Sedimentation of open-framework gravels in alluvial-fan settings: Quaternary Poplar Fan, northwest China

Zhang, Yue; Colombera, Luca; Mountney, Nigel P.; Gao, Chonglong; Ji, Youliang; Wu, Hanning; Du, Wei; Liu, Dawei; Bai, Donglai; Song, Wanda

doi:10.1016/j.marpetgeo.2021.105376

Cited by 4 publications

(5 citation statements)

References 97 publications

(150 reference statements)

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“…This process occurs when the stream loses capacity, resulting in a vertical and upslope accumulation of finer sediments in the upper and back part of the lobe. The difference in clast size between the proximal and distal parts of an individual lobe could be the main feature that distinguishes sieve lobes from other open‐framework facies typical of alluvial fans (Lunt & Bridge, 2007; Zhang et al, 2021). However, the difference in mean clast size is only in the range of one clast size class, which could be difficult to detect during mapping in outcrop scale (especially for smaller grain sizes that are difficult to distinguish in the field).…”

Section: Discussionmentioning

confidence: 99%

Section: Sieve-lobe Faciesmentioning

confidence: 99%

“…Sediment building alluvial fans is transported out of the catchment area by a suite of different processes, ranging from dilute flows (stream and sheet flows) to dense ones (gravity flows). The interlinked occurrence of different sedimentary facies forms a complex sedimentary architecture of an individual fan (Blair, 1999; Blair & McPherson, 1994; Brenna et al, 2020; Chen et al, 2017; Franke et al, 2015; Zhang et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

“…First, the sieve‐lobe facies has been described only qualitatively, without detailed quantitative analyses of the sedimentary structure and texture of individual sieve lobes. In a stratigraphic sequence of alluvial fans, a sieve‐lobe deposit can easily be mistaken for another open‐framework gravel facies formed by other processes (Lunt & Bridge, 2007; Zhang et al, 2021). Second, the depositional conditions (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…The interlinked occurrence of different sedimentary facies forms a complex sedimentary architecture of an individual fan (Blair, 1999;Blair & McPherson, 1994;Brenna et al, 2020;Chen et al, 2017;Franke et al, 2015;Zhang et al, 2021).…”

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confidence: 99%

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Facies analysis, depositional activity, and internal structure of sieve deposits on an active alluvial fan

Novak

Vrabec

Popit

et al. 2022

Earth Surf Processes Landf

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Sieve lobes typically appear in gravel‐rich and matrix‐poor alluvial fans. Despite being extensively studied, the sieve‐lobe facies has been defined largely based on qualitative field observations without quantitative sedimentological analyses. Additionally, depositional activity of sieve lobes has not been monitored over extended periods (monthly to annually) and not directly associated with specific precipitation triggers. Furthermore, the internal geometry of sieve‐lobe built alluvial fans has not yet been imaged by subsurface methods. We performed a multi‐method analysis of sieve lobes in the Julian Alps (NW Slovenia) on an alpine alluvial fan composed of carbonate gravels. We performed a detailed textural and structural sedimentological analysis of 11 recent sieve lobes differing in size and age. A three‐year aerial survey of the alluvial fan surface with a small unmanned aircraft and photogrammetric modelling was used to detect active sieve‐lobe evolution. Detected sieve‐lobe formation events and volumetric surface changes were paired with triggering precipitation events. Ground‐penetrating radar (GPR) profiling depicted the geometry of the sieve‐lobe built alluvial fan. The sieve‐lobe facies consists of over 80% poorly sorted, open‐framework gravels and less than 2% mud. Lobes exhibit downward coarsening and increase in clast mean size. These textural and structural characteristics are present in all sieve lobes regardless of their age and size. Sieve lobes form with a sub‐annual frequency, usually following 24 h rainfall events exceeding 50 mm. Over 1000 m3 of sediment was deposited during these events. The GPR profiles confirm that the studied alluvial fan is formed predominantly by stacked sieve lobes. Quantitative sedimentary analysis of sieve lobes, monitoring of their recent evolution, and depiction of their subsurface geometry—demonstrated in this study—reinforce the challenged concept that sieve lobes are one of the main building blocks of alluvial fans. This work also demonstrates that, under specific conditions, sieving may become the dominant alluvial fan‐forming process.

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Section: Discussionmentioning

confidence: 99%

Section: Sieve-lobe Faciesmentioning

confidence: 99%