35 Sediments, Carbonates (Posters)

Sunday, 31 October 2010
8:00 AM - 6:00 PM
Hall D

A MULTI-SCALE ANALYSIS AND STRATIGRAPHY OF MICROBIALITES OF THE LOWER ORDOVICIAN STRATA OF CENTRAL MISSOURI

Paper number: 35-6
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Microbialites can be useful paleoenvironmental indicators and productive hydrocarbon reservoir facies. This study focuses on the depositional environments and stratigraphic distribution of Lower Ordovician microbialite structures in and around Westphalia, Osage County, Missouri. The units represented at this location 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. Microscopic-scale analysis reveals heavy dolomitization of most of the strata. However, remnant syndepositional features provide vital clues about the microbialite development. The laminated stromatolites tend to contain alternating “laminar” vugs. Those where the vugs are not present have laminae that alternate between micritic texture and coarser dolomite. Meso and macro-scale features reveal more prominent characteristics than at the micro scale.

The occurrence of these microbialite structures can be placed within a stratigraphic framework and were deposited in shallow marine environments with evidence of subtle variation in water depth. The cycles in this study are separated using subtidal, intertidal, and supratidal environments. Two general cycle types were defined based on depositional environment. Type 1 cycles were deposited within subtidal to intertidal environments. Type 2 deposits represent subtidal to supratidal environments. Each of these cycles can be subcategorized further. 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 deposit 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.