GATES FORMATION

(Albian)

The Grande Cache tracksites

Barret Wall

9 Mine (L.E.L.)

Center Limb Pit

9 Mine W.Ext.

South Pit Lake

E2-Pit

W1a

W1b

W1c

W2

W3 Bird

W3 Main

W3 Extension

W3 Corner

12 Mine S. A-Pit

8 Mine

 In the late 1980's, employees of the former Smoky River Coal Mine (Smoky River Coal Ltd.) reported finds of fossil footprints and trackways to researchers at the Royal Tyrrell Museum of Palaeontology.  It was apparent early on that this was a significant locality for vertebrate traces.  Over the next decade twenty tracksites were found within the boundaries of the former coal mine.  All reported tracksites occur on the surface and were exposed as a result of open pit mining of the Number Four coal seam (see below)

Stratigraphic column (modified from Langenburg et al., 1987)

showing the occurrence of tracks below the Number 4 coal seam

A small portion of the Grande Cache Member in outcrop from the

former Smoky River Coal Mine, near Grande Cache, Alberta

The mine is located just north of the town of Grande Cache, Alberta and is within the foothills region of the Rocky Mountains.  The beds on which the vertebrate footprints are found have been structurally deformed into anticlines and synclines.  All tracksites are found on footwalls of anticline limbs or fold axes which have been excavated for coal.  Some sites are situated on nearly vertical walls up to 60 meters high.  These tracksites can be quite extensive covering up to a few thousand square meters in some cases, with over 10,000 footprints.

    As most of these sites are located on cliff faces, they are susceptible to erosion.

The Grande Cache tracksites are the largest in situ exposures of vertebrate tracks and trackways in Canada and are some of the largest in the world. With so many large track surfaces it is possible for researchers to see a full range of preservational morphologies within a single ichnotaxon. Such observations are beneficial to the field of vertebrate ichnology in general as it has in the past been plagued by a profusion of new ichnotaxa based on slight differences in morphology rendering vertebrate ichnotaxonomy cumbersome at best.

The vertebrate ichnofauna of the Gates Formation near Grande Cache has quite a few similarities to that of the Gething Formation (Lower Cretaceous: Aptian/Albian) of the Peace River Canyon. There are some distinct differences though, such as the complete absence of large ornithopods from the Gates Formation. No prints or trackways of the large ornithopod ichnogenus Amblydactylus ichnosp. have yet been found in the former Smoky River Coal Mine, yet they were the dominant component of vertebrate ichnofauna of the Gething Formation. Also, C.M. Sternberg (1932) defined the characteristics of Tetrapodosaurus borealis from only two trackways from the Peace River, but in the Gates Formation near Grande Cache, they are the overwhelmingly dominant component of the vertebrate ichnofauna. In fact, ankylosaur footprints are common in several western Canadian track-bearing formations, but they are extremely rare world-wide.

Studies of the Grande Cache tracksites have changed the perception of the composition and distribution of "Middle" Cretaceous vertebrate ichnofaunas in North America. North America was divided into a southern region dominated by sauropod and theropod ichnotaxa, a central region (Colorado) dominated by large ornithopod and theropod ichnotaxa, and a northern region (Peace River) also dominated by ornithopod and theropod ichnotaxa. The ankylosaur trackways described by Sternberg, were not a significant component of the Peace River ichnofauna, but they are the dominant track type of the Gates Formation ichnofauna.

 

National Geographic Interview