干旱气候环境下小型冲积扇—辫状河沉积特征——以坎苏瓦特剖面紫泥泉子组为例

Arid climate alluvial fan-braided river system deposition:A case of Ziniquanzi formation in Kansuwate outcrop

为了认识准噶尔盆地南缘古近系沉积体系,以盆地南缘坎苏瓦特剖面古近系紫泥泉子组露头为研究对象,通过地球化学元素分析、沉积构造特征观察及地层实测,分析古气候条件、建立岩性序列、总结岩石相类型及其组合特征、明确沉积体系,建立沉积模式。结果表明:坎苏瓦特剖面紫泥泉子组发育一类干旱气候环境下的冲积扇—辫状河沉积体系,受气候影响显著,与潮湿环境下形成的冲积扇—辫状河沉积体系相比,砂地比明显偏低;冲积扇扇体具有规模局限、叠置频繁、隔夹层广泛发育的特点;辫状河具有改道频繁、持续时间短、延伸距离有限的特点。该研究结果对认识准噶尔盆地南缘古近系沉积体系具有参考意义。

The outcrop of Ziniquanzi unit from Kansuwate section was chosen to study for improving the research of the depositional systems in southern margin of Junggar basin. All of the paleo sedimentary environment,the lithologic sequence,the type of lithofacies,the depositional systems and the depositional model have been cleared based on analysis of geochemical element,sedimentary structure and actual measurement of field section. We believe that from Niquanzi unit of Kansuwate section developed a alluvial fan braided stream sedimentary system under arid climate environment. This sedimentary system is remarkably affected by climate and has significant differences with alluvial fan braided stream sedimentary system under humid environment. Clearly on the low side,compared with soorgorica,limited distribution of alluvial fan with constant overlies and has features of widespread development of arrier beds and interbeds; braided stream is characterized by constant re-channels,limited duration and extending distance. Based on the fact that typical sedimentary characteristics are clear,we have further discussed the sedimentary model of this sedimentary system and analyzed reasons of its formation.