Spatial variation in the sedimentary architecture of a dryland fluvial system

Abstract

Ancient dryland terminal fluvial systems are often recognized within the rock record for having a progressive downstream decrease in the size and amalgamation of channel elements and systematic downstream increase in sheet and overbank elements, alongside the downstream decrease in grain size that is displayed by most fluvial systems. The spatial distribution and downstream trends displayed by the fluvial sediments of the Lower Jurassic Kayenta Formation of south-western USA, have been examined quantitatively. The results indicate many trends that are similar to those of a dryland terminal fluvial system, including; a lack of confinement of the fluvial system, a downstream decrease in channel and sheet element amalgamation and width-to-thickness ratios, a downstream decrease in grain size, albeit very small, and an increase in the percentage of overbank elements downstream. However, the study highlights several downstream relationships that are atypical. While some of these relationships may be the result of external factors inherent in this study, others, including the thicknesses of channelfill and sheet elements that display no significant relationships to distance downstream, and channel-fill elements that display no significant variation in average grain size with distance downstream, may be a consequence of fluvial interaction with a competing and coeval aeolian system. This work demonstrates the inherent complexity in arid dryland fluvial systems and the downstream architectural and compositional relationships that they depict. Consequently, models for fluvial style may provide only a first-order approximation for downstream trends in dryland systems, because the controlling factors upon these systems are inherently difficult to unravel, and the sedimentary detail is strongly dependent upon external setting and internal complexity. Consequently, a generalized model may not always be applicable to these systems.

Evolution from shallow‐water deltas to fluvial fans in lacustrine basins: A case study from the Middle Jurassic Shaximiao Formation in the central Sichuan Basin, China

“…The extensive erosion also implies that the original thickness of each bed may have been thicker. The rounded, red mud clasts suggest that the fluvial system eroded into up‐dip floodplain areas (Cain & Mountney, 2009; Priddy & Clarke, 2021). The vertical arrangement of lithofacies from lithofacies Sc to lithofacies Cs indicates accumulation via bedload transport and deposition under high flow velocity and sediment load conditions in the channel complexes (Bridge, 2006).…”

“…(Edmonds et al, 2011). These new discoveries generally emphasize the long-distance transport and widespread sedimentary characteristics of fluvial systems (Priddy & Clarke, 2021;Xu et al, 2021). However, identifying this knowledge in ancient successions is difficult, because the differences between fluvial fans and shallow-water delta deposits are not clear yet (Olariu & Bhattacharya, 2006;Fielding et al, 2012Fielding et al, , 2018Weissmann et al, 2015;Owen et al, 2017).…”

“…Shallow‐water deltas are large fan‐shaped depositional systems formed by frequent river bifurcations and diversions (Edmonds et al ., 2011; Xu et al ., 2021; Reynolds, 2022). These features are very similar in terms of their characteristics and distribution of deposits, because both are characterized by extensively developed channel fill deposits and common palaeosols (Donaldson, 1974; North & Warwick, 2007; Moscariello, 2018; Zeng et al ., 2019; Wang & Plink‐Björklund, 2019; Priddy & Clarke, 2021; Xu et al ., 2021). However, there are essential differences in the depositional process between them.…”

“…However, there are essential differences in the depositional process between them. For example, fluvial fans grow through river avulsion on land, while shallow‐water deltas grow through river bifurcations in subaerial and shallow‐water environments (North & Warwick, 2007; Moscariello, 2018; Priddy & Clarke, 2021; Xu et al ., 2021; Reynolds, 2022). In addition, shallow‐water deltas have a subaqueous component that makes it easier to differentiate them from the record of fluvial environments (Xu et al ., 2021; Reynolds, 2022).…”

The sedimentological expression of transgression–regression cycles upon aeolian–marine margins

“…Many aeolian successions comprise vast and apparently homogeneous deposits, documenting millions of years of geological time, which is recorded within both the preserved successions and by the unconformities that separate them. Aeolian systems are subject to both allogenic and autogenic forcing, when these systems interact with neighbouring fluvial, lacustrine and marine margins complex interbedded successions of aeolian, alluvial, lacustrine, coastal and shallow‐marine deposits are produced (Al‐Masrahy & Mountney, 2015; Kemp et al, 2017; Langford, 1989; Mountney & Jagger, 2004; Pettigrew et al, 2020, 2021; Priddy & Clarke, 2020, 2021; Rodríguez‐López, 2008).…”