The role of pre-subduction sediment diagenesis in a shallow tsunami-generated slip, Sunda Trench, south of Sumatra

Abstract

Abstract The progressive development of microfabrics in sediments was investigated in an active subduction zone using cores recovered during the Integrated Ocean Drilling Program Expedition 362. A sequence of Paleocene–Holocene rock was recorded at Site U1480, which is located in the Sunda Trench, south of Sumatra. Hemipelagic clayey sediments from the drilled succession were recovered from a depth of 1327.23 m. Cardhouse fabrics were observed initially, consisting of clay flakes with edge-to-edge (E–E) or edge-to-face (E–F) contacts. These initial microfabrics developed into compacted bookhouse fabrics (which are random and consolidated), and consist of clay flakes with E–F or face-to-face (F–F) contacts as the domain. These microfabrics developed due to individual particle sliding. Bookhouse fabric developed into a shape-preferred orientation of clay minerals with F–F contacts as a shaly fabric due to domain sliding. Finally, clay flakes with F–F contacts deformed into an undulated shape due to further increased overburden pressure. These pervasive fabrics comprising clay flakes stacked with F–F contacts resisted shear deformation due to their strong cohesion. This strong cohesion in the undulated shaly fabric might be an important factor in the locking of shallow tsunami-generating slip in subduction zones.