Abstract

The Orinoco delta occupies a large re-entrant of the coast of northeastern South America between the Peninsula of Paria and the Guayana highlands. Offshore, it is partially sheltered by the island of Trinidad, while the southern part is fronted by a wide continental shelf. The coastal plain has been built entirely by the Orinoco, whereas the northern part has been constructed mainly by small lateral rivers descending from higher ground in the west and was invaded only recently by Orinoco distributaries. River levee systems are developed only in the apex of the delta; a wide outer zone of swamps and marshes with local chenier systems has been formed over the entire width of the delta front, largely by rapid coastal accretion. The sediments forming the delta are supplied only in part by the Orinoco; a large volume of sediment is contributed by longshore transportation from the east, probably from the Amazon River. The shape and structure of the modern delta are the result of the interaction, on a shallow sheltered shelf, of a large, dominantly fine-grained sediment supply with strong currents producing lateral redistribution. Comparison of the Orinoco delta with the deltas of the Mississippi, Rhone, and Niger Rivers shows that the facies distributions of the four deltas are fundamentally different, but can be viewed as responses to relative variations in the texture and rate of sediment supply, and in the intensity and direction of marine sorting and dispersal.

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