High-resolution magnetostratigraphic and lithostratigraphic correlations in Middle Triassic pelagic carbonates from the Dolomites (northern Italy)

Abstract

New magnetostratigraphic and lithostratigraphic data are reported from the Pedraces and Belvedere limestone sections from the Dolomites region of northern Italy. These sections are comprised of the Buchenstein Beds of Late Anisian to Ladinian (Middle Triassic) age. The results from Pedraces and Belvedere are compared with data from the biostratigraphically and isotopically constrained Frötschbach and Seceda sections from the literature. A satisfactory magnetostratigraphic correlation is obtained on laterally traceable limestone and volcaniclastic intervals. These marker beds are then used to extend lithostratigraphic correlations to additional key sections from a palaeogeographically coherent area of around 500 km 2. The aim of this study is to unravel the spatial and temporal evolution of the Buchenstein basin and the surrounding carbonate platforms. Platforms in the northwestern Dolomites show an early stage of aggradation followed by progradation, whereas in the central Dolomites the Cernera platform, after fast initial aggradation, drowned and became a pelagic seamount. In the intervening Buchenstein basin, the differential subsidence between the northwestern and central Dolomites is manifested by the lateral increase of thickness of “Lower Pietra Verde” volcaniclastic sediments. Accumulation of volcaniclastic material reworked from adjacent carbonate platform slopes characterised the more subsiding and unstable central Dolomites. In the pelagic carbonate intervals, the persistence over tens of kilometres of bedding patterns suggests that carbonate material presumably washed out from the surrounding, still active carbonate platforms was volumetrically small and homogeneously distributed throughout the uniformly subsiding Buchenstein basin. A Milankovitch precessional origin for the platform interior cycles at Latemar as suggested elsewhere implies a net accumulation rate of 2 m/Ma or less for the correlative interval of pelagic Buchenstein Beds. This value differs significantly from the average value of around 10 m/Ma as calculated using high-resolution isotopic age data for the Buchenstein Beds.