Abstract:

The Upper Triassic Xujiahe Formation in Sichuan Basin has abundant trace fossils. In accordance with ecological and behavior features of trace makers, these fossils can be classified into three categories, including trace fossils of animals with clear shape, escape structures and Rhizolithos （predominantly fibrous Rhizolithos）. Trace fossils of animals with clear shape can be classified into ten species in seven genera in three categories （including two species indeterminata）, namely, ① Domichnia. Skolithos linearis, S.verticalis, Arenicolites ichnosp., Cylindrium ichnosp., Ophiomorpha nodosa; ②Fodinichnia. Planolites beverleyensis, P.montanus, Palaeophycus tubularis, and P.striatus;③Pascichnia. Cochlichnus anguineus. Most of trace makers for these trace fossils can be classified as arthropod （especially insecta）. There are also a small quantity of mollusks （predominantly gastropods and bivalves） and worms. They are preserved in fine sandstones, siltstones or silty mudstones as full relief and epirelief. In accordance with distribution of trace fossils and analyses of sedimentary environments, three ichnofabrics can be identified：①Cochlichnus-Planolites ichnofabric, which is predominantly composed of fodinichnia and pascichnia, formed in sedimentary environments of supratidal mudflat with swamps developed locally; ②Cylindricum-Planolites ichnofabric, which is dominated by dwelling burrows and feeding burrows. High abundance and diversity of trace fossils may reflect their sedimentary environment of intertidal zone; ③ Skolithos linearis ichnofabric, which is dominated by long, vertical or high-angle dwelling burrows of suspension feeders, formed in subtidal zone, in which energies in surrounding water changed periodically with changes in relative sea levels.

Key words: seismic frequency extension, seismic characteristics, seismic waveform classification, frequency divider interpretation, Yingzijie area