Chemostratigraphy of the Lower Cretaceous dinosaur-bearing Xiagou and Zhonggou formations, Yujingzi Basin, northwest China

The Early Cretaceous of northwest China has yielded abundant vertebrates, invertebrates, and plant fossils from numerous intermontane basins. Developing a chronostratigraphic context for these important fossil finds is important to understanding the development of modern terrestrial ecosystems, the evolution of dinosaurs, and the Cretaceous greenhouse climate. This study utilizes carbon isotope chemostratigraphy of the fossil-rich Xinminpu Group in the Yujingzi Basin in northwest Gansu Province. Lithostratigraphic descriptions defined three facies. The lowest is a tan, coarse arkosic sandstone, overlain by gray to variegated mudstones, sandstones, and thin limestones, which transition to red sandstones, conglomerates, and mudstones. Depositional environment interpretation of these lithofacies assisted in refining 450 samples of bulk sedimentary organic carbon as well as charcoal samples to develop a composite curve to correlate to existing carbon isotope curves from the region and to better constrained Cretaceous sections globally. The carbon isotope curve is correlated based on the broad positive excursion associated with carbon isotope fluctuations of the Paquier Episode that spans the late Aptian to early Albian. Based on this correlation, the middle gray mudstone facies, which contains a diverse fauna including theropods, sauropods, and ornithopods, as well as turtles and invertebrates, is placed within the upper Aptian. The upper red sandstone facies, which contains therizinosaurs and the ceratopsian dinosaur <i>Auroraceratops</i>, is placed in the lower Albian. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Suarez, M. B., T. Milder, P. Nan, C. A. Suarez, H. You, D. Li, and P. Dodson 2019. Chemostratigraphy of the Lower Cretaceous dinosaur-bearing Xiagou and Zhonggou formations, Yujingzi Basin, northwest China; pp. 12–21 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), <i>Auroraceratops rugosus</i> (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1510412.

中国西北早白垩世的多个山间盆地产出了大量脊椎动物、无脊椎动物与植物化石。为这些重要化石发现建立年代地层框架，对于理解现代陆地生态系统的演化、恐龙的演化进程以及白垩纪温室气候的形成与变化均具有重要意义。本研究针对甘肃西北部榆井子盆地（Yujingzi Basin）内富含化石的新民堡群（Xinminpu Group）开展碳同位素化学地层学（carbon isotope chemostratigraphy）研究。研究人员通过岩石地层学分析识别出三种岩相：最下部为黄褐色粗粒长石砂岩，其上覆岩层为灰色至杂色泥岩、砂岩与薄层灰岩，进而过渡为红色砂岩、砾岩与泥岩。对上述岩相的沉积环境进行解译，有助于对450件块状沉积有机碳样品与木炭样品开展精细化分析，进而构建复合碳同位素曲线，以与该区域已有的碳同位素曲线进行对比，并更好地约束全球范围内的白垩纪地层剖面。该碳同位素曲线基于跨越阿普第阶晚期至阿尔布阶早期的帕基尔事件（Paquier Episode）对应的显著正碳同位素漂移完成对比。基于该对比结果，产出包括兽脚类、蜥脚类、鸟脚类以及龟类与无脊椎动物在内的多样化石群的中部灰色泥岩岩相，被归为阿普第阶（Aptian）上部。而产出镰刀龙类与角龙类恐龙*曙光角龙（Auroraceratops）*化石的上部红色砂岩岩相，则被归为阿尔布阶（Albian）下部。补充数据——本文补充材料可通过www.tandfonline.com/UJVP免费获取。本文引用信息：Suarez, M. B., T. Milder, P. Nan, C. A. Suarez, 尤海鲁（Hailu You）, 李大庆（D. Li）, 彼得·多德森（P. Dodson）2019. 中国西北榆井子盆地早白垩世含恐龙的下沟组与中沟组化学地层学；收录于尤海鲁、彼得·多德森与埃里克·莫尔绍瑟主编的《中国甘肃西北部早白垩世皱纹曙光角龙（Auroraceratops rugosus，鸟臀目，角龙下目）》，古脊椎动物学会纪要18，《古脊椎动物学报》38(增刊)，第12–21页。DOI: 10.1080/02724634.2017.1510412。