GeoNotes CYPRESS HILLS AND AREA
CYPRESS HILLS FORMATION
flora, fauna, and topography before the emergence of the Cypress Hills Plateau
The Cypress Hills Formation is mainly a fluvial (water transported) quartzitic conglomerate with a sandy matrix, and in places consists of unconsolidated deposits that unconformally overlie the Ravenscrag, Bearpaw, and Frenchman Formations. It forms the caprock of the Cypress Hills Plateau. It is the youngest of the sedimentary rock formations in the area ranging in age from Upper Eocene to Miocene (Fig. 1). The Cypress Hills Formation is also the last phase of any major sedimentation on the western interior plains of North America.
Figure 1: A generalized geologic time scale. ‘Ma’ is an abbreviation for millions of years of age. Image from USGSThe Cypress Hills are a small erosional remnant of a once widespread plain that extended across the southern regions of Saskatchewan and Alberta (Fig. 2). The plain had a general NE paleoslope with a significant SW rise caused by the Eocene igneous intrusive uplifts in north-central Montana. This was one of the last orogenic phases from tectonic activity in this area that built the Western Cordilleran Mountains. This event produced the Sweetgrass Hills, Bearpaw Mountains, Little Rocky Mountains, Highwood Mountains, and other minor intrusive uplifts in north-central Montana. These now eroded uplifts were once much higher in elevation during the Eocene than they are today.
Figure 2: Example of a braided alluvial plain. The Eocene (45 Ma) geography before the emergence of the Cypress Hills Plateau. From Leckie and Cheel (1989). The mechanically eroded rocks from these Eocene intrusive uplifts in Montana were carried by valley restricted rivers and streams flowing roughly in a NE direction with an eastern paleotopographical dip depositing the sand and gravel onto the broad braided alluvial plain (similar to a delta) beyond the valley terminus, and in some instances, into temporary lakes and backwaters across an eroded surface or disconformity of the Ravenscrag (Paleocene), Bearpaw (Late Cretaceous), and the Frenchman (Late Upper Cretaceous) Formations. There was a constant source of clasts not only from the initial uplift but also from the isostatic rebound as the uplifted area was being unloaded of its source rocks through mechanical erosion.
Geologists using paleocurrent proxies such as cross-bedding and clast imbrication (pebbles piggy-backing each other) were able to determine the general direction of current flow and the source of the gravel and sand. The Rose Diagram (Fig. 3) is a plot of the amount and directional orientation of the long axis of imbricated clasts. The source was nearby, within 300+ km, and the current had a strong flow as indicated by the cross-bedding and clast imbrication. The diagram shows the source rock and headwaters to be located in north-central Montana with another source in the extreme corners of SW Alberta and SE British Columbia.
Figure 3: The source rock for the Cypress Hills Formation (CHF). Abbreviations: Adel Mountains (AM), Pioneer Batholith (P), Aksaroka region (A), and Elkhorn Mountains (E). The general river and stream flow direction is indicated by the NE arrow above the Rose diagram. From Leckie and Cheel (1989). Another feature indicating strong current flow are the commonly visible percussion marks on the surface of quartz-rich (quartzite) clasts in the Cypress Hills conglomerate as they slammed into each other with some force. The depositional climate for the Cypress Hills Formation is somewhat debatable and is thought by some to have been semi-arid with seasonal rainfall.
Today, much of the Cypress Hills Formation has eroded, 180 m, leaving an average thickness of 38 m with a maximum thickness of 76 m. Only the Late Eocene to Early Oligocene (44-35 Ma) of the formation is present in the Cypress Hills with younger Miocene deposits of the formation located outside the Cypress Hills. The deposit is seen as a multi-cyclic braided plain alluvial deposit with clast sizes decreasing from boulder-sized gravel deposits in longitudinal bars in the west to finer-grained inter-channel material with debris flows (landslides) in the east. It’s at the eastern end of the Cypress Hills in the finer sediments of the Cypress Hills Formation where fossils of many different species have been collected since 1883.
“Most of the mammalian fossils reported from the Cypress Hills Formation represent brontotheres, rhinoceri, a small three-toed horse, entclodsnts, camels, antelopes, oreodonts, anthracotheres, small dogs, medium-sized saber-tooth cats, a bear-like carnivore, and fragmental remains of rodents, rabbits, and insectivores. Bird remains represent a small quail, a sandpiper, and a cuckoo. Fish fossils represent catfishes, bowfins, and gars. Amphibians and reptiles remains are represented by an extinct mole salamander, extinct cone-nosed toad, extinct spade-foot toad, extinct tree frog, extinct soft-shelled turtle, land tortoise, extinct water turtle, crocodile, large extinct worm lizard, small worm lizard, extinct sceloporine lizard, extinct collared lizard, extinct anquid lizard, extinct night lizard, extinct medium-sized boa, extinct small boa, and a species of small boa” (Holman, 1972).
