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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 9. (September)

First Page: 1359

Last Page: 1380

Title: Depositional Model for Understanding Geometry of Cretaceous Coals: Major Coal Seams, Rock Springs Formation, Green River Basin, Wyoming

Author(s): Raymond A. Levey (2)


The Upper Cretaceous Rock Springs Formation of the Green River basin ranges from marine strata of prodelta origin to marginal marine and nonmarine equivalents of delta-front and delta-plain-fluvial strata. Coal exploration drill holes, measured sections, and underground mine data have been analyzed to reconstruct the depositional setting of the Rock Springs Formation. Extensive sheet sandstones are inferred to be delta-front deposits reflecting the cuspate to arcuate geometry of wave-dominated deltaic deposits.

Extensive coal deposits up to 22 ft (6.7 m) thick that developed on top of delta-front sandstones extend for 15 mi (24.1 km) along depositional dip, and 36 mi (58 km) along depositional strike. These coal deposits are referred to as type A coal seams. Coal deposits 1-17 ft (0.3-5.2 m) thick that developed in upper delta-plain-fluvial environments are less than 20 mi (32.2 km) in length. These deposits are referred to as type B coal seams. Type C seams are persistent, thin coal deposits 1-8 ft (0.3-2.4 m) thick, developed on top of delta-plain-fluvial deposits less than 25 mi (40.2 km) in length, and they mark the delta-lobe abandonment phase. Approximately 15 major coal zones exist in the Rock Springs Formation.

The geometry of types A, B, and C reflects a genetic relationship to both deltaic and fluvial units in the marginal marine and nonmarine components of the Rock Springs Formation. A model for predicting coal-Previous HitseamTop thickness and continuity is believed to be applicable to additional exploration in the Green River basin and in other Cretaceous coal-bearing basins in the Western Interior.

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