川南—黔北地区晚奥陶世凯迪期早期与凯迪期晚期岩相古地理

晚奥陶世凯迪期早期与凯迪期晚期之交,是沉积演化和盆山转换极为关键的时期,在这个短暂时期内,川南—黔北地区几乎全部从碳酸盐沉积转换为碎屑岩沉积,详细研究这一转换时期的沉积特征及其岩相古地理变迁对探讨该区的沉积演化和盆地演化具有重要的意义。为了良好地揭示凯迪期早期与凯迪期晚期之交这一沉积转换关键时期的岩相古地理变化,采用层序岩相古地理编图思路,以凯迪阶涧草沟组与五峰组之间的界面作为编图的等时界面,编制了凯迪期早期涧草沟组顶部与凯迪期晚期五峰组底部2幅岩相古地理图,凯迪期早期涧草沟组顶部古地理面貌表现为古隆起、古暴露区、古剥蚀区、潮坪、局限台地、开阔台地和浅滩7个古地理单元;凯迪期晚期五峰组底部古地理面貌表现为古隆起、潮坪、浅水陆棚、深水陆棚和浅滩5个古地理单元。首次恢复了暴露区及其分布范围,更加客观地反映了凯迪期早期与凯迪期晚期之交岩相古地理格局及其演化过程。

Lithofacies palaeogeography of the early Katian and late Katian of Late Ordovician in southern Sichuan-northern Guizhou Provinces

The turn from the early to the late Katian of the Late Ordovician is considered to be a key point during the history of sedimentary evolution and basin-mountain conversion. At that period,almost all of the carbonate sediments changed into clastic sediments in southern Sichuan-northern Guizhou Provinces. Therefore, the research on sedimentary characteristics and lithofacies palaeogeographic transition has an important significance on recognizing sedimentary evolution and basin-mountain conversion. In order to reveal the change of lithofacies palaeogeography at this turning point,two lithofacies palaeogeography maps of the topof Jiancaogou Formation of the early Katian and the bottom of Wufeng Formation of the late Katian are mapped with the method of sequence lithofacies palaeogeography. The early Katian is divided into seven palaeogeographic units, i.e., pelaeouplift,exposed zone, denuded zone, tidal flat,restricted platform,open platform and shoal;and the late Katian is divided into pelaeouplift,tidal flat,shallow shelf,deep-water shelf and shoal. By the means of sequence lithofacies palaeogeography,the exposed zone and its distribution range is restored for the first time and the evolution process of lithofacies palaeogeography at the turn of the early-late Katian is revealed more clearly.