芭蕉口组(Bajiaokou Fm)的时代为晚奥陶世晚期。该组分布局限。命名剖面位于陕西紫阳芭蕉口村附近。为黑色含炭板岩、含硅质板岩、凝灰质板岩互层。与上覆志留系麻柳湾组硅质板岩和下伏任河组凝灰质板岩均呈整合接触。自下而上包含五个笔石带:Amplexograptus disjunctus yangtzensis带,Dicellograptus szechuanensis(=D.complexus)带、Diceratograptus mirus带、Paraorthograptus pacificus带和Climacograptus extraodinarius带。厚11.1~30.9米。[1]