al Adaid (KAD) region of Southern Qatar hosts the evaporitic “Inland Sea”, a shallow restricted embayment connected to open Arabian Gulf waters through a deeper lagoon and channel system. The Inland Sea covers an area of greater than 50 km2; however its average depth is approximately only 1 meter. In summertime the sea commonly reaches salinities of >70 ppt, and is the site of subaqueous gypsum precipitation. An effort is underway to sample and map the sediments deposited in this unique channel and lagoon system. This effort is part of an integrated study that includes measurements of seawater chemistry (temperature, salinity, pH, and dissolved oxygen), and modeling of physical oceanography using data acquired using acoustic doppler current profilers. Although the marine system under study is primarily dominated by clastic deposition from the reworking of quartz-rich dune sand, there is also a prominent population of mollusks including Cerithium scabridum gastropods, and the bivalve Marcia Flammea. The isotopic and trace elemental composition of mollusks can be useful as proxy indicators for oceanographic parameters such as temperature, salinity, and productivity. This work explores the isotopic (δ18O, δ13C) and trace-elemental (Mg/Ca, Sr/Ca, Mn/Ca, Fe/Ca, Zn/Ca, Al/Ca, and Cu/Ca) composition of these mollusk shells, and their relationship to measured physical and chemical oceanographic parameters. Additionally these measurements are compared against those of mollusks from Al Ruwais, a much less restricted carbonate-dominated barrier island system in northern Qatar. Initial results show that the δ18O values of mollusks from Kor Al Adaid are consistently high relative to Al Ruwais equivalents, whereas the δ13C values are similar. This is interpreted to result from greater evaporation of restricted Inland Sea waters. Correlations between different trace elemental ratios and between trace elemental ratios and isotopic ratios are not consistent across the Cerithium scabridum and Marcia Flammea datasets, likely reflecting differences in habitat and diet. This study has implications for the employment of chemostratigraphy in the correlation of subsurface rocks deposited in the evaporative marine realm.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017