| Popis: |
Exploration in the Rukwa rift, using gravity and seismic reflection surveys, fieldwork, and drilling has defined the structure and stratigraphy of the basin in greater detail than any other part of the Western rift. The stratigraphy comprises Precambrian basement, Karroo sandstones, shales and coals, upper Miocene red beds, and Miocene-Recent lacustrine and fluvial sediments. During Miocene-Recent rifting the greatest sediment input apparently came from axial fluvial systems flowing from the northwest and southeast. The southwestern area experienced alternating shallow lacustrine and fluviodeltaic conditions during the Miocene-Recent. Cenozoic age rift structures have a dominant NW-SE and a subordinate N-S trend. The NW-SE trend tends to follow a Precambrian basement and later Karroo structural trend. NE-SW seismic lines indicate up to 10 km extension of the Tertiary section in a direction oblique to the probable E-W regional extension direction. In the southeastern portion of the basin both Karroo and Tertiary-Quaternary sediments expand into the Lupa fault zone, reaching thicknesses of up to 3 and 7 km, respectively. Tertiary-Quaternary sediment thicknesses decrease northwestward, accompanied by a decrease in the amount of extension and a broadening of the basin as extension is transferred to the Lake Tanganyika rift. |
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