Holocene sea-level and climatic fluctuations: Pulicat lagoon - a case study.

Abstract

Pulicat lagoon situated in the Palar Basin, is the se c- ond largest lagoon on the east coast of India. The north-western margin of the desiccated lagoon is an irregular and elevated hard surface. Palynological studies were carried out in sedime ntary soil samples from four pits dug across this part of the lagoon. Vegetational reconstruction from peat beds at 4.98 m (a.m.s.l.) and 1 m (a.m.s.l.) in the west at Sulurpet and Kasdredinilem, respectively, is indicative of a palaeoshoreline. The sea level reached its maximum around 6650 ± 110 yrs BP in Sulurpet, 18 km west from the present shoreline. The radiocarbon dates of peat bed at Kasdreddinilem reveals an age of 4608 ± ± 122 yrs BP, indicating the shift in mangrove line eastwards during the regressive phase. The Late Holocene radiocarbon dates of shells (bivalves) at Attakanitippa and Sriharikota island are the chain of intermittent regressive phases since then. The peat sediment below this shell bed at 9 and 15 m below the mean sea level was perhaps deposited during the transgressive phase. No evidence of mangrove pollen in the late Holocene soil sediments indicates that sea- level fluctuation and climatic conditions during mid and late Holocene led to the decline in ma ngroves in the area. The present-day vegetation mainly comprises psammophytes around the semi-stabilized strand with commercially planted woody forest on the stabi- lized strands. Casuarina, Prosopis and Acacia sps. are grown and exploited commercially around the lagoon that hinders the natural vegetational succes- sion and the ecosystem not favourable for man- groves. The past and present vegetation coupled with sea-level fluctuations, climate and the anthropogenic activity since Holocene has been discussed in the p a- per.