Sadlerochit Group, undivided

Unit symbol: TrPsg
Age range Lower Triassic to Permian (298.9 to 247.2 Ma)
Lithology: Sedimentary
Group name: Sadlerochit Group, undivided
A “heterogeneous assemblage of rocks that includes orthoquartzite, chert, limestone, sandstone, siltstone, and shale” (Detterman and others, 1975) that has been divided into two formations: an upper Ivishak Formation and a lower Echooka Formation, each of which is subdivided into formal members. Largely restricted to northeast Alaska and in the subsurface of the North Slope, it begins as a regressive sequence sourced from the north (Wilson and others, 2001) and transitions upward from shelf to fluvial deposits. A third formation, stratigraphically in the middle of the group, the Kavik Shale is recognized in the subsurface and is a medium to dark gray silty shale with minor siltstone and sandstone (Jones and Speers, 1976; Crowder, 1990; Wilson and others, 2001). The Kavik Shale of the subsurface is considered equivalent to the Kavik Member of the Ivishak Formation on the surface. The Sadlerochit Group includes the main reservoir rocks for the Prudhoe Bay oil field, which is estimated to hold as much as 25 billion barrels of oil and 46 trillion cubic feet (tcf) of natural gas (British Petroleum, 2013). Unit locally subdivided into the following two units, Trif and Pe

Source map information

Source map Keller, A.S., Morris, R.H., and Detterman, R.L., 1961, Geology of the Shaviovik and Sagavanirktok Rivers region, Alaska, in Exploration of Naval Petroleum Reserve No. 4 and adjacent areas, northern Alaska, 1944-1953, Part 3, Areal Geology: U.S. Geological Survey Professional Paper 303-D, p. 169-222, 6 plates, scale 1:63,360.
Symbol TrPs
Unit name Sadlerochit Formation
Description The Sadlerochit Formation is well exposed and is one of the most persistent units within the mapped area. It crops out in a belt 1 to 3 miles wide extending northeasterly along the north front of the Brooks Range. Typically the rocks are the flanking beds of the east- and west-plunging en echelon anticlines which form the mountain front, and generally are exposed best in cutbanks on smaller streams. The rocks which lie stratigraphically between the Lisburne Group and the Shublik Formation in the Canning River area and elsewhere in the mapped area include siltstone, shale, limestone, and chert, in addition to sandstone. The formation is divided into two members; the Echooka member of Permian age and the Ivishak member of Early Triassic age
Lithology Sedimentary

Correlated geologic units

Label TrPsg
Description Sadlerochit Group, undivided
Geologic age Permian to Early-Triassic
Geologic setting Undivided
Lithology Form Importance
Sandstone < Clastic < Sedimentary Bed Major
Shale < Mudstone < Clastic < Sedimentary Bed Indeterminate, major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major
Shale < Mudstone < Clastic < Sedimentary Calcareous Minor