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At least 1,009 records · Page 56Linked to original sources
USGS2003

Graphic comparison of reserve-growth models for conventional oil and accumulation

The U.S. Geological Survey (USGS) periodically assesses crude oil, natural gas, and natural gas liquids resources of the world. The assessment procedure requires estimated recover-able oil and natural gas volumes (field size, cumulative production plus remaining reserves) in discovered fields. Because initial reserves are typically conservative, subsequent estimates increase through time as these fields are developed and produced. The USGS assessment of petroleum resources makes estimates, or forecasts, of the potential additions to reserves in discovered oil and gas fields resulting from field development, and it also estimates the potential fully developed sizes of undiscovered fields. The term ?reserve growth? refers to the commonly observed upward adjustment of reserve estimates. Because such additions are related to increases in the total size of a field, the USGS uses field sizes to model reserve growth. Future reserve growth in existing fields is a major component of remaining U.S. oil and natural gas resources and has therefore become a necessary element of U.S. petroleum resource assessments. Past and currently proposed reserve-growth models compared herein aid in the selection of a suitable set of forecast functions to provide an estimate of potential additions to reserves from reserve growth in the ongoing National Oil and Gas Assessment Project (NOGA). Reserve growth is modeled by construction of a curve that represents annual fractional changes of recoverable oil and natural gas volumes (for fields and reservoirs), which provides growth factors. Growth factors are used to calculate forecast functions, which are sets of field- or reservoir-size multipliers. Comparisons of forecast functions were made based on datasets used to construct the models, field type, modeling method, and length of forecast span. Comparisons were also made between forecast functions based on field-level and reservoir- level growth, and between forecast functions based on older and newer data. The reserve-growth model used in the 1995 USGS National Assessment and the model currently used in the NOGA project provide forecast functions that yield similar estimates of potential additions to reserves. Both models are based on the Oil and Gas Integrated Field File from the Energy Information Administration (EIA), but different vintages of data (from 1977 through 1991 and 1977 through 1996, respectively). The model based on newer data can be used in place of the previous model, providing similar estimates of potential additions to reserves. Fore-cast functions for oil fields vary little from those for gas fields in these models; therefore, a single function may be used for both oil and gas fields, like that used in the USGS World Petroleum Assessment 2000. Forecast functions based on the field-level reserve growth model derived from the NRG Associates databases (from 1982 through 1998) differ from those derived from EIA databases (from 1977 through 1996). However, the difference may not be enough to preclude the use of the forecast functions derived from NRG data in place of the forecast functions derived from EIA data. Should the model derived from NRG data be used, separate forecast functions for oil fields and gas fields must be employed. The forecast function for oil fields from the model derived from NRG data varies significantly from that for gas fields, and a single function for both oil and gas fields may not be appropriate.

Bulletin↗
USGS2018

River otter distribution in Nebraska

The river otter ( Lontra canadensis ) was extirpated from Nebraska, USA, in the early 1900s and reintroduced starting in 1986. Information is needed regarding the distribution of river otters in Nebraska before decisions can be made regarding its conservation status. Understanding distribution of a species is critically important for effective management. We investigated river otter distribution in Nebraska with occupancy modeling and maximum entropy (Maxent) modeling using 190 otter sign observations on Nebraska's navigable rivers and 380 historical otter records from November 1977 to April 2014. Both methods identified the Platte River, Elkhorn River, central and eastern Niobrara River, and southern Loup River system as core areas within the distribution of otters in Nebraska. The Maxent model provided more liberal estimates of site occupancy and identified some smaller rivers as being within the distribution of otters in Nebraska, which were not identified using occupancy modeling. We recommend that multiple data sets and analysis methods be used to estimate species distribution because this allows for the broadest geographical coverage and decreases the likelihood of overlooking areas with fewer animal records. If further reintroduction efforts or translocation efforts are to take place in the future, we recommend focusing on areas with high modeled occupancy but few historical and survey records

Nebraska↗
USGS2022

Synthetic aperture radar volcanic flow maps (SAR VFMs): A simple method for rapid identification and mapping of volcanic mass flows

