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Preliminary Study on Lacustrine Sediments at Diexi in the Upper Reach of the Minjiang River During the Last Deglaciation

Author: MaoXue
Tutor: YangGuiFang；JiangHanChao
School: Chinese Geology University (Beijing)
Course: Geography
Keywords: Lacustrine deposits Paleoenvironmental Last deglaciation Paleoseismic Diexi
CLC: P532
Type: Master's thesis
Year: 2011
Downloads: 43
Quote: 0
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Abstract


Lake on the upper reaches of Minjiang River Diexi the mill village thickness 11m sedimentary records of multi-indicators analysis of sediments Diexi dating back about 20 ~ 12 ka paleoclimatic and paleoenvironmental explore and restore the The structure of the study area and climate change history. Mainly supported by the following research: (1) to establish the upper reaches of Minjiang River Diexi new grinding the village 11m lacustrine depositional age sequence ago come to the section about 20.18 ~~ 12.6 ka. Sediment grain size composition, REE distribution patterns and morphological characteristics of the surface of the quartz grains show the new mill village fine-grained lacustrine sediments for aeolian sources initially speculated that the joint action of the near-source deposition plateau monsoon and westerly belt. (2) study the various sedimentary indicators of 16 ka for the sector, the the late deposition rate significantly speed up the relatively sharp fluctuations. Overall finer granularity, mainly silt and clay (the average content of 76.2% and 20.6%, respectively), and sand content of only 3.3%. Susceptibility median diameter roughly synchronous changes in grain size and magnetic susceptibility records are obviously there are several sudden increases and then decreases slowly. Study area organic carbon (TOC) and inorganic carbon (TIC) content were lower, with an average of 0.35% and 1.91%, respectively, with the study area is semi-arid areas coincide; fluctuations downward trend was on the TOC content overall, TIC also slightly significantly decreased but the changes in a narrow range. The dominant pollen samples herbaceous pollen content of 46.3 to 94.3%, an average of 55.4%; tree pollen subordinated, an average of 31.2%. (3) the use of pollen and carbon content indicators reconstruction study area paleoenvironmental evolution, drawn in the study area during 20 ~ 12 ka main veld is covered, and the stability of the changes in vegetation type, paleoclimate experienced cold and dry - warm cool moist - cool dry evolution: 20.18 ~~ 19 ka during the sparse vegetation, dry and cold climate and environment; 19 to 16 ka, broadleaf plant some development, the overall environment turned cool and wet, but the early (19 to 17.4 ka) and warm-dry, late (17.4 ~ 16 ka) transition to moist; 16 ~~ 12.6 ka during environmental fluctuations exacerbate remains savanna vegetation types, the richer vegetation types, slightly cool environment and accompanied by a strong alternating wet and dry evolution law. (4) the study area, particle size and magnetic susceptibility indicators clearly tectonic changes recorded in the study area. Initially speculated last deglaciation occurred strong seismic events, especially in the late deposition (16 ~~ 12.6 ka). Combined the granularity curve and the fluctuations of the magnetic susceptibility values, 20.18 ~ 12.6 ka period can be broadly identified seismic events, speculated that time occurred in 19.54 ka, 18.97 ka, 15.49 ka, 14.87 ka, 14.10 ka, 13.78 ka, 13.46 ka and 12.93 ka. , 16 ka ago only two earthquakes occurred spaced about 1500; 6 earthquakes occurred after 16 ka, with an average interval of 512 years.

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