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Braidplain deposition of the Upper Triassic Molteno Formation in the main Karoo (Gondwana) Basin, South Africa

 

作者: BRIAN R. TURNER,  

 

期刊: Sedimentology  (WILEY Available online 1983)
卷期: Volume 30, issue 1  

页码: 77-89

 

ISSN:0037-0746

 

年代: 1983

 

DOI:10.1111/j.1365-3091.1983.tb00651.x

 

出版商: Blackwell Publishing Ltd

 

数据来源: WILEY

 

摘要:

ABSTRACTThe Upper Triassic (Carnian?) Molteno Formation in the main Karoo (Gondwana) Basin, South Africa forms a northerly thinning, intracratonic clastic wedge comprising sandstones, shales and coals occurring within thick (up to 140 m) laterally persistent fining‐upward sequences. These sequences were deposited by braided streams draining an alluvial plain which may have been built on to the distal slopes of alluvial fan complexes of glacial outwash type. Geometric relations between sequences indicate three phases of tectonic activity. The lowermost fining‐upward sequence in the south accumulated against a rising mountain front; cessation of movement and an eastward shift in the main locus of tectonism and sedimentation was followed by renewed uplift and basinwide progradation of the second fining‐upward sequence adjacent to a fault‐block granite terrain located close to the present south‐east coastline of South Africa. This is believed to be the granite at the eastern end of the Falkland Island Plateau, an interpretation consistent with its position on most continental reconstructions and the fracture zone marking its northern scarp face. Faulting is attributed to the first phase of extension prior to continental breakup. The sourceward recession and lack of gross fining‐upward trends shown by the uppermost fining‐upward sequences is accounted for by limited back‐faulting of the still active basin margin. Cessation of activity and further basin margin recession occurred with deposition of the overlying floodplain deposits (Elliot Formation) which were distal equivalents of the braided

 

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