Reconstructing the morphologies and hydrodynamics of ancient rivers from source to sink: Cretaceous Western Interior Basin, Utah, USA

Abstract

Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four-dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USAthese rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grainsize and cross-set measurements and span five parallel fluvial systems, two of which include up-dip to down-dip transects, across seven stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2 to 4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10 −3 to 10 −4 , decreasing downstream by an order of magnitude. The most prominent spatio-temporal change is an up to four-fold increase in palaeoslope at the Blackhawk-Castlegate transition; associated alluvial palaeorelief is tens of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. This study observed no change in unit water discharges at the Blackhawk-Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive previous work in this region, which enables the efficacy of quantitative reconstruction tools to be tested. Comparison of results with facies-based interpretations indicates that quantitative tools work well, but inconsistencies in more complex reconstructions (for example, planform morphologies) highlight the need for further work.

Fine-sediment Supply Can Control Fluvial Deposit Architecture: An Example From the Blackhawk Formation-Castlegate Sandstone Transition, Upper Cretaceous, Utah, USA

“…Detrital zircon studies of Blackhawk-Castlegate sandstones show a consistent source area across this boundary (Pettit et al, 2019), and duplexing along the Paxton thrust likely exposed quartz-rich source rocks within the drainage basin (Decelles & Coogan, 2006;Horton et al, 2004;Lawton et al, 2007;Pujols et al, 2020). Paleocurrents are consistent across the formation boundary (Supplement; Franczyk & Pitman, 1991), and there is no change in fluvial style (Adams & Bhattacharya, 2005;Lyster et al, 2021Lyster et al, , 2022, so it is unlikely that this shift represents a change from a transverse to longitudinal system at these sites in Salina Canyon. Quartz-rich source units are difficult to distinguish using detrital zircons (e.g., Lawton et al, 2010), which may explain why Pettit et al (2019) did not identify a shift in source rock between these formations.…”

“…Other variables that could influence fine sediment deposition at the bed and reach scales, such as changes in the discharge variability, tidal influence, or fluvial style are assumed to be constant across this interval, because the climatic regime was constant (Kauffman & Caldwell, 1993), there is no sedimentologic evidence for tidal influence at the outcrops in Salina Canyon, and channels in the Blackhawk and Castlegate Sandstone were likely multi-threaded (e.g., braided) (Adams & Bhattacharya, 2005;Lyster et al, 2022). Furthermore, there is no evidence for significantly different flow variability or morphodynamic processes between these units (Lyster et al, 2021). Therefore, we expect that consistent changes in mud preservation across observation scales reflect changes in mud supply between the units.…”

Analyzing Sedimentary Rocks to Evaluate Paleo Dimensions and Flow Dynamics of Permian Barakar River of Rajmahal Gondwana Sub-Basin of Eastern India

“…Additional approximation of the paleoslope can be derived using the Manning equation for the open channel flow systems. This same relationship has been used to determine the paleochannel slope in many ancient fluvial rivers [5,8].…”

“…Internal sedimentary bed forms such as dunes and ripples, which are believed to be truncated in the preserved geologic record, can now have their full heights estimated from cross bedding-sets and cosets within quantitative uncertainty and order of magnitude [1][2][3][4]. Recent researches provide a methodology to evaluate paleo dimensions and flow dynamics of ancient fluvial systems [5][6][7]. Fluvial paleo-channels can be scaled from numerical equations based on grain size along with channel depth and width measurements and augmented by flow depth estimated from estimated dune bed form height from cross bedding set thickness using data of cross bedding set thickness [2,3,8].…”

Down-delta hydraulic geometry and its application to the rock record

“…This model also assumes a fixed position and dimension of a rectangular paleochannel geometry. Values of dimensionless bankfull Shields' stress and the Chezy friction coefficient are assumed, from which paleoslope, velocity and bankfull depth hence paleodischarge are calculated (Brewer et al, 2020;Lyster et al, 2021). The Shield's stress (Ganti et al, 2019) and median formative flow depth (Trampush et al, 2014) are challenging to estimate from ancient deposits, although they can be constrained using information on, for example, grain-size distribution.…”