--> ABSTRACT: Holocene Reef Associated Carbonate Sediments and Their Pleistocene Counterparts, Miyako Islands, Ryukyus, Southwest of Japan, by Yoshihiro Tsuji, Tsuneo Yamamura, Toshio Kodato, Hisao Sunouchi, and Tomoya Yuki; #91030 (2010)

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Holocene Reef Associated Carbonate Sediments and Their Pleistocene Counterparts, Miyako Islands, Ryukyus, Southwest of Japan

Yoshihiro Tsuji, Tsuneo Yamamura, Toshio Kodato, Hisao Sunouchi, Tomoya Yuki

Holocene carbonate sedimentary facies distribution, from sea level to shelf slope about 1,000 m in depth, and its relationship to bathymetry, off Miyako Island, Ryukyus, southwest of Japan were clarified by surveys with sidescan sonar, sparker, uniboom, sea-bottom camera, and sediment sampler.

Six facies were recognized using the acoustic data, sample analytical data, and sea-bottom photographs. These are as follows. (A) Reef facies: made mainly of autochthonous hermatypic corals and encrusting algae, 0-60 m deep. (B) Inter-reef muddy facies: consists of very fine sand-size carbonate fraction and line mud, 20-60 m deep surrounded area by reefal relief and islands. (C) Inter-reef and near-reef sandy facies: characterized by tests of shallow benthic foraminifera Calcarina and Marginopora, and Halimeda fragments, 0-90 m deep. (D) Rhodolith and large foraminiferal gravelly shelf facies: contains pebble to cobble-size rhodolith and/or foraminifera Cyclolypeus and Operculina, 60-200 m deep. (E) Bryozoan sandy shelf facies: rich in bryozoan fragments, 80-200 m deep. (F) Shelf slop pelagic foraminiferal facies: dominated by pelagic foraminifera and pteropod molluscan tests, deeper than 200 m.

Counterparts of these facies in emerged Pleistocene limestone sequences have been recognized in outcrops and core samples. The results of the marine survey on Holocene deposits made it easy to interpret the Pleistocene depositional environments and sea level changes.

Furthermore, relationships between the facies distribution and the velocity of sea-bottom currents will also be documented.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.