塔里木盆地西部地区中奥陶统一间房组沉积演化及其控制因素

Depositional evolution and its controls of the Middle OrdovicianYijianfang Formation in western Tarim basin

塔里木盆地中奥陶统一间房组沉积演化和沉积层序的发育特征及其控制因素目前还存在争议。选择塔里木盆地西部良里塔格山地区一间房组为研究对象,基于沉积相和高频米级沉积旋回类型的识别及其垂向叠置样式的分析,明确一间房组的沉积演化和沉积层序的发育特征及其控制因素。研究表明:(1)一间房组沉积时期,良里塔格山地区整体为一个碳酸盐岩缓坡沉积体系,主要发育10种岩相类型和2个沉积相带(潮缘—局限潮下带和开阔潮下带);(2)一间房组发育两种高频米级沉积旋回,分别为潮缘—局限潮下沉积旋回和开阔潮下沉积旋回;(3)识别出2个半三级层序,层序界面主要为岩性转换面,其中一个完整的三级层序包括海侵体系域和海退体系域两部分;(4)沉积演化与层序发育的主要控制因素包括古地理格局、沉积微地貌及不同级次的相对海平面变化。其中古地理格局控制着整体的沉积相带分布,沉积微地貌决定着特定岩相(如瓶筐石礁)发育的优势部位,不同级次相对海平面变化则制约着沉积相的时空演化。

Factors controlling the depositionalevolution and sequence development of the Middle Ordovician Yijianfang Formation inthe Tarim basin are still controversial. Based on the identification of sedimentary facies and high-frequency meter-scale sedimentary cycles and their vertical stacking patterns, the Yijianfang Formation of the Lianglitage Mountain area(western Tarim basin) is systematically studied, in order to clarify the depositionalevolution and sequence development and their controls. The conclusions are as follows:(1) During the deposition of the Yijianfang Formation, the Lianglitage Mountain area was represented by a carbonate ramp system, on which ten types of lithofacies and two depositional facies belts(peri-restricted and open-marine subtidal facies).(2) Two types of high-frequency meter-scale sedimentary cycles were recognized, including peri-restricted and open-marine subtidal sedimentary cycles.(3) Two and half third-order depositional sequences were identified, whose boundaries were characterized by transitional lithology zones. A complete third-order depositional sequence consists of a lower transgressive part and an upper regressive one.(4) The depositionalevolution and sequence creation were primarily dictated by paleogeographic configuration, sedimentary microreliefs, relative sea-level variations of different orders. The paleogeographic configuration controlled the overall distributional patterns of depositional faciesbelts;the sedimentary microreliefs determined the preferable positions of specific lithofacies(i.e., Calathium reef);relative sea-level variations of different orders governed the tempo-spatial distribution of depositional facies.