The foraminiferal and palynological biostratigraphy of subsurface Jurassic and Neocomian (Early Cretaceous) age strata from the North Slope were investigated to better define biostratigraphic zone boundaries and to help clarify the correlation of the stratigraphic units in the National Petroleum Reserve in Alaska (NPRA). Through use of micropaleontologic data, eight principal biostratigraphic units have been identified. The Neocomian and Jurassic strata have each been subdivided into four main units.

The gamma-ray zone (GRZ), or "hot zone," sediments include both northern and southern source starved-basin deposits. These deposits range from Barremian to possibly middle Albian age in NPRA. East of NPRA, these Early Cretaceous starved-basin deposits coalesce with Late Cretaceous starved-basin deposits and form a GRZ at least as young as Senonian.

Early Cretaceous starved-basin deposits of northern source are recognized by the presence of dispersed, rounded, frosted quartz sand grains. These sand grains, floating in a mudstone matrix, are essentially absent from the starved-basin deposits of southern source.

The Lower Cretaceous unconformity occurs within the Hauterivian to Barremian biostratigraphic interval in the Tunalik, Peard, and Inigok wells on the NPRA; it cannot be recognized through microfossil evidence in those particular areas. In most other areas of the North Slope, the unconformity occurs at the base of the Hauterivian to Barremian biostratigraphic interval. This unconformity truncates progressively older strata eastward along the present coastal region and onto the Barrow arch.

A mid-Jurassic sandstone unit appears to be of Early to Middle Jurassic rather than Late Jurassic (Oxfordian) age.

Lower to Middle Jurassic strata are characterized by southward depositional thinning and distal (starved-basin) deposition in certain areas.

The Sag River Sandstone is a time transgressive unit that ranges from Late Triassic in the north and northwestern NPRA to Early Jurassic on the Fish Creek platform to the east.

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