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Morphodynamics and facies architecture of streamflow-dominated, sand-rich alluvial fans, Pleistocene Upper Valdarno Basin, Italy

By
Massimiliano Ghinassi
Massimiliano Ghinassi
1
Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, 35121 Padova, Italy
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Alessandro Ielpi
Alessandro Ielpi
2
Department of Earth Sciences, Laurentian University, Sudbury, Ontario, P3E 2C6, Canada
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Published:
January 01, 2018

Abstract

The overwhelming documentation of coarse-grained alluvial fans dominated by mass flow contrasts with the scarce accounts of finer grained, traction-dominated alluvial fans. To fill this gap, we present sedimentological and architectural data from a set of sand-rich, streamflow-dominated Pleistocene fans flanking the eastern Upper Valdarno Basin, Italy. The routing of sand-rich sediment resulted from the fast, intense weathering of the feldspar-rich, carbonate-deprived sandstone bedrock underlying the fan catchments. Although capable of entraining large boulders, high water discharge sustained tractional reworking along the proximal facies belts, hindering mass flow. The medial facies belts have a channelized, braided planform and are dominated by processes hardly distinguishable from those characterizing fluvial environments. Along the distal facies belts, extensive overbank tracts are composed of terminal splays and crevasse lobes, the spatial arrangement of which controlled the evolution of through-going tributary channels connected to the axial basin drainage. This study focused on the sedimentary processes, stratal architecture and morphodynamics of the alluvial fans and considered the effect of bedrock inheritance on their development. The results underline how granulometry and mass flow dominance are not distinctive of alluvial fan sedimentation per se and indicate how the critical detection of piedmont, radial palaeomorphology is crucial in the identification of ancient alluvial fans.

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Contents

Geological Society, London, Special Publications

Geology and Geomorphology of Alluvial and Fluvial Fans: Terrestrial and Planetary Perspectives
CONTAINS OPEN ACCESS

D. Ventra
D. Ventra
Utrecht University, the Netherlands
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L. E. Clarke
L. E. Clarke
University of Gloucestershire, UK
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Geological Society of London
Volume
440
ISBN electronic:
9781786203809
Publication date:
January 01, 2018

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