Volcanic mass flows, including lava, pyroclastic density currents, and lahars, account for the bulk of fatalities and infrastructure damage caused by volcanic eruptions. Mapping these flows soon after their emplacement is vital to understanding their impact and to forecasting the likely behavior of potential future flows. Synthetic aperture radar (SAR) can provide useful information about surface properties and changes regardless of environmental conditions or time of day, but no individual SAR product can unambiguously detect and map surface mass flows in all conditions. Combining SAR products, however, can capitalize on the strengths and compensate for the weaknesses of individual data types. SAR volcanic flow maps (SAR VFMs) merge cross-polarized amplitude imagery from two different dates with interferometric coherence spanning those dates. The combination of amplitude change with coherence provides a means of detecting volcanic mass flows regardless of surface conditions, and data collected by satellite provide the spatial coverage needed to detect changes over broad areas. Application to eruptions of Kīlauea (Hawaiʻi), Nyiragongo (Democratic Republic of Congo), Sinabung (Indonesia), and Fuego (Guatemala) demonstrate the value of SAR VFMs for monitoring hazardous volcanic activity, and the importance of acquiring cross-polarized satellite SAR imagery for volcano applications. The ever-growing number of public and private satellite SAR missions will provide for improved temporal resolution in SAR VFMs in the future, and the technique may be suitable for automated analysis that is capable of timely identification of changes due to volcanic activity, even in areas that are otherwise unmonitored.

Hawaii↗
USGS1996

Earthquake mechanisms from linear-programming inversion of seismic-wave amplitude ratios

The amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first-motion polarities, but amplitudes are severely distorted by the effects of heterogeneity in the Earth. This distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases, rather than simple amplitudes, but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal. Searching methods are particularly costly if general (moment tensor) mechanisms are allowed. Efficient linear-programming methods, which do not suffer from these problems, have previously been applied to inverting polarities and wave amplitudes. We extend these methods to amplitude ratios, in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation. Three-component digital data for an earthquake at the Hengill-Grensdalur geothermal area in southwestern Iceland illustrate the power of the method. Polarities of P , SH , and SV waves, unusually well distributed on the focal sphere, cannot distinguish between diverse mechanisms, including a double couple. Amplitude ratios, on the other hand, clearly rule out the double-couple solution and require a large explosive isotropic component.

Bulletin of the Seismological Society of America↗
USGS1994

A field-trip guide to Yellowstone National Park, Wyoming, Montana, and Idaho: Volcanic, hydrothermal, and glacial activity in the region

This field-trip guide was originally prepared for the 7th International Symposium on Water/Rock Interaction (WRI-7) held in July 1992 in Park City, Utah. A large and diversified group of earth scientists and accompanying family members participated in this 3 1/2-day field trip that focused on water/rock interactions over widely ranging temperatures and pressures in the Yellowstone/Grand Teton region. Emphasis was placed on the geochemical and hydrologic characteristics of the thermal waters in the major "geyser basins" of Yellowstone National Park. Information specific to the WRI-7 trip about logistics, lodging, and meals has been deleted from the present guide. The scientific content remains mostly unchanged, except for the addition of a glossary, two illustrations, all photographs, and some text previously presented to the field-trip participants in supplementary materials (see appendix A). Most of the geyser basins in Yellowstone National Park are on a high volcanic plateau at elevations of 2,000 to 2,200 m and are surrounded by much higher mountain ranges. In the middle of summer there generally are cool evenings and early mornings and warm afternoons. Visits to the localities described require short walks, mostly on boardwalks, but some are on what may be wet ground. No long, strenuous climbs are required. Expect brief afternoon thunder showers, particularly at Old Faithful. Please remember that the collecting of any kind of sample in a national park is prohibited except by those who have specific sampling permits issued by the National Park Service. Field-trip participants are asked to leave geologic picks and hammers at home or in their luggage while in Yellowstone National Park.

Idaho, Montana, Wyoming↗
USGS2013

New insights into the diets of harbor seals in the Salish Sea revealed by quantitative fatty acid signature analysis

Harbor seals ( Phoca vitulina ) are an abundant predator along the west coast of North America, and there is considerable interest in their diet composition, especially in regard to predation on valued fish stocks. Available information on harbor seal diets, primarily derived from scat analysis, suggests that adult salmon ( Oncorhynchus spp.), Pacific Herring ( Clupea pallasii ), and gadids predominate. Because diet assessments based on scat analysis may be biased, we investigated diet composition through quantitative analysis of fatty acid signatures. Blubber samples from 49 harbor seals captured in western North America from haul-outs within the area of the San Juan Islands and southern Strait of Georgia in the Salish Sea were analyzed for fatty acid composition, along with 269 fish and squid specimens representing 27 potential prey classes. Diet estimates varied spatially, demographically, and among individual harbor seals. Findings confirmed the prevalence of previously identified prey species in harbor seal diets, but other species also contributed significantly. In particular, Black ( Sebastes melanops ) and Yellowtail ( S. flavidus ) Rockfish were estimated to compose up to 50% of some individual seal diets. Specialization and high predation rates on Black and Yellowtail Rockfish by a subset of harbor seals may play a role in the population dynamics of these regional rockfish stocks that is greater than previously realized.

