西秦岭古代地层记录中内波、内潮汐沉积及其成因解释

内波、内潮汐沉积是近十年来在古代深海环境中新发现的一种具牵引流性质的沉积相类型。西秦岭海西-印支造山带深海沉积中发现了多种样式的内波、内潮汐沉积,据沉积构造特征归纳为 7种微相类型 :1)具双向交错层细-中砂岩;2 )羽状交错纹理粉砂岩;3)束状透镜体叠加的交错纹理粉砂岩;4)复杂交织的双向交错纹理粉砂岩;5 )双向交错纹理粉砂岩;6 )波状、脉状和透镜状复合层理砂泥岩互层;7)波浪波痕细砂岩。研究表明,它们分别形成于 3种不同环境的深海浊流沉积体系内。内波、内潮汐沉积在深海环境中的分布特点 :一是具有普遍性;二是数量不够丰富;三是在层位上具有明显的选择性。通过研究说明,这些分布特点是与其形成和保存条件密切相关。

Internal-wave and Internal-tide Deposits in the Paleostratigraphic Record of the Western Qinling Mountains and Their Origin

Internal-wave and internal-tide deposits are akind of dragging-flow deposits recently found in ancient deep-sea environments. A variety of internal-wave and internal-tide deposits has been identified in the deep-sea deposit along the Hercynian-Indosinian orogeny of the western Qinling Mountains. According to their depositional structures they can be divided into 7 microfacies, 1. Fine- and medium-grained sandstone with bi-directional cross-bedding structure, 2. Siltstone with pinnate cross-lamination structure, 3. Siltstone with fascicular lens superposed cross-lamination structure, 4. Siltstone with complicatedly interweaving bi-directional cross-lamination structure, 5. Siltstone with bi-directional cross-lamination structure, 6. Sand and mud interbed with wave-, vein-and lens-like composite stratification, and 7. Fine sandstone with wave and ripple structure. The present study shows that they are formed in deep-sea turbidite systems of 3 different environments. The distribution of internal-wave and internal-tide deposits in deep sea is characterized by generality, non-abundance and evident selection for layers. All of these characteristics are closely related with their formation and preservation conditions.