End_Page 670------------------------------

No formations have been formally defined within the Cretaceous clastic deposits of the regionally extensive Kuskokwim Group of southwestern Alaska. Near Cairn Mountain, in its southeastern area of exposure, the Kuskokwim Group may be divided into two distinctive stratigraphic units. The widespread lower unit (Hook Creek unit) consists mainly of shale and siltstone with interbedded sandstone turbidites and is at least 5,000 m thick. The upper unit (Cairn Mountain unit) is characterized by poorly cyclical massive sandstone and granule to cobble conglomerate. This unit is at least 6,000 m thick at Cairn Mountain, but thins dramatically to the southwest to about 750 m.

Based on measured sections and other sedimentologic data, we interpret the Cairn Mountain area as part of a Cretaceous submarine-fan complex. The Hook Creek unit consists of mid-fan channel and levee deposits that thin and fine upward, whereas the coarser grained Cairn Mountain unit comprises inner-fan channel deposits. Paleocurrent and compositional evidence indicate that the submarine fan was shed southwestward, mainly from the Mystic terrane in the western Alaska Range.

End_of_Article - Last_Page 671------------