1 Introduction The ophiolitic and slightly metamorphic complexes in northeastern Jiangxi have been traditionally considered to be related to the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift in South China and have become a classic area for the study of pre-Sinian stratigraphy. However, since Zhao et al. (1995, 1996) and He et al. (1996, 2000) (the Zhao-He research group) reported their discoveries of Paleozoic Radiolaria from the siliceous rocks in the ophiolitic and metamorphic strata, their interpretation of the regional tectonic and paleogeographic settings have been changed as follows: 1) there were deep oceanic sedimentation during the Late Paleozoic times, possibly of the Tethys; 2) the presence of Late Paleozoic radiolarian chert in the ophiolitic complexes would indicate the characteristics of a Late Paleozoic (or post-Late Paleozoic) suture zone in the region; and 3) because the putative Late Paleozoic radiolarian-bearing strata have suffered metamorphism, this would suggest that a post-Late Paleozoic tectonic event (i.e., the Indo-Sinian Orogeny) occurred in the area. However, a number of authors have disputed the above- mentioned new interpretations. For example, Chen et al. (1995, 1997) and Chen and Rong (1999) presented their interpretation of the regional geology from a series of different view points that the relevant rock suites of the Banxi are products of the Proterozoic times, suggesting the absence of a Paleozoic oceanic crust in the region, an opinion concordant with those of many traditional geologists who have long been working on this subject. The core of the dispute lies in the validity and nature of the findings of the putative radiolarian chert and the age of the relevant rocks and fossils (if any) therein. Aiming to resolve the dispute and realizing that the authors reporting the putative radiolarian findings did not include any radiolarian specialist, we organized an interdisciplinary team including micropaleontologists, tectonic specialists and regional geologists in an effort to investigate the stratigraphy and formation of the relevant rock units and to test the validity of the “radiolarian chert” findings. 2 A Re-examination of Reported Radiolarian- bearing Sections According to the Zhao-He research group, their On the Age of the Ophiolitic Complexes in Northeastern Jiangxi: A Micropaleontological Analysis YANG Qun 1 , WANG Yujing 1 , YIN Leiming 1 , SHU Liangshu 2 , LOU Fasheng 3 , WANG Bo 2 1 Nanjing Institute of Geology & Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu 210008; Email: qunyang@nigpas.ac.cn 2 Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu 210093 3 Geological Survey of Jiangxi Province, Nanchang, Jiangxi 330201 Abstract 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. Key words: radiolarians, chert, Banxi Group, northeastern Jiangxi Vol. 79 No. 3 pp. 801–805 ACTA GEOLOGICA SINICA June 2005