冷水碳酸盐岩研究现状与展望

Cool-water Carbonates: A Review of the Current Status and Prospects

长期以来,海相碳酸盐沉积物被广泛认为是温暖浅海沉积环境中的产物,然而近年来国外研究表明,在冷水陆架环境中,也可以形成规模的碳酸盐沉积,即冷水碳酸盐岩。通过对大量文献的调研,综述了冷水碳酸盐岩的概念、地质特征、沉积模式等方面的研究进展,并展望了该研究领域未来的发展方向。研究表明,冷水碳酸盐沉积是指在(古)纬度约30°~35°以上的温带及寒带地区、温度约20℃以下的沉积水体中,或是在富营养的寒冷上升流水体中形成的碳酸盐沉积物或岩石,其沉积特征与暖水碳酸盐岩不同。冷水碳酸盐沉积物中的生物颗粒组合以底栖有孔虫、软体动物、苔藓虫等异养生物和钙质红藻为主,缺乏造礁珊瑚和钙质绿藻以及鲕粒、集合颗粒等非骨架颗粒,而且沉积物中灰泥基质含量较少,矿物成分以方解石为主,氧同位素较重,胶结作用弱,以破坏性成岩作用为主。冷水碳酸盐沉积形态以缓坡为主,波浪磨蚀和再沉积作用较强。古代冷水碳酸盐岩的沉积特征、识别标志及其作为储层的油气资源潜力尚处于探索阶段,仍需进一步深入研究。

Marine carbonate sediments is widely considered to be the products deposited in a warm and shallow sea environment for a long time, however, in recent years some overseas researches showed that the massive carbonates also can deposit in a cool-water shelf environment, namely cool-water carbonates. Based on the investigation of a large number of literatures, this paper reviews the concept, geological characteristics, sedimentary models of cool-water carbonates. Cool-water carbonates refers to the carbonate sediments or rocks deposited on the bottom of water bodies in a temperate zone or a polar zone with the latitude/palaeolatitude above about 30°~35° and the temperature below 20℃,or in a upwelling cool nutrient-rich water, so its sedimentary characteristics are different from the warm-water carbonates.The skeletal grain assemblages in cool-water carbonate sediments mainly consist of heterotrophic organisms, including benthic foraminifera, mollusks and bryozoans, and calcium red algae, but lack hermatypic coral reefs, calcified green algae and non-skeletal grains such as ooids and grain aggregates. The cool-water carbonates has less lime mud, more calcite, and heavier oxygen isotope. Its cementation is weak and its diagenesis is predominantly destructive. The cool-water carbonates has the geometry of ramp predominantly with strong wave erosion and re-sedimentation.