Heavy mineral provinces as a tool for palaeogeographic reconstruction: A case study from the Buntsandstein of Nurra (NW Sardinia, Italy

In the Nurra region, mid-Permian to Anisian red beds, commonly referred to as "Verrucano Sardo", are exposed. In the two main outcrop areas (Torre del Porticciolo and Monte Santa Giusta), however, stratigraphic sections stron gly differ as to thickness, lithofacies and sandstone detrital modes. In or der to better understand the relationships between the two outcrop areas, a study on the heavy mineral (HM) suites of the roughly coeval upper part of both stratigraphic sections, underlying Middle Triassic carbonates, has be en carried out. For this part of the elastic succession, the name "Buntsand stein" seems more appropriate than "Verrucano Sardo". The HM suites of the studied sandstones comprise dominantly tourmaline, zir con and rutile, along with variable amounts of apatite, garnet, chloritoid, staurolite, epidotes, amphiboles, pyroxenes, monazite and sphene; other HM s, such as spinel, andalusite, xenotime, dumortierite, vesuvianite, anatase and brookite are very minor, whereas detrital phyllosilicates (biotite, mu scovite and chlorite) are widespread. Authigenic baryte and dolomite are th e most abundant transparent HMs in some samples, and hydrous Mn-oxides (lar gely romanechite) locally dominate the opaque suite. In the Torre del Porti cciolo province, the HM composition is consistent with provenance from prev ailing volcanic and subordinate basement (intrusive to metamorphic) rocks, with abundant recycled detritus from older sediments. By contrast, in the M onte Santa Giusta province the HMs were sourced essentially from metamorphi c and intrusive basement rocks, with lesser contribution from volcanic and sedimentary successions. Facies characters, palaeocurrent indicators and regional data suggest that the Torre del Porticciolo elastics were deposited in a large alluvial syste m fed from the north; the Monte Santa Giusta elastics, instead, are better restored to a distinct alluvial fan, mostly deriving first-cycle basement d etritus from the nearby medium-grade (garnet-staurolite zones) Variscan met amorphics. Locally abundant authigenic hydrous Mn-oxides, formed as a result of sedime nt weathering in climatic conditions favourable to lateritisation, are cons istent with tropical palaeolatitudes indicated for Sardinia at Early Triass ic times in recent palaeogeographic reconstructions and support the idea of seasonal rainfall in a generally semiarid climatic context.