Sedimentary and stratal patterns in Jurassic successions of western Madagascar : Facies, stratigraphy, and architecture of Gondwana breakup and drift sequences
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|Other Titles:||Sediment- und Schichtungsmuster der jurassischen Abfolgen in West-Madagaskar: Fazies, Stratigraphie und Architektur der Aufbruch- und Driftsequenzen Gondwanas||Authors:||Geiger, Markus||Supervisor:||Kuss, Jochen||1. Expert:||Kuss, Jochen||2. Expert:||Jacobs, Joachim||Abstract:||
The breakup of Gondwana along the former East African Orogen is widely interpreted to have lasted from the Late Palaeozoic to the Callovian. The present study indicates that the Permian-Triassic or Karoo phase of rifting was not responsible for the separation of East- and West-Gondwana, since that rift system failed in the Late Triassic. Instead the breakup of Gondwana occurred in the Late Liassic. The pre-rift phase in the Morondava Basin is represented by the Karoo deposits, and the syn-rift phase is recorded by Toarcian marine shales, locally overlain by Aalenian sandstones. A major Early Bajocian unconformity is interpreted as the breakup unconformity. The initial post-rift or drift phase is represented by the Bajocian-Bathonian carbonates, marls and sandstones of coastal plain environment and a coastal barrier/lagoon complex. During the Bathonian the siliciclastic shoreface system moved basinward. Callovian-Early Kimmeridgian shales with interbedded iron-oolites represent a shallow-deeper shelf system, in which a Lower Oxfordian shoreface sandstone is intercalated. Based on outcrop and literature data in combination with subsurface data sets four transgressive-regressive (T-R) cycles within the syn-and post-breakup successions were recognised: T-R1 cycle is represented by the Toarcian shales and the Aalenian sandstones. After breakup a widespread flooding formed the Bajocian carbonate platform (T2), followed by the Bathonian sandstones (R2) when a sea-level fall forced the siliciclastic shoreline to move basinward. In the Early Callovian again a widespread transgression established shelf conditions (T3). During a short regressive phase during the Early Oxfordian (R3), siliciclastic shoreface deposits prograded onto the shelf. From the Early Oxfordian onwards a transgressive trend continued (T4). The recognised T-R cycles are generally consistent with sea-level changes observed in other parts of the world and are therefore interpreted to reflect eustacy.
|Keywords:||Madagascar; Jurassic; Karoo; Gondwana; Breakup; Rift; Microfauna; Macrofauna; Ammonites; Indian Ocean||Issue Date:||9-Nov-2004||URN:||urn:nbn:de:gbv:46-diss000012454||Institution:||Universität Bremen||Faculty:||FB5 Geowissenschaften|
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