Elemental Distribution and Microfabric Characterization Across a Buried Slump Scar: New Insights on the Long-Term Development and Reactivation of Scar Surfaces from a Microscopic Perspective

摘要

This study presents a detailed characterization of the sedimentology, microfabric and elemental distributions across a prominent unconformity drilled at 78 m below sea floor at Integrated Ocean Drilling Program (IODP) Site C0004 in the Nankai accretionary prism, offshore Japan. This stratigraphic contact has previously been interpreted as buried landslide scar, which likely experienced multiple failure events. Our study aims at testing this hypothesis and at contributing new insights on the long-term development and reactivation of submarine landslide scars from a microscopic perspective. X-ray fluorescence spectroscopy documents increased values of sulfur and iron across the unconformity. Pyrite mineralization occurring in small fractures immediately below the unconformity is identified with energy dispersive X-ray analysis. Cross-cutting relationships between fractures and pyrite minerals, as imaged by X-ray computed tomography and scanning electron microscopy reveals that precipitation has occurred before the formation of the unconformity. A few mm-to-cm above the studied surface and thus within the overlying hemipelagic sediment, preferred mineral alignment along thin deformation bands arc observed. Inferred shear bands are hypothesized as incipient evidence for a potential future submarine landslide. Compiled data confirm the hypothesis of recurrent submarine landslides along the same surface.