Formation and origin of tuffaceous sandstones from IODP Expedition 322, Nankai Trough

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Author(s): Kutterolf, S.; Schindlbeck, Julie C.; Freundt, A.; Scudder, R. P.; Pickering, K. T.; Labanieh, S.; Naruse, H.; Underwood, M.; Wu, H.
Author Affiliation(s): Primary:
Leibniz Institute of Marine Sciences, Dynamics of the Ocean Floor, Kiel, Germany
Boston University, United States
University College London, United Kingdom
Université Joesph Fourier, France
Chiba University, Japan
University of Missouri-Columbia, United States
China University of Geosciences, China
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: During IODP Expedition 322 one major new discovery was an interval of tuffaceous and volcaniclastic sandstones, which has been defined as the middle Shikoku Basin facies. This lithologic Unit II is late Miocene (>7.07 to ∼9.0 Ma) in age and can be divided into two subunits by the abundance of volcanic glass shards, mineral and/or lithic contents, and bulk-rock XRF data. The upper subunit IIA consists of moderately lithified and bioturbated silty claystone including three 1 to 10 meter thick interbeds of tuffaceous sandstones containing 35 to 60 vol% pyroclasts. The tuffaceous sandstone packages are build up by one to three density-graded units with lithic fragments and minerals enriched at the base and pumice clasts (remnants) accumulated at the top, interpreted as turbidity current deposits. Major and trace element glass-shard compositions in each sandstone package either have homogeneous composition or define a well-constrained compositional variation trend, implying that each package derived from a single pyroclastic deposit or a single eruptive event as opposed to gravity currents resulting from collapse of large, heterogeneous slope sections. Moreover, glass compositions show that the tuffaceous sandstones all came from a similar source region either at the Izu Bonin rear arc or the Japanese mainland. Magmatic compositions at both regions would be compatible with the moderate K2O concentrations (2 to 3.5 wt%), but high Ba/Zr, Zr/Nb and La/Sm ratios of the glass shards favors the latter one; the Izu Bonin arc can be excluded as a source due to generally lower potassium concentrations. The high incompatible trace element contents of the glasses suggest a source region where the mantle source of magmas lies below continental crust. Therefore, the Japanese mainland seems to be the most likely provenance for the tuffaceous sandstones found ∼ 350 km away in the Shikoku Basin.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 12 Stratigraphy, Historical Geology and Paleoecology; Asia; Biogenic structures; Bioturbation; Cenozoic; Clastic rocks; Concentration; Depositional environment; Expedition 322; Far East; Igneous rocks; Integrated Ocean Drilling Program; Interpretation; Izu-Bonin Arc; Japan; Lithification; Lithofacies; Magmas; Miocene; NanTroSEIZE; Nankai Trough; Neogene; North Pacific; Northwest Pacific; Ocean floors; Pacific Ocean; Provenance; Pumice; Pyroclastics; Sandstone; Sedimentary rocks; Sedimentary structures; Sedimentation; Shikoku Basin; Tertiary; Trace elements; Upper Miocene; Volcanic rocks; Volcaniclastics; West Pacific
Coordinates: N324400 N325000 E1365600 E1365200
Record ID: 2015099590
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