Beach sands of Elba Island, Tuscany, Italy: Roundness study and evidence of provenance

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 2 ; most are less than 5 km 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. Figure 1. Generalized geologic map of Elba showing numbered sample localities. Complex I = Carboniferous and Triassic marble, dolomite, and quartzite; Complex II = Carboniferous to Jurassic metasedimentary rocks; Complex III = Carboniferous to Jurassic limestone, argillite, and sandstone; Complex IV = Jurassic and Cretaceous ophiolitic rocks, bedded chert, limestone, and argillite; Complex V = Cretaceous and Paleogene limestone, sandstone, and shale. Modified from Trevisan and Marinelli (1967). Numbers 1 through 18 indicate beach sites.

Grain Shape Evolution of Sand‐Sized Sediments During Transport From Mountains to Dune Fields

“…No textural and mineralogical maturation trends were observed in the fluvial environments along the sediment routes; instead, the grain shape parameters show overall stable values for the samples in different positions of rivers (Figure 2). These observations confirm that fluvial processes have limited effects on modifying the grain shape, as stated in previous studies (e.g., Garzanti, 2017; Picard et al., 1993; Resentini et al., 2018). However, the sand from dune fields shows significantly higher maturity in terms of geochemical and textural features (Figures 2 and 4), elucidating the sharp contrast of modification effects on sand grains between fluvial and eolian processes.…”

“…Hence, detrital sediments can carry valuable information concerning past geological conditions in paleoenvironment reconstructions (Folk, 1980). The sedimentological features of detrital sediments, including grain size, shape, and surface microtextures, are critical diagnostic parameters for inferring the sediment depositional environment, transport history, and associated surface processes (Boggs, 2012; Folk, 1951, 1980; Krumbein, 1941b; Picard et al., 1993). In addition, the geochemical signatures carried by detrital sediments can be used to identify the provenance, weathering intensity, and related climate they have experienced (Basu, 2017; Dutta et al., 1993; Liang et al., 2022; Muhs, 2004; Pye & Mazzullo, 1994).…”

Immature beach/dune sands along a passive continental margin: Composition, grain size and hydraulic properties of coastal sands, Parque del Plata and Las Vegas, Uruguay

“…The roundness of the beach sand is largely controlled by the source sediment added to the beach (Picard & McBride, ; Resentini, Andò, & Garzanti, ). Associated coastal dunes can have an increased degree of roundness compared to the source beach sand based on selective transport (Reineck & Singh, ).…”

Recycling and chemical weathering in tectonically controlled Mesozoic–Cenozoic basins of New Zealand

“…However, several studies have shown that quartz enrichment can be due to a combination of factors. These include: (i) the composition of the source area (Basu, 1976; Mack, 1981; Picard & McBride, 1993; Nesbitt et al. , 1996; Youngson & Craw, 1996), (ii) relief (Johnsson & Stallard, 1989), (iii) extensive chemical weathering (Franzinelli & Potter, 1983; Suttner & Dutta, 1986; Corcoran et al.…”