川中地区上三叠统小塘子组障壁砂坝及其成因分析

Barrier Island and Its Genesis Analysis of Xiaotangzi Formation of Upper Triassic in Central Sichuan Basin

障壁砂坝(障壁岛)不仅是重要的人类生活居住地,还是重要的油气聚集单元。川中上三叠统由滨岸向海方向,障壁砂坝与沼泽、潮坪、泻湖和浅海陆棚相伴生,滨岸局部地区发育有小型三角洲。纵向上,由下至上,障壁砂坝依次与浅海陆棚相、潮汐沟道相、沼泽相和泻湖相等沉积相构成一个完整的沉积旋回。障壁砂坝的形成与海平面稳定上升、小的地形坡降、地形坡折带发育和稳定的砂质物源供给有关。海平面稳定上升,波浪对沉积物进行改造,并在潮下带地形坡折带附近形成长条状的砂体。小的地形坡降有利于波浪和潮汐能量逐渐减弱,砂质沉积物在波折带附近逐渐堆积。随着海平面的持续上升,稳定的砂质物源供给保证障壁砂坝能够持续生长,不被海水淹没。

Barrier island is not only important for human residence, but also an important oil and gas accu- mulation unit. By the shore seaward, barrier dam and marshes, tidal flats, lagoons and shallow continental shelf accompanied each other,some areas of the coastal developed small delta. From the bottom,the shallow continental shelf, tidal channel, swamp and lagoon sedimentary facies constitute a complete sedimentary cy- cle in vertical. The barrier dam formation was related to the sea level rise,the small slope of the terrain,the development of terrain slope break belt and stability sandy source supply. Stable sea level rise and wave transformation formed terrain slope break belt near the body of a long strip of sand in the subtidal area. Small terrain slope is conducive to the gradually weaken of wave and tidal energy,and the sandy sediments gradual accumulated near the twists. With the source can ensure, the barrier dam to grow and continue arise of sea level, stable supply of sandy material not be submerged.