White Mountain sequence, basinal facies

Unit symbol: DCd
Age range Devonian to Cambrian or older (541 to 358.9 Ma)
Lithology: Sedimentary
Group name: Farewell basinal facies carbonate rocks
Finely laminated limestone and dolomitic limestone and subordinate chert and siliceous siltstone, indicative of deep-water deposition. Rocks included here were originally considered part of the now-abandoned Holitna Group and later were assigned to the Dillinger terrane, now considered the basinal facies of the White Mountain sequence of the Farewell terrane (Decker and others, 1994). They were originally assigned an Ordovician to Devonian age on the basis of a sparse conodont fauna (Dutro and Patton, 1982). More recent work, however, indicates that the unit also contains conodonts of Cambrian age (Dumoulin and others, 1997). Includes East Fork Hills, Post River, and Lyman Hills Formations, Terra Cotta Mountains Sandstone, and Barren Ridge Limestone, all interpreted as slope or basinal deposits (Patton and others, 2009). Includes lime-rich sedimentary rocks in unit Pzd of Reed and Nelson (1980) in the Talkeetna quadrangle; unit Pzs of Gamble and others (2013) in eastern Lime Hills quadrangle; and unit Pzdu of Bundtzen (written commun., 1998) in western Lime Hills quadrangle. In the northwestern Mount McKinley quadrangle, includes chert and slate that yielded Ordovician graptolites, and, in the southern Mount McKinley quadrangle, quartz-rich turbiditic sandstones and minor interbedded limestone yielded early Silurian (Llandovery) conodonts (Dumoulin and others, 1998), and quartzite that yielded Silurian to Devonian corals (William Oliver, written commun., 1997). Where subdivided, includes the following units, DSbr, DSpf, Stc, and SCpl:

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 DOsl
Unit name Shaly limestone
Description Dark-gray to grayish-orange finely laminated limestone and dolomitic limestone. Subordinate laminated dolomite, dark chert, and siliceous siltstone. Interpreted as deep-water facies of Osl, Od, and DSl carbonate units. Now named East Fork Hills Formation (Patton, 2002)
Lithology Sedimentary

Correlated geologic units

Label DCd
Description Dillinger stratigraphic sequence, undivided; sedimentary rocks of Dillinger River, lime mudstone and shale, etc, Paleozoic. Now part of White Mountain sequence of Decker and others, 1994
Geologic age Cambrian to Givetian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Shale < Mudstone < Clastic < Sedimentary Bed Major
Dolostone < Carbonate < Sedimentary Bed Minor
Chert < Chemical < Sedimentary Bed Minor
Siltstone < Clastic < Sedimentary Bed Minor