滇中梅树村剖面筇竹寺组等深流沉积的发现及其意义

寒武系筇竹寺组是中国南方页岩气勘探的重要目标层位之一，同时也是澄江动物群的寄主层位，但对其沉积环境和沉积作用的研究相对薄弱。文章以滇中地区昆阳梅树村剖面为研究对象，在详细的野外观察基础上，应用指向沉积构造进行了古水流分析，并对广泛发育的条纹、条带构造进行了详细研究。结果表明：（1） 交错层理与小型槽模所表示的古水流夹角在43°和108°之间，集中分布的区间为50°和79°之间，其中同一薄层粉砂岩中两者的夹角平均值为50°，大于45°；（2） 条纹、条带构造在垂向上多数显示出双向递变的周期性特征，其中有的条纹构造还表现为多个周期的复合。结合当时的古地理特征和筇竹寺组的深水沉积环境，可推断沉积流体流动方向与古区域斜坡倾向存在大角度夹角，并且水流具有明显周期性特征，故可能为深水等深流。筇竹寺组深水等深流沉积的发现对于中国南方筇竹寺组页岩气烃源岩和储集层的分布研究以及澄江动物群的生存条件、死亡因素和软体化石的保存条件的研究均具有重要意义。

Discovery of Contourite and Its Significance in Qiongzhusi Formation of Meishucun Section,Central Yunnan Province,China

Although Qiongzhusi Formation of Cambrian is one of the most important shale gas exploration targets in South China andthe host rock of Chengjiang Fauna, studies of its sedimentary environments and processes are still inadequate. This study is focused onthe Meishucun Section of Kunyang in central Yunnan Province, where palaeocurrents with directional sedimentary structures areanalyzed and the extensive stripped-and-banded structures in Qiongzhusi Formation are studied based on detailed field observations.The results show that (1) the palaeocurrent angles between cross-beddings and small flutes are from 43°to 108°, with distributionmainly between 50° and 79°, and the average angle in the same thin-bedded siltstone is 50°, greater than 45°; (2) most stripped andbanded sedimentary structures have a bidirectional periodic evolution in vertical and some of stripped structures behave a compound ofmultiple periods. According to the palaeogeography and the deep-water deposition environment of Qiongzhusi Formation, we suggestthat the deep-water contour currents are responsible for these deposits because of the large angle between the flow direction ofsedimentary currents and the dip azimuth of the ancient regional slope, and also an obvious period of the depositional currents. Thediscovery of deep-water contourites in Qiongzhusi Formation has an important significance for understanding the distribution of shalegas source rocks and reservoir of Qiongzhusi Formation in South China, as well as the survival conditions, death factors andconservation conditions of the mollusks fossil in Chengjiang fauna.