Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A Multi-scale Analysis and Stratigraphy of Microbialites of the Lower Ordovician of Central Missouri and Kansas
(1) Department of Geology, Wichita State University, Wichita, KS.
Microbialites are useful paleoenvironment indicators as well as proven hydrocarbon reservoirs. This study focuses on the depositional environments and stratigraphic distribution of Lower Ordovician microbialites in central Missouri as outcrop analogs to subsurface reservoirs in Kansas. The units represented in the vicinity of Westphalia, Missouri include the Roubidoux and Jefferson City Formations. To determine the depositional environments suitable for microbialite development, we are currently examining the micro, meso, and macro-scale features of these structures and their relationship to surrounding lithologies.
These microbialites were deposited in a shallow marine environment and are grouped into two cycle types. Type 1 deposits include 1) subtidal deposits of very coarse crystalline dolomite with green shale grading upward to intertidal stromatolites, 2) subtidal deposits of channel sandstones grading upward to intertidal stromatolites, 3) subtidal deposits of oolitic pack/grainstone grading upward to intertidal stromatolites, and 4) subtidal green mudstones that grade upward to intertidal blocky, very fine crystalline dolomite or intertidal deposits of elongated chert nodules. Type 2 deposits include subtidal sediments of medium to fine crystalline, mottled dolomite that grade upward to supratidal deposits containing cauliflower chert (possibly replacing supratidal evaporite) and brecciated chert.
Most Arbuckle reservoirs drilled in Kansas are located in the upper karsted zones. Outcrop analogs indicate that potential microbialite reservoirs may exist below this target. Porosity and permeability studies of Missouri and Kansas microbialites are used to investigate this reservoir quality and conduct a comparison study. Porosity within Missouri microbialites include intercrystalline, fenestrae, and vuggy porosity. Elevated permeabilities are associated with “laminar” vuggy porosity.