9:30 AM - 9:45 AM
[SCG45-03] Sedimentation process at the South Shetland Trench in the Antarctic Ocean
Keywords:the Antarctic Ocean, the South Shetland Trench, Hakuho-maru
Sediments incoming subduction zones affect mechanics of plate boundary fault and mass balance in subduction zones. The nature and distribution of sediments incoming trenches such as Nankai Trough, Japan Trench, Cascade, Costa Rica, Barbados, Hikurangi, Sumatra, etc. were elucidated by ocean drilling. On the other hand, the nature of sediments in trenches around the Arctic and Antarctic region are not well-understood, though the existence of abundant Iceberg-Rafted Debris (IBRD) and biogenic opal derived from diatom is speculated. In this study we report preliminary result of characteristics of surface sediments sampled from the South Shetland Trench in the Antarctic Ocean to reveal sedimentation process in a trench in the polar regions.
The South Shetland Trench in the northwest of Antarctic Peninsula is the boundary between the former Phoenix Plate and Antarctic Plate. Although active back-arc spreading is on-going at the Bransfield Strait located in between the South Shetland Islands and the Antarctic Peninsula, forearc seismicity is inactive. 9 piston cores were sampled from the Antarctic and Atlantic Ocean during R/V Hakuho-maru KH-19-6 cruise (Dec. 2019-Jan. 2020), and 4 cores (PC02, PC03, PC04, PC5) were sampled from around the South Shetland Trench. Sample localities include bottom of the trench (PC02 and PC04), landward trench slope (PC03) and seaward trench slope (PC05). All the cores were shipped to Kochi Core Center and X-CT analysis was conducted prior to splitting. Visual core description, MSCL and ITRAX analyses were performed by using split core.
PC02 and PC04 are characterized by turbidite layers which contain fine sands at the bottom. At least 28 and 10 turbidite layers were found in PC02 and PC04, respectively. Sand layers are enriched in Ca and Sr. Mud layers sandwiched in between sand layers show gradual color change, from brown at the lower part to olive gray at the upper part, which would correspond to turbidite mud and hemipelagic mud, respectively. 14C ages of total organic carbon (TOC) in hemipelagic mud of PC02 range from 19076-18826 to 9684-9531 cal BP, suggesting ~0.4 m/1 ky of hemipelagic sedimentation rate and ~300 years of turbidite recurrence interval. PC03 includes poorly sorted subangular gravel, and is interpreted as diamicton or channel deposit. PC05 contains inclined and disrupted sand and silt layers in bluish gray mud matrix, which are characteristic in slump deposit. IBRD are rare in all the cores.
Preliminary analyses of four cores suggest sediments were transported to the South Shetland Trench by gravity flow from both landward and seaward sides. On the other hand, IBRD are not common in the bottom of the trench, reflecting that icebergs mainly drift towards eastern side of the Antarctic Peninsula.
The South Shetland Trench in the northwest of Antarctic Peninsula is the boundary between the former Phoenix Plate and Antarctic Plate. Although active back-arc spreading is on-going at the Bransfield Strait located in between the South Shetland Islands and the Antarctic Peninsula, forearc seismicity is inactive. 9 piston cores were sampled from the Antarctic and Atlantic Ocean during R/V Hakuho-maru KH-19-6 cruise (Dec. 2019-Jan. 2020), and 4 cores (PC02, PC03, PC04, PC5) were sampled from around the South Shetland Trench. Sample localities include bottom of the trench (PC02 and PC04), landward trench slope (PC03) and seaward trench slope (PC05). All the cores were shipped to Kochi Core Center and X-CT analysis was conducted prior to splitting. Visual core description, MSCL and ITRAX analyses were performed by using split core.
PC02 and PC04 are characterized by turbidite layers which contain fine sands at the bottom. At least 28 and 10 turbidite layers were found in PC02 and PC04, respectively. Sand layers are enriched in Ca and Sr. Mud layers sandwiched in between sand layers show gradual color change, from brown at the lower part to olive gray at the upper part, which would correspond to turbidite mud and hemipelagic mud, respectively. 14C ages of total organic carbon (TOC) in hemipelagic mud of PC02 range from 19076-18826 to 9684-9531 cal BP, suggesting ~0.4 m/1 ky of hemipelagic sedimentation rate and ~300 years of turbidite recurrence interval. PC03 includes poorly sorted subangular gravel, and is interpreted as diamicton or channel deposit. PC05 contains inclined and disrupted sand and silt layers in bluish gray mud matrix, which are characteristic in slump deposit. IBRD are rare in all the cores.
Preliminary analyses of four cores suggest sediments were transported to the South Shetland Trench by gravity flow from both landward and seaward sides. On the other hand, IBRD are not common in the bottom of the trench, reflecting that icebergs mainly drift towards eastern side of the Antarctic Peninsula.