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a vast depression (about 1,000 km in diameter) in Central Africa, lying within a ring of uplands. Structurally it corresponds to the syneclise of the African Platform, laid down in the Upper Precambrian. An underground projection of the crystalline foundation of the platform (at depths of 500–1,000 m) divides the syneclise into a southern and northern basin; in the middle of these basins the foundation drops to depths of more than 3,000 m. The syneclise is filled with a thick layer of Upper Proterozoic, Upper Paleozoic, and Mesozoic sedimentary rocks, covered by relatively thin, loose Cenozoic deposits.
The relief of the Congo Basin has a tiered structure. The lowest (300–400 m) and youngest (Holocene) tier is formed by broad, mostly marshy floodplain valleys that merge into a single, flat, periodically flooded alluvial plain in the central part of the basin. Above this may be traced several levels of Anthropogenic terraces and Pliocene-Anthropogenic terrace-like plateaus rising toward marginal uplands with an elevation of more than 500 m in the north and west and more than 1,000 m in the south and east. The basin is drained by the Congo River. It has a hot, humid, equatorial climate (subequatorial on the northern and southern peripheries), with average monthly temperatures ranging from 23°-25° to 26°-27° C and an annual precipitation exceeding 1,500–2,000 mm. The area is completely covered by dense, wet evergreen and deciduous-evergreen forests.
I. N. OLEINIKOV