PALEOZOIC AND MESOZOIC PALEOPRECIPITATION ESTIMATES FOR CENTRAL AFRICA

Two deep boreholes drilled in the Congo Basin in Central Africa preserve a detailed paleoclimate record in continental deposits extending from the Mississippian to the Quaternary. Preliminary elemental analysis of paleosol B-horizons in the Paleozoic and Mesozoic parts of the cores reveals long-term trends in paleoprecipitation during a period when the African continent experienced substantial paleogeographic and paleoclimatic change. Application of weathering indices to elemental data yields paleoprecipitation estimates around 1000 mm/yr for the Mississippian–Pennsylvanian, as Pangea was beginning to assemble and the paleolatitudinal position of the borehole localities was greater than 50°S. Permian strata, deposited in the arid interior of the Pangean supercontinent, produce much lower paleoprecipitation estimates of approximately 100 mm/yr. In the Jurassic, northward drift shifts the localities to much lower paleolatitudes of 10–20°N. Paleoprecipitation estimates for this period are higher on average (900 mm/yr) and highly variable, ranging from 500 to 1500 mm/yr. Early Cretaceous paleoprecipitation estimates are somewhat lower (500 mm/yr), reflecting southward movement of Central Africa back toward arid mid-latitudes.