Abstract

Carboniferous and Permian rocks are present in the southern Eagle Plain subsurface and occur in outcrop in adjacent areas. These rocks attain a thickness greater than 5,000 feet (1500 metres) in South Ogilvie Mountains and are truncated progressively to the north at the sub-Permian and sub-Cretaceous unconformities; rock unit subcrop trends are east-west.

Five major lithostratigraphic divisions are recognized:

Unit 1 (Kinderhookian to Meramecian) — shale with thin beds of siltstone and sandstone.

Hart River Formation (Chesterian to Morrowan) — fine-grained, cherty, spicular limestone; the Chance Sandstone Member is a significant coarse clastic unit within this formation.

Unit 2 (Morrowan to Atokan) — calcareous siltstone and sandstone, sandy limestone.

Ettrain Formation (Atokan to Desmoinesian) — fine- to coarse-grained, cherty, skeletal limestone.

Jungle Creek Formation (Wolfcampian to Leonardian) — conglomeratic sandstone and shale.

Age determinations based mainly on study of palynomorphs, foraminifers and brachiopods, and seismic data of excellent quality, provide the bases for correlation and document rock unit geometry of a complex stratigraphic regime.

Carboniferous sediments form a series of north to south prograding sedimentary wedges within which facies changes from limestone and sandstone to fine clastic equivalents occur as each wedge thins to the south. Basinal sandstones occur at the base of some depositional slopes. Permian terrigenous clastics were deposited on eroded Carboniferous sediments and were truncated by erosion prior to deposition of the Cretaceous succession. Conglomeratic sandstones at the northern erosional limit are represented southward by shale and siltstone equivalents. The entire Carboniferous and Permian sequence in South Ogilvie Mountains is represented by shales and siltstones, with the exception of a thin section of fine grained Hart River limestone.

Oil and gas have been discovered in Chance sandstones, and gas in Hart River basinal sandstones and Jungle Creek sandstones.