GMEG - Geology and Geophysics
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TASK 3 - Geologic studies of selected areas in Mojave National Preserve, CaliforniaTask Leader: Paul Stone
Statement of Problem: Mojave National Preserve encompasses much of the mountainous desert region between Interstate Highways 15 and 40 in southeastern California. The mountains are composed of variably deformed bedrock that includes Proterozoic crystalline rocks, latest Proterozoic to Early Mesozoic sedimentary rocks, Jurassic and Cretaceous plutonic and volcanic rocks, and Tertiary volcanic rocks and sedimentary rocks; the valleys are filled with relatively undeformed Quaternary sediments. The complex geologic framework has a primary influence on the varied physiography, hydrology, and biology of the Preserve. Thus, an understanding of the geologic framework is essential both for resource management of the Preserve by the NPS and for appreciation of the Preserve’s landscape and natural history by the public.
In 1991 the USGS published a preliminary geologic map of the region now encompassed by Mojave National Preserve at a scale of 1:100,000. More detailed mapping, however, is needed in many areas. One such area is the Providence Mountains in the south-central part of the Preserve. This range exposes the most complete section of Paleozoic strata in the southeastern Mojave Desert region, yet no modern, detailed geologic map of these strata is in existence. Present knowledge of the Paleozoic strata of the Providence Mountains dates back to the classic studies of John Hazzard in the 1930s; little work has been done on these rocks since that time. Despite the high quality and detail of Hazzard’s work, his mapping cannot be fit to a modern topographic base and therefore is of limited practical utility. A thorough reexamination of the Paleozoic strata and of the complex faults that cut these strata would be a valuable addition to the geologic information base of the Preserve, both for resource management and scientific purposes.
The relationship between geology and resource management in Mojave National Preserve was discussed by NPS and USGS participants at a Geologic Resources Evaluation scoping meeting in 2003. The report from that meeting identifies several resource management issues that are closely related to geology, including the inventory and monitoring of caves and karst features, the need for a more complete inventory of fossil resources, concerns about abandoned mine safety, a variety of water issues, geologic hazards such as slope failure, and the preservation of geologically recent volcanic features. Most of these issues are pertinent to the Providence Mountains and could be better addressed with the availability of a modern geologic map. Such maps contribute directly to the NPS mandate to develop inventories of baseline natural resource information, of which geology is a principle component.
Afternoon sunlight on the Providence Mountains in the Mojave National Reserve, southern California
|New geologic mapping in the Providence Mountains will improve regional correlations of Paleozoic strata in the
southwestern U.S. and contribute to increased understanding of the paleogeography and evolution of the Paleozoic
continental margin. Mapping of faults and other structural features that deform rocks in the Providence Mountains will expand knowledge of the regional Mesozoic and Cenozoic tectonic history, which has been studied in more detail in the northern and northeastern parts of the Preserve (Clark Mountain area and New York Mountains).
Other areas in need of new, detailed geologic mapping include Old Dad Mountain and the Cowhole Mountain area in the west-central part of the Preserve. These areas expose Paleozoic rocks cut by major low-angle faults that have been interpreted as Mesozoic thrust faults but which alternatively could be Cenozoic or Mesozoic detachment faults. Remapping of these areas could uncover evidence needed to resolve this issue. Major Cenozoic detachment faults have been documented just northwest of the Preserve, but the full regional extent of this type of structural feature is not yet known.
Objectives: databases of selected areas in Mojave National Preserve. In addition to their basic research value, these maps and databases will provide detailed information on the geologic setting of features important for NPS resource inventories such as caves, springs, abandoned mines, fossil localities, unstable slopes, and potential flash-flood or debris-flow hazards. The proposed initial target for new geologic mapping, as determined jointly by the task leader (Paul Stone) and the scientific staff at Mojave National Preserve (led by Debra Hughson), is the Fountain Peak 7.5’ quadrangle in the Providence Mountains. This quadrangle has the most continuous exposures of Paleozoic rocks in the range and also contains several important springs, the prime cave and karst resources in the Preserve, and many significant fossil localities that need to be accurately mapped in conjunction with the geology.
In FY2008 the task initiated a second objective of completing and publishing maps in other Federal lands of southeastern California, specifically in and near Death Valley National Park. Field work in these map areas was largely or entirely completed prior to initiation of this task, but the maps had not been compiled and published. The objective now is to compile and publish these maps in digital form. The first map area selected for this objective was the southern Inyo Mountains, important both for its mineralization and for its unusually complete record of Paleozoic to Mesozoic tectonism along the western margin of North America. A second area, around Marble Canyon in Death Valley National Park, was initiated in FY2009. The Inyo map was completed in FY2010, and the Marble Canyon map is currently in progress. An additional study is in progress at Black Mountain near Victorville in the western Mojave Desert, an important area of Mesozoic sedimentary and volcanic rocks.
The proposed geologic mapping will require systematic examination of exposed rocks and sediments at closely spaced locations in the field, combined with geologic interpretation of aerial photography and remote-sensing imagery. Mapping of the rocks and structural features such as faults will be accompanied by accurate location of features such as springs, caves, and fossil occurrences using GPS. As needed, fossils will be collected and sent to paleontologists for identification, geologic age assignment, and interpretation of paleoenvironment. All relevant data, including some existing geologic map information acquired by previous USGS projects, will be entered into GIS and compiled as multilayer databases.
