Late Quaternary Variations in Sedimentation Rate in the Laccadive Trough, Southeast Arabian Sea

Radiocarbon measurements of a core from the Laccadive Trough, SE Arabian Sea have yielded ages which show that sediments from the Pleistocene, Holocene and a transition zone can be recognized by virtue of colour variation. The mean sedimentation rate decreases from 4.11 to 3.15 cm/10³yr for Pleistocene and Holocene respectively, witha peak of 6.36 cmcm/10³yr determined for the transitional zone. A sediment slump or turbidite emplacement resulting from higher terrigenous influx during the transition period has been inferred. This is in contrast to the bioclastic turbidite of the central continental margin-pelagic region (off Bombay-Ratnagiri sector of western India). The decrease in sedimentation rate from Pleistocene to Holocene can be most likely ascribed to entrapment of riverine sediments in estuaries and continental shelf, as a result of Holocene sea level rise.

The mean sedimentation rate in the Laccadive Trough (3.84 cm/10³yr) is lower than that on the northwestern continental margin of India (4.6-9.8 cm/10³yr) because of relatively low terrigenous influx from the small west-flowing rivers of Peninsular India. The Holocene sediment thickness in the Laccadive Trough is 35 cm as against 50 cm in the northeastern Arabian Sea. The onset of environmental conditions representative of Holocene is estimated at ca. 9300 yr B.P. which corroborates the date proposed for the northern Indian Ocean.