Whirlwind Creek Formation and correlative units

Unit symbol: DSwc
Age range Upper Devonian, Frasnian, through Silurian, Ludlow (433.4 to 372.2 Ma)
Lithology: Sedimentary
Group name: Farewell platform facies
Several repeated cycles of shallow-marine limestone and dolostone. In the lower part of the formation, the cycles grade from algal-laminated dolostone into pelletoidal limestone and then into silty limestone and siltstone. In the upper part, the cycles grade from thick-bedded reefy limestone to thin-bedded limestone. The formation contains an abundant late Silurian and Devonian conodont, brachiopod, coral, and ostracode fauna. In the Taylor Mountains and adjacent Sleetmute quadrangles, rocks representative of the lower part of the Whirlwind Creek Formation consist of thick to massive bedded, locally dolomitized, light-gray algal boundstone; composed primarily of spongiostromate algal heads (including abundant oncoid forms). Unit represents a barrier reef complex on the outer or seaward margin of the Silurian carbonate platform (Blodgett and Clough, 1985; Blodgett and Wilson, 2001). Contains scattered pockets of brachiopods, which mostly belong to the superfamily Gypiduloidea. Locally abundant are aphrosalppingid sponges (notably Aphrosalpinx textilis Miagkova; Rigby and others, 1994), which are known elsewhere only from the Ural Mountains of Russia and the Alexander terrane of southeastern Alaska. Equivalent to unit Sl of Gilbert (1981) as well as the Cheeneetnuk Limestone (Blodgett and Gilbert, 1983) and Soda Creek Limestone (Blodgett and others, 2000b)

Source map information

Source map Patton, W.W., Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811A, 1 sheet, scale 1:250,000.
Symbol DSl
Unit name Reefy limestone and dolomite
Description Unit composed of a lower sequence of dolomite containing ostracodes of probable Late Silurian age, a middle sequence of mixed limestone and dolomite having favostid reefs and shelly fossils of probable Early Devonian age and an upper sequence of Amphipora-bearing dolomite and rugose coral bearing limestone
Lithology Sedimentary

Correlated geologic units

Label DSwc
Description Whirlwind Creek Formation and unnamed correlative units (Late Devonian, Frasnian through mid-Silurian, Wenlockian), reefy limestone and dolomite
Geologic age Wenlock to Frasnian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Dolostone < Carbonate < Sedimentary Reef Major
Limestone < Carbonate < Sedimentary Reef Major