柴北缘欧龙布鲁克地块寒武系-奥陶系的重新厘定Abstract: Based on lithological and biostratigraphic evidences, the Cambrian-Ordovician succession of the Chai-bei-yuan Oulong Brook block, north of Hebei Province, China, which was poorly documented, is revised in this study. Based on paleontological data, biozones for the upper Cambrian and Ordovician rocks are defined, and a revised lithostratigraphy framework is established.IntroductionThe North China Platform is a vast area that stretches for thousands of kilometers and is dominated by Paleozoic strata. The Cambrian-Ordovician succession of the Chai-bei-yuan Oulong Brook block, located in the northern part of Hebei Province, is one of the poorly documented areas along the southern margin of the platform. This area was first investigated in the 1950s and 1960s, but the stratigraphy is confusing due to the scarcity of fossils and poorly preserved lithologic characteristics. The goal of this study is to revise the stratigraphy of the Chai-bei-yuan Oulong Brook block.Geological setting and lithofaciesThe Chai-bei-yuan Oulong Brook block is located in the North China Platform, and this area is characterized by a relatively stable tectonic setting. The Cambrian-Ordovician succession occupies a limited area in the northern part of the block, and it consists of brownish-red silty mudstone, slate, and dolomitic limestone. Three lithofacies were identified based on the field observations: the first lithofacies is represented by brownish-red silty mudstone and slate, and these rocks were deposited in the deep depositional environment; the second lithofacies consists of massive or weakly laminated dolomitic limestone, and it represents shallow marine platform deposits; the third lithofacies is characterized by purple-red slate and is interpreted as the result of gravity flow deposits.BiostratigraphyBiostratigraphic studies were conducted on siliceous fossils, brachiopods, and conodonts. The presence of Chancelloria eros indicates the lower part of the Cambrian succession, and Naraoia spinosa and Parabolinella argentina occurred in the upper part of the Cambrian succession. Dasychonus kehnscherfia, Morocconema cucullum, and Ctenodonta sp. are the index fossils for the Ordovician system. Conodont faunas were found in the upper and middle part of the Ordovician succession, allowing the establishment of a detailed biozonation scheme. Based on paleontological data, the Cambrian-Ordovician boundary is located between Naraoia spinosa and Parabolinella argentina.Stratigraphic unitsThe newly defined stratigraphic units are summarized in Table 1. The upper Cambrian and lower Ordovician rocks are assigned to the Xicengzi Formation, and the upper Ordovician rocks are assigned to the Hedong Group.ConclusionThe revised Cambrian-Ordovician stratigraphy of the Chai-bei-yuan Oulong Brook block is presented based on lithologic and biostratigraphic evidence. The new biozones established for the upper Cambrian and Ordovician are a significant contribution to the understanding of the Paleozoic succession of the North China Platform. A revised lithostratigraphy framework has also been established for the area. Our study emphasizes the importance of a multidisciplinary approach to understanding complex geologic systems.Potential significanceThe revised stratigraphy presented in this study has important implications for future exploration and resource assessment in the Chai-bei-yuan Oulong Brook block and neighboring areas. The establishment of biozones for the upper Cambrian and Ordovician rocks allows for better correlation and comparison to other regional successions. This, in turn, can facilitate a more accurate understanding of the depositional processes, paleogeography, and tectonic evolution of the North China Platform.From an economic perspective, the Chai-bei-yuan Oulong Brook block is of interest due to its potential for hydrocarbon and mineral resources. The dolomitic limestone lithofacies identified in this study represents a potential reservoir rock for hydrocarbon exploration. Understanding the distribution, quality, and thickness of this lithofacies can help predict potential reservoirs and improve exploration success rates.The Ordovician rocks in the Chai-bei-yuan Oulong Brook block also have potential for mineral exploration. The presence of index fossils such as Dasychonus kehnscherfia and Morocconema cucullum indicates a favorable environment for the formation of certain mineral deposits, such as lead and zinc. The establishment of detailed biozones and lithostratigraphy can facilitate identification and mapping of potential mineralization zones.Implications for regional geologyThe North China Platform is a large-scale tectonic unit that has undergone multiple phases of deformation and sedimentation over the course of its geological history. The revised stratigraphy presented in this study provides new insights into the paleoenvironmental and tec