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Why does the Athabasca region of Alberta have major tar sand deposits?

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Arabian-Iranian basin oil fields — heavy oil and tar sand Major oil fields of the Arabian-Iranian basin region.

The Athabasca region of Alberta contains massive tar sand deposits because it sits within the Alberta Basin, a vast sedimentary region where organic matter was buried, heated, and pressurized over millions of years to form oil and natural gas.1

These specific deposits are considered degraded remnants of conventional oil accumulations. As this oil migrated toward the surface, it encountered descending, oxygenated, bacteria-rich rainwater at temperatures below 93° C (200° F). This process removed the lighter crude-oil fractions and consumed the paraffins, leaving behind highly viscous bitumen that saturated the local sand and sandstone.2

The resulting Athabasca tar sands, located along the Athabasca River near Fort McMurray, hold nearly three-quarters of the world's estimated bitumen endowment.234