CLIMATIC CONTROL ON DEPOSITION OF UPPER PLIOCENE DEEPWATER,GRAVITY-DRIVEN STRATA IN THE APENNINES FOREDEEP (CENTRAL ITALY):CORRELATIONS TO THE MARINE OXYGEN ISOTOPE RECORD

摘要

The thick upper Pliocene to lower Pleistocene succession of hemipelagic mudstones of the Marche Apennines foredeep (central Italy) is punctuated by several mostly coarse-grained, cyclic turbidite systems. Integrated and detailed analyses of sedimentary facies, physical stratigraphy, biostratigraphy, and magnetostratigraphy have provided a high-resolution sequence stratigraphic framework for sediments of two of these coarse-grained systems, each resulting from the stack of five deepwater, high-frequency depositional sequences backfilling the mouth and lower reaches of a long-lived submarine canyon. The tight chronostratigraphic control available on these two turbidite systems and encasing hemipelagic sediments allows a precise correlation of the component high-frequency sequences with the Pliocene marine oxygen isotope curve. This reveals that the cyclic arrangement occurred near the Gauss–Matuyama polarity transition and the onset of the Olduvai subchron in response to recurring, obliquity-driven global changes in sea level. Each depositional sequence, 20 to 65 m thick, includes sediments that were deposited by a range of gravity-driven processes, resulting in sedimentary motifs that contain a deep marine record of both glacial and interglacial stages. A typical depositional sequence comprises: (1) a lowstand systems tract composed of cohesionless-debris-flow conglomerates (braided submarine channel complex), which passes down-dip into turbidite sandstones (frontal-splay complex); (2) an overlying transgressive to early falling-stage systems tract composed of a mud-rich mass--transport complex of slumped horizons and cohesive-mud-flow pebbly mudstones eventually overlain by a thin interval of hemipelagic mudstones. This stacking pattern records variations in depositional style, and hence, variations in canyon activity during eustatic changes in sea level.