The Geologic History of ANWR

The purpose of this section is to provide everyone with a basic understanding of how ANWR came about, geologically speaking. This information is important in understanding why hydrocarbons are where they are, and is also important in understanding its current geological condition (such as seismic activity, how that impacts exploitation, and so forth). The information is very brief, and the sources used are at the conclusion.

Geographic Placement

The 1002 area of the Arctic National Wildlife Refuge is a 1.5-million-acre area in northeastern Alaska. It is bounded on the east by the Canning and Staines Rivers, on the north by the Beaufort Sea, on the east by the Aichilik River and the Canadian border, and to the south by Brooks Range, and is roughly 105 miles east-west and 16-40 miles north-south.

Most of the 1002 area lies within the Arctic Coastal Plain physiographic province, a marshy area that slopes gradually towards the Arctic Ocean on the north. A small part along the southern margin that constitutes less than 5% of the total area lies within the Arctic Foothills physiographic province, a series of hills and ridges that descend from more than 500 m in the Brooks Range to 300 m in elevation to the northern foreland. The area is treeless, tundra covered, and 99% wetland.

Topographically speaking, it is comprised of foothills (95% of area), river flooded plains (25%), hilly coastal plains (22%), lagoons and oceans (5%), thaw lake plains (5%) and mountains (less than 1%). It also has beaches, low steep cliffs, barrier islands, shallow lagoons, and river deltas form the coast of the 1002 area, with hills rising to more than 300 m in the south. Many rivers and stream flow between these hills towards the Arctic Ocean.

History

The geologic history of ANWR is briefly as follows:

· "Development of Devonian to Triassic south-facing (in present-day coordinates) passive continental margin."

· "Northern Part- margin rifted in Jurassic to early cretaceous time for an unknown parent continent"

· "Coeval with the North, and arc-continent collision occurred in the south, producing and organic land  mass and adjacent foreland basin."

· "As the foreland basin filled, continuing deformation resulted in a foreland fold and thrust belt."

· "Youngest foreland basin sediments, where fold and thrust belt intersects and overrides the earlier formed rift margin and when the deformation and related sedimentation continues to present."

· More geologically complex that anywhere in Northern Alaska.

· Part of the North Slope geologic provinces.

· Petroleum-prospective rocks are restricted to mostly the Mississippi and younger rocks.

· same as in Prudhoe Bay and Mackenzie Delta region of Canada

The plate that ANWR rests upon is part of small continental fragment call Artic Alaska micro plate. Historically, most hypotheses regarding plate tectonics hold that Cretaceous rifting and the opening of the oceanic Canadian basin of the Artic ocean is what gave rise to the eventual positioning of ANWR.

Tectonic Activity

The North Slope and its continental shelves, Brooks Range and the northeaster part of Siberia are considered to form the Arctic Alaska microplate, a small lithospheric plate with boundaries that are not clearly known. One hypothesis for the plate tectonic history of northern Alaska suggests that the region was originally next to the Canadian Arctic Islands. Creation of oceanic crust in the Canada basin during the Jurassic and Early Cretaceous caused the microplate to rotate 60 degrees counter clockwise, placing it in its current position.