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Abstract

Following a period of Early Cretaceous Hauterivian uplift and erosion, the Deep basin area of western Alberta and northeastern British Columbia began to subside and receive sediments from the rising Cordillera to the west.

During Barremian time, the alluvial fan and braid plain conglomerates of the Cadomin Formation were deposited in a belt flanking the eastern margin of the Cordillera.

In Aptian time, the developing trough continued to deepen resulting in the accumulation of the fluvial and delta plain sediments of the Gething Formation.

In early Albian time, continued subsidence of the trough coupled with a eustatic rise in sea level resulted in a major transgression of the Deep basin from the north by the Boreal sea. This event is represented by the coastal and shallow marine sandstones of the Bluesky Member. The Bluesky was capped by the marine shales of the Moosebar Formation/Wilrich Member as the Boreal sea continued to deepen and advance southward.

Due probably to increased Cordilleran tectonism, marine conditions did not persist. During middle- to late-early Albian time, a major flood of sediment restored the Deep basin to continental conditions. The regressive, coastal/deltaic sandstones and conglomerates of the Falher and Notikewin members represent the northward advance of the coastline during this period of marine retreat.

A second major marine transgression advanced across the Deep basin during early-middle Albian time. This event is represented by the marine shales of the Hulcross/Harmon members which cap the Notikewin Member. A well-developed regressive cycle, represented by the coastal plain to shallow marine sediments of the Paddy and Cadotte members occurs within this transgressive pulse, which continued until at least the end of Albian time.

Lower Cretaceous sandstone reservoirs in the Deep basin exhibit average porosities around 8.0% and average permeabilities near 0.001 millidarcys, reflecting the “tight sand” nature of the Deep basin. In coarse-grained sandstone and conglomerate reservoirs however, average permeabilities are much higher, ranging from 20 to 80 millidarcys. As a result, in areas of the Deep basin containing such reservoir rock, gas productivity is quite high.

To provide an understanding of the depositional framework of Lower Cretaceous sandstones of the Deep basin, the paleogeography of all Lower Cretaceous sandstone units has been mapped. This will aid in defining hydrocarbon exploration fairways as well as in outlining potential areas of coarser grained sediments where higher permeabilities should be present.

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