Sedimentary rocks, typical of petroleum producing formations, underlie most of the NPR-A. As a result, the bedrock formations contain a wide array of plant and animal fossils. To date, the earliest reported fossil from within the NPR-A is the tooth plate of a lungfish recovered from a Middle Devonian formation about 380 million years old (Lindsey, 1986). Most subsequent rock formations in the NPR-A exhibit some evidence of a fossil record.

Most of the limestone, sandstone, siltstone, conglomerate, and shale underlying the NPR-A have marine origins, as reflected by their fossils. By far, the most common fossils are brachiopods, cephalopods, gastropods, pelecypods, sponges, bryozoans, corals, and crinoids. Terrestrial plant fossils originate in the middle part of the Jurassic Period, roughly 160 million years ago. This indicates at least a temporary retreat of the ancient seas that had previously covered most of the region. Following this period, the seas repeatedly advanced and retreated over most or all of the NPR-A.

One-hundred-million-year-old lower Cretaceous rocks in the NPR-A produce some of the best examples of that period's flora found anywhere in North America (Lindsey, 1986). These plant fossils also document a change from a warm to a cool climate. It is at this time that modern conifers begin to appear on the North Slope.

Late Cretaceous vertebrate fossils from 70 to 65 Ma are also common. Significant world-class dinosaur remains lie within the Northwest NPR-A Planning Area along banks of the Colville and other major river drainages. These remains represent the farthest north occurrence of dinosaurs in North America. Data gathered through research of this fossil evidence have challenged long-held theories concerning dinosaur physiology and extinction (Brouwers et al., 1987; Paul, 1988; Clemens and Nelms, 1993; Gangloff et al., 2002). Most of the bones are beautifully preserved with varying degrees of mineralization. Some exhibit few void fillings and approach the low density of nonpermineralized, or petrified, bone. The bone is often encapsulated with iron oxide, sulfide, and quartz. This unusual preservation and entombment in permafrost offers the possibility of DNA and other bimolecular extraction that has not been attainable in fossils this ancient before now (Gangloff, 1997).

Mollusks, ostracods, brachiopods, and bryozoans primarily represent Tertiary (65 to 1.6 Ma) fossils, although the record is incomplete because of a period of nondeposition and/or erosion that occurred during the Late Tertiary (Lindsey, 1986). Fossil remains from 50,000 to 10,000 years ago, the latest portion of the Pleistocene (the last Ice Age), are also abundant in Quaternary deposits across the Northwest NPR-A Planning Area (Hamilton and Ashley, 1993; Guthrie and Stoker, 1990). The bones of horses, camels, mammoths, and bison are important data sources reflecting the climate, environment, and ecosystem that existed when the first humans entered the Western Hemisphere from the Old World (Kunz and Mann, 1997). Primary sources for these fossils are the Ikpikpuk, Colville, and other major river drainages.

Most of the paleontological resources in the NPR-A are, by virtue of their isolation and remoteness (Map 87 ), protected from most types of impact, other than those caused by natural forces. The bulk of the deposits are deeply buried and the landscape is covered by snow and remains frozen nine months of the year. It is therefore, adequately protected by nature. However, most of the major known deposits are somewhat vulnerable, because they are most often exposed in an eroding bluff face. In fact, were it not for these exposures, most paleontological deposits in the area would not be discovered. However, the circumstance that led to their discovery also allows unauthorized collection and loss of valuable and important scientific and educational material. Most exposed bluff faces are formed through river and stream erosion. Fossils are commonly exposed or washed from these bluff faces during annual high-water events. Even in a place as remote as the NPR-A, a river may allow access by boat or by small aircraft. Currently, unauthorized collection occurs at several locations in the Northwest NPR-A Planning Area. A visible presence, such as active research rather than irregular law-enforcement patrols, is the best deterrent to unauthorized collection (Gangloff, 1997).

These paleontological resources are nonrenewable and contain a wealth of information about life forms, geography, and environments of the past, and they must receive adequate protection. Most of the paleontological resources of the NPR-A are yet to be located, and work toward that end is another important step in the protection of this resource.