Rivers, Vegetation and Extinction

河流、植被和灭绝

• 批准号: RGPIN-2014-03877
• 负责人: Gibling, Martin
• 金额: $ 2.7万
• 依托单位: Dalhousie University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633791
• 关键词: Rivers; Vegetation; Extinction

The “greening” of the terrestrial surface as plants started to colonize the landscape nearly 500 million years ago was among the Earth’s most profound evolutionary changes. For the next 200 million years, plants diversified from poorly rooted herbs to deeply rooted forests, increased their cover of the landscape, and attacked the bedrock more effectively to generate mud. In parallel with these changes, our earlier work has shown that meandering and multi-thread rivers appeared, virtually for the first time, as rooted vegetation stabilized river banks and floodplains. This resulted in a total reworking of the Earth’s landscapes, highlighting the importance of vegetation as a forcing factor in landscape evolution. As the supercontinent Pangea assembled, much of the land surface became more arid, and vast volcanic eruptions in Siberia contributed to the most profound extinction in Earth history, affecting both animals and plants at what is known as the Permian-Triassic boundary. Forests were replaced by a low herbaceous cover but were re-established after about 5 million years. Did this major floral dieback and reorganization cause a detectable change in river styles and the terrestrial landscape? If so, did the land surface briefly revert to pattern of simple braided rivers much as before vegetation evolved, as suggested by some local studies? Answers to these questions require a global assessment of the geological record. Based on a compilation of literature for ancient river deposits over a period of 100 million years that includes the extinction event, the proposed research will document the relative abundance of fluvial styles and fossil materials through this important time. During field investigations at selected sites, we will work closely with fossil experts to assess the interaction of vegetation and river systems, focusing on the degree of preservation of the plants (a key problem in assessing changes in the original plant communities) and links with animal evolution and extinction. Because of arid conditions in Pangea, vegetation may have been under pressure before the extinction period, and detailed studies of ancient river systems and plants will be conducted at fossiliferous sites in Texas, New Mexico, and Germany, among other sites. Over the next grant cycle, we aim to document the landscape effects of a major extinction, which is relevant to the ongoing anthropogenic extinction and loss of biodiversity in the 21st Century. A complementary programme will learn more about how rivers before landscapes were vegetated. The simple “sheet-braided” rivers that existed on Earth for more than three billion years before vegetation may be virtually unknown on Earth today: how did they function? This issue will be explored through field studies in northern Canada and the English Channel Islands. Although the development of meandering rivers was clearly promoted by plant evolution, there are other means of stabilizing river banks, including cohesive mud, early hardening of sand, and ice. Meandering rivers have been inferred for some pre-vegetational systems on Earth and have been identified in images of Mars. Evaluating bank strength and the dimensions of channels in these enigmatic rivers will be a key aspect of the studies.

近5亿年前，随着植物开始在陆地上定居，陆地表面的“绿化”是地球最深刻的进化变化之一。在接下来的2亿年里，植物从扎根不深的草本植物变成了扎根很深的森林，增加了它们对景观的覆盖率，并更有效地攻击基岩以产生泥浆。在这些变化的同时，我们早期的工作表明，蜿蜒和多线程的河流出现，几乎是第一次，作为扎根植被稳定河岸和洪泛平原。这导致了地球景观的彻底改造，突出了植被作为景观演变的推动因素的重要性。随着超大陆泛大陆的聚集，大部分陆地表面变得更加干旱，西伯利亚的大规模火山爆发导致了地球历史上最深刻的灭绝，影响了被称为二叠纪-三叠纪边界的动物和植物。森林被低草本植被所取代，但在大约500万年后重新建立。这种主要的植物枯死和重组是否导致了河流风格和陆地景观的可察觉的变化？如果是这样的话，陆地表面是否像一些当地研究所建议的那样，短暂地恢复到植被进化之前的简单辫状河流的模式？要回答这些问题，需要对地质记录进行全球评估。基于1亿年来古代河流沉积物的文献汇编，包括灭绝事件，拟议的研究将记录这一重要时期河流样式和化石材料的相对丰富。在选定地点的实地调查期间，我们将与化石专家密切合作，评估植被和河流系统的相互作用，重点是植物的保存程度（评估原始植物群落变化的关键问题）以及与动物进化和灭绝的联系。由于盘古大陆的干旱条件，植被在灭绝期之前可能已经受到压力，将在得克萨斯州、新墨西哥州和德国等地的含盐遗址对古代河流系统和植物进行详细研究。在下一个赠款周期，我们的目标是记录一个重大灭绝的景观影响，这是相关的持续人为灭绝和生物多样性的损失在21世纪。一个补充方案将更多地了解河流景观之前是如何植被。在植被出现之前，地球上存在了30多亿年的简单的“片状编织”河流在今天的地球上可能几乎是未知的：它们是如何运作的？将通过在加拿大北方和英吉利海峡群岛进行实地研究来探讨这个问题。虽然植物的进化明显促进了曲流河的发展，但还有其他稳定河岸的方法，包括粘性泥，早期硬化的沙子和冰。蜿蜒的河流被推断为地球上一些前植被系统，并在火星图像中被识别。评估这些神秘河流的河岸强度和河道尺寸将是研究的一个关键方面。