鄂尔多斯中生代陆相盆地层序地层格架及多种能源矿产聚集

鄂尔多斯盆地上三叠统-下中侏罗统发育的大型陆相盆地层序类型包括河流层序、湖泊层序和湖泊三角洲层序等,并构成上三叠统河流-湖泊-湖泊三角洲和下中侏罗统河流-湖泊三角洲-河流-湖泊层序序列。构造沉降的幕次、周期性控制层序的旋回性与层序内部发展的阶段性;古气候制约烃源岩和煤层的形成与保存;沉积物供给影响陆相盆地的可容纳空间变化;湖平面变化受构造、物源及古气候变化的综合影响,是陆相盆地层序形成的主要因素。多种能源矿产聚集与层序地层格架有关。低位体系域发育良好的储层,形成延长组三角洲砂体和延安组河道砂体的地层-岩性油气藏;湖进体系域的密集段是最佳的烃源岩和盖层,延安组煤层发育在湖进体系域晚期的废弃三角洲平原之上。除了高位体系域外,直罗组低位体系域的下切谷和辫状河道砂体也是层间氧化带砂岩型铀矿的重要成矿层位。

Sequence stratigraphic framework and its control on accumulation of various energy resources in the Mesozoic continental basins in Ordos

The types of sequences developed in the Upper Triassic and Lower-Middle Jurassic in Ordos basin inelude fluvial sequence, lacustrine sequence, and lake delta sequence, and they constitute two serial sequences namely the fluvial-lacustrine-lake-delta sequences in the Upper Triassic and the fluvial-lake-delta-fluvial-lacustrine sequences in the lower-Middle Jurassic. The episodes and cyclicity of tectonic subsidence controlled the cyclicity of the sequence and the stage of sequence development ; paleoclimate controlled the formation and preservation of the source rocks and coalbeds; sediment supply influenced the accommodation space of the basin; and the change of lake level was caused by the combined forces of tectonics, source and paleoclimate. These are the main factors leading to the formation of sequences in continental basins. The accumulation of various energy resources maight be related with the sequence stratigraphic framework. The well-developed reservoirs in lowstand system tract formed stratigraphic-lithological traps in the delta sand bodies in the Yanchang Formation and the channel sand bodies in the Yanan Formation. The condensed intervals of transgressive system tract are good source rocks and caps. The Yanan Formation coalbed was developed on the abandoned delta plain in the late transgressive system tract. In addition to the highstand system tract, the incised valley and braided channel sand bodies developed in the lowstand system tract of the Zhiluo Formation are also important potential target horizons for uranium deposits of interlayer oxidation zone and of sandstone-type.