46234-GB8
Three Dimensional Structural and Geomechanical Analysis of Syn-sedimentary Deformation of a Prograding Carbonate Reef Complex, Guadalupe Mountains, New Mexico and Texas
In the first year and a half of the project we have completed two summers of fieldwork in our study areas: Slaughter-West Slaughter Canyons and Big-McKittrick Canyons, begun 3D mapping using digital photogrammetry, and completed a suite of two-dimensional finite element models. In the next year we plan to complete 3D mapping and expand our modeling efforts to incorporate more realistic 2D and 3D geometries.
Our fieldwork in the Guadalupe Mountains has included geologic mapping and real-time kinematic (RTK) GPS surveying in support of photogrammetric mapping. Using tablet PCs and differential GPS we have mapped syn- and post-sedimentary faults in Slaughter, West Slaughter, McKittrick, and Big Canyons. We have documented synsedimentary faulting in all of these locations. In Big and McKittrick Canyons the high-angle faults cut across slope beds suggesting that fault-related extension is relatively deep-seated, rather than tied directly to shallow slope failure. In contrast to previous suggestions, our mapping results do not suggest a direct relationship between tilted outer shelf (fall-in) beds and synsedimentary faulting. Five individual undergraduate students have participated in this fieldwork, with two completing independent summer research projects, and two planning to complete thesis studies. In 2009 we plan to trace out faults along strike to better constrain lateral continuity and investigate other areas of interest suggested by photogrammetric mapping this winter.
We are in the process of constructing 3D structural models for each of the study areas by integrating our field observations with previously published work and interpretation of digital stereo imagery. This 3D work has already demonstrated the presence of significant post-depositional deformation of the Slaughter Canyon section (Figure 1) and promises to provide better constraint on fault geometry including along strike continuity of fault systems.
Finally, in collaboration with Dr. Eric Flodin of Chevron Energy Technology Company, we have constructed two-dimensional mechanical models to explore controls on synsedimentary deformation. These models incorporate both subsidence due to compaction of underlying sediments and extension associated with the steep-sloped margin. The patterns of displacement predicted by these models contain features that are strikingly similar to the present-day geometry of the Capitan reef, including down-warping of the outer shelf. Furthermore, the models predict stresses that are consistent with jointing and faulting within the platform of a highly prograding system (Figure 2). In the next year we plan to model more realistic 2D and 3D geometries and compare these results to our 3D structural models.
Figure 1. Cross section of Slaughter
Canyon showing Yates Formation high frequency sequence boundaries and
margin-parallel faults. The
section was constructed by orthographically projecting three-dimensional
surfaces interpreted from stereo imagery (black dots).
Figure 2. Stress distributions predicted by stepped
elastic model of a prograding carbonate
platform. Color contours of positive
maximum Coulomb stress highlight regions of likely synsedimentary faulting
while the red contour outlines the region with tensile stress greater than 5 MPa, where synsedimentary jointing is likely.
