The Guadalupe Mountains (USA) expose shelf to basin cross-sections of the Permian Capitan depositional system along 70 km of depositional strike, providing an excellent outcrop analog for studying the processes that generate early fractures within carbonate platform strata.
The Guadalupe Mountains (USA) expose shelf to basin cross-sections of the Permian Capitan depositional system along 70 km of depositional strike, providing an excellent outcrop analog for studying the processes that generate early fractures within carbonate platform strata. Although the Capitan has been the focus of intensive study for more than half a century, the presence and significance of early-formed fractures, particularly syndepositional faults, was only recognized in the last decade. In the Guadalupe Mountains syndepositional dip-slip faults generally parallel the platform margin, have unusually steep dips, and tip out upward and are buried by younger platform strata. Two-dimensional numerical modeling suggests that the faults may initiate in response to the combined effects of a steep slope and differential compaction of underlying fine-grained sediment during platform growth.
Recent acquisition of range-wide lidar topography is now providing a truly three-dimensional view of the strata and structures of the Capitan system. Mapping of stratigraphic markers within back reef strata reveals consistent platform architecture with a scalloped margin that persisted throughout the growth of the platform. Syndepositional fault systems parallel the platform margin with major segment boundaries at significant changes in fault (and margin) strike. The along-strike persistence of individual fault systems is variable leading to changes in fault density that appear to correlate with local margin geometry.
Similar syndepositional faults and other early-formed fractures may play an important role in many carbonate platform hydrocarbon systems. These fractures can act as long-lived fluid conduits that localize karst formation, diagenesis, and hydrocarbon charging, storage, and production. Syndepositional faults may also create localized accommodation space leading to changes in the thickness and facies of carbonate strata. By integrating field mapping with numerical modeling we are gaining a better understanding of the processes that drive early fracturing.