Shallow-marine carbonate-dominated rocks

Unit symbol: DSld
Age range Devonian and Silurian? (427.4 to 358.9 Ma)
Lithology: Sedimentary
Group name: Shallow-marine, carbonate-dominated rocks
Limestone, dolostone, and lime mudstone of Late Devonian and possibly as old as Silurian age in central Alaska. These limestone bodies occur between strands of the Tintina Fault System in the so-called Preacher Block in the Circle quadrangle (Foster and others, 1983) as well in the eastern Eagle quadrangle (Foster, 1976). These generally appear to be shallow-marine, carbonate-dominated rocks. In the Circle quadrangle, medium-gray, generally massive, locally recrystallized limestone is found in scattered outcrop belts between strands of the Tintina Fault System (Foster and others, 1983). It has yielded Early Devonian conodonts from several localities (Foster and others, 1983) and is thought to possibly correlate with the Tolovana Limestone (unit DSt). In the Tanana quadrangle, includes a number of units mapped by J.N. Dover (unpub. data, 1997) that consist of light- to medium-gray or tan, sandy, platy limestone, gray bioclastic limestone, and massively bedded silicified limestone and dolostone of Late Devonian (Famennian) age and the informally named limestone of Raven Ridge, which consists of gray micritic and brecciated limestone, also of Late Devonian(?) age. In the Kantishna River quadrangle, medium- to dark-gray limestone, in part dolomitic, and medium-gray shaly to phyllitic siltstone has yielded Late Devonian (Frasnian) corals from one locality (Chapman and others, 1975)

Source map information

Source map Foster, H.L., Laird, Jo, Keith, T.E.C., Cushing, G.W., and Menzie, D.W., 1983, Preliminary geologic map of the Circle quadrangle, Alaska: U.S. Geological Survey Open-File Report, 83-170-A, scale 1:250,000.
Symbol Pzl
Unit name Limestone and chert
Description Two separate(?) units. Eastern unit is light-gray to medium-dark-gray at top, mostly fine-grained, partly recrystallized, blocky fracturing limestone. Possible algal structures. Western unit ranges from light- to dark-gray limestone apparently interlayered with black, gray, and mottled chert, tan and gray argillite, amygdaloidal basalt, and gabbro.
Lithology Sedimentary

Correlated geologic units

Label DSl
Description Limestone (Late Devonian to mid-Silurian)
Geologic age Ludlow to Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Dolostone < Carbonate < Sedimentary Bed Minor