Xixiang Biota——Another Rare Scientific Window of the Cambrian Explosion

ObjectiveThe Xixiang biota is a specially preserved micro oryctocoenose discovered in the Lower Cambrian Kuanchuanpu member of Dengying Formation at Zhangjiagou section of Xixiang County in southern Shaanxi Province. The Kuanchuanpu member is a set of neritic carbonate sedimentary formation containing phosphorus and silicon. Its lithology is mainly grey massive fine crystalline, dense massive phosphoruscontaining biolithite and flaggy microcrystallinecrystalline dolomitic limestone. It is in a conformable contact with the underlying upper dolomite member of Dengying Formation and a parallel unconformable contact with the overlying Guojiaba Formation. The fossil assemblages of the Xixiang biota could be compared with the microfbssils from the Lower Cambrian Meishucun Stage, and their age is the Early Cambrian Meishucun Stage.

Lower limit law of welding windows for explosive welding of dissimilar metals

The influence of explosive charge thickness on the quality of explosive welding of dissimilar metals was investigated.The lower limit law should be followed in the course of explosive welding.Three welding experiments of stainless steel（410S）and steel（Q345R）were carried out in three different kinds of explosive charge thicknesses,namely 15,25and 35mm.Interfaces of morphology and mechanical properties of three samples were observed and tested.It was found that micro and small wavy bonding is mainly formed for charge thickness of 15mm whose strength is the highest with minor deformation and few defects in the interface;small and middle wavy bonding are mainly formed for charge thickness of 25 mm whose strength is comparatively mediocre;big wavy bonding is mainly formed for charge thickness of 35 mm whose strength is the lowest.The cause of high bonding strength of the micro and small wavy interface was analyzed and verified on the basis of the results of Electron Probe Micro-Analyzer（EPMA）tests of three selected samples.