EAR-PF: Using distributions of channel geometry and channel belt properties to distinguish meandering and braided fluvial deposits in the rock record

Dong, Tian Y, Houston TX

Investigators

Abstract

An NSF EAR Postdoctoral Fellowship has been granted to Dr. Tian Dong to carry out research and education plans at the University of Texas at Austin under the mentorship of Dr. Timothy Goudge. This project will study the distinctions between the two dominant river morphologies observed on Earth: single-thread and braided patterns. Distinguishing between these river types is straightforward in the modern environment as they can be directly observed or predicted using hydrological data. However, distinguishing channel patterns in the sedimentary rock record has proven more difficult, as only remnants of the river channels are preserved and they only account for a small fraction of the overall record. Identifying channel patterns in geologic records is important for predicting the quality and heterogeneity of groundwater and hydrocarbon reservoirs. Through this project, a new set of metrics will be developed for distinguishing river types using distributions of the dimensions of river channels and channel belts (i.e., collections of channel deposits from the same river at different times), measured from modern rivers on Earth using remote sensing data. These metrics will then be interpreted in the context of distinguishing between river types in the ancient rock record, with the anticipated findings relevant for the security of energy and water resources in the United States and related industries. This project also aims to promote participation of underrepresented groups in STEM fields at all levels (K-12 and undergraduate) through outreach programs such as GeoFORCE and research opportunities at the University of Texas at Austin. Formation of the two main river morphologies, single-thread and braided patterns can be relatively well predicted in modern environments using hydraulic variables of channel slope, width, depth, and water discharge. However, recognition of channel patterns in the rock record is difficult because only remnants of the original river channels are preserved. Since hydraulic variables such as slope and discharge cannot be measured directly in rock formations, this work will rely on geologic proxies. In addition to the significance of distinguishing river types to assess subsurface reservoir quality, this distinction is important for testing the hypothesis that whether single-thread rivers were rare prior to the arrival of land plants in the Silurian (~415 to 445 Ma). Previous studies have reconstructed the above four hydraulic variables to distinguish channel patterns in the rock record, but such results have uncertainties that range up to an order of magnitude due to compounded calculation errors. This study proposes to develop new diagnostic metrics using distributions of hydraulic variables and channel belt properties (e.g., width and radius of curvature), measured from modern fluvial systems worldwide via remote sensing techniques, with the ultimate aim for distinguishing channel types in the rock record. Specifically, we aim to test the hypothesis that braided and single-thread rivers have distinct distributions of channel geometry and channel belt properties as supported by theories on river branching. We anticipate that the results of this study will be widely applicable, as geometry variables, such as width and depth, and channel belt width are easily measurable or can be reconstructed with minimum calculation steps across observational length scales, from outcrops to seismic images, timescales, from modern systems to ancient sedimentary deposits, and across localities, from Earth to other planets. This project received co-funding from the Geomorphology and Land-use Dynamics program in the Earth Science division. 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.