Sedimentary record of the evolution of the Kumano Forearc Basin, offshore southwest Japan

Open Access
Author:
Xu, Yang
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 20, 2017
Committee Members:
  • Elizabeth Ann Hajek, Thesis Advisor
  • Demian Saffer, Committee Member
  • Donald Myron Fisher, Committee Member
Keywords:
  • Kumano
  • basin
  • forearc
  • sequencestratigraphy
  • basinanalysis
  • nankai
  • sedimentology
  • iodp
Abstract:
Forearc basins have been poorly understood due to their complex formation history and the loading patterns that affect sediment dispersal and topography on active margins. Compared to foreland basins and passive margins where the subsidence histories follow consistent patterns, forearc basins exhibit a wide range of subsidence characteristics, owing to multiple driving mechanisms such as sedimentary and tectonic loading. In addition, accretionary forearc basins are particularly sensitive to changes in margin geometry related to wedge dynamics. Sequence stratigraphic analyses of forearc basin fills can be used to constrain the tectonic and depositional controls on basin evolution in this type of setting. Here, sequence stratigraphic analysis of a high-resolution 3-D seismic volume in the Kumano forearc basin located offshore SW Japan was used to decipher the relative timing and pattern of infill in the lower portion of the basin. Sediments in this lower unit were deposited in a paleo-outer wedge setting and sit stratigraphically above the present-day inner accretionary prism and below upper forearc sediments. Stratal terminations were mapped to identify depositional patterns and unconformities that signify major basin reorganizations. In-depth mapping of a lower drape-like sub-unit revealed three distinct stages of downlap that each span ~0.5 Myr. Evidence from these stratal patterns suggests that, in addition to the fill-and-spill model of ponded basin assemblages such as those caused by salt tectonics in the Gulf of Mexico, episodic uplift and deformation of the accretionary prism significantly affected early evolution of the Kumano Basin. This emphasizes the interplay between the dynamic generation of accommodation in accretionary prism depositional systems and sediment distribution, and contrasts with passive margins where eustatic sea level change plays a more significant role.