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Shape difference of mud clasts depending on depositional facies; application of newly modified elliptic Fourier analysis to hybrid event beds

Sojiro Fukuda and Hajime Naruse
Shape difference of mud clasts depending on depositional facies; application of newly modified elliptic Fourier analysis to hybrid event beds
Journal of Sedimentary Research (October 2020) 90 (10): 1410-1435

Abstract

Hybrid event beds are the deposits from sediment gravity flows that change their rheological behavior through their passage, entraining muddy sediments and damping turbulence. Muddy facies of hybrid event beds are often associated with abundant mud clasts which show a wide variety of size and shape. The variation of clast occurrence in hybrid event beds is expected to preserve the information of entrainment and transport processes of muddy sediments in submarine density currents. However, previous analyses of hybrid event beds have focused on describing the overall clast occurrence rather than the statistical size and shape analyses because traditional shape parameters are incapable of characterizing the complex shape of mud clasts. Here, a new quantitative grain-shape analysis of mud clasts is conducted and allows visualization of the spatial variation of clast size and shape, which suggests the wide variety of origin and transport systems of entrained mud clasts. This new method revises the traditional elliptic Fourier analysis, substituting Fourier power spectra (FPS) for traditional elliptic Fourier descriptors to overcome the mirror-wise shape problem. Further, principal-component analysis is shown to capture significant shape attributes more effectively than traditional shape parameters. The proposed method is applied to mud clasts in sediment-gravity-flow deposits in the lower Pleistocene Otadai Formation, central Japan. Results imply that there are distinctive shape and size differences of mud clasts that are strongly associated with depositional facies rather than the distance from the source. The clasts have a higher angularity than other facies in the debrite intervals in hybrid event beds. It is also shown that clasts in sandy, structureless facies have different characteristics in shapes based on elongation and convexity compared to laminated facies. Comparison between different shape-analysis methods demonstrates that none of the traditional methods are able to visualize these trends as effectively as the method presented herein. These results highlight the importance of the quantitative shape analysis of sediment grains and the effectiveness of FPS-based elliptic Fourier analysis.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 90
Serial Issue: 10
Title: Shape difference of mud clasts depending on depositional facies; application of newly modified elliptic Fourier analysis to hybrid event beds
Affiliation: University of Hull, Energy and Environment Institute, Kingston upon Hull, United Kingdom
Pages: 1410-1435
Published: 202010
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 87
Accession Number: 2021-003324
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 2 tables, geol. sketch maps
N35°16'60" - N35°16'60", E140°15'00" - E140°15'00"
Secondary Affiliation: Kyoto University, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 2021
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