塔里木盆地西南地区早中寒武世岩相古地理

Lithofacies Paleogeography of Early-Middle Cambrian in Southwestern Tarim Basin

塔里木盆地西南地区早中寒武世岩相古地理存在一定争议,这制约了该区的勘探评价。综合利用露头、钻井和地震资料,开展沉积相、地震相分析,并结合区域构造背景,恢复了岩相古地理格局,提出了相应的沉积模式。中下寒武统发育陆棚相、开阔台地相、局限台地相、蒸发台地相和缓坡相。震旦纪末期麦盖提斜坡南部形成水下低隆起,向南在西南坳陷区残留部分被动陆缘,主要发育缓坡相、陆棚相;麦盖提斜坡区地势较高,地层较薄,主要发育局限台地和蒸发台地潮坪;巴楚隆起区水体局限,在干燥炎热气候下形成了厚度较大的蒸发台地膏盐湖沉积。巴楚隆起区和麦盖提斜坡区中下寒武统膏盐岩分布广泛,与下伏碳酸盐岩可构成良好的储盖组合,西南坳陷区残留部分被动陆缘,烃源岩发育条件较好,这表明塔西南具有较好的油气前景。

The controversy over lithofacies paleogeography of Early-Middle Cambrian affected the hydrocarbon evaluation in southwestern Tarim Basin. According to outcrops, well and seismic data,the study of sedimentary facies and seismic facies was carried out, and the model of lithofacies paleogeography of Early-Middle Cambrian in southwestern Tarim Basin was reconstructed based on the tectonical background. Controlled by sea level change and paleogeographic pattern, there developed some facies including shelf, open platform, restricted platform, evaporate platform and gentle slope in Lower-Middle Cambrian. In Late Sinian,low uplifts formed in southern Maigaiti Slope, and thus a paleogeographic pattern of ocean basin-passive continental margin-intercraton depression distributed from south to north. In passive margin（south to the uplifts）, gentle slope facies and shelf facies developed. In the south margin of craton depression（Maigaiti Slope）, the tidal-flat facies of restricted platform and evaporate platform mainly developed with thin stratum. In the inner part of craton depression（Bachu Uplift）, gypsum-salt lake developed due to hot and dry climate, and poor water circulation. Source rock developed in the residual part of passive continental margin.Reservoir-cap assemblage of gypsum-salt rock and underlying carbonate distributed in Bachu Uplift and Maigaiti Slope. Thus there are good prospects for petroleum exploration in Lower-Middle Cambrian, southwestern Tarim Basin.