COLLABORATIVE RESEARCH: A combined phytolith-isotope geochemistry approach to paleo-vegetation reconstruction in Montana

合作研究：蒙大拿州新生代古植被重建的植硅体同位素地球化学方法内森谢尔顿和赛琳娜史密斯，华盛顿大学卡罗琳斯特朗贝格草地占地球陆地植被的40%，为人类提供主食（例如，玉米、大米、小麦）。持续的人为气候变化将如何影响草原生态系统和农作物生产力是一个关键问题，解决这个问题需要首先了解这些重要的生物群落是如何组装的。基于植物宏体化石、共同进化的哺乳动物、稳定同位素数据、土壤化石和植硅体（植物硅）数据，科学界知道草原生态系统在中新生代的某个时候以洲际地理尺度分散。然而，由于不同的替代指标在总的空间和时间模式方面提出了不同的草地出现情景（例如，北美与非洲），这一深刻的生态转型的细节不太确定。在大多数地区，只有一个古植被代理已被应用，所以很少了解潜在的采样和埋藏偏差，在不同的记录，可能会影响植被的解释。此外，潜在的重要环境异质性仍然没有记录。 为了解决这些问题，PI将使用跨学科的，多代理的方法来重建蒙大拿州草原的演变在过去的~40马，可以直接与基于古土壤的古气候重建进行比较。具体来说，PI将使用植硅石、成土碳酸盐和从古土壤中收集的有机质（即，C同位素以评估光合途径）。他们将重点关注三个关键的气候转变，这些转变被广泛认为对北美草的存在和丰富程度产生了重大影响，即始新世-渐新世转变（EOT），渐新世-中新世转变（OMT）和中晚中新世转变（MLMT）。

Collaborative Research: A combined phytolith-isotope geochemistry approach to Cenozoic paleo-vegetation reconstruction in MontanaNathan Shelton and Selena Smith, University of MichiganCarolyn Stroemberg, University of WashingtonGrasslands make up ~40% of Earth's terrestrial vegetation and provide humans with our staple foods (e.g., corn, rice, wheat). Exactly how ongoing anthropogenic climate change will impact grassland ecosystems and agricultural crop productivity is a crucial question, and addressing it requires knowledge of how these important biomes were assembled in the first place. Based on plant macrofossils, co-evolved mammals, stable isotopic data, fossil soils, and phytolith (plant silica) data, the scientific community knows that grassland ecosystems dispersed at an intercontinental geographic scale sometime during the mid-Cenozoic. However, because different proxies suggest different scenarios for the emergence of grasslands both in terms of gross spatial and temporal patterns (e.g., North America vs. Africa), the details of this profound ecological transition are less certain. In most areas, only one paleo-vegetation proxy has been applied, so very little is understood about potential sampling and taphonomic biases in different records that could affect vegetation interpretation. In addition, potentially important environmental heterogeneity remains undocumented. To resolve these issues, the PIs will use an interdisciplinary, multi-proxy approach to reconstructing the evolution of grasslands in Montana over the past ~40 Ma that can be compared directly with a paleoclimatic reconstruction based on paleosols. Specifically, the PIs will construct a long-term, high-resolution record of paleovegetation using phytoliths, pedogenic carbonates, and organic matter collected from paleosols (i.e., C isotopes to assess photosynthetic pathways). They will focus on three critical climatic transitions that are broadly believed to have significantly impacted the presence and abundance of grasses in North America, namely the Eocene-Oligocene transition (EOT), the Oligocene-Miocene transition (OMT), and the Middle-Late Miocene transition (MLMT).