ABSTRACT

The upper Givetian Slave Point Formation of the Sawn Lake area reflects four major shoaling-upward stages or cycles of sedimentation. Each stage occurred in response to accelerated rates of relative sea level rise and subsequent stillstand.

The four stages correspond to two major depositional units, which abruptly overlie the laminated platform carbonates of the basal Slave Point Formation. The first stage, equivalent to the Biostromal unit, is characterized by minor aggradation and a poorly defined lateral zonation of facies. The second, third and fourth stages, which make up the Reef unit, are commonly separated by subtidal marine hardgrounds and a massive deeper water facies. Each of these stages is represented by a range of laterally correlative facies, including reef interior to foreslope and basinal limestones. The second stage is marked by progradation of the reef margin and represents the period of optimum growth for the carbonate complex. The best porosities are developed in the higher energy environments, typically the reef margin. Reef interior sediments comprise smaller-scale shoaling-upward cycles consisting of subtidal and tidal-flat limestones. The third and fourth stages of the Reef unit correspond to a backstepping of the reef margin and a net reduction of carbonate sediment production in comparison to the second stage.

Shoaling-upward stages govern the distribution of reservoir-quality depositional facies; therefore, the recognition and delineation of these stages may better define reservoir continuity.

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