Late Quaternary stratigraphy, Paleoclimate and neotectonism of the Persian(Arabian) Gulf region

The last glacial deposits in the Persian (Arabian) Gulf consist of a > 22,0 00 year old paralic terrigenous sequence in the Mesopotamia Shelf, the fore deep in front of the Iranian Zagros Mountains and the northern side of the Biaban Shelf. Elsewhere, the Gulf, and probably the Biaban Shelf, were mant led by > 30,000 year old carbonates. Comparison of C-14 data from foraminif era from the last glacial terrigenous unit in the foredeep off Iran with cu rves published by Hopley [Hopley, D., 1982. The Geomorphology of the Great Barrier Reef: Quaternary Development of Coral Reefs. Wiley, New York, 453 p p.] and Chapell et al. [Chapell, J., Omura, A., Tezer, E., McCulloch, M., P andolfi, J., Ota, Y., Pillans, B., 1996. Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxyg en isotope records. Earth Planet. Sci. Lett. 141, 227-236.] indicates that the region may have experienced uplift during the last glacial, whereas oth er geologic data indicate that the foredeep has had a history of continuous subsidence during the Cenozoic. A possible explanation for this discrepanc y is that the foraminifera analyzed are not in place, but were reworked int o shallower water during the Holocene transgression. However, the foraminif era analyzed do not display any evidence of wear, indicating that such tran sport was limited. A third alternative is that sea level during the last gl acial was much higher than indicated by the curves of Hopley and Chapell et al. At the peak of the last glaciation 21,000 to 20,000 years ago, when sea lev el was 120 m lower than now, the Gulf was a waterless basin and deposition was negligible. On the Biaban Shelf, the Holocene transgressive sequence re sting unconformably on last glacial sediments consists of 14,000 year old c arbonates, a > 11,000 year old terrigenous delta on the northern end of the Biaban Shelf and 11,000-10,000 year old intertidal-tidal aragonite deposit ed in a dry climate. On the northeast side of the Gulf, the last glacial se diments are covered by 10,000 to 7000 year old aragonite muds (younging tow ard the northwest). Resting on the aragonites on the Biaban Shelf and on th e northeast and northwest sides of the Gulf are marls deposited under the p resent humid climate. The southwest side of the Gulf continued to be a site of carbonate deposition throughout the Holocene. Comparison of AMS C-14 me asurements of the late Holocene marls with the sea level curve of Fairbanks [Fairbanks, R.G., 1989. A 17,000 year glacio-eustatic sea level record; in fluence of glacial melting rates and the Younger Dryas event and deep-ocean circulation. Nature 342, 637-642.] indicates that the axial zone of the Gu lf off Iran experienced subsidence during the Holocene. This subsidence cou pled with a rapid rise in sea level during a major glacial melt 9500 to 850 0 years ago, when global sea level rose from -50 to -28 m, led to the repla cement of marl with a shallow (8-25 m) water fauna by a 'deep' (> 50 m) wat er one. Similar measurements and other geologic data indicate that the Meso potamia Shelf and the mouth of the Mesopotamian Depression on the northwest side of the Gulf underwent both subsidence and uplift during the Cenozoic. These vertical oscillations, however, were more subdued than these in the foredeep off iran. The Arabian Shelf along the Gulfs southwest side appears to have experienced minor uplift during the Cenozoic. (C) 1999 Elsevier Sc ience B.V. All rights reserved.