Photomicrographs of fusulinids, a fairly common type of fossil from Permian-age sedimentary rocks in southern California.
|Highlights and Key Findings:
Providence Mountains (Fountain Peak 7.5' quadrangle, Mojave National Preserve): Detailed bedrock geologic mapping generally confirms the remarkably accurate and insightful original mapping by J. C. Hazzard in the 1930s, with locally significant modifications facilitated by a modern topographic base map, aerial photographs, and GPS. Mapping upgrades in the Paleozoic sequence that underlies most of the area include delineation of the Lower Cambrian Zabriskie Quartzite and the Papoose Flat and Banded Mountain members of the Middle Cambrian Bonanza King Formation. In addition, no evidence was found to support Hazzard’s mapping of the base of the Devonian Sultan Formation, which could not be definitively recognized. Instead, dolomite and sandy dolomite of the lower Sultan are here included as part of an undivided Upper Cambrian to Devonian unit, and limestone of the upper Sultan, the base of which is a sharp, definitive contact, is mapped separately. The true nature of the Cambrian-Devonian contact or transition remains uncertain. The new mapping confirms Hazzard’s conclusion that most faulting in the Providence Mountains predated emplacement of abundant felsic to intermediate-composition dikes that cut the Paleozoic rocks; in addition, the new mapping strongly suggests that the faulting largely predated emplacement of the Fountain Peak Rhyolite, which intrudes and overlies the Paleozoic rocks.
Finally, the new mapping suggests that the mineralized East Providence Fault Zone probably developed prior to intrusion of Jurassic(?) granitic rocks that appear to cut across the southern end of the fault trace. Southern Inyo Mountains, eastern California: An updated digital geologic map and accompanying pamphlet documents and interprets the stratigraphy and structure of the area around Conglomerate Mesa in the southern Inyo Mountains. The geology of this area records a protracted period of coeval deformation and sedimentation on a tectonically unstable part of the late Paleozoic to early Mesozoic continental margin. A key feature, exposed only in this map area, is a folded and thrust-faulted uplift that separated two deep-water sedimentary basins during the Early Permian and remained tectonically active into latest Permian time.
Marble Canyon-Cottonwood Canyon area, Death Valley National Park, California: Updated geologic mapping and stratigraphic investigations in this area provide new insights into the regional history of late Paleozoic sedimentation and deformation in eastern California. The mapping, together with biostratigraphic study of conodonts, documents major breaks in sedimentation at the Mississippian-Pennsylvanian and the Pennsylvanian-Permian boundaries. Black Mountain area near Victorville, western Mojave Desert, California: Geologic mapping and geochronologic studies in this area document magmatic and sedimentary events that took place on the continental margin in early Mesozoic time. This work shows that Early Jurassic sedimentary strata of the Fairview Valley Formation were deposited nonconformably on an exhumed, early Middle Triassic pluton and were unconformably overlain by late Early Jurassic felsic extrusive rocks of the Sidewinder Volcanics. Faults and folds within the Fairview Valley Formation and along its upper boundary are interpreted to represent relatively minor deformation of post-Sidewinder age, rather than as significant episodes of Jurassic deformation that punctuated the depositional sequence.
Stevens, C. H., and Stone, P., 2007, The Pennsylvanian-Early Permian Bird Spring carbonate shelf, southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications: Geological Society of America, Special Paper 429, 82 p.
Stevens, C. H., and Stone, P., 2009, New Permian durhaminid cerioid corals from east-central California: Journal of Paleontology, v. 83, no. 6, p. 946-953.
Stevens, C. H., and Stone, P., 2009, New Permian fusulinids from Conglomerate Mesa, southeastern Inyo Mountains, east-central California: Journal of Paleontology, v. 83, no. 1, p. 9-29.
Stevens, C. H., and Stone, P., 2009, New fusulinids from Lower Permian turbidites at Conglomerate Mesa, southeastern Inyo Mountains, east-central California: Journal of Paleontology, v. 83, no. 3, p. 399-404.
Stone, P., Swanson, B. J., Dunne, G. D., Stevens, C. H., and Priest, S. S., 2009, Geologic map of the southern Inyo Mountains and vicinity, Inyo County, California: U.S. Geological Survey Scientific Investigations Map 3094, scale 1:24,000, 22 p.
Wrucke, C. T., Stone, P., and Stevens, C. H., 2007, Geologic map of the Warm Spring Canyon area, Death Valley National Park, Inyo County, California, with a discussion of the regional significance of the stratigraphy and structure: U.S. Geological Survey Scientific Investigations Map 2974, scale 1:24,000, 39 p.
Map, Planned: Stone, P., Barth, Andrew P., and Wooden, Joseph L., 2011, Geologic map of the Black Mountain area northeast of Victorville, San Bernardino County, California, USGS, Scientific Investigations Map
Map, Planned: Stone, P., Stevens, C. H., Belasky, Paul, Wardlaw, B. R., Sandberg, C. A., and Greene, Lauren, 2012, Geologic map and late Paleozoic stratigraphy of the Marble Canyon-Cottonwood Canyon area, Death Valley National Park, Inyo County, California, USGS, Scientific Investigations Map.
Map, Planned: Stone, P., and others(?), 2012, Preliminary geologic map of the northern part of the Fountain Peak quadrangle, California, USGS, Open-File Report.
Report, Planned: Stone, P., Stevens, C. H., and Howard, K. A., 2012, Stratigraphy of the Pennsylvanian-Permian Bird Spring Formation in the Ship Mountains, Mojave Desert, San Bernardino County, California, USGS, Open-File Report.