Late Holocene Geomorphic Evolution of Cauvery Delta, Tamil Nadu

The Cauvery delta is a major Bird-Root shaped delta with its apex located east of Tiruchirappalli with the mother channel Cauvery flowing along Thanjavur- Kumbakonam - Kaveripoompaitinam. The distributary drainages are radialing over an arc towards east from its apex with a fan shape and finally debouch into the sea from south of Tiruthuraipoondi in the south to Kaveripoompattinam in the north. All these distributary drainages are now seen as palaeochannels including the mother channel Cauvery. which is now called as "Palam Cauvery". The present day flow of Callvery river is confined to the northernmost rim of the delta as river Coleroon. On he basis of the archaeological, epigraphic and historical data analysed earlier and the ¹⁴C dating carried out recently, the present authors infer that the age of the delta may vary from 2300 Y.B.P. (Years Before Present) to 750 Y.B.P. and the age of the palaeochannels are also younging from 2300 Y.B.P. in the south to 750 Y.B.P. in the north. In the southern part of the Cauvery delta, the Mio-Pliocene Sandstone of Pattukottai-Mannargudi area is undergoing upliftment along N-S faults. On the basis of the rapid land progradation during 6085±233 Y.B.P. - 1020±80 Y.B.P. in Vedaranniyam coast, it is visualized that the Mio-Pliocene Sandstone must be undergoing upliftlnenl significantly since 6 100 Y.B.P. onwards. On the basis of the occurrence of older palaeochannels in the south, the gradual younging palaeochannels towards the north and the land emergence in the south of the Cauvery delta in Pattukottai - Mannatgudi area, i t is concluded that the distributary drainages of river Cauvery would have become sequentially defunct/shifted from south to north and linally the mother channel Cauvery also would have been pushed towards north to reach the present tract of Coleroon river. The thinner palaeochannels in the south and the gradual wider palaeochannels in the north of the delta further indicate that as the land was already undergoing emergence in the south even before the river Cauvery had entered into Thanjavur plains, the river could not comfortably spread its distributaries in the south. Hence the southern distributaries, alter a brief flow, would have started drying sequentially from south to north during 2300-750 Y.B.P. thereby the floodwater of each of the southern distributary channel would have been pushed to its successive northern counterpart, i.e. the southern distributary (say 1 ) , pushing its water to its immediate northern counterparl (say 2). then the combined flow of 1 and 2 pushing the water to 3 and so on. The anomalous eyed drainage and its modifications during the last 50-60 years and compressed meanders in Coleroon river. deflected drainages in Palam Cauvery, truncation and punctuation of beach ridges by the E-W faults along the N-S coast and such faults acting as pathways for the sub parallel creeks indicate vibrant Late Holocenc geological history predominated by the tectonic movements in Cauvery delta.