Guide to a Waulsortian Buildup: Muleshoe Mound and Associated Strata; Sacramento Mountains, New Mexico, USA
Published:January 01, 2011
Kent C. Kirkby, Dave Hunt, J. A. Toni Simo, 2011. "Guide to a Waulsortian Buildup: Muleshoe Mound and Associated Strata; Sacramento Mountains, New Mexico, USA", The Carboniferous Geology of the Sacramento Mountains New Mexico, Robert J. Stanton, Jr.
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Muleshoe Mound is a composite Waulsortian buildup that forms a distinctive promontory along the western escarpment of the Sacramento Mountains (New Mexico, U.S.A.). Excellent exposures allow detailed study of the mound's fades, paleontology, geometry, internal architecture, and off mound stratal relationships. Recent work suggests that many Waulsortian mounds may have originated and grown in more agitated, shallower water environments than previously thought. The previously 'enigmatic' character of these Lower Carboniferous buildups may largely be due to differences in basin stratification, oxygen and possibly nutrient levels.
Muleshoe Mound can be separated into at least five distinct stratal packages or 'growth phases'. Successive growth phases differ in fades, geometry, and symmetry, reflecting different environmental conditions (energy, carbonate production, oxygenation and accommodation space). Intervening surfaces represent periods of hiatus and erosion. The architecture of this mound growth phase pattern strongly suggests that accommodation space was a critical control on mound growth.
Field study, serial slabbing, and petrographic examination of the mound facies indicate that Muleshoe grew in appreciable currents and intermittent high energy. Much of the micrite in the buildup originated as a microbial precipitation within an organic (algal?) host, rather than as depositional carbonate mud. This process of microbial precipitation, combined with extensive marine cementation, built the mounds' depositional relief and created a relatively rigid growth framework.
These features appear to conflict with the common interpretation of Waulsortian mounds as deep, quiet water buildups and Muleshoe may have formed in depths and energy conditions not dissimilar to many modern reefs. These features are not unique to Muleshoe, but occur in many Waulsortian mound suites. Differences between these ancient buildups and modern reefs suggest the modern ocean is an imperfect model for Early Carboniferous seas.
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The Carboniferous Geology of the Sacramento Mountains New Mexico
This field guide was originally put together for the SEPM Research Conference on Permo-Carboniferous Carbonate Platforms and Reefs in 2000 (SEPM SP 78 contains the research papers from the conference) and was only distributed to those attending the conference. After receiving copyright permissions, it has become an official publication of SEPM - Field Guide No. 12 and is available on CD. This guide begins in the Dry Canyon area of the Sacramento Mts. devoted to platform evolution during Missourian and Virgilian times, focusing on mounds and cycles of the Holder Fm. Also covered is the Mississippian Lake Valley Formation's sedimentology and depositional environments in Indian Wells Canyon and Alamo Canyon again with focus on mound biota and comparative sedimentology of mound versus level-bottom biota. Muleshoe Mound in the southern part of the Sacramento Mts. is used to examine mound growth history and an example of differential compaction and modern day appearance of outcrops. This volume includes background geology on all of the areas that are visited as well as detailed discussions about each of the field trip stops.