STRATIGRAPHIC MODELLING OF MIOCENE COMPOUND CLINOFORMS OF THE NEW JERSEY SHALLOW CONTINENTAL SHELF

International audienceThe New Jersey passive margin with well-developed clinoforms has long been a key location for pastsea-level reconstructions and an end-member of passive margin sedimentary geometries. Recently, IODPExpedition 313 brings new insights on the facies architecture of Miocene clinothems preserved on the NewJersey shallow continental shelf feeding discussions on their depositional model and stratigraphic organization.This paper uses Dionisos, a process-based numerical modelling software, to reproduce the geometry and thearchitecture of Miocene clinothems. The objective is two-fold: (1) validate the hypothesis that a depositionalmodel involving compound clinoform geometry (i.e. paired subaerial and subaqueous delta clinoforms)explains the facies architecture of Miocene clinothems, (2) evaluate the amplitude of sea-level fluctuationsrequired to produce such a geometry.Simulations that consider waves and river discharge as equal contributors in the transport of sedimentsucceed in reproducing most key aspects of the Miocene clinothems: the seismic architecture (dip andgeometry of reflectors), the stratigraphic architecture (systems tracts stacking patterns), the facies architecture(spatial distribution of facies), and the scale and geometry of the clinoforms (dip of the shelf, thickness of thesequences and height of the clinoforms). The action of waves exerts the prime control on the geometry of thecompound clinoforms, which is characterized by a sandy subaerial delta at the shoreline feeding a muddysubaqueous delta clinoform that progrades on the shelf below wave base. Our results support recentdepositional models of subaqueous deltas characterized by deepwater mud-dominated material on the topsetsand toesets, and shoreface sand-dominated material on the rollover and foresets. This supposes that topsetsmuds were emplaced during highstand times, while the rollover sands mark lowstand times in clinothems,which are composed of four systems tracts (TST, HST, FSST, LST) building individual T-R sequences. Majorseismic bounding surfaces (i.e. the clinoforms) correspond to Maximum Regressive Surfaces –MRS, whichlandward of Expedition 313 coreholes, merge with the sequences boundaries –SB– recognized in onshorecoreholes.According to this reappraised stratigraphic model and based on Expedition 313 age framework, the NewJersey clinothems arrange in third-order, ~1.2 Myr-long megasequences. Those megasequences likelycorrespond to obliquity cycles that control the growth and decay of large Antartica ice sheets in the Miocene.A set of simulations was run to test this hypothesis and evaluate the amplitude of sea-level fluctuations. Thebest-fit simulation corresponds to a sinusoid-like curve characterized by 1.2 Myr-long cycle with amplitude ofc.60 m. Even though those values are consistent with astronomical and paleoclimate estimates, such sealevelcurve differs from the ones proposed in the literature