Objectives:Isolated carbonate platforms are widely observed in Youjiang River area, northwestern Guangxi. Many neptunian dykes, carbonate debris, synsedimentary normal faults, and special surfaces showing as local lost strata are observed in margins around those isolated carbonate platforms. There were different ideas about the relationships among these elements. Buttress unconformity refer to that megabreccia rapidly deposit in topographic low when synsedimentary normal faulting change flat terrain to steep topography, and cause the younger beds laterally abuts the older basement strata, and result in the unconformity between the younger beds and the older basement. Buttress unconformity generally formed in unstable structural regions. Until Davis (1984) named it as buttress unconformity, foreign geologists named it as angular unconformity, shelf- margin unconformity, platform- margin unconformity etc. Chinese geologists also observe those special surfaces of unconformity which shown as fault surface in some crops and shown as unconformity interface in some others, and named them as syntectonic sedimentary unconformity, carbonate- platform- margin limited fault zone, angular unconformity contact zone, escarpment- style pseudounconformity, event- sediment unconformity, unconformability of overlap, even tectonic window or klippe etc. Consequently cause argument for they are fault or unconformity, and for their different names. Methods:When study Late Palaeozoic isolated carbonate platform margin neptunian dyke and carbonate- breccia- body, author observes the paragenetic special surface and their difference from the sorts of known reported surfaces in Guangxi. Suppose to classify the special surface to the known reported sorts, there are competing between the names and the geologic crop facts. Special surface should belong to different type. In a key field crop of Fengshan of Guangxi, the special surface is in coexistence with the neptunian dyke and carbonate- breccia- body, and shows its lower part as normal fault surface and its upper part as solution unconformity interface. It is solution fault surface. Results:Due to the frequently large amplitude synsedimentary normal faulting, lower part of the fault plane could be hidden by present deposits, but the upper part of the fault plane could expose to be eroded and hidden by later deposits, cause steep topography and the younger beds laterally abuts the older basement strata in buttress unconformity, coincide with Davis’s concept of buttress unconformity. Conclusions:The special surface of Guangxi could be named buttress unconformity. The collected reports show the unconformity between the Late Palaeozoic strata and the subjacent Cambrian strata, as well as the overlaying Triassic strata, are buttress unconformity. Buttress unconformity could be observed widely in Late Palaeozoic strata of Guangxi and become its geologic feature, which means the frequent regional structural activity have being developed from Palaeozoic to Mesozoic in northwestern Guangxi. The characteristics of strata and tectonic activity record of Guangxi is similar to that of Tethys. Guangxi belongs to the part of east Tethys. Therefore, the argument about the special surface is ended, and approaching geologic materials could help to the study for the strata and the tectonic of northwestern Guangxi.