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 | Experts: | 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 | Type: | Dissertation | Secondary publication: | no | URN: | urn:nbn:de:gbv:46-diss000012454 | Institution: | Universität Bremen | Faculty: | Fachbereich 05: Geowissenschaften (FB 05) |
Appears in Collections: | Dissertationen |
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