Submerged forest off Nyuzen, Kurobegawa alluvial fan, Toyama Bay, Central Japan

Abstract

Remnants of a submerged ancient forest have been found on the continental shelf of NW Japan off the Kurobe alluvial fan in Toyama Bay. The remains, standing tree stumps and roots, are located at depths between 20 and 40 m and ages of 8,000 years B.P. to 10,000 years B.P. have been determined by the 14C method. Alnus and Salix are the most commonly preserved genera and the trees grew on the now sub‐merged seaward margin of the alluvial fan. Pollen analysis permits an estimate of palaeo‐temperatures 2°C to 4°C lower than at present. Diatoms give some indication of salinity variations at the time of forest development and suggest brackish water, possible lagoonal conditions. The distribution of the stumps and roots suggests that there were probably two separate forests which were overwhelmed by rising sea‐level and flash flood deposits. The present day submarine exposures may be due to recent submarine erosion related to the seaward movement of flood waters which passed from the fan into the upper reaches of the Toyama submarine canyon system.