Tectonic control of synrift sedimentation patterns, Reserve graben, southwestern New Mexico
Steven G. Crews
The Reserve graben is part of a Miocene and younger extensional corridor that lies between the Mogollon Plateau volcanic center and the Colorado Plateau; it comprises a series of distinct half-graben subbasins, each associated with one or more bounding normal faults, and each filled with alluvial deposits of the Gila Group. Topography and uplift/subsidence patterns created by extensional faulting directly influenced nearly every aspect of synrift sedimentation. Thickness, texture, sediment-transport direction and depositional environment of the synrift sediments were all directly affected by episodic movement on basin-bounding normal faults. The primary depositional environments represented in the deposits in these half grabens are hanging wall dip-slope alluvial fans, axial fluvial systems and footwall-derived alluvial fans. The footwall-derived fans are coarser grained, but areally smaller and less common than the dip-slope fans, which dominate the basin. Mass-flow deposits filling arroyos (which probably fed the hanging wall fans), and small colluvial wedges originating from fault scarps, have also been recognized. No lacustrine deposits have been identified. Two tectonic influences stand out. First, paleoflow was mostly either down structural dip or along strike—i.e., dipslope fans and axial fluvial systems dominate the basin fill. This suggests that fault kinematics directly affected drainage patterns. Second, the finest-grained deposits in each half graben often occur adjacent to the fault scarps, in spite of the high topographic relief found there. Many individual processes probably contributed to this situation, but most can be traced back ultimately to the influence of fault kinematics on topography and on the distribution of uplift and subsidence within the basin. In general, footwall uplifts in the Reserve graben do not act as prolific line sources of sediment. Large influxes of footwall sediment occur only at a few special points, such as topographic gaps associated with transfer zones in the border fault system.
- Crews, Steven G., 1994, Tectonic control of synrift sedimentation patterns, Reserve graben, southwestern New Mexico, in: Mogollon Slope, west-central New Mexico, Chamberlin, Richard M.; Kues, Barry S.; Cather, Steven M.; Barker, James B.; McIntosh, William C., New Mexico Geological Society, Guidebook, 45th Field Conference, pp. 125-134.