煤沉积过程成煤构造环境中英文对照外文翻译文献.docx

1、煤沉积过程成煤构造环境中英文对照外文翻译文献中英文对照外文翻译Coal-Producing Tectonic EnvironmentsThis final chapter in the investigation of coal sedimentation is concerned with depositional aspects of the highest order of magnitude, namely, the influence of the crustal setting on peat accumulation. This is a broad and complex fi

2、eld which draws on information, gathered from many different disciplines of the earth sciences. Some of these are currently evolving quite rapidly, while others re in a “mopping up” stage, insensu Kuhn (1970) and Walker (1973), following recent scientific revolutions. An example of the latter is the

3、 replacement of the geosynclinal hypothesis in the early 1970s by the concept of plate tectonics. Even after a life span of 20 years, this new paradigm is still in the process of being refined and fitted out with conceptual subsets, as shown by the current emphasis on terrane analysis. It is therefo

4、re not possible at this stage to make a definitive statement on the chosen subject, but merely to outline the principle on which a modern geotectonic classification of coalfields can be established. Even this modest goal is fraught with difficulty, because the change from the predominantly static ge

5、osynclinal view of global tectonics to its modern, largely mobilistic interpretation has complicated the tectonic classification of some coalfields. While the tectonic status of many coalfields, e.g. those in foredeeps or foreland basins has changed relatively little, the setting of coals found in i

6、nter- and intramontane troughs, i.e. within orogenic cordilleras, cannot be properly assessed without very careful study. According to the geosynclinal concept, practically all of these intradeeps, together with fore- and backdeeps, their extra-orogenic counterparts, were regarded as part of a group

7、 of molasses basins, the development of which accompanies or follows “terminal geosynclinal tecto-orrgenic” (Aubouin 1965). This fixist and strictly sequential interpretation (highlighted by the term “epieugeosyncline” of Kay 1951) has no place in modern geotectonic analysis, which views most orogen

8、ic belts as collages of autochthonous and allochthonous terranes, i.e. as tectono-stratigraphic assemblages with possibly coeval but heterogeneous stratigraphic records reflecting their origin in different geological and geographical domains (Monger and Price 1979, Monger et al. 1982). The tectonic

9、setting, which influenced the formation of an allochthonous terrane assemblage before accretion, may have been very different in style and physically far removed from its resting place after docking. It follows that a multi-terrane orogen may contain a variety of coals formed at different times befo

10、re and after terrane accretion. Moreover, contemporaneous pre-accretionary coal deposits formed in different terranes are likely to vary in coal types, coalification histories and tectonic styles, and all of these will in turn differ from the post-accretionary molasses coals, which alone reflect the

11、 conditiona prevailing in the orogen itself. Indeed, the situation may even be more complex, as will be discussed in Chap.9.3.2.2. Plate tectonics has created its own nomenclature, of which only the essential terms will be used here. They will be supplemented by terms which are either descriptive, a

12、nd therefore independent of geotectonic theory, or which have stood the test of time because they are useful in spite of their generic association with now obsolete concepts. For example, the expressions “mio-” and “eugeosynclinal assemblage” have been kept here as reference term for shallow water m

13、arine (mainly shelf), and ocean floor pelagite, turbidite and ophiolite associationa, respectively. Moreover, reduced to a “miogeocline”, the miogeosyncline has in the North-American literature become a standard term for autochthonous, sedimentary terrace wedges onlapping continental margins. Also t

14、ectonic attributes of sediments, such as “synorogenic” flysch and “late syn- (folded) to postorogenic (non-folded)” molasses, respectively, can still be used in a plate tectonic context without unduly corrupting their relatively loose definitions. Particularly in the discussion of coalfields situate

15、d near convergent plate edges, the concept of molasses as the product of the destruction of the uplifted orogen is very useful. As in the previous discussion, it is not the purpose of this chapter to give detailed descriptions of a large number of cases but to select a few typical examples of coalfi

16、elds and relate the essence of their architecture to their respective plate tectonic settings.1 Early Examples of a Tectonic Classification of CoalfieldsLarge-scale coal formation can take place only in actively subsiding regions, for example in sedimentary basins. It is possible therefore to charac

