A fluvial record of active fault-propagation folding, Salsomaggiore anticline, northern Apennines, Italy

摘要

Fault-propagation folds offer the potential to relate folding to underlying fault propagation and slip provided that fold kinematics can be established. Fluvial terraces have been recognized as kinematic indicators, but precise relationships between surface uplift and various folding mechanisms remain largely unexplored. This study takes advantage of a well-preserved, progressively deformed suite of middle Pleistocene to Recent fluvial terraces above a growing fault-propagation fold at the Apennine mountain front, northern Italy, to constrain the recent fold kinematics and place them in the context of a longer growth history gleaned from older growth strata. The geometry of straths and overlying terrace deposits defines a fixed anticlinal hinge, a rolling synclinal hinge, proxies for fault tip propagation rates, rock uplift rates, and tilting rates, and how these features and rates vary over the last ~800 ka along ~ 15 km of strike length. Field studies are augmented with DEM-based quantitative geomorphic analyses that document catchment hypsometry, mean anticlinal hinge elevation, and long profile form. Notably, long-term rock uplift rates (using incision as a proxy) are uniformly correlated with fault propagation and associated synclinal hinge migration, mean anticlinal hinge elevation and variations in catchment hypsometries. Channels that cross the forelimb at a high angle to the fold hinge generally have higher concavities, but channel steepness, commonly thought to reflect rock uplift, is more strongly adjusted to rock type. This study elucidates a new understanding of a complex fold growth history extending back at least 10 Ma and provides a novel demonstration of how fluvial terraces may be utilized to constrain fault-related fold kinematics.