Abstract

The lithologic and microfaunal facies of the Cretaceous sediments of the Arctic Slope of northern Alaska are discussed and their depositional environments suggested. The faunas differ from usual Cretaceous assemblages in being controlled by high turbidity and turbulence and rapid deposition, as well as rapid fluctuations of sea level, with resultant intertonguing marine and nonmarine strata. Nonmarine strata (fluviatile environment) and the coastal deposits (supralittoral) contain charophyte ooegonia, but no Foraminifera; the intertidal coastal deposits contain environmentally tolerant arenaceous species, which are represented by stunted specimens with little variety, but are locally present in large numbers. The nearshore deposits of turbidity-controlled facies contain large robust specimens of arenaceous Foraminifera, in general of the same cosmopolitan species as those of the intertidal region. A few calcareous Foraminifera and some Radiolaria are also present, but occur as pyritic casts, a further indication of their rapid burial. The more usual offshore faunas are less characteristic of Alaska, occurring in the subsurface of the present coastal region; there the arenaceous and calcareous species occur in nearly equal variety, and the calcareous Foraminifera and the Radiolaria occur as shells rather than as casts. Strong currents from land seem to have prevented the influx of planktonic Foraminifera, except for a single zone in the Seabee formation, of Turonian age, which locally contains Heterohelix and Hedbergella.

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