Depositional sequences and sequence boundaries in fore-arc coastal embayments: case histories from Central America

From Oligocene to Recent times a series of tectomcally controlled coastal embayments fonned on the Pacific fore-arc side of the southern Central American island-arc system. Each of these basins shows characteristic stratal geometries and facies distributIOns reflecting the complex interaction of changes of sea level. volcaniclastic input. and tectonic activity (subsidence, uplift). Sequential stratigraphlc correlations based on sequence analysis and diseontinuity surfaces mdicate that eustatic sea-level changes control architecture. geometry. and facies distribution of depositional sequences at the level of second-order cycles. Owing to the particular tectonic position. complete sets of systems tracts are seldom developed. Volummous sediment supply. espeCIally dunng episodes of strong volcamc activity. may overcompensate transgressions. Strong uplift may annihilate any sedimentary documentation or reduce sequences to a strongly condensed package with random preservation of estuarine or deltaic facies. The bounding unconfonnities (sequence boundaries) are traceable on a regIOnal scale and are related at the level of second-order sequence boundanes to tectonic events that repeatedly affected the island arc during the episode In question.