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Abstract

The Belize coastal areas are largely covered by mangrove swamps, which mantle a variety of landforms. Assemblages of landforms define six physiographic provinces, controlled by the hydrographic regime and mainland geology. North of Belize City, the shelf is shallow and the coast is somewhat protected by numerous cays. Only a few streams drain the low, karst surface of the Yucatan platform of the mainland opposite Chetumal Bay. Consequently, little clastic material is brought to the coast. Barrier lagoons and marshes dominate the northern coast. South of Belize City, the shelf lagoon is deep and the coastline is exposed to heavy surf. The Maya Mountains dominate the southern mainland and are drained by abundant small streams which transport large volumes of sediment. Numerous small deltas characterize the coast east of the mountains. Farther south, marshes are again prevalent.

Holocene coastal sediments are present in a narrow, discontinuous band a few hundred feet wide.This band is bordered by Pleistocene limestone and clay inland, and by marine sediments of the shelf lagoon. Within this narrow zone, there are many environments in which sediments are accumulating. These environments are differentiated readily by means of morphology and vegetation.

Analysis of 105 sediment samples from numerous locations along the coast indicates no simple correlations between sediment type and environment. The sediments show continuous gradations in properties with no environmental restrictions. The differences in the physical settings of similar depositional environments, even within a limited area, and the large number of factors prevent a simple correlation between sediment type and environment.

The problem of relating sediment to environment is largely resolved when only the sediments from a local area are considered. Comparisons of sediment properties from adjacent sample stations indicate differences in environment. Furthermore, the changes in sediment properties between adjacent environments are similar along the entire coast.

The stratigraphy and history of the Holocene coastal sediments were determined from 95 piston cores. The coastal areas north of Belize City are underlain by a regular and persistent sequence: Pleistocene limestone, weathered Pleistocene limestone, sandy terrigenous clay, fibrous mangrove peat, and differentiated carbonate mud and sand. This sequence is interpreted to record the Flandrian transgression. South of Belize City, however, there is no consistent Stratigraphie sequence. The greater relief on the Pleistocene surface prevented the flooding of wide areas. Consequently, widespread environments and lithologic units did not form.

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