四川盆地西北部中三叠世雷口坡期岩相古地理

Sedimentary facies and palaeogeography of northwestern Sichuan Basin during the Leikoupoan (Middle Triassic)

关键词:  四川盆地西北部  中三叠世  雷口坡期  岩相古地理

Key words:  northwestern Sichuan Basin  Middle Triassic  Leikoupoan  sedimentary facies and palaeogeography

摘要:

四川盆地西北部中三叠统雷口坡组发育有蒸发台地、局限台地和开阔台地3种沉积亚相,其中局限台地是主要的沉积亚相。雷口坡一至五期沉积环境经历了水体逐渐加深※变浅※加深的过程:一期,在广元-旺苍、梓潼-三台等地区发育了蒸发台地沉积,且梓潼地区膏湖分布范围较广;二期,蒸发台地范围缩小,仅发育于旺苍和梓潼地区,其它地区为局限台地沉积;三期,水体加深,旺苍地区为开阔台地沉积,梓潼地区已无膏湖沉积;四期,主体为局限台地沉积,梓潼地区膏盆沉积再次发育;五期演变为开阔台地沉积,水体又加深。海平面升降变化是控制沉积相发育和空间分布的重要因素。

Abstract:

Three sedimentary subfacies are recognized in the Middle Triassic Leikoupo Formation in northwestern Sichuan Basin, including the evaporate platform, restricted platform and open platform subfacies, of which the restricted platform subfacies is accentuated. The sedimentary environments during Stages 1 -5 of the Leikoupoan spanned the evolutionary processes from deepening to shallowing to deepening again.During Stage 1, the evaporate platform deposits were developed over a vast area of the Guangyuan-Wangcang and Zitong-Santai regions, and the gypsum lake deposits occurred extensively in the Zitong region. During Stage 2, the evaporate platform deposits were restricted only in the Wangcang and Zitong regions, and the restricted platform deposits appeared in other regions. With the deepening of water body during Stage 3, the Wangcang region was occupied completely by the open platform deposits, and the gypsum lake deposits disappeared in the Zitong region. During Stage 4, the restricted platform deposits were organized in much of the study area and the gypsum lake deposits became into existence once again in the Zitong region. During Stage 5, the open platform deposits covered the study area once again. The sea-level fluctuations are believed to be the important factors controlling the development and spatial distribution of sedimentary facies.