REVIEW OF THE PRECAMBRIAN GEOLOGICAL HISTORY OF THE CENTRAL UNITED STATES AND THE MIDCONTINENT RIFT SYSTEM

by
R.R. Anderson

Iowa Department of Natural Resources, Geological Survey Bureau
Special Paper Series No. 2, 1990, p. 1-26.
The Amoco M.G. Eischeid #1 Deep Petroleum Test, Carroll County, Iowa
R.R. Anderson, ed.

ABSTRACT


The Midcontinent Rift System (MRS) developed about one billion years ago, initially in response to extensional stresses probably related to the Grenville Orogeny. The rift cut through a number of Archean and Proterozoic terranes over its 940 mile length from central Lake Superior to central Kansas (Fig. 1). The structural grains of these terranes exerted significant influence on the morphology and trend of the MRS, and led to the development of four distinct segments, each with characteristic structural attributes.

Exposures of MRS volcanic, plutonic, and sedimentary rocks are limited to the Lake Superior area where they have been extensively studied for many years. These studies have led to the interpretation of a sequence of events that led to the initial deposition of a thin suite of sedimentary rocks followed by the emplacement of a thick sequence of mafic-dominated bimodal volcanic rocks that have been divided into two suites. The cessation of MRS development is marked by the deposition of two distinct suites of clastic sedimentary rocks.

The Iowa segment of the MRS is characterized by an axial horst, the Iowa Horst, and deep, clastic-filled flanking basins. The Amoco M.G. Eischeid #1 petroleum test well was drilled into one of these flanking basins (Figs. 1 & 2), and it provided the deepest penetration of MRS clastic rocks anywhere along the trend of the structure. The clastic rocks observed in the Eischeid well are similar in many ways to the MRS clastics that are exposed in the Lake Superior area.

 

Location map
Figure 1. Location of the Midcontinent Rift System.

 

Location of Eischeid well in Iowa
Figure 2. Location of the M.G. Eischeid #1 deep petroleum test well.