The migration of the Qinzhou-Fangcheng trough in Guangxi and associated sedimentary-tectonic transform surfaces

The Qinzhou-Fangcheng trough in Guangxi refers to a residual sea sandwiched between the post-Caledonian Yangtze and Cathaysian landmasses, and bounded by the Damingshan uplift to the west and Yunkaidashan uplift to the east. Four tectonic elements are recognized: Bobai depression, Liuwandashan uplift, Qinzhou depression and Shiwandashan depression. The tectonic alignment shows that the Qinzhou-Fangcheng trough was migrated as a deep-marine basin or a shallower deep- water basin from east to west during the Early Palaeozoic to Mesozoic.
The basin migration during the Late Palaeozoic resulted in the formation of eight sedimentary-tectonic transform surfaces as the depositional boundaries of: (1) Early Ordovician/Late Cambrian, (2) Early Silurian/Late Ordovician, (3) early Early Devonian/Late Silurian, (4) Middle Devonian, (5) Middle/Late Permian, (6) Early Triassic, (7) Early Triassic/Middle-Late Triassic, and (8) Early Jurassic/Late Triassic. The former two represent the basin-range transitional surfaces in response to the compression-dominated Caledonian orogeny in southern China. The third boundary indicates a subaqueous depositional hiatus separated the Lower Devonian from the Upper Silurian strata. The fourth boundary indicates the Hercynian transgressive onlap surface formed during the strike-slip extension of the basin. The fifth boundary was developed during the initial stage of the Indosinian orogeny. The sixth boundary represents the transform surface showing the migration of the Mesozoic basin. The seventh boundary represents the basin-range transitional surface during the Indosinian orogeny. The eighth boundary indicates the Yanshanian mountain- and basin-building transform surface. The variation in the transform surfaces cited above might have recorded a complex history of the Qinzhou-Fangcheng trough as a continental marginal foreland basin.