Late middle Pleistocene fossil coral reef growth history in the subtropical Northwest Pacific

Abstract During the Middle and Late Pleistocene, the Earth experienced rapid millennial-scale climate and sea-level fluctuations associated with 100 kyr-glacial-interglacial cycles. However, understanding of the timing and amplitude of these changes, and their impact on coral reef ecosystems remains incomplete. The Ryukyu Islands in southwestern Japan, with their extensive exposure of uplifted Quaternary coral reef limestones, are ideal to investigate the Quaternary record of high-latitude coral reef growth and fossil coral assemblages in the Northern Hemisphere. In this study, we focus on the late Middle Pleistocene Minatogawa Formation exposed in southern Okinawa Jima and nearby islets. We examined in detail the taxonomic compositions of fossil coral assemblages and their temporal and spatial variations in sections of coral limestone exposed in a quarry. We identified seven distinct coral assemblages each indicating a particular environment, from shallow (< 5 m) to deeper (up to 30 m) reef settings. Coral assemblages and sedimentary facies show spatial variations among outcrops and vertical (temporal) trends reflecting both relative sea-level changes and different exposure to wave energy. Our results suggest that the Minatogawa Formation formed in response to at least four cycles of relative sea-level change with minimum amplitudes of 20 to 30 m.