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GEOREF RECORD

Beach sands of Elba Island, Tuscany, Italy; roundness study and evidence of provenance

M. Dane Picard and Earle F. McBride
Beach sands of Elba Island, Tuscany, Italy; roundness study and evidence of provenance (in Processes controlling the composition of clastic sediments, Mark J. Johnsson (editor) and Abhijit Basu (editor))
Special Paper - Geological Society of America (1993) 284: 235-245

Abstract

We studied the composition and roundness of medium sand from 18 small beaches of Elba Island. Six are pocket beaches less than 100 m long; the longest is 1.3 km long. The drainage basins of streams that supply the beaches are all less than 25 km (super 2) ; most are less than 5 km (super 2) . Beach sands range widely in composition owing to diverse source terrane. For the various drainage basins, comparison of the outcrop areas of the different types of bedrock with the compositions of beach sand grains yields the following conclusions: (1) the relative area of granodiorite outcrop is accurately represented by the amount of quartz + feldspar + quartzofeldspathic rock fragments in all beaches, although plagioclase in beach sand is significantly reduced relative to K-feldspar; (2) the relative areas of outcrop of ophiolitic and limestone bedrock are accurately represented by beach sand in pocket beaches, but are only moderately represented (ophiolitic rocks) or poorly represented (limestone) in other beaches; (3) the relative area of outcrop of metamorphic rocks is poorly represented in beach sand (metamorphic rock fragments + polycrystalline quartz) except in one anomalous beach supplied in part by mine tailings; (4) the relative area of bedded chert outcrop is poorly represented in beach sand because bedded chert does not break down into sand-size grains; and (5) shale bedrock is not represented or is only marginally represented in beach sand. For Elba beaches in general, the order of increasing roundness of grains, and thus increasing rate of abrasion, is: quartz < plagioclase < K-feldspar and igneous rock fragments (quartzo-feldspathic) < serpentine < metamorphic rock fragments < carbonate rock fragments (CRFs). There are no significant differences in roundness with beach length for quartz, K-feldspar, or CRFs. There are also no significant differences in roundness for the same three grain types from beaches of different size drainage basins, which indicates there is no perceptible rounding of grains by streams. First-cycle monocrystalline quartz grains of medium sand are unrounded, although coarser grains show minor blunting of edges. The roundness of quartz, K-feldspar, and CRFs are all greater on the eastern, more protected part of the island. This reflects a significant proportion of recycled quartz and K-feldspar in the eastern beaches, but CRFs may undergo more rounding in beaches of low to moderate wave activity than in high-energy beaches.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 284
Title: Beach sands of Elba Island, Tuscany, Italy; roundness study and evidence of provenance
Title: Processes controlling the composition of clastic sediments
Author(s): Picard, M. DaneMcBride, Earle F.
Author(s): Johnsson, Mark J.editor
Author(s): Basu, Abhijiteditor
Affiliation: University of Utah, Department of Geology and Geophysics, Salt Lake City, UT, United States
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: 235-245
Published: 1993
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 28
Accession Number: 1994-013900
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, sketch maps
N42°10'00" - N43°10'00", E10°00'00" - E12°00'00"
Secondary Affiliation: Indiana University, USA, United StatesUniversity of Texas at Austin, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 199406
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