Browsing by Subject "Facies tracts"

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Anatomy, dimensions, and significance of the penultimate Yates tepee-shelf crest complex, G25 Hairpin HFS, Guadalupe Mountains, New Mexico and Texas
(2016-05) Voorhees, Kristopher James; Kerans, C. (Charles), 1954-; Janson, Xavier; Fisher, William L.
The steep-rimmed Permian Capitan platform in the Guadalupe Mountains has been studied in extensive detail to understand the effect of eustacy on platform architecture as seen in continuously exposed 700 m relief shelf-to-basin depositional profile. The Guadalupian Hairpin member (G25 High-Frequency Sequence) of the Yates Formation represents a major regional shelf marker and displays continuous 2.5 km dip-width exposures of the Capitan platform in McKittrick, Big, Double, Gunsight, Slaughter, Rattlesnake, and Walnut Canyons. Compared to the sequences above and below it, the G25 HFS is unique in that it reveals pronounced expansion of the shelf crest tepee-pisolite complex from an average of 1 km width to greater than 2 km. Tepee structures are 2-20 m diameter expansion megapolygons with compressional ridges formed by syndepositional expansive crystallization of micritic cement in arid to evaporitic supratidal settings. Increased dip-width of the shelf crest tepee-belt reflects a prolonged period where repeated cycles of wetting, evaporation, precipitation, and buckling of storm-ridge washover facies (grainy tidal flats/beaches) dominated the shelf. This study seeks to examine the role that eustacy/accommodation play in expansion of the shelf crest tepee complex by quantifying the dimensions of Capitan-equivalent shelf facies in McKittrick and Rattlesnake Canyons. Dip-oriented regional cross sections in Rattlesnake and McKittrick Canyons were created from 21 measured sections from 50-500 m spacing covering 30 to 70 m in thickness calibrated to 3 high-resolution gigapan photomosaics that are in turn constrained spatially using airborne lidar data. Cross sections in both canyons constrain facies tract dimensions as well as depositional topography and spatial distribution of the tepee complexes, allowing construction of a new tightly controlled depositional profile. 29 thin sections aid in grain identification, cement composition, and facies classification. Two main results of this study are (1) a new tightly constrained model for the Capitan shelf unequivocally showing that the tepee-belt is the topographic high-point of the profile, and (2) the Hairpin G25 highstand marks a period of prolonged supratidal exposure of the shelf and rapid volumetrically significant marine cementation from a supersaturated fluid, marking the first phase of silling of the Delaware Basin and onset of basinal restriction prior to end-Capitan Castile evaporite deposition.
Application of ground-based LIDAR to constrain topographic strike-variability and facies proportions of progradational San Andres Formation clinoforms, Last Chance Canyon, NM
(2007) Scott, Samuel Zephyr; Kerans, C. (Charles), 1954-
Progradational mixed-carbonate/siliciclastic San Andres Formation clinoforms at Last Chance Canyon, New Mexico were quantitatively mapped and modeled using techniques developed for use with LIDAR (Light Dectection and Ranging). Fundamental questions addressed by this thesis are: (1) What is the nature of topographic strikevariability within a progradational mixed-siliciclastic setting, (2) How is topgraphic strike variability related to a sequence stratigraphic framework?, and (3) Can construction of a LIDAR-based digital outcrop model provide insight into the three dimensional relationship between clinoform morphology and resultant clinothem facies distributions within high-frequency cycles (HFCs)? Chapter one relates facies distributions within HFCs to depositional processes predominantly utilizing measured section and mapping data. Results indicate highstand Guadalupian 9 (G9) high-frequency sequence (HFS) clinoforms built basinward as a sinuous front composed of promontories and reentrants. Low relief lenticular bioherms composed of sub-wave base open-marine fauna colonized upper-slope settings in response to reduced sediment supply subsequent to HFC maximum flood. Resumed production of the carbonate factory near the previous slope break filled topographic lows between intervening autochthonous open marine bioherms during progradation of regressive hemicycles. Differential along-strike topography on the upper-slope was largely filled at HFC termini during the early highstand of the G9 HFS, while during the late-highstand strike exposures exhibit nested topographic depressions that persist through multiple HFCs. It is suggested that persistent topographic lows were generated and accentuated by siliciclastic bypass of the slope in response to increasing slope declivity, and a narrowing of the area of the carbonate factory. Focus of bypassing siliciclastic sands through persistent topographic lows reduced siliciclastic influx on adjacent topographic highs and provided a stable substrate for nucleation of a late highstand build-up. Chapter 2 documents construction of a LIDAR based Digital Outcrop Model (DOM), and demonstrates topographic strike-variability existed throughout the G9 HFS. Quantitative mapping of clinoform surfaces demonstrates the nature of siliciclastic bypass is sensitive to an equilibrium threshold in slope angle of approximately 15 degrees. When clinoform declivity exceeds this threshold, the slope is entrenched through bypass of shelf-derived siliciclastics. A reduction in HFC boundary slope angle below 15 degrees in youngest clinoforms is suggested to reflect a period of forced regression. Finally results of facies modeling for HFC 2 developed using experimental variograms derived from catergorical facies values along measured sections and a deterministic indicator kriging algorithm are presented. Results honor measured section date and further indicate clinoforms during the G9 highstand prograded as a sinuous clinoform margin characterized by promontories and reentrants