The Arctic Islands region has had a complex geologic development. The most conspicuous structural element consists of a major orogenic system, approximately 1,400 miles long, that extends in two broad arcs from north Greenland to the Beaufort Sea. Part of this system can be divided into three sub-parallel belts. A northernmost eugeosynclinal igneous and metamorphic belt occurs in the mountainous area of northwestern Ellesmere Island. The middle Eureka Sound Belt consists mainly of gently folded unmetamorphosed Mesozoic and late Paleozoic sedimentary beds. The southernmost and easternmost orogenic zone consists of two parts: a western unmetamorphosed Parry Islands Fold Belt, and an eastern and northern part, the Ellesmere-Greenland Fold Belt, containing low-grade metamorphic rocks.

Stages of orogeny in different parts of the orogenic system appear to have taken place in: (1) pre-Silurian(?), (2) Silurian-Devonian, (3) late Paleozoic(?), and (4) post-Lower Cretaceous-pre-Middle(?) Tertiary time.

Two large Paleozoic miogeosynclinal basins occur south and east of the orogenic system. The eastern basin, genetically related to the Ellesmere-Greenland Fold Belt, contains at least 10,000 feet of sedimentary beds that range from the Cambrian to the Devonian. The western basin may have similar relations to the Parry Islands Fold Belt.

Three shallow(?) cratonic basins, separated by elongate arches of exposed pre-Cambrian crystallines, occur between the miogeosynclinal basins and the Shield. These contain dominantly carbonate rocks of Ordovician and Silurian age.

A widespread Arctic Coastal Plain of Mesozoic and Cenozoic rocks lies northwest and southwest of the orogenic system, and extends to the Arctic Sea. In the Sverdrup area of the Coastal Plain, piercement domes containing evaporites in their cores occur over a broad area.

Surface indications of petroleum consist of abundant rocks having a petroliferous odor and asphaltic residues. Active oil and gas seeps have not been found. On Cornwallis Island asphaltic residues in a basal conglomerate indicate an exhumed reservoir. Marine and fresh-water oil shales and low-rank coals have been identified in several widely scattered areas.

An analysis of the miogeosynclinal, cratonic, and coastal plain regions of the Arctic Islands indicates lithologic, structural, and deposition-environmental conditions similar to other regions in the world in which oil fields have been found.

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