ABSTRACT

The Reynolds Point Formation is the second lowest unit in the Late Precambrian Shaler Group of Victoria Island in the western part of the Canadian Arctic Archipelago. It has a maximum known thickness of about 1,100 m. The formation may be divided into four members. The lowest member is made up of shale followed by a sandstone-dominated sequence. The overlying lower carbonate member is thicker than the others. It is overlain by a second terrigenous sandstone unit (mainly tidalites) that is succeeded by the topmost, carbonate-dominated member. The lower carbonate member may be considered as three units. Unit I (the lowest) is about 100 m of fine-grained shaly carbonate with sole, and ball and pillow structures, together with some thick and extensive stromatolitic banks. Unit I is interp eted as representing minor subsidence of the depositional basin, followed by gradual infilling and stabilization. Unit 2 is about 100 m of shaly nodular dolostone and limestone that was probably deposited below wave base in a lagoonal system protected by a barrier complex. A thin purple shale in this unit is an excellent stratigraphic marker. Unit 3 (450 m) consists mainly of interbedded oolites (commonly associated with stromatolites) and shaly carbonates. This unit was deposited under a warm (dry?) climatic regime, adjacent to a continental area of low relief in a depositional setting comparable in some ways to that of the Persian Gulf The oolites probably formed on tidal bars or in tidal deltas from which they were spread into topographic lows that normally received fine-grained muddy carbonate sediment. The upper part of Unit 3 includes some thin cross-bedded fine-grained quartzarenites which were mainly deposited as subtidal sand sheets.

Hematitic oolites in the northern part of central Victoria Island are interpreted as an early diagenetic replacement phenomenon. Molar-tooth structure is common in shaly carbonates interbedded with oolites of Unit 3. The molar-tooth is interpreted as being due to early dewatering of muddy carbonate sediment, controlled in part by interbedding of very permeable sediment (oolite) with water-saturated mud.

Carbonate sedimentation was interrupted by the influx of fine silt and sand (upper clastic member; 130 m thick) that spread over the depositional area (from the east?) and was deposited mainly from tidal currents. A return to carbonate deposition (upper carbonate member; 200 m thick) was followed by the evaporitic-red bed sequence of the Minto Inlet Formation.