ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00813.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00814.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00815.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTIf we are to develop valid models for predicting the future of the global environment, anthropogenic forcing must become the major component of study. The technological developments needed to supply food, water and materials for 10 billion humans will dominate environmental change over thenext decades.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00816.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe global changes of the past took place during the progress of geological cycles and marked a drastic passage from an ancient Pangaean regime of continental emergence to a new Tethyan regime of submergence. They occurred with a certain violence and rapidity, and represented critical phases in the destabilization and subsequent reorganization of the geosphere and biosphere. This process resulted in the destruction of certain assemblages (e.g. biotic mass extinctions) and the rise of new ones (e.g. the emergence of new taxa). These major phases of evolution and growth were probably connected to the upwelling of hot mantle material from great depths and a subsequent process of lateral spreading and outward migration of the mantle melt. The ensuing marked increase in mantle activity, degassing and explosive volcanicity produced catastrophic environmental perturbations with turning points in tectonics, global climate, sea level, ocean and atmospheric chemistry, palaeocirculation and palaeogeography.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00817.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTWe constructed a detailed relative sea‐level rise curve for the last 1500 years using a novel approach, i.e. charting the rate of relative sea‐level rise using microfaunal and geochemical data from a coastal salt marsh sequence (Clinton, CT, USA). The composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively. The resulting sea‐level rise curve, with age control from14C dating and the onset of anthropogenic metal pollution, shows strong increases in the rate of relative sea‐level rise during modern global warming (since the late nineteenth century), but not during the Little Climate Optimum (ad 1000–1300). There was virtually no rise in sea‐level during the Little Ice Age (ad 1400–1700). Most of the relative sea‐level rise over the last 1200 years in Clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years. Changes from slow to fast rates of relative sea‐level rise apparently occurred over periods of only a few decades. We suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea‐level rise along the northeastern USA seaboard. Relative sea‐level rise in that area is currently faster than the worldwide average, which may result partially from an ocean surface effect caused by hydrodynamics. Our data show no unequivocal correlation between warm periods (on a decaal to centennial time‐scale) and accelerated sea‐level rise. One period of acclerated sea‐level rise may have occurred between about ad 1200 and 1450, which was the transition for the Little Climate Optimum to the Little Ice Age, i.e. a period of cooling (at least in northwestern Europe). Local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea‐level, however. The second period of accelerated sea‐level rise occurred during the period of modern global warming that started

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00818.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe ultimate cause of the onset of glaciations remains elusive, but in the case of northem hemisphere glaciation it is probable that several factors acted in combination. General global cooling resulted from reduction of atmospheric C02by weathering of silicate rocks exposed by erosion of late Cenozoic uplifts. Uplifts in south Asia, southwestern North America and Scandinavia occurred at distances appropriate for the generation of quasi‐permanent Rossby waves in the atmosphere. The resulting winds, given suitable moisture sources, were favourable for causing large‐scale precipitation at mid‐latitudes on the northern continents. Moisture sources were provided by the closure of the Central American isthmus. Gulf Stream flow increased, carrying warm subtropical waters to high latitudes. The Denmark Strait deepened permitting greater outflow of deep water from the Norwegian‐Greenland Sea. The relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00819.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTLandscape evolution is on the same time‐scale as global tectonics, biological evolution, and major climatic change. Some features of global change reflected in landscape evolution result from the breakup of Pangaea. Others relate to major climatic changes, and yet others to a major change from a dominantly plains landscape of the Mesozoic to an increasingly mountainous landscape in the Tertiary. Worldwide deep weathering profiles of Cretaceous and early Tertiary age suggest widespread planation and warm, moist climates. Erosion of deeply weathered regolith following the formation of new continental margins and tectonic uplift led to the deposition of unusual mature sediments. Many river patterns can be traced to early Tertiary or older antecedents.Some climatic changes are due to orbital forcing, but others may be related to changing positions of continents, creation of new seaways, or to mountain building. The timing of mountain uplift, climatic changes and biological changes must be resolved to test models of their mutual interaction. Geomorphic input on tectonics, drainage evolution, and deep weathering will be an essential component in dealing with these problem

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00820.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTOver the past one hundred years North American geologists have been influenced by concepts of Earth history based on periodic events involving marked (‘Neocatastrophic’) changes and competing concepts involving steady‐state (‘Uniformitanan’) behaviour. T.C. Chamberlin, a late 19th‐/early 20th‐Century exponent of a nonuniformitarian scenario of earth history, proclaimed ‘diastrophism as the ultimate basis of correlation’ ‐ meaning that geological history is punctuated by orogenic paroxysms causing retreat of epicontinental waters to oceanic basins, creating segmentation of the stratigraphic and chronological record. At mid‐Century James Gilluly gained wide support for the proposition that orogeny has followed a Uniformitarian, near‐steady‐state course. Accordingly, episodic diastrophism is a myth and cannot be the basis for periodic eustatic sea‐level change, interregional unconformities, etc.In more recent decades two powerful new influences on geological thought have emerged. The global tectonic paradigm has forced upon us the realization that rearrangements of lithospheric plates are capable of changing the freeboard of continents. At the same time technological advances in the acquisition and processing of seismic‐reflection data have been seized by receptive minds to organize the newly available stratigraphic imagery for application to the discipline of seismic stratigraphy which emphasizes the identification and correlation of unconformity‐bounded successions of strata. Expansion of the methodology to the outcrop, beyond the limitations of seismic resolution, has brought about the flowering of the New Sequence Stratigraphy, doctrine that has deservedlyachieved wide application and acclaim. Practitioners of sequence stratigraphy, impressed by the distances over which unconformity‐bounded stratal units can be correlated, hew to the belief that eustatic (commonly glacially engendered) sea‐level change is the control.This paper examines evidence of tectonic episodes affecting cratons and their margins. These offer promise of a more satisfactory understanding of stratigraphic sequences and of the Earth history they represent. Consideration of these matters makes it inescapable that the elevation and subsidence of cratons (and their component basins and arches) reflect tectonic phenomena of the continental lithosphere q

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTCurrent geodynamic models pose many serious problems for the description of continental tectonic processes, Serious difficulties arise also in the description of some of the ocean basins.Deformation of the Earth's crust appears to be concentrated along several mobile megashear belts. It is proposed that these could be the surficial expression of ‘mantle chimneys’ which extend to great depths. Within these structures, post orogenic high plateaux form, and as time passes these develop a central depression enclosed within arcs or indeed full‐scale rings of mountains. The enlargement and deepening over time of the back‐arc depression occurs in concert with the radial migration of a ‘topographic wave’. In this respect, the following structures represent different phases in an evolutionary sequence: (a) the Tibetan Plateau, (b) the North American Cordillera, and (c) the Tyrrhenian Basin and Calabrian Arc. The development of this succession reflects a particularly high degree of activity in the mantle, in which diapiric rising of asthenospheric matter elevates the land and causes tensional rifting. The resulting centrifugal movement of the mantle melt results in crustal foundering and engulfment of the area behind the arc, which thus becomes susceptible to the subsequent processes of com‐pressiona

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY