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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 775 records · Page 43Linked to original sources
USGS2002

The Commerce geophysical lineament and its possible relation to Mesoproterozoic igneous complexes and large earthquakes in the central Illinois Basin

New inversions of existing magnetic and gravity data lead to insights on upper crustal structures in the central Illinois basin. The results of 2D and 3D inversion techniques suggest that the source of the Commerce geophysical lineament follows the southeast boundary of a dense and magnetic, northeast-trending igneous center, named the Vincennes igneous center. Thus the Commerce geophysical lineament, defining the 5- to 10-km-wide Commerce deformation zone, appears to have influenced the structural development of the Vincennes igneous center. Overlying this igneous center is the Centralia seismic-reflection sequence, expressed as highly coherent reflectors ( McBride and Kolata, 1999 ). We suggest that the buried Vincennes igneous center is the source of inferred volcanic units of the Centralia sequence and is related to a rifted margin or a Proterozoic plate boundary. A comparison of gravity and magnetic fields over the Vincennes igneous center and the St. Francois Mountains igneous center in southeastern Missouri suggests that the associated sources in these regions are similar in composition and perhaps origin. Such a conclusion, although speculative, suggests that ∼1.47 Ga-year-old volcanic fields of high-silica rocks, with more abundant mafic components at depth, characterize basement in the regions of the Vincennes igneous center and the St. Francois Mountains. Further, we conclude that the Commerce deformation zone evolved in the Mesoproterozoic (1.1 to 1.5 Ga) as a major cratonic rheological boundary and was the focus of episodic reactivation related to varying stress regimes throughout its history. Spatial relations of the Commerce deformation zone with large Pleistocene and Holocene earthquakes suggest that the zone represents a major rheological boundary intimately related to both surface and deep structures and to the seismic hazard of the Illinois basin region. Assuming recent right-lateral slip along the Commerce deformation zone, we propose that a jog or left step in the Vincennes area leads to thrusting or a restraining bend, where associated stress accumulations may have resulted in nearby large prehistoric earthquakes and may also be the nucleation sites of future large earthquakes.

Illinois, Indiana, Kentucky↗
USGS2020

Black oystercatcher (Haematopus bachmani) population size, use of marine reserve complexes, and spatial distribution in Oregon

The Black Oystercatcher is a large shorebird found along the west coast of North America. Because of their small global population size, low reproductive rate, and dependence on rocky intertidal habitats, they are considered a “species of high conservation concern” and may act as an indicator of intertidal ecosystem health. In 2015, the Audubon Society of Portland initiated a 3-year shore-based population survey in Oregon building upon long-term monitoring previously conducted by the U.S. Geological Survey (USGS) and others. The objectives were to 1) Estimate the current minimum population of breeding Black Oystercatchers in Oregon and to compare that to previous estimates to better understand the population trend; 2) Document oystercatcher abundance adjacent to the Oregon’s system of Marine Reserves and Marine Protected Areas; and 3) Describe spatial distribution of breeding oystercatchers along the coast. We targeted all rocky shoreline habitats along Oregon’s coastline to perform abundance surveys each spring. A total of 75 survey routes were sampled using a standardized protocol. Trained volunteer community scientists conducted the majority of the surveys. We used N-mixture statistical models to estimate oystercatcher population size and probability of detection. Population estimates from the best fitting models were consistent, with estimates ranging from 506 oystercatchers in 2016 (95% credible interval, 463-560) to 629 (548-743) in 2015. These estimates indicated a small but stable population. Probability of detection remained consistent across years (ranging from 0.51 to 0.53). The effect of geographic region corresponded with greater bird density in the southern region of Oregon. Oystercatcher abundance adjacent to MR/MPAs accounted for between 12.4-18.3% of the total population estimate which was lower than expected (~25%). We recommend that subsequent conservation efforts directed on Black Oystercatchers in Oregon balance limiting human disturbance, particularly on the north and central coasts, with ensuring protection of core habitats on the south coast where much of the population resides.

