Fracture-related paleohydrology of the La Popa Basin, northeastern Mexico

This thesis characterizes the paleohydrology of the La Popa Basin in northeastern Mexico and focuses on related salt structures. These structures include a sub-vertical secondary salt weld and a salt diapir. These features are hypothesized to control the distribution of fluids and hydrocarbons due to the physical properties of salt and the deformation related to the evolution of the structures. The paleohydrology is characterized by combining mesostructural analyses with geochemical analyses of calcite veins that formed in fracture networks created by salt deformation and regional tectonics. The last part of this study tests the viability of sampling techniques of calcite veins by collecting and analyzing samples from bed-parallel veins that are ∼500 meters long.;Fluid flow pathway formation was characterized and modeled from mesostructural analyses of fracture networks along the weld and around the diapir. Relative timing of the formation of fracture networks was related to regional and local deformation events and was modeled using structural relationships along with previously published works. Minerals that precipitated from fluids moving through these fracture networks formed veins that were collected to observe a snapshot of what the hydrologic system was like during the formation of the vein material. Different hydrologic patterns were recognized and controlled by the different structural features within the basin. One important factor that controlled fluid migration along the weld was recognized to be the stratigraphy juxtaposed against each feature. Sand units with higher porosity and permeability allowed for migration of exotic fluids, including hydrocarbons, through the unit. Units consisting of shales, mudstones, siltstones, and carbonates indicate fluid regimes that have slower advection rates therefore longer residence times. Another important control on fluid migration is the structural geometry of the weld. A major bend in the map trace of the weld shows an influence on the migration of deeply sourced exotic fluids as well. This study has identified that the important controls on fluid migration is related to stratigraphy and structural position along the weld.;The second part of this study is intended to recognize the fluid regimes around a salt diapir that is recognized at the surface within the basin. There have been numerous studies from other researchers that utilize data collected while drilling oil/gas wells around these salt features. Conclusions from these studies are used as analogs to interpret the data I have collected from vein geochemistry around the El Papalote diapir. It was found that like the conclusions from the weld study, stratigraphy and structural location play and important role to the hydrologic system influenced by a salt diapir. The results are favorable in comparison to the previous geochemical studies and numerical models proposed by other researchers.;The last part of this thesis examines the variability of bedding-parallel veins to identify whether previous strategies of vein sampling and analyzing is viable for concluding the paleohydrology of a basin. Strategically sampling along a 500m bed-parallel vein and analyzing for stable isotopes, fluid inclusions, and strontium isotopes indicates that similar fluids have formed the veins. This study recognizes that collection methods do not influence the outcome for resolving the paleohydrology that formed these types of veins in this tectonic setting.