Limestone and similar rocks

Unit symbol: Dbfl
Age range Upper and Middle Devonian (393.3 to 358.9 Ma)
Lithology: Sedimentary
Group name: Beaucoup Formation, undivided
Light- and dark-gray limestone and dolostone, locally cherty; weathers to gray, orange, or brown (Mayfield and Tailleur, 1978; Nelson and Grybeck, 1980; Brosgé and Reiser, 2000; Dover and others, 2004). As mapped, unit includes the limestone of Nakolik River of Karl and others (1989a), which consists of fossiliferous metalimestone and marble and subordinate quartz-carbonate metasandstone, metasiltstone, and phyllite. Descriptions vary, but unit is locally distinguished from Lisburne Group by lack of chert. Adjacent to the Arrigetch pluton in the Survey Pass quadrangle, unit contains calc-silicate skarn (Nelson and Grybeck, 1980). Megafossils are locally abundant and include brachiopods, corals, pelmatozoans, and stromatoporoids. Megafossils and conodonts, where most precisely dated, are of Middle and early Late Devonian age (Dover and others, 2004)

Source map information

Source map Brosge', W.P., Reiser, H.N., Dutro, J.T., Jr., and Detterman, R.L., 1979, Bedrock geologic map of the Phillip Smith Mountains quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-879-B, 2 sheets, scale 1:250,000.
Symbol Dbl
Unit name Beaucoup Formation, Limestone member
Description Gray weathering dark-gray limestone, commonly fetid or carbonaceous; commonly overlain, underlain or interbedded with brown and orange weathering argillaceous or shaley limestone and minor amounts of brown sandstone. Abundant corals and stromatoporoids. Marine.
Lithology Sedimentary

Correlated geologic units

Label DSol
Description Beaucoup Formation, dark gray to orange weathering limestone (see also 7360)
Geologic age Middle-Devonian to Devonian
Geologic setting Undivided
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major
Limestone < Carbonate < Sedimentary Bed Major
Metasandstone < Metaclastic < Metasedimentary < Metamorphic Minor
Metasiltstone < Metaclastic < Metasedimentary < Metamorphic Minor
Metaconglomerate < Metaclastic < Metasedimentary < Metamorphic Incidental
Phyllite < Metaclastic < Metasedimentary < Metamorphic Incidental