Abstract: Mixed sedimentation of siliciclastic and carbonate deposits is a kind of deposition that has a special and important sedimentary mechanism. The mixed deposits are well developed in the the upper member of the Middle Jurassic Ma'ao Formation in the Jiyuan Basin, western Henan, and consist dominantly of compositionally or texturally mixed deposits composed of muddy limestone, limy mudstone and lime-bearing mudstone. The slightly-oxidized and slightly-reduced brackish environments generated in the arid and scorching conditions may facilitate the development of the mixed deposits, which resulted from the combination of the palaeotectonic movements, palaeoclimates and sediment supply. The results of research in this study provide one useful approach to interpreting the sedimentary mechanism and continental mixed siliciclastic and carbonate deposits.