Studies About The Modern Biogenic Traces In The Tidal Flat Deposits Along The Coastal Zones Of Eastern China

On the basis of the detail observation and description of the modern biogenicstructures in the deposits of intertidal zones from Luanhe deata shore area of Bohai Bay,Qingdao and Rizhao shore area and Andong shore area of Hangzhou Bay,as well as tests and analyses of the substrate properties(such as granularity,water content,salt content,organic content),this paper mainly deals with the kinds,morphologies,Occurrence features,the composition and distribution characteristics of modern trace-makers and their traces,and their sedimentary environments.Meanwhile,by the comparison with the trace fossils,the ichnoassemblages were established.Chief results were obtained as follows:(1)16 kinds of modern trace-makers were found,such as Bullactaexarata,Cerithideacingulata,Periophthalmuacantonensis,Brachyura,Moerellairidescens,Solenstrictus,Nereissuccinea,Seaanemone,Oratosquillaoratoria,Paguridae,Lingulaanatina,Mactraveneriformis Reeve,Glossaulaxdidyma,Naticamaculosa,Gryllotalpa and mud Beetles,they made various ethological traces,including repichnia(crawling,creeping,trails,trcaceways),domichnia,fodinichnia,augerisignia,cubichnia,digestisignia,fugichnia,avipedia and root traces.(2)By tests and analyses of the total organic carbon content,particle granularity,water content and salt content in the substrates,it has been indicated that different properties of substrates have an important effect on the kinds,quantity and distribution of the trace-makers and their traces.(3)Based on the morphology characteristics of the modern biogenic traces and their sedimentary environments comparison with the similar trace fossils,10 kinds of similar ichnogenus were discovered including Arenicolites-like,Skolithos-like,Psilonichnus-like,Thalassinoides-like,Planolite-like,Gordia-like,Psammichnites-like,Diplichnite-like,Didymaulichnus-like and Bipodomorpha-like.(4)8 ichnoassemblages in different sedimentary environments were suggested.They are(1)Skolithos-Arenicolites-Psammichnites-likei chnoassemblage may indicate the low-energy brinish environment near the estuary of delta shore zone,it always occurs in the lower tidal flat.(2)Planolites-Thalassinoides-Psilonichnus-like ichnoassemblagege may indicate the low-energy brinish environment far away the estuary of delta shore zone,it usually locates in the high tidal flat.(3)Diplichnites-Psilonichnus-like ichnoassemblage occurred in the middle-low tidal flat environment far away the estuary of delta shore zone,where influenced mainly by the sea water,and the grain size is coarser in the substrate sediments.(4)Gordia-Skolithos-like ichnoassemblage found in the intertidal zone of changeable coast environment.(5)Psilonichnus-Didymaulichnu-like ichnoassemblage mainly located in the high tidal flat environment belonging to monsoon climate of variable zone in the mid-latitude.(6)Skolithos-Arenicolites-Gordia-like ichnoassemblage can indicate the brackish-water estuary flat environment under monsoon climate of variable zone,their substrates are fine-grained sediments with high water content,or commonly the soft ground.(7)Planolites-Diplichnites-Psilonichnus-like ichnoassemblage existed in the brackish-water estuary flat environment under monsoon climate of variable zone and in the semi-consolidated substrate,in which the sediments are mainly composed of the grey silt or silt containing sand with low water content.(8)Skolithos-Psilonichnus-like ichnoassemblage commonly generated in the brackish-water estuary flat environment under monsoon climate of variable zone and mainly distributed in the mid-low tidal flat,their substrates are fine-grained sediments with high water content,or oversaturated muddy soup ground.(5)Sedimentary environment models of ichnoassemblages were established in terms of the analyses of the composition,distribution and substrate properties of above mentioned ichnoassemblages.