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Stratigraphic relationships of the Triassic Halfway Formation in the Western Canada Sedimentary Basin

Geological Survey of Canada, 3303 – 33 Street NW, Calgary, AB T2L 2A7

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Although the lithostratigraphic definition of the Middle Triassic Halfway Formation at the type section is quite precise and should be a clear guide to identifying the formation, there has been some confusion in its usage in the Western Canada Sedimentary Basin (WCSB). Some of the problems were identified by Dixon (2005) and schematically illustrated in his figure 6 but his work focused more on the identification of an unconformity rather than on nomenclatural problems. A lithostratigaphic unit is a mappable, usually contiguous, lithological body, which may or may not have chronological significance. The Halfway Formation fits this definition, for the most part, but depending on how you interpret stratigraphic relationships within the Middle to lowermost Upper Triassic succession, there are significant chronostratigraphic implications about the position of strata commonly identified as Halfway Formation.

After studying the Triassic in the WCSB for a number of years (Dixon, 2002a, b, 2004, 2005, 2007, 2008) I believe some light can be shed on the problem and it is the intent of this brief note to attempt some clarification by illustrating the stratigraphic relationships in the Doig to lower Charlie Lake succession and show that strata identified lithostratigraphically as Halfway Formation can be chronostratigraphically very different in various parts of the basin.

DEFINITION OF HALFWAY FORMATION
Hunt and Ratcliffe (1959) defined the Middle Triassic Halfway Formation from the Southern Production No. B-14-1 well, located at 1-12-84-23W6 in northeast British Columbia (Fig. 1), between log depths 5000 and 5148 ft (equivalent to 1523.5 and 1567.9 m in the re-entered 2/1-12-84-23W6 well). In the type well the Halfway Formation is defined as the predominantly sandstone interval underlain by thinly interbedded mudstone, siltstone, and sandstone of the Doig Formation, and overlain by thinly to thickly interbedded mudstone, dolostone, anhydrite, and sandstone of the . . . [Full Text of this Article]