British Columbia, Washington↗
USGS1960

Mineral paragenesis of precambrian rocks in the Tenmile Range, Colorado

A Precambrian complex of granulite, gneiss, and migmatite, intruded by numerous plutons of granitic rocks correlated with the Silver Plume granite, is exposed in a long narrow belt along the crest and upper slopes of the Tenmile Range , Colorado . The metamorphic rocks are predominantly felsic; bands, lenses, and irregular bodies of mafic rocks rich in biotite, hornblende, and locally in sillimanite and garnet, are interlayered with the felsic rocks . The major lithologic variations in the metamorphic rock complex are believed to be due chiefly to variations in the original sedimentary rocks , which probably were interbedded sandstone, shale, and limestone. The metamorphic rocks and the Silver Plume granite reveal the age relations of quartz and the feldspars, and these relations afford considerable information on the origin and progressive transformation of the rocks . Quartz is the earliest mineral in the metamorphic rocks and is probably a relict mineral of a sandstone. It has been partially replaced by feldspar. It occurs chiefly in irregular clusters, some of which show sutured grains, enclosed in a ramifying network of feldspar. Irregular small apophyses, barbs, and prongs of feldspar penetrate the quartz clusters along grain boundaries and healed fractures in the quartz. In some of the least feldspathized quartzose metamorphic rocks the feldspar is clearly interstitial to the quartz. Quartz also occurs in feldspar as small spherical inclusions. The relations of the quartz to the feldspars show clearly that a quartzose host rock was replaced by feldspar along quartz grain boundaries, pre-existing healed fractures, and margins of shadowy areas in strained quartz grains. The textural relations of the other principal minerals in the metamorphic rocks show that plagioclase formed earlier than the microcline and that the micas were the last of the principal minerals to form. Identical paragenetic relations are found in the Silver Plume granite, and the writer concludes that the Silver Plume granite was derived by partial fusion of quartzose metamorphic rocks .

Colorado↗
USGS1960

Review of paleomagnetism

This review is an attempt to bring together and discuss relevant information concerning the magnetization of rocks, especially that having paleomagnetic significance. All paleomagnetic measurements available to the authors are here compiled and evaluated, with a key to the summary table and illustrations in English and Russian. The principles upon which the evaluation of paleomagnetic measurements is based are summarized, with special emphasis on statistical methods and on the evidence and tests for magnetic stability and paleomagnetic applicability. Evaluation of the data summarized leads to the following general conclusions: (1) The earth's average magnetic field, throughout Oligocene to Recent time, has very closely approximated that due to a dipole at the center of the earth oriented parallel to the present axis of rotation. (2) Paleomagnetic results for the Mesozoic and early Tertiary might be explained more plausibly by a relatively rapidly changing magnetic field, with or without wandering of the rotational pole, than by large-scale continental drift. (3) The Carboniferous and especially the Permian magnetic fields were relatively very “steady” and were vastly different from the present configuration of the field. (4) The Precambrian magnetic field was different from the present field configuration and, considering the time spanned, was remarkably consistent for all continents.

GSA Bulletin↗
USGS2026

Rupture into slow-slip fault regime during the 2018 Mw 6.9 Island of Hawaiʻi earthquake is followed by modest postseismic slip

