Quaternary climatic changes over Southern Arabia and the Thar

Desert, India

K. w. GLENNIEI, A. K. SINGHVI2, N. LANCASIER3 & I. I. IELLEj.4

I Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB9

2UE, UK (e-mail: glennie-ken@hotmail.com)2 Earth Science Division, Physical Research Laboratory, Ahmedabad, 380 009, India

3 Desert Research Institute, Reno, NV 89512, USA

4 Department of Geological Sciences, University of Manitoba, Winnipeg, Man. R3T 2N2,

Canada

Abstract: The distribution of sand dunes over the southern half of Arabia confonns to theinfluence of two wind systems. the northern Shamal, which is a strong wind that blows to theSSE down the Persian (Arabian) Gulf and then swings to the SW across the hyperarid Rub alKhali towards North Yemen; and the strong winds of the SW Monsoon system, which wereresponsible for fonning linear dunes that trend north-south in the Wahiba Sands of easternOman and SW-NE in the Thar Desert (NW India). In the Thar Desert, the SW Monsoonalternates with the weaker NE Monsoon. The dating of exposures of older dune systems byisotopic, radiometric and optically stimulated luminescence (OSL) analyses has shown that theShamal was active throughout the latter part of the Quaternary period, and probably as long agoas Mid-Miocene time (c. 15 Ma). At times of glacial maxima, when global sea level was some100-120 m or more lower than now, siliciclastic and carbonate grains were deflated from theexposed surface of the Persian Gulf and transported into the NE Rub al Khali within the UnitedArab Emirates. It is suspected that occasionally the Shamal also transported some quartz sandsfrom the NW onto the exposed narrow continental shelf of SE Arabia, with silt-size particlesbeing carried into the Arabian Sea. The SW Monsoon, on the other hand, was re-establishedover the coast of SE Arabia several millennia after the last glacial maximum and was fullyestablished near the coast of SE Arabia during the early Holocene interglacial after theatmospheric high-pressure system associated with the glacial period had become weaker. Earlyduring the Holocene interglacial periods when the SW Monsoon dominated, a combination ofquartz and carbonate sands was deflated from the exposed continental shelf and transported tothe north into the Wahiba Sands. Aeolian activity in the Thar Desert also peaked during thisperiod of transition from full glacial to interglacial conditions. The dune systems of SE Arabiaoverlie the distal edges of older alluvial fans that in Oman date back at least 350 ka. Thesediments of some of these fluvial sequences in Oman reached the Arabian Sea via Wadi Batha,only to be removed by along-shore currents driven by the SW Monsoon. In the Thar Desert, thesppply of aeolian sediment is mostly from fluvial sources. Marine sediments from the ArabianSea between Arabia and Thar record the contrasting effects of the Shamal and the SWMonsoon: the fonner mostly as a source of wind-blown dust from Arabia and the latter bycausing upwelling of nutrient-rich waters leading to organic blooms.

The expansion and contraction of deserts and their been implicitly assumed. However, more recentrelationship to changes in climate including the luminescence dating studies indicate that aeolianalbedo and atmospheric circulation patterns, have activity occurs over more specific time windows.

long been investigated (e.g. Tricart et al. 1957; The window of opportunity for aeolian activityFairbridge 1962; Sarnthein 1978; McClure 1978, depends on a variety of factors that regulate the

1984; Dhir et al. 1992; Sanlaville 1992a, 1992b; sediment production, supply, transport and preser-

Yan & Petit-Maire 1994). Conventionally, the arid vation (Kocurek & Lancaster 1999). Consequently,expansion episodes have been associated with high- both local and global factors influence this activity,latitude glacial epochs and the contraction episodes implying that the event chronology in differentwith more humid phases. A synchronous response deserts under apparently identical global climatic

of different desert systems to climate change has regimes need not be in phase, sensu stricto.

From: CLIFf, P.D., KROON, D., GAEDICKE, C.. & CRAIG, J. (eds) 2002. The Tectonic and Climatic Evolution of 301

the Arabian Sea Region. Geological Society, London, Special Publications, 195, 301-316.0305-8719/02/$15.00 c<::J The Geological Society of London 2002.