Stratigraphy of Mid-Continent Rift System in Kansas as Revealed by Recent Exploration Wells

K. David Newell, Peter Berendsen, W. Lynn Watney, John H. Doveton, Don Steeples

The Texaco 1 Poersch well in Kansas (11,300 ft TD) was the first significant exploration test of the Mid-Continent Rift System (MRS). An upper succession of rift-related rocks (2,846-7,429 ft) contains approximately 90% mafic igneous rocks with minor pegmatites and 10% oxidized siltstone and arkose. Arkose and subarkose with minor siltstone and shale make up 90% of a lower succession (7,429 ft to TD). The remaining lower succession is composed of mafic igneous rocks.

Mafic rocks are typically alkali basalts. Individual flows (detected by presence of amygdules, interflow sediments, compositional differences, and oxidized zones) range in thickness from 20 to 250 ft.

Sedimentary rocks in the lower succession are divided into three sequences, each 1,000-2,000 ft thick. The sequences overlie relatively thin mafic flows or intrusives. Each sequence is generally composed of fining-upward units (50-150 ft thick) attributed to episodic movement and erosion of fault blocks in alluvial fan-dominated sedimentary environments. Shales and siltstones are too oxidized to be viable petroleum source rocks, but gray shale with approximately 0.5% total organic carbon was found in the MRS by the 1-4 Finn well, 21 mi to the northeast.

Geologic examination of several shallower Precambrian test holes near 1 Poersch shows considerable variability in sedimentary and tectonic settings along the MRS. Correlation between wells in Kansas and exposed areas of the MRS is still problematic. Additional wells will be necessary to better understand its hydrocarbon potential.

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