Architecture of a distal pre‐vegetation braidplain: Cambrian middle member of the Wood Canyon Formation, southern Marble Mountains, California, USA

Abstract

Architectural element analysis and detailed mapping of a 300 m along-strike exposure of the middle member Wood Canyon Formation, southern Marble Mountains, California, USA, provides new evidence for extensive braidedfluvial channel-belt deposits with adjacent overbank environments. Threedimensional models constructed using 'Structure from Motion' techniques, combined with field-based observations, allowed interpretation of outcropscale trends, barforms, channel fills and fine-scale features. The ca 80 m thick member is divisible into five distinct units, including units M1 to M3 that form the bulk of the stratigraphy. Units are defined by stacking patterns of three facies associations (Facies Association 1 to Facies Association 3), each representing the product of a subenvironment within the fluvial system. In Facies Association 1, stacked cosets, interpreted as low-relief fluvial bars and channel fills, preserve vertical-accretion and downstream-accretion elements under unimodal north-north-west palaeoflow, with minor lateral accretion near bar edges. Deposits of Facies Association 2 to Facies Association 3, linked to overbank environments, are found only in unit M2, in the middle 27 m of the middle member. Floodplains, represented by Facies Association 2, include crumbly red-orange intervals of fine to mediumgrained sandstone and thinner sets of cross-bedding than Facies Association 1, interbedded with thicker cross-stratification indicative of overbank splay or overland flow aggradation from adjacent channel belts during flood stage. Possible aeolian beds of Facies Association 3 preserve broad festooned trough cross-strata that average 23 cm in thickness; their small size, medium-grained sandstone and iron oxide cement suggest a high water table. The diverse assemblage of interpreted subenvironments, paired with bedform and facies patterns, implies a perennial fluvial system that gradually built large sand bars as the channel belt migrated and avulsed across an unconfined braided-fluvial reach, leaving the overbank area on its flanks subject to weathering and aeolian transport. Despite the occurrence of strata deposited in low-energy and ponded settings, and a marine influence proposed for nearby sections of middle member, no ichnofossils were encountered.

Sedimentological and Geochemical Perspectives on a Marginal Lake Environment Recorded in the Hartmann's Valley and Karasburg Members of the Murray Formation, Gale Crater, Mars

“…Given the proximity of Facies 1 with Facies 3 and the lacustrine basin environment (Section 4.3; Figure 5), such a large‐scale river system would be unlikely. Additionally, there is an absence of evidence for fluvial architectural elements such as channel fills, accretion elements, and barforms within the stratigraphy (e.g., Ielpi & Rainbird, 2015; Long, 2006; Muhlbauer et al., 2020). Additionally, fluvial facies identified in the Bradbury group consist of granule‐ and pebble‐sized clasts and exhibit varying degrees of sorting (Edgar et al., 2017; Williams et al., 2013).…”

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

“…Late Ordovician present) from regions dominated by erosion (ripple marks absent), where energy was channelized within a sedimentary system (e.g. Muhlbauer et al, 2020).…”

“…17), and their uneven distribution within a lithologically‐similar section may assist in differentiating regions dominated by stasis (ripple marks present) from regions dominated by erosion (ripple marks absent), where energy was channelized within a sedimentary system (e.g. Muhlbauer et al ., 2020).…”

“…If the preservation of true substrates is conceptually likely, it is pertinent to consider converse factors that lead to their destruction. There is a primary facies control on this, in that some parts of any environment are more likely to experience continuous deposition or frequent erosion (and an accordant dominance of depositional or constructed boundaries), such as within fluvial or estuarine channels (McMahon et al ., 2020; Muhlbauer et al ., 2020). However, even in those parts of environments where stasis dominates, signatures registered on substrates can diminish with prolonged exposure (e.g.…”

Use of drones to analyse sedimentary successions exposed in the foreshore

“…Most sedimentological studies to date, have been in locations with little or no vegetation, such as arid regions (Pierce at el., 2016;Hansman and Ring, 2019), glacially scoured areas (Buckley et al, 2010;Nesbit et al, 2018) and extensive well-exposed vertical cliffs (Eide et al, 2015;Muhlbauer et al, 2020). As illustrated by many of the studies cited above, a key advantage of the use of drones for sedimentological and stratigraphic studies is that the large-scale view can be used to detect subtle changes in geometry and lateral variation that are a common characteristic of sedimentary successions.…”