Sedimentary petrography and depositional environments of the type section of the Mississippian Lake Valley Formation, Sierra County, New Mexico
Karl Krainer and Spencer G. Lucas
At its type section, located in the historic Lake Valley mining district in southwestern Sierra County, New Mexico, the Mississippian Lake Valley Formation rests on the Mississippian Caballero Formation, has an exposed thickness of 71 m and includes the (ascending order) Andrecito, Alamogordo, Nunn and Tierra Blanca members. The Caballero Formation represents a transgressive succession of hummocky cross-bedded siltstone to fine-grained sandstone of the lower shoreface, grading into muddy limestone and marly shale with intercalated thin limestone beds of a deeper shelf environment. The Andrecito Member of the Lake Valley Formation is composed of a shallowing upward succession of marly shale and intercalated limestone beds, grading upward into dominantly limestone. Grain size of the fossiliferous limestone increases upwards, and near the top, limestone is partly cross-bedded, indicating a facies change from near storm wave base to lower shoreface. The Caballero Formation and Andrecito Member form a depositional sequence composed of a transgressive systems tract, represented by the Caballero Formation, and a progradational systems tract, represented by the Andrecito Member. The Alamogordo Member is composed of mudstone and wackestone indicating deposition in a low-energy deeper shelf environment below storm wave base. The overlying Nunn Member, represented by marl and marly shale with intercalated thin limestone beds, appears to have been deposited on a deeper shelf near storm wave base. The Tierra Blanca Member is characterized by coarse-grained fossiliferous limestone (grainstone, packstone and rudstone), partly displaying trough cross-bedding. We interpret these limestones as storm deposits (tempestites), which accumulated when storm-generated currents transported sediment from a shallower shelf setting into deeper water between fair weather and storm wave base. The Alamogordo, Nunn and Tierra Blanca members represent a transgressive-regressive depositional sequence, composed of a transgressive systems tract (Alamogordo and basal Nunn members) and a progradational systems tract (Nunn and Tierra Blanca members). Both Lake Valley Formation depositional sequences correlate with depositional sequences recorded from the Lake Valley Formation in the San Andres and Sacramento Mountains to the east. Limestones of the Lake Valley Formation, particularly of the Andrecito and Tierra Blanca members, are composed of a bryonoderm grain association dominated by skeletons of echinoderms and bryozoans that is common in Late Paleozoic successions. This association indicates that sediments of the Lake Valley Formation probably were deposited on a thermocline-stratified ramp.
- Krainer, Karl; Lucas, Spencer G., 2012, Sedimentary petrography and depositional environments of the type section of the Mississippian Lake Valley Formation, Sierra County, New Mexico, in: Geology of the Warm Springs region, Lucas, Spencer G.; McLemore, Virginia T.; Lueth, Virgil W.; Spielmann, Justin A.; Krainer, Karl, New Mexico Geological Society, Guidebook, 63rd Field Conference, pp. 293-304.