From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005

Interaction of Tectonism and Eustasy in Icehouse Carbonate Buildups and Shelf Strata, Pennsylvanian Holder Formation, New Mexico

Xavier Janson, Charlie Kerans, J. A. Bellian, Ryan Phelps, Ned Frost, and Ted Playton

Abstract:

The Virgilian strata exposed in the western Sacramento Mountains have long been considered classic exposures documenting reciprocal high-frequency mixed carbonate siliciclastic cyclicity and shelf-edge algal-mound growth. Using lidar technology, we mapped the Holder Formation stratigraphy in 3D on the basis of several canyons. The stratigraphic architecture of the Holder Formation consists of four lower order sequences that can be recognized throughout the area. Within these lower frequency sequences, numerous high-frequency cycles can be recognized, some of which show reciprocal sedimentation between siliciclastic and carbonate sediments, whereas others show lateral mixing of the two systems. Algal-mound growth is recognized in the transgressive systems tract (TST) of the first two sequences. The TST of the first sequence is characterized by at least three distinct intervals of algal-mound growth. The growth style and internal architecture of these mounds depend on their position on the shelf and are controlled by potential accommodation, depth of the photic zone, and hydrodynamic energy. These parameters are extracted from the outcrop on the basis of the amount of reworked debris compared with in-situ mound core growth and the mound core fauna. In addition, the growth of the La Luz anticline is superimposed on this stratigraphic control of the mound distribution. Three-dimensional mapping allowed for the building of accurate isochores of the sequences. These isochore maps show that the La Luz anticline had the most effect on the stratigraphic architecture during the younger sequence. The influence of the anticline growth is very hard to detect in the older sequences.