Oregon↗
USGS2005

Integrated provenance analysis of a complex orogenic terrane: Mesozoic uplift of the Bogda Shan and Inception of the Turpan-Hami Basin, NW China

We employ petrographic and advanced geochemical techniques to better document the evolution of the Turpan–Hami basin based on the unique geologic histories of the arc terranes that served as potential sources of Turpan–Hami deposits. First, a provenance study of Permian through Cretaceous sandstone of the Turpan–Hami basin reveals temporal and spatial changes in dominant source terranes that provided detritus to the basin. Volcanic-lithic-rich Upper Permian sandstone (mean Qm 19 F 18 Lt 63 ; Qp 7 Lvm 89 Lsm 4 ; Qm 48 P 39 K 13 ) followed by more quartzose compositions in Triassic sandstone (mean Qm 41 F 19 Lt 40 ; Qp 20 Lvm 75 Lsm 5 ; Qm 68 P 21 K 11 ) indicate progressive unroofing of the extinct northern and central Tian Shan arc terranes to the south of Turpan–Hami. A sharp change to sedimentary-lithic-rich Lower Jurassic sandstone (mean Qm 47 F 16 Lt 37 ; Qp 16 Lvm 42 Lsm 42 ; Qm 75 P 12 K 13 ) overlain by a return to volcanic–lithic-rich Middle Jurassic sandstone (mean Qm 39 F 21 Lt 40 ; Qp 14 Lvm 51 Lsm 35 ; Qm 65 P 21 K 14 ) points to the initial uplift and unroofing of the largely andesitic Bogda Shan to the north, which first shed its sedimentary cover as it emerged to become the partition between the Turpan–Hami and southern Junggar basins. Second, geochronological, trace-element, and Sm-Nd isotopic variations among granitoids in the late Paleozoic Tian Shan orogenic belt provide a further test of Mesozoic uplift of the Bogda Shan. On the basis of previous models of crustal compositions throughout the South, Central, and North Tian Shan, Bogda Shan, and East and West Junggar terranes, we infer that isotopically enriched granitic cobbles (average εNd i = −0.50, n = 6) contained in Lower Triassic deposits in the north-central Turpan–Hami basin were derived from the continental crustal Central Tian Shan terrane, south of Turpan–Hami, and not from the more oceanic North Tian Shan, Bogda Shan, and East and West Junggar terranes, north of the Turpan–Hami basin. We therefore infer that the ancestral Bogda Shan had not been uplifted by the Early Triassic, and that prior to this time, a unified Junggar–Turpan–Hami basin existed during Late Permian deposition of extensive lacustrine deposits

Turpan-Hami Basin↗
USGS2001

Effect of the 1997-1998 ENSO-related drought on hydrology and salinity in a Micronesian wetland complex

The potential effects of global climate change on coastal ecosystems have attracted considerable attention, but the impacts of shorter-term climate perturbations such as ENSO (El Niño-Southern Oscillation) are lesser known. In this study, we determined the effects of the 1997–1998 ENSO-related drought on the hydrology and salinity of a Micronesian mangrove ecosystem and an adjacent freshwater swamp. A network of 9 piezometer clusters installed at the study site served as sampling points for continuous and manual measurements of salinity and water level. During the drought period from January through April 1998, mean water table levels in the mangroves and freshwater swamp were approximately 12 and 54 cm lower, respectively, than during May through December when precipitation returned to near normal levels. At the peak of the drought (February 1998), the most dramatic result was a reversal in groundwater flow that sent groundwater from the mangroves upstream toward the freshwater swamp. Flow nets constructed for this period and immediately after illustrate the strong hydrological linkage between the two systems. This linkage was also illustrated by measurements of groundwater salinity in the piezometer network. Ninety-six percent of the salinity measurements taken in the mangroves during the study were at least 10‰ less than the salinity of sea water, indicating that the mangroves were consistently receiving freshwater flows. An analysis of variance of groundwater salinity measurements during and after the drought showed that salinity levels in the 0.5 and 1.0 m depth piezometers were greater during than after the drought. In a comparison of salinity values in 0.5-m wells during low tide, mean salinity was approximately twice as high during the drought than after (14.7‰ versus 6.2‰, respectively). This study demonstrates that short-term climate perturbations such as ENSO can disrupt important coastal processes. Over repeated drought cycles, such perturbations have the potential to affect the structure and function of mangrove forests and upstream ecosystems.

Kosrae↗
USGS1967

The Peromyscus guardia-interparietalis complex

Peromyscus interparietalis is considered to be specifically distinct from P. guardia , of which it was originally considered a subspecies. Each species includes three subspecifically distinct populations, each endemic to an island in the northern Gulf of California, Baja California, Mexico. Two subspecies of P. interparietalis and one of P. guardia are newly described here. The mice are widespread on the islands, apparently favoring no particular microhabitat. Reproduction takes place in early spring.

