The Jehol Biota represented a diverse ecosystem in the Cretaceous world, particularly with respect to the high diversity and abundance of fossil species  . The study of the Jehol Biota has mainly focused on the Yixian and Jiufotang formations of Western Liaoning, China, which represent the middle and late stage of this biota  . The early Jehol Biota and its relevant strata, however, remain to be studied further  . The Luanping Basin and other basins in the northern Hebei Province, China, preserve abundant fossils of the early Jehol Biota, including non-marine ostracods  . Detailed fieldwork on representative sections of the Lower Cretaceous Dabeigou, Dadianzi and Xiguayuan formations of the Luanping Basin have revealed a diverse ostracod fauna with ostracods occurring frequently in the sections and in high abundance     . Previous taxonomical and biostratigraphical analyses of the ostracods contribute to the improved age assignment and correlation of respective formations, the correlation with the relevant stage of the Jehol Biota, and on the controversy on the position of the J-K boundary in the Luanping basin and adjacent basins  . These studies demonstrated the need for more detailed work and thorough taxonomical revision of the ostracod fauna and its biostratigraphical and paleoenvironmental utility.
2. Materials and Methods
In an ongoing PhD project, detailed studies on relevant sections of the Dabeigou (Yushuxia section), Dadianzi (Shangying-Xiaying section), and Dadianzi or Xiguayuan (Liying section) formations of the Luanping Basin are carried out, including high-resolution measuring and sampling for microfossils as well as detailed sedimentological descriptions to establish the lithostratigraphic framework.
3. Results and Discussion
Preliminary taxonomic analysis of non-marine ostracods from the Lower Cretaceous interval of Luanping Basin revealed (depending on sections and formations) 7 - 17 genera, including Cypridea, Yumenia, Luanpingella, Pseudoparacypridopsis, Daurina, Yanshanina, Ocrocypris, Eoparacypris, Limnocypridea, Djungarica, Darwinula, Alicenula, Rhinocypris, Timiriasevia, Damonella, Lycopterocypris and Mongolianella, and around 44 species (Detailed discussion will be on another paper). Fieldwork on the Lower Cretaceous interval of the Liying section, the stratigraphical assignment of which either to the Dadianzi or the Xiguayuan Formation is still debated, revealed abundant fossils of gastropods, bivalves, ostracods, spinicaudatans, fishes, shrimps and plants. The ostracod biostratigraphy of the Dabeigou, Dadianzi and Xiguayuan formations can be recognized as the Luanpingella-Ocrocypris-Eoparacypris (Late Valanginian-Early Hauterivian age), Cypridea-Timiriasevia-Daurina (Late Huaterivian-Barremian age) and Cypridea-Limnocypridea-Lycopterocypris (Aptian stage) assemblage zones, respectively. In addition, the ostracod assemblage zone of the Dadianzi Formation can be subdivided into the Cypridea stenolonga, C. luanpingensis, C. sulcata, and C. pangi subzones, which mainly distributed at members 1 - 4 of this formation, respectively. Based on biostratigraphic correlations of the Dadianzi Formation to stratigraphically equivalent formations of adjacent basins, it is concluded that the earliest occurrence of Cypridea-species in the northern Hebei-western Liaoning area, North China, is ~130 Ma (lowermost Barremian).
Based on preliminary analysis, 17 genera and around 44 species of the nonmarine ostracods from the Lower Cretaceous interval of Luanping Basin have been recognized.
The ostracod assemblages of the Dabeigou, Dadianzi and Xiguayuan formations of Luanping Basin have been temporarily proposed as the Luanpingella-Ocrocypris-Eoparacypris (Late Valanginian-Early Hauterivian age), Cypridea-Timiriasevia-Daurina (Late Huaterivian-Barremian age) and Cypridea-Limnocypridea-Lycopterocypris (Aptian stage) zones, respectively.
This work was supported by the National Natural Science Foundation of China (41688103, 41790452, 41302008, 41172037), the Program of China Geological Survey (DD20190009, DD20160207), as well as the Austrian Science Fund (FWF) project P 27687-N29 (to BS). Zuohuan Qin was also supported by the Chinese Scholarship Council. The authors have benefitted greatly from the discussions with Yaqiong Wang, Chunlin Sun, Shaowu Niu, Xiaomin Fang and Xuri Wang. We also sincerely thank Yankang Xu, Feng Wei, Xinhua Li, Xuetang Li, Fei Xu, Junjie Zhou, Cong Ding, Zhiqiang Yu, Qian Zhang, Guannan Wang, Anqi Gu, Xin Xiong, Baoxu Wu, Yunqi Ye, Xuejiao Wang, Muhammad Kamran, Jizhe Du, Daben Deng and Jialiang Dai for their help in the field. This is a contribution to UNESCO/IUGS/IGCP 679 project.