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von Rad, Ulrich; Thurow, Juergen W (1992): Mineralogy and chemistry of bentonitic clays from the Wombat and Exmouth Plateaus [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.761342, Supplement to: von Rad, U; Thurow, JW (1992): Bentonitic clays as indicators of Early Neocomian post-breakup volcanism off Northwest Australia. In: von Rad, U; Haq, BU; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 122, 213-232, https://doi.org/10.2973/odp.proc.sr.122.185.1992

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Abstract:
Bentonites (i.e., smectite-dominated, altered volcanic ash layers) were recovered in Berriasian to Valanginian hemipelagic sediments of the Wombat Plateau (Site 761) and southern Exmouth Plateau (Site 763). They are compared to coeval bentonites in eupelagic sediments of the adjacent Argo Abyssal Plain (Sites 261 and 765) and Gascoyne Abyssal Plain (Site 766).
A volcaniclastic origin with dacitic to rhyolitic ash as parent material is suggested by the abundance of well-ordered montmorillonite, fresh to altered silicic glass shards, volcanogenic minerals (euhedral sanidine, apatite, and long-prismatic zircon), and volcanic rock fragments, and by a vitroclastic ultrafabric (smectitized glass shards). We distinguish (1) pure smectite bentonites with a white, pink, or light gray color, a waxy appearance, and a very homogeneous, cryptocrystalline smectite matrix (water-free composition at Site 761: 68.5% SiO2, 0.27% TiO2, 19.1% Al2O3, 3.3% Fe2O3, 0.4%-1.1% Na2O, and 0.6% K2O) and (2) impure bentonitic claystones containing mixtures of volcanogenic smectite and pyroclastic grains with terrigenous and pelagic components.
The ash layers were progressively altered during diagenesis. Silicic glass was first hydrated, then slightly altered (etched with incipient smectite authigenesis), then moderately smectitized (with shard shape still intact), and finally completely homogenized to a pure smectite matrix without obvious relict structures. Euhedral clinoptilolite is the latest pore-filling or glass-replacing mineral, postdating smectite authigenesis.
Volcanic activity was associated with continental breakup and rapid subsidence during the "juvenile ocean phase." Potential source areas for a Neocomian post-breakup volcanism include the Wombat Plateau, Joey and Roo rises, Scott Plateau, and Wallaby Plateau/Cape Range Fracture Zone. Westward-directed trade winds transported silicic ash from these volcanic source areas to the Exmouth Plateau into the adjacent abyssal plains. The Wombat Plateau bentonites are interpreted as proximal ash turbidites.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: -18.282696 * Median Longitude: 114.233858 * South-bound Latitude: -20.587000 * West-bound Longitude: 110.454100 * North-bound Latitude: -15.976000 * East-bound Longitude: 117.575200
Date/Time Start: 1988-07-19T00:00:00 * Date/Time End: 1988-10-26T00:00:00
Event(s):
122-761 * Latitude: -16.737333 * Longitude: 115.535000 * Date/Time Start: 1988-07-19T00:00:00 * Date/Time End: 1988-07-25T00:00:00 * Elevation: -2179.0 m * Penetration: 732.9 m * Recovery: 281.2 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg122 * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 67 cores; 732.9 m cored; 0 m drilled; 38.4% recovery
122-761B * Latitude: -16.737000 * Longitude: 115.535000 * Date/Time Start: 1988-07-19T10:00:00 * Date/Time End: 1988-07-21T09:00:00 * Elevation: -2179.0 m * Penetration: 286.7 m * Recovery: 199.08 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg122 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 33 cores; 286.7 m cored; 0 m drilled; 69.4 % recovery
122-761C * Latitude: -16.737000 * Longitude: 115.535000 * Date/Time Start: 1988-07-21T09:00:00 * Date/Time End: 1988-07-25T02:00:00 * Elevation: -2179.0 m * Penetration: 436.7 m * Recovery: 72.24 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg122 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 33 cores; 436.7 m cored; 0 m drilled; 16.5 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
3 datasets

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Datasets listed in this publication series

  1. von Rad, U; Thurow, JW (1992): (Table 1) Bentonite and mineralogy of ODP Site 122-761 and Hole 123-763C. https://doi.org/10.1594/PANGAEA.761259
  2. von Rad, U; Thurow, JW (1992): (Table 2) Chemical composition of pure bentonites and impure bentonitic clays. https://doi.org/10.1594/PANGAEA.761262
  3. von Rad, U; Thurow, JW (1992): (Table 3) Minor and trace element concentrations of pure bentonites and impure bentonitic clays. https://doi.org/10.1594/PANGAEA.761330