陆相伸展盆地的层序类型、结构和序列与充填模式--以冀中坳陷下第三系为例

陆相层序受自然地理景观、影响地层发育的地质营力及地层类型等因素影响,因此层序类型多种多样。在冀中坳陷同伸展期发育洪积层序、湖泊层序和冲积层序等三种层序类型。洪积层序是盆地伸展初期地貌反差较大物源供给充分气候干旱条件下发育的一种陆相层序类型,以冲积扇沉积为主,山高盆窄,汇水湖泊面积较小;湖泊层序发育在盆地强烈伸展基底快速沉降气候湿润湖泊水域宽深时期,湖泊水域宽,连通好,湖水深,是烃源岩发育的黄金时期。湖泊层序以湖泊沉积为主,其次为河流和少许冲积扇沉积。冲积层序是在盆地伸展末期地貌反差强度减弱物源距离逐渐加大时的沉积产物,主要为干旱气候条件下的河流、三角洲沉积,湖泊沉积局限。研究表明,影响陆相层序形成的构造、物源、气候等因素与湖泊水体或水平面变化构成一种多元“函数”关系,湖平面变化是上述因素的综合体现。陆相断陷盆地的层序结构大多与湖泊水体之间存在密切联系,因此层序的结构以三分为主。受地壳构造运动控制,断陷盆地发育的层序具有序列性,即下部洪积层序、中部湖泊层序和上部冲积层序。这种序列性是盆地充填对地壳幕式伸展的沉积响应。在盆地充填过程中,不同类型的陆相层序其体系域发育程度具有较大差异。一般地,洪积层序的低位域沉积?

Types, Textures and Series of the Continental Sequences and Model of Sedimentary Basin-Fill in Rift Basin: A Case Study from Jizhong Basin, China

The continental sequence deeply affected by natural geographic districts, geological forces and strata types, therefore occurred some kinds of types. There are three kinds of sequence types including alluvial sequence, lacustrine sequence and fluvial sequence that present in Jizhong basin during the syn extensional stage. The alluvial sequence is mainly composed of alluvial fan systems and grows up in the initial stages of the basin development. Here the relief contrast was strong, provenance supply was abundant and climate was arid, so the lacustrine area was narrow in proportion to the alluvial and fluvial area. The lacustrine sequence mainly made up of lacustrine sedimentary systems, and partially fluvial sediments and a little of alluvial interlayer. The stage was a period of rapid growth of the rift basin. The basin base subsidized fast and climate humid, lacustrine area larger, thereby gaining a period for hydrocarbon rock to form. The fluvial sequence began to form in last stage of the basin extend. The geographic contrast gradually was reduced. The deposit was far from the source region,and the area of the fluvial systems was deadly larger than the area of the lacustrine. The authors suggested that a polynomial relation exists between the lake level change and tectonic movement, provenance, climate factor and so on, the former only incarnates the synthetically changes of the latter. The sequence texture of the continental rift basin is under the control of the lake level change, like the sequence texture of the marine basin is controlled by sea level change. Therefore, the continental sequence may be trisection according to the lake level change. The sequences of the continental rift basin controlled by tectonic movement develop in succession, as the alluvial sequence located at the bottom, the lacustrine sequence at the middle and the fluvial sequence at the upper. This serial sequences is a response that sedimentary basin fill to the episodic tectonic movement. During the basin fill, there is clearly a difference among the sedimentary system tract growth of each sequence. In general, the lowstand system tract (LST) of the alluvial sequence is superior to the lacustrine and fluvial sequences. The LST of the lacustrine is absent and/or lack, but the transgressive system tract (TST) and/or highstand system tract (HST) deposited in the lake level rise are best of all development. The LST and/or HST deposited in the lake level fall of the fluvial sequence are the best in the each sequence. The tectonic movement is primary factor to control the continental sequence type, and the lake level change controls the texture of the sequences.