四川盆地上三叠统小塘子组沉积特征及地质意义*

利用四川盆地内750口单井资料和26条露头剖面资料，采用单因素编图、多因素综合分析的方法，重现了四川盆地小塘子组的岩相古地理，为正确评价其天然气资源状况和龙门山的演化过程奠定了基础。研究认为，川中和川南地区小塘子组发育障壁砂坝—潟湖沉积，川西坳陷北部和南部发育三角洲沉积，中部发育浅海陆棚沉积。晚三叠世早期，龙门山北段开始隆升，并为盆地提供物源，从而形成川西北部的三角洲沉积；川中和川南地区由于地势平缓，波浪和潮汐改造强烈，从而形成障壁砂坝—潟湖沉积；川西南部物源来自于康滇古陆。小塘子组烃源岩大面积分布，厚度较大，有机碳含量和成熟度均较高，以Ⅱ型至Ⅲ型干酪根为主，泥质烃源岩具有较高的成熟度且有机碳含量范围较宽，为小塘子组的大面积生烃提供了物质保障。

Depositional characteristics and its geological significance of the Upper Triassic Xiaotangzi Formation in Sichuan Basin

Correct understanding of depositional systems of the Upper Triassic Xiaotangzi Formation of Sichuan Basin，is not only conducive to the restoration of the early Late Triassic palaeogeography，but also helps to be a correct evaluation of hydrocarbon potential.Comprehensive analysis of outcrops and single well manifest 3 types of depositional systems，namely，delta，barrier island-lagoon and shallow shelf，developed.Delta depositional systems are mainly distributed in the northwest and southwest of Sichuan，with a small delta developed in central Sichuan.Barrier island-lagoon depositional system is chiefly located in central and southern Sichuan，shallow shelf depositional system situated in the middle of western Sichuan Basin. In the Late Triassic，collision of the Yangtze Plate and North China Plate closed from east to west，leading to uplifting of the northern section of the Longmenshan Mountain and formation of the delta depositional systems in northern Sichuan.Provenance of the southern section of the western Sichuan is from Kangdian Old Land.In central and southern Sichuan，because of flat terrain and strong tidal reworking，a barrier island-lagoon depositional system formed.Be a large area of distribution of thick source rocks，with Ⅱ-Ⅲ kerogen mainly argillaceous source rock has a wide scope of carbon content and high organic carbon content of maturity.In shallow shelf areas and the lagoon subfacies，source rock with type Ⅱ kerogens based，TOC content has the highest average content of greater than 2％.In remote sand bar and prodelta，TOC content is higher，ranging from 2％ to 3％，and type Ⅲ kerogen based.