摘要： 等深流沉积是深水沉积中的常见类型之一。古代地层记录中等深流沉积的鉴别及形成机理研究相对薄弱。在鄂尔多斯盆地西缘奥陶系克里摩里组发现了一种新的等深流沉积类型,即透镜状等深流沉积。研究表明: (1)研究区发育4种岩相及组合。岩相1为透镜状泥晶灰岩,岩相2以透镜状粉晶灰岩为主,岩相3为透镜状泥晶及亮晶方解石胶结砾屑-砂屑灰岩,岩相4以层状砾屑灰岩最为常见。(2)透镜状泥晶、粉晶及砾屑-砂屑灰岩相单层厚度相对较小,波状界面,呈透镜状,局部见泥质纹层、条带及斑点,粉晶方解石多呈斑块状,整体呈细—粗—细沉积序列,为等深流持续作用而成; 层状砾屑灰岩相中砾屑见叠瓦状构造,局部见倒“小”字排列,可能与风暴相关。(3)碳氧同位素反映相对海平面及古温度具有2个升高—降低旋回及1个持续上升半旋回。(4)研究区等深流为相对低能的温盐环流。等深流活动强度与海平面升降、盐度变化呈正相关。(5)从下至上,等深流活动逐渐加强,局部存在短暂极强现象,并可能受风暴影响。

关键词: 等深流, 等深流沉积, 克里摩里组, 奥陶系, 鄂尔多斯盆地

Abstract: Contour current deposits are a common type of deep-water deposits. However,limited work has been done on identification and formative mechanisms of contour current deposits in the rock record. Here,a new type of contour current deposits(lenticular contour current deposits)is documented in the Ordovician Kelimoli Formation of the study area in the Ordos Basin. The results show that There are four types of lithofacies and lithofacies associations in the study area,including lenticular micrite(lithofacies 1),mainly lenticular silt-sized silt-crystalline limestone(lithofacies 2),micrite and sparry calcarenite or calcirudite(lithofacies 3),and bedded calcirudite(lithofacies 4). It is found that lenticular micrite,silt-sized silt-crystalline limestone,and calcarenite or calcirudite are present as fine-grained through coarse-grained to fine-grained facies sequences. These deposits are characterized by relatively thin bed thickness,wavy surface,lenticular geometry,and association with muddy lamina,stripe,and spot,which are attributed to the persistent effect of contour current. Silt-sized silt-crystalline limestones are usually mottled. Bedded calcirudites with imbricate structures and the inverse Chinese character of “small”are likely to be storm deposits. In addition,carbon and oxygen isotopes indicate that relative sea level and paleotemperature show two rising to falling cycles and a continously-rising half cycle. It is also found that the contour current in the study area are low energy thermohaline circulation and that the strength of the contour current is positively correlated with eustatic sea level and salinity change. Finally,the energy of the contour current increases gradually upsection with occassional transient extremes,which might be also effected by storms in the Kelimoli stage.

Key words: contour current, contour current deposit, Kelimoli Formation, Ordovician, Ordos Basin

中图分类号: 

• P512.32