Opportunities for Incorporating Deep-Time Insight About Landscape Dynamics into Engineering and Decision-Making Models

Abstract

Landscape dynamics fossilized in sedimentary rocks contain important information about the sensitivity and resilience of fluvial, coastal, and shallow marine systems, particularly under boundary conditions that cannot be observed on Earth’s surface today or in the recent (~Holocene) geologic record. However, this insight is rarely incorporated into models used for decision making, engineering, and hazard mitigation, in large part because even best imaginable age control for ancient deposits is orders of magnitude too coarse for reconstructing the absolute rates and recurrence intervals of sediment-transport processes. Here we propose that reconstructing relative rates of sediment-transport dynamics in ancient deposits presents a new opportunity for translating observations from deep-time landscapes into a form that could be used for conditioning and testing predictive models of landscape change. In rivers, the scale, shape, and preservation of bedform, bar, and channel-belt deposits reflect channel kinematics resulting from bedform migration, bar and channel migration, and channel avulsion. Measuring the shape and preservation of fluvial deposits at a range of scales provides a way to compare the relative rates of different morphodynamic processes in an ancient fluvial system. As a proof-of-concept, we compare deposit characteristics of several ancient fluvial systems including the Eocene Willwood Formation (Wyoming, USA), the Upper Cretaceous Castlegate Sandstone (Utah, USA), and the Middle to Upper Proterozoic Applecross Formation (Scotland). Results suggest that the architecture and preservation potential of fluvial morphodynamics reflects the presence and relative rates of different morphodynamic hierarchies across these systems. Evaluation of deposit variability within member-to-formation-scale units provides a potential avenue for evaluating the sensitivity or resilience river systems to different types of boundary-condition changes. Presently this insight is helpful for more accurately predicting compartmentalization and connectivity in fluvial reservoirs. We suggest that further development of this type of analysis could be expanded to help condition engineering models of river response to climate, sea-level and land-use change to more accurately explore how rivers behave under conditions outside of those represented in historical and Holocene records.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019