Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece

Abstract

The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain-size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain-size increases westward along the southern coast of the Gulf of Corinth, with the coarse-fraction grain-sizes (84 th percentile of weighted grain-size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain-size export is primarily controlled by the input grain-size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain-size-specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475-16 cm). Our results suggest that the grainsize of sediment export at the rift scale is particularly sensitive to catchment lithology | 1601 EAGE WATKINS eT Al.

Short communication: Field data reveal that the transport probability of clasts in Peruvian and Swiss streams mainly depends on the sorting of the grains

“…Only grains larger than a few millimeters (> 4-5 mm, depending on the quality and resolution of the photos) could be measured. While the limitation to precisely measure the finest-grained particles potentially biases the determination of D 50 , it will not influence the measurements of the D 84 and D 96 grain sizes, as the comparison between sieving and measuring of grains with the Wolman (1954) method has disclosed (Watkins et al, 2020). In addition, as will be shown below, the consideration of the D 96 /D 84 instead of the D 96 /D 50 ratios yields a similar positive relationship to the mobility of grains.…”

“…We finally assigned an uncertainty of 20 % to the D 84 threshold grain size, which considers the variability in D 84 within a gravel bar as the analysis of the intra-bar variation in D 84 for selected gravel bars in Switzerland shows (Table S2). The assignment of a 20 % uncertainty to the D 84 threshold grain size also considers a possible bias that could be related to the grain size measuring technique (e.g., sieving in the field versus grain size measurements using the Wolman method; Watkins et al, 2020). However, it is likely to underestimate the temporal variability in the grain size data.…”

Times associated with source-to-sink propagation of environmental signals during landscape transience

“…The second group of parameters focuses on differences in the characteristics of grains within a certain sediment package, such as grain size distributions (Duller et al, 2010(Duller et al, , 2019Whittaker et al, 2010Whittaker et al, , 2011Foreman et al, 2012;Parsons et al, 2012;Foreman, 2014;D'Arcy et al, 2017), median or other characteristic grain sizes (D50, D84, sortable silt; McCave and Hall, 2006;Schlunegger and Norton, 2015;Chen et al, 2018;McCave and Andrews, 2019;Watkins et al, 2020), the location of the gravelsand transition in alluvial fans and river systems (Allen et al, 2015;Dubille and Lavé, 2015;Blom et al, 2017;Dingle et al, 2017Dingle et al, , 2020Armitage et al, 2018a), sorting and related textural characteristics (e.g., in glacio-marine sediments: Anderson et al, 1980;D'Orsay and Van De Poll, 1985;Pudsey, 1992;Helland et al, 1997;Passchier et al, 2019), or grain shape (Stanley and De Deckker, 2002;Kalińska and Nartišs, 2014).…”

“…The dominant transport mode of a distinct hydraulic grain size fraction exerts a major control on sediment transport times along SRSs. And sediment transport times, in turn, have direct implications for signal propagation and modification within SRSs (Chabaux et al, 2012;Carretier et al, 2019Carretier et al, , 2020Watkins et al, 2020). Therefore, we propose to investigate signal propagation not for bulk sediments, but for hydraulic grain size fractions individually.…”

“…As previously discussed, we suggest grouping sediments by hydraulic grain size fractions when investigating environmental signal reconstruction from stratigraphy. Consider a simple hypothetical scenario where hydraulic grain size fraction is directly related to signal transfer time such that finegrained sediment transmits catchment signals quickly, whereas signals associated with coarse-grained sediment are comparably slower (Carretier et al, 2020;Watkins et al, 2020). The implication is that the onset of the signal of interest in fine-grained parameters would be at a lower stratigraphic position compared to parameters associated with coarse-grained sediment for the same change in boundary conditions (Fig.…”