| The Lake Saint-Martin aquifer system includes crater fill deposits of the Lake Saint-Martin Impact Structure and the surrounding carbonate formations of the Manitoba Interlake.
The Impact Structure exhibits a central uplifted core of Precambrian basement rocks surrounded by a shallow concentric crater basin. The crater-fill sediments consist of impacted-related carbonate breccia, granitic microbreccias and meltrock of the Permian St. Martin Complex overlain by Jurassic red beds, dolomitic mudstones and evaporites. The permeability of the surrounding carbonate aquifer can be quite high due to intense impact-related fracturing and faulting along the crater rim. Considering the high permeabilities in both the carbonate and breccia aquifers, their heads are continuous across the crater rim and they are viewed as a single aquifer system. In the central portion of the impact structure, the red bed aquitard is overlain by a shallow phreatic aquifer hosted by karstic evaporites. Outside the impact structure, The most significant recharge zone is in the northwest uplands and is usually associated with partial or complete bedrock outcrop. Another recharge zone is located between Lakes Manitoba and Pineimuta. Within the impact structure, north and northeast of Gympsumville, is the recharge area for the shallow, unconfined karst-hosted aquifer . From these recharge areas, groundwater flows radially, outward, toward lakes and organic deposits, such as swamps, marshes and bogs. A regional discharge zone for deep aquifers has developed in the concentric area of structural uplift surrounding the crater. Except in upland regions, the bedrock aquifers are confined by tills and glacio-lacustrine clays of varying thickness. In general, the aquifer vulnerability is low, except in the recharge areas where it is higher. Outside the impact structure, Groundwater quality is good, but within the impact structure total dissolved solids, hardness, sodium and fluoride occur naturally at elevated levels. |
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