THE ROLE OF MANTLE DYNAMIC TOPOGRAPHY AND SEA LEVEL ON THE U.S. ATLANTIC PASSIVE-AGGRESSIVE CONTINENTAL MARGIN ARCHITECTURE

The importance of tectonism versus global mean sea-level (“eustasy”) on the stratigraphic record has been debated. Eustasy determines the template of sequences preserved on the Myr scale, whereas tectonism is important on long time scales (10-100 Myr) due to thermal cooling, loading, and flexure and on shorter time scales (>1-2 Myr scale) to due changes in mantle dynamic topography. Here, we take two independent means to estimate Oligocene-Miocene sea-level changes that allows us to untangle tectonic and eustatic effects: 1) backstripping of coreholes from the onshore and offshore U.S. Atlantic coastal plain and continental shelf progressively accounting for the effects of compaction, loading, and thermal subsidence; and 2) scaling deep-sea benthic foraminiferal oxygen records using Mg/Ca to remove temperature effects. Our scaled-isotopic and onshore backstripped eustatic changes are remarkably similar on the Myr scale for the interval 40-10 Myr and testify to the importance of glacioeustasy. However, there are differences between the onshore and offshore backstripped estimates and between New Jersey, Delaware, and Virginia. Backstripping quantifies longer-term (2-10 Myr scale) differential uplift and subsidence of 20-100 m at rates of ~3-15 m/My. The differential subsidence is consistent with mantle dynamic topographic models that predict these differences due to the influence of the subducting Farallon slab. Changes in mantle dynamic topography also complicate estimates of the absolute position of globally averaged sea level, though glacioeustatic amplitudes of 20-65 m are well-constrained (±10 m) by backstripping and isotope-Mg/Ca methods. We note that the margin shows a patchwork preservation of blocks of sequences from the Jurassic to present. This, together with the rejuvenation of Appalachian topography in the Miocene, is attributed to mantle dynamics that overprinted the stratigraphic and geomorphologic evolution of this passive-aggressive margin.