Associated carbonate rock

Unit symbol: SOdc
Age range Silurian, Llandovery, and Ordovician (485.4 to 433.4 Ma)
Lithology: Sedimentary
Group name: Sedimentary and volcanic rocks of Prince of Wales Island
Light- to dark-gray beds of limestone up to 1 m in thickness, massive dark gray limestone interbedded with siliceous black argillite, and cross-laminated sandy limestone interbedded with shale, argillite, mudstone, and siltstone of the Descon Formation (Eberlein and Churkin, 1970). Sedimentary structures indicate deposition by turbidity flows (Gehrels, 1992). Locally includes patch reefs, associated with Luck Creek volcanic unit (unit SOv here), that consist of algal, micritic, massive gray limestone that contain stromatolites, corals, crinoids, pentacrinites, and bivalves (Karl and others, 1999). Also includes thin dark-gray metalimestone lenses associated with black graptolitic argillite associated with the Moira Sound unit of Slack and others (2007). Locally includes thin-bedded, wavy-bedded, crossbedded, or rhythmically bedded metalimestone turbidites with interbedded calcareous metamudstone. In Ketchikan area, consists of tan-weathering, sugary, white calcite and dolomite, intercalated with subordinate green metavolcanic and gray metasedimentary phyllite and schist (S.M. Karl, unpub. data). East of Peril Strait in the Sitka quadrangle, unit generally also includes massive blocks and layers of dark-gray to white, fine- to medium-grained, and gray-weathering Paleozoic(?) marble in layers that range from less than1 cm to several meters in thickness

Source map information

Source map Karl, S.M., Haeussler, P.J., and McCafferty, Anne, 1999, Reconnaissance geologic map of the Duncan Canal-Zarembo Island area, southeast Alaska: U.S. Geological Survey Open File Report 99-168, 1 sheet, scale 1:125,000.
Symbol SOdl
Unit name Descon Formation limestone
Description Intraformational limestone breccia, fossil hash, and conglomerate.
Lithology Sedimentary

Correlated geologic units

Label SOl
Description Descon Formation limestone
Geologic age Ordovician to Llandovery
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Calcareous Indeterminate, major