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Depositional history, contact relationships, and characterization of Upper Miocene Baogeda Ula Formation in central Nei Mongol with a description of fossil skunks

WANG Xiao-Ming1,2  SUN Lu3  LI Lu2  LI Qiang2,4  QIU Zhu-Ding2  Zhijie Jack TSENG1,5   

  1. (1 Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County Los Angeles CA 90007, USA  xwang@nhm.org)
    (2 Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences Beijing 100044, China)
    (3 School of Earth Science, East China University of Technology Nanchang 330013, China)
    (4 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences Beijing 100049, China)
    (5 Department of Integrative Biology and Museum of Paleontology, University of California Berkeley CA 94720, USA)

内蒙古上中新统宝格达乌拉组沉积历史、接触关系、分布特征及臭鼬化石的描述

王晓鸣1,2   孙  蕗3   李  录2   李  强2,4   邱铸鼎2   曾志杰1,5   

  1. (1 美国洛杉矶自然历史博物馆 洛杉矶 CA 90007)
    (2 中国科学院古脊椎动物与古人类研究所，脊椎动物演化与人类起源重点实验室 北京 100044)
    (3 东华理工大学 南昌 330013)
    (4 中国科学院大学 北京 100049)
    (5 美国加州大学伯克利分校 伯克利 CA 94720)

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Abstract:

In addition to its well-known fossils, the Upper Miocene Baogeda Ula Formation is coupled with multiple basaltic lava flows, creating an ideal setting for studying its depositional history, geochronology, and associated vertebrate fossils. This paper, in honor of Prof. Qiu Zhanxiang for his widely admired emphasis on the geological contexts of vertebrate fossils, attempts to synthesize known contact relationships, existing K-Ar dates, and capping basalt elevations to reframe our concept of the lithostratigraphy, magnetostratigraphy, and lateral distribution of the Baogeda Ula Formation. Within this new framework, the Baogeda Ula Formation is defined by unconformable contact with the underlying Tunggur Formation at the lower boundary and a capping basalt at the upper boundary. In many sections, two or three layers of basalts are interbedded within sedimentary strata, with the capping basalts typically belonging to the top two basalts. The newly defined Baogeda Ula Formation includes a lower member as exemplified by Halajin Hushu section and Ulan Hushuyin Nur section, and an upper member at Baogeda Ula section. This expanded concept of the Baogeda Ula Formation includes two major faunas, i.e., the Bahean Halajin Hushu Fauna and Baodean Baogeda Ula Fauna, both falling within the Upper Miocene. We also describe rare fossil skunks (Promephitis) found in recent years that support the age assessments presented herein.

Key words:  , Nei Mongol, Miocene, Baogeda Ula Formation, stratigraphy, skunks

摘要： 内蒙古上中新统宝格达乌拉组不仅出产丰富的脊椎动物化石，它还与若干层玄武岩流互层，为探讨其沉积历史、接触关系及分布特征提供了理想条件。能够应用地层中出产的生物化石、玄武岩同位素年龄及磁性地层的相互制约进行综合年代学研究更为中国乃至东亚少有。结合过去30年来积累的地质观察对玄武岩与沉积岩的接触关系、火山岩盖板的海拔高度并综合近年来发表的K-Ar测年提出一个新的岩石地层框架。除了重新定义宝格达乌拉组外，还试图估算玄武岩风化速率并还原其原始分布。在此新的框架下，宝格达乌拉组被定义为以不整合方式上覆于中中新统通古尔组之上及以整合或假整合方式下伏于阿巴嘎玄武岩盖层之下。除玄武岩盖层外，在不同剖面上可以观察到一层或一层以上玄武岩夹层。这些夹层不仅显示同沉积时的火山活动，也提供了探讨玄武岩夹层测年对地层沉积年代的有效控制。重新定义的宝格达乌拉组包括两段：下段的哈拉津胡舒剖面，或许还包括乌兰呼舒音剖面的上部砾岩，该段出产晚中新世早期(灞河期)的哈拉津胡舒动物群；而上段则由宝格达乌拉剖面代表，其中出产晚中新世晚期(保德期)的宝格达乌拉动物群。但上、下两段之间的准确界限目前还不清楚。此外，还描述了宝格达乌拉组中出现的臭鼬化石，其对年代的估计也略有帮助。本文为庆祝邱占祥先生90寿辰专辑献稿。邱先生是内蒙古化石研究的早期领导之一，也是宝格达乌拉组化石的最初鉴定者。

关键词: 内蒙古, 中新世, 宝格达乌拉组, 地层, 臭鼬

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