Depositional processes of the Miocene Tokiguchi Porcelain Clay Formation and hydraulic behavior of plant macrofossils in the formation: an example from Ohbora, Tajimi, central Japan

Abstract

Sedimentary environment of the Late Miocene Tokiguchi Porcelain Clay Formation at Ohbora, central Japan was studied together with occurrence and composition of plant macrofossils. Sandy braided river system distributed between surrounding hills and ponds in a sedimentary basin was reconstructed based on 10 types of sedimentary facies. The results indicated that fluvial systems dominated by sand and mud was a common characteristic to the sedimentary basins in the porcelain clay formation in the Tokai Group. Based on occurrence of plant macrofossils included in flood flow deposits, depositional processes of plants in the river system were reconstructed: 1) Two types of plant particles transported with bedload and suspension were recognized; 2) the difference was due to morphology and specific gravity of the particle which were influenced by permeability of water into the wooly surface and woody tissue; 3) as the result, plant macrofossils were hydrologically sorted and deposited; and 4) sedimentary facies of flood flow deposits which include plant macrofossils were classified into three types and different depositional processes were reconstructed based on vertical change of grain size distribution both of plants and the matrix.