On 4 May 2018, a M w 6.9 earthquake occurred on the south flank of Kīlauea, in the midst of an historic event that included a voluminous eruption from Kīlauea’s lower East Rift zone and caldera collapse at its summit. The earthquake was a consequence of both short‐ and long‐term stress buildup due to magmatic activity associated with the eruption and steady flank motion, respectively, and it revealed features of Kīlauea’s décollement fault that can inform understanding of future earthquake activity. We used geodetic data to determine the distributions of slip during the coseismic and postseismic periods and compared these with areas of known fault slip during past earthquakes and slow‐slip events (SSEs). The 2018 earthquake ruptured into an area of the décollement fault that was active during quasi‐regular SSEs that occurred in the two decades prior to 2018 but that have not been observed since. The coseismic slip model indicates that the amount of motion on the décollement fault was several times greater than what typically occurred during SSEs, suggesting that it may take decades for the fault to rebuild stress to the point at which SSEs will occur again. Postseismic afterslip also occurred in an area of the fault known to experience slow slip; however, unlike at other creeping faults, postseismic afterslip was rapid, being largely over within 2–3 days. The rapid nature and small magnitude of the postseismic afterslip may be due to the lack of a viscoelastic relaxation component, which is possibly a result of the shallow dip of the décollement fault not transferring stress efficiently into the lower crust.

Hawaii↗
USGS1992

Text and References To Accompany "Map Showing the Thickness and Character of Quaternary Sediments in the Glaciated United States East of the Rocky Mountains"

A 1:1,000,000-scale map of Quaternary deposits has been compiled for the glaciated area of the United States east of the Rocky Mountains (that is, the area covered by the Laurentide ice sheets). Parts of southern Ontario, areas beneath the Great Lakes, and parts of the submerged eastern seaboard are also included on the map. The map has three components that, together, provide the first regional three-dimensional view of these deposits. These map components are the surface distribution of Quaternary sediments, the total thickness of Quaternary sediments, and the distribution of significant buried Quaternary units. For many areas, this is the first map of Quaternary sediment thickness published at any scale. This report provides supporting information for the map, preliminary interpretations of sediment distribution, and the list of geologic sources used to generate the map. Within the mapped area, there is a particular need for three-dimensional geologic mapping to support decisions on water resources and land use. Approximately 40 percent of the U.S. population resides within the mapped area, which is less than one-quarter the size of the conterminous United States. This map is intended to supplement the more detailed mapping on which it is based and is designed to be a regional planning tool. Through the Pleistocene, large deposits of thick glacial sediment accumulated between certain late Wisconsinan glacial lobes, on bedrock topographic highs, whereas relatively thin deposits generally accumulated in the adjacent bedrock lowlands occupied by drainage and ice lobes. The lithology of the bedrock and its resistance to erosion in part controlled the patterns of ice lobation and the distribution of thick sediment. On a local scale, the spatial relation of these sediment masses to ice lobation has been suggested in places, and a regional correlation may have been assumed. This map provides the first comprehensive, regional view of glacial sediment thickness to permit such a correlation to be assessed.

Bulletin↗
USGS1948

Submarine geology of Bikini atoll

The program of investigations made in connection with the atomic bomb tests in the summer of 1946 at Bikini Atoll provided a rare opportunity for obtaining information on the physiography and sediments of atolls. The outer slopes around Bikini Atoll rise from a depth of about 2500 fathoms in a long gradually steepening curve. Between 0 and 200 fathoms the average slope is 25°. On the windward side, the reef at the top of the slope is bordered by a narrow 15-fathom terrace, but on the leeward side by a steep, locally vertical, cliff extending to 35 fathoms. Contours of the outer slopes reveal that a flat-topped mass having nearly the area of Bikini lagoon but below 700 fathoms extends to the northwest. The lagoon itself is saucer-shaped and has a maximum depth of 34 fathoms. Around the lagoon and bordering the inner side of the reef and islands is a 12-fathom terrace. Coral knolls rise abruptly from the lagoon floor, and some of them reach to within a few fathoms of the surface. The middle of the lagoon is floored chiefly by algal debris, whereas the shallow edges are covered by algal and foraminiferal sand. Coral comprises a relatively small percentage of the bottom materials. The outer slopes consist of algal debris grading outward to fine sand and finally to Globigerina sand.

