Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Abstract Bathymetric mapping and observations of the seafloor using a remotely operated vehicle ( ROV , Hyper‐Dolphin 3 K ) were carried out on the slopes of the M iyako‐ S one submarine platform, east of M iyako‐jima in the R yukyu I slands, northwestern P acific O cean. 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 R yukyu I sland A rc. 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 M iddle– L ate P leistocene age, which suggests that the rocks correlate with the Q uaternary reef and fore‐reef deposits of the R yukyu G roup ( R yukyu L imestone) on the R yukyu I slands. No siliciclastic deposits corresponding to the upper M iocene–lower P leistocene S himajiri G roup (as exposed on O kinawa‐jima and M iyako‐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 M iyako‐ S one 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 M a.
This study examines the fidelity of carbon ( δ 13 C) and oxygen ( δ 18 O) isotope compositions of two modern brachiopod species ( Kikaithyris hanzawai and Basiliola lucida ) to use as proxies of δ 13 C values of total dissolved inorganic carbon and temperature and/or δ 18 O values of seawater, respectively. Well‐preserved shells of K. hanzawai and living individuals of B. lucida were collected from a subtropical shelf environment off Amami‐o‐shima, southwestern Japan. Some portions of the shells are in isotopic equilibrium with the ambient seawater, while other portions are not. The degree of disequilibrium differs between the two species and between different portions of each shell. Statistically significant positive correlations are recognized between the δ 13 C and δ 18 O values of these samples, which can be ascribed to a kinetic fractionation effect. Far from the posterior shell edge and along the axis of shell growth, the δ 18 O values of the secondary shell layer of K. hanzawai mostly fall within the expected range of equilibrium calcite. The δ 13 C values from the inner surface of the secondary shell layer in both species are relatively constant and are equivalent to or very close to equilibrium calcite. Therefore, these portions of the shells are most suitable for collecting reliable environmental proxy data. Although the δ 13 C and δ 18 O values of modern brachiopod shells are predominantly controlled by a kinetic fractionation effect, the appropriate selection of species and shell portions that reflect the isotopic composition of ambient seawater can facilitate the reconstruction of secular variations in oceanic δ 13 C or δ 18 O values.
