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J. M. O’Neill

Publications and source records attributed to J. M. O’Neill.

At least 19 recordsLinked to original sources
USGS2017

Tree-ring dated landslide movements and their relationship to seismic events in southwestern Montana, USA

To determine periods of incremental landslide movement and their possible relationship to regional seismic events, the tree-ring records of 32 titled and damaged conifers at three sites on landslides in the Gravelly Range of southwestern Montana were examined. Several signs of disturbance in the tree-ring record indicating landslide movement were observed. Commonly, the tree-ring record displayed a marked reduction in annual ring width and/or the reaction wood formation. The tree-ring records from the three landslide sites indicate multiple periods of movement during the 20th century. Many of the periods of movement indicated by the strongest signals (most trees) at the sites occurred the year following significant earthquakes in the region. Those seismic events for which evidence in the tree-ring record was found at one or more of the three sites are the 1983 Borah Peak, 1959 Hebgen Lake, 1935 Helena, 1925 Clarkson, and 1908 Virginia City earthquakes. This study suggests that many of the landslide movements were triggered by, or are coincident with, earthquakes as much as 200 km from the study area.

Montana↗
USGS2008

Regional Geochemical Results from Analyses of Stream-Water, Stream-Sediment, Soil, Soil-Water, Bedrock, and Vegetation Samples, Tangle Lakes District, Alaska

We report chemical analyses of stream-water, stream-sediment, soil, soil-water, bedrock, and vegetation samples collected from the headwaters of the Delta River (Tangle Lakes District, Mount Hayes 1:250,000-scale quadrangle) in east-central Alaska for the period June 20-25, 2006. Additionally, we present mineralogic analyses of stream sediment, concentrated by panning. The study area includes the southwestward extent of the Bureau of Land Management (BLM) Delta River Mining District (Bittenbender and others, 2007), including parts of the Delta River Archeological District, and encompasses an area of about 500 km2(approximately bordered by the Denali Highway to the south, near Round Tangle Lake, northward to the foothills of the Alaska Range (fig. 1). The primary focus of this study was the chemical characterization of native materials, especially surface-water and sediment samples, of first-order streams from the headwaters of the Delta River. The impetus for this work was the need, expressed by the Alaska Department of Natural Resources (ADNR), for an inventory of geochemical and hydrogeochemical baseline information about the Delta River Mining District. This information is needed because of a major upturn in exploration, drilling, and general mineral-resources assessments in the region since the late 1990s. Currently, the study area, called the 'MAN Project' area is being explored by Pure Nickel, Inc. (http://www.purenickel.com/s/MAN_Alaska.asp), and includes both Cu-Au-Ag and Ni-Cu-PGE (Pt-Pd-Au-Ag) mining claims. Geochemical data on surface-water, stream-sediment, soil, soil-water, grayleaf willow (Salix glauca L.), and limited bedrock samples are provided along with the analytical methodologies used and panned-concentrate mineralogy. We are releasing the data at this time with only minimal interpretation.

Open-File Report↗
USGS2007

Crustal structure of Wrangellia and adjacent terranes inferred from geophysical studies along a transect through the northern Talkeetna Mountains

Recent investigations of the Talkeetna Mountains in south-central Alaska were undertaken to study the region's framework geophysics and to reinterpret structures and crustal composition. Potential field (gravity and magnetic) and magnetotelluric (MT) data were collected along northwest-trending profiles as part of the U.S. Geological Survey's Talkeetna Mountains transect project. The Talkeetna Mountains transect area comprises eight 1:63,360 quadrangles (∼9500 km 2 ) in the Healy and Talkeetna Mountains 1° × 3° sheets that span four major lithostratigraphic terranes ( Glen et al., this volume ) including the Wrangellia and Peninsular terranes and two Mesozoic overlap assemblages inboard (northwest) of Wrangellia. These data were used here to develop 2½-dimensional models for the three profiles.

