Geology topics

F. Gray

Publications and source records attributed to F. Gray.

5 recordsLinked to original sources

USGS2018

Findings and lessons learned from the assessment of the Mexico-United States transboundary San Pedro and Santa Cruz aquifers: The utility of social science in applied hydrologic research

Study Region This study region encompasses the Transboundary San Pedro and Santa Cruz aquifers which are shared between the states of Sonora (Mexico) and Arizona (US). Special regional considerations include a semi-arid climate, basin-fill aquifers with predominantly montane recharge areas, economic drivers in the mining, trade, and military sectors, groundwater-dependent cities with expanding cones of depression, interbasin groundwater transfers, ground- and surface-water contamination, and protected aquatic and riparian habitats that act as significant migration corridors for hundreds of species, including some that are threatened and endangered. Study Focus We focus on lessons learned from the hydrologic assessment of the Transboundary San Pedro and Santa Cruz aquifers. We conducted the work, in two phases: (1) laying the groundwork and (2) implementation. The “laying the groundwork” phase consisted of binational meetings with stakeholders and key actors (agencies and individuals), and the development of an understanding of the physical, institutional, historical, and socio-political context. This led to signing of the binational Transboundary Aquifer Assessment Program (TAAP) agreement in 2009 and detailed the process for cooperation and coordination in the assessment of shared aquifers. The implementation phase began with an agreement to proceed with the study of four “focus” aquifers (Santa Cruz, San Pedro, Mesilla (Conejos-Médanos in Mexico), and Hueco Bolson (Bolsón del Hueco in Mexico)) and development of associated technical teams. Though we do include a brief discussion of the lessons learned from the physical science portion of the study, the results have been described and published elsewhere. The bulk of the paper instead focuses on the findings and lessons learned from the integration of social-science perspectives into a largely physical-science based program, since there is a growing recognition of the need for this type of approach especially in the management and assessment of transboundary aquifers. New Hydrological Insights for the Region The Sonora-Arizona effort succeeded because both countries were adequately represented, and because of flexibility of skills and ability of teams comprising both university and government scientists. Teams included social and earth scientists. Including the social sciences was critical to research design and implementation, and to addressing the cultural, institutional, and socio-political contexts of transboundary aquifer assessment. Significant components of the continuing implementation phase include strategic planning, data compilation and analysis, cross-border integration of datasets, geophysical and geochemical surveys, and internal, peer, and stakeholder engagement.

Arizona, Sonora↗

USGS2011

Transient electromagnetic study of basin fill sediments in the Upper San Pedro Basin, Mexico

The Upper San Pedro River Basin in Mexico and the United States is an important riparian corridor that is coming under increasing pressure from growing populations and the associated increase in groundwater withdrawal. Several studies have produced three-dimensional maps of the basin fill sediments in the US portion of the basin but little work has been done in the Mexican portion of the basin. Here, the results of a ground-based transient electromagnetic (TEM) survey in the Upper San Pedro Basin, Mexico are presented. These basin fill sediments are characterized by a 10–40 m deep unsaturated surficial zone which is composed primarily of sands and gravels. In the central portion of the basin this unsaturated zone is usually underlain by a shallow clay layer 20–50 m thick. Beneath this may be more clay, as is usually the case near the San Pedro River, or interbedded sand, silt, and clay to a depth of 200–250 m. As you move away from the river, the upper clay layer disappears and the amount of sand in the sediments increases. At 1–2 km away from the river, sands can occupy up to 50% of the upper 200–250 m of the sediment fill. Below this, clays are always present except where bedrock highs are observed. This lower clay layer begins at a depth of about 200 m in the central portion of the basin (250 m or more at distances greater than 1–2 km from the river) and extends to the bottom of most profiles to depths of 400 m. While the depth of the top of this lower clay layer is probably accurate, its thickness observed in the models may be overestimated due to the relatively low magnetic moment of the TEM system used in this study. The inversion routine used for interpretation is based on a one-dimensional geologic model. This is a layer based model that is isotropic in both the x and y directions. Several survey soundings did not meet this requirement which invalidates the inversion process and the resulting interpretation at these locations. The results from these locations were rejected.

Arizona↗

USGS2007

Tracking acid mine-drainage in Southeast Arizona using GIS and sediment delivery models

This study investigates the application of models traditionally used to estimate erosion and sediment deposition to assess the potential risk of water quality impairment resulting from metal-bearing materials related to mining and mineralization. An integrated watershed analysis using Geographic Information Systems (GIS) based tools was undertaken to examine erosion and sediment transport characteristics within the watersheds. Estimates of stream deposits of sediment from mine tailings were related to the chemistry of surface water to assess the effectiveness of the methodology to assess the risk of acid mine-drainage being dispersed downstream of abandoned tailings and waste rock piles. A watershed analysis was preformed in the Patagonia Mountains in southeastern Arizona which has seen substantial mining and where recent water quality samples have reported acidic surface waters. This research demonstrates an improvement of the ability to predict streams that are likely to have severely degraded water quality as a result of past mining activities. ?? Springer Science+Business Media B.V. 2007.

