The origin of Island mammoths and the quaternary land bridge history of the Northern Channel Islands,California     

Donald Lee Johnson 《Quaternary Research》1978,10(2):204-225

Pygmy proboscidean remains of Mammuthus exilis occur abundantly in late Quaternary deposits on the Northern Channel Islands, California. On the assumption that ancestral elephants could not have swum to the islands and must therefore have walked out, various land bridges have been hypothesized that link the northern islands to the mainland by a peninsula. Geological evidence for a land bridge, however, is lacking, and new evidence shows that elephants are excellent swimmers and skilled at crossing watergaps. The Santa Barbara Channel was narrowed to only 6 km during glacially lowered sea levels. Modern elephants swim much further, and at speeds ranging from 0.96–2.70 km/hr. Motives for California elephants to cross Pleistocene watergaps are inferred from motives that lead modern elephants in Asia and Africa to cross watergaps. These are the visual and olfactory sensing of islands and of insular food during times of drought or fire-induced food shortage. Diminutive size of M. exilis principally reflects lack of island predators, an adaption to periodic food stress in a finite forage area affected by periodic drought and fire, and an adaptation for keeping population numbers high to maintain genetic variability and to ensure survival despite accidents. A late Quaternary scenario describes the environmental setting of the Santa Barbara Channel and the conditions that led to proboscidean dispersal to the preexistent super-island Santarosae.  相似文献   

A theory of concentric, kink, and sinusoidal folding and of monoclinal flexuring of compressible, elastic multilayers: I. Introduction     

Arvid M. Johnson  Stephenson D. Ellen 《Tectonophysics》1974,21(4):301-339

Most folds in stratified rock are similar in form to ideal kink, concentric or chevron folds, in which there are discontinuities in slope or curvature of bedding planes. In this respect most folds appear to be closely related to faults, traces of which can be considered to be lines across which there are discontinuities of displacement of layers. Further, the close association of reverse faults and folds or monoclinal flexures seems to indicate that theories of faulting and folding should be closely related.The theory of characteristics is a mathematical tool with which we can obtain insights into processes involving discontinuities. Theoretical characteristic lines are directions across which certain variables might be discontinuous and they are directions along which discontinuities propagate. The theory has been widely applied in plasticity theory and in fluid mechanics and theoretical studies of faulting have suggested that faults are analogous to the lines of discontinuity predicted by plasticity theory. Elasticity and viscosity theories, on which theories of folding have been founded, exclude the existence of characteristic lines in the materials unless the equilibrium equations, rheological properties or strains are nonlinear. However, all folding theories are nonlinear to some extent and the theories can be modified so that they predict lines of discontinuity for some conditions of loading and deformation.Theories of folding will be developed in subsequent papers of this series in order to predict conditions under which characteristic lines can exist in multilayered materials and in order to determine the conditions that must be satisfied across and along the characteristic lines. The theory should help us to recognize lines of apparent discontinuity in natural and experimental folds and study of these lines should provide further understanding of mechanisms of folding.Experimental studies of folding of a wide variety of materials, including alternating layers of rubber and gelatin, modeling clay and grease or graphite, and potter's clay and rubber or cardboard, suggest that the patterns of folding in these materials begin with sinusoidal forms, transform into concentric or kink forms and then into chevron forms as the multilayers are shortened axially. A suitable theory of folding of multilayers should account for these observations.  相似文献   

Strontium isotope ratios of quaternary volcanic rocks from Papua New Guinea     

R.W Page  R.W Johnson 《Lithos》1974,7(2):91-100

Strontium isotope data for Quaternary volcanic rocks from six separate areas in Papua New Guinea suggest a subdivision into two broad groups. One group consists of island volcanoes that have lower Sr³⁷/Sr³⁸ ratios (0.7034–0.7043) and show isotopic homogeneity within each area sampled. Except for the St. Andrew Strait samples, it is considered that these rocks were produced from relatively homogeneous source regions in the upper mantle. Volcanoes of the second group (on the Papua New Guinea mainland) have generally a higher and wider range of Sr³⁷/Sr³⁶ ratios, compared to those of the first group. It is thought that the magmas of these mainland volcanoes were affected by different degrees of sialic crustal contamination, or were derived from heterogeneous sources in the upper mantle.  相似文献   

Greater India's place in Gondwanaland and in Asia     

J.J. Veevers  C.McA. Powell  B.D. Johnson 《Earth and Planetary Science Letters》1975,27(3):383-387

Evidence from the eastern Indian Ocean implies a Greater India in Gondwanaland. Translated without distortion to Asia, the northeast part of Greater India is found to correspond in shape with the Tibetan Plateau. With geophysical evidence, this suggests that the northeast part of Greater India underlies, presumably by underthrusting, the Tibetan Plateau.  相似文献   

Paleopedology ofRamapithecus-bearing sediments,North India     

Dr. Gary D. Johnson 《International Journal of Earth Sciences》1977,66(1):192-216

The utility of using fossil soils in addition to other sedimentologic evidence in reconstructing past environments is considered with a preliminary analysis of the character of pedogenic alteration of selected floodplain deposits which have yielded the hominoid primatesRamapithecus andDryopithecus in the vicinity of Haritalyangar, District Bilaspur, H. P., India. The alluvial paleosols studied reflect variance of properties which are related to original depositional fabric modified by secondary pedogenic processes. The Nagri aged paleosols of Haritalyangar are ferruginous tropical soils or low-grade oxisols developed on typical floodplain toposequences, all reflecting somewhat varied histories as a function of proximity to ancient active stream courses.

