DATA RELATING TO THE STUDY OF THE PROBLEM OF GLACIATION IN THE LOWER YANGTZE VALLEY     

李四光 《地质学报》1934,(1)

In a commemorable evening—I believe it was in the early part of December, 1933—when I happened to discuss the problem of Pleistocene climate in China with the late Dr. Davidson Black, I informed him, without  相似文献   

NOTE ON THE STRATIGRAPHY OF THE ENVIRONS OF THE MAPING CITY, CENTRAL KWANGSI     

李捷  朱森 《地质学报》1934,13(1)

Maping, formerly named Liuchow, is one of the well known cities in Central Kwangsi. The geology of the Maping district and its neighbouring areas were preliminarily surveyed by S. S. Yoh in 1929. In our journey across the Nanling Range we passed through t  相似文献   

Coordinated observations of two large Leonid meteor fireballs over northern New Mexico,and computer model comparisons     

J. ZINN  J. WREN  R. WHITAKER  J. SZYMANSKI  D. O. Revelle  W. PRIEDHORSKY  J. HILLS  G. GISLER  S. FLETCHER  D. CASPERSON  J. BLOCH  R. BALSANO  W. T. ARMSTRONG  C. AKERLOF  R. KEHOE  T. McKAY  B. LEE  M. C. KELLEY  R. E. SPALDING  S. MARSHALL 《Meteoritics & planetary science》1999,34(6):1007-1015

Abstract— This paper describes the coordinated results of several sets of measurements of two Leonid meteor fireballs over northern New Mexico at 1:32 and 3:06 MST, respectively, on the night of 1998 November 17. The measurements included visible band photometry on both events, as well as filtered 5890 Å all-sky images of the Na airglow. Also, for the 3:06 a.m. event, we obtained an infrasound measurement of the hydrodynamic yield. For the 1:32 a.m. event, we obtained a set of visible band charge-coupled device (CCD) camera images of the meteor train for times extending to 30 min after the initial impact. The measurement results have been combined to derive an optical efficiency for the intense early-time optical flash, and the total explosion yields and masses for both of the meteors. We have also done a set of numerical radiation, hydrodynamic, and chemistry computations to investigate the nature and distribution of the long-lasting airglow. We attribute the brightest visible airglow to atomic O 5577 Å line emission, with additional contributions from atomic Na emission and NO₂ chemiluminescence. The near-infrared atmospheric bands of molecular O₂ should be very strong as well. All of the band emissions are expected to show a hollow limb-brightened structure.  相似文献   

Anthropogenic versus natural sources of atmospheric sulphate from an Alpine ice core   总被引：1，自引：0，他引：1  

BY M. SCHWIKOWSKI  A. DÖSCHER  H.W. GÄGGELER  U. SCHOTTERER 《Tellus. Series B, Chemical and physical meteorology》1999,51(5):938-951

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Unusual intraclastic limestones in Lower Triassic carbonates and their bearing on the aftermath of the end-Permian mass extinction   总被引：5，自引：0，他引：5  

PAUL B. WIGNALL  & RICHARD J. TWITCHETT 《Sedimentology》1999,46(2):303-316

Flat pebble conglomerates were a common carbonate facies in Cambrian to Early Ordovician open marine settings, but they become extremely rare in these environments after this time. However, the Early Triassic witnessed an anachronistic reappearance of flat pebbles, together with other intraclast types, in a range of carbonate depositional settings. In south China, flat pebble conglomerates are encountered in storm-dominated, platform carbonates to deep basinal settings, while prefossilized bivalve intraclasts and flat pebbles are common in mid-ramp facies of northern Italy. The emplacement mechanisms of the intraclast-bearing beds appear to have been diverse and to have included basinal turbidity flows and storm-generated hyperconcentrated flows: true storm beds, deposited under combined flow conditions, are rare. The cause of the widespread early lithification implied by the Early Triassic intraclasts appears to have been twofold: suppression of bioturbation, allowing the preservation of thin beds, and rapid submarine lithification. Both features appear to be a response to the widespread development of benthic dysoxia/anoxia during and following the end-Permian mass extinction. This event appears to have temporarily recreated the conditions that pertained in Cambro-Ordovician shelf seas. Flat pebble conglomerates may, therefore, constitute a proxy indicator of stressed environmental conditions associated with global anoxic/dysoxic events.  相似文献   

MULTIVARIATE GEOMORPHIC ANALYSIS OF FOREST STREAMS: IMPLICATIONS FOR ASSESSMENT OF LAND USE IMPACTS ON CHANNEL CONDITION     

RICHARD D. WOOD-SMITH  JOHN M. BUFFINGTON 《地球表面变化过程与地形》1996,21(4):377-393

Multivariate statistical analyses of geomorphic variables from 23 forest stream reaches in southeast Alaska result in successful discrimination between pristine streams and those disturbed by land management, specifically timber harvesting and associated road building. Results of discriminant function analysis indicate that a three-variable model discriminates 10 disturbed from 13 undisturbed reaches with 90 per cent and 92 per cent correct classification respectively. These variables are the total number of pools per reach, the ratio of mean residual pool depth to mean bankfull depth, and the ratio of critical shear stress of the median surface grain size to bankfull shear stress. The last variable can be dropped without a decrease in rate of correct classification; however, the resulting two-variable model may be less robust. Analysis of the distribution of channel units, including pool types, can also be used to discriminate disturbed from undisturbed reaches and is particularly useful for assessment of aquatic habitat condition. However, channel unit classification and inventory can be subject to considerable error and observer bias. Abundance of pool-related large woody debris is highly correlated with pool frequency and is an important factor determining channel morphology. Results of this study yield a much needed, objective, geomorphic discrimination of pristine and disturbed channel conditions, providing a reference standard for channel assessment and restoration efforts.  相似文献   

