Abstract

Syndepositional deformation is increasingly recognized as an important process in many carbonate systems that leads to the development of a platform-scale fluid-flow network. However, open questions remain regarding the link between syndepositional fracture-controlled fluid flow and the distribution of diagenetic products, and whether syndepositional fractures serve as active fluid conduits during subsequent burial diagenetic events. The Tansill-age (Permian) outcrops of Dark Canyon, located in the Guadalupe Mountains of New Mexico, provide an ideal locality to investigate these questions.

Syndepositional fractures are widespread in Dark Canyon, and are typically oriented parallel to the platform-margin trend with subvertical traces, and millimeter- to meter-scale apertures. Syndepositional normal faults are less frequent, with fault offsets ranging from tens of centimeters, to tens of meters. In most instances, fault offsets were large enough to alter sedimentation patterns and stratal architecture of the Tansill shelf in the form of growth monoclines or small-scale grabens. Regional mapping indicates that the individual fault segments mapped in Dark Canyon are part of a series of laterally persistent, yet internally complex, fault zones that run parallel to the Tansill platform margin.

Fracture-related dolomite bodies, which range in lateral extent from a few centimeters to tens of meters, provide evidence for the early flow of diagenetic fluids along syndepositional deformation features. Isotopic data from individual fracture-related dolomite bodies indicate temporal variability in the dolomitizing fluids, suggesting that those fluids moved through different syndepositional fractures systems at different times. Detailed field mapping shows that tepee features developed at the upper tip of many syndepositional fractures. This relationship suggests that 1) syndepositional fractures and tepees are intimately linked as part of the same early fluid-flow network, and 2) the brines that formed the fracture -related dolomites of Dark Canyon were likely derived from overlying shelf-crest tepee complexes.

Calcite fracture-fills include both syndepositional and burial cement phases. Isotopic, cathodoluminescence, and temperature data from fluid inclusion and clumped isotope analysis, demonstrate that multiple fluids of varied isotopic composition and temperature migrated through the Dark Canyon deformation features. We interpret these findings to indicate that the syndepositional deformation features in Dark Canyon were frequently reactivated and served as long-lived fluid conduits, from deposition through burial, hydrocarbon migration, and Tertiary uplift.