Trace fossils were discovered in the Middle Ordovician Badou Member ofFengfeng Formation and the Member 1 of Jinsushan Formation in Mt. Jinsu of the Fuping region whichlies at the southeastern margin of the Ordos basi...Trace fossils were discovered in the Middle Ordovician Badou Member ofFengfeng Formation and the Member 1 of Jinsushan Formation in Mt. Jinsu of the Fuping region whichlies at the southeastern margin of the Ordos basin. The rocks of the fore-mentioned parts contain aconsiderable amount of bioturbation structures, in which ichnogenus and ichnospecies can not beidentified, and abundant stromatolites. The distributions and characteristics of the bioturbationstructures are analyzed and summarized in this paper. The paleoenvironments of related formationsand members were interpreted in the method of semiquantitative analysis of bioturbation structureswith researches on stromatolites and sedi-mentology. It is suggested that Fuping zone, located inthe southeastern margin of the Ordos basin, was a carbonate platform where stromatolite-developingtidal flat and low-energy subtidal open platform environments dominated. Also that this zoneexperienced three paleogeographic evolutions from tidal flat to low-energy subtidal open platformenvironments, that is, three larger-scale eustatisms occurred during the sedimentary period ofMiddle Ordovician Badou Member of Fengfeng Formation to the Member 1 of Jinsushan Formation.展开更多
Bioturbation is one of the important processes that affect the structure and function of sedimentary environments.The particle mixing and element migration processes caused by bioturbation can interfere with the circu...Bioturbation is one of the important processes that affect the structure and function of sedimentary environments.The particle mixing and element migration processes caused by bioturbation can interfere with the circulation of matter and the explanation of sedimentary records.Therefore,the quantitative characterization of bioturbation structures in the sedimentary sequence is of great significance in the field of sedimentology.Estuaries,where fresh and saltwater mix,exhibit high ecological heterogeneity and biodiversity,making them ideal places to explore bioturbation.This paper targets the subaqueous Yellow River Delta to quantitatively characterize bioturbation structures and their spatial distribution patterns using computed tomography(CT)scanning and three-dimensional reconstruction technology.By combining sediment characteristics and sedimentary environment analysis,the main factors affecting bioturbation structures are elucidated.The results show that bioturbation structures in the subaqueous Yellow River Delta can be divided into four types based on their morphology:uniaxial type,biaxial type,triaxial type,and multiaxial type.Skolithos,Palaeophycus in the uniaxial type,and Thalassinoides in the multiaxial type are the most developed structures.Different types of bioturbation may be constructed by trace-making organisms belonging to the same category or functional group.The intensity of bioturbation in this area ranges from 0 to 4%,with a decreasing trend from nearshore to offshore.There is a downward decreasing trend in the intensity of bioturbation overall in the sedimentary cores,with three vertical distribution patterns:exponential decay pattern,fluctuating decay pattern,and impulsive pattern.The impulsive pattern of bioturbation in a core may indicate the abrupt change in sedimentary environment induced by the Yellow River channel shift in 1996.These results suggest that factors affecting the development of bioturbation include grain size,porosity,consolidation,organic matter content of sediments,and sedimentation rate that is mainly influenced by local hydrodynamic conditions.The environment with clayey silt(average grain size 10μm)and moderate sedimentation rate(around 0.5 cm yr^(-1))is the most suitable area for the development of bioturbation in the Yellow River subaqueous delta.展开更多
文摘Trace fossils were discovered in the Middle Ordovician Badou Member ofFengfeng Formation and the Member 1 of Jinsushan Formation in Mt. Jinsu of the Fuping region whichlies at the southeastern margin of the Ordos basin. The rocks of the fore-mentioned parts contain aconsiderable amount of bioturbation structures, in which ichnogenus and ichnospecies can not beidentified, and abundant stromatolites. The distributions and characteristics of the bioturbationstructures are analyzed and summarized in this paper. The paleoenvironments of related formationsand members were interpreted in the method of semiquantitative analysis of bioturbation structureswith researches on stromatolites and sedi-mentology. It is suggested that Fuping zone, located inthe southeastern margin of the Ordos basin, was a carbonate platform where stromatolite-developingtidal flat and low-energy subtidal open platform environments dominated. Also that this zoneexperienced three paleogeographic evolutions from tidal flat to low-energy subtidal open platformenvironments, that is, three larger-scale eustatisms occurred during the sedimentary period ofMiddle Ordovician Badou Member of Fengfeng Formation to the Member 1 of Jinsushan Formation.
基金supported by the National Natural Science Foundation of China(No.42176077)。
文摘Bioturbation is one of the important processes that affect the structure and function of sedimentary environments.The particle mixing and element migration processes caused by bioturbation can interfere with the circulation of matter and the explanation of sedimentary records.Therefore,the quantitative characterization of bioturbation structures in the sedimentary sequence is of great significance in the field of sedimentology.Estuaries,where fresh and saltwater mix,exhibit high ecological heterogeneity and biodiversity,making them ideal places to explore bioturbation.This paper targets the subaqueous Yellow River Delta to quantitatively characterize bioturbation structures and their spatial distribution patterns using computed tomography(CT)scanning and three-dimensional reconstruction technology.By combining sediment characteristics and sedimentary environment analysis,the main factors affecting bioturbation structures are elucidated.The results show that bioturbation structures in the subaqueous Yellow River Delta can be divided into four types based on their morphology:uniaxial type,biaxial type,triaxial type,and multiaxial type.Skolithos,Palaeophycus in the uniaxial type,and Thalassinoides in the multiaxial type are the most developed structures.Different types of bioturbation may be constructed by trace-making organisms belonging to the same category or functional group.The intensity of bioturbation in this area ranges from 0 to 4%,with a decreasing trend from nearshore to offshore.There is a downward decreasing trend in the intensity of bioturbation overall in the sedimentary cores,with three vertical distribution patterns:exponential decay pattern,fluctuating decay pattern,and impulsive pattern.The impulsive pattern of bioturbation in a core may indicate the abrupt change in sedimentary environment induced by the Yellow River channel shift in 1996.These results suggest that factors affecting the development of bioturbation include grain size,porosity,consolidation,organic matter content of sediments,and sedimentation rate that is mainly influenced by local hydrodynamic conditions.The environment with clayey silt(average grain size 10μm)and moderate sedimentation rate(around 0.5 cm yr^(-1))is the most suitable area for the development of bioturbation in the Yellow River subaqueous delta.
