Luminescence chronology of late Holocene extreme hydrological events in the upper Penner River basin, South India PUTHUSSERRY J. THOMAS, 1,2 * NAVIN JUYAL, 1 VISHWAS S. KALE 3 and ASHOK K. SINGHVI 1 1 Planetary and Geo Sciences Division, Physical Research Laboratory, Ahmedabad, India 2 Luminescence Dating Laboratory, National Geophysical Research Institute, Hyderabad, India 3 Department of Geography, University of Pune, Pune, India Thomas, P. J., Juyal, N., Kale, V. S. and Singhvi, A. K. 2007. Luminescence chronology of late Holocene extreme hydrological events in the upper Penner River basin, South India. J. Quaternary Sci., Vol. 22 pp. 747–753. ISSN 0267–8179 Received 13 March 2006; Revised 6 October 2006; Accepted 23 October 2006 ABSTRACT: Field stratigraphy, sedimentology and optically stimulated luminescence (OSL) dating have been used to reconstruct the southwest monsoon variability in the semi-arid region of southern India during the late Holocene. Facies architecture and OSL dating of the water-lain sediment suggest prevalence of a weak hydrological regime around 3 ka. Following this, a progressive strengthening of monsoon occurred till 2 ka. After 2 ka and until 1 ka fluvial activity was nearly dormant, indicating weakening of the monsoon. Presence of high-magnitude flood deposits, overbank sedimentation and pedogenesis during 1–0.6 ka indicate intensification of the southwest monsoon in the basin. The onset of aridity was associated with episodic storm surge events that are manifested in the pond sedimentation and localised aeolian accretion. This phase is bracketed between 0.5 ka and 0.2 ka. A renewed phase of monsoonal activity was observed in the form of floodplain aggradation between 180 and 90 years ago. In the past 70 years no significant change in the monsoon performance has been observed. Copyright # 2007 John Wiley & Sons, Ltd. KEYWORDS: late Holocene; fluvial deposits; OSL dating; southwest monsoon; Penner River; South India. Introduction Arid and semi-arid regions cover nearly 50% of the global land area and support more than 20% of the global population (Middleton and Thomas, 1997). Poor understanding of the complex interactions among geological and ecological pro- cesses in arid regions currently limit our ability to predict landscape response to climatic and human influences. Efforts are currently being made to understand the natural and human-induced changes in these regions (IGCP-413) as these areas are most sensitive to climatic variability and land use practices. In dryland regions, rivers are among the important geomorphic agents and a river’s fluvial dynamics, flood histories, water budget and sediment fluxes are determined by the climate. In conjunction with lacustrine and aeolian deposits, fluvial sequences provide great potential for a detailed palaeoenvironmental reconstruction in dryland areas (Reid, 1994; Reid and Frostick, 1997; Nanson and Tooth, 1999; Singhvi and Derbyshire, 1999; Juyal et al., 2000; Kale et al., 2000). Given the scenarios for anticipated global change, such palaeoenvironmental reconstructions are crucial for devising appropriate land use planning and adaptation strategies in arid zones. In India, beside the Thar Desert, the Rayalaseema region of Andhra Pradesh has a predominantly arid climate. The fluvial processes of rivers in this region are intimately connected to the periodicity and intensity of the southwest (SW) monsoon that account for ca. 80% of the total precipitation in the region (Rao, 1981). In this paper, reconstructions of southwest monsoon variability based on chronologically constrained fluvial and aeolian deposits are presented from the upper Penner basin. Owing to the paucity of organic material in the dryland river sediments, conventional radiocarbon dating has limited applicability. In view of this, we have used optically stimulated luminescence (OSL) dating of quartz mineral extracted from the fluvial and aeolian sediments. The chronometric data thus obtained are then combined with the sedimentological data to reconstruct the temporal changes in contemporary climatic regimes. Study area The upper Penner River basin is located in Anantapur district (138 41 0 –158 14 0 N, 768 47 0 –788 26 0 E), in the southwestern part of Andhra Pradesh in southern India (Fig. 1(a)). The region has a JOURNAL OF QUATERNARY SCIENCE (2007) 22(8) 747–753 Copyright ß 2007 John Wiley & Sons, Ltd. Published online 8 March 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jqs.1097 * Correspondence to: P. J. Thomas, Luminescence Dating Laboratory, National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India. E-mail: thomas@ngri.res.in