From incision to infill: What a Late Quaternary valley system records?
Monday, 15 December 2014
Erosional sequence boundaries and incised valleys buried in modern continental shelves represent the response of alluvial and coastal systems to Quaternary sea level oscillations. The study of the processes leading to valley incision reveals, at both regional and global scales, the influence of tectonics and eustatism on the evolution of fluvial landforms in coastal plains, while the sedimentary infill of the valley may represents one of the best archives to investigate past environmental changes. Although the time registered in the stratigraphic record represents only a small portion of the geological history, informations about the processes governing the evolution of past landscapes can be quantified by looking to erosional surfaces, where much of the time is condensed. The Manfredonia Incised Valley (southern Adriatic Sea), is a very interesting case of valley as it formed during a single episode of incision related to the last glacial sea level fall and was completely filled during the post-glacial sea level rise. The inverse-funnel shape of the incision, and its confinement toward the mid-inner shelf reveal the impact of the step-wise sea level fall on preexisting coastal morphologies, in particular during the MIS5-4 and MIS3-2 transitions. The 45 m thick sedimentary succession filling the valley recorded the post-glacial sea level rise, as revealed by the upward transition from fluvial to shallow-marine deposits, and the impact of base level and high-frequency climate change on river to coastal systems. The upper 15 m of infill, in particular, consist of multiple bayhead delta progradations occurred synchronously to the formation of sapropel S1, and represent the very-shallow water equivalent of the cm-thick sapropel layers accumulated offshore in the deeper southern Adriatic basin.