楚雄盆地晚三叠世古地理变迁

The palaeogeographic changes of the Chuxiong Basin in Yunnan during the Late Triassic

关键词:  楚雄盆地  晚三叠世  盆地演化  古地理  云南

Key words:  Chuxiong Basin  Late Triassic  basin evolution  palaeogeographic change  Yunnan

摘要:

楚雄盆地晚三叠世为一建立在扬子板块西缘前寒武纪基底之上的海相-海陆过渡相-陆相沉积盆地。中三叠世拉丁期-晚三叠世卡尼期沉积了一套深水的灰色薄层状粉砂质泥岩和泥质粉砂岩;诺利期早期以华坪隆起为界有两个沉降中心,华坪隆起以西的推覆体之上为广海陆架相的细碎屑岩沉积、远源浊积岩,以东为局限环境下的细碎屑岩沉积夹浊积岩;诺利期晚期为大规模的三角洲前缘砂体组成下超的复合体,古地理格局继续保持东西向分带,呈对称分布,盆地西部为陆相、海陆过渡相,盆地中部为海相沉积。瑞替期在原形盆地中形成舍资组的河流-滨岸沉积,在推覆体上形成白土田组的冲洪积物。总之,表现古地理变迁为一个由西东逐渐超覆、由下向上粒度逐渐变粗、由海相变为陆相的过程。

Abstract:

The Chuxiong Basin in Yunnan was a marine-continental sedimentary basin during the Late Triassic, grounded upon the Precambrian basement on the western margin of the Yangtze plate. The deep-water grey thin-bedded silty mudstone and muddy siltstone were laid down during the Ladinian to the Carnian. During the early Nornian, there occurred two depocenters in the basin separated by the Huaping uplift:the open sea shelf fine-grained clastic rocks and distal turbidites above the nappes west of the uplift, while the (fine)-(grained) clastic rocks intercalated with turbidites in the restricted environments east of the uplift. Till the late Nornian, the (large)-(sized) delta front sandstones constituted downlapping complexes. The palaeogeographic framework displays a symmetrical EW-trending zonation. The continental and (continental)-(marine) deposits occur in the western part of the basin, while the marine deposits in the central part of it. During the Rhetian, the fluvial-littoral deposits were formed in the Shezi Formation, and the alluvial-pluvial deposits in the Baitutian Formation above the nappes. Collectively, the palaeogeographic changes are characterized by the gradual (overlapping) from west to east and coarsening from bottom to top, and the transition from marine to continental deposits.