The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic ...The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic complexes in northeastern Jiangxi have been traditionally regarded as part of the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift. However, recent reports of Late Paleozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and paleogeographic framework in the region; but other workers are suspicious about these findings. In order to test the validity of the putative radiolarians, we, an interdisciplinary study group including micropaleontologists, tectonic specialists and regional geologists, conducted field investigations and multiple re-samplings of the localities where the reported fossils were collected. Our comprehensive study shows that the chert of the ophiolitic complex and the associated low-grade metamorphic slate yield Mesoproterozoic and Neoproterozoic acritarchs, confirming the traditional view of their age assignment (Proterozoic); on the other hand, no recognizable radiolarian fossils have been discovered therein, thus raising questions about the recently published result of Paleozoic radiolarian findings. Probable causes for the putative radiolarian findings are thus discussed herein. Geochemical characteristics indicate that the chert sedimentation most probably occurred under a continental margin setting.展开更多
Abundant and well-preserved organic-walled microfossils including acanthomorphic acritarchs have been found in Mesoproterozoic Beidajian Formation in the Yongji area of Shanxi Province, North China. The morphological ...Abundant and well-preserved organic-walled microfossils including acanthomorphic acritarchs have been found in Mesoproterozoic Beidajian Formation in the Yongji area of Shanxi Province, North China. The morphological and ultrastructural features of these acanthomorphic acri-tarchs resemble living dinoflagellates (e.g. double-walled and polygonal structures), which leads to the interpretation of these fossils as probably the oldest dinoflagellates. The detec-tion of dinosterane, a dinoflagellate biomarker, from pyro-lytic product of these fossils further supports the morpho-logical inference. This finding is consistent with molecular clock estimate that dinoflagellates may have diverged 700 to 900 million years (Ma) before previously known fossil re-cord.展开更多
基金support from the National Natural Science Foundation of China(Grant 40172004)Chinese Academy of Sciences(Grant KZCX2-SW-129).
文摘The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic complexes in northeastern Jiangxi have been traditionally regarded as part of the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift. However, recent reports of Late Paleozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and paleogeographic framework in the region; but other workers are suspicious about these findings. In order to test the validity of the putative radiolarians, we, an interdisciplinary study group including micropaleontologists, tectonic specialists and regional geologists, conducted field investigations and multiple re-samplings of the localities where the reported fossils were collected. Our comprehensive study shows that the chert of the ophiolitic complex and the associated low-grade metamorphic slate yield Mesoproterozoic and Neoproterozoic acritarchs, confirming the traditional view of their age assignment (Proterozoic); on the other hand, no recognizable radiolarian fossils have been discovered therein, thus raising questions about the recently published result of Paleozoic radiolarian findings. Probable causes for the putative radiolarian findings are thus discussed herein. Geochemical characteristics indicate that the chert sedimentation most probably occurred under a continental margin setting.
基金supported by the National N atural Science Foundation of China(Grant No.40472003)the Ministry of Science and Technology of China(Grant Nos.G2000077701 and 2003CB7 16805)the Chinese Academy of Sciences(Grant No,KZCX3-SW-141).
文摘Abundant and well-preserved organic-walled microfossils including acanthomorphic acritarchs have been found in Mesoproterozoic Beidajian Formation in the Yongji area of Shanxi Province, North China. The morphological and ultrastructural features of these acanthomorphic acri-tarchs resemble living dinoflagellates (e.g. double-walled and polygonal structures), which leads to the interpretation of these fossils as probably the oldest dinoflagellates. The detec-tion of dinosterane, a dinoflagellate biomarker, from pyro-lytic product of these fossils further supports the morpho-logical inference. This finding is consistent with molecular clock estimate that dinoflagellates may have diverged 700 to 900 million years (Ma) before previously known fossil re-cord.
