Influx of the Kuroshio Current into the Okinawa Trough and Inauguration of Quaternary Coral-Reef Building in the Ryukyu Island Arc, Japan.

Koba, Motoharu

doi:10.4116/jaqua.31.359

Cited by 21 publications

(11 citation statements)

References 18 publications

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“…The Shimajiri Group emerged and was eroded, and antecedent edifices for the coral‐reef formation were constructed during this period. A similar scenario was presented by Koba (1992). He stated that the Yonaguni Depression formed at the boundary between the Ryukyu Arc and Taiwan because of the collision of the Luzon Volcanic Arc with Taiwan, which made the Kuroshio current flow into the back‐arc side, and that coral reefs began to flourish at 0.6–0.7 Ma.…”

Section: Scientific Objectives Of Combined Ocean and Land Drillingmentioning

confidence: 58%

“…Molecular and evolutionary biological investigations of amphibian and reptile lineages in the present‐day Central and South Ryukyus by Ota (1998) indicate that the Central Ryukyus have been isolated from the Eurasian Continent and the South and North Ryukyus since Pliocene time. These new data suggest the interpretations of Ujiié (1989, 1994) and Koba (1992) are incorrect. As just described, the paleogeographic evolution around the Ryukyus has not been well understood.…”

Section: Scientific Objectives Of Combined Ocean and Land Drillingmentioning

confidence: 90%

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Introductory perspective on the COREF Project

Iryu¹,

Matsuda

Machiyama

et al. 2006

Island Arc

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Coral reefs are tropic to subtropic, coastal ecosystems comprising very diverse organisms. Late Quaternary reef deposits are fossil archives of environmental, tectonic and eustatic variations that can be used to reconstruct the paleoclimatic and paleoceanographic history of the tropic surface oceans. Reefs located at the latitudinal limits of coralreef ecosystems (i.e. those at coral-reef fronts) are particularly sensitive to environmental changes -especially those associated with glacial-interglacial changes in climate and sealevel. We propose a land and ocean scientific drilling campaign in the Ryukyu Islands (the Ryukyus) in the northwestern Pacific Ocean to investigate the dynamic response of the corals and coral-reef ecosystems in this region to Late Quaternary climate and sealevel change. Such a drilling campaign, which we call the COREF (coral-reef front) Project, will allow the following three major questions to be evaluated: (i) What are the nature, magnitude and driving mechanisms of coral-reef front migration in the Ryukyus? (ii) What is the ecosystem response of coral reefs in the Ryukyus to Quaternary climate changes? (iii) What is the role of coral reefs in the global carbon cycle? Subsidiary objectives include (i) the timing of coral-reef initiation in the Ryukyus and its causes; (ii) the position of the Kuroshio current during glacial periods and its effects on coral-reef formation; and (iii) early carbonate diagenetic responses as a function of compounded variations in climate, eustacy and depositional mineralogies (subtropic aragonitic to warm-temperate calcitic). The geographic, climatic and oceanographic settings of the Ryukyu Islands provide an ideal natural laboratory to address each of these research questions.

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Section: Scientific Objectives Of Combined Ocean and Land Drillingmentioning

confidence: 58%

Section: Scientific Objectives Of Combined Ocean and Land Drillingmentioning

confidence: 90%

Introductory perspective on the COREF Project

Iryu¹,

Matsuda

Machiyama

et al. 2006

Island Arc

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“…The existence of such land bridges has been proposed by other geologists as well (e.g. Koba ). The paleogeography reconstructed by geologists is, however, in conflict with that proposed by molecular biologists.…”

Section: Introductionmentioning

confidence: 89%

Subsidence of the Miyako‐Sone submarine carbonate platform, east of Miyako‐jima Island, northwestern Pacific Ocean

