5:15 PM - 6:45 PM
[SCG48-P33] Widespread distribution and formation process of authigenic carbonates on the western slope of the northern Okinawa Trough
Keywords:East China Sea, Okinawa Trough, cold seep, carbonate, seismic reflection survey
Okinawa Trough is an active back-arc basin where rifting is undergoing due to the subduction of the Philippine Sea Plate beneath the continental Eurasian Plate. There are few reports about authigenic carbonate rocks which originated from cold seepage system (Oiwane et al., 2011; Sun et al., 2015), and their spatial distributions and the formation ages are not well revealed.
In this study, we used the dredged carbonate samples collected from several points ranging over an area of about three hundred kilometers along the northern slope area of the Okinawa Trough, based on our bathymetric and backscatter data. We will discuss about their formation process and distribution in this presentation.
Some of the samples are carbonate chimneys, and almost all samples have critically low δ13C values, indicating that these carbonate samples are methane-derived. The rare earth element (REE) and yttrium (Y) concentrations analyzed by ICP-MS show Y enrichment compared to holmium (Ho), indicating that seawater affected carbonate samples during its precipitation process. Furthermore, some species of foraminifera as indicator fossil were picked up by using Na2SO4 and naphtha from the selected samples for age determination, and they were successfully dated to early Pliocene.
We also conducted seismic reflection surveys by using mini-GI gun around Oki-Danjo Hills located on the slope of the Okinawa Trough, and analyzed the unconformities and faults (Aoki et al., 2023). These faults have huge displacement and old face may be exposed at the top of the hills. Therefore, our results may possibly reveal the formation of the carbonate samples and the timing and process, and the geological structure.
References: [1] Oiwane et al. (2011) Marine Geology 288(1-4), 49-60. [2] Sun et al. (2015) Deep-Sea Research I 95, 37-53. [3] Aoki et al. (2023) JpGU2023
In this study, we used the dredged carbonate samples collected from several points ranging over an area of about three hundred kilometers along the northern slope area of the Okinawa Trough, based on our bathymetric and backscatter data. We will discuss about their formation process and distribution in this presentation.
Some of the samples are carbonate chimneys, and almost all samples have critically low δ13C values, indicating that these carbonate samples are methane-derived. The rare earth element (REE) and yttrium (Y) concentrations analyzed by ICP-MS show Y enrichment compared to holmium (Ho), indicating that seawater affected carbonate samples during its precipitation process. Furthermore, some species of foraminifera as indicator fossil were picked up by using Na2SO4 and naphtha from the selected samples for age determination, and they were successfully dated to early Pliocene.
We also conducted seismic reflection surveys by using mini-GI gun around Oki-Danjo Hills located on the slope of the Okinawa Trough, and analyzed the unconformities and faults (Aoki et al., 2023). These faults have huge displacement and old face may be exposed at the top of the hills. Therefore, our results may possibly reveal the formation of the carbonate samples and the timing and process, and the geological structure.
References: [1] Oiwane et al. (2011) Marine Geology 288(1-4), 49-60. [2] Sun et al. (2015) Deep-Sea Research I 95, 37-53. [3] Aoki et al. (2023) JpGU2023