渤海湾盆地孤南洼陷沙三中亚段风暴沉积基本特征及其地质意义

Basic characteristics of tempestite sediments of Middle Sha 3 Formation in Gunan Subsag of Bohai Bay Basin and their geological significance

首次提出在孤南洼陷沙河街组沙三中亚段发育风暴岩沉积。根据岩心观察及分析,发现两处风暴岩沉积分别发育于浅湖和三角洲前缘沉积环境中。本区风暴岩沉积中发育以下相互伴生而具有指相作用的沉积构造,层面构造包括:渠模、截切、风暴形成的冲刷面;层理构造包括:块状层理、丘状交错层理、洼状交错层理、波状层理和浪成砂纹交错层理5种层理构造;以及生物逃逸迹及同生变形构造。本区风暴岩理想的垂向沉积序列可概括为"似鲍马序列",自下而上为:SA,递变层理段;SB,平行层理段;SC,风暴浪振荡作用段;SD,波状层理段;SE,泥岩段。本次风暴沉积的发现,将有助于对孤南洼陷沙三中亚段地层沉积时期滨浅湖范围的界定,增加了新的沉积相类型,为岩石地层的划分提供了新依据;此外,也为寻找良好的油气储集层和生油层提供了新空间。

This paper has proposed for the first time that tempestites were developed in the Middle Sha 3 Member of Shahejie Formation in Gunan Subsag.Based on core observation and analyses,the authors found two places of tempestites which were developed respectively in sediments of shallow lake and those of delta front.Some sedimentary structures were developed in this zone which were co-existent to serve as facies marks：Surface structures include gutter cast,truncated structure,surface of scour due to storms,whereas bedding structures include massive bedding,hummocky cross stratification,swale cross stratification,wavy bedding and wave-ripple bedding;in addition,life-escaping structures and contemporaneous deformation were also developed.The ideal vertical sequence of the tempestites in this zone is a Bouma-like sequence,and consists from bottom to top of five segments,namely SA,graded bedding;SB,parallel bedding;SC,storm wave oscillating effect;SD,wavy bedding;SE,mudstone segment.The discovery of tempestites is helpful to defining the shore-shallow lacustrine boundary,adds some new sedimentary facies types to this area,provides the new basis for lithostratigraphic division,and also supplies new space to the prospecting for ideal oil and gas reservoirs and source rocks.