Original paper

Chronology and weathering history of red dunes (Teri Sands) in the southwest coast of Tamil Nadu, India

Alappat, Linto; Joseph, Sabu; Tsukamoto, Sumiko; Kaufhold, Stephan; Frechen, Manfred

Abstract

Red dune sands in the southwest coast of Tamil Nadu, India, were examined to understand its chronology of formation using OSL chronometry. Degrees of weathering of these sands were deduced from field observation, clay mineral composition and geochemistry of the bulk sample. The sands were found to have been deposited in two episodes, i.e.between 16–9 ka and at 4.5 ka in the middle and lower parts of the dune field. The late Pleistocene deposition of sand in the upper terrace was associated with abundant sand supply owing to the lower sea level. The second stage of dune accretion at 4.5 ka was observed at the lower level relative to the present day coast. It was presumably associated with late Holocene higher sea level in the coasts of south India and deposition of sand in the backshore region on top of the previous indurated aeolian deposits. The elevated topography of the area acted as an obstruction to trap the sand-laden onshore winds and facilitated accumulation. Spatio-temporal variation in sand accretion was observed in terrace I at the central part of the dunes. The geochemistry and mineralogy of the sands is controlled by initial aeolian sediment sorting and chemical weathering leading to the alteration of feldspars to kaolinite and associated compositional variations in the major elements. The red colour in the sands is found to be related to the concentration of hematite in the fine fraction.

Keywords

red duneschemical index of alterationholocenepleistoceneosl datingchemical weathering