Special Paper of the Geological Society of America↗
USGS2007

Pre-, syn-, and postcollisional stratigraphic framework and provenance of upper triassic-upper cretaceous strata in the northwestern talkeetna mountains, alaska

Mesozoic strata of the northwestern Talkeetna Mountains are located in a regional suture zone between the allochthonous Wrangellia composite terrane and the former Mesozoic continental margin of North America (i.e., the Yukon-Tanana terrane). New geologic mapping, measured stratigraphic sections, and provenance data define a distinct three-part stratigraphy for these strata. The lowermost unit is greater than 290 m thick and consists of Upper Triassic-Lower Jurassic mafic lavas, fossiliferous limestone, and a volcaniclastic unit that collectively we informally refer to as the Honolulu Pass formation. The uppermost 75 m of the Honolulu Pass formation represent a condensed stratigraphic interval that records limited sedimentation over a period of up to ca. 25 m.y. during Early Jurassic time. The contact between the Honolulu Pass formation and the overlying Upper Jurassic-Lower Cretaceous clastic marine strata of the Kahiltna assemblage represents a ca. 20 m.y. depositional hiatus that spans the Middle Jurassic and part of Late Jurassic time. The Kahiltna assemblage may to be up to 3000 m thick and contains detrital zircons that have a robust U-Pb peak probability age of 119.2 Ma (i.e., minimum crystallization age/maximum depositional age). These data suggest that the upper age of the Kahiltna assemblage may be a minimum of 10-15 m.y. younger than the previously reported upper age of Valanginian. Sandstone composition (Q-43% F-30% L-27%-Lv-71% Lm-18% Ls-11%) and U-Pb detrital zircon ages suggest that the Kahiltna assemblage received igneous detritus mainly from the active Chisana arc, remnant Chitina and Talkeetna arcs, and Permian-Triassic plutons (Alexander terrane) of the Wrangellia composite terrane. Other sources of detritus for the Kahiltna assemblage were Upper Triassic-Lower Jurassic plutons of the Taylor Mountains batholith and Devonian-Mississippian plutons; both of these source areas are part of the Yukon-Tanana terrane. The Kahiltna assemblage is overlain by previously unrecognized nonmarine strata informally referred to here as the Caribou Pass formation. This unit is at least 250 m thick and has been tentatively assigned an Albian-Cenomanian-to-younger age based on limited palynomorphs and fossil leaves. Sandstone composition (Q-65% F-9% L-26%-Lv-28% Lm-52% Ls-20%) from this unit suggests a quartz-rich metamorphic source terrane that we interpret as having been the Yukon-Tanana terrane. Collectively, provenance data indicate that there was a fundamental shift from mainly arc-related sediment derivation from sources located south of the study area during Jurassic-Early Cretaceous (Aptian) time (Kahiltna assemblage) to mainly continental margin-derived sediment from sources located north and east of the study area by Albian-Cenomanian time (Caribou Pass formation). We interpret the threepart stratigraphy defined for the northwestern Talkeetna Mountains to represent pre- (the Honolulu Pass formation), syn- (the Kahiltna assemblage), and post- (the Caribou Pass formation) collision of the Wrangellia composite terrane with the Mesozoic continental margin. A similar Mesozoic stratigraphy appears to exist in other parts of south-central and southwestern Alaska along the suture zone based on previous regional mapping studies. New geologic mapping utilizing the three-part stratigraphy interprets the northwestern Talkeetna Mountains as consisting of two northwest-verging thrust sheets. Our structural interpretation is that of more localized thrust-fault imbrication of the three-part stratigraphy in contrast to previous interpretations of nappe emplacement or terrane translation that require large-scale displacements. Copyright ?? 2007 The Geological Society of America.

Special Paper of the Geological Society of America↗
USGS2004

Early Tertiary Anaconda metamorphic core complex, southwestern Montana

A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts, overprinted by late Tertiary Basin and Range faulting. ?? 2004 NRC Canada.

Canadian Journal of Earth Sciences↗
USGS2004

Precambrian basement geologic map of Montana– An interpretation of aeromagnetic anomalies

