Origin of the ripple marks from the Xujiajuan Formation of the Xiangshan Group in Ningxia

The Xiangshan Group in Ningxia consists of the Xujiajuan Formation in the abyssal slope environment,and the Langzuizi and Mopanjing Formations in the abyssal plain environment.The ripple marks from the lower part of the Xujiajuan Formation of the Xiangshan Group in Ningxia have the wave lengths in 13~15 cm and the wave heights about 2 cm in Daliushugou,and the wave lengths in 8~12.5 cm and the wave heights in 1.1~2 cm in Xiashipeng.The flute casts are observed in the basal and underlying beds,while the cross-beddings appear in the overlying beds.The palaeocurrents indicated by the ripple marks,flute casts and cross-beddings are oriented to SSE,SSE and NE,respectively in Daliushugou while to NW,SSW and SWW,respectively in Xiashipeng.The ripple marks in the study area may owe their origin to the combined flows.