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This study examines the interplay between sediment dispersal along the Panama margin and the evolution of the North Panama deformed belt (NPDB) using SeaMARC II swath-mapping data and migrated seismic profiles. The NPDB is composed of folded and thrusted strata of the Colombian basin that rise to within 800 m of the sea surface along the San Bias ridge. The ridge extends for more than 200 km along strike, thereby acting as an important barrier to sediment dispersal in the eastern region of the NPDB and the Colombian basin. Sediments derived from eastern Panama are trapped in the San Bias basin, located along the landward margin of the ridge, and deflected westward before traversing the lower slope along the San Bias canyon in the central region of the NPDB.

Sediment entrapment within the San Bias basin and the westward deflection of transport paths by the San Bias ridge have contributed to a recent decrease in sediment thickness along the thrust front in the eastern region of the NPDB. Sediment thickness on the underthrusting basement of the Colombian basin also decreases in the region as a result of the blockage of Magdalena fan deposits by a basement ridge located less than 20 km from the thrust front. The decrease in sediment thickness is accompanied by a decrease in the width of the NPDB in this region, suggesting a concomitant decrease in the rate of frontal accretion as compared to other regions of the NPDB. A marked decrease in the thickness and fold wavelength of accreted strata from the interior of the belt to the thrust front may result from the diversion of terrigenous sediments away from the eastern region of the belt. Convergence rates along the frontal thrust are also significantly less in this region than elsewhere in the belt. Decreased frontal accretion along the eastern region has, however, been partially offset by the incorporation of thick deposits of the San Bias basin into the rear of the belt along backthrusts. Recent accretionary growth is therefore two-sided but may have varied considerably in the past in response to shifting patterns of sediment dispersal.

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