Pieces of petrified wood are also locally abundant in the Cypress Hills Formation and are of Oligocene in age. They are comprised of several diverse species that grew in a warmer temperate-subtropical climate similar to that of the southern US today. The species include the following tree families; pine (Pinus), redwoods (Sequoia), magnolia (Magnolia), hickory/walnut (Carya), sweetgum (Liquidamber), varnish tree (Ailanthus), and witch hazel (Saxifragales). Sequoia, Liquidambar, and Ailanthus are no longer part of the Canadian flora and are confined to warmer temperate-subtropical climates of the world. Pinus continue to flourish across Canada, and the Magnolia and Carya tree families can only be found in the warmer parts of southern Ontario and other warmer temperate-subtropical climates throughout the world.
The trees and other flora, and fauna inhabiting this warmer temperate-subtropical climate began to disappear from the area towards the end of the Tertiary Period as the climate began to gradually change and get cooler. The cooling period culminated with many rhythmic glacial maximums in the Quaternary Period ending with the last glacial maximum 20,000 years ago. It’s also during this time the Cypress Hills emerged and became a prominent topographical feature in SW Saskatchewan and SE Alberta.
Sources:
Bell, Sean D.; Aplodontid, Sciurid, Castorid, Zapodid and Geomyoid Rodents of the Rodent Hill Locality, Cypress Hills Formation, Southwest Saskatchewan; https://harvest.usask.ca/handle/10388/etd-12222004-162111; University of Sasktachewaan, Department of Geological Scineces; Saskatoon, SK; December, 2004
Holman, Alan J.; Herpetofauna of the Calf Creek Local Fauna (Lower Oligocene: Cypress Hills Formation) of Saskatchewan; https://cdnsciencepub.com/doi/pdf/10.1139/e72-143; Canadian Jounal of Earth Sciences; Vol 9; Pgs. 1612-1631; 1972
Leckie, D. A., Cheel, R. J.; The Cypress Hills Formation (Upper Eocene to Miocene): a semi-arid braidplain deposit resulting from intrusive uplift; https://cdnsciencepub.com/doi/pdf/10.1139/e89-162; Canadian Journal of Earth Science; Ottawa, ON; Vol. 26, No. 10; Pgs. 1918-1931; 1989
Lerbekmo, J. F, Rutter, Nat; Geology of the Alberta Cypress Hills, including the Eagle Butte Impact Structure; http://www.egs.ab.ca/Resources/FieldGuides/2000_Cypress_Hills.pdf; Edmonton Geological Society; Edmonton; Sept 29-Oct 1, 2000
Roy, S.K., Stewart, W. N.; Oligocene Woods From the Cypress Hills Formation in Saskatchewan, Canada; https://cdnsciencepub.com/doi/10.1139/b71-264; Canadian Journal of Botany; Vol. 49; Pgs. 1867-1877; 1971
USGS; File:Geologic time scale; https://commons.wikimedia.org/wiki/File:Geologic_time_scale.jpg; Washington, DC; July 2010
Wikipedia; Imbrication (sedimentology); https://en.wikipedia.org/wiki/Imbrication_(sedimentology); Washington, DC; April 16, 2020
Wikipedia; List of Trees and Shrubs by Taxonomic Family; List of trees and shrubs by taxonomic family – Wikipedia; Washington, DC; September 18, 2020.
Outcrop of the Cypress Hills Formation at the Conglomerate Cliffs. The Conglomerate Cliffs are located at the end of Conglomerate Cliff Rd 4.4 km NNE from Range Stn Rd and, the Conglomerate Cliff Rd turn off is located 3.2 km NW along Range Stn Rd from the end of HWY 271 at the turn off to Fort Walsh. Photo: Charles Kuss
Close-up of the Cypress Hills Formation outcrop at the Conglomerate Cliffs, 8.6 km NNE of Fort Walsh, SK. Photo: Charles Kuss 
Contact
between the loosely and poorly consolidated conglomerate of the
Cypress Hills Formation and the underlying fine grained sandstone of
the Ravenscrag Formation at Jones’ Peak north of the Frenchman
River Valley on the Middle Bench Road. Jones’ Peak overlooks the
beautiful Frenchman River Valley and is 12 km NE and east off grid
road 614 or 5.50 km west off grid road 614. Both directions take you
on to the Middle Bench Road. At the Jones’ Peak sign post it’s
another 3 km south to the peak. Photo: Charles Kuss
An example of imbricated clasts piggy backing each other. Image: Wikipedia.org
The brontothere of Eocene age at the T-Rex Discovery Centre, Eastend, SK. Photo: Charles Kuss
Example of a Cypress Hills Formation cobble displaying arcuate percussion marks indicating strong current flow as cobbles slammed into each other. Photo: Charles Kuss
