Forum communication Consequences of sea level and climate changes on the morphodynamics of a tropical coastal lagoon during Holocene: An evolutionary model D. Padmalal a , K.P.N. Kumaran b, * , K.M. Nair a , Ruta B. Limaye b , S. Vishnu Mohan a , B. Baijulal a , S. Anooja a a Centre for Earth Science Studies, Thiruvananthapuram 695031, Kerala, India b Palynology and Palaeoclimate Laboratory, Palaeobiology Group, Agharkar Research Institute, G.G. Agarkar Road, Pune 411004, Maharashtra, India article info Article history: Available online xxx abstract Vembanad Lagoon is the largest backwater system in the southwestern coast of India, and it is one of the wetlands of international importance, as defined by the Ramsar Convention. The coastal area encom- passing the Vembanad Lagoon comprises a spectrum of barrier islands, ridges and swales, lagoons, and flood plains. The lagoon and its adjoining coastal lands are known for economically viable deposits of ilmenite rich beach placers, lime shells, and high purity silica sands. The sedimentological, palynological, and geochronological studies reveal that the sea level and climate changes have brought significant modifications in the geomorphic settings of the system. The depositional regimes and the evolutionary phases showed marked differences in the northern and southern reaches of the Lagoon. The geomor- phological settings, occurrence of a suite of major heavy minerals (sillimanite þ opaque) and predom- inance of marine elements in the palynological assemblage in the southern reach of the lagoon are indicative of barrier spit development, which is further influenced by reworked Neogene sediments with characteristic sillimaniteeopaque heavy mineral suite of khondalitic affinity. The northern half evolved during the transgressiveeregressive events of EarlyeMiddle Holocene from a sheltered coastal water body surrounded by thick coastal vegetation. The opaqueeinosilicate dominant heavy mineral suite in the northern sector indicates contribution of sediments from charnokitic source rocks in the area north of the Achankovil Shear Zone. The proposed four stage evolutionary model of the Vembanad Lagoon indicates that it evolved from an embayment of the Arabian Sea by the progradation and development of a barrier spit during transgressiveeregressive cycles under heavy rainfall events of the Holocene. Ó 2013 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The Indian coastline, stretching over 6500 km, is the sixth longest in the world and has been subjected to several episodes of sea level variations that followed the Last Glacial Maximum (LGM). Since the LGM, it has been undergoing physical changes, and the present coastal geomorphology has evolved largely in the back- ground of the post-glacial transgression over the pre-existing topography of the shore, coast and offshore zones (Merh, 1992; Hashimi et al., 1995; Banerjee, 2000; Somayajulu, 2002; Nair et al., 2006). The Holocene sea fluctuated in the course of the last 10,000 years, and its oscillations between 3000 and 6000 BP have left significant imprints in the sedimentary archives, throwing light on the evolution of the coast. The sea level and climate changes have strongly influenced the coastal marine processes. Much of the coastal land and associated landforms around the world have been carved out during the Late Quaternary and the geomorphic evo- lution has greatly influenced the history of humanity (Woodroffe, 2002). Coastal lagoons are considered to be an important ecosystem in many low-lying coastlines of continents and constitute 13% of the global coastal environment (Bird, 1994; Kjerfve, 1994). Coastal la- goons are highly productive ecosystems, as they contribute to the overall productivity of coastal waters by supporting a variety of habitats, including salt marshes, sea grasses, and mangroves. Several attempts and reviews on this unique ecosystem have added considerable knowledge while appraising their physical and ecological dimensions (Roy, 1984, 1994; Carter et al.,1989; Cheng et al., 1993; Oliveira and Kjerfve, 1993; Cooper, 1994; Kjerfve, 1994; Isla, 1995, 2002; Bird, 2000; Caldara et al., 2002; Davis, * Corresponding author. E-mail address: kpnkumaran@gmail.com (K.P.N. Kumaran). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2013 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2013.12.018 Quaternary International xxx (2013) 1e17 Please cite this article in press as: Padmalal, D., et al., Consequences of sea level and climate changes on the morphodynamics of a tropical coastal lagoon during Holocene: An evolutionary model, Quaternary International (2013), http://dx.doi.org/10.1016/j.quaint.2013.12.018