The Columnar Jointing in Cretaceous Clastic Rocks and the Rotation of Rift Shoulder in Sudan
Lu Hongbo Lu Huafu O. M. Abdullatif M. KheirDepartment of Earth Sciences, Nanjing University, Nanjing, 210093.China Department of geology, University of Khartoum , Khartoum, Sudan
The Tertiary basaltic rocks are discontiously distributed from the west to the northeast of Sudan, in the Sahara Desert, overlying the Cretaceous clastic rocks. The authors of this paper found a kind of columnar jointing in the Cretaceous clastic rocks in the Mellit area, western Sudan. The Cretaceous sedimentary rocks were baked by the basaltic lava flow erupted in the Early Miocene, contracting in volume owing to loss of water contained mainly in the clays of the clastic rocks, and thus forming the columnar jointing. According to the occurrences of jointing and the sedimentary strata the authors calculated the two different rotations of the Mellit block: the block tilted toward 338° for 18° from Late Cretaceous to the beginning of Miocene, and tilted toward 138°for 18°since Miocene. By analyzing in detail the structural evolutionary history, from Mesozoic to Cenozoic, of different rift belts in western, northern, central and eastern Africa, the authors think that the Mellit area was on the northwestern shoulder of the South Sudan Rift. The rotation of the Mellit block toward northwest was the outward rotation of the northwestern shoulder of the South Sudan Rift during the rifting phase, and the rotation toward southeast was the inward rotation of the rift shoulder during the post-rift thermal sag episode. The authors also conclude that the South Sudan Rift entered the post-rift thermal sag phase because of the development and evolution of the East African Rift and Red Sea in the Cenozoic.
【CateGory Index】： P588.21