Pybus Formation and correlative? limestone

Unit symbol: Plps
Age range Permian (298.9 to 259.9 Ma)
Lithology: Sedimentary
Group name: Limestone and calcareous clastic rocks
Characteristically “light-brownish-gray to white, medium-bedded, fossiliferous, fine- to medium-grained dolomite [dolostone], which contains irregular layers and scattered angular fragments of bluish-white chert. The chert content increases upward and near the top of the formation constitutes as much as 90 percent of the rock” (Lathram and others, 1965). On northern Kuiu and Kupreanof Islands and Admiralty Island, unit consists of medium-bedded dolostone, limestone, and subordinate gray chert beds and nodules (Lathram and others, 1965; Muffler, 1967; and Brew and others, 1984). The Pybus Formation contains very late early Permian conodonts (Premo and others, 2010), Cisuralian (early Permian) brachiopods (Muffler, 1967; Brew and others, 1984), and Guadalupian (middle Permian) conodonts (Karl and others, 1999). In the Glacier Bay area, light- to medium-brownish-gray, fine- to medium-grained crystalline, fossiliferous limestone contains sparse, paper-thin, reddish brown separations and is overlain by nodular bedded, light-brownish-gray, fine- to medium-grained limestone interbedded with light-greenish-brown chert. The upper limestone and chert varies along strike from an interbedded sequence to apparent limestone-chert conglomerate, which is, in turn, overlain by dark-gray slate, interbedded with very fine-grained and silty calcareous graywacke (Brew and Ford, 1985)

Source map information

Source map Brew, D.A., Ovenshine, A.T., Karl, S.M., and Hunt, S.J., 1984, Preliminary reconnaissance geologic map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open File Report 84-405, 43 p., scale 1:250,000.
Symbol Pp
Unit name Pybus Formation
Description Pybus Formation - limestone, dolomite, and chert; conspicuous cliff-forming medium-bedded to massive non-bedded coarsely crystalline white to very light gray dolomitic limestone with light gray replacement chert as thin beds, nodules, fragments, and crosscutting masses; minor coarse-grained light gray limestone, fetid medium-gray dolomite near top of unit.
Lithology Sedimentary

Correlated geologic units

Label Pp
Description Pybus Formation, limestone and dolostone
Geologic age Artinskian to Guadalupian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Dolostone < Carbonate < Sedimentary Bed Major
Limestone < Carbonate < Sedimentary Bed Major
Chert < Chemical < Sedimentary Bed Minor