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In the area of the international boundary, in northern North Dakota, carbonates and evaporites of the Madison group attain maximum thickness in the central Williston basin near the town of Williston, North Dakota. Recent drilling has resulted in scores of Madison discoveries in the United States and Canada in which the oil-trapping mechanism can be classified into one or more of the following: (1) predominantly, structurally controlled pools, (2) tilted and truncated porous units sealed under a Triassic shale cap rock, and (3) updip porosity wedgeouts resulting from facies change.
The area has gained prominence in recent years as a new province for stratigraphic oil exploration, and as such, offers the stratigrapher abundant opportunity to apply his ideas.
Considerable effort has been put forth in recent years to introduce a system of nomenclature which is tenable throughout the basin. It is held that the use of local terminology, based on rock types, is a workable answer to the problem. Long-range correlation across the basin is feasible with present well control and stratigraphic correlation is extended from the "east side" truncation belt of Saskatchewan and North Dakota to the Poplar anticline of Montana.
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