PLACE MAKING,HAZARDOUS WASTE,AND THE DEVELOPMENT OF TOOELE COUNTY,UTAH*     

J. MATTHEW SHUMWAY  RICHARD H. JACKSON 《Geographical review》2008,98(4):433-455

ABSTRACT. Declining populations, aging inhabitants and infrastructure, limited economic opportunities, and under‐ or unappreciated natural environments characterize a number of rural communities in the western United States. Faced with the challenges of providing for their residents, some of these communities have chosen to permit undesirable land‐use activities, including the disposal of hazardous or nuclear waste. Central to the development of such sites is how a place is perceived and portrayed. Our purpose in this article is to examine how a dominant perception and portrayal of one such place—Tooele County, Utah—was created and used to facilitate the development of hazardous‐waste‐disposal sites. We use the geographical concept of “place” to illustrate how meanings and values are attached to a region in order to justify its becoming what it is and how such views persist.  相似文献   

ESTABLISHING LICHENOMETRIC AGES FOR NINETEENTH- AND TWENTIETH-CENTURY GLACIER FLUCTUATIONS ON SOUTH GEORGIA (SOUTH ATLANTIC)     

BY STEPHEN J. ROBERTS  DOMINIC A. HODGSON  SAMANTHA SHELLEY  JESSICA ROYLES  HUW J. GRIFFITHS  TARA J. DEEN  MICHAEL A.S. THORNE 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):125-139

Glaciers in small mountain cirques on South Georgia respond rapidly and sensitively to changes in South Atlantic climate. The timing and rate of their deglaciation can be used to examine the impact that nineteenth- and twentieth-century climate change has had on the glacial dynamics and terrestrial ecosystems of South Georgia. As part of a reconnaissance study in Prince Olav Harbour (POH), South Georgia, we measured the size of lichens ( Rhizocarpon Ram. em Th. Fr. subgenus. Rhizocarpon group) on ice-free moraine ridges around two small mountain cirques. Our aims were twofold: first, to provide age estimates for lichen colonization, and hence, deglaciation of the moraine ridges, and second, to examine the potential of applying lichenometry more widely to provide deglacial age constraints on South Georgia. In the absence of lichen age-size (dating) curves for South Georgia, we use long-term Rhizocarpon lichen growth-rates from recent studies on sub-Antarctic Islands and the western Antarctic Peninsula to calculate likely age estimates. These data suggest ice retreat from the two outermost moraines occurred between the end of the 'Little Ice Age' (post c. 1870) and the early twentieth century on South Georgia. Lichen colonization of the innermost moraines is probably related to glacier retreat during the second half of the twentieth century, which has been linked to a well-defined warming trend since c. 1950. Patterns of possible nineteenth- and twentieth-century glacial retreat identified in POH need to be tested further by establishing species- and site-specific lichen age-size (dating) curves for South Georgia, and by applying lichenometry to other mountain cirques across South Georgia.  相似文献   

LICHENOMETRIC STUDIES ON MORAINES IN THE POLAR URALS     

BY OLGA SOLOMINA  MIKHAIL IVANOV  TOM BRADWELL 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):81-99

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A REVIEW OF LICHEN GROWTH AND APPLIED LICHENOMETRY IN SOUTHWEST AND SOUTHEAST GREENLAND     

BY ERIC STEEN HANSEN 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):65-79

This paper presents a critical review of previous lichenometric and lichen growth studies in southern parts of West and East Greenland. These studies include classic work from around Søndre Strømfjord, Sukkertoppen, Sermilik and Angmagssalik. Particular emphasis is placed on those studies examining the role played by climatic continentality on the growth rate of crustose lichens in Greenland. The latter part of the paper presents new data on lichen growth rates from Sermilik, between 2001 and 2006, in 22 different lichen species. Measurements show that different species grow at different rates and growth rates vary from site to site. In this study Rhizocarpon geographicum generally grows slowly (<0.2 mm a⁻¹) while other species such as Pseudephebe minuscula grow more rapidly (1.0 mm a⁻¹) in the same environment. Comparison with other studies shows that taxa-specific growth rates are slightly greater in West than in East Greenland – probably as a result of the slightly more favourable climate and higher precipitation levels. It is suggested that recent climate change, most marked in southern Greenland, will probably result in changed growth curves (over time) for species such as Rhizocarpon geographicum . However, only more precise growth curves and lichenometric dating curves can demonstrate such a phenomenon.  相似文献