Trace fossils and sedimentary environments of the upper cretaceous in the Xixia Basin, Southwestern Henan Province, China

The Upper Cretaceous Gaogou, Majiachun and Sigou formations in the Xixia Basin are composed of terrestrial clastic deposits, which are dominated by red-violet mudstones, muddy siltstones, siltstones, grayish fine-grained sandstones, intercalated with grayish, off-white medium- and coarse-grained sandstones or conglomerates. They contain 10 ichnogenera and 22 ichnospecies and Rhizoliths, including Arenicolites isp., Archaeonassa isp., Beaconites antarcticus, B. capronus, B. coronus, Cylindricum isp., Gastruichnus xixiaensis, Palaeophycus megas, P. tubularis, P. heberti, P. sulcatus, P. cf. sulcatus, P. striatus, Planolites beverleyensis, P. isp., Scoyenia gracilis, Skolithos verticalis, S. linearis, S. isp., Taenidium irregularis, T. serpentinum and T. barretti. From north to south across the basin, alluvial fan, braided and meandering fluvial and fluvio-lacustrine systems are recognised on the basis of sedimentary features. In reference to them, four ichnoassemblages are recognised: (1) Skolithos-Gastruichnus ichnoassemblage in the channel environment of braided and meandering river, (2) Beaconites-Taenidium ichnoassemblage in the natural levee and crevasse splays, (3) Beaconites-Palaeophycus ichnoassemblage in the flood plain and (4) Taenidium-Scoyenia ichnoassemblage in the periodically exposed fluvio-lacustrine (pond or very shallow lacustrine) sedimentary environments. The present work not only enrich the trace fossils database of terrestrial origin but also offer new data to complete further continental ichnofacies mode and also provide the constraints on palaeoenvironments of the Xixia Basin.