Monday, 12 May, 2025/ Edition 58

Canada has vast and amazing geology from Archean rocks to the Canadian Rockies; it is rich in geological resources, including various types of mineral deposits and hydrocarbons. This edition of Core Elements focuses on some recent studies from The Great White North. 

Rasoul Sorkhabi

Editor, Core Elements

The Cretaceous Western Interior Seaway

Cretaceous Atlas of Ancient Life

Some 100 million years ago, one could sail from the present Yukon territory of Canada through Montana, all the way to Texas. This Cretaceous Western Interior Seaway (CWIS) is now the locus of the Rockies basins and home to prolific oil and gas fields.

To what degrees did tectonic forces or global climate changes control the CWIS sea level fluctuations? A recent article in GSA Bulletin examines this.

Study design:

• Researchers examined the stratigraphic records of the Turonian age (94–90 Ma) in four localities along the 1,500-kilometer CWIS:

  • The Cardium Formation in Alberta

  • The Ferron Notom and Last Chance Delta complexes in Utah

  • The Gallup Sandstone in New Mexico

• Ar40-Ar39 data obtained from bentonite layers within the formations established the rocks’ Turonian age.

• Based on the Airy isostasy model, researchers performed two-dimensional stratigraphic back-stripping and high-resolution sequence stratigraphy on coastal clastic sediments within the formations examined. This helped estimate the magnitudes of sea-level changes and distinguish between tectonic and climate controls.

Key findings:

• The magnitude and symmetry of sea-level changes along the CWIS indicate global climate drive for the Turonian age.  

• Net sea-level changes amounted to tens of meters, a value which exceeds the sea-level changes of 5–10 meters caused by changes in water temperature (thermal), water density (steric), or coastal groundwater budget (aquifer-eustasy).

• Researchers observed regularity of sea-level curves along the CWIS, which suggests global climate-driven eustasy more than local tectonic forcing.

• Some stratigraphic units showed local tectonic rebound that enhanced the magnitude of sea-level drops.

Further studies: This type of study needs to be conducted in other stratigraphic units within the Cretaceous system to better understand how both tectonics and eustasy fashioned the sedimentary packages along the CWIS.

Go deeper: Read the full article here.

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Depths and Heights of the Canadian Cordillera

Marina Poushkina/Shutterstock.com 

The North American (Western or Pacific) Cordillera—a term derived from the Spanish word “cordilla” (little rope)—is one of the longest mountain ranges in the world, spanning western Canada, the western United States, and Mexico. Two studies published in the Canadian Journal of Earth Sciences offer new insights into what geophysical forces support these mountains and basins.

Study No. 1: 3D geometry of sedimentary basins

Design: Researchers constructed a 3D shear seismic wave velocity model derived from ambient seismic noise tomography from 151 seismic stations between 2003 and 2016.

They applied the seismic model data to estimate the thickness of sedimentary basins and the depth to Moho in Western Canada.

About the Cordillera:

• The Canadian Cordillera, about 1,200 kilometers wide, is the area bordered by the Canadian Deformation Front Thrust to the west and the Queen Charlotte-Fairweather transform fault to the offshore west.

• The Canadian Cordillera are divided into five morphological units:

  • Insular belt corresponding to nearshore to offshore basins

  • Coast Mountains (igneous complex)

  • Intermontane basins

  • Omineca Belt

  • Foreland basins

Results by morphological unit:

• Offshore basins in the Insular zone: The Queen Charlotte Basin (more than 10 kilometers thick) and the Georgia Basin (more than seven kilometers thick)

• Intermontane basins: Seven to seven and a half kilometers thick

• Rocky foreland: Alberta Deep Basin (more than six kilometers)

• The deepest Moho underlies the Williston Basin (46 kilometers deep), Alberta Deep Basin (45 kilometers), and the Queen Charlotte Basin (44 kilometers).

Study design: Zhang and colleagues constructed a crustal thickness and isostatic model based on teleseismic data for four distinct zones in the Canadian Cordillera (west to east): Forearc, Backarc, Foreland, and Craton.

Results:

• The researchers’ model indicates that the 700-meter-higher elevation beneath the Backarc and Foreland zones is related to hot, low-density buoyant materials from the mantle.

• The study supports Roy Hyndman’s hypothesis about this problem.

Metal Deposits in the Golden Triangle, Western Canada

BJP7images/ Shutterstock.com

An article in Ore Geology Reviews describes the formation processes and resource potential of “critical raw materials” such as antimony, bismuth, platinum-group elements, and tellurium in the Golden Triangle in western Canada.

The new study: Researchers analyzed 331 samples from the Golden Triangle to characterize the concentration and position of CRM in the area. They used mineral microscopy and trace-element mapping to complete the analyses.

Porphyry deposits:

• Porphyry deposits are economic minerals that form from hydrothermal fluids circulating through porphyritic igneous rocks typically generated at subduction plate boundaries.

• Porphyry deposits comprise several billions of tons of ores and are major sources of copper, gold, molybdenum, and silver. They also produce various CRM as by-products.

The Golden Triangle:

• The Red Mountain (1890 discovery), Red Chris (1968), and Galore Creek (1955) deposits form the borders of the Golden Triangle, an area in northwest British Colombia. 

• The Golden Triangle lies in the Stikine Terrane with stratigraphic formations and magmatism from the Permian to the Jurassic.

Key findings:

• The main finding was that porphyry copper-gold deposits in the Golden Triangle are associated with oxidized and water-rich magmas that suppressed sulfide crystallization and pre-enriched melts with CRM.

• The results also show that the highest CRM concentrations are associated with more than 58 ore minerals within the most hydrothermally altered samples. This diversity is an indicator of economic potential.

Go deeper: Read the full article here.

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✉️ To get in touch with Rasoul, send an email to editorial@aapg.org.