A rock magnetic record of Pleistocene rainfall variations at the Palaeolithic site of Attirampakkam, Southeastern India

Attirampakkam, an open-air stratified Palaeolithic site in southeastern India is the focus of ongoing studies to investigate the nature of Lower and Middle Palaeolithic occupation in relation to changing Pleistocene environments. The paucity of faunal or palaeobotanical remains at the site required the use of rock magnetic properties (χ_lf, χ_fd, χ_fd %, χ_ARM, SIRM, χ_ARM/SIRM, SIRM/χ_lf, χ_ARM/χ_lf, χ_ARM/χ_fd, S-ratio, HIRM and HIRM/IRM_300mT) as proxies for deciphering the palaeoenvironments and palaeoclimates of the region. Rock magnetic data from stratified deposits within excavated trenches show that the bulk of the sedimentation was intermittent with no subaerial exposure of sediments for long periods, and points to fluctuating wetter and drier climates associated with the Acheulian to Late Middle Palaeolithic levels. There is a general trend towards a wetter climate from Layer 5 upwards. Layer 7 offers evidence of bacterial magnetite (χ_ARM/χ_lf>40 and χ_ARM/χ_fd>1000), suggesting the onset of micro-anaerobic environments as a result of floods. Greigite is indicated in Layer 5 (SIRM/χ_lf>30×10³Am^-1), which indicates a reducing environment. Layer 2 represents an arid climate (higher proportion of haematite and a coarser magnetic grain size). Layer 1a again is indicative of an arid climate (presence of calcrete, magnetically "hard" minerals and coarser magnetic grain size). Results indicate that the southeast coast of India experienced a mostly dry tropical climate during the Pleistocene. The detected occurrence of a few notably more arid intervals did not disrupt occupation of the site by successive groups of hominins.