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

HENAN Sheng (China); 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, includingArenicolitesisp.,Archaeonassaisp.,Beaconites antarcticus,B.capronus,B.coronus,Cylindricumisp.,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.serpentinumandT.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-Gastruichnusichnoassemblage in the channel environment of braided and meandering river, (2)Beaconites-Taenidiumichnoassemblage in the natural levee and crevasse splays, (3)Beaconites-Palaeophycusichnoassemblage in the flood plain and (4)Taenidium-Scoyeniaichnoassemblage 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. [ABSTRACT FROM AUTHOR]

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