--> Abstract: A Comparison Study Of Mississippian Mounds In The Lodgepole Formation Of Montana And North Dakota, by A. S. Adams; #90928 (1999).

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ADAMS, ANDREA S.
Texas A&M University, College Station, TX

Abstract: A Comparison Study of Mississippian Mounds in the Lodgepole Formation of Montana and North Dakota

Three distinct lower Mississippian (Kinderhookian) carbonate buildups are found at the mouth of Swimming Woman Canyon, located on the southern flank of the Big Snowy Mountains, in central Montana. These massive Lodgepole Formation buildups are characterized by mudstone-cementstone fabrics, a diverse assemblage of fossils and porosity-enhancing stromatactis vugs.

These Lodgepole buildups demonstrate a resemblance to subsurface mounds located in the Dickinson, North Dakota area. The Dickinson mound facies have been proven as good hydrocarbon reservoirs. These deep-water limestones appear to have similar depositional features, mound facies and diagenetic histories to the mounds outcropping at Swimming Woman Canyon.

Both sets of mounds are composed primarily of submarine cements, especially radiaxial calcite, clotted lime mud, and pore-filling blocky calcite cements. There are also parallels seen in diagenetic features of the mounds - most notably the appearance of "stromatactis" vugs, which enhance porosity in both mounds, and have contributed to the total reservoir porosity in the subsurface Williston Basin mounds. In addition, the biota from both localities is quite diverse, composed of macro and microorganisms, although they differ somewhat from the typical, zoned Waulsortian biota that has been described from Europe and New Mexico.

Cathodoluminesence and isotope data also show correlations between the Mississippian mounds of Montana and North Dakota, suggesting that both areas formed in related paleoenvironmental conditions and experienced similar diagenetic alterations.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas