【摘要】 <正> 抚仙湖地处云南高原东部,是我国地壳断陷形成的第二深水湖。湖面海拔1721米,面积211平方公里,平均水深89米,最大水深155米,为滇东湖群中面积仅次于滇池的大湖。除湖盆南北两端为面积不大的湖积—冲积平原外,四周均被石灰岩、砂砾岩、玄武岩组成的断块山所环绕。湖岸陡峭,植被稀疏,在温湿气候条件下,发育了厚达数十米的疏松风化壳,为现代湖泊沉积提供了丰富的碎屑物质。湖岸间歇性山间小溪源短流急,每年雨季,暴雨洪流携带大量碎石、泥砂倾泻入湖充填湖盆。更多还原

【Abstract】 Fuxian Lake is situated in the east of Yunnan Plateau. It is a lake of the graben or intermontane type with fault blocks and scarps prevailing in its neighbourhood. Its area covers 211 km~2, and its maximum depth reaches 155 m with its mean 89 m.Only minor rivulets run into the lake. The slopes of the lakeshore zone are, generally, rather abrupt. Floods containing a large amount of detritus swiftly flow into the lake in rainy season. Its deposit characterizes lake basin sediment of grab-en type. On the plane, the deposits are distributed from the highenergy zone of lake-shore to the low-enery zone of deep-lake and their grain size is from coarse to fine. Both the belts of lakeshore gravel and shallow-lake sand-silt are comparatively narrow. The water of sand-silt belt is generally deep up to 10-20 m, and the central part of the lake with muddy sediments covers 85% of the whole lacustrine area.The frequency curve of lakeshore deposits is of polykurtosis. Its grain size range is very wide, σφ-about 2.5, SK>0 ; the cumulative curve presents an irregular arc, deposits mainly concentrate on the coarse end of the curve; traction population shows dominant in both log-probability plot and C/M diagram, which indicates coarser grains and poor sorting.The frequency curves of shallow-lake deposits are strongly bimodal and the main peak of grain size concentrates on 3-5φ, it shows that the deposits are mainly made of silt and sand which contain mud, σφ-2 to 3 ,skewness being positive; the probability plot reflects that the deposits move in the way of saltation and suspension or hypersaltation; in the C/M pattern the range of grain size is wider, which indicates the great differentiation of sorting.The kurtosis of the deep-lake deposits has a single peak, the grains are coarser than 4 φ, and their main peak concentrates on 8-9φ. It illustrates that all the deposits consist of suspension population with σφ of 1.5 to 2.0 and skewness being negative; probability plot has three log-normal segments, which represent coarse-silt, fine-siIt and clay respectively. The position of their junction correspondingly shifts towards fine size with the increasing depth of water; the C/M diagram corresponds to the sedimentary area of suspension of the deep-sea.The turbidite deposits in the northern deep-lake are deposits of density flows triggered by slumping and moving downslope, the grain size is coarser than that of other deep-lake sediments.The vertical section of turbidite deposits is interbedding of sand/mud with flysch feature.The monocyclic bed from the lower to the upper is moderate fine sand containing gravel, silt-sand and clay in turn, which reflects the feature of graded bedding.The cyclic bottom is obviously separated from underlying clay bed. The kurtos-is of the turbidite deposits is not obvious, and the grain size range is wider in frequency curve; the probability plot in a straight line has a low slope, indicating poor sorting; the position of points on C/M diagram corresponds to the grabed suspension deposits. C/M pattern in long belt shape is parallel to C = M straight line.In other deep-lake areas, the sediment sections show isotropic clay.In this article the grain size data on 260 samples are adopted. These samples were collected from the bottom of the lake, the core and partly from the lakeshore, among them the coarse ones are analyzed with sieve analysis and those fine-grained ones of 4.38φ are determined by automatic particle size distribution determination appartus ( Type RS-11 ) after being given separation treatment with supersonic wave. Moreover, statistical parameters should be made to the grain size data with moment measure.更多还原