Open File Report 1983-12

Open File Report 1983-12

OFR 1983-12

Field Trip Guidebook - Sedimentology of the Upper Cretaceous Judith River (Belly River) Formation, Dinosaur Provincial Park, Alberta

Author(s) Koster, E.H. Date 1983-05-01

The late Jurassic to Paleogene stratigraphic record of foreland molasse wedges intercalated with epeiric marine episodes, along the western interior of North America, has been the subject of an enormous amount of geologic attention over the last hundred years. Perhaps no other geologic province in the world has stimulated such a massive volume of interdisciplinary literature that is so well communicated across international borders (Caldwell, 1975).

An intensive search for hydrocarbons and regional surface/subsurface stratigraphic work occurred in the wake of early geologic mapping. This pre-1950 body of literature was followed by a growing series of site-specific studies. Sedimentological interest accelerated during the 1970's and particularly in the present decade, due partly to a rejuvenated interest in coal resources and further recovery of hydrocarbons. In turn, process orientated field excursions have occurred with increasing frequency, and the associated research papers have reaped considerable benefits for the overall advance in knowledge of interdisciplinary sedimentology.

The Alberta segment of the Western Interior Seaway has certainly shared in the above-mentioned trends. However, one could argue that the field excursions run in conjunction with the AAPG/SEPM 1982 Calgary meeting, the 1982 IAS Congress in Hamilton, this CSPG Mesozoic Conference, as well as several other regional meetings over recent years have all contributed to an enhanced profile for the current variety of detailed sedimentological and paleontological research being conducted in the plains and disturbed belt. Additionally, the field areas increasingly serve to integrate the interests of the Calgary resource industry with the work of universities and federal/provincial research agencies.

In actual fact, this recent body of work has been primarily concerned with transitional sequences between marine and coastal margin paleo-environments within the foothills (Fernie/Kootenay, Wapiabi/Belly River, Bearpaw/St. Mary River). Alluvial processes apparently predominated during the accumulation of molasse wedges during regressive phases of the Seaway (Walker, 1982). However, as Walker and Cant (1979; p. 31) pointed out:'....There is an astonishing absence in the Canadian literature of detailed interpretations of ancient sandy fluvial depositional environments There are, of course, many examples described as fluvial, with some petrographic and paleocurrent information. However, none contains the necessary data on sedimentary structures and their sequence, integrated with paleoflow data in such a way that they contribute to sandy fluvial facies models....'

Notable initial steps to remedy this situation have been by Walker (1982) on the lowermost Belly River Formation at Ghost Dam, and by Waheed (1983) on the higher parts of the Horseshoe Canyon Formation exposed around Drumheller. Also, a good understanding of the anastomosed channel type has emerged in recent years using several modern and ancient Canadian examples (Smith and Putnam, 1980).

Rahmani's work (Walker, 1982; p. 31-60) on the lowermost Horseshoe Canyon Formation at Drumheller has triggered an awareness of tides as an Interior Seaway process. Given the extensive, gently-sloping nature of bordering coastal plains, his conclusions serve to remind researchers working on the main ''internal'' parts of clastic wedges in the plains of the likelihood that paleodrainage courses became estuarine below high tide limits located quite far inland. Presently unknown for Judith River time is the abundance and length of any intertidal inlet channels without river connection.

The 1980's is an exciting, vital period for work on fluvial sequences. The First International Fluvial Conference in Calgary, 1977 (Miall, 1978) was characterized by presentations on a limited number of broadly applicable facies models. Its successor in 1981 at Keele, England (Collinson and Lewin, 1983) witnessed a general realization that a ''cookbook'' style of interpretation in fluvial sequences was intractable.

The locally excellent exposures of molasse units in the badlands of the plains and in outcrops of the disturbed belt provide valuable opportunities to advance the degree and quality of knowledge in fluvial sedimentology. This excursion to Dinosaur Provincial Park, with its unsurpassed circumstances for detailed sedimentological research in western Canada, will hopefully demonstrate one example of how sedimentology may be profitably linked with resource evaluation and dinosaur taphonomy.