A submerged late Pleistocene delta and other features related to sea level changes in the Malacca Strait

Abstract

Bathymetry, sea floor echo characteristics, and shallow subbottom reflectors in the Malacca Strait and the slope of the Mergui—North Sumatra Basin of the southern Andaman Sea show a varied and locally complex character, which we interpret as a Pleistocene lowered sea level alluvial-delta-fan system. Sediment waves and elongate banks in the narrow and shoal southern part of the Strait indicate strong bottom currents, and a rugged subbottom topography demonstrates erosion during low sea level of the late Quaternary. Shallow subbottom reflectors at the northwest approaches to the Strait show progradation and cut and fill valleys and the presence of a compound late Pleistocene delta of the confluent Sumatran and Malayan rivers. The younger prograding layers are probably of mid-Wisconsin (Würm) age (ca. 40− 20 × 10 3 yr B.P. ), and the deeper foresets may be early Illinoian glacial stage (Riss, ca. 150 × 10 3 yr B.P. ). Farther seaward, a small fan progrades from the slope a short distance into the shallow northeastern part of the Mergui—North Sumatra Basin.