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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 496

Last Page: 496

Title: Sedimentology of Paleochannels on Foreland Coastal Plain, Judith River Formation (Upper Cretaceous), Southeast Alberta: ABSTRACT

Author(s): Emlyn H. Koster


The upper 90 m (295 ft) of the sub-Bearpaw Judith River Formation, continuously exposed in the badlands along the Red Deer River 185 km (115 mi) east of Calgary, is famous for the unrivaled assemblage of dinosaur fossils. Dinosaur Provincial Park presents a rare opportunity to view the architecture of a foreland coastal-plain sequence as well as to clarify the origin and distribution of subbituminous coal zones and gas reservoirs associated with this formation across southeast Alberta.

The distal reaches of paleodrainage from the developing Cordillera to the Western Interior seaway are being examined by north-south traverses across the badlands. Sharp-based paleochannel units, enclosed by rooted, olive-gray mudstone sequences that are commonly 4-6 m (13-20 ft) thick, vary between 2 end members. The first contains laterally accreted sand-mud couplets with abundant macrofloral debris, and represents cyclical, low-energy growth of point bars, possibly with an estuarine influence. The second, mainly comprising cosets of large trough cross-beds with mudstone intraclasts, was formed by episodic aggradation of high-energy systems. An intermediate composite type displays evidence for an energy increase as channel sinuosity decreased. This variation in paleochannel type is a tributed to alternating alluviation/rejuvenation associated with an unstable base level. Coal zones and potential reservoirs appear to be associated with the transgressive and regressive phases, respectively, of the Bearpaw coast. Amalgamation of paleochannels--marked by laterally extensive horizons of bone fragments, lithic and intraclastic gravel--is more common seaward over the axial region of the Sweetgrass arch.

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