Abstract: Source Rock Potential of Impact Craters

John R. Castano, James H. Clement, Michael D. Kuykendall, Virgil L. Sharpton

A number of impact craters have associated hydrocarbon production; for example, Red Wing and Newporte fields in North Dakota, and the Ames structure in Oklahoma. Our thesis is that a meteorite impact can create a closed basin which is favorable for the deposition of hydrocarbon source rocks. The Bosumtwi crater in Ghana is a modern analogue; the crater encloses a deep lake which contains organic-rich sediments and abundant methane seeps.

We interpret the structure at the Newporte field in North Dakota as an astrobleme; production is obtained from the Cambrian Deadwood Sandstone and brecciated, weathered granite. The locally developed lower Winnipeg Shale (Ordovician) has been identified as the source rock. Compared with Red River (Ordovician) oils, Newporte oils have a much higher isoparaffin content; they have a higher C₂₀₊ content; they are waxy (65-90°F pour point); and they lack the marked odd predominance typical of the Red River. Red River source rocks are dominated by alginite while the Winnipeg contains only amorphous kerogen.

The Ames structure produces from brecciated granite and brecciated and fractured Arbuckle dolomite (Ordovician). The Oil Creek Shale (Ordovician) provides the seal. The lower part of the Oil Creek is the likely source of the oil; this facies is 8 to 225 feet thick and is restricted to the crater. Curiously, the oil is similar to Newporte oils with a high wax content and relatively high isoprenoid contribution; the source rocks are also comparable.

The development of thick source rock units in impact craters, particularly where source rocks would not be present otherwise, enhances the exploration prospects for these features.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994