Miocene subtidal sandwave deposits in southwest Japan were
influenced by periodic flow and steady flow. The sandwave
deposits can be divided into five units, based on lithofacies and
thickness. In order of accretion, unit 1 consists of unidirectional
sand bedforms without mud drapes, unit 2 of unidirectional
sand bedforms with thin, discontinuous mud drapes, unit 3 of
bidirectional sand bedforms with thin continuous mud drapes,
and units 4 and 5 of relatively thinner and smaller bidirectional
sand bedforms with continuous mud drapes. The thickness of
units 1 to 3 increase progressively to 2.6 m, and units 4 to 5 subsequently
decrease from 2.0 to 1.0 m. Variations between the
units are due to differing combinations of periodic and steady
flow velocities. Palaeoflow velocity is estimated from grain size
and unit thickness. Depth-mean velocities of steady flow components
gradually decrease from 0.72 ms−1 to 0.16 ms−1
with unit accumulation.