The Lansing-Kansas City "E" zone consists of carbonate packstones and grainstones deposited during the shallowest parts of the marine phase of a complex marine-nonmarine sedimentary cycle. The packstones and grainstones are best developed on ancient positive seafloor features (15 to 30 ft or 4.6 to 9.1 m of paleorelief) which were subjected to more wave agitation than surrounding low-lying areas where mud-supported textures prevail.

Postdepositional processes during subaerial exposure (nonmarine phase of the "E" zone sedimentary cycle) led to porosity development on paleotopographic highs and porosity destruction in lows. The mild topographic variations resulted in two distinct diagenetic environments. Percolating meteoric waters dissolved aragonitic skeletal grains and intergranular carbonate mud in the packstones and grainstones on paleotopographic highs. Surface runoff and groundwater collected in topographic lows. Here, large-scale dissolution accompanied by infiltration of nonmarine silt and clay totally destroyed all original reservoir potential.

An isopachous map of the nonmarine terrigenous rocks directly overlying the marine "E" zone carbonate rock is believed to reflect paleotopography. All significant oil production occurs where this interval is thin. Porosity in the "E" zone carbonate rock is nearly nonexistent where overlying nonmarine sedimentary rocks are thick. Therefore, thickness maps of these nonmarine rocks should facilitate future oil exploration and production efforts in this area.

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