Underwood, Michael B. and Hoke, Kimberly D. (2000): Composition and provenance of turbidite sand and hemipelagic mud in northwestern Cascadia Basin

ODP 168


Underwood, Michael B.
University of Missouri, Department of Geological Sciences, Columbia, MO, United States

Hoke, Kimberly D.
Geological Survey of Canada, Canada

Composition and provenance of turbidite sand and hemipelagic mud in northwestern Cascadia Basin
In: Fisher, Andrew T., Davis, Earl E., Firth, John V., Andersson, Eva M., Aoike, Kan, Becker, Keir, Brown, Kimberly A., Buatier, Martine D., Constantin, Marc, Elderfield, Henry, Goncalves, Carlos A., Grigel, Jens S., Hunter, Arlene G., Inoue, Atsuyuki, Lawrence, Roisin M., Macdonald, Robert D., Marescotti, Pietro, Martin, Jeffrey T., Monnin, Christophe, Mottl, Michael J., Pribnow, Daniel F. C., Stein, Joshua S., Su, Xin, Sun, Yue-Feng, Underwood, Michael B., Vanko, David A., Wheat, C. Geoffrey, Miller, Christine M. (editor), Peters, Lorri L. (editor), Proceedings of the Ocean Drilling Program, scientific results, hydrothermal circulation in the oceanic crust, eastern flank of the Juan de Fuca Ridge; covering Leg 168 of the cruises of the drilling vessel JOIDES Resolution, San Francisco, California, to Victoria, British Columbia, sites 1023-1032, 20 June-15 August 1996
Texas A & M University, Ocean Drilling Program, College Station, TX, United States
Sequences of late Pliocene to Holocene sediment lap onto juvenile igneous crust within 20 km of the Juan de Fuca Ridge in northwestern Cascadia Basin, Pacific Ocean. The detrital modes of turbidite sands do not vary significantly within or among sites drilled during Leg 168 of the Ocean Drilling Program. Average values of total quartz, total feldspar, and unstable lithic fragments are Q = 35, F = 35, and L = 30. Average values of monocrystalline quartz, plagioclase, and K-feldspar are Q (sub m) = 46, P = 49, and K = 5, and the average detrital modes of polycrystalline quartz, volcanic-rock fragments, and sedimentary-rock plus metamorphic-rock fragments are Q (sub p) = 16, L (sub v) = 43, and L (sub sm) = 41. Likely source areas include the Olympic Peninsula and Vancouver Island; sediment transport was focused primarily through the Strait of Juan de Fuca, Juan de Fuca Channel, Vancouver Valley, and Nitinat Valley. Relative abundance of clay minerals (<2-mu m-size fraction) fluctuate erratically with depth, stratigraphic age, and sediment type (mud vs. turbidite matrix). Mineral abundance in mud samples are 0%-35% smectite (mean = 8%), 18%-59% illite (mean = 40%), and 29%-78% chlorite + kaolinite (mean = 52%). We attribute the relatively low content of smectite to rapid mechanical weathering of polymictic source terrains, with little or no input of volcanic detritus from the Columbia River. The scatter in clay mineralogy probably was caused by converging of surface currents, turbidity currents, and near-bottom nepheloid clouds from several directions, as well as subtle changes in glacial vs. interglacial weathering products.
Coverage:Geographic coordinates:
West:-129.0000East: -127.3000

Oceanography; Stratigraphy; bathymetry; Cascadia Basin; Cenozoic; clastic sediments; clay minerals; composition; East Pacific; hemipelagic environment; Juan de Fuca Ridge; Leg 168; lithostratigraphy; marine environment; marine sediments; mineral composition; mud; Neogene; North Pacific; Northeast Pacific; Ocean Drilling Program; ocean floors; Pacific Ocean; Pliocene; provenance; Quaternary; sand; sediments; sheet silicates; silicates; Tertiary; turbidite;