Late Quaternary highstand deposits of the southern Arabian Gulf: a record of sea-level and climate change
Published:January 01, 2002
Alun H. Williams, Gordon M. Walkden, 2002. "Late Quaternary highstand deposits of the southern Arabian Gulf: a record of sea-level and climate change", The Tectonic and Climatic Evolution of the Arabian Sea Region, P. D. Clift, D. Kroon, C. Gaedicke, J. Craig
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The southern Arabian (Persian) Gulf is at present the site of extensive carbonate sedimentation, as was the case during Pléistocène interglacial marine highstands. During glacial lowstands the basin was subaerially exposed, and aeolian sedimentation predominated. Most of the southern Arabian Gulf floor is underlain by Quaternary carbonates, and scattered outcrops may be found onshore. These belong to three formations: the aeolian Ghayathi Formation, the continental Aradah Formation and the marine Fuwayrit Formation. The Fuwayrit Formation consists of three members, separated by subaerial exposure surfaces. These are, from the base upwards, the shallow marine Futaisi and Dabb'iya Members, and the aeolian Al Wusayl Member. Offshore, at least six Quaternary sequences are present within the uppermost 50 m of sediment. No reliable direct age dates have been acquired from Pléistocène shallow marine or coastal deposits in the southern Arabian Gulf. It has therefore been necessary to infer the ages of these sediments by a comparison of their stratigraphy and elevation with deposits known from other parts of the world. We regard this approach as valid because the southern Gulf coastline lacks evidence for significant widespread neotectonic uplift, and halotectonic effects are localized. This comparison indicates that the Fuwayrit Formation was deposited during the last interglacial (oxygen isotope substage 5e), as (1) these sediments represent the youngest pre-Holocene marine deposits, and (2) they are found at an elevation correlative with many substage 5e deposits from other parts of the globe. Sedimentary evidence reveals two highstands during this period, peaking at around 1.5 m and 6 m above present sea level, respectively. Offshore sediments indicate that sea level did not fall as far as 24 m below present level in the intervening regression. Following the second highstand, sea level fell to more than 23 m below present level, before briefly rising once again (late isotope stage 5). This later highstand probably peaked between 17 and 7 m below present level. The sequence underlying the Fuwayrit Formation was probably deposited during the penultimate interglacial (late oxygen isotope stage 7). It is also likely that the Ghayathi Formation aeolianites were largely sourced from this sequence. Facies analysis of offshore core sediments indicates that sea level reached at least 15 m below present level during this period. Widespread evidence exists for a Holocene sea level higher than at present in the southern Arabian Gulf, indicating that it peaked at 1 -2 m above present level, c. 5.5 ka bp. Pléistocène deposits preserved in the southern Arabian Gulf provide a record of changing palaeowinds and palaeoclimates. Currently, the region experiences a hyper-arid to arid climate, with facies patterns dominated by the northwesterly shamal wind. The Ghayathi Formation was originally deposited under an arid climatic regime, which allowed the sediments to remain unconsolidated. The dunefield was later remodelled under conditions of increasing wind speed, with a change in wind direction from NNW to WNW. These changes are thought to reflect the onset of glaciation. Palaeocurrent directions from the Al Wusayl Member, combined with sedimentary evidence from the Futaisi and Dabb'iya Members, indicate that during the peak of the last interglacial the prevailing wind (the 'palaeo-shamal') blew from the NE. Compelling evidence for a pluvial episode during this period is provided by abundant and widespread dissolution (palaeokarstic) pits found in the top surface of the Futaisi Member, believed to represent the former positions of abundant trees or large plants.
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The Tectonic and Climatic Evolution of the Arabian Sea Region
Over long periods of time the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate: (i) through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean; (ii) through the growth and erosion of orogenic belts, resulting in changes in oceanic chemistry and disruption of atmospheric circulation. The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet.
The Tectonic and Climatic Evolution of the Arabian Sea Region brings together a collection of recent studies on the area from a wide group of international contributors. The paper range from high resolution, Holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic. Marine geophysics, stratigraphy, isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea. while much work remains to be done to understand fully the tectonic and climatic evolution of the Arabian Sea, a great deal has been achieved since the last major review, as detailed in the 26 contributions. This volume is essential reading for palaeoceanographers, sedimentologists and geophysicists. It will also be interest to structural geologists and those working in the petroleum industry.