Cyclic sedimentation of the Upper Pennsylvanian (Lower Wolfcampian) Bursum Formation, central New Mexico: tectonics versus glacioeustasy
Karl Krainer and Spencer Lucas
In New Mexico, the Bursum Formation represents the transitional facies between underlying, dominantly shallowmarine Upper Pennsylvanian carbonate deposits and overlying Lower Permian continental red beds. The Bursum Formation in the Joyita Hills and hilly area east of Socorro, central New Mexico, is as much as 120 m thick and composed of alternating shallow marine limestone and shale and nonmarine red beds. These alternating marine and nonmarine sediments locally form well-developed cyclic successions. However, strong lateral variations in thickness and stratigraphic distributions of facies are observed, which has led to the recognition of three regional members of the Bursum Formation: (a) Bruton Member, (b) Red Tanks Member and (c) Oso Ridge Member. The cyclic succession and lateral variability in thickness and distributions of lithofacies indicate that sedimentation of the Bursum Formation in the Joyita Hills and hilly area east of Socorro was influenced by both glacio-eustatic sea-level changes and tectonic movements of the ancestral Rocky Mountain (ARM) orogeny. Sea-level changes are responsible for the cyclic pattern, and tectonic movements for the strong lateral variability.Unconformities are present at the base and at the top of the Bursum Formation that are the result of major tectonic pulses. The tectonic pulse responsible for the lower unconformity caused a sharp facies change from dominantly shallow marine carbonate sedimentation to mixed siliciclastic-carbonate sedimentation of alternating nonmarine and marine sediments. The upper unconformity resulted from a major tectonic event of the ARM deformation, causing a rejuvenation of basement uplifts that resulted in increased siliciclastic influx and deposition of nonmarine red beds of the Abo Formation. There is also evidence for tectonic activity during sedimentation of the Bursum Formation.
- Krainer, Karl; Lucas, Spencer, 2009, Cyclic sedimentation of the Upper Pennsylvanian (Lower Wolfcampian) Bursum Formation, central New Mexico: tectonics versus glacioeustasy, in: Geology of the Chupadera Mesa, Lueth, Virgil W.; Lucas, Spencer G.; Chamberlin, Richard M., New Mexico Geological Society, Guidebook, 60th Field Conference, pp. 167-182.