江西德安夏家铺S_1/O_1~1呈假整合剖面的发现

Discovery of a disconformity between the Lower Silurian and lower Lower Ordovician in Xiajiapu, Dean of Jiangxi

江西北部的奥陶系研究程度较高,但存在扬子地层区(介壳相)与江南地层区(笔石相)之过渡带的地层划分对比及与志留系的接触关系。

The Ordovician strata of southern Jiangxi are well developed within the Jiangnan stratigraphic region and dominated by the graptolite shale facies. They are comformable with the overlying beds. In the Yangzi stratigraphic region they are composed mainly of carbonate tidal flat of shelly facies lacking late Middle Ordovician rocks and underlie disco-nformably the overlying Early Silurian strata. Transitional belt between these two regions is the Lushan-Xiajiapu-Shuangqiaoshan area with an east-west strike. Within the transitional belt, there are only early Early Ordovician rocks and between these.rocks and the overlying Early Silurian strata may be seen an ancient weathered crust of eluvial quartz and limonites and a disconformity. This disconformity is in contact with that of the Late Silurian strata in the Yangzi region. It is considered by the authors that no deep fracture exists between the two stratigraphic regions, but a underwater uplift formed a natural barrier between the shallow sea and tidal flat from middle Early to middle Middle Ordovician. The Caledonian orogeny began in middle Early Ordovician, its nature being an uneven elevation-subsidence of continetal crust.