桦甸盆地始新统桦甸组扇三角洲和水下扇粒度分析与对比

摘要

桦甸盆地始新统桦甸组扇三角洲主要划分出泥石流、水上分流河道、水下分流河道、河口坝、席状砂等沉积微相；水下扇主要划分出辫状沟道和远源浊积岩等沉积微相.扇三角洲沉积物以颗粒支撑为主,自下而上按席状砂、河口坝、水下分流河道、水上分流河道、泥石流的顺序,沉积物粒度和标准偏差递增；频率曲线尖度递减；概率累计曲线由高-较高斜度两段式逐渐过渡为中-低斜度两段式、微向上凸的弧线式.反映出上述各微相向上粒度由细变粗的反粒序沉积特征,分选由好变差,杂基含量和水介质能量均逐渐增加.水下扇沉积普遍为杂基支撑,自下而上从远源浊积岩到辫状沟道沉积,粒径和标准偏差增大；频率曲线尖度减小；概率累计曲线主要由斜度较高的一段式过渡为斜度不大的一段式或微向上凸的弧线式,说明从远源浊积岩到辫状沟道微相粒度逐渐变粗,分选逐渐变差,杂基含量和水介质能量也逐渐增强.本区扇三角洲CM图像呈“S”形,主要表现为牵引流沉积特征；水下扇CM图像表现为与C=M线平行的长条带状重力流沉积特征.%In Eocene Huadian Formation in Huadian Basin, the fan delta can be mainly divided into the following microfacies; debris flow, overwater distributary channel, underwater distributary channel, river mouth bar and sheet sand. The microfacies of the underwater fan in the Huadian Formation are mainly braided channel and far source turbidite. The sediments of the fan delta mainly show grain-supported structure. According to the bottom-up sequential pattern of sheet sand, river mouth bar, underwater distributary channel, overwater distributary channel and debris flow, the grain size and standard deviation are increasing; the sharpnesses of frequency curves are decreasing ; the shapes of the probability cumulative curves change from higher-high slope two segments through medium-low slope two segments to slightly upward convex curvilinear style. The microfacies show the characteristics of reverse grain size order, sorting degrees decreasing, contents of matrix and water body energies increasing in as-cending order. The sediments of the underwater fan show matrix-supported structure. According to the bottom-up sequential pattern of far source turbidite and braided channel, the grain sizes and standard deviations are increasing; the sharpnesses of frequency curves are decreasing; the shapes of the probability cumulative curves mainly change from higher slope one segment to lower slope one segment or slightly upward convex curvilinear style. These changes reflect that from far source turbidite to braided channel, grain sizes become coarse, sorting becomes poorer, contents of matrix and water body energies are increasing. The CM diagram of the fan delta in the study area has S-shap, which mainly corresponds to traction current deposits; the CM diagram of underwater fan shows long-band paralleling to the C = M line, which corresponds to gravity flow deposit.