Biogenic Sedimentary Structures of the Yellow River Delta in China and Their Composition and Distribution Characters

摘要

The biogenic sedimentary structures(i.e., the morphology and trace makers of burrows, tracks,trails and traces made by extant organisms) and their composition and distribution characters in different micro environments and sub environments of the Yellow River delta in China are described. Three ichnocoenosis can be recognized:(1) Steinichnus-like ichnocoenosis, includes F, Y-shaped traces, birds' footprints on bedding plane, and Y, U-shaped burrows in intrastratal bedding, produced by Coleoptera(Heteroceridae), Orthoptera(Gryllotalpidae) and birds. It is majorly found at the delta plain point bar deposits, denoting the fresh water-related terrestrial environments.(2) Steinichnus-Psilonichnus-like ichnocoenosis, consitsis of Steinichnus-like traces on the bedding plane and Psilonichnus-like burrow which a vertical, irregularly J-, Y-, or U-shaped burrows, some of them with bulbous basal cells burrows in the intrastratal bedding, created by Coleoptera(Heteroceridae), Orthoptera(Gryllotalpidae) and crabs. It is observed in the delta plain abandoned distributary channels, and the delta front tidal creek and subaquous distributary channels, indicating the brackish water environment.(3) Palaeophycus-like ichnocoenosis, includes the round entrance burrows or with craters-shaped loop-protrusionsand and the parallel forked trails on the bedding plane, and the U, J or vertical shaped feeding burrows are in the intrastratal bedding, majorly produced by the clam(bivalve molluscs), gastropods and Nereis. It is present in the subaqueous interdistributary bay, reflecting the intertidal related environment.