Stratigraphic Sequences, Geometry, and Tectonic History of Mid-Continent Rift System: Alternate Hypotheses

S. Duff Kerr, Jr.

Prior to late 1981, geologic models for the Mid-Continent rift system (MRS) were based almost entirely on potential-field geophysical data and studies of outcrops along the periphery of only one segment of the structural trend. Since that time, several thousand miles of reflection seismic data and two deep borehole penetrations have provided significant (although largely proprietary) data to expand our understanding of the MRS.

Seismic-defined geometry confirms that sources of the large-scale gravity anomalies which characterize the MRS are not entirely, if even mostly, within the rift-fill sequences. In addition to layered basic volcanics, sedimentary rocks must comprise a significant part of the fill. Magnetic signatures distinguish between volcanic and sedimentary lithic packages near the Proterozoic surface, thereby allowing better delineation of seismic stratigraphic sequences. A review of known rock properties from outcrops and boreholes, in conjunction with seismic and potential-field data, provides alternatives for reconstructing stratigraphic sequences in the fill. This approach gives better insight into the tectonic history of the MRS.

The presence of large volumes of sedimentary fill and the probability that such sedimentary fill developed at different times and places during rift history allow a variety of models for hydrocarbon entrapment to be constructed. The fact that over the entire extent of the MRS only two deep tests have resulted from an intense exploration effort spanning more than five years indicates that very few hydrocarbon models have actually been tested.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.