| 其他摘要 | It's an important task to reconstruct Paleoclimatic and Paleoecological-Paleoenvironmental changes of global change. Based on the microbanding structure, stable oxygen carbon isotope and trace elements, like other natural materials (loess, ice-core, tree rings, sea deposits and peat), Speleothems especially stalagmite are important repositories of Paleoclimatic and Paleoecological-Paleoenvironmental data. In recent decades, the paleoclimatic records and paleoecological-paleoenvironmental meanings of speleothems achieved significiant progress. The stable oxygen isotopic sequences of speleothems can give information about precipitation and temperature, the history of changing vegetation can be traced by the stable carbon isotopic sequences of speleothems, and much high resolution climatic-environment information, such as precipitation, temperature, soil and vegetation are involved in microbanding type and trace elements character of stalagmite. Based on the systematical studies of the sedimentary characteristics and the carbon (oxygen) isotopes of stalagmite from Liangfeng cave, Guizhou, China., the following conclusions we have been drawn: 1. Based on the systematical studies of the water, gas and soil above Liangfeng cave, the results indicated that some information about climatic and ecological-environmental changes have been recorded well by cave drip water. The Liangfeng cave is a good place to study Paleoclimatic and Paleoecological- Paleoenvironmental changes of global change by stalagmite. 2. The combinations, thickness, grain size and bedding plane structure of depositional laminates in stalagmite are material bases of resuming drip water trends forming stalagmite and the relative paleo-hydrological condition. The sedimentary characteristics and trend changes of paleo-drip water records in stalagmite from Liangfeng cave are studied by examing composition of calcite, rock chemistry, texture, bedding-stucture, as well as typical marks of depositional break or weathering crust ect. Based on the TIMS dating along the axis cores of the stalagmite, during 8000-1570 aBP, the depositional laminates is the smooth peak (or column) shape of the symmetrical superimposed laminates, indicating the drip water amount is great and steady, the growth rate of the stalagmite varies from 22 um/yr to 51 um/yr. During 14220-8000 aBP, the depositional laminates is the peak (or oblique) cone shape of the unsyrnmetrical superimposed laminates, indicating the drip water amount is small and unsteadily, the growth rate of the stalagmite is 16um/yr. 3. Great difference exists between the development of microbanding of stalagmite in the north part of China and that in the south. Microbanding of stalagmite in Northern China usually are thin, with the dark impurities dispersed as a very thin layer. However, the microbanding of stalagmite in Southern China are much thicker, with a high content of dark impurities and high variation of porosity. The difference of these microbanding of stalagmite was controlled by the differently combined seasonally of precipitation and temperature. Comparing TIMS (ICP-MS) dating with microbanding of stalagmite, it is possibly that microbanding of stalagmite equal to annual band. 4. In Guizhou province, the oxygen isotopic characteristics of rain waiter are mainly controlled by the monsoon type and the precipitation cloud cluster origins and the amount of rainwater. There is a quite good normal correlation between the 5 I8O values of the drip water of cave and the average 5 l8O values of the rainwater, which shows that the characteristics of the δ13C values of the drip water for forming stalagmite can reliably reflect the δ18C values characteristics of rainwater, and then, the climate characteristics. Based on the systematical studies of the water, gas and soil above Liangfeng cave, the δ18C values of stalagmite can be regarded as an ecological-environmental proxy, namely, the smaller the δ13C values, the larger the proportion of C3 plants, and the more plentiful the rainfall. On the contrary, the proportion of C4 plants may be increased or the ecological-environment may be a strong desert ecological-environment caused by climatic changes. 5. On the basis of the above studies, the Paleoclimatic Records and Paleoecological-Paleoenvironmental Meanings of Stalagmite from Liangfeng Cave in Guizhou have been made, which gives records from 14220 to 1570 aBP as follows: (1) 14220-10500 aBP, Among Last Glaciation to Holocene, cold, the δ13C values of stalagmite varies from -9.314‰ to -7.290‰, average -8.552‰, the C4 plants take some proportion of vegetation above Liangfeng cave. The δ18C values of stalagmite varies from -5.651‰ to -6.942‰. (2). 10500-9300 aBP, The temperature increased after the end of Younger Dryas event, the 5 13C values of stalagmite varies from -10.37754 to -9.267%o, average -9.910‰, the vegetation above Liangfeng cave be dominated by C3 plants. The518O values of stalagmite decreased obviously, varies from -7.420‰ to H5.077‰, average -6.854‰, the amount of rainwater increased and Southweat monsoon was strong. (3). 9300-8300 aBP, The temperature fluctuates obviously along with the changes of δ13C vahies (varies from -10.155‰ to -9.096‰, average -9.712‰) of stalagmite, and the proportion of C4 plants of vegetation above Liangfeng cave was unsteady. The δ18C values of stalagmite varies from -6.796‰ to -6.260‰, average -6A90‰, the affect of East-Asian monsoon increased. (4). 8300-3100 aBP, this period is so-called Megathermal, the temperature increased obviously, the δ13C values of stalagmite is much low (average -9.910‰), the vegetation above Liangfeng cave be dominated by C3 plants. The 5 18O values of stalagmite changes greatly, varies from -7.373‰ to -5.047‰, average -6.26 1‰, indicted that the climatic of monsoon is unsteady. (5). 3100-1570 aBP, The δ13C values and 5 18O values of stalagmite increased greatly, the 5 13C values of stalagmite varies from -12.097‰ to -6.495‰, average -10.275%o, the δ18C values of stalagmite varies from -8.65O‰ to -4.677‰, average -6.184‰, the vegetation above Liangfeng cave be dominated by C3 plants mainly, the climatic of monsoon is unsteady. The drastic changes of 5 13C values and δ18C values of stalagmite during 1690-1570 aBP is understanding. |
修改评论