Lisburne Group, undivided

Unit symbol: Clg
Age range Carboniferous (358.9 to 298.9 Ma)
Lithology: Sedimentary
Group name: Lisburne Group, undivided
Carbonate and chert unit widely distributed in northern Alaska. As thick as 1,800 m, chiefly limestone and dolomite, in part cherty, with variable but generally minor amounts of interbedded shale. Exposed throughout the Brooks Range, it is also a well-developed horizon in the subsurface of the North Slope. The Lisburne Group is divided formally into several units. In eastern Alaska, in ascending order, these are the Wachsmuth Limestone, Alapah Limestone, and Wahoo Limestone. In western Alaska, the Lisburne Group includes, in ascending order, the Nasorak and Utukok Formations, Kogruk Formation, and Tupik Formation. Two other formations of the group, the Akmalik Chert and the Kuna Formation, are locally mapped, primarily in the central and western part of northern Alaska. The unit descriptions here, after the Kuna Formation, list the western units first followed by the eastern units of the group. The Lisburne Group is a component of most of the allochthons of the Brooks Range, and its various formations and their facies are important tools used in defining the allochthons. In general, the Mississippian rocks consist of crystalline and hydroclastic limestone, which locally is oolitic and lithographic. The limestone ranges from thin-bedded to massive. The massively bedded limestone is generally lighter in color than the somewhat siliceous blue-gray thin-bedded variety. Chert lenses and nodules, both primary and diagenetic, are common throughout. Phosphate-rich shale and limestone are present in the Lisburne Group, typically in the Tupik, Kuna, or Kogruk Formations or the Alapah Limestone (see Dumoulin and others, 2008, 2011). The entire sequence of rocks in the group has a strong organic odor and is generally fossiliferous. The carbonates of the Lisburne Group represent a variety of marine environments, the trend is that the portion of deep-water units increases westward; the eastern third of the Brooks Range exposures are almost entirely shallow water facies (J.A. Dumoulin, oral commun., 2012). In the Philip Smith Mountains quadrangle, the mapped upper part of the Lisburne Group contains Late Mississippian corals and brachiopods, Pennsylvanian brachiopods, and in upper 30m near Galbraith Lake, brachiopods that may be early Permian (Brosgé and others, 1979; although this age assignment is considered unlikely, J.A. Dumoulin, oral commun., 2012). Late Mississippian and Early Pennsylvanian foraminifera are common (Brosgé and others, 1979). In some areas, the Lisburne Group is mapped as informally recognized upper and lower units. Locally subdivided into the following eight formal units: Mlgk, Clgt, Clgk, Mlgac, Mlgnu, IPlgw, Mlga, Mlgw

Source map information

Source map Mayfield, C.F., Curtis, S.M., Ellersieck, Inyo, and Tailleur, I.L., 1990, Reconnaissance geologic map of the De Long Mountains A-3 and B-3 quadrangles and parts of A-4 and B-4 quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1929, 2 sheets, scale 1:63,360.
Symbol Mml1
Unit name Micritic limestone, Brooks Range allochthon, Key Creek sequence
Description Dark-gray, light-weathering, thin-bedded limestone with subordinate interbedded black shale. Part of the Brooks Range allochthon, Key Creek sequence.
Lithology Sedimentary

Correlated geologic units

Label IPMl
Description Lisburne Group, undivided
Geologic age Mississippian to Pennsylvanian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Dolostone < Carbonate < Sedimentary Bed Major
Limestone < Carbonate < Sedimentary Bed Major
Chert < Chemical < Sedimentary Bed Minor