Abstract
The basin formation process at a contractional bend of a large transcurrent fault is studied here from the viewpoint of extensive subsidence history. The Kobe and northern Osaka Basins in southwest Japan are located at the easternmost left-stepping bend of the dextral Median Tectonic Line (MTL), a fault system activated throughout the Quaternary. Many subordinate faults in these basins accommodate compressive stress, whereas differential vertical motion of fault-bounded blocks results in complex sedimentation patterns within the basins. We compiled stratigraphic information of the Late Pliocene to Pleistocene Osaka Group using core samples of 19 drill holes distributed in the study area. On the basis of magnetostratigraphy, tephrochronology and paleoenvironmental analysis, 15 datum horizons of transgression, which are recognized as bases of marine clays (Ma −1 to 13), in cores are assigned to the oxygen isotope events. An interval accumulation rate between two successive horizons represents a cycle of eustatic sea level changes, and thus provides us with an indicator of tectonic subsidence rate. Subsidence curves and temporal changes in subsidence rates at the drill holes visualize differential subsidence in detail. The northern Osaka Basin is divided into western and eastern depocenters and the central N–S Uemachi Basement high, which grew rapidly during the Ma 7/8 interval (ca. 550 kyr), whereas the subsidence pattern in the Kobe Basin is controlled by constant vertical displacements on the NE–SW Wada-misaki Fault. An interbasinal tectonic episode of sharp decline in subsidence is also detected in the Ma 5/6 interval (ca. 670 kyr), coinciding with the Mantidani Unconformity in the Osaka Group.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.