Alignment of saline springs with evaporite karst structures in northeast Alberta, western Canada: analogue for cretaceous hypogene brine seeps to the surface

Calcite-cemented sand intervals are widely distributed in the lower interval of the McMurray Formation of the Lower Cretaceous Athabasca Oil Sands deposit, northeastern Alberta. Flows of Devonian brine were driven up-section upon mixture with meteoric-charged groundwater that came in contact with the Prairie Evaporite Formation only 200 m below. Voluminous migrations of carbonate-saturated Devonian formation water during lower McMurray Formation deposition account for the distribution of decimetre to multi-metre thick calcite-cemented sand intervals and giant concretions within the syndepositional fill of the Bitumount Trough, a 100 km long salt dissolution-collapse structure that floored the northern Athabasca Oil Sands deposit. Precipitations of calcite cement concurrent with deposition of the lower McMurray Formation provide insight into the eventual disposition of the voluminous brine that would have resulted from the dissolution of as much as 130 m of Middle Devonian salt section below the Bitumount Trough in contrast to deep basin storage elsewhere. Breccia pipes developed in Middle-Upper Devonian carbonate beds flooring the Bitumount Trough provided migration pathways up-section for the carbonate-saturated Devonian brines. Giant concretions of calcite-cemented sand, 1-2 m across, developed in homogeneous sands proximal to collapse-breccia pipes that vent along the Trough floor, whereas brine flows directed along heterogeneous sands resulted in tabular calcite-cemented beds. Similar but volumetrically less significant Quaternary brine migrations diluted with glacial meltwater were discharged at the surface as saline springs along the modern river valleys, resulting in geochemical trends characterized by concentration of total dissolved solids but without associated precipitations of calcite cement.

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Morphogenesis of Hollow Bulbous Gypsum Structures Along a Brine Spring in Northeast Alberta

Broughton

2024

The Canadian Journal of Mineralogy and Petrology

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The stromatolite tufa mound at La Saline Lake developed along the Athabasca River Valley in northeast Alberta consists of a 30 m-high structure with a multi-meter thick caprock of stratified gypsum. The gypsum caprock developed when the meteoric-charged groundwater channeled along shallowly buried Upper Devonian limestone was redirected deeper and encountered anhydrite beds of the Middle Devonian Prairie Evaporite Formation, only 175–200 m below. Discharge of the sulfate-saturated brine from the central vent of the gypsum caprock eventually ceased and the flow was redirected to the western lakefront bank of the tufa mound. This active brine spring, characterized by total dissolved solids level of ∼79,000 mg/L, is channeled along a 25 m gully toward La Saline Lake. The bottom sediment in each of the interconnected brine pools along the gully consists of a 2–4 cm-thick calcite-gypsum thrombolite and an overlying gypsum crust. This sulfate crust developed as densely packed arrays of hollow botryoidal to hemispheroidal and bulbous gypsum protuberances, each 0.5–1.5 cm long, that extend upward into the brine. This is the first documented example of bulbous protuberances of gypsum that developed within brine pools with hollow interiors. The unusual hollowness of these bulbous gypsum protuberances resulted from the rapid encasement of gas bubbles that ascended from the underlying thrombolite ooze and were trapped within the overlying microbial mats and meshwork of gypsum crystallites on the surface of the bottom pool sediment. Nanoscale biomineralization of gypsum developed along the parallel arrays of microbial stalks within the enveloping mat, resulting in a meshwork of parallel aligned crystallites that encased the surfaces of the trapped bubbles. Continued abiotic gypsum precipitation transitioned the abiotic crystallites into enlarged needle-form crystallites distributed as parallel arrays along curvilinear growth surface laminae. Sufficient rigidity on the bubble surfaces precluded implosion-collapse or detachment. Strontium adsorption widely stabilized the acicular crystals, inhibiting complete coalescence as gypsum spar.

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Alignment of saline springs with evaporite karst structures in northeast Alberta, western Canada: analogue for cretaceous hypogene brine seeps to the surface

Cited by 3 publications

References 46 publications

Special Features Associated with Evaporites

Special Features Associated with Evaporites

Migrations of Devonian brine up-section and the origin of calcite-cemented sand in the Lower Cretaceous McMurray Formation, Athabasca Oil Sands

Morphogenesis of Hollow Bulbous Gypsum Structures Along a Brine Spring in Northeast Alberta

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