Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

Abstract

Flume experiments and field observations show that bank vegetation promotes the formation of narrow and deep single‐thread channels by strengthening riverbanks. Consistent with this idea, the pre‐Silurian fluvial record generally consists of wide monotonous sand bodies often interpreted as deposits of shallow braided rivers, whereas single‐thread rivers with muddy floodplains become more recognizable in Silurian and younger rocks. This shift in the architecture of fluvial deposits has been interpreted as reflecting the rise of single‐thread rivers enabled by plant life. The deposits of some single‐thread rivers, however, have been recognized in pre‐Silurian rocks, and recent field studies have identified meandering rivers in modern unvegetated environments. Furthermore, single‐thread‐river deposits have been identified on Mars, where macroscopic plants most likely never evolved. Here we seek to understand the formation of those rarely recognized and poorly characterized single‐thread rivers in unvegetated landscapes. Specifically, we quantitatively explore the hypothesis that cohesive muddy banks alone may enable the formation of single‐thread rivers in the absence of plants. We combine open‐channel hydraulics and a physics‐based erosion model applicable to a variety of bank sediments to predict the formation of unvegetated single‐thread rivers. Consistent with recent flume experiments and field observations, results indicate that single‐thread rivers may form readily within muddy banks. Our model has direct implications for the quantification of riverbank strengthening by vegetation, understanding the hydraulic geometry of modern and ancient unvegetated rivers, interpreting pre‐Silurian fluvial deposits, and unraveling the hydrologic and climate history of Mars.

Sustained fluvial deposition recorded in Mars’ Noachian stratigraphic record

“…The abundance of mudstone in the studied outcrop here is not known or speculated upon, as their intrinsic fine-grained components require rover-based observations. However, the preserved channel-belt architecture, comprising relatively intact channels and barforms, suggests some degree of original channel-belt stability, with naturally shear-resistant sediment such as mud a possible candidate 47,48 . With regard to channel and barform facies, evidence of relatively stable, deep-channelled drainage on pre-vegetation Earth is being increasingly reported 37 .…”

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

“…Martian sinuous ridges have long been interpreted as remnants of meandering channel belts (e.g., Burr et al, 2006Burr et al, , 2010Cardenas et al, 2018;DiBiase et al, 2013;Kite et al, 2015;Williams, Irwin, et al, 2013). Although adjoining floodplain materials appear to have been eroded, as commonly observed in inverted fluvial landscapes on Earth (e.g., Hayden et al, 2019), river flows were most likely confined by banks that contained fine-grained materials (e.g., Lapôtre et al, 2019). Clay minerals have been detected globally on Mars by orbiting spectrometers (e.g., Ehlmann & Edwards, 2014;Mustard et al, 2008;Poulet et al, 2005), including within delta deposits (e.g., Ehlmann et al, 2008;Goudge et al, 2015).…”

“…Therefore, the empirical calibration of migration rates is typically performed on a case-by-case basis (e.g., Matsubara & Howard, 2014). While vegetation plays a critical role in bank stabilization (e.g., Braudrick et al, 2009;Davies & Gibling, 2010;Parker et al, 2011;Smith, 1976), recent field and modeling studies demonstrated the stability of single-thread rivers in unvegetated or sparsely vegetated basins (Ielpi, 2019;Ielpi & Lapôtre, 2019a, 2019bLapôtre et al, 2019;Li et al, 2015;Matsubara et al, 2015;Santos et al, 2017Santos et al, , 2019. Because their morphodynamics are unaffected by plant life, modern unvegetated single-thread rivers may offer particularly relevant analogs for ancient Martian single-thread rivers.…”

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

“…Some efforts have centred on connecting landscape surface kinematics to stratal preservation (Paola & Borgman, 1991;Castelltort & Van Den Driessche, 2003;Jerolmack & Mohrig, 2005;Jerolmack & Paola, 2010;Hajek & Wolinsky, 2012;Ganti et al, 2013;Ganti et al, 2014;Reesink et al, 2015;Romans et al, 2016;Ganti et al, 2020;Straub et al, 2020) and a number of these studies have focused on Late Cretaceous fluvial strata in central Utah Trower et al, 2018;Ganti et al, 2019a). Meanwhile, other quantitative work has applied fluid and sediment transport models to stratigraphic field data, with an overarching goal of constraining the characteristics of catchments, regional systems or entire fluvial landscapes in the geological past (Ganti et al, 2019b;Lapôtre et al, 2019), or even on other planetary bodies (Lamb et al, 2012;Buhler et al, 2014;Hayden et al, 2019;Lapôtre et al, 2019). This includes using quantitative palaeohydrological tools to reconstruct water and sediment discharges within mass balance frameworks (Holbrook & Wanas, 2014;Lin & Bhattacharya, 2017;Sharma et al, 2017), decipher local palaeogeographies (Bhattacharyya et al, 2015;Li et al, 2018), characterise pre-vegetation rivers (Ganti et al, 2019b), and reconstruct fluvial response to climatic perturbations for well-preserved fluvial strata straddling events such as the Paleocene-Eocene Thermal Maximum (PETM) (Foreman et al, 2012;Foreman, 2014;Colombera et al, 2017;Chen et al, 2018;Duller et al, 2019).…”