Event stratigraphy, paleoenvironment and chronology of SE Arabian deserts

Abstract

The geological record of the SE Arabian desert is exhibited in a variety of geomorphic features and their characteristic sediments, ranging from alluvial fans to inland and coastal dunes and sabkhas. Together, they suggest a large range of environmental and climatic variability between periods of relative aridity and humidity. Sedimentary events in the Emirates appear to correlate broadly with high-latitude glaciations, which affected both the Shamal winds and the extent of exposure of the Arabian Gulf. In general, the aeolian sands in the Rub al Khali responded to glacial events as a consequence of exposure of the floor of the Arabian Gulf. During glacials when Global sea level was low, quartz sands from across the exposed floor of the Arabian Gulf were transported by the Shamal winds south-eastwards to the Emirates and then south to the Rub al Khali. The supply of Shamal-transported sand from the floor of the Arabian Gulf was cut off by high stands of sea level during interglacial periods. The new coastal dunes ('miliolite'), rich in foraminifera and other cement-assisting calcareous shell fragments, were deflated down to the water table as their sand was transported further to the south, leading to the creation of coastal sabkhas. Studies on aeolianites and the lacustrine deposits provide evidence of phases of enhanced humidity prior to the last glacial maximum and during the Holocene. In contrast, the bedding attitudes of miliolites in SE Oman suggest that the Wahiba Sands were transported from south to north by a branch of the SW Monsoon. The depositional ages of these dunes indicate a close connection between the winds and coeval fluctuations of the SW Monsoon. The interdunal lakes and underlying dune sands reflect an active SW Monsoon during the Holocene. This is also indicated by the aeolian and lacustrine records of the Thar desert in India, which likewise are controlled by the SW Monsoon. South and west of the Oman Mountains is a broad alluvial fan (bajada) that is mostly inactive today. The oldest fluvial sediments are undated but preliminary age estimates suggest that some correlate with more humid earlier interglacials.