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Exploration in Mid-Continent Geophysical Anomaly: Rift or Riffraff?

Jeffrey M. Yarus, Alan Hinks

Geologic and geophysical exploration for oil and gas in the Mid-Continent geophysical anomaly (MGA) resulted in acquiring millions of acres and thousands of miles of seismic data in areas previously considered nonprospective for economic hydrocarbon production. Interpreted to be a rift, this 700-mi feature extends from northern Kansas through Lake Superior into Michigan. Factors influencing major company interest in the feature include: oil occurring in Keweenawan sediments from Michigan; gravity and magnetic data suggesting that clastic-filled basins are present; and extensive folding and faulting of Precambrian rock units seen on seismic sections.

Little attention has been given to other important factors, including lithostratigraphy, thermal and burial history of reservoir and source rocks, and distribution of observed gravity and magnetic anomalies throughout the rift. Although such data are sparse or highly susceptible to interpretation, any ensuing model should attempt to explain the observations. The observed data constrain exploration modeling within certain boundaries. These constraints are: (1) proximity of the reservoir rock to the potential source rock; (2) different thermal histories for the flanks of the rift versus the center; and (3) high versus low densities and magnetic susceptibilities in the central part versus the flanking positions of the MGA south of Lake Superior.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.