Geologic description
About 53 meters (175 ft) of highly manganiferous beds crop out in the middle the of pebble-shale member of the Lower Cretaceous Kongakut Formation which is 158 meters (520 ft) thick at this locality. This manganiferous section is black, with small pellets and thin beds of sedimentary manganese carbonates; exact chemical composition of this interval not known. The term Kongakut Formation is no longer widely used; the interval described here is currently referred to as the pebble shale unit and is widely recognized in the subsurface of northern Alaska. The pebble shale unit depositionally overlies the Kemik Sandstone of Early Cretaceous age. At Bathtub Ridge the pebble shale unit depositionally underlies siltstone (see Bird and Molenaar, 1987, Figure 5.6 A) whereas north of Bathtub Ridge, the pebble shale unit depositionally underlies shales of Early Cretaceous age, some of which are radioactive and tuffaceous. |
