14 / 2021-06-19 19:42:26

基于偏正态概率分布的粒度分布次总体的分离及其沉积环境指示意义——以鄱阳湖现代沉积物为例

skew normal probability distribution, grain-size distribution, parameters of subpopulations, sedimentary environment, Poyang Lake

Operated by multiple sedimentary processe, the occurrence frequencies of different diameter particles, called grain-size distribution (GSD) in sedimentology and geology, records original sedimentary information. GSD is superposed by multi-subpopulations, and the corresponding frequency curve could be bimodal or multimodal. Traditional methods for sedimentological analysis do not research the subpopulations in GSD deeply. Based on 214 GSDs form modern sediments in Poyang Lake, skew normal probability distribution is used to decompose totally 977 subpopulations in this paper. Statistical parameters of subpopulations, mean, sorting, skewness, kurtosis, percentage and maximum-frequency, are all calculated. Similarities and differences of these parameters from various sedimentary environments are compared. Means of subpopulations focus in six intervals: 0~1ϕ, 1~2ϕ, 2~3ϕ, 4~5ϕ, 6~7ϕ and 7~8ϕ. Subpopulations with means in 0~2ϕ, 2~3ϕ and 4~5ϕ are excellent, excellent-well and excellent-moderate sorted respectively; sorting of subpopulations with means in 6~8ϕ are negative linear correlated with means. Subpopulations with means in 4~5ϕ and 6~8ϕ are mainly very-coarse skewed. Kurtosis of all subpopulations are less than 0.8. Percentages of subpopulations with means in 4~5ϕ and 6~8ϕ are generally less than 30%. Maximum frequencies of all subpopulations are less than 12%, and that of subpopulations with means in 4~5ϕ and 6~8ϕ are less than 3% and 2% respectively. Percentages of subpopulations with different means are positive linear correlated with corresponding maximum-frequencies. From channel to terminal of river, and downstream or left and right away from channel in river terminal, means of main-subpopulations decrease gradually. There is no obvious main-subpopulation in GSDs from sediments from interchannel hollows and lake regions. In island of Kangshan River, GSDs of sediments from channels and floodplains are constituted by three and five different types of subpopulations respectively. This paper would offer reference information for distinguishing sedimentary environments and researching sedimentary processes quantificationally.