How Much did the Variscan Relief Influence the Permian climate of Mesoeurope?

Did the Variscan relief influence the Permian climate of Mesoeurope? Insights from geochemical and mineralogical proxies from Sardinia (Italy)

Authors:

Sinisi et al

Abstract:

Red beds deposits of Permian-Triassic basins of Sardinia (western Italy), where a wide segment of the Variscan orogen is exposed, were studied. The basins were selected according to their position within the structural zones of Variscan orogen, i.e. from the external to the inner sectors of the chain. Detailed mineralogical, petrographical, and chemical analyses were performed on shale and calcrete layers laying along the sedimentary sequences, to examine their compositional features and stratigraphic variation. In this regard, enrichment factors (F(e)) for major and trace elements (relative to the PAAS composition) were calculated and discussed. Several geochemical proxies were also calculated and used to assess the palaeoclimate conditions during the red beds deposition. The weathering indices (CIA and CIW) accounted for more humid conditions in the basins of the axial zone relative to the basins those of the foreland, which instead were characterized by an arid climate. However, the presence of carbonates, albeit discontinuous, and the values of calcification, salinity, and hydrolysis indices suggest that, in the axial zone, dry and hot periods also occurred. Compositional data of the sedimentary records were correlated to the Sardinia geological setting and significant information were obtained on the palaeoenvironment characterizing the south-western Mesoeurope during Permian and Triassic. Al2O3-TiO2-Zr ternary plot and Zr/Sc vs. Th/Sc diagram show that both sorting and sedimentary recycling affected the studied basins. Precisely, our data lead us to suppose that a wide regional subsidence caused both the recycling of uplifted Variscan rocks and the diagenetic K-metasomatism of Permian sediments revealed by the A-CN-K diagram. Finally, a supply from upper continental source has been suggested by the provenance proxies (such as (Gd/Yb)N and Eu/Eu*) and the La-Th-Sc plot that also reflect the paucity of mafic rocks in feeding areas.