Dispersal pathways in the early Messinian Adriatic foreland and provenance of the Laga Formation (Central Apennines, Italy)

The early Messinian Laga Formation represents a turbidite complex deposited in the Late Neogene foreland basin system of the growing Apenninic chain. While the stratigraphy and physiography of the Laga Basin are well known, the source of its sediments is contentiously claimed to be either recycled Apenninic or primary Alpine. Furthermore, a shift in paleocurrent was proposed as a marker of provenance change around 6Ma. By combining double-dating of detrital zircons (fission-track and U-Pb dating) with compositional analyses, the sedimentary provenance of the lower Laga arenites and differences between the proximal channelized and distal lobe facies are addressed. Due to sediment sorting processes, the lobe facies shows a reduced heavy mineral spectrum relative to the channelized facies. Hence, proximal deposits reflect their hinterland lithologies better than their distal counterpart and should be preferred in provenance analyses. The petrographic composition of the Laga units implies a major metamorphic source combined with an additional dolomite and carbonate source. No compositional difference spanning the shift in paleocurrents is observed, which therefore likely reflects the evolving topography of the foreland due to syn-sedimentary tectonics. Detrital zircon fission-track data reveal youngest age populations at ~16–17Ma and lag times in the range of 9 to 11Ma that can be related to modern fission-track ages observed in the Central Alps. The two major 238U/206Pb age populations, centered at 277.5 and 37.5Ma, represent (post-)Variscan events and the Paleogene magmatic activity in the Central Alps, specifically the Adamello complex. The Central and Southern Alps are thus inferred as the major source for the early Messinian Laga arenites. The pathways of the sediments from the Alps to the Laga Basin crossed the Alps-Apennines foreland and passed on the outer Apenninic wedge-top along elongated and tectonically controlled basins and channels that entered the basin from the north and northwest. The transfer could have been direct along the Apenninic depozones. Additionally, late Tortonian sediments from the Alps could have been temporarily stored on top of the Apenninic wedge, e.g. in the Marnoso-arenacea Basin, and then seamlessly cannibalized into the Laga Basin.