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| From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
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 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. |