| Abstract Submission No. | ABS-3.1-0023 |
| Title of Abstract | Millennial-Scale Geochemical and Tsunami Records in the Deep Sediments of the Japan Trench |
| Authors | Sankhadip Poyra, Dhananjai K Pandey*, Mahesh Haldar, Sambudha Misra |
| Organisation | Jawaharlal Nehru University, New Delhi |
| Address | JNU, New Delhi New Delhi, Delhi, India Pincode: 110067 E-mail: dhananjai@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The deepest oceanic trenches on Earth, which are less studied than Mars, preserve unique records of tectonic and sedimentary activities. This research examines geochemical signatures and paleoseismicity in the deepest sediment core retrieved worldwide (8,060.74 mbsl; IODP Exp. 386, Japan Trench). A thorough geochemical analysis of 150 samples considered from 18 different basins reveals a felsic continental source, peculiar to the Honshu-Hokkaido region. The provenance is characterized by silica (SiO⿿) concentration ranging from 53 to 59 wt.% and alumina (Al⿿O⿿) content ranging from 10 to 13 wt.%. The sediments were conveyed through the Nakaminato-Ogawara canyon system and display intermittent contributions from arc volcanic activity, as indicated by elevated concentrations of iron (Fe), magnesium (Mg), and calcium (Ca). Limited mafic input is reflected in the measured Fe⿿O⿿ (3.9⿿5.5 wt.%) and MgO content (1.9⿿2.3 wt.%), while the potassium and sodium oxides range between 1.6⿿2.0 wt.% and 3.7⿿4.9 wt.%, respectively, possibly suggesting derivation from weathered granitoid sources. Notably high sedimentation rates, ranging from 1 to 4 meters per thousand years, enable the development of stratigraphic records at the millennial scale. These records identify regionally extensive turbidite deposits, exceeding 120 kilometers in length, which have been correlated through tephrochronological analysis and tsunami event records with megathrust earthquakes of moment magnitude (Mw) 9 or greater, such as the 869 CE Jogan and 1454 CE Kyotoku events. Computed weathering indices (CIA, CIW, PIA) indicate moderate chemical changes. Moreover, irregularities in manganese oxidation detected at the bases of these event layers indicate the discharge of fluids following seismic events. Such occurrences transpire at intervals ranging from 260 to 880 years and correspond to more than 90% of the global seismic energy released in subduction zones. Our findings indicate that hadal trenches are essential records for interpreting subduction risks, sediment routes, and tectonic drivers. |
| Keywords | Hadal zone, IODP Expedition 386, Japan Trench, Sediment provenance |