辽西地区早白垩世义县组大康堡层沉积特征及沉积环境演化

Sedimentary characteristics and environmental evolution of Dakangpu layer of Early Cretaceous Yixian Formation in western Liaoning

辽西义县盆地下白垩统义县组大康堡沉积层分布范围广,为"热河生物群"的重要产出层位。通过对王家沟西山典型剖面的沉积学研究,识别出11种岩相类型,包括基质支撑砾岩相、凝灰质中-粗粒砂岩相、平行层理中-细砂岩相等,并将该时期的湖泊沉积划分为滨浅湖和深-半深湖环境。分析大康堡层垂向序列特征及纹泥特征,将该时期的湖泊演化划分为4个阶段:早期浅水湖泊沉积,见大量浅水生物化石;中期深-半深湖沉积,处于相对封闭-半封闭的状态,盐度增加;晚期湖泊水体变浅,水文动力条件增强,盐度降低;末期深-半深湖环境,纹泥指示陆源碎屑供给极少,降水较少。湖泊的演化过程受古气候控制明显。

Widely distributed in Yixian Basin in western Liaoning, Dakangpu layer of the Yixian Formation belongs to Lower Creta- ceou and is an important horizon of uJehol Biota”. A typical section was measured in detail for sedimentology and 11 lithofacies types were recognized, such as matrix supported conglomerate facies, tuffaceous medium-coarse grained sandstone facies and medium-fine grained sandstone facies with parallel bedding. Dakangpu layer comprises mainly lacustrine sediments including shore shallow lake fa-cies and deep and semi-deep lake facies. Based on analyzing the changes of vertical sequence characteristics and varves characteristics of Dakangpu layer, the authors divided it into four depositional stages. At the initial stage, the lake was just formed with a large num-ber of shallow water fossils. After that it entered into the middle-range stage with deep and semi-deep water in the relatively closed and semi-closed state, during which the salinity increased. In the late depositional stage, the lake became shallow with higher hydro-dynamic condition and low salinity. At the end of the deposition the lake had deep and semi-deep water, and the varves were devel-oped which indicated poor terrigenous clast and little precipitation. The evolution of the lake was controlled by paleoclimate obviously.