Devonian fossil zones in wells from southwestern Ontario
A systematic study of the cuttings from a number of oil and gas wells located in southwestern Ontario has led to the establishment of a number of reliable horizons based upon microfossils. Graphs have been prepared to show the consistency of the relationships of these horizons in several of the well-known fields. A graphic comparison has also been made between the fossil horizons and the physical horizons commonly used by the well drillers. The investigation has shown that the top of the Big Lime, a physical horizon used by the well drillers, is invalid at least in the Dawn field. Furthermore, it has been demonstrated that another physical horizon—the bottom of the Big Lime—is present which may be relied upon more generally.