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Grain counts and XRD mineralogy of turbidite sand and hemipelagic mud from ODP Leg 168 sites

Authors
Publisher
PANGAEA
Publication Date
Identifiers
DOI: 10.1594/pangaea.788844
Keywords
  • Acce
  • Accessories
  • Biogenic Indeterminata
  • Biog Indet
  • Chl
  • Chl (002)
  • Chl+Kaol
  • Chl Fwhm
  • Chlorite
  • Full Width At Half Maximum
  • Chlorite
  • Intensity
  • Chlorite (Peak Area)
  • Chlorite+Kaolinite
  • Chl Peak Area
  • Counting
  • Counts
  • Feldspar
  • Fossil Fragments And Sparry Calcite
  • Heavy Mineral Grains
  • Hm Grains
  • Ill
  • Ill (001)
  • Ill Fwhm
  • Illite
  • Illite
  • Full Width At Half Maximum
  • Illite
  • Intensity
  • Illite (Peak Area)
  • Ill Peak Area
  • Kalifeldspar
  • Kfsp
  • Label
  • Lithic
  • Lithic Grains
  • Lithologic Unit/Sequence
  • M = Hemipelagic Mud
  • T = Matrix From Turbidite Sand/Silt
  • Metamorphic
  • Metasediments
  • Mica
  • Monoquartz
  • Muscovite And Biotite
  • Ocean Drilling Program
  • Odp
  • Odp Sample Designation
  • Of Total Lv-Ls-Lm (Unstable Lithics)
  • Of Total Q-F-L
  • Of Total Q-F-L
  • Unstable Lithics
  • Of Total Qm-F-Lt
  • Of Total Qm-F-Lt
  • Total Lithics
  • Of Total Qm-P-K
  • Of Total Qm-P-K (Monocrystalline)
  • Of Total Qp-Lv-Lsm (Polycrystalline)
  • Of Total Qp-Lv-Lsm (Polycrystalline)
  • Including Metasedimentary Lithics
  • Opaque And Non-Opaque
  • Plag
  • Plagioclase
  • Polyquartz
  • Quartz
  • Quartz
  • Monocrystalline
  • Quartz
  • Polycrystalline
  • Sample Code/Label
  • Sed Fragm
  • Sediment
  • Sediment
  • Sedimentary Fragments
  • Sediment Type
  • Smec
  • Smec (001)
  • Smec Fwhm
  • Smec Peak Area
  • Smectite
  • Smectite
  • Full Width At Half Maximum
  • Smectite
  • Intensity
  • Smectite (Peak Area)
  • Total Counts
  • Chl (002)
  • Total Counts
  • Ill (001)
  • Total Counts
  • Smec (001)
  • Total Points Counted
  • Trace Constituents
  • Altered Grains And Unknown
  • Unit
  • Volcanic
  • Volcanic
  • Volcanic Components
  • X-Ray Diffraction
  • Clay Fraction
Disciplines
  • Earth Science

Abstract

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 Qm = 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 Qp = 16, Lv = 43, and Lsm = 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-µm-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.

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