No oil in commercial quantities has been found in South Dakota. The geology, however, is replete with the promise that oil will be found in this state. The north-plunging Lemmon syncline, that is, the south end of the Williston basin, occupies the west half of South Dakota. Paleozoic sediments, the source of oil in North Dakota and in adjacent areas in Montana, are known in the subsurface of South Dakota and comprise 37,000 square miles. Cretaceous sediments, which produce oil in Nebraska, occur throughout the state, over an area of about 77,000 square miles. Mesozoic and Paleozoic sediments may range up to 10,000 feet in thickness.

Cross sections indicate the wedging-out of formations of Ordovician, Silurian, Devonian(?), Mississippian, and Pennsylvanian age. These wedge-ends should form porosity traps and be prolific sources of oil. A pre-Jurassic unconformity overlies the truncated edges of most, if not all, of the older formations. Oil reservoirs may be found here. Isopach maps indicate a wide areal distribution of several potential oil-bearing formations.

End_Page 946------------------------------

Surface structures are known, especially in the western part of the state, and also around the Black Hills and along the Missouri River. Some structures have been drilled.

In comparison with the great potential area for oil finding in South Dakota, only scattered drilling has so far been accomplished, and few wells have tested the deeper possible oil and gas zones.

At present more wells are being drilled, seismic information is being accumulated, and surface parties are evaluating the areas of exposed Cretaceous and Tertiary rocks. Interest is high and this frontier may soon become another oil state.

End_of_Article - Last_Page 947------------