Barren Ridge Limestone and correlative units

Unit symbol: DSbr
Age range Devonian to Silurian? (443.4 to 358.9 Ma)
Lithology: Sedimentary
Group name: Farewell basinal facies carbonate rocks
As defined by Churkin and Carter (1996), unit consists of “* * * two more-or-less pure limestone members separated by a siltstone member of calcareous siltstone and sandy limestone.” Lower limestone is medium-dark-gray, medium-gray-weathering, well-bedded, thick- to thin-bedded, and has orange-weathering silty beds in upper half of member that form less than 50 percent of section, which is about 100 m thick. Siltstone member is about 200 m thick and is composed of very thin-bedded, cross-laminated, yellowish-orange-weathering, silty and sandy limestone and calcareous siltstone which contain occasional 3-m-thick pure limestone interbeds and rare argillaceous beds. Uppermost member is massive, indistinctly bedded to laminated, medium-dark-gray, finely crystalline limestone more than 100 m thick and contains minor lighter gray dolostone (Churkin and Carter, 1996). Unit is known from the McGrath quadrangle and correlative rocks are found in the Lime Hills quadrangle; the unit undoubtedly extends into the Talkeetna quadrangle, where is it included in unit DCd. Bundtzen and others (1997a) reported late Silurian to Late Devonian conodonts from unit, based on a report in Bundtzen and others (1994) where the reported conodont has an age range of middle Silurian to Early Devonian. Churkin and Carter (1996) interpreted the lower contact of the Barren Ridge Limestone with the underlying Terra Cotta Sandstone as a thrust fault and noted that rocks of latest Silurian age are not present

Source map information

Source map Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic map of the eastern half of the McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14a, 34 p., 1 sheet, scale 1:125,000.
Symbol DSl
Unit name Barren Ridge Limestone; calcarenite, calcareous siltstone, and laminated limestone
Description Thin- to thick-bedded, buff to orange-weathered, light- to medium-gray, phyllitic calcarenite, thin-bedded orange to buff siltstone, and light-gray silty limestone. Dillinger subterrane
Lithology Sedimentary

Correlated geologic units

Label DSca
Description Barren Ridge limestone, calcarenite, calcareous siltstone, and limestone
Geologic age Silurian to Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Calcarenite < Arenite < Sandstone < Clastic < Sedimentary Bed Major
Siltstone < Clastic < Sedimentary Calcareous Indeterminate, major