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EAR-PF: Unraveling Fluvial Kinematics before the Rise of Land Plants: Bridging Laboratory and Geologic Scales

EAR-PF：揭示陆地植物兴起之前的河流运动学：连接实验室和地质尺度

基本信息

批准号：
2053029
负责人：
Jeffery Valenza
金额：
$ 17.4万
依托单位：
Valenza, Jeffery Michael
依托单位国家：
美国
项目类别：
Fellowship Award
财政年份：
2021
资助国家：
美国
起止时间：
2021-08-01 至 2023-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2053029&HistoricalAwards=false
关键词：
EAR PF Unraveling Fluvial Kinematics

项目摘要

Dr. Jeffery Valenza has been awarded an NSF EAR Postdoctoral Fellowship to carry out research and education activities at the University of California Santa Barbara under the mentorship of Dr. Vamsi Ganti, and at Imperial College London under Dr. Alexander Whittaker. This study aims to understand how rivers function in the absence of bank-strengthening vegetation. While nearly all modern river environments are impacted by vegetation, this has only been the case for the most recent ~10% of earth’s history. Prior to the evolution of terrestrial plants, rivers drained the continents without the stabilizing effects of rooted plants, much like extraterrestrial environments on Mars and Titan. The research will characterize the ways that vegetation-free rivers change through time using physical experiments and outcrop analysis. Experiments will focus on discovering conditions that produce a vegetation-free, winding river and will measure the resulting features. These data will be used to characterize and interpret ancient environmental conditions using sandstone exposures in NW Scotland. Bridging laboratory and geologic scales will provide new measures of how pre-vegetation rivers evolved and is applicable to other planetary bodies such as Mars, with preserved river features in an environment with no plants. The project also included outreach and mentoring activities that highlight the laboratory experiments through educational demonstrations and scientific training. Mentoring of undergraduates will be facilitated by the California Alliance for Minority Participation program and mentoring of high-school students and science teachers will be accomplished through the Apprentice Researchers program at University of California Santa Barbara. An irreversible shift occurred in the rock record of ancient rivers, which coincides with the evolution of land plants during the Silurian period approximately 450 million years ago. This stratigraphic shift was hypothesized to mark the transition from the predominance of shallow, multi-threaded rivers in un-vegetated landscapes to the widespread occurrence of low-gradient meandering rivers that developed due to the bank-stabilizing effect of vegetation. However, recent observations indicate that single-threaded rivers can readily form in barren desert landscapes, and their occurrence is increasingly recognized on extraterrestrial surfaces and from sediments pre-dating the greening of the continents. These observations challenge the paradigm that the Silurian transition in fluvial strata occurred due to a geometric shift in river planform. Through a combination of reduced-scaled physical experiments of single-threaded river evolution in the absence of plants and field observations of Proterozoic fluvial deposits in NW Scotland, I will test the hypothesis that the Silurian-age stratigraphic shift occurred due to a kinematic shift in the rates of river evolution that was coeval with plant evolution. Specifically, I will test the hypotheses that: (1) pre-vegetation single-threaded rivers were sustained by fine-grained cohesive bank sediment but their lateral channel migration rates were an order-of-magnitude greater than their vegetated counterparts; (2) high lateral migration rates—relative to river avulsion rates—caused the rapid reworking of floodplain deposits and flushed fine-grained sediment from the fluvial realm, resulting in vertically-truncated, poorly preserved, laterally extensive bar packages and a paucity of preserved alluvial mudrock. New experimental and field data generated from this study will enable the critical evaluation of the causes and consequences of an enigmatic shift in fluvial strata that records the co-evolution of life and surface processes on our planet.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.

Jeffery Valenza博士已被授予NSF博士后奖学金，在Vamsi Ganti博士的指导下在加州圣巴巴拉大学开展研究和教育活动，并在亚历山大惠特克博士的指导下在伦敦帝国理工学院开展研究和教育活动。本研究的目的是了解在没有固岸植被的情况下，河流是如何发挥作用的。虽然几乎所有的现代河流环境都受到植被的影响，但这只是最近地球历史的10%。在陆地植物进化之前，河流在没有生根植物的稳定作用的情况下排干了大陆，就像火星和泰坦上的外星环境一样。这项研究将利用物理实验和露头分析来描述无植被河流随时间变化的方式。实验将集中在发现产生无植被，蜿蜒河流的条件，并将测量由此产生的功能。这些数据将被用来描述和解释古代环境条件下使用砂岩暴露在苏格兰西北部。连接实验室和地质尺度将提供新的措施，以了解前植被河流如何演变，并适用于其他行星机构，如火星，在没有植物的环境中保存河流特征。该项目还包括通过教育示范和科学培训突出实验室实验的外联和辅导活动。本科生的辅导将由加州少数民族参与联盟方案提供便利，高中生和科学教师的辅导将通过加州大学圣巴巴拉分校的学徒研究人员方案完成。在古代河流的岩石记录中发生了不可逆转的转变，这与大约4.5亿年前志留纪期间陆地植物的进化相吻合。这种地层变化被假设为标志着从无植被景观中的浅水多线程河流的优势向由于植被的河岸稳定作用而发展的低梯度曲流河流的广泛发生的过渡。然而，最近的观察表明，单线河流很容易在贫瘠的沙漠景观中形成，而且越来越多的人认识到它们出现在地外表面和大陆绿化之前的沉积物中。这些观察结果挑战了河流地层中志留纪过渡是由于河流平面形状的几何变化而发生的范式。通过组合的缩小规模的物理实验的单线程河流的演变在没有植物和实地观察的元古代河流沉积在苏格兰西北部，我将测试的假设，志留纪地层的转变发生由于运动学的变化，河流的演变率，是同时代的植物进化。具体来说，我将测试的假设：（1）植被前的单线程河流是由细粒粘性银行沉积物，但他们的横向通道迁移率是一个数量级大于他们的植被同行;（2）相对于河流撕脱速率而言，较高的侧向迁移速率导致了洪泛平原沉积物的快速改造，并将细粒沉积物从河流区域冲走，导致垂直截断、保存不良、横向延伸的砂坝群和保存的冲积泥岩的缺乏。这项研究产生的新的实验和现场数据将使河流地层的神秘转变的原因和后果的关键评估，记录了我们星球上生命和地表过程的共同进化。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。