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  • Writer's pictureShahin Dashtgard

Dinosaur bones in Drumheller? Depends where you look.

Drumheller, Alberta is a must visit as it is home to the Royal Tyrell Museum and is surrounded by some amazing geological scenery. The museum curators at the Tyrell have done an excellent job showcasing the evolution of life preserved in sedimentary rocks across Alberta and their dinosaur exhibits are exquisite. Interestingly enough though, there are very few dinosaur bones in rocks immediately around Drumheller, and for the most part, you need to head north to find them. Why? Great question....

Paleogeography of Drumheller
Left: Paleogeographic map of North America when the sedimentary rocks exposed in Drumheller were deposited (about 73 million years ago; image source: 1). Right: The Drumheller area showing about where the shoreline, land, and sea were 73 million years ago and where dinosaur fossils are mainly found (satellite image source: Google Earth).

Geology of Drumheller

Sedimentary rocks are made of sediments (gravel, sand, and mud) that are cemented together (lithified). Sediments accumulate as the land surface sinks, and in large part, are deposited in seaways and oceans or on the margins of them. On the margins of seaways, sediments form beaches, deltas, estuaries and lagoons and these are collectively referred to as marginal-marine environments. Sedimentary rocks deposited in marginal-marine environments record changing climate conditions and shifting shorelines through time.

The rocks exposed in the Red Deer River Valley at Drumheller are part of the Horseshoe Canyon Formation and are about 72.5 to 74 million years old (2). The mudstone that underlies the Horseshoe Canyon Formation (older rock) is called the Bearpaw Formation and contains marine animal fossils that lived in a large seaway that extended throughout Alberta. The Bearpaw Formation is exposed further to the east because virtually all of the sedimentary rocks below Alberta dip west towards the Rocky Mountains meaning progressively older rocks are exposed further east. The Horseshoe Canyon Formation comprises sedimentary rocks deposited in both marginal-marine and terrestrial environments (2,3). Terrestrial environments are those on land and include, rivers, swamps, soil and floodplains. Further west, the rocks get progressively younger, and were deposited exclusively in terrestrial environments.

Geological map of Drumheller
A snipet of the geological map of Alberta showing the progressively older rocks exposed further east. The blue box is the area shown in satellite photo in the previous image ( map source: 4).

Why are there virtually no dinosaur bones in the rocks in Drumheller?

The reason why there are virtually no dinosaur bones in the sedimentary rocks exposed in the Town of Drumheller and further south along the Red Deer River Valley is because these rocks were mainly deposited in or very close to the paleo-sea (marginal-marine environments) and these were not easy settings for dinosaurs to live in (2,3). North and west of Drumheller the rocks exposed along the Red Deer River Valley were deposited further from the sea and these environments were probably easier for dinosaurs to live in, and so dinosaur bones are more prevalent in this region (5). However, to preserve dinosaur bones, they have to be buried quickly, and so bones are found most commonly at the bottom of old channels (channel fills) and on the floodplains of old rivers.

Scenery around Drumheller
Yellow arrows point to the top or bottom of channel fills in the outcrops exposed along the Red Deer River Valley. Black arrows point to coal and light blue arrows point to dinosaur bones in the bottom of channel fills.

Coal in the Red Deer River Valley

Today Drumheller is best know for it's dinosaur museum and incredible landscapes, but the town's origin and that of many close by towns includes a long legacy of coal mining (6). Coal mining began in the 1910s and continued till the 1970s (7). Mines were established where coal seams thickened and the coal was used mainly in heating. The furthest east mine is at East Coulee (7) and this is also close to the eastern extent of sedimentary rocks of the Horseshoe Canyon Formation exposed along the Red Deer River Valley.

Collecting dinosaur bones is allowed in Alberta if you are on crown land or private land and you are only picking up the bones from the ground (see Found a Fossil? | Royal Tyrrell Museum). However, every bone tells an important story that may lead to the next major discovery of these fascinating creatures. If you find a cool bone, take a photo, record the GPS location, and contact the Tyrell Museum to let them know of your find.

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Info Sources:

1) Williams, G. D., and Stelck, C. R., 1975, Speculations on the Cretaceous paleogeography of North America, in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America, Volume Special Paper 13: St. John's, Canada, Geological Assocation of Canada, p. 1-20.

2) Ainsworth, R. B., Vakarelov, B. K., Lee, C., MacEachern, J. A., Montgomery, A. E., Ricci, L. P., and Dashtgard, S. E., 2015, Architecture and evolution of a regressive, tide-influenced marginal marine succession, Drumheller, Alberta, Canada: Journal of Sedimentary Research, v. 85, p. 596-625.

3) Ainsworth, R. B., Vakarelov, B. K., MacEachern, J. A., Nanson, R. A., Lane, T. I., Rarity, F., and Dashtgard, S. E., 2016, Process-Driven Architectural Variability In Mouth-Bar Deposits: A Case Study From A Mixed-Process Mouth-Bar Complex, Drumheller, Alberta, Canada: Journal of Sedimentary Research, v. 86, p. 512-541.

5) Wu, X.-c., Brinkman, D. B., Eberth, D. A., and Braman, D. R., 2007, A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada: Canadian Journal of Earth Sciences, v. 44, no. 9, p. 1243-1265.

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