| Techniques in sedimentology, radiochemistry, sediment transport, and seismic analysis are applied to study muddy shoreline deposits along the 350-km-long coastline of Amapa (Brazil). Amazon-derived mud deposits of 500-1300 y age are eroding along the shoreline from the Amazon mouth 280 km northward. Holocene strata were deposited from Amazon suspended-sediment in intertidal flat, mangrove, and supratidal environments, and record at least two cycles of shoreline progradation-retreat in the last ;Decreasing tidal currents and onshore migration of high-turbidity, near-bottom sediment suspensions initiates modern intertidal mudflat accumulation along the northern Amapa shoreline, backed by prograding Avicennia mangrove swamps. Mud (mean grain size 10-12 O accumulates on the intertidal flats below a 50-150 cm, yogurt-like, surface sediment layer deposited annually (1.5 ;Mudflat offlap is accompanied by alongshore accretion of spit-like mudcapes at river mouths. Alongshore migration of the 65 km long, 10 km wide, Cassipore mudcape at 57-114 m y... |
