Conglomerate, sandstone, and lignite

Unit symbol: TKs
Age range lower Tertiary to Upper Cretaceous (83.6 to 33.9 Ma)
Lithology: Sedimentary
Group name: Conglomerate, sandstone, and lignite
Sandstone, mudstone, thin coal seems, and conglomerate exposed in the Charley River and Rampart areas. In the Charley River area, the unit consists of poorly consolidated sandstone, grit, pebble-to cobble-conglomerate, and carbonaceous mudstone with coal seams and occurs just east of the Kandik basin and along the Tintina Fault Zone. Late Cretaceous, Paleocene, and Eocene pollen have been recovered from exposures within and immediately south of the map area (Miyaoka, 1990) and from shallow core holes (unpublished oil industry data, 2002, cited in Till and others, 2006a). In the western Rampart area, along the Victoria Creek Fault Zone, quartz- and chert-rich fluvial conglomerate, sandstone, and mudstone are typical, and palynoflora of probable Maastrichtian age (Farmer and others, 2003) as well as of early Tertiary age (Chapman and others, 1982) have been collected. Younger part of the unit likely correlative to rocks of unit Tsu, sedimentary rocks, undivided. Rocks of this unit also occur in a 25-m-thick section along the Sethkokna River in the northeast Medfra quadrangle (Patton and others, 1980). There, the conglomerate contains clasts of quartz, chert, felsic volcanic rocks, and talc schist, which Patton and others (1980) provisionally assigned a latest Cretaceous age (Campanian-Maastrichtian) on the basis of pollen in the lignite beds. Unit is overlain by rhyolite and dacite flows. On the Seward Peninsula, Till and others (2011) mapped two separate sedimentary sequences as their unit TKs. Here, only the more northern Late Cretaceous to Tertiary rocks are included; the older middle-Cretaceous rocks are assigned to map unit Kcc of this map. The rocks included here from the unit TKs of Till and others (2011) consist of gray and brown siltstone, mudstone, sandstone, coal, and minor conglomerate poorly exposed in narrow slices along the Kugruk Fault Zone in the northeastern and southeastern Bendeleben quadrangle; it has been explored for coal and uranium (Retherford and others, 1986; Dickinson and others, 1987). Pollen assemblages of Late Cretaceous and Tertiary (Eocene to early Miocene?) ages have been found in finer grained parts of the sequence (Till and others, 1986; Haga, in Retherford and others, 1986)

Source map information

Source map Brabb, E.E., and Churkin, Michael, Jr., 1969, Geologic map of the Charley River quadrangle, east-central Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-573, 1 sheet, scale 1:250,000.
Symbol TKs
Unit name Sandstone, mudstone, and conglomerate
Description Sandstone and conglomerate, poorly sorted, friable, composed mostly of lithic fragments and about 5 percent potash feldspar. Thin, lignitic coal beds common. Non marine. Thickness 200 to at least 3,000 feet
Lithology Sedimentary

Correlated geologic units

Label TKcg
Description Conglomerate, sandstone, and lignite
Geologic age Campanian to Eocene
Geologic setting Sedimentary, continental
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Major
Sandstone < Clastic < Sedimentary Bed Major
Mudstone < Clastic < Sedimentary Carbonaceous Indeterminate, major
Lignite < Coal < Sedimentary Bed Minor