SEDIMENTARY FACIES OF THE CRETACEOUS LUOHE AND HUANHE-HUACHI FORMATIONS IN THE ORDOS BASIN

The sedimentary facies and facies distribution of the Cretaceous Luohe and Huanhe-Huachi formations in the Ordos Basin are analyzed using regional structure, outcrop, drill core, lithological, sedimentary, palaeontological, and well log data. Major sedimentary facies in the Luohe Formation include alluvial fans facies, eolian facies,braided fluvial facies, and desert facies. Major sedimentary facies in the Huanhe-Huachi Formation include lacustrine facies, delta facies, meandering fluvial facies, and interbedded eolian sandstone facies. Alluvial facies and alluvial-fluvial conglomerate facies are found mostly in the margin of the Ordos Basin, whereas fluvial and lacustrine mudstone facies occur in the central Ordos Basin. This spatial pattern of facies distribution is controlled by the configuration of the basin. Sandstone beds of the Luohe Formation thin from the margin to the center of the basin. Sediments in the Huanhe-Huachi Formation coarsen to the north and to the east. In the northern part of the basin, sandstone beds thin to the east and to the northeast. In the southern part of the basin, sandstone bodies extend in the north-south direction and thin to the east and to the south.