Nearshore facies

Unit symbol: Kkn
Age range Upper Cretaceous, Santonian to Cenomanian (100.5 to 83.6 Ma)
Lithology: Sedimentary
Group name: Shallow to moderate depth sedimentary rocks
Consists of well-sorted, quartz-rich, cross-bedded sandstone interbedded with siltstone and shale. Includes the thick-bedded quartzose sandstone, pebbly sandstone, and subordinate siltstone and shale of the deltaic facies which consist of chert clasts, which was described by Box and others (1993). Also includes pebble to boulder conglomerate, coarse sandstone, and minor interbedded medium-grained sandstone, siltstone, and shale of the basal conglomerate of Box and others (1993). As described by Hoare and Coonrad (1959a), this nearshore facies chiefly consists of conglomerate facies of interbedded graywacke and siltstone, with lesser amounts of pebble grit conglomerate and a small amount of coal. Well-indurated, commonly light- to dark-gray, and weathers brown. Varies from volcanic wacke to quartz-chert-feldspar-rich sandstone. Fossils collected from basal conglomerate member of Box and others (1993) are considered Late Cretaceous (Cenomanian) age and fossils from the deltaic facies of Box and others (1993) are considered Late Cretaceous (Turonian). Murphy (1989) reported an Albian ammonite, Paragastroplites, from this unit in the Bethel quadrangle. This informal subdivision of the Kuskokwim Group was originally defined by Platt and Muller (unpub. data, 1957, cited in Wilson and others, 2006a, in press [Scientific Investivgations Map 2942]) in the northeastern Taylor Mountains quadrangle; subsequent mapping in the Iditarod quadrangle to the north (Miller and Bundtzen, 1994) also described a nearshore facies

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 Ksc
Unit name Sandstone and conglomerate
Description Chiefly fine- to coarse-grained, greenish-gray to gray, thinly cross-bedded "salt and pepper" sandstone and quartz-chert pebble conglomerate. Poorly exposed interbeds of dark shale and siltstone.
Lithology Sedimentary

Correlated geologic units

Label Kkn
Description Kuskokwim Group, nonmarine to marginal marine quartzose sandstone and siltstone
Geologic age Cenomanian to Santonian
Geologic setting Sedimentary, deltaic-and-nearshore
Lithology Form Importance
Quartzose-sandstone < Sandstone < Clastic < Sedimentary Bed Major
Siltstone < Clastic < Sedimentary Bed Major
Conglomerate < Clastic < Sedimentary Bed Indeterminate, major