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Zusammenfassung Es wird untersucht, inwieweit es für die Rekonstruktion des früheren Bildungsmilieus sinnvoll ist, in Verbindung mit anderen sedimentologischen Erscheinungen fossile Böden mit heranzuziehen, und zwar nach einer Analyse der Merkmale pedogenetischer Veränderungen in bestimmten Ablagerungen der Alluvialebenen in der Umgebung von Haritalyangar, Bilaspur, H. P., Indien, in denen die hominoiden PrimatenRamapithecus undDryopithecus gefunden worden sind. Die untersuchten alluvialen Paleoböden zeigen, verglichen mit der ursprünglichen Ablagerungsstruktur, Abweichungen in ihren Eigenschaften, die durch sekundäre pedogenetische Prozesse bestimmt sind.Die Paleoböden der Nagri-Stufe von Haritalyangar sind eisenreiche tropische Böden oder schwächere Oxiböden, die in den typischen Toposequenzen der Alluvialebenen entstanden sind und die aufgrund ihrer verschiedenen Entfernung zu alten Flußläufen alle eine etwas unterschiedliche Vergangenheit widerspiegeln.

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Résumé On considère ici la possibilité d'utiliser des sols fossiles en plus d'autres évidences sedimentologiques pour reconstruire les environnements du passé. On présente aussi une analyse préliminaire des caractéristiques de modifications pédogéniques de certains sédiments de plaines alluviales, qui ont livré les primates hominoïdesRamapithecus etDryopithecus, au voisinage de Haritalyangar, district de Bilaspur, H. P., Inde. Les paléosols alluviaux étudiés révèlent diverses propriétés caractéristiques de dé pôts originaux, modifiés par des processus pédogéniques secondaires. Les vieux paléosols de Nagri, aux environs de Haritalyangar, sont des oxisols peu évolués, formés sur des séquence topographique typique de plaines alluviales. Tous reflètent quelque peu des stages divers selon leur proximité d'anciens cours fluviatiles actifs.

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, , , , Haritalyangar'a, Bilaspur'a H.P., , . , , . Haritalyangar , , , , .

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Potassium variation across the New Britain volcanic arc   总被引：1，自引：0，他引：1  

R.W. Johnson 《Earth and Planetary Science Letters》1976,31(1):184-191

Late Cainozoic volcanoes of the New Britain island arc overlie an inclined Benioff zone that extends to a depth of at least 580 km. The rocks are tholeiitic basalt, andesite, dacite, and rhyolite. Unlike many other examples of island arcs described in the literature, K₂O contents in rocks with the same SiO₂ content do not increase progressively as depth,h, to the New Britain Benioff zone increases. The most complex relationships between K₂O, SiO₂, andh are shown by volcanoes overlying the deeper part of the Benioff zone. In these, the K₂O contents of rocks containing more than about 60% SiO₂,decrease as depth to the Benioff zone increases. The New Britain volcanic arc provides a striking exception to the generalisation thatK-h relationships are essentially similar in all island arcs.  相似文献   

Estimation of Tigris-Euphrates streamflow from regional paleoenvironmental proxy data     

Paul A. Kay  Douglas L. Johnson 《Climatic change》1981,3(3):251-263

A six thousand year history of streamflow in Mesopotamia is derived from a synthesis of regional paleoenvironmental proxy data. The proxy data are interpreted with consideration to the climatic signals represented in the records and to the temporal resolution of the records. A consideration of modern synoptic climatology suggests the spatial patterns of streamflow-generating precipitation in relation to atmospheric circulation. These patterns provide a framework for the interpretation of streamflow from the regional proxies. Given the nature of the data at hand, only a low frequency signal is reconstructed. Assessment of the role of small scale climatic fluctuations as a forcing function of population dynamics must await the availability of finer resolution environmental data.  相似文献   

The seaward margin of belize barrier and atoll reefs: Special Publication No. 3 of the International Association of Sedimentologists. N.P. James and R.N. Ginsburg. Blackwell,Oxford, 1979, 191 pp., £10.00.     

Kenneth G. Johnson 《Sedimentary Geology》1981,30(3):243

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Morphology of the Weddell Sea and southwest Indian Ocean     

Dr. G. Leonard Johnson  Prof. Jean-René Vanney  Anders Elverhøi  John L. LaBrecque 《Ocean Dynamics》1981,34(6):263-272

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A Practical Approach to the Design, Operation, and Monitoring of In Situ Soil-Venting Systems   总被引：9，自引：0，他引：9  

P.C. Johnson  C.C. Stanley  M.W. Kemblowski  D.L. Byers  J.D. Colthart 《Ground Water Monitoring & Remediation》1990,10(2):159-178

When operated properly, in situ soil venting or vapor extraction can be one of the most cost-effective remediation processes for soils contaminated with gasoline, solvents, or other relatively, volatile compounds. The components of soil-venting systems are typically off-the-shelf items, and the installation of wells and trenches can be done by reputable environmental firms. However, the design, operation, and monitoring of soil-venting systems are not trivial. In fact, choosing whether or not venting should be applied at a given site is a difficult decision in itself. If one decides to utilize venting, design criteria involving the number of wells, well spacing, well location, well construction, and vapor treatment systems must be addressed. A series of questions must be addressed to decide if venting is appropriate at a given site and to design cost-effective in situ soil-venting systems. This series of steps and questions forms a "decision tree" process. The development of this approach is an attempt to identify the limitations of in situ soil venting, and subjects or behavior that are currently difficult to quantify and for which future study is needed.  相似文献