Limestone, shale, and chert

Unit symbol: JTrls
Age range Lower Jurassic and Upper Triassic, Norian (228 to 174.1 Ma)
Lithology: Sedimentary
Group name: Volcanic and sedimentary rocks of southwest Alaska
Medium-gray to yellowish-gray-weathering, medium- to thick-bedded, dominantly chert and sandstone unit with locally abundant phosphatic nodules developed in more cherty phases (Wilson and others, in press [Scientific Investigations Map 2942]; R.B. Blodgett, 2005, unpub. data). These rocks are exposed along the periphery of and intercalated with the Paleozoic limestone of the Farewell terrane in the northeastern Taylor Mountains quadrangle. Sandstone beds dominate in lower part of section; chert-rich beds dominate upper part of unit. Contains megafauna (mostly bivalves and belemnites) of undifferentiated Early Jurassic age (R.B. Blodgett, 2005, unpub. data) and radiolarians of undifferentiated Early Jurassic age (C.D. Blome, written commun., 2000; E.A. Pessagno Jr., Univ. of Texas, written commun. to M.L. Miller; 2005) as well as fossils of Norian age. Minimum estimated thickness of unit is 100 m

Source map information

Source map Blodgett, R.B., Wilson, F.H., Miller, M.L., and Blome, C.D., 2005, Unpublished data
Symbol eJTrl
Unit name Limestone, shale, and chert
Description Cream colored to dark-gray limestone, shale, and chert.
Lithology Sedimentary

Correlated geologic units

Label JTrmc
Description Limestone, shale, and chert (Early Jurassic(?)-Late Triassic (Norian))
Geologic age Norian to Early-Jurassic
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Indeterminate, major
Chert < Chemical < Sedimentary Bed Indeterminate, major
Shale < Mudstone < Clastic < Sedimentary Bed Indeterminate, major