GSA Bulletin↗
USGS1999

Variation in glycogen concentrations within mantle and foot tissue in Amblema plicata plicata: Implications for tissue biopsy sampling

With the development of techniques to non-lethally biopsy tissue from unionids, a new method is available to measure changes in biochemical, contaminant, and genetic constituents in this imperiled faunal group. However, before its widespread application, information on the variability of biochemical components within and among tissues needs to be evaluated. We measured glycogen concentrations in foot and mantle tissue in Amblema plicata plicata (Say, 1817) to determine if glycogen was evenly distributed within and between tissues and to determine which tissue might be more responsive to the stress associated with relocating mussels. Glycogen was measured in two groups of mussels: those sampled from their native environment (undisturbed mussels) and quickly frozen for analysis and those relocated into an artificial pond (relocated mussels) for 24 months before analysis. In both undisturbed and relocated mussels, glycogen concentrations were evenly distributed within foot, but not within mantle tissue. In mantle tissue, concentrations of glycogen varied about 2-fold among sections. In addition, glycogen varied significantly between tissues in undisturbed mussels, but not in relocated mussels. Twenty-four months after relocation, glycogen concentrations had declined by 80% in mantle tissue and by 56% in foot tissue relative to the undisturbed mussels. These data indicate that representative biopsy samples can be obtained from foot tissue, but not mantle tissue. We hypothesize that mantle tissue could be more responsive to the stress of relocation due to its high metabolic activity associated with shell formation.

American Malacological Bulletin↗
USGS2021

Towards building a sustainable future: Positioning ecological modelling for impact in ecosystems management

As many ecosystems worldwide are in peril, efforts to manage them sustainably require scientific advice. While numerous researchers around the world use a great variety of models to understand ecological dynamics and their responses to disturbances, only a small fraction of these models are ever used to inform ecosystem management. There seems to be a perception that ecological models are not useful for management, even though mathematical models are indispensable in many other fields. We were curious about this mismatch, its roots, and potential ways to overcome it. We searched the literature on recommendations and best practices for how to make ecological models useful to the management of ecosystems and we searched for ‘success stories’ from the past. We selected and examined several cases where models were instrumental in ecosystem management. We documented their success and asked whether and to what extent they followed recommended best practices. We found that there is not a unique way to conduct a research project that is useful in management decisions. While research is more likely to have impact when conducted with many stakeholders involved and specific to a situation for which data are available, there are great examples of small groups or individuals conducting highly influential research even in the absence of detailed data. We put the question of modelling for ecosystem management into a socio-economic and national context and give our perspectives on how the discipline could move forward.

Bulletin of Mathematical Biology↗
USGS2017

A spatiotemporal clustering model for the Third Uniform California Earthquake Rupture Forecast (UCERF3‐ETAS): Toward an operational earthquake forecast

We, the ongoing Working Group on California Earthquake Probabilities, present a spatiotemporal clustering model for the Third Uniform California Earthquake Rupture Forecast (UCERF3), with the goal being to represent aftershocks, induced seismicity, and otherwise triggered events as a potential basis for operational earthquake forecasting (OEF). Specifically, we add an epidemic‐type aftershock sequence (ETAS) component to the previously published time‐independent and long‐term time‐dependent forecasts. This combined model, referred to as UCERF3‐ETAS, collectively represents a relaxation of segmentation assumptions, the inclusion of multifault ruptures, an elastic‐rebound model for fault‐based ruptures, and a state‐of‐the‐art spatiotemporal clustering component. It also represents an attempt to merge fault‐based forecasts with statistical seismology models, such that information on fault proximity, activity rate, and time since last event are considered in OEF. We describe several unanticipated challenges that were encountered, including a need for elastic rebound and characteristic magnitude–frequency distributions (MFDs) on faults, both of which are required to get realistic triggering behavior. UCERF3‐ETAS produces synthetic catalogs of M ≥2.5 events, conditioned on any prior M ≥2.5 events that are input to the model. We evaluate results with respect to both long‐term (1000 year) simulations as well as for 10‐year time periods following a variety of hypothetical scenario mainshocks. Although the results are very plausible, they are not always consistent with the simple notion that triggering probabilities should be greater if a mainshock is located near a fault. Important factors include whether the MFD near faults includes a significant characteristic earthquake component, as well as whether large triggered events can nucleate from within the rupture zone of the mainshock. Because UCERF3‐ETAS has many sources of uncertainty, as will any subsequent version or competing model, potential usefulness needs to be considered in the context of actual applications.

California↗
USGS2020

Interpreting and reporting 40Ar/39Ar geochronologic data

The 40 Ar/ 39 Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40 Ar/ 39 Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40 Ar/ 39 Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40 Ar/ 39 Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40 Ar/ 39 Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity.