Arai¹,

Machiyama

Chiyonobu

et al. 2013

Island Arc

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Bathymetric mapping and observations of the seafloor using a remotely operated vehicle (ROV, Hyper‐Dolphin 3K) were carried out on the slopes of the Miyako‐Sone submarine platform, east of Miyako‐jima in the Ryukyu Islands, northwestern Pacific Ocean. The bathymetric map indicates that terraces are present at water depths of approximately 140 m, 330 m, 400 m, and 680 m on the northwestern slope of the platform. A number of NW–SE trending lineaments, probably faults, extend perpendicular to the axis of the Ryukyu Island Arc. Two ROV surveys were conducted at water depths ranging from 519 m (on the slope) to 121 m (shallowest part of the platform). The surveys revealed that well‐indurated carbonate rocks are exposed at terrace margins and on upper slopes, and that the lower slopes are covered with modern sediments consisting of unconsolidated, coarse‐sand‐sized bioclastic carbonates. Calcareous nannofossils from the well‐indurated carbonate rocks indicate a Middle–Late Pleistocene age, which suggests that the rocks correlate with the Quaternary reef and fore‐reef deposits of the Ryukyu Group (Ryukyu Limestone) on the Ryukyu Islands. No siliciclastic deposits corresponding to the upper Miocene–lower Pleistocene Shimajiri Group (as exposed on Okinawa‐jima and Miyako‐jima islands) were recovered during the surveys. Coeval well‐indurated carbonate rocks, all of which formed in a similar sedimentary environment, have been downthrown towards the west due to displacements on the western sides of normal faults. Subsidence of the Miyako‐Sone submarine platform was the result of large vertical displacements on such normal faults. The timing of initial subsidence cannot be tightly constrained, but the presence of the youngest limestone at progressively lower levels towards the west suggests the subsidence continued until after 0.265 Ma.

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“…During the Pleistocene glacial–interglacial cycles, reef‐complex deposits in the Ryukyus formed near the limit of coral‐reef formation known as the coral‐reef front (COREF) of the northwest Pacific (Iryu et al, ). The warm Kuroshio Current flows through the area, supporting the coral‐reef ecosystems around the Ryukyus, in spite of the relatively high latitude (Koba, ). The archipelago is located on a tectonically active margin, where the Philippine Sea Plate subducts beneath the Eurasian Plate along the Ryukyu (Nansei‐shoto) Trench (Konishi, ).…”

Section: Introductionmentioning

confidence: 99%

“…However, the main body of the Ryukyu Group formed later in the Middle Pleistocene (0.451–0.853 Ma). Increased sea‐surface temperature and amplitude of sea‐level changes together with tectonic subsidence possibly have promoted the accumulation of reef‐complex deposits in the Ryukyus after the Mid‐Pleistocene Climate Transition (Koba, ; Sagawa et al, ; Sakai, ; Yamamoto et al, ). In contrast, reef‐complex deposits younger than 0.4 Ma, known as the “younger limestone”, are a minor component and offlap the main body of the Ryukyu Group (Iryu et al, ; Koba, ; Omura & Ota, ; Takayasu, ).…”

Section: Introductionmentioning

confidence: 99%

Depositional environments of well‐sorted detrital limestone from the Minatogawa Formation in the southern part of Okinawa Island, the Ryukyu Archipelago, Japan

et al. 2018

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Well‐sorted detrital limestone is one of the typical lithofacies of the latest interval of the Pleistocene Ryukyu Group, which is exposed in the Ryukyu Archipelago in southwestern Japan. The depositional environments of the limestone are interpreted to be extremely shallow and to include back‐reef lagoons or moats and subaerial sand dunes. However, detailed micropaleontological analyses have not been performed on this limestone. In this study, the interpretation of the depositional environments and paleo‐water depths was improved by quantitative examination of foraminiferal assemblages for the well‐sorted detrital limestone of the Minatogawa Formation in the southern part of Okinawa Island. Thin sections of limestone collected from the Minatogawa (Horikawa) quarry were subjected to sedimentological and foraminiferal analyses. Comparison with modern foraminiferal distribution within the Ryukyu Archipelago indicates that back‐reef and fore‐reef dwelling foraminifers characterize the fossil assemblages from the well‐sorted detrital limestone (bioclastic grainstone). Three ratios of indicator foraminiferal taxa (ratios of back‐reef to fore‐reef taxa, planktonic foraminifers to Amphistegina lobifera and Amphistegina lessonii, and Calcarina gaudichaudii to other Calcarina species), as well as multivariate analyses suggest that the well‐sorted detrital limestone was deposited in fore‐reef setting shallower than 40 m in water depth. A comparable depth range was reconstructed from the coral assemblage in the associated coral limestone, suggesting that the Minatogawa Formation was deposited in a gently inclined ramp setting with patch reefs and/or fringing reefs. Stratigraphic changes in paleo‐water depth, together with evidence of several unconformities associated with paleosol layers suggest that there were repeated transgressions and regressions, with an amplitude up to several tens of meters, when the Minatogawa Formation was deposited.

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Influx of the Kuroshio Current into the Okinawa Trough and Inauguration of Quaternary Coral-Reef Building in the Ryukyu Island Arc, Japan.

Cited by 21 publications

References 18 publications

Introductory perspective on the COREF Project

Introductory perspective on the COREF Project

Subsidence of the Miyako‐Sone submarine carbonate platform, east of Miyako‐jima Island, northwestern Pacific Ocean

Depositional environments of well‐sorted detrital limestone from the Minatogawa Formation in the southern part of Okinawa Island, the Ryukyu Archipelago, Japan

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