Weathering trends in the Norian through geochemical and rock magnetic analyses from the Pignola–Abriola section (Lagonegro Basin, Italy)

Abstract

We investigated the geochemical and rock magnetic properties of the magnetostratigraphically calibrated Pignola–Abriola section (Italy) in order to understand the climatic perturbations that characterize the late Norian–early Rhaetian interval (Late Triassic). We performed experiments on anhysteretic and isothermal remanence (ARM and IRM) and on magnetic susceptibility (χ) to obtain the rock magnetic parameters necessary for our paleoclimatic investigation. An episode of increase in the relative quantity of hematite, suggesting the enhanced subaerial oxidation of iron minerals, was identified in the Norian from ∼ 217 Ma in the Alaunian up to ∼ 211 Ma in the early Sevatian, followed by a decline up to 207–206 Ma at the end of the Norian (late Sevatian). The results of geochemical and multivariate statistical analyses support a long-term increase and reduction in rock weathering, confirming and extending previous 87Sr / 86Sr data from the Pizzo Mondello section (Italy). Possible causes of these long-term weathering trends are the multiphase uplifting of the Cimmerian orogen, occurring at mid-northern latitudes along the southern margin of Asia in the Late Triassic, and/or the northward motion of Pangea across the equatorial humid belt. Rapid excursions in oxidized iron minerals have also been observed across the Norian–Rhaetian boundary, the origin of which still has to be determined.