Quaternary Geology of South Kerala Sedimentary Basin - An Outline

The South Kerala Sedimentary Basin(SKSB) extending along the coast between Kollam and Kodungallur, is the landward extension of the offshore Kerala-Konkan Basin (KKB). The SKSB has a fill of about 700 m of sediments, of which > 80 m are made up of Quaternary sediments, the rest being Miocene formations. Data from over 120 bore holes drilled for groundwater extraction from Tertiary aquifers, geotechnical investigations and stratigraphic studies form the basis of this paper. Based on sediment characteristics and tectonic setting, the SKSB can be divided into three separate blocks (a) Southern Block (uplifted during Pleistocene end), (b) Central Depression (undergoing subsidence from Early Miocene to Present) and (c) Northern Block (uplifted during Pleistocene-Holocene transition but undergoing subsidence during Holocene).

The Late Pleistocene sedimentary sections indicate continental environments at the bottom. The marine influence during Pleistocene predates 42 ky BP. Ecology and environment deduced from sedimentology, palynology micropalaentology and geochemistry suggest climatic variations from higher-Than-Present to low rainfall rates during deposition of Pleistocene sediments.

Holocene sedimentation also started in continental environments. The marine transgression giving rise to littoral-Lagoonal environments dates back to 7-6 ky BP. The high precipitation in Holocene gradually got reduced and by ca 3 5 ky BP the area witnessed prolonged exposure and development of ferruginous palaeosols.

Within the constraints imposed by insufficient samples and inadequate geochronological data, the paper gives a broad picture of the structural framework, stratigraphy, palynology and depositional environments of SKSB. From these, inferences on sea level oscillations, palaeoclimatic variations and depositional environments are made.