皖南早白垩世晚期新潭组新知

NEW UNDERSTANDING OF THE XINTAN FORMATION IN LATE EARLY CRETACEOUS IN SOUTH ANHUI

根据钻孔资料,安徽区调队在《安徽地层志》中将黄山市新潭镇岩塘组之上,一套底部砾岩与砂岩,下部粉砂质泥岩与粉砂岩互层,上部夹三层膨润土矿层的粉砂质泥岩与粉砂岩,定名新潭组。因当时认为地表未见其出露,故后来在岩石地层清理中未采用该组名,而是将其划归徽州组。笔者在屯溪-休宁地区区域地质调查中,在地表发现了该套岩层,岩性与徽州组层型剖面存在明显差异,而与原钻孔岩性相似。根据新资料,笔者认为应恢复新潭组名并对其重新厘定。厘定后的新潭组为:不整合于岩塘组之上徽州组之下的一套砾岩与灰黄、紫红色粉砂岩、泥质粉砂岩、粉砂质泥岩韵律互层,中上部含恐龙化石和多层膨润土层。空间上在郑家坞至岩寺线以南,屯溪三充至王村以北,原1∶5万屯溪幅划为徽州组的广大地区。时代为早白垩世晚期。

Based on drilling data, Anhui Regional Geological Survey named a new formation Xintan, located above the Yantang Formation in Xintan Town, Huangshan City, in Stratigraphic Records of Anhui for a suite of silty mudstone and siltstone, which consists of conglomerate and sandstone in the bottom, silty mudstone interbedded with siltstone in the lower part, and silty mudstone and siltstone intercalated with 3 layers of bentonite. But this formation was not finally accepted and included into the Huizhou Formation because of the lack of its outcrops. The authors found the stratum on the surface during regional geological survey in the Tunxi- Xiuning area, which is largely different from the stratotype section of the Huizhou Formation lithologically, but similar to the previous borehole log. With the new data, the authors argue that the Xintan Formation should be established again, which overlies disconformably the Yantang Formation and underlies the Huizhou Formation as a suite of cyclothem interbeds of conglomerate with grayish yellow, purplish red siltstone, muddy siltstone and silty mudstone, having dinosaur fossils and multi-layers of bentonite in the upper part of it. Spatially, the formation is situated to the south of Zhengjiawu to Yanshi, north of Sanchong to Wangcun of Tunxi, and in the broad area of the 1：50000 Tunxi Sheet where it was formerly included in the Huizhou Formation. It formed in late Early Cretaceous.