NSF GEO-NERC: Collaborative Research: Impact of the Plio-Pleistocene Transition on Provenance and Sediment Routing from the Himalaya to the Deep-Sea Bengal Fan

喜马拉雅山脉是地球上最大的山脉，主要分布在尼泊尔、印度、巴基斯坦和中国。数百万年前，当印度与亚洲碰撞时，喜马拉雅山开始上升，这改变了地球的气候，改变了海洋环流和化学，并影响了生物进化的进程。喜马拉雅山的侵蚀导致地球上最大的沉积物堆积在孟加拉湾，深海孟加拉扇。这些沉积物记录了喜马拉雅山脉的历史——现在被侵蚀的过去的珠穆朗玛峰，埋在大陆架和印度洋最深处的沉积物下。2015年，一支多国探险队乘坐专门设计的科学钻探船“JOIDES Resolution”号，回收了约1.5英里的沉积物岩心，其中包含了这一记录。新的研究将利用这些沉积物来追踪喜马拉雅侵蚀的历史，以及世界上最大的两条河流——恒河和雅鲁藏布江——在过去的300万到500万年里是如何将这些沉积物输送到孟加拉湾的。在地质历史上，像喜马拉雅山这样的巨大山脉是罕见的，但没有喜马拉雅山，就没有亚洲季风，没有肥沃的洪泛平原或含水层，没有古老的印度河文明，也没有世界上那个地区的珠穆朗玛峰。因此，这项研究的结果将告诉我们气候变化、景观演变，以及世界上人口最稠密的地区之一是如何变成今天的样子的。以这种方式了解过去可以帮助我们更好地了解生活在这一令人难以置信的地理特征影响下的世界10%人口的未来。该项目还支持来自美国、英国和几个亚洲国家的几所大学的科学家和学生之间的国际合作，这些大学将进行实地工作。喜马拉雅山脉的恒河-雅鲁藏布江水系和深海的孟加拉扇代表了地球上最大的从源到汇的沉积物扩散系统。IODP 354考察队在距离现代恒河-布拉马普特拉河三角洲海岸线近1000英里的孟加拉扇中部钻取了7个样带，以扩大从喜马拉雅到深海的侵蚀和沉积物路线的记录。先前的研究利用IODP 354岩心砂质浊积岩的碎屑锆石（DZ） U-Pb数据，总结了中新世到中更新世的沉积物路径模式。本研究确定了特定DZ U-Pb年龄群的主要变化，对应于上新世到更新世的过渡，并指出了由于环境强迫导致的主要物源变化。新的研究将建立在早期结果的基础上，并检查导致这种物源变化的气候和构造过程。这项研究将基于对来自IODP 354岩心的25个新的上新世-更新世沙子样本的分析，这些样本代表了海平面较低的冰川期向孟加拉扇的沙子运输，以及来自现代恒河-雅鲁藏布江流域的60个新的河流沙子样本，这些样本将用于建立全新世间冰期季风主导气候的特征模式。从这些样品的砂粒中回收的碎屑锆石和金红石将作为主要的信号载体，并将进行U-Pb年代学分析，同时检测锆石的(U-Th)/He热年代学和铪同位素。这些样本和方法将从喜马拉雅山脉的主要构造地层单元到孟加拉扇在冰期和间冰期的贡献，并显示喜马拉雅山脉的侵蚀和通往深海的沉积物路线如何随时间变化。生成的数据集将作为社区几十年的基线，并将作为专业会议和研讨会的公共宣传工具，强调源到汇的概念，以及喜马拉雅到孟加拉的风扇系统如何响应和记录气候变化和构造活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Himalayas represent the largest mountain chain on Earth, and reside mostly in Nepal, India, Pakistan and China. The Himalayas began rising many millions of years ago when India collided with Asia, which changed Earth’s climate, altered ocean circulation and chemistry, and impacted the course of biological evolution. Erosion of the Himalayas resulted in deposition of the largest pile of sediment on the planet in the Bay of Bengal, the deep-sea Bengal Fan. Within this sediment record lies the history of the Himalayas – the now eroded Mt. Everests of the past, buried under sediment of the continental shelf and the deepest parts of the Indian Ocean. In 2015, a multi-national expedition on the JOIDES Resolution, a specially designed scientific drilling ship, recovered ~1.5 miles of sediment cores that contains this record. New research will use these sediments to trace the history of Himalayan erosion and how two of the world’s largest rivers, the Ganges and Brahmaputra, delivered it to the Bay of Bengal over the last 3-5 million years. Giant mountain ranges like the Himalayas are a rarity through geologic history, but without the Himalayas there are no drenching Asian monsoons, no fertile floodplains or aquifers, no ancient Indus Civilization, and no Mt. Everests in that part of the world. The results of this research will therefore tell us about climate change, landscape evolution, and how one of the world’s most densely populated areas came to be as seen today. Understanding the past in this way can help us better understand the future for the 10% of the world’s population that lives under the influence of this incredible geographic feature. This project also supports international collaboration between scientists and students from several universities in the U.S., the U.K. and several Asian countries where field work will be conducted.The Himalaya-sourced Ganges-Brahmaputra river system and the deep-sea Bengal Fan represent Earth’s largest source-to-sink sediment-dispersal system. IODP Expedition 354 drilled a 7-site transect in the middle Bengal Fan, almost 1000 miles from the modern Ganges-Brahmaputra delta shoreline, to expand the record of erosion and sediment routing from the Himalaya to the deep sea. Previous research examined detrital-zircon (DZ) U-Pb data from sandy turbidites in IODP 354 core to summarize Miocene to middle Pleistocene patterns of sediment routing: this research identified major changes in specific DZ U-Pb age populations that correspond to the Plio-Pleistocene transition, and indicate major changes in provenance due to environmental forcing. New research will build on earlier results and examine climatic and tectonic processes that drove this provenance change. This research will be grounded on analyses of 25 new samples of Plio-Pleistocene sand from IODP 354 core, which represent sand transport to the Bengal Fan during glacial periods when sea level was low, as well as 60 new river sand samples from the modern Ganges-Brahmaputra drainage that will be used to establish patterns characteristic of the Holocene interglacial monsoon-dominated climate. Detrital zircons and rutiles recovered from the sand fraction in these samples will be used as the primary signal carrier and will be analyzed for U-Pb geochronology, with zircons examined for (U-Th)/He thermochronology and Hafnium isotopes as well. These samples and methods will fingerprint contributions from the main tectonostratigraphic units of the Himalaya to the Bengal Fan in glacial vs. interglacial periods and show how Himalayan erosion and sediment routing to the deep sea changes over time. The dataset generated will serve the community as a baseline for decades, and will be leveraged as a tool for public outreach at professional meetings and workshops that emphasize source-to-sink concepts and how the Himalaya to Bengal fan system responds to and records climate change and tectonic activity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.