High-Resolution Mammal Biostratigraphy and Response to Transient Climate Change at the Paleocene-Eocene Carbon Isotope Excursion

在距今5550万年前的古新世-始新世时代边界，与85000年的短暂气候变化温室事件的突然爆发相吻合，即古新世-始新世热最大值（PETM），它涉及到从浅海甲烷储层向大气中释放大量轻碳。由此产生的负碳同位素偏移（CIE）首先在深海中被发现，然后在怀俄明州比格霍恩盆地北部的陆地上被发现。在大角盆地，CIE与“Wa-0”动物迁徙事件同时发生，包括现代哺乳动物的首次出现，如偶蹄目、短趾目和北美灵长类动物，以及一些哺乳动物谱系的突然但短暂的缩小。这里的研究包括对PETM期陆相哺乳动物的高分辨率生物地层学调查。在Bighorn和Clarks Fork盆地的边缘，研究人员正在研究一个50米厚的地层剖面，其中包含CIE和Wa-0哺乳动物区系。具体目标包括测量地层剖面，记录该层段的标志层和横向相变化；利用差分GPS米级精度对不同标记层进行制图；已知化石相对于测量和绘制的地层单元的位置；可生产新岩性的位置；各系在Wa-0区间的体大小变化量化；对Wa-0型哺乳动物的新标本和旧标本的制备和描述，重点介绍了Wa-0基部新发现的Meniscotherium priscum间隔；并收集已知层位的其他动物标本（黄鳞、齿齿兽等），通过大陆CIE/Wa-0区间进行高分辨率的氧同位素和古温度研究。总体目标是更好地理解生物对短期气候变化的反应。

The Paleocene-Eocene epoch boundary at 55.5 million years before present coincides with the sudden onset of an 85,000-year greenhouse event of transient climate change, the Paleocene-Eocene thermal maximum or PETM, that involved release of massive amounts of light carbon into the atmosphere from shallow marine methane reservoirs. The resulting negative carbon isotope excursion [CIE] was first recognized in the deep sea, and then on land in the northern Bighorn Basin, Wyoming. In the Bighorn Basin the CIE coincides with a "Wa-0" faunal immigration event including the first appearance of modern orders of mammals such as Artiodactyla, Perissodactyla, and Primates in North America, and with an abrupt but short-lived diminution in size of some mammalian lineages. Research here involves high resolution biostratigraphic investigation of continental mammals in the PETM interval. A 50-m-thick stratigraphic section containing the CIE and Wa-0 mammalian fauna is being studied around the margin of the Bighorn and Clarks Fork basins. Specific objectives include measurement of stratigraphic sections documenting marker beds and lateral facies changes in this interval; mapping of distinctive marker beds tying sections together using differential GPS with meter-scale precision; location of known fossils relative to measured and mapped bed units; location of productive new lithologies; quantification of body size change in all lineages crossing the Wa-0 interval; preparation and description of previously collected and new specimens of Wa-0 mammals focusing on the newly-discovered Meniscotherium priscum interval at the base of Wa-0; and collection of additional faunal specimens (gar scales, Coryphodon teeth, etc.) of known bed level for high resolution study of oxygen isotopes and paleotemperature through the continental CIE/Wa-0 interval. The overall objective is better understanding of biotic response to short-term climate change.