The Siksikpuk assemblage is peculariarly limited to a small number of kinds of specialized brachiopods, corals and gastropods. In addition, pyrite is encountered in may places in these strata. The enviornment of depositon clearly was not normal shallow-water marine; it may have been a deedper stater, restricted and reducing regimen.

Collection 59ACr87, from the upper part of the Lisburne group, also consists of a small number of specialized forms. They represent the "culm" facies of the Mississippian; it has been found elsewhere in the Brooks Range in the Alapah limestone of the central Brooks Range and in the Tupik formation of the DeLong Mountains region. The age is late Mississippian. I would suggest that unit Ml₅ of the measured sequence is a Tupik equivalent.

The "culm facies" commonly is applied to the dark shaly phase of the Carboniferous as contrasted to the more normal marine shelly and bioclastic limestones. Some workers have interpreted cephalopod-bearing strata as pelagic. Oths have attributed to pelecypod-rich beds a lagoonal or even deltaic origin. In the north Alaska "culm", deposition is characterized by an influx of clay or silt, as in the shaly limestone member at the base of the Wachsmuth and the shaly limestone and black chert-shale members of the Alapah in the central Brooks Range. The Tupik formation and an unnamed formation in the eastern DeLong Mountains are other examples of this facies.

Doubtless, no one mode of origin could explain all these occurrences. In the case of the Point Hope region, I have would suspect that a new source of fine clastic sediment became available late in Mississippian time. The environment changed, becoming unfavorable for the more normal coral-brachiopod assemblage that characterizes many of the Lisburne beds below. Direct evidence is sparse, but the occurrence of Lingula, a generally shallow-water brachiopod, suggests shallow restricted marine basins. As in the Siksikpuk, widespread pyrite in this facies point to recuding conditions, at least in part.

Dutro (written commun., 1961) considers the age of these collections as "probable Early Permian." Thus, the Siksikpuk Formation is herein considered to be of Early(?) Permian age. (from Campbell, 1967, p. 20)

(Note by R.B. Blodgett: from description of Siksikpuk Fm., unit 4 on p. 53): Near base of unit, two argillite beds contain sparsely scattered carbonate fossils that include only brachiopods and gastropods. 59ACr-89f is a collection of fossils. (from Campbell, 1967, p. 53)