Climatic forcing and tectonic control on environments in evolving lake basins of Africa and North America

影响地球表面太阳能量的轨道周期和构造活动共同控制着气候变化和演化时期的古环境。湖盆对受这些控制因素影响的降水和沉积物输入的变化特别敏感，并保存了解释环境变化及其对古生态系统影响的最佳证据。我的研究通过对沉积物和动物行为（即化石痕迹）的详细研究来识别岩石记录中的循环和变化的环境，用于重建随时间变化的景观。结合其他证据（如矿物、元素组成、硅藻组合），我们可以解释每个周期内和周期之间的环境条件是如何变化的。我的研究计划集中在三个长期项目上：1)肯尼亚裂谷中部的上新世湖泊；2)埃塞俄比亚阿法尔上新世湖泊；3)阿尔伯塔省白垩纪湖泊。这些项目的重点是进化变化的重要时期，即东非的上新世-更新世，早期人类是在北半球“冰窖”条件开始时进化的（~5- 150万年前），以及北美的白垩纪“温室”，恐龙化石尤其丰富（~ 8000 - 7500万年前）。初步结果表明，在约380万年前发现古猿和人属化石的肯尼亚中部Baringo盆地（项目1），由于轨道周期的影响，湖泊水位发生了巨大的波动，导致了极端不同的环境，周期为约23000年（岁差），由约10万年和40万年的离心率调节。这些短期周期并不是唯一的控制因素；裂谷事件和对湖盆的热液输入也影响了湖泊系统，长期的全球气候变化也影响了湖泊系统，导致了北半球的冰河时代。在非洲北部埃塞俄比亚的阿法尔地区也观察到短期气候周期，“露西”生活在上新世晚期（约350万年前；项目2），但这些周期的沉积记录也因火山活动和断层事件而变得复杂。一旦我们能够区分更局部的地质控制，我们就可以比较肯尼亚中部和埃塞俄比亚东北部，以更好地解释全球气候变化和早期人类居住环境变化的影响。上新世-更新世所采用的方法也将应用于最近发现的阿尔伯塔白垩纪周期性沉积的湖盆（项目3），为气候控制恐龙进化的潜力提供一个全新的视角。通过关注气候变化时期构造活跃的湖盆和动物化石组合中不同的周转事件，我的研究影响了我们对地球和大气过程如何反复影响地球上生命的理解。

Orbital cycles, which affect the amount of solar energy on the surface of the Earth, and tectonic activity together controlled paleoenvironments during periods of climate change and evolution. Lake basins are particularly sensitive to changing inputs of precipitation and sediment as influenced by these controls, and preserve the best evidence to interpret changing environments and their impact on paleoecosystems. My research uses detailed studies of sediments and animal behaviour (i.e., trace fossils) to recognize cycles and changing environments in the rock record, used to reconstruct changing landscapes through time. Integrated with other lines of evidence (e.g., minerals, elemental composition, diatom assemblages), we can interpret how conditions in environments change within and between each of the cycles. My research program focuses on three long-term projects: 1) Pliocene lakes of the central Kenya Rift Valley; 2) Pliocene lakes of Afar, Ethiopia; and 3) Cretaceous lakes of Alberta. These projects focus on important periods for evolutionary change, namely the Pliocene-Pleistocene in East Africa, where early humans evolved (~5-1.5 million years ago) during the onset of "icehouse" conditions in the northern hemisphere, and the Cretaceous "greenhouse" of North America, where dinosaur fossils are especially abundant (~80-75 million years ago). Initial results indicate that, in the Baringo Basin of central Kenya where Austrolopithecus and Homo fossils are known after ~3.8 million years ago (Project 1), wide swings in lake level occurred due to orbital cycles and resulted in extremely different environments with periodicity of ~23,000 years (precession) modulated by ~100- and 400-thousand-year eccentricity. These short-term cycles are not the only controls; rifting events and hydrothermal input to the lake basin also influenced the lake system, as did longer term global change in climate, which led to the ice age in the northern hemisphere. Short-term climate cycles are also observed further north in Africa in the Afar region of Ethiopia, where "Lucy" lived during the late Pliocene (~3.5 million years ago; Project 2), but the sedimentary record of these cycles is also complicated by volcanism and faulting events. Once we are able to distinguish the more local geological controls, we can compare between central Kenya and northeast Ethiopia to better interpret the influence of global climate change and changing environments home to early humans. The approach taken for the Plio-Pleistocene will also be applied to a recently recognized lake basin with cyclical deposits in the Cretaceous of Alberta (Project 3) to provide an entirely new look at the potential for climate control on dinosaur evolution. By focusing on tectonically active lake basins during times of climate change and distinct turnover events in animal fossil assemblages, my research impacts our understanding of how Earth and atmospheric processes have repeatedly impacted life on Earth.