阿克库勒凸起东河砂岩的沉积相与层序地层

Sedimentary facies and sequence stratigraphy of Donghe Sandstone in Akekule Uplift

阿克库勒地区东河砂岩包括了含泥砾砂岩、分选好的中-细粒砂岩、粉砂岩及泥岩,是一个具有完整海侵-海退旋回的标准层序,顶、底分别为两个不整合面所限,为Ⅰ型层序边界。东河砂岩自下而上明显地分为低位体系域、海侵体系域与高位体系域。由于低位体系域是陆上河流的充填沉积,因此,盆地内低位体系域不发育,分布局限。海侵体系域主要为受潮汐控制的滨岸沉积,由一系列向上变浅和变细的副层序堆积成退积的副层序组,副层序由下部的潮下砂坝向上逐渐变化为潮间砂坪、砂泥混合坪及泥坪。高位体系域主要分布于东河砂岩的上段,由于东河砂岩的不断沉积,在达到最大海泛面之后,滨岸带海水循环畅通,形成了以波浪作用为主的浪控滨岸沉积体系,主要是以分选好的灰白色中-细粒砂岩为特征,构成了特色十分鲜明的“东河砂岩”。

Donghe sandstone in Akekule, composed of mud-pebbly sandstone, well sorted medium-to finegrained sandstones, siltstone and mudstone, is a normal sequence with a complete transgressive-regressive cycle, the top and bottom of which are defined by unconformities, i. e. , type Ⅰ sequence boundaries. Donghe sandstone can evidently be divided, from bottom to top, into lowstand system tract, transgressive system tract and highstand system tract. As the lowstand system tract is subaerial fluvial deposit, it is underdeveloped in the basin with limited distribution. The transgressive system tract is mainly composed of shore deposit controlled by tide. A series of shallowing and fining upward parasequences constitute the retrograding parasequence group. The parasequences gradually change upward from subtidal sandbar in the lower part to intertidal sand flat, mixed sand and mud flat, and mud flat. The highstand system tract is mainly distributed in the upper Donghe sandstone. Duing the continuous deposition of Donghe sandstone, the inshore sea water circulated smoothly and unimpededly after the largest marine flooding surface was reached, leading to the formation of wave-controlled shore deposition system with wave action as the main geologic agent, which is mainly characterized by grayish white medium-to fine-grained sandstone. They constitute the characteristic “Donghe sandstone”.