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 Wilson, F.H., Mohadjer, Solmaz, Labay, K.A., and Shew, Nora, 2006, Digital datasets for geologic map by Wilson, F.H., Blodgett, R.B., Blome, C.D., Mohadjer, Solmaz, Preller, C.C., Klimasauskas, E.P., Gamble, B.M., and Coonrad, W.L.—Preliminary Integrated Geologic Map Databases for the United States: Digital Data for the Reconnaissance Bedrock Geologic Map for the Northern Alaska Peninsula area, Southwest Alaska: U.S. Geological Survey Open File Report 2006-1303, on-line only. http://pubs.usgs.gov/of/2006/1303/
Symbol Sab
Unit name Algal boundstone
Description Thick to massive bedded, light gray algal boundstone, locally dolomitized; composed primarily of spongiostromate algal heads (including abundant oncoid forms). Inferred from air photos
Lithology Sedimentary

Correlated geologic units

Label Sab
Description Algal boundstone in SW Alaska, equivalent to lower part of Whirlwind Creek Formation [NSA 6960]
Geologic age Ludlow to Pridoli
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major