内蒙古阿拉善左旗乌兰塔塔尔最晚始新世-渐新世剖面的区域年代地层意义

doi:10.19615/j.cnki.2096-9899.210716

摘要/Abstract

摘要：

精确的区域年代地层框架是探究地质历史时期气候变化与动物群演化事件的基础。过去5000万年中亚洲地区发生的最明显陆地哺乳动物群转换事件可能发生在始新世-渐新世转折时期(约34 Ma)。然而由于缺乏连续的地层记录或者对经典哺乳动物化石地点的地层划分与对比存在较大争议,这一重要转折时期动物群的演变尚不明晰。内蒙古阿拉善左旗乌兰塔塔尔地区丰富的最晚始新世-渐新世(白音期、乌兰塔塔尔期与塔本布鲁克期)哺乳动物化石及连续的地层记录为建立该时段区域年代地层框架奠定了基础。基于岩石地层学、生物地层学以及磁性地层学研究结果,推荐将乌兰塔塔尔剖面作为渐新统乌兰塔塔尔阶的区域单位层型剖面。乌兰塔塔尔阶底界位于克克阿木剖面15.9 m处(33.89 Ma); 塔本布鲁克阶底界位于综合剖面98 m处(27.7 Ma), 对应古地磁极性年表的C9r, 以中华鼠兔Sinolagomys的最低出现为标志。

关键词: 内蒙古, 始新统, 渐新统, 层型剖面, 地层对比, 年代地层学, 生物地层学, 磁性地层学

Abstract:

Robust regional chronostratigraphic framework is the basis of understanding climatic and faunal events in the geologic history. One of the most dramatic faunal turnovers of the past 50 million years in Asia is linked to the Eocene-Oligocene Transition (EOT) at about 34 Ma. However, the chronostratigraphic relationships between faunal modulation and geologic events associated with the EOT in China have remained uncertain before and after the epoch boundaries, mainly due to the scarcity of continuous records and problems in correlating and subdividing the classic areas containing abundant mammalian fossils. Past decades have seen developments in establishing Chinese regional Paleogene Land Mammal Ages, and albeit many ages are well constrained, some, such as those of the latest Eocene and the Oligocene, have remained unsettled. In this paper, we present how recent evidence from the fossiliferous Ulantatal sequence, Nei Mongol, China, provides better constraints to the latest Eocene and Oligocene Chinese Land Mammal ages (Baiyinian, Ulantatalian, and Tabenbulukian). We propose Ulantatal sequence as a new regional unit stratotype section of the Ulantatalian stage, and the lower boundary of Tabenbulukian stage to be reassigned to Chron C9r (27.7 Ma), with the lowest occurrence of Sinolagomys as the marker horizon.

Key words: Nei Mongol, Eocene, Oligocene, stratotype section, stratigraphical correlation, chronostratigraphy, biostratigraphy, magnetostratigraphy

中图分类号:

P534.611

Joonas Wasiljeff, 张兆群. 内蒙古阿拉善左旗乌兰塔塔尔最晚始新世-渐新世剖面的区域年代地层意义. 古脊椎动物学报, 2022, 60(1): 42-53.

Joonas Wasiljeff, ZHANG Zhao-Qun. Stratigraphical significance of Ulantatal sequence. Vertebrata Palasiatica, 2022, 60(1): 42-53.

图/表 3

Fig. 1 Chinese Paleogene Mammal Ages in relation to Asian Land Mammal Ages Abbreviation: LTT. Lutetian

Fig. 2 Simplified lithological column of the Ulantatal sequence with its sections and magnetic polarity column (based on Wasiljeff et al., 2020), and regional terrestrial mammal stages Focal fossil localities are indicated in the figure (bone symbol) in addition to First Appearance Datum (FAD) of the lagomorph taxon Sinolagomys (star symbol) Eocene-Oligocene Boundary (EOB) and the FAD (Sinolagomys) with their respective ages are also depicted

Fig. 3 Field images from the Ulantatal sequence A. middle of Kekeamu section (top ca. 23 m in the local section, interpolated as 32.97 Ma) with the Eocene-Oligocene Boundary (EOB, 33.89 Ma, 15.9 m local section) and sampling sites for paleomagnetic analyses visible; B. the uppermost Ulantatal main section (top ca. 110 m in the composite sequence, overlain by Miocene deposits). The lowest occurrence of Tabenbulukian fauna and the FAD of Sinolagomys can be pinpointed to the lower half of the picture B (ca. 27.7 Ma at 98 m level of the composite sequence) Pictures by courtesy of Anu Kaakinen

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