Abstract:
The shore-shallow lacustrine sediments of Upper Triassic in Central and South Sichuan Basin is enriched with ichnocoenosis, which consists of at least 6 ichnogenera, 8 ichnospecies, namely, Skolithos linearis, S.verticalis, Ophiomorpha nodosa, Planolites beverleyensis, P. montanus, Palaeophycus tubularis, Taenidium satanassi and Cochlichnus anguineus. The ichnocoenosis represents Domichnia, Fodinichnia and Pascichnia of invertebrates, and is preserved in full relief and epirelief. In addition, escape structure is also abundant. Based on the composition and distribution characteristics of these trace fossils and their country rock features, three types of ichnocoenosis under different sedimentary environments have been recognized as follows:1) Skolithos linearis ichnocoenosis,which mainly consists of dwelling burrows,generates in high-energy shore lacustrine sedimentary environment;2) Cochlichnus-Planolites ichnocoenosis, which mainly consists of pascichnia and fodichnia, forms in lower-energy zone of shore-lake swamp;3) Skolithos-Planolites assemblage,which is characterized by dwelling burrows and feeding burrows, and presents itself in shallow lacustrine sediments under moist climate. Based on analysis of bioturbation index, two types of bioturbation assemblages in shallow lacustrine deposits are identified as follows: 1) bioturbation near boundary between sandstone and mudstone, which occurs mainly in sediments of lower shallow lake; 2) bioturbation in thin-bedded sandstones, which develops mainly in sediments of middle to lower shallow lake.