The Rongxian Fm. birdeye or hollowbearing calcarenaceous bioclast algal bindstones build up the carbonate shelf margin of the Upper Devonian, in which limestone dykes occur around Miaotou area, Guilin, Guangxi. Limestone dykes cut perpendicularly through the surrounding rocks and could be observed centimeters to tens centimeters wide and more than ten meters long from an outcrop. Limestones inside the dykes are younger than the surrounding rocks, even though both of them belong to the Rongxian Fm. The dykes are composed of breccia retrodolomitized algal bindstones, breccia bindstones (both are rapid deposition, breccia are from surrounding rocks), fine ooid grainstones, calcispherebearing calcarenaceous wackestones, algalcalcarenaceous gastropod pckstones (normal sediments, or liquefied sediments flows, all younger than the surroundings), and amounts of pectinate calcites dykes (tensional background). Soft sediments deformation and liquefied vines are identified inside limestone dykes (seismic). Later dykes cut early ones. At the same outcrop, amounts of breccia limestone wedges or cumulates are observed lying in the west. The breccia are sharpedged gray thickbedded algal bindstones and calcispherebearing calcarenaceous wackestones, some of which are shatter breccia. Writers notice that limestone dykes outcropped only in the footwall of the northeastern strike normal fault (eastern wall), however breccia limestone bodies outcropped only in the overwall of the normal fault (western wall). In fact, the strike of the limestone dykes and the breccia bodies roughly along the strike of the normal fault. The breccia in the breccia limestone bodies indicated they were from higher position than the sounding rocks, roughly the same as the fillings inside the limestone dykes. Therefore, the northeastern strike normal fault controlled the deposition of the Late Devonian. In other words, the fault was synsedimentary normal fault occurring during Late Devonian carbonate shelf margin. The limestone dykes are tensional fissures caused by the faulting and filled with surrounding rocks breccia or later normal marine sediments. The breccia limestone bodies are scarp fall breccia, suggest a nearly disappeared Late Devonian synsedimentary normal fault scarp. Therefore the northwestern boundary of the Guiling carbonate shelf margin, the same as which of those in the Youjiang basin, should be drawn as a (paleo)fault boundary in geological maps. The limestone dykes, the breccia limestone bodies and the synsedimentary normal fault are the response of the Guilin carbonate shelf margin to the structural stretch during Late Devonian. Thus the tensional stretch of the Late Palaeozoic Guangxi marine started at least at the Late Devonian, rather than the reported Middle Permian. The palaeogeographic pattern had been founded since Late Devonian.