Gulf of California↗
USGS1990

Search path of a fossorial herbivore, Geomys bursarius , foraging in structurally complex plant communities

The influence of habitat patchiness and unpalatable plants on the search path of the plains pocket gopher ( Geomys bursarius ) was examined in outdoor enclosures. Separate experiments were used to evaluate how individual animals explored (by tunnel excavation) enclosures free of plants except for one or more dense patches of a palatable plant ( Daucus carota ), a dense patch of an unpalatable species ( Pastinaca sativa ) containing a few palatable plants ( D. carota ), or a relatively sparse mixture of palatable ( D. carota ) and unpalatable ( Raphanus sativus ) species. Only two of eight individuals tested showed the predicted pattern of concentrating search effort in patches of palatable plants. The maintenance of relatively high levels of effort in less profitable sites may reflect the security afforded food resources by the solitary social system and fossorial lifestyle of G. bursarius . Unpalatable plants repelled animals under some conditions, but search paths in the sparsely planted mixed-species treatment suggest animals can use visual or other cues to orient excavations. Evidence supporting area-restricted search was weak. More information about the use of visual cues by G. bursarius and the influence of experience on individual search mode is needed for refining current models of foraging behavior in this species.

Journal of Mammalogy↗
USGS2008

A morphological review of the Cuora flavomarginata complex (Testudines: Geoemydidae)

A reevaluation of the morphometric and color pattern differences within the Asiatic box turtle, Cuora flavomarginata sensu latu, was conducted in view of determining the taxonomic position of the three currently recognized subspecies: C. f. flavomarginata (Taiwan), C. f. sinensis (southern mainland China), and C. f. evelynae (Ryukyu Islands, Japan). Recent analyses indicate that the allopatric population of C. f. evelynae is the most divergent of the three taxa and shares little possibility for gene exchange with the other two populations. In contrast, the populations of C. f. flavomarginata and C. f. sinensis share many characters. We recommend the recognition of the Ryukyu population as a full species, C. evelynae.

Proceedings of the Biological Society of Washingto↗
USGS2016

Long-term deer exclusion has complex effects on a suburban forest understory

Herbivory by deer is one of the leading biotic disturbances on forest understories (i.e., herbs, small shrubs, and small tree seedlings). A large body of research has reported declines in height, abundance, and reproductive capacity of forbs and woody plants coupled with increases in abundance of graminoids, ferns, and exotic species due to deer herbivory. Less clear is the extent to which (and the direction in which) deer alter herbaceous layer diversity, where much of the plant diversity in a forest occurs. We examined the effect of 15 y of deer exclusion on the understory of a suburban hardwood forest in Connecticut exposed to decades of intensive herbivory by white-tailed deer ( Odocoileus virginianus ). We compared species richness (at subplot and plot scale), individual species and life form group abundance (% cover), and community composition between grazed and exclosure plots, as well as between mesic and wet soil blocks. Forb cover was more than twice as abundant in exclosure as in grazed plots, whereas sedge ( Carex spp.) cover was 28 times more abundant, and exotic species cover generally higher in grazed than in exclosure plots. Native and exotic species richness were both higher in grazed than exclosure plots at the subplot scale, and native herbaceous richness was higher in grazed plots at both spatial scales. In contrast, native shrub richness increased with deer exclusion at the plot scale. Our results suggest that deer exclusion had contrasting effects on species richness, depending on plant life form, but that overall richness of both exotic and native plants declined with deer exclusion. In addition, site heterogeneity remained an important driver of vegetation dynamics even in the midst of high deer densities.

Rhodora↗
USGS1975

Flood hazards in the Seattle-Tacoma urban complex and adjacent areas, Washington

Floods are natural hazards that have complicated man's land-use planning for as long as we have had a history. Although flood hzards are a continuing danger, the year-to-year threat cannot be accurately predicted. Also, on any one stream, the time since the last destructive flood might be so long that most people now living near the stream have not experienced such a flood. Because of the unpredictability and common infrequency of disastrous flooding, or out of ignorance about the danger, or perhaps because of an urge to gamble, man tends to focus his attention on only the advantages of the flood-prone areas, rather than the risk due to the occasional major flood. The purposes of this report are to: (1) briefly describe flood hazards in this region, including some that may be unique to the Puget Sound basin, (2) indicate the parts of the area for which flood-hazard data are available, and (3) list the main sources of hydrologic information that is useful for flood-hazard analysis in conjuction with long-range planning. This map-type report is one of a series being prepared by the U.S. Geological Survey to present basic environmental information and interpretations to assist land-use planning in the Puget Sound region.

Washington↗