Late Cenozoic evolution of the Nankai trench-slope system; evidence from sand petrography and clay mineralogy

Author(s): Underwood, Michael B.; Fergusson, Christopher L.
Author Affiliation(s): Primary:
University of Missouri, Department of Geological Sciences, Columbia, MO, United States
Other:
University of Wollongong, Australia
Volume Title: Submarine slope systems; processes and products
Volume Author(s): Hodgson, David M., editor; Flint, Stephen S.
Source: Geological Society Special Publications, Vol.244, p.113-129; Submarine slope systems, SLOPE 2003, Liverpool, United Kingdom, April 2003, edited by David M. Hodgson and Stephen S. Flint. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719 CODEN: GSLSBW
Note: In English. 104 refs.; illus., incl. geol. sketch map, sect.
Summary: Submarine slope systems in subduction zones evolve in response to a combination of tectonic and sedimentary forcing. It can be difficult to determine how and when tectonic forcing affects sedimentation, especially when investigating ancient rock successions, but one of the more reliable indicators is a change in sediment composition. During Leg 190 of the Ocean Drilling Program, sandy turbidites were recovered from a Quaternary trench wedge (Nankai Trough), a Pliocene-Pleistocene slope basin, the underlying Pliocene-Miocene accretionary prism, and a Miocene turbidite facies in the Shikoku Basin. Differences in detrital provenance between the sand and clay-sized fractions indicate that turbidity currents did not follow pathways of suspended-sediment transport during the past 10 Ma. During the middle and late Miocene, the sand probably was eroded from a newly exposed accretionary complex (Shimanto Belt). In contrast, high contents of detrital smectite in Miocene mudstones (>50 wt% of the <2 µm size fraction, relative to illite, chlorite+kaolinite, and quartz) point to a strong volcanic component of suspended-sediment input (Izu-Bonin island arc). The sand in accreted Pliocene turbidites was also eroded from the Shimanto Belt and transported by transverse flow down the insular slope. The trench-wedge facies then switched to axial flow during the Quaternary, when the sand supply tapped a mixed volcanic-metasedimentary provenance in the rapidly uplifted Izu-Honshu collision zone. Progressive depletion of smectite during the Pliocene and Pleistocene (<20 wt%) points to increased movement of illite-and chlorite-rich clay toward the east and NE from sources on Kyushu and Shikoku. That shift in mud composition coincides with intensification of the North Pacific western boundary current (Kuroshio Current) at approximately 3 Ma. Overall, the depositional system in the Nankai Trough and Shikoku Basin shifted its sand sources because of regional tectonics, whereas the suspended-sediment budget was modulated by hemispheric changes in ocean-water circulation.
Year of Publication: 2005
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; 16 Structural Geology; Bathymetry; Cenozoic; Chemical ratios; Clastic rocks; Clay mineralogy; Clay minerals; DSDP Site 582; DSDP Site 583; Deep Sea Drilling Project; Depositional environment; Grain size; IPOD; Leg 190; Leg 87; Marine environment; Metamorphic rocks; Metasedimentary rocks; Mineral composition; Nankai Trough; Neogene; North Pacific; Northwest Pacific; ODP Site 1174; ODP Site 1175; ODP Site 1176; ODP Site 1177; ODP Site 1178; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Pleistocene; Pliocene; Quaternary; Sandstone; Sedimentary rocks; Sheet silicates; Shikoku Basin; Silicates; Slope environment; Smectite; Subduction zones; Tectonics; Tertiary; Trench-slope system; Turbidite; Upper Cenozoic; West Pacific
Coordinates: N300000 N360000 E1400000 E1320000
N313900 N314000 E1340100 E1340000
Record ID: 2006010628
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