Environmental Monitoring and Assessment↗

USGS2002

Stratigraphy and paleontology of Lower Permian rocks north of Cananea, northern Sonora, Mexico

Lower Permian carbonate and overlying red bed clastic rocks are present in a 2 km2 stratigraphic window in the vicinity of Rancho La Cueva, Santa Cruz sheet (scale 1:50,000), northern Sonora, Mexico. This exposure lies unconformably beneath predominantly intermediate Upper Cretaceous volcanics yielding 40Ar/39Ar ages of 73.4?? 0.18 and 71.1 ?? 0.35 Ma. The lower part of the Permian succession consists of light- to medium-gray colored limestones of the Colina Limestone, with a minimum thickness of 235 m. Sedimentary features suggest shallow water, slightly restricted depositional environments. Although lacking observable fossils for the most part, two intervals of richly fossiliferous, silicified shell beds are present near the base and top of the Colina Limestone. The lower fauna consist mostly of gastropods and bivalves. The presence of a new microdomatid gastropod species. Glyptospira sonorensis n. sp., close to Glytospira arelela Plas, suggests a late Wolfcampian age for this horizon. The upper fauna are predominantly molluscan dominated (gastropods and bivalves), but some brachiopods (productids and the rhynchonellid genus Pontisia) are also present. Gastropod genera include Bellerophon, Warthia, Euomphalus (represented by the species, Euomphalus kaibabensis Chronic), Baylea, Worthenia, Naticopsis, Goniasma, Kinishbia, Cibecuia, and Glyptospira. The gastropods suggest a Leonardian (late Early Permian) age for this horizon, and many of the species have previously been recorded from the Supai Group and Kaibab Formation of northern and central Arizona. The Colina Limestone is conformably overlain by 11.2 m of light-gray lime mudstone and dolostone, assigned here to the Epitaph Dolomite, which in turn is succeeded by 58.8 m of red-colored sandstone and gray lime mudstone, assigned here to the Scherrer Formation. This Lower Permian succession is significant because it further strengthens the stratigraphic ties of southeastern Arizona rocks with those of northern Sonora and confirms the presence of North American cratonal stratigraphy in the northern part of the state of Sonora, Mexico. Published by Elsevier Science Ltd.

Journal of South American Earth Sciences↗

USGS1986

Platinum-group element geochemistry of zoned ultramafic intrusive suites, Klamath Mountains, California and Oregon

Three postorogenic Alaskan-type ultramafic to mafic intrusive suites in the Klamath Mountains, ranging in age from 142 to 163 m.y. and intruding metavolcanic, metasedimentary, or ophiolitic cumulate ultramafie to gabbroic rocks, were examined for their platinum-group element content. The Lower Coon Mountain pluton consists of layered clinopyroxene-rich lithologies occurring in chronological sequence whereas the intrusive suite at Tincup Peak consists of a cogenetic sequence of wehrlite, clinopyroxenite, magnetite clinopyroxenite, feldspathic hornblende-magnetite clinopyroxenite, dunite-olivine clinopyroxenite, and hornblende gabbro. The ultramarie-mafic intrusive suite at Chanchelulla Peak, part of the Wildwood pluton, consists predominantly of clinopyroxenite, minor interlayered dunite, and wehrlite with minor hypabyssal gabbroic rocks. Clinopyroxene compositions in the three intrusive suites are calcium rich and range from Wo (sub 54.7) -En (sub 45.1) -Fs 19 to Wo (sub 44.9) -En (sub 43.8) -Fs (sub 11.3) and resemble clinopyroxene with alkalic affinities. Olivine ranges from Fo 72 to Fo 83 and plagioclase from An 68 to An 96 . Cyclic units of layered cumulus magnetite + spinel (+ or -ilmenite) and coarse interstitial magnetite occur at Tincup Peak and Lower Coon Mountain. All three intrusive suites contain disseminated pyrrhotite + chalcopyrite + or - pentlandite, but the Chanchelulla Peak intrusive body also contains lenticular zones of disseminated to interstitial sulfides near its contact with sulfide-bearing horn-felsic rocks. Characteristics of rocks from these three Klamath Mountains Alaskan-type intrusive suites are (1) Rh contents of near or less than 1 ppb, (2) Ir and Ru contents less than 100 and 20 ppb, (3) variable Pd contents between rock units within intrusive suites and among suites, and (4) relatively similar Pt contents within intrusive suites and among suites. Concentrations of Pd average 6.3 ppb at Lower Coon Mountain, 13.7 ppb at Chanchelulla Peak, and 36.4 ppb at Tincup Peak. Cohen-corrected abundance data for individual rock units within each intrusive suite yield a Pt/(Pt + Pd) ratio that is greater in olivine-rich rocks than in clinopy-roxenite than in gabbro suggesting chemical fractionation of Pd within intrusive suites.

Economic Geology↗