ABSTRACT

A detailed sedimentological investigation of over 4000 feet (1220 m) of core and 500 well logs of the Middle Devonian "Granite Wash" and Keg River clastics in the Red Earth Field, North Alberta Basin, has led to the recognition of a "Granite Wash" subaerial fan-delta. This fan-delta is laterally continuous with a Keg River subaqueous delta component along an eastern shoreline of the ancestral Peace River Arch.

The subaerial fan-delta includes: 1) alluvial fan facies, 2) sheet wash and mud flows, and 3) playa lakes. The subaqueous delta component includes 1) lower shoreface, 2) upper shoreface, 3) beach-foreshore, 4) eolian sand dunes, 5) lagoon, 6) washover sands, 7) tidal channels and flats, and 8) supratidal carbonates and anhydrites. Within this system, six mappable units are defined. These are, in ascending order: 1) Granite Wash A sand member, 2) Granite Wash B sand member, 3) Granite Wash shale member, 4) Keg River A member, 5) Keg River B member and 6) Keg River C member.

A conceptual depositional model for the sequence depicts four main events:

1. Erosion of the Peace River Arch uplifted fault blocks producing coarse grained fan-delta sediments in the adjacent fault-bounded margins. Subsequent fluvial reworking resulted in the deposition of thick, lenticular and wedge-shaped alluvial fans of Granite Wash.
2. Tectonically triggered progradation of alluvial fans seaward into the Keg River Sea.
3. Transgression by Middle Devonian seas from the east, reworking alluvial fans and leading to deposition of discontinuous linear sand bodies represented by the landward (backstepping) migration of Keg River shoreline sediments westward.
4. Restriction of the sea by the Presqu'ile Barrier Reef to the north, depositing evaporites of the Muskeg Formation over the whole sequence.

A modern analogue to this fan-delta system is the system of coastal fans in the Gulf of Aqaba, Red Sea (Hayward, 1985). The Red Earth

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Field contains over 27 million barrels (4.29 10⁶m³) of recoverable oil in a combination structure-stratigraphic trap. The main production is from the Keg River B member marine sand. Potential for future oil discoveries similar to the Red Earth Field is very high, provided certain conditions for oil entrapment are met: 1) sand source provided by both "Granite Wash" and Precambrian inselbergs; 2) basement ridges (highs) oriented normal to the Keg River marine transgression; 3) strike - parallel basement faults that are more favourable potential hydrocarbon traps; 4) favourable timing of faults.

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