东濮凹陷白庙地区沙三段重力流沉积的研究

本文论述了东濮凹陷白庙地区沙三段重力流沉积成形的条件、层序特征、水下扇的时空变迁和砂体展布。认为本区沙三段时期满足重力流的形成条件,主要表现在六个方面:(1)干旱-半干旱的气候环境有利于母岩的机械风化和山洪的形成;(2)母岩的组合及其产状容易发生机械破碎,形成泥石流;(3)盆地边缘地形高差悬殊;(4)高密度的水下泥石流;(5)堆积速率大;(6)水深位于半深湖以下。重力流沉积(湖底扇)的垂向层序特点是:扇推进式层序发育,但都不完整,而主水道单独出现。构造运动控制着湖水的深浅和范围,也控制着水下扇的时空变迁;伴随着沙三段构造活动的弱→强→弱变化,水下扇的变迁也显示出一个周期,即推进→后退→推进。而扇的分布又明显地控制了砂体的展布,决定着湖底扇砂体呈扇形(平面)或楔形和透镜状(剖面)。

A STUDY ON GRAVITY FLOW DEPOSITION OF ES_3 AT BAIMIAO DISTRICT IN DONGPU DEPRESSION

The favorable conditions for developing gravity flows at Baimiao district in Dongpu Depression are as follows. (1)Arid-subarid palaeoclimate was helpful for mechanical weathering of source rocks and torrent forming; (2) The combination of source rocks and their occurrence were liable to cause mechanical breakdown of rocks and form mudflow, (3)There was a considerable height difference along the border of the basin, (4) The density of subaqueous mudflow was 2.4-2.7g/cm3; (5)There was a high rate of accumulation in the district; (6)The depositional enviroment was located below the semi-deep lake. The sublacustrine fan in the area,compared with R.G.Walker's (1978) subaqueous fan sequencers of developed and incomplete fan-prograded sequence and independently occurred main channels. Tectonic activity controled both the depth and area of lake water and the vicissitude of sublacustrine fans with time andspace. The fan vicissitude showed one cycle, i.e.progressive--regressive--progressive with the tectonic movement from strong to weak in the member, The distribution of fans evidently controlled sandbody occurrence.