Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska     

Florence R. Weber  Thomas D. Hamilton  David M. Hopkins  Charles A. Repenning  Herbert Haas 《Quaternary Research》1981,16(2):167-180

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000–17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf.O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode.  相似文献   

Aspects of the mineralogy and hydrometallurgy of chrysocolla,with special reference to the Cuajone,Peru, ores     

Jonathan M. Horlick  W. Charles Cooper  Alan H. Clark 《International Journal of Mineral Processing》1981,8(1):49-59

Chrysocolla in the Cuajone ores appears to be microcrystalline and to exhibit a fibrous structure.Sulphuric acid leaching of the chrysocolla is facilitated by a microcracked surface structure. A marked surface structural change is evidenced as hydrogen ions replace the copper. The end result is a noncontinuous surface layer of silica from which the copper has been essentially completely removed.The results of this study provide confirmatory evidence for the structure and hydrometallurgy of chrysocolla.  相似文献   

Defining hydroclimatic regions using daily rainfall characteristics in the southern Appalachian Mountains     

Johnathan W. Sugg  Charles E. Konrad II 《International Journal of Digital Earth》2020,13(7):785-802

ABSTRACT

This paper addresses warm season hydroclimatic variability in the southern Appalachian region of the southeastern U.S., where precipitation can vary as much as 127?mm or more, with maximum seasonal totals exceeding 736?mm in extreme cases. Despite the occurrence of droughts, floods, and their socioecological impacts, hydroclimate variability is still poorly understood. This study characterizes the regional scale variations in the hydroclimate by examining the daily distribution of precipitation patterns in different topographic environments. Parameter-elevation relationships on independent slopes model (PRISM) gridded precipitation estimates are used to identify the location and frequency of different types of rainfall events. Several types of clustering algorithms are used as a regionalization approach to define areas where the precipitation regime exhibits similarities in its frequency of occurrence. The results are compared with internal validation statistics and a visualization is used to assess how well the resulting hydroclimatic regions align with different topographic environments. This study reveals the intricate spatial footprint of dry and wet regimes and demonstrates how clustering applications can be used with gridded climate data to determine where extremes are most likely to develop across mountain catchments.  相似文献   

Estimates of the position of sea level between 140,000 and 75,000 years ago     

Charles E. Stearns 《Quaternary Research》1976,6(3):445-449

The absolute elevations of sea level 103,000 and 82,000 years ago have been estimated as ?15 and ?13 m, respectively, from the present elevations of emergent reefs on Barbados (Broecker et al., 1968; Matthews, 1973; Bloom et al., 1974). The “Barbados model” requires two assumptions: (1) that sea level was +6 m 124,000 years ago, and (2) that rates of uplift on short individual traverses have been uniform during the last 125,000 years.A test of the derived values on Barbados itself does not yield uniform rates of uplift between 124,000 and 82,000 years ago. Less reliably dated strand line features on less uplifted coasts suggest that sea level 124,000 years ago differed from sea levels 103,000 and 82,000 years ago by smaller amounts than those suggested by the “Barbados model.” Such smaller differences yield more uniform rates of uplift between 124,000 and 82,000 years ago, on New Guinea as well as on Barbados, than do the larger. The “Barbados model” is not sufficiently precise to yield close estimates of past elevations of sea level. Better values will eventually be derived from low uplift coasts, when stratigraphic and radiometric data from them have achieved the credibility of data from moderate to high uplift coasts.  相似文献   

Blake polarity episode in two cores from the Greater Antilles Outer Ridge     

Charles R. Denham 《Earth and Planetary Science Letters》1976,29(2):422-434

Two large-diameter cores from the Greater Antilles Outer Ridge have confirmed the Blake episode 0.1 m.y. B.P. as a genuine paleomagnetic reversed interval at least in that region. The feature is clearly defined in more than 125 stably magnetized specimens of Last Interglacial abyssal brown clay, but its precise age and duration cannot yet be estimated reliably from these or other available data. During the reversed period, positions of the virtual geomagnetic pole lay about 20° from the south geographic pole, with polarity transitions traversing paths in the eastern hemisphere. Each core also recorded a normally polarized excursion within the Blake feature. Because the most acceptable Blake episode data presently span only a small geographic area, they are insufficient for distinguishing between global and local geomagnetic models for the feature.  相似文献   

The Anderson Reservoir seismic gap — Induced aseismicity?     

Charles G. Bufe 《Engineering Geology》1976,10(2-4):255-262

A persistent 10-km seismicity gap along the Calaveras fault appears to be related to the presence of the Leroy Anderson Reservoir in the Calaveras-Silver Creek fault zones southeast of San Jose, California. A magnitude-4.7 earthquake occurred at a depth of 5 km in the centre of the gap on October 3, 1973. The sequence of immediate aftershocks usually accompanying shallow earthquakes of this magnitude in central California did not occur. A bridge crossing the reservoir near its southeast end has been severely deformed, apparently the result of tectonic creep on the Calaveras fault. The occurrence of creep and absence of small earthquakes along the Calaveras in the vicinity of the reservoir suggest a transition from stick slip to stable sliding, possibly brought about by increased pore pressure.  相似文献   

Generation of available buoyant energy by cloud glaciation     

Charles F. Chappell  David R. Smith 《Pure and Applied Geophysics》1975,113(1):825-836

