Ficheiro:Volcaniclastic graywacke turbidites in Descon Formation.jpg

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