Collaborative Research: Tectonic Significance of Long Run-Out Coarse-Grained Facies in the Cordilleran Foreland Basin

褶皱冲断带前缘盆地的沉积记录了褶皱冲断带的构造生长发育，也称为前陆盆地。在这些盆地中，一种普遍的沉积模式是，细粒沉积物在逆冲带的构造发育时期形成，而粗粒沉积物在逆冲带不活动时期形成。该项目旨在使用创新方法测试该模型，以确定爱达荷-怀俄明州褶皱冲断带的沉积时间。对流行模型的成功挑战有可能改变对褶皱-冲断带如何发育的地质认识。这一点尤其重要，因为爱达荷-怀俄明州冲断带及其相关的前陆盆地蕴藏着重要的油气资源。更好地了解盆地的发育将为油气勘探提供重要的见解。该项目将通过以下方式促进其他预期的社会成果：(1)女性充分参与STEM；(2)通过让一名K-12科学教师或本科生参与UTeach项目，以及参加面向K-12科学教师的地球科学教师研讨会，改善STEM教育和教育工作者的发展；(3)通过为亚利桑那大学弗兰道中心开发展示和视频，提高公众的科学素养和公众对STEM的参与；(4)通过培养研究生和本科生，培养具有全球竞争力的STEM劳动力。二十多年来，前陆盆地地层学家和沉积学家一直使用前陆盆地沉降两期模型来解释前陆环境下的地层层序。该模型假设细粒远端沉积是造山带生长和快速弯曲沉降的同构造反应，而粗粒远端沉积则是在逆冲带不活动、侵蚀和均衡反弹期间积累的。本研究项目将通过对犹他州东北部和怀俄明州西南部（典型的前陆）中上白垩世前陆盆地沉积物的地热年代学和磁极性地层学研究来验证该模型。碎屑年代学（碎屑锆石和磷灰石的U-Pb）和热年代学（磷灰石裂变径迹）将确定碎屑滞后时间（源地沉积物颗粒的发掘年龄与其在盆地中的沉积年龄之间的时间差）。其次，利用磁极性地层学对位于主要逆冲断层附近的厚冲积扇沉积物的细粒互层进行研究，可以更好地控制盆地近端欠定年的年龄。这种组合方法可以精确地对比近端和远端相，并建立远端粗粒层段的挖掘年龄和沉积年龄之间的时间差。远端粗粒相较长的滞后时间和不规则的滞后时间长期趋势支持两相模型，而相对较短（5 Myr）的滞后时间和稳定到递减的滞后时间趋势表明，在逆冲带的构造事件期间，粗粒沉积物直接进入远端盆地，因此将使两相模型无效。

Sediments deposited in basins in front of fold-and-thrust belts, also known as foreland basins, record the tectonic growth and development of the belts. One prevalent model for sedimentation in these basins is that fine-grained sediments in record tectonic growth of the thrust belt whereas coarse-grained sediments accumulate during periods of thrust belt inactivity. This project aims to test this model using innovative methods to determine the timing of sedimentation in the Idaho-Wyoming fold-and-thrust belt. A successful challenge of the prevalent model has the potential to change geological understanding of how fold-and-thrust belts belts develop. This is of particular importance because the Idaho-Wyoming thrust belt and associated foreland basins host important hydrocarbon resources. A better understanding of basin development will provide important insights into hydrocarbon exploration. The project would advance other desired societal outcomes through: (1) full participation of women in STEM; (2) improved STEM education and educator development through engagement of a K-12 science teacher or undergrad student in the UTeach program, and participation in the Geoscience Teacher Symposium for K-12 science teachers; (3) increased public scientific literacy and public engagement with STEM through development of displays and videos for the University of Arizona Flandau Center; and (4) development of a globally competitive STEM workforce through training of graduate and undergraduate students.For over two decades foreland basin stratigraphers and sedimentologists have used the two-phase model of foreland basin subsidence to interpret stratigraphic sequences in foreland settings. This model hypothesizes that episodes of fine-grained distal sedimentation are the syntectonic response to orogenic growth and rapid flexural subsidence, whereas coarse-grained distal facies accumulate during periods of thrust belt inactivity, erosion, and isostatic rebound. This research project will test this model using geo/thermochronologic and magnetic polarity stratigraphic study of mid- to Upper Cretaceous foreland basin deposits in northeast Utah and southwest Wyoming, a classic foreland. Detrital geochronology (U-Pb on detrital zircon and apatite) and thermochronology (apatite fission track) will determine detrital lag-times (the time difference between the exhumation age of a sediment grain from the source terrane and its depositional age in the basin). Second, better age control in the poorly dated proximal part of the basin fill will be established by using magnetic polarity stratigraphy on fine-grained interbeds within thick alluvial fan deposits located adjacent to major thrust faults. This combined approach allows accurate correlation of the proximal and distal facies, and establishment of the time difference between exhumation and depositional ages of the distal, coarse-grained intervals. Long lag-times in the distal coarse-grained facies and irregular long-term trends in lag-time, this would support the two-phase model whereas relatively brief (5 Myr) lag-times and a steady to decreasing lag time trend would indicate that coarse-grained sediments prograded directly into the distal basin during tectonic events in the thrust belt and therefore would nullify the two-phase model.