The available buoyant energy (ABE, energy from the environment which becomes available to a parcel for buoyant accelerations) arising from glaciation is computed by integrating upward the differences in temperature between a parcel that undergoes instantaneous and isenthalpic freezing followed by an ice-saturation ascent, and one that experiences only a water-saturation ascent from the same initial cloud base conditions. This quantity is computed for three initial cloud base conditions representative of tropical, High Plains summertime, and Great Lakes wintertime cumuli. Substantial increases in parcel updraft speed are realized for all clouds if the ABE arising from glaciation is completely converted to parcel kinetic energy. Variations of the three components of parcel heating involved in the glaciation process (i.e., (1) release of latent heat of fusion from freezing of liquid water, (2) cooling or warming from sublimation or deposition as vapor pressure adjusts from water saturation to ice saturation at the post glaciation temperature, and (3) the additional warming or cooling relative to the intial water-saturation adiabat as the parcel follows an icesaturation ascent to a specified upper reference level) are also determined as functions of glaciation temperature. It is found that sublimation substantially counteracts the parcel warming arising from the freezing of liquid water in the case of warm moist cumuli. In addition, it is found that in some instances ice-saturation ascent following glaciation can produce cooling relative to the initial departure from the water saturation adiabat. This was indicated for Great Lakes wintertime cumuli and also for warm moist cumuli with glaciations at very cold temperatures. The effect upon the buoyancy force, of the change in the mass of condensate during glaciation, is small and can usually be neglected.  相似文献   

Evolved lavas from the Snake River Plain: Craters of the Moon National Monument,Idaho   总被引：4，自引：0，他引：4  

William P. Leeman  Charles J. Vitaliano  Martin Prinz 《Contributions to Mineralogy and Petrology》1976,56(1):35-60

Holocene lavas from Craters of the Moon (COM) National Monument are representative of differentiated lavas which occur around the margins of the Snake River Plains (SRP) and they range serially in composition from alkali- and phosphorous-rich ferrobasalts to ferrolatites. Petrographic study indicates that these lavas evolved primarily by cotectic crystallization of olivine, plagioclase, magnetite and apatite in the mafic members of the suite (ferrobasalts), and by cotectic crystallization of plagioclase, magnetite, clinopyroxene and minor olivine in the salic members. Quantitative phase relations in the COM lavas, calculated by means of a leastsquares mixing program, indicate that the observed range in composition among these lavas corresponds to at least 70 percent crystallization of a magma similar to the most mafic COM lavas. Anhydrous one-atmosphere experimental crystallization studies fail to reproduce exactly the inferred phase relations; the discrepancy is attributed to the presence of water in the naturally crystallized magmas. The origin of COM parental magma cannot be unequivocably resolved. Available evidence suggests that COM lavas do not represent melts derived directly from the mantle: (1) high Sr⁸⁷/Sr⁸⁶ ratios (0.708 to 0.712), (2) relatively high Fe/(Fe+Mg) and excluded-element content in even the most mafic COM lavas, (3) occurrence of megacrysts of inferred high-pressure origin in the Lava Creek flow. Megacrysts occur in the Lava Creek flow as clusters of labradorite, aluminous clinopyroxene, and olivine. Analogy with the experiments of Thompson [1] and least squares mixing calculations indicate that intermediate (ca. 8 to 10 Kbar) pressure fractionation of such megacrysts from olivine tholeiite magma may yield derivative COM-type liquids.  相似文献   

An approach to the modeling of lakes     

Prof. Charles R. O’Melia 《Aquatic Sciences - Research Across Boundaries》1972,34(1):1-33

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The sillimanite-potash feldspar isograd in Western Maine,U.S.A.     

Bernard W. Evans  Charles V. Guidotti 《Contributions to Mineralogy and Petrology》1966,12(1):25-62

The techniques of electron probe microanalysis and x-ray diffractometry have been utilized in a study of the sillimanite-potassium feldspar isograd in western Maine. The isograd reaction is theoretically a discontinuous one, calling for the nearly instantaneous loss of muscovite and crystallization of sillimanite and orthoclase, with a small contribution of albite from the pre-existing plagioclase. In fact, muscovite coexists with orthoclase, sillimanite, and plagioclase for a distance of at least seven miles from the isograd (marked by the initial coexistence of orthoclase and sillimanite). In this assemblage, muscovite has an extremely narrow range of composition, about an average of Ms_93.5Pg_6.5. A possible explanation for the divariant character of the isograd reaction is that, during dehydration, PH₂O slowly increased from initial values less than P_total + rock strength, under conditions of low permeability, the actual value of PH₂O being controlled by a buffer assemblage and local conditions of P and T. An alternative explanation postulates the flattening of thermal gradients following the onset of fractional melting. The isograd reaction is dependent in only a minor way upon the anorthite content of the plagioclase. Below the isograd, a continuous reaction takes place leading to a diminution in paragonite content of muscovite stable in the presence of quartz. It is possible that this reaction leads to the nearly ubiquitous normal zoning of the plagioclase. Changes in the composition of biotite at the isograd are not conspicuous, and can be satisfactorily explained by the release of Mg, Fe, and Ti impurity from the muscovite, and a continuous reaction between ilmenite, quartz, and muscovite. Garnets are not abundant and are high in Mn, both facts probably due to the low pressure of metamorphism, The presence of garnet probably relates to the Mn content of the rock, and seems to be independent of the Mg/Fe ratio of the biotite. The garnets are zoned with respect to Mn and Mg, but often Mn is enriched and Mg depleted in the marginal zone. The Mg/Fe ratio of the biotite varies twofold depending on the presence or absence of pyrrhotite. The transition: microcline → orthoclase depends upon the amount of dissolved albite; the polymorph is orthoclase in the pelitic schists but microcline in the calc-silicate rocks which are much lower in sodium. The plagioclases are of “low” structural type, although is slightly greater than many other “low” plagioclases. A correlation of d(002) of muscovite and paragonite solid solution for the range 0 to 20 % paragonite is given. An appreciable positive volume of mixing for the binary system muscovite-paragonite is indicated.  相似文献