ELSEVIER Marine Geology 117 (1994) 207-225 MARINE OB LOOY JNTEANa~O~aL jo~aaa mr ~aR~E OfOLO0~ G E O ~ ANO GEOfWYS~S Holocene submarine terraces on the western continental shelf of India; Implications for sea-level changes B.G. Wagle, K.H. Vora, S.M. Karisiddaiah, M. Veerayya, F. Almeida National Institute of Oceanography, Dona Paula, Goa, 403004, India (Received May 18, 1993; revision accepted November 4, 1993) Abstract Detailed echosounding, side-scan sonar and high-resolution seismic-reflection profiling on the western continental shelf of India have revealed a series of submarine terraces at different depths between the outer fringe of the inner shelf and the shelf break, being more common between 11° and 20°N. The terraces are prominent between water depths of 50 and 115 m and occur at six distinct levels: (1) 55-60 m, (2) 65-70 m, (3) 75-80 m, (4) 85-90 m, (5) 95-100 m and (6) 110-115 m. They are categorized into: (1) wave-cut terraces, (2) coral/algal reef-induced terraces and (3) palaeo-beach/barrier terraces. The reef-induced terraces occur predominantly in the carbonate-rich province (20°-13°N), while both the wave-cut and palaeo-beach/barrier terraces are discernible in the terrigenous regime, which is located north and south of these latitudes. Despite their genetic differences, their evolution is ascribed to reef growth, progradation and wave activity during the lowstands of sea level and reflect different phases of stiUstands of the late Pleistocene to mid-Holocene age. 1. Introduction The topography of the continental shelves is mainly governed by depositional and erosional processes which occur during glacio-eustatic sea- level fluctuations. Other factors involved, directly or indirectly, are the original relief, lithology, sedimentation, tectonic movements and climatic changes (Kaplin et al., 1968). The majority of the continental shelves world-wide have been affected to a considerable extent by Pleistocene glaciation (Emery, 1968). The rate of sea-level rise has varied frequently and the sea-level stillstands produced wave-cut terraces and platforms. In other words, the surface of a terrace can be accepted as a reasonable record of former sea level (Sirkin et al., 1990). 0025-3227/94/$7.0o© 1994ElsevierScience B.V. All rights reserved SSDI 0025-3227(93)E0141-R Submarine terraces have been reported from continental margins throughout the world (Emery, 1958; Garrison and McMaster, 1966; Veeh and Veevers, 1970; Coulbourn et al., 1974; Marshall, 1977; FiUon et al., 1978; Wenke, 1985; Mullins et al., 1988; Harris and Davies, 1989, Paulay and McEdward, 1990; Pirazzoli et al., 1991; Barrie et al., 1991). The presence of terraces has also been reported on the western continental shelf of India (Nair, 1971, 1974). This paper presents the results of a detailed study and new information on the occurrence of submarine terraces in two distinct sedimentary regimes char- acterized by carbonate and terrigenous provinces off the west coast of India and discusses their implications in terms of glacio-eustatic sea-level changes.