Newly compiled aeromagnetic anomaly data of Montana, in conjunction with the known geologic framework of basement rocks, have been combined to produce a new interpretive geologic basement map of Montana. Crystalline basement rocks compose the basement, but are exposed only in the cores of mountain ranges in southwestern Montana. Principal features deduced from the map are: (1) A prominent northeast-trending, 200-km-wide zone of spaced negative anomalies, which extends more than 700 km from southwestern Montana's Beaverhead Mountains to the Canadian border and reflects suturing of the Archean Mexican Hat Block against the Archean Wyoming Province along the Paleoproterozoic Trans-Montana Orogen (new name) at about 1.9-1.8 Ga; (2) North-northwest-trending magnetic lows in northeastern Montana, which reflect the 1.9-1.8 Ga Trans-Hudson Orogen and truncate the older Trans-Montana Zone; and (3) Subtle northwest- and west-trending negative anomalies in central and western Montana, which represent the northernmost segment of brittle-ductile transcurrent faults of the newly recognized Mesoproterozoic Trans-Rocky Mountain fault system. Structures developed in the Proterozoic provided zones of crustal weakness reactivated during younger Proterozoic and Phanerozoic igneous and tectonic activity. For example, the Trans-Montana Zone guided basement involved thrust faulting in southwestern Montana during the Sevier Orogeny. The Boulder Batholith and associated ore deposits and the linear belt of alkaline intrusions to the northeast were localized along a zone of weakness between the Missouri River suture and the Dillon shear zone of the Trans-Montana Orogen. The northwest-trending faults of Trans-Rocky Mountain system outline depocenters for sedimentary rocks in the Belt Basin. This fault system provided zones of weakness that guided Laramide uplifts during basement crustal shortening. Northwest-trending zones have been locally reactivated during Neogene basin-range extension.

Montana↗
USGS2002

Geologic investigations in the Lake Valley area, Sierra County, New Mexico

At the request of the Bureau of Land Management, the U.S. Geological Survey evaluated the area of the historic Lake Valley mining district and townsite, Sierra County, New Mexico, for its potential for undiscovered mineral resources. The four chapters of this report describe the geology of the area, present the results of geophysical investigations carried out to aid in interpreting subsurface geology, describe the mining history and character of the region's ore deposits, and present geochemical data on potential for contamination from abandoned mine dumps in the mining district.

New Mexico↗
USGS1998

Geology and mineral resources of the Lake Valley area, Sierra County, New Mexico

At the request of the Bureau of Land Management, the U.S. Geological Survey assessed the Lake Valley Area of Critical Environmental Concern (ACEC), which includes the historic Lake Valley townsite and silver-manganese mining district, for undiscovered mineral resources. The Lake Valley ACEC is along the southeastern margin of the Black Range of western Sierra County, New Mexico. The Black Range contains eleven mining districts from which silver, lead, zinc, manganese, copper, gold, and tin have been recovered. As part of the study, an area of over 75 square mi (195 square km) in the area of the Lake Valley ACEC was mapped to understand ore controls and to assess mineral-resource potential. Lake Valley mining district is in Mississippian Lake Valley Formation carbonate rocks, but much of the surrounding terrane consists of volcanic rocks on the southeastern edge of the Emory cauldron which formed about 34.9 Ma. Volcanic rocks are part of the Mogollon-Datil volcanic province which include flows, breccias, ash-flow tuffs, and intrusive rhyolites. The Lake Valley mining district is located about 20 mi (32 km) south of the Late Cretaceous Laramide copper-gold porphyry intrusion at Hillsboro. It is also located at the western boundary of the Rio Grande rift basin.The Lake Valey fault is the major structural feature of the study area. Geological and geophysical data suggest the fault is composed of two segments: a southern, northwest-striking segment that may have a pre-Tertiary history and a northerly-striking segment that is part of the Emory cauldron ring fracture. The mining district is bounded by the southern, northwest-striking segment of the fault which may have up to 800 ft (240m) of normal offset. Deposit types identified in the Black Range, and for which we assess mineral potential, are Laramide porphyry, Laramide skarns, Laramide veins, gold placer, carbonate-hosted, volcanic-epithermal, and rhyolite tin; no Rio Grande Rift baritefluorite-galena deposits are known, but they are included in the assessment. The most likely deposits to be discovered in the Lake Valley district are carbonate-hosted silver-manganese deposits. These deposits could be deposited by hydrothermal fluids or be related to intrusion of Oligocene rhyolite or Laramide porphyry. An aeromagnetic high south of the district probably reflects a small felsic intrusion of unknown age. We assess the Lake Valley ACEC as having low to moderate potential for undiscovered carbonate-hosted deposits associated with volcanic rocks or Laramide porphyry plutons, and low potential for gold placer and rhyolite tin deposits.

New Mexico↗
USGS1993

Geologic map of the Dillon 1° x 2° quadrangle, Idaho and Montana

The digital ARC/INFO databases included in this website provide a GIS database for the geologic map of the Dillon 1 degree by 2 degree quadrangle of southwest Montana and east-central Idaho. The geologic map was originally published as U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H. This website directory contains ARC/INFO format files that can be used to query or display the geology of USGS Map I-1803-H with GIS software.

Montana↗