Geologic Map of Alaska: Limestone and similar rocks

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	Mull, C.G., Moore, T.E., Harris, E.E., and Tailleur, I.L., 1994, Geologic map of the Killik River quadrangle, Brooks Range, Alaska: U.S. Geological Survey Open-File Report 94-679, 1 sheet, scale 1:125,000.
Symbol	Dls
Unit name	Limestone and Marble
Description	Coarse-grained, light-gray limestone, commonly recrystallized, forms white-weathering pinnacles up to 10 m high surrounded by tundra near Nogak Creek and Otuk Creek. Distinguished from limestone of Lisburne Group by light-gray color and absence of chert; resembles Baird Group carbonates in southern Brooks Range. Probably emplaced as tectonic slivers at base of Ipnavik River allochthon. Unfossiliferous, but similar rocks in Howard Pass quad contain Middle or Late Devonian fossils.
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