One type of basin known as "residual basin of passive continental margin" has been overlooked in all basin classifications.It is usually formed in mid-oceanic ridge and was subducted under active continental margin with plate convergence.However

its basic features of passive continental margin remain unchanged except that normal faulting is rather intensive due to surface tension caused by flexing of the subducted plates.The "Qinfang trough" and "Shiwandashan basin" in Guangxi province was not a unified ancient continent block with the Cathaysia in Eopaleozoic.Therefore

when Wuyi and Mintai mini-blocks attached to South China ancient plate

the "Qinfang trough" was in the evolution stage of the "residual basin of passive continental margin".Later

it evolved successively into a remnant ocean basin in Early Devonian

a Tethyan passive continental margin basin in Neopaleozoic

a foreland basin in early Late Permian

a foreland basin in Mesozoic

and a strike-slip fault basin in Cenozoic.