GSA Bulletin↗
USGS2002

Magnitude estimates of two large aftershocks of the 16 December 1811 New Madrid earthquake

The three principal New Madrid mainshocks of 1811-1812 were followed by extensive aftershock sequences that included numerous felt events. Although no instrumental data are available for either the mainshocks or the aftershocks, available historical accounts do provide information that can be used to estimate magnitudes and locations for the large events. In this article we investigate two of the largest aftershocks: one near dawn following the first mainshock on 16 December 1811, and one near midday on 17 December 1811. We reinterpret original felt reports to obtain a set of 48 and 20 modified Mercalli intensity values of the two aftershocks, respectively. For the dawn aftershock, we infer a Mw of approximately 7.0 based on a comparison of its intensities with those of the smallest New Madrid mainshock. Based on a detailed account that appears to describe near-field ground motions, we further propose a new fault rupture scenario for the dawn aftershock. We suggest that the aftershock had a thrust mechanism and occurred on a southeastern limb of the Reelfoot fault. For the 17 December 1811 aftershock, we infer a M W of approximately 6.1 ± 0.2 . This value is determined using the method of Bakun et al. (2002), which is based on a new calibration of intensity versus distance for earthquakes in central and eastern North America. The location of this event is not well constrained, but the available accounts suggest an epicenter beyond the southern end of the New Madrid Seismic Zone.

Arkansas, Illinois, Missouri, Tennessee↗
USGS2000

The northeastern states' waterfowl breeding population survey

Efforts to tailor waterfowl hunting regulations to conditions in the Atlantic Flyway have been hampered by lack of information on local breeding populations. The Atlantic Flyway Council's technical section voted at its 1987 winter meeting (Atlantic Flyway Council Technical Section, Toronto, Canada) to establish a regional waterfowl breeding survey. Consequently, an annual survey was started in 1989 and further refined in 1993 using results from 1989 to 1992. During 1993-1997, annual spring surveys of more than 1,450 randomly selected 1-km2 plots, stratified by physiographic strata, were conducted in the Atlantic Flyway from New Hampshire to Virginia to estimate breeding populations of mallards (Arias platyrhynchos), American black ducks (A. rubripes), wood ducks (Aix sponsa), and Canada geese (Branta canadensis). Ground crews systematically surveyed all potential waterfowl habitat for these species in each plot. The adjusted mean mallard pair estimate over the 5-year period was 375,962 (range 310,299-415,182, mean SE 25,761) for the region surveyed. The estimate for black duck pairs was 31,1 54 (range 27,164'37,521, mean SE 4,978), and for wood duck pairs it was 240,473 (range 218,959-281,916, mean SE 25,408). Total number of Canada geese increased from 526,663 in 1993 to 892,278 in 1997. Population estimates for other species had unacceptably large standard errors.

Wildlife Society Bulletin↗
USGS2022

Late Cretaceous time-transgressive onset of Laramide arch exhumation and basin subsidence across northern Arizona−New Mexico, USA, and the role of a dehydrating Farallon flat slab

Spatiotemporal constraints for Late Cretaceous tectonism across the Colorado Plateau and southern Rocky Mountains (northern Arizona−New Mexico, USA) are interpreted in regards to Laramide orogenic mechanisms. Onset of Laramide arch development is estimated from cooling recorded in representative thermochronologic samples in a three-step process of initial forward models, secondary HeFTy inverse models with informed constraint boxes, and a custom script to statistically estimate timing of rapid cooling from inverse model results. Onset of Laramide basin development is interpreted from increased rates of tectonic subsidence. Onset estimates are compared to published estimates for Laramide timing, and together suggest tectonism commenced ca. 90 Ma in northwestern Arizona and progressed eastward with later onset in north-central New Mexico by ca. 75−70 Ma. The interpreted sweep of onset progressed at a rate of ∼50 km/m.y. and was approximately half the 100−150 km/m.y. rate estimated for Late Cretaceous Farallon-North America convergence during the same timeframe. Previous suggestions that the Laramide tectonic front progressed at a rate similar to convergence via basal traction are not supported by our results. We thereby suggest that (1) a plate margin end load established far field compression and that (2) sequential Laramide-style strain was facilitated by progressive weakening of North American lithosphere from the dehydrating Farallon flat slab. Results are compared to models of sweeping tectonism and magmatism in other parts of the Laramide foreland. Discussions of the utility of the custom script and the potential for stratigraphic constraints to represent only minimum onset estimates are also presented.

Arizona, New Mexico↗