陆相深水沉积层序和体系域边界识别方法初探——以东营凹陷牛38井为例

THE PRIMARY STUDY ON HOW TO DIVIDE SQUENCES AND SYSTEM TRACTS OF THE LACUSTRINE DEEP WATER ENVIRONMENTAL STRATA——A CASE STUDY OF WELL NIU 38 IN DONGYING DEPRESSION

浅水环境中 ,在水体由深变浅或者由浅变深变化过程中 ,沉积岩的特性会发生明显的变化。但在深水环境中 ,沉积岩的特征对水体深度的小范围变动的反应并不明显。如何进行偏深水陆相沉积地层的沉积旋回划分 ,是层序地层学研究中一个薄弱的环节。以位于东营凹陷牛庄洼陷内资料较为齐全的牛 38井为研究对象 ,选用对水深变化较敏感的指标 ,如总有机碳含量、稀土元素、声波时差等 ,并结合Fischer曲线法 ,对深水沉积地层的层序地层单元划分进行了初步探讨 ,取得了较好的对应效果。研究结果表明 ,在层序和体系域边界上 ,总有机碳含量较低 ,声波时差曲线的斜率会发生明显的变化 ,稀土元素的相对含量较低 。

Certain properties of sedimentary rocks are a function of the depths of waterbody in shallow water environment. However they are not sensitive to the variation of the depth of waterbody in deep water environment. It is still a weak point in sequence stratigraphy to recognize the sedimentary cycles of lacustrine strata formed in deep water environment. Well Niu 38 with fairly full data, located in the Niuzhuang region, Dongying depression,is chosen to study in this paper. Some indexes sensitive to the variations of the depth of water, such as TOC, acoustic time, REE, etc., combined with Fisher plot, are used to recognize the sequences and system tracts of deep water environment, and good results have been obtained. As shown in this paper, low contents of TOC and REE, together with the variation of the slopes of acoustic time curves and Fisher plot, appear on the boundaries of sequences and system tracts.