Browsing by Subject "Mechanical stratigraphy"
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Item Analysis of the effects of carbonate mounds on associated stratal geometry and fracture development, Sacramento Mountains, New Mexico, USA(2016-12) Tinker, Nathan Scott; Janson, Xavier; Zahm, Christopher Kent; Kerans, Charles; Fisher, William LThe objective of this research is an integrated structural‐stratigraphic analysis of compaction‐related fracturing in carbonate mounds and associated cover strata. The influence of early-cemented carbonate mounds on subsequent sediment deposition (such as creation of hard substrates and topographic relief) is relatively well-understood. The effect of early-cemented carbonate mounds during burial, however, has not been studied in detail. Early marine cementation of mounds enhances mechanical rigidity, which reduces mound compaction during burial as compared to less-resistant sediments surrounding and overlying the mound. This rigidity difference facilitates differential compaction of sediments overlying the mound, which are warped over the inflection point created by the mound topography. This study hypothesizes that there is a measurable increase in fracture intensity associated with differential compaction above early-lithified carbonate mounds. Thus, this work analyzes and quantifies the effects of differential compaction on stratal geometry, mechanical stratigraphy, and fracture development in Mississippian strata overlying carbonate mounds which are well-exposed in the Sacramento Mountains in southeast New Mexico. Methods employed in this study are drawn from structural geology, sedimentology, petrography, and remote sensing in an effort to adequately determine facies, examine fracture characteristics (e.g. size, orientation, and intensity), and to better understand which process(es) most directly control those characteristics (e.g. host rock facies type, diagenesis, bed thickness, mound proximity, mound size). Innovative methods of outcrop characterization such as high-resolution gigapan photography and unmanned aerial vehicle (UAV) photography were combined with photogrammetric techniques to create photo-realistic 3D outcrop models. The resulting models enabled a cost-effective, more detailed, less-distorted, and more comprehensive interpretation compared to previous methods, and improved understanding of the relationship between stratigraphy, rock mechanical evolution, and structural deformation in carbonate mound systems. Field work documented facies, stratal geometries, folds, faults, and fracture sets which validated observations and characterizations made using high-resolution field photographs and 3D outcrop models. Results of this work show that paleotopographic relief which has been early lithified (in this instance, Mississippian carbonate mounds) directly controls fracture development and overlying stratal geometry, in that there is a significant increase in tension fracture (mode 1) intensity above pre-existing rigid structures and over-steepening of bed dips beyond an expected and reasonable angle of repose. Additionally, this work outlines a multi-stage tectonostratigraphic sequence of the development of the stratigraphically complex Teepee Mound assemblage based on field observations of facies, fractures, stratal geometries, and diagenetic effects (e.g. cementation, compaction, and chertification), which includes new evidence of late-Mississippian tectonic compression. This result emphasizes the importance of understanding both syndepositional and post-depositional processes in outcrop characterization. Specifically, syndepositional processes establish the original mechanical stratigraphy and control the formation and propagation of early mechanical discontinuities, which in turn set up the fabric of weaknesses preferentially utilized by later fracture development. Post-depositional mechanical and diagenetic processes alter mechanical stratigraphy and rock brittleness, and thus influence fracture propagation through time.Item Mechanical stratigraphic control on deformation in a fault-propagation fold, Gobbler Anticline, Sacramento Mountains, New Mexico, USA(2021-05-06) Syzdek, Joseph C.; Zahm, Christopher Kent; Kerans, C. (Charles), 1954-Folded carbonates are host to a significant portion of the world’s hydrocarbon reservoirs. To date, analog data to aid prediction of the style, intensity, and distribution of critical strain elements such as opening-mode fractures is limited. Prediction of strain distribution and connectivity of fracture systems is especially problematic within interstratified carbonate and siliciclastic/argillaceous lithologies that create strong mechanical anisotropies. Documentation of the structural processes and stratigraphic architecture on a full spectrum of scales and across a well-constrained structure was conducted to provide a better understanding of deformation styles. The geometry and structural mechanisms associated with the growth of the Gobbler Anticline, a north-trending, doubly plunging, fault-propagation fold above a blind, basement rooted reverse fault with en echelon tear faults was constrained via a balanced cross-section, virtual outcrop models, and orthomosaic photographs. The Gobbler Anticline consists of tightly folded and faulted mixed lithofacies; specifically, thick-bedded (1.0-10.0 m) limestones intercalated with thin-bedded (laminated - 1.0 m) clay-rich intervals, characteristic of the Bug Scuffle Member of the Gobbler Formation. Measured sections (totaling 470 m) assess the distribution of facies while mechanical rock property analyses document the unconfined compressive strength of the rocks. Thin sections and X-Ray fluorescence provide improved understandings of lithological controls on deformational mechanisms. Pre-Permian unconformities and thinning of the overlying mid-upper Pennsylvanian strata indicate shallow overburden (< 500 m) at the time of initial fold deformation (Missourian, ~307 Ma). We find that argillaceous wackestones are disproportionately weakened when involved in folding soon after deposition and mechanical layering is the dominant control on fracture development in more deformed areas. This study illustrates the value of a tightly constrained mechanical stratigraphic model for the prediction of fracture distribution and fold geometry