Tahkandit Limestone

Unit symbol: Ptl
Age range lower Permian (298.9 to 272.3 Ma)
Lithology: Sedimentary
Group name: Limestone and calcareous clastic rocks
Tan to light-gray, fine- to coarse-grained bioclastic limestone that weathers to gray to dark-gray. Locally cryptocrystalline and nonfossiliferous, but generally contains abundant brachiopods, solitary corals, crinoids, and bryozoan fragments (Brabb and Grant, 1971). Unit is a facies equivalent of the Step Conglomerate (unit Pstc). Where interbedded with Step Conglomerate, unit contains abundant rounded chert pebbles (Clough and others, 1995). As shown here, includes gray nodular siltstone and yellow-weathering silty limestone, at least 120 m thick, as mapped by Brosgé and Reiser (1969) in the Coleen quadrangle

Source map information

Source map Brabb, E.E., and Churkin, Michael, Jr., 1969, Geologic map of the Charley River quadrangle, east-central Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-573, 1 sheet, scale 1:250,000.
Symbol Pt
Unit name Tahkandit Limestone
Description Very pale orange, coarse-grained bioclastic limestone. Forms massive cliffs. Grayish-green glauconitic sandstone and chert-pebble conglomerate in basal 75 feet. Contains abundant brachiopods and a few corals, arenaceous foraminifers and bryozoa. Maximum thickness about 350 feet.
Lithology Sedimentary

Correlated geologic units

Label Ptl
Description Tahkandit Limestone, massive bioclastic limestone [NOTE: may be equivalent to NSA 5715, Echooka Formation]
Geologic age Cisuralian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Conglomerate < Clastic < Sedimentary Bed Incidental
Sandstone < Clastic < Sedimentary Bed Incidental