干旱区生态环境知识资源中心

Little is known about the lateral dimensions of distal (outer-fan to fan-fringe) ancient turbidites because of outcrop limitations. The Zebraputs and Brak River Formations of the Zerrissene turbidite system, well exposed in the hyper-arid Namib Desert of south-western Africa, provide a good opportunity of examining facies types, facies associations, vertical sequences and lateral continuity of distal turbidites. The two formations are characterised by sequences of Mutti and Ricci Lucchi facies B1, C2, D1, D2, F, G and a glacial facies. Facies F represents small scale slumps related to the glacial facies, and not slumping from shelf areas. Four facies associations have been recognised (designated 1 to 4) and these represent lobe sandstone, fan-fringe, glacial-marine/turbidite and basin plain facies. No large scale thinning- or thickening-upward sequences are present, but minor (compensation) cycles have been recognised. In only one instance are these statistically significant. Individual units are laterally continuous for at least several kilometres. One shallow channel has been identified in the lobe sandstones.