The effects of source rocks and chemical weathering on the petrogenesis ofsiliciclastic sand from the Neto River (Calabria, Italy): implications forprovenance studies

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 profile s, a combination of chemical weathering and granular disintegration process es occurred. Chemical weathering involves a loss of both plagioclase (mainl y during grus generation) and K-feldspar (mainly during soil formation). Th is loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of K-feldspar. Sand composition is quartzofeld spathic and nearly homogeneous along the main channel of the Neto River, ev en where the river cuts across a blanket of sedimentary cover. Thus, fluvia l transport does not alter sand composition within the Neto drainage basin. Petrographic indices are effective in (1) discriminating between contribut ions from similar (granite and gneiss) source rocks (Qm/F); (2) relating th e provenance of plutoniclastic and gneissiclastic sand found in the headwat ers to grus horizons (Qm/F; Q/Rg); and (3) distinguishing between upstream first-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 pr oducer 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 proven ance interpretations of ancient quartzofeldspathic sandstones.