Geomorphic response to sea level and climate changes during Late Quaternary in a humid tropical coastline: Terrain evolution model from Southwest India

摘要

The coastal lands of southern Kerala, SW India in the vicinity of Achankovil and Thenmala Shear Zones reveal a unique set of geomorphic features like beach ridges, runnels, chain of wetlands, lakes, estuaries, etc. The chain of wetlands and water bodies that are seen in the eastern periphery of the coastal lands indicates the remnants of the upper drainage channels of the previously existed coastal plain rivers of Late Pleistocene age that are later broadened due to coastal erosion under the transgressive phase. The terrain evolutionary model developed from the results of the study shows that the Late Pleistocene transgressive events might have carved out a major portion of the land areas drained by the coastal plain rivers and as a result the coastal cliff has been retreated several kilometers landwards. The NNE—SSW trending beach ridges located close to the inland wetlands indicate the extent of shoreline shift towards eastwards during Late Pleistocene period. The present beach parallel ridges in the younger coastal plain indicate the limit of the Mid Holocene shoreline as the transgression was not so severe compared to Late Pleistocene event. The zone of convergence of the two sets of beach ridges coincides with the areas of economically viable heavy mineral placers that resulted from the size and density based sorting under the repeated transgressive events to which the coast had subjected to. The chain of wetlands in the eastern side of the study area has been evolved from a mega lagoon existed during Late Pleistocene. The Pallikkal River that links discrete eastern wetland bodies has been evolved into its present form during Early Holocene.