Publication: The effects of source rocks and chemical weathering
on the petrogenesis of siliciclastic sand from the Neto River
(Calabria, Italy): implications for provenance studies
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Publication Date
2001
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Blackwell Publishing Ltd
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Abstract
Plutonic and gneissic rocks of the Sila Massif in the uppermost portion of the
Neto drainage basin (Calabria, Southern Italy) weather and erode under a
humid Mediterranean climate. During the development of weathering pro®les,
a combination of chemical weathering and granular disintegration processes
occurred. Chemical weathering involves a loss of both plagioclase (mainly
during grus generation) and K-feldspar (mainly during soil formation). This
loss is attributed to transformation of plagioclase to clay minerals and to
leaching and dissolution of K-feldspar. Sand composition is quartzofeldspathic
and nearly homogeneous along the main channel of the Neto River, even where
the river cuts across a blanket of sedimentary cover. Thus, ¯uvial transport
does not alter sand composition within the Neto drainage basin. Petrographic
indices are effective in (1) discriminating between contributions from similar
(granite and gneiss) source rocks (Qm/F); (2) relating the provenance of
plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons
(Qm/F; Q/Rg); and (3) distinguishing between upstream ®rst-cycle and
downstream multicycle sand (Q/Rg). This last distinction is further
emphasized by considering both aphanitic and phaneritic varieties of rock
fragments (RgRmRs diagram). Chemical weathering is the main sand producer
within the regolithic environment in northern Calabria. In addition, rapid
erosion resulting from steep slopes removes weathered products, and rapid and
short transport leads to minimal sediment maturation. In general, the F/Q
index is climate and relief dependent; thus, it should be used in conjunction
with palaeoclimatic and palaeophysiographic evidence for provenance
interpretations of ancient quartzofeldspathic sandstones.