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Summary
Descon Formation graywacke (Lower Ordovician to Lower Silurian): Volcaniclastic graywacke turbidites, quartzofeldspathic wacke, conglomerate, siliceous shale, chert, and subordinate basalt flows and pyroclastic rock. Massive to thick-beds, graded beds, rhythmic beds, and slumped beds. High sand/shale ratios. Proximal turbidite facies. Graywacke clasts include mainly mafic volcanic rock fragments, and lesser graywacke, feldspar, quartz, chert, limestone, and plutonic rock in a chloritic matrix. Conglomerate varies from wholly volcaniclastic containing clasts of augite porphyritic andesite and basalt, to polymictic, containing clasts of chert, felsite, graywacke and gabbro (Eberlein and others, 1983). Thin-bedded black chert and siliceous shale represent slope and interchannel depositional facies. Graptolites on argillaceous partings (map numbers 72-75, Table 1). Thickness exceeds 3000m, base not exposed. Top of unit grades to Bay of Pillars Formation. Prince of Wales Island.
Copyright status:
This image is public domain because it was first published by the U.S. Geological Survey
Source:
http://pubs.usgs.gov/of/1999/of99-168/of99-168-pamphlet.html
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| Date/Time | Thumbnail | Dimensions | User | Comment |
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| current | 22:55, 17 April 2009 |  | 480 × 296 (51 KB) | Ashcraft | Descon Formation graywacke (Lower Ordovician to Lower Silurian): Volcaniclastic graywacke turbidites, quartzofeldspathic wacke, conglomerate, siliceous shale, chert, and subordinate basalt flows and pyroclastic rock. Massive to thick-beds, graded beds, rh |
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