Unraveling tectonic and climatic controls on synorogenic growth strata (Northern Apennines, Italy)

Abstract

We develop a new high-resolution stratigraphic age model to unravel the contributions of tectonic and climatic processes on early to late Pleistocene synorogenic growth strata. We capitalize on excellent, continuous exposures along the flank of the Po foreland in northern Italy to elucidate hydrologic, geomorphic, and sedimentologic processes that are regularly attributed to, but rarely proven to be caused by, glacial-interglacial climatic changes and unsteady rock uplift. We perform our analysis on the Enza section, a succession of marine and terrestrial strata exposed along the Enza River, between Parma and Reggio Emilia, northern Italy. Bedding in the Enza section displays synorogenic growth strata geometry, with bedding dips that range from 2° to 55°, that becomes progressively shallower upsection. We develop an age model that incorporates biostratigraphy, magnetostratigraphy, rock-magnetic cyclostratigraphy, cosmogenic radionuclide burial dating, and optically stimulated luminescence dating and shows that the Enza section spans the interval between 0.04 and 1.65 Ma. Furthermore, the age model pins the time of deposition for several lithostratigraphic units of regional significance and shows that sediment accumulation was unsteady, ranging from 14–31 cm/k.y. in the marine part of the section to 5–362 cm/k.y. in the overlying littoral and terrestrial part of the section. Unsteady deposition is most pronounced in the terrestrial deposits where thick fluvial gravel packages accumulated in short (∼10–15 k.y.) time periods that coincide with Quaternary glacial intervals. There is direct evidence for a dominant tectonic control in the older, marine part of the section. Here, sediment accumulation rates on the limb of the fold growing along this portion of the Northern Apennine mountain front show that between 1.07 and 1.65 Ma, repetitive progradation of neritic sand units directly followed pulses of rapid, punctuated uplift. In contrast, the cyclic terrestrial facies variations in the Enza section reveal that once the section became emergent at ca. 1 Ma and uplift slowed, climate was the dominant control on sediment production and deposition.