Characterising the Ongole Coastal Dunefield of SE India: Formation and Temporal Constraints
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Characterising the Ongole Coastal Dunefield of SE India: Formation and Temporal Constraints Devender Kumar1*, Dontireddy Venkat Reddy1, Robin Davidson-Arnott2 1
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, India Department of Geography, Environment and Geomatics, University of Guelph, ON, Canada *E-mail: [email protected] 2
ABSTRACT The Ongole coastal dunefield (OCD) is about 20 km long and 2.5 to 3 km wide, and is located to the east of Ongole town between the mouth of the Paleru river in the south and a small creek in the north. Much of the dunefield lies 3-5 m above sea level with some large dune ridges reaching 10-12 m. The area landward of the dune field consists of an extensive marsh. Optically stimulated luminescence (OSL) dating of 12 sub-surface sediments from three sites near the western edge of the dunefield gives almost concurrent age of 5.1±0.4 ka. Radiocarbon dating of one shell from a similar location also corroborates the OSL age while the age of another shell taken closer from the modern shoreline gives a date of 3.29±0.5 ka. The age of the deposits and morphology of the dunefield indicate that it was probably initiated on some form of barrier system at the end of the Holocene transgression. INTRODUCTION At the peak of the last glacial period around 30-20 ka BP, global sea level was about 110-130 m below the present sea level. As a result, the shoreline was considerably further offshore than today and large areas of the continental shelves outside the areas of glaciation were exposed to sub-aerial processes. Beginning around 20-18 ka BP melting of the continental ice sheets led to a rapid increase in eustatic sea level producing the Holocene transgression which terminated about 7-6 ka BP (Peltier and Fairbanks 2006; Ranasinghe et al., 2013; MurrayWallace and Woodroffe, 2014). On relatively gently sloping continental shelves of passive margins, the transgression was accompanied by reworking of sediments deposited on the coastal plain during the Pleistocene low-stand and the transgression of sandy beach and dune systems in the form of mainland dunes as well as barrier spits and barrier islands. Examples of this have been described from the east coasts of North and South America (e.g., Swift et al., 1972; Dillenburg et al., 2017) and Australia (Kinsela et al., 2016; Dillenburg et al., 2020) and a number of other locations around the world, including India (Banerjee, 2000; Mukhopadhyay and Karisiddaiah, 2014). There are extensive modern sandy beach systems along the Coromandel coast of eastern India at the south end of the Bay of Bengal. These systems include numerous sandy spits built across shallow river estuaries and the beaches and associated foredunes that occur along much of the coast between the estuaries (Mukhopadhyay and Karisiddaiah, 2014). In addition, there are several deltas along the Coromandel coast associated with large rivers draining the eastern Ghats and the very large Ganges delta at the head of the Bay of Bengal. Dating of beach ridges in the
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