中上扬子地区寒武纪第三世—芙蓉世古地理

中上扬子寒武纪第三世—芙蓉世台地相与滩相分布区是中上扬子地区重要的油气勘探目标区。利用野外露头资料、钻井资料和区域地质资料,识别出潮坪相、台地相、台地边缘相、浅海陆棚相和深水盆地相5种沉积相类型。在此基础上,编制了寒武纪第三世—芙蓉世古地理图,并探讨了储盖层的沉积地质条件。(1)第三世,发育大规模潟湖的局限台地广阔分布,西部为混积潮坪,台内及台缘发育滩相沉积。东南缘未形成完整的台缘带,湘西北一带为混积陆棚环境。东南缘向东,碳酸盐沉积物减少。(2)芙蓉世,随着海退的持续,隆起区扩大,深水盆地范围减小。中上扬子地区形成了镶边碳酸盐台地,浅滩沉积大量发育。(3)第三世—芙蓉世,以大套的厚层至块状的白云岩为主、分布广阔的局限台地与开阔台地,发育鲕粒及砂屑浅滩沉积的台地内部及边缘,均是有利的储集层沉积区。第三世广泛发育的潟湖沉积白云岩夹膏质白云岩、白云质膏岩、膏岩和粉砂岩,厚度较大,是中上扬子地区寒武纪重要的盖层沉积区。

Palaeogeography of the Cambrian Epoch 3-Furongian in the Middle and Upper Yangtze region

The platform facies and bank facies are important petroleum exploration target areas of the Cambrian Epoch 3-Furongian in the Middle and Upper Yangtze region. Based on the data of outcrops,wells,regional geology and previous studies,five types of sedimentary facies were identified, i.e., tidal-flat,platform,platform margin,shelf and deep-water basin, and palaeogeography maps were drawn and the basic geological conditions of the reservoirs and caprocks in Epoch 3-Furongian were discussed. (1)In the Epoch 3,restricted platform on which extensive lagoon developed nearly occupied the most areas of the Middle and Upper Yangtze region, the tidal flat distributed in the west, and banks developed at the margin and inside of platform. But the complete platform margin had not formed,the mixed shelf developed in northwestern Hunan Province. To the east of southeastern margin of Yangzte region,carbonate rocks reduced gradually. (2)As the regression in the Furongian,the uplifts expanded and deep-water basin shrunk sharply. The rimmed carbonate platform gradually formed with banks. (3)From the Epoch 3 to Furongian, restricted platform and open platform with dolostones were beneficial reservoir traps, as well as widely distributed oolitic banks and sand-sized intraclast banks. The widely developed lagoon deposits in the Epoch 3 were the significant caprocks,where the dolosontes with intercalated beds including gypsum-dolostones,dolomitic-gypsum rocks,gypsum rocks and siltstones with large thickness were deposited.