SO232 – Late Cretaceous onset of current controlled sedimentation in the African–Southern Ocean gateway


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maximilian.fischer [ at ] awi.de

Abstract

The Mozambique Ridge is a Large Igneous Province emplaced between 140 and 125 Ma (König and Jokat, 2010; Fischer et al., 2016). During the breakup of Gondwana the Mozambique Ridge was located in the evolving African–Southern Ocean gateway. Therefore it represents an archive of the evolving exchange of water masses between the South Atlantic and Indian Oceans via the development of surface, intermediate, and bottom circulation. An extensive seismic survey was carried out during Sonne expedition SO232 imaging two Cretaceous seismic units on top of magmatic basement: the Aptian to early Cenomanian seismic unit S1 and the middle Campanian to Maastrichtian seismic unit S2a (Fischer et al., 2016). The units are separated by a ~25 Myr hiatus that appears to represent a local erosion event possibly correlative with a proposed uplift of the Mozambique Ridge (Girdley et al., 1974; Leclaire, 1974; Simpson et al., 1974). Unit S1 mostly shows seismic reflections parallel to the top of the basement and no indications of current activity (Fig. 1). Within seismic unit S2a we observe the first evidence of current controlled sedimentation with several sediment drifts (Fig. 1). We observe a strong dependency between the