page_title: Clastic dike
section_title: Clastic dikes in the Columbia Basin
hierarchical_section_title: Clastic dike / Environments of formation / Clastic dikes in the Columbia Basin
caption_attribution_description: English: Sheeted clastic dike in Missoula flood slackwater rhythmites at Cecil, OR.
context_page_description: A clastic dike is a seam of sedimentary material that fills an open fracture in and cuts across sedimentary rock strata or layering in other rock types. Clastic dikes form rapidly by fluidized injection or passively by water, wind, and gravity. Diagenesis may play a role in the formation of some dikes. Clastic dikes are commonly vertical or near-vertical. Centimeter-scale widths are common, but thicknesses range from millimetres to metres. Length is usually many times width.
  Clastic dikes are found in sedimentary basin deposits worldwide. Formal geologic reports of clastic dikes began to emerge in the early 19th century.
  Terms synonymous with clastic dike include: clastic intrusion, sandstone dike, fissure fill, soft-sediment deformation, fluid escape structure, seismite, injectite, liquefaction feature, neptunian dike, paleoseismic indicator, pseudo ice wedge cast, sedimentary insertion, sheeted clastic dike, synsedimentary filling, tension fracture, hydraulic injection dike, and tempestite.
context_section_description: Tens of thousands of unusual clastic dikes (1 mm—350 cm wide, up to 50 m deep) penetrate sedimentary and bedrock units in the Columbia Basin of Washington, Oregon and Idaho. Their origin remains in question. The dikes may be related to loading by outburst floods. Other evidence suggests they are sediment-filled desiccation cracks (mudcracks). Some have suggested the dikes are ice wedge casts or features related to the melting of buried ice. Earthquake shaking and liquefaction is invoked by others to explain the dikes (i.e., sand blows).
  The silt-, sand-, and gravel-filled dikes in the Columbia Basin are primarily sourced in the Touchet Formation (or the Touchet-equivalent Willamette Silt) and intrude downward into older geologic units, including:
  Pleistocene hillslope colluvium with developed caliche horizons in the Umatilla Basin near Alderdale, Washington
  Pleistocene landslide deposits along Hwy 14 in the Columbia Gorge (Umatilla Basin)
  Pleistocene Clearwater Gravels in the Lewiston Basin
  "Pre-late Wisconsin" outburst flood and flood-related deposits (includes the "ancient cataclysmic flood deposits" of Allen et al., 2009) in the Walla Walla Valley/Pasco Basin  and Columbia Gorge
  Post-basalt basin fill sediments (Dalles Group, etc.) exposed in tributary stream valleys downstream of Wallula Gap
  Miocene-Pliocene Snipes Mountain Conglomerate in the Yakima Valley at Granger, Washington
  Miocene-Pliocene Ringold Formation in the Pasco Basin
  Miocene-Pliocene Ellensburg Formation at Craig's Hill near Ellensburg, Washington (outside Missoula flood track)
  Miocene-Pliocene Ellensburg Formation at Foster Coulee (WDFW Foster Ck Wildlife Area) near Bridgeport, Washington
  Miocene Columbia River Basalt (CRB) in the Walla Walla Valley and Pasco Basin at Gable Mountain
  Latah Formation (interbeds in CRBs) west of Finley, Washington along Hwy 397 and elsewhere
  
  In 1925, Olaf P. Jenkins described the clastic dikes of eastern Washington state as follows: 
  It appears, then, that in every case fissures formed and then fragmental materials are dropped, washed, or pressed into them, from above, below, or from the sides. This action has taken place in open fissures; under water in fissures on the bed of the sea or other bodies of water; and also far below the surface of the earth in consolidated rocks. The filling from below has come about by pressure of some sort, in some cases undoubtedly hydrostatic.
caption: Vertically sheeted clastic dike typical of those found in rhythmically bedded Missoula flood slackwater deposits of the Columbia Basin. Yellow field book for scale. Willow Creek Valley at Cecil, OR.
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