滑塌型深水重力流沉积特征及沉积模式:以渤海湾盆地临南洼陷古近系沙三中亚段为例*

综合运用钻井岩心、测录井等资料,通过岩心观察、薄片鉴定和粒度分析等方法,对渤海湾盆地临南洼陷古近系沙三中亚段深水重力流沉积类型及其沉积特征、沉积模式展开研究。研究表明,临南洼陷沙三中亚段深水重力流沉积主要发育滑塌沉积、碎屑流沉积和浊流沉积3种成因类型。滑塌沉积以包卷层理、液化砂岩脉、阶梯状小断层、变形岩层与未变形岩层叠置为典型特征。碎屑流沉积中砂质碎屑流沉积分布较广,以突变的底部接触面、块状层理、泥岩撕裂屑、土黄色泥砾、突变或不规则的上接触面为典型识别标志。浊流沉积则以正粒序层理、底部冲刷面和槽模、薄层砂泥互层、不完整的鲍马序列为典型识别标志。滑塌沉积主要发育在三角洲前缘斜坡根部,在滑塌沉积前方形成碎屑流沉积,碎屑流向前搬运的过程中,流体被稀释逐渐转化成浊流。滑塌型深水重力流沉积整体分为近源沉积、中部沉积和远源沉积3个部分: 近源沉积主要发育具变形构造的滑塌沉积和厚层块状砂质碎屑流沉积;中部沉积主要发育砂质碎屑流沉积及浊流沉积;远源沉积以薄层浊流沉积为主。

Sedimentary characteristics and depositional model of slumping deep-water gravity flow deposits:A case study from the middle Member 3 of Paleogene Shahejie Formation in Linnan subsag,Bohai Bay Basin

Based on drilling cores,logging data,the types,characteristics and model of deep-water gravity flow deposits in the middle Member 3 of Paleogene Shahejie Formation in Linnan subsag were studied according to core observation,thin-section identification and grain size analysis. The research shows that the deep-water gravity flow deposits in the middle Member 3 of Shahejie Formation in Linnan subsag of Bohai Bay Basin are mainly developed of three kinds of sedimentary types: Slumping deposits,debris flow deposits and tubidity current deposits. The convolute bedding,liquefied sandstone vein, small terraced fault and superposition between deformed rock and undeformed rock are the typical characteristics of the slumping deposits. The sandy debris flow deposits are well developed in the research area which can be recognized with the mutant bottom contact surface,massive bedding,spliting muddy clastics,khaki muddy gravels and the mutant or irregular top contact surface. The tubidity current deposits can be recognized with marks of the normal gradings,erosional basal surface,flute casts,thin interbedding of sandstone and mudstone and the incomplete Bouma Sequence. Slumping deposits mainly developed in the root of the delta front slope while sandy debris flow deposits developed in the front of the slump deposits. Debris flow was diluted and transformed to turbidity current gradually during its forward transportation process. The slumping gravity flow deposits can be divided into three parts: Near source deposits,middle deposits and the distal deposits. The near source deposits are mainly composed of slumping deposits with deformation structures and thick massive sandy debris flow deposits. The middle deposits mainly contain sandy debris flow and tubidity current deposits. The distal deposits are dominated by thin bedded turbidite deposits.