UNRAVELING TECTONIC AND CLIMATIC CONTROLS ON SYNOROGENIC GROWTH STRATA, NORTHERN APENNINES, ITALY

Synorogenic sediments are often used to decipher the tectonic histories of mountain belts. In doing so it is typically assumed that the stratigraphic architecture of these sediments are primarily controlled by tectonics, yet it is not always understood what role climate and unsteady surface processes play in controlling the stratigraphy of synorogenic sections and how these climatic controls can be distinguished from tectonic ones. Here we separate tectonic and climatic controls on the middle-late Pleistocene Enza growth section, deposited in the Po plain adjacent to the Northern Apennine mountain front, Italy using sedimentological, structural, geophysical, and geochronological data. The Enza section represents a transition from outer shelf muds, to near-shore sands, to continental palustrine, fluvial and alluvial deposits towards the top of the section. Superimposed on this overall shallowing are several lithologic cycles that represent climatically forced changes in depositional environment. Bedding dips range from 55° to 2° and becoming progressively shallower up-section. The marine part of the section displays progressive unconformities suggesting steady deformation, while the fluvial and palustrine rocks contain multiple angular unconformities suggesting punctuated deformation. Biostratigraphy, magnetostratigraphy, rock-magnetic cyclostratigraphy, and cosmogenic and OSL burial dating were used to develop a high-resolution age model and determine incremental deformation rates. The age model shows sediment accumulation rates decreased towards the present and were remarkably non-steady. The magnetostratigraphy and cyclostratigraphy show rapid, but constant, marine sediment accumulation during the middle Pleistocene accompanied by punctuated deformation. Contrastingly, cosmogenic and OSL burial ages from fluvial channel sands deposited in the late Pleistocene indicate sediment accumulation was unsteady, but deformation rates were fairly constant. Results from the Enza section show that the temporal resolution of synorogenic deposits has a large impact on the ability to separate tectonic and climatic signals.