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[SCG52-01] Spatial time series variation of contourite drifts on the Kuril Trench Outer Rise
Keywords:Contourite drifts, LCDW, Active margin
Contourite drifts are sediments that accumulate, either deposited or reworked, on the side of the flow due to the persistent action of bottom currents (e.g., Faugères et al., 1999). Previous research has revealed that the characteristics of drift types and sedimentary facies in these accumulations vary widely depending on deep-sea environments (e.g., Stow et al., 2002). A detailed understanding, particularly at passive margins, has been gained through the identification and study of contourite drifts in the North Atlantic and Antarctic Oceans, related to the formation of deep water (e.g., Rebesco et al., 2014). In contrast, our understanding of contourite drifts is less advanced on the active margin due to differences in features during their identification (Bailey et al., 2021). Against this background, the discovery of contourite drifts and depositional processes in active margins has become an important issue in marine geology in recent years.
The outer slope to the outer rise of the Kuril Trench in the northwestern Pacific, situated within the active margin, serves as the pathway for the northward flow of the Lower Circumpolar Deep Water (LCDW) originating from the Antarctic Ocean (Ando et al., 2013). While previous seismic studies have suggested the influence of bottom currents on developed erosional features in this region, the identification of contourite drifts remains elusive (e.g., Nakamura et al., 2023). Therefore, this study aims to use four sets of Multichannel Seismic Reflection (MCS) data acquired in the outer rise region of the Kuril Trench in the northwestern Pacific to achieve the following objectives: 1) identify and determine the spatiotemporal distribution of contourite drifts, 2) elucidate the changes in ancient oceanic environments, revealing the impact of bottom currents on deep-sea sedimentation.
In this study, we used four MCS data sets (KT093, KT150, A2, R1) provided by the JAMSTEC Seismic Survey Database (JAMSTEC (2004), doi:10.17596/0002069). Mapping the seismic units and their horizons due to changes in sedimentary structure was conducted across several hundred meters of sediment beneath the seafloor. The horizons were defined based on four criteria: onlap, downlap, apparent truncation, and vertical seismic facies change. To assign depositional ages to these horizons, we integrated them with the DSDP Site 436 stratigraphic package (Langseth et al., 1977).
As a result, we stratigraphically interpreted five seismic units (U1-U5) for four seismic reflection profiles and assigned depositional ages to these horizons. The depositional ages were estimated to range from 113 to 94 (U1), 54 to 16 (U2), 16 to 12.1 (U3), 12.1 to 5.3 (U4), and 5.3 to 0 Ma (U5).
In U4 and U5, we identified a mound drift deposited beside seamounts, a patch drift deposited behind seamounts, and a sheet drift with sediment waves, along with their associated erosional discontinuities. We propose three stages in the evolution of the deep-sea environment acting on these sediments: 1) a period dominated by pelagic sedimentation that commenced immediately after the formation of the basal region (U1 to U3), 2) a period dominated by weak bottom currents (U4), and 3) a period dominated by LCDW influenced by active orogeny and trench development (U5). Additionally, our conclusion posits that the sedimentary structure of contourite drifts deposited during the LCDW-dominated period U5 reflects water mass relationships and their evolution on a global scale.
References: Faugères, JC., et al. (1999) Mar. Geol.; Stow, DAV, et al. (2002) Geol. Soc. Lond. Mem.; Rebesco, M., et al. (2014) Mar. Geol.; Bailey, WS., et al. (2021) Sed.; Ando, K., et al. (2013) J. Oceanogr.; Nakamura, Y., (2023) PEPS; JAMSTEC Seismic Survey Database (2004) Japan Agency for Marine-Earth Science and Technology, https://doi.org/doi:10.17596/0002069. Accessed 12. 7, 2023.; Langseth et al. (1977) Initial rep. Deep Sea Drill. Proj.
The outer slope to the outer rise of the Kuril Trench in the northwestern Pacific, situated within the active margin, serves as the pathway for the northward flow of the Lower Circumpolar Deep Water (LCDW) originating from the Antarctic Ocean (Ando et al., 2013). While previous seismic studies have suggested the influence of bottom currents on developed erosional features in this region, the identification of contourite drifts remains elusive (e.g., Nakamura et al., 2023). Therefore, this study aims to use four sets of Multichannel Seismic Reflection (MCS) data acquired in the outer rise region of the Kuril Trench in the northwestern Pacific to achieve the following objectives: 1) identify and determine the spatiotemporal distribution of contourite drifts, 2) elucidate the changes in ancient oceanic environments, revealing the impact of bottom currents on deep-sea sedimentation.
In this study, we used four MCS data sets (KT093, KT150, A2, R1) provided by the JAMSTEC Seismic Survey Database (JAMSTEC (2004), doi:10.17596/0002069). Mapping the seismic units and their horizons due to changes in sedimentary structure was conducted across several hundred meters of sediment beneath the seafloor. The horizons were defined based on four criteria: onlap, downlap, apparent truncation, and vertical seismic facies change. To assign depositional ages to these horizons, we integrated them with the DSDP Site 436 stratigraphic package (Langseth et al., 1977).
As a result, we stratigraphically interpreted five seismic units (U1-U5) for four seismic reflection profiles and assigned depositional ages to these horizons. The depositional ages were estimated to range from 113 to 94 (U1), 54 to 16 (U2), 16 to 12.1 (U3), 12.1 to 5.3 (U4), and 5.3 to 0 Ma (U5).
In U4 and U5, we identified a mound drift deposited beside seamounts, a patch drift deposited behind seamounts, and a sheet drift with sediment waves, along with their associated erosional discontinuities. We propose three stages in the evolution of the deep-sea environment acting on these sediments: 1) a period dominated by pelagic sedimentation that commenced immediately after the formation of the basal region (U1 to U3), 2) a period dominated by weak bottom currents (U4), and 3) a period dominated by LCDW influenced by active orogeny and trench development (U5). Additionally, our conclusion posits that the sedimentary structure of contourite drifts deposited during the LCDW-dominated period U5 reflects water mass relationships and their evolution on a global scale.
References: Faugères, JC., et al. (1999) Mar. Geol.; Stow, DAV, et al. (2002) Geol. Soc. Lond. Mem.; Rebesco, M., et al. (2014) Mar. Geol.; Bailey, WS., et al. (2021) Sed.; Ando, K., et al. (2013) J. Oceanogr.; Nakamura, Y., (2023) PEPS; JAMSTEC Seismic Survey Database (2004) Japan Agency for Marine-Earth Science and Technology, https://doi.org/doi:10.17596/0002069. Accessed 12. 7, 2023.; Langseth et al. (1977) Initial rep. Deep Sea Drill. Proj.