17、terise the geotectonic environment occupied by a coal measure sequence in a manner similar to that which is applied to other sedimentary environments. Stutzer (1920) and Stille (1926) were among the first to recognise the genetic links between tectonism and the formation of coal. Stille, in particul

18、ar, referred to the striking difference in terms of basin fill, number of coal seams present, their average thickness and proportion in relation to total coal measure thickness, which exist between the Carboniferous and Tertiary coal measures of Europe. He attributed such dissimilarities to contrast

19、ing degrees of crustal mobility in the areas affected by the two main European coal-forming periods. His results are summarized in Table 9. 1. Even if differences in compaction ratios between the Tertiary brown and Carboniferous bituminous coals are taken into account (to a lesser degree the compact

20、ion applies to inter-seam sediments) the contrast is quite remarkable.Later it was shown by von Bubnoff (1937) that the distribution of the world reserves of coal is also related to the geotectonic setting of coalfields. His conclusions are summarized in Table 9.2, which indicates that of all coal d

21、eposits known up to 1937, some 71% developed in former tectonically very active environments, particularly in the molasses foredeeps which develop adjacent to orogenic belts and receive much of the weathered debris washed down from the uplands.Carboniferous coal measures in mobile Varican basinsTert

22、iary coal measures in cratonic basins of Central EuropeAverage coal measure thickness3000m150mAverage number of coal seams2002Average seam thickness1m15mCumulative thickness of coal180m25mProportion of total coal6%16.7%Proportion of economic in situ coal3.6%12%Table 9.1. Stilles (1926) comparison (s

23、lightly modified) between some characteristics of coal measures formed in tectonically mobile and cratonised parts of Europe, respectivelyTable 9.2. The distribution of world reserves of coal in reference to the geotectonic setting of coalfields. (After von Bubnoff 1937)Foredeeps marginal to orogeni

24、c belts 70%Intradeeps within orogenic belts 1%Shelf basins on cratonic margins 21%Cratonic interior 8%The concentration of coal in the regions associated with orogenic belts is even more highlighted when the lateral extent of the deposits is considered. Coalfields situated within or on the shelf mar

25、gins of cratons cover a wider area than the comparatively narrow foredeeps, but its areal restriction is compensated by the frequency of coal seams occurring in a thick stack of coal measures. As will be discussed later, this is related to the substantial and prolonged subsidence that the continenta

26、l margin is subjected to near a subduction complex, as an orogenic belt is accreted onto the plate edge. It is not surprising, therefore, that von Bubnoff (1937) found also a close temporal relationship between orogenies and coal formation in North America, Europe, Asia and Southern Continents. Of c

27、ourse, there are major orogenies known which are not associated with coal deposits. However, invariably, their absence is related to factors affecting the vegetable source. For example, all pre-Devonian orogenies occurred at a time when the plant kingdom was still insufficiently equipped by evolutio

28、n to fulfil its role as an effective producer of peat.The continental shelf environment, being less mobile, has produced fewer coal deposits than the orogenic domain. In this context it is important to define the term shelf. To the geographer, the shelf region is usually that part of the sea which e

29、xtends between the strand-line and the continental slope. However, as von Bubnoff (1948a) noted, the position of the strandline is quite incidental depending on crustal movements and relative sea level positions.From the geological viewpoint, it appears therefore useful to extend the definition of t

30、he shelf so that the time factor can be accommodated. Shelf regions may then be regarded as those marginal but fuully integrated zones of continents which are occasionally affected by shallow marine transgressions. Typical areas are the trailing edges of continental plates and the cratonic margins o

31、f foredeeps. Commonly two types of shelf environments are distinguished, called stable and unstable, respectively (von Bubnoff 1948a; Krumbein and Sloss 1963). The majority for their associated coalfields is paralic in character, which is highlighted by the intercalation of coal measures with marine

32、 strata, a feature that is also common to the molasses foredeeps. However, marine strata may not always be recognized because of lack of fossils, which is related to the dilution of sea water by an excessive influx of fresh water from the nearby coastal swamps (Duff and Walton 1962).Intracratonic co

33、alfields and those formed in intramontanc basins are frequently limnic in character, i.e. they have no hydrological connection to the sea, because they have been formed in land-locked basins above the then prevailing sea level. A spectacular modern example of intramontane peat formation occurs in the reed marshes