Syndepositional deformation features are fundamental components of carbonate platforms both in the subsurface and in seismic-scale field analogs. These deformation features are commonly opening-mode, solution-widened fractures that can evolve into extensional faults, and reactivate frequently through the evolution of the platform. They also have potential to behave as fluid flow conduits from the earliest phases of platform growth through burial and uplift, and can be active during hydrocarbon generation. As such, diagenetic alteration in the margins of these carbonate platforms is often intense, may demonstrate a preferential spatial relationship to the deformation features rather than the depositional fabrics of the strata, and may impact the permeability development of reservoir strata near deformation features. This study focuses on a syndepositional graben known as the Cave Graben fault system in the Yates Formation of Rattlesnake Canyon in the Guadalupe Mountains, and investigates the distribution of dolomite around the faults and associated opening-mode fractures, in an effort to understand the control the Cave Graben faults exert on fluid flow through the platform margins. Two generations of dolomite are identified on the outcrop: a fabric retentive dolomite located in the uppermost facies of the platform, and a fabric destructive dolomite that forms white, chalky haloes around syndepositional deformation features. The first generation of dolomite is dully luminescent and has very small crystal sizes, as well as a low trace element concentration and an ¹⁸O-enriched stable isotopic signature compared to Permian marine carbonate ratios. This dolomite is interpreted to have formed from the penecontemporaneous refluxing of concentrated lagoonal brine, and shows little fault control on its distribution. The second generation of dolomite is brightly luminescent and has much larger crystal sizes, as well as a higher trace element concentration and a slightly ¹⁸O-depleted isotopic signature compared to the first generation of dolomite, though it is still enriched in ¹⁸O compared to Permian marine carbonate. This dolomite is interpreted to have formed in a burial environment due to the transport of concentrated brines from the overlying evaporites through syndepositional deformation features. Overall, this study suggests that, once open, syndepositional deformation features may become the primary fluid conduit through otherwise impermeable strata, and may control the distribution of diagenetic products over a long period of geologic time. It provides valuable insight into the interaction of syndepositional faults and fractures and fluid flow, and may improve understanding of diagenesis in analogous subsurface carbonates reservoir intervals. / text

An appreciation of the extent of syndepositional fracturing, faulting, and cementation of carbonate platform margins is essential to understanding the role of early diagenesis and compaction in margin deformation. This study uses integrated lidar and outcrop data along the Capitan Reef from an area encompassing the mouths of both Rattlesnake and Walnut Canyons. Mapping geomorphic expressions of syndepositional faults and fractures at multiple scales of observation was the main approach to delineating zones of syndepositional fractures. Ridge- groove couplets visible in exposures of the Capitan Reef throughout the Guadalupe Mountains were targeted because the ability to identify these as signs of syndepositional fracture development would have implications for the entire reef complex. Results show that these ridgegroove couplets are the product of differential weathering of syndepositional as well as burial-related fractures. Recessive grooves have an average syndepositional fracture spacing of ~13 m whereas ridges have a spacing of ~33 m. vi Smaller (~5-20 m-wide) scale erosional lineaments common in the study area and mappable on airborne lidar are formed by differential erosion of planes of syndepositional faults. Maps of these fault lineaments on the lidar show that syndepositional faults extend laterally for 300 m - 2000 m and relay near the terminations of the faults at each end. Faults can be further grouped into fault systems consisting of sets of faults connected by fault relays that extend for at least the entire length (~12 km) of the study area. Although vertical displacement along faults is typically less than 11 m, syndepositional faults result in changes in structural dip domain of 1-6 degrees across an individual fault. Even smaller erosional lineaments (10 cm-1 m) are visible on the airborne lidar that form as a result of differential erosion of individual fractures. Larger fractures (> 20 cm) can be reliably mapped on the lidar, but smaller features (< 20 cm) cannot be reliably mapped with currently available data and can only be captured using field studies. Fracture fill types are heterogeneous along strike as shown by comparisons of field study locations. Siliciclastic-dominated fills are likely sourced from overlying siliciclastic units of the shelf, which, in this area, were from the Ocotillo Siltstone. These silt-filled fractures are broadly distributed, indicating preferential development and infill of syndepositional fractures during the deposition of the Ocotillo Siltstone in the G27/28 high-frequency sequences. Development of early fractures is also shown to have been influenced by mechanical stratigraphy with changes in fracture spacing between massive to thick-bedded shelf-margin (~17 m fracture spacing) and outer-shelf facies tracts versus thin-bedded outer-shelf and shelf-crest (~28 m fracture spacing). Ultimately, this study demonstrated that the Capitan shelf margin was ubiquitously overprinted by syndepositional fracturing and faulting and that this nearsurface structural modification influenced early diagenetic patterns and internal vii sedimentation throughout the reef margin. Before this study, the extent and nature of syndepositional fracture/fault development within the margin were largely unquantified. Here, by integrating field observations and surface weathering reflections of these fractures as observed in the lidar, we can demonstrate a widespread impact of early fracturing more akin to analogous early-lithified margins such as the Devonian of the Canning Basin of Australia. / text