1、山东科技大学 学士学位 论文 附录 附录 Dating of coal fires in Xinjiang, north-west China23 Xiangmin Zhang, Salomon B.Kroonenbergand Cor B.de Boer Department of Earth Resources Surveys, ITC,PO Box 6, Enschede, the Netherlands； Faculty of Applied Earth Sciences, Delft University of Technology, PO Box 5028,2600 GA Delf
2、t, the Netherlands； Palaeomagnetic Laboratory, Faculty of Earth Sciences, University of Utrecht, 3584 CD Utrecht, the Netherlands ABSTRACT Coal fires in China consume vast amounts of fuel and cause serious environmental problems. Most of these coal fires are related to mining activity. However, natu
3、rally produced palaeo coal fires in Xinjiang, north-west China, have been recognized via burnt rocks. The burnt rocks in the study area are found at different river terraces underlying unburnt alluvial and river terrace deposits. Several age groups of coal fires have been identified based on the pos
4、itions of burnt rocks at river terraces and the relationship between the burnt rocks and the terrace deposits. These palaeo coal fires are: (1) PlioceneEarly Quaternary in age at 200 m above present river terrace deposits； (2) Middle Pleistocene in age, at90m； (3) Late Pleistocene, at 9070 m； (4) Ho
5、locene； (5) burnt rocks relating to active coal fires.Palaeomagnetic data of the burnt rocks from different terraces give normal remanent magnetization and help further to constrain the ages of the coal fires. Terra Nova, 16, 6874, 2004 Introduction 山东科技大学 学士学位 论文 附录 Coal fires are one of the most s
6、erious problems for the Chinese coal industry. The estimated annual loss of coal by fires in China ranges from about 1020 million tones (Guan et al, 1998) to 100200 million tones (Schalke et al, 1993； Cassells and Van Genderen, 1995). Besides the huge loss of coal resources and mining safety, coal f
7、ires cause considerable environmental problems, such as air pollution and land degradation. Coal fires have a global impact as well； the emission of CO2 might contribute considerably to the increase in green- house gases in the atmosphere. If the latter estimate for annual loss of coal is correct, C
8、O2 emission by coal fires in China would account for 23% of the world CO2 output from the burn- ing of fossil fuels for the year 1992 (Cassells and Van Genderen, 1995). Active coal fires in China are usually related to mining activity； however, the direct cause of the coal fires is essentially spont
9、aneous combustion. Spontaneous combustion is a process of oxidation of coal in which the temperature of the coal increases until a fire starts. Fires can also start at surface outcrops as a result of natural processes such as forest fires, lightning or even solar heating. Exposure of the coal seam i
10、s essential for these types of coal fire. Several geological processes, such as faulting, folding and erosion by river action, can bring the coal to the surface thus lead to coal fires.In our study area, coal fires have repeatedly occurred because of river downcutting and exposure of coal seams. The
11、 cap rocks and sediments enclosing the seams have been greatly altered thermally by the coal fires. These thermally altered rocks (burnt rocks) indicate that the palaeo coal fires occurred during geological history.The ages of the palaeo coal fires can be constrained from the ages of the river denud
12、ation that exposed the coal seam and from the terrace deposits overlying the burnt rocks. The temperature of the burnt rocks is believed to have exceeded the Curie point (Guan, 1963) and hence they record the geomagnetic direction of that point in time. Ten orientated specimens of burnt rock from di
13、fferent age groups were collected and examined in the laboratory. The palaeomagnetic data 山东科技大学 学士学位 论文 附录 provide further constraints on the absolute ages of the coal fires. Our study shows that coal fires have repeatedly occurred since the Pliocene and that most of the burnt rocks are of Pleistoc
14、ene age. Geological setting The Toutunhe study area is situated 30 km south-west of Urumqi, the capital city of Xinjiang, China, in the transition zone between the Tianshan mountain range and the Junggar basin, at an altitude of 10001400 m. It is crossed by the Toutunhe river, which is fed by the gl
15、aciers of the TianshanMountains and by its tributary rivers the Qianshuihe, Gangou and Haojiagou (Fig.1). The core of the EW-trendingTianshanMountain range consists of preMesozoic basement rocks (Peng and Zhang, 1989； BGXJ, 1993； Carroll et al, 1995). On the northern side of the Tianshan, Mesozoic a
16、nd Cenozoic sedimentary rocks have been detached from the underling pre-Mesozoic rocks and folded into three lines of EW-trending anticlines and synclines. The Kelazha anticline in the study area is situated in the first line, with Jurassic strata forming the core of the folds. Unfolded Pliocene sed
17、iments unconformably cover the Jurassic and Cretaceous rocks. The main coal-bearing strata that have burnt out belong to the Middle Jurassic Xishanyao Group, which consists of freshwater deltaic sediments (BGXJ, 1993； Schneider, 1996). The coal layers are concentrated in the lower parts of the Xisha
18、nyao Group, with thickness varying from 1 to 27 m. The lowest mineable layer is the Dacao coal layer, with a constant thickness of 1517 m. The Toutunhe river dissects the folded Jurassic rocks and has a flight of at least six river terraces in the valley (Fig.2； Huang and Zhao, 1981； Qiao, 1981； Mol
19、naretal, 1994). The uppermost terraces are situated about 90 m above the river, the lowermost one about 15 m above the present river level. The other terraces are situated between these, with a regular height interval of about 1015 m. Most of the terraces are cut into bedrock and capped by 13 m of coarse
