This report summarizes and synthesizes information on the 225-foot sandstone sequence that unconformably overlies the chert-phyllite member of the Neruokpuk Formation near the headwaters of the Kongakut River in the southwest corner of the Demarcation Point quadrangle. The sequence is, in turn, unconformably overlain by the early Mississippian Kekiktut Conglomerate.

From the conglomerate at the base of the unit, O. L. Karklins has examined the abundant bryozoans and suggests that they may be Late Silurian or Devonian in age (see report dated 2/3/72). The sample was also examined for microfossils but none were found (see report by Huddle dated 3/29/72).

A coquinoid bed about 50 feet above the base (71ABe463D – USGS 8898-SD) is composed almost entirely of brachiopods and pelecypods. There are also some fragmentary bryozoans like those at the base. Although poorly preserved, the brachiopod is probably Warrenella, as in the beds above. The pelecypods are indeterminate.

The upper 50 feet of thin-bedded sandstone contains an abundant fauna of brachiopods and pelecypods, with a few trilobite fragments. Two collections from this unit (71ABe463C – USGS 8899-SD and 71ABe459E – USGS 8900-SD) contain molds and casts of the following forms: [see fossil list below]

An earlier identification of Actinopteria was not verified after further preparation by Pojeta.

The brachiopod may be a new genus, but is close to Warrenella, common in Middle Devonian rocks elsewhere. The pelecypods are consistent with this age assignment but really could occur anywhere in the Devonian. An Early Devonian age cannot be ruled out.

This assemblage probably represents a very shallow water, nearshore marine environment and, because of the limited diversity, is difficult to date precisely. We suggest an Early Devonian-Middle Devonian range, with a slight preference for the latter. For mapping purposes, we would favor a Middle(?) Devonian assignment.