Limestone of the Hasen Creek and Eagle Creek Formations

Unit symbol: Pehls
Age range lower Permian (298.9 to 272.3 Ma)
Lithology: Sedimentary
Group name: Skolai and Mankomen Groups, undivided
Thin- to thick-bedded, fossiliferous limestone (MacKevett, 1978) associated with the Hasen Creek Formation. Also includes thin- to thick-bedded fossiliferous limestone at the base of the Eagle Creek Formation (Richter, 1976). Locally, base of limestone is a coarse-grained clastic limestone. Fossils include corals, crinoids, brachiopods, bryozoans, and fusulinids, which together indicate early Permian (Wolfcampian, which corresponds to the earlier part of the Cisuralian stage) age. Unit also includes white to gray marble, which forms conspicuous deformed and folded bands and pods throughout the Strelna Metamorphics (unit P*sm). Individual marble beds vary markedly in thickness along strike; maximum measured thickness of the marble is about 1,200 m. The marble is typically found in association with greenschist and quartz-rich schist, but also forms pods as much as a few hundred meters thick within predominantly phyllitic schist or as inclusions within associated metaplutonic rocks (Winkler and others, 1981; George Plafker, written commun., 2000). Age equivalent to parts of the Cache Creek Group of the Yukon, although the Cache Creek Group has Tethyan fauna, whereas the Hasen Creek and Eagle Creek Formations have boreal fauna (R.B. Blodgett, written commun., 2014)

Source map information

Source map Richter, D.H., 1976, Geologic map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-932, 1 sheet, scale 1:250,000.
Symbol Pel
Unit name Limestone
Description Part of Mankomen Group. Thin- to thick-bedded fossiliferous limestone occurring at the base of the Eagle Creek Formation. Base is a coarse-grained clastic limestone. Gabbroic dikes and sills. Equivalent to parts of the Cache Creek Group and the Skolai Group
Lithology Sedimentary

Correlated geologic units

Label Pels
Description Limestone of the Eagle Creek Formation
Geologic age Cisuralian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Indeterminate, major
Gabbro < Gabbroic < Plutonic < Igneous Dike or sill Incidental