CENOZOIC SEDIMENTATION RATES AND DISTRIBUTION ON THE NE U.S. ATLANTIC CONTINENTAL MARGIN

We apply time slice stratigraphy to measure and map changing rates and distribution of sediment accumulation on the NE U.S. continental margin and inferred erosion rates to estimate terrestrial denudation rates during the past 70 Ma. The Cenozoic is divided into three intervals by previously mapped regional seismic horizons:

(1) A*-Au (70-33.4 Ma): The total regional average sediment budget of 6.6 x 10¹² kg/10³ yr was relatively low. Sediment accumulation was concentrated in a depocenter on the continental slope and upper rise off New Jersey attaining a thickness of about 2.3 km, a mass accumulation rate of 6.4 g/cm²/10³ yr, and containing approximately 1.8 x 10¹⁷ kg derived largely from the paleo-Hudson and Connecticut drainage systems. The estimated coeval Appalachian highland denudation rate of 10 m/Ma yields a terrestrial source-continental margin sink mass balance deficit of about 25%.

(2) Au and X (33.4-19 Ma): The total regional average sediment budget doubles to 1.3 x 10¹³ kg/10³ yr. The regional depocenter shifts southwestward to the continental rise off Virginia and North Carolina, apparently related to a corresponding shift in Appalachian uplift. The sediment attains a thickness of 1.3 km, a mass accumulation rate of 8.5 g/cm²/10³ yr, and contains approximately 9.9 x 10¹⁸ kg derived largely from the Chesapeake, Roanoke, Pee Dee, and Cape Fear drainage systems. An estimated coeval highland denudation rate of 20 m/Ma yields a mass balance deficit of 10%.

(3) Post-X (19 Ma to present): The total regional average sediment budget increases to 1.4 x 10¹³ kg/10³ yr. Deposition is more equally distributed over the continental margin with a shift back to the northeast where it attains a thickness of 1.2 km, a mass accumulation rate of 6.5 g/cm²/10³ yr, and contains in excess of 2.7 x 10¹⁷ kg of sediment derived from the regional drainage systems and distributed by the Western Boundary Undercurrent. An estimated coeval highland denudation rate of 20 m/ Ma yields a terrestrial-marine mass balance. The net estimated excess of sediment derived from terrestrial denudation over continental margin accumulation is inferred to have bypassed the margin by transport through submarine canyons and to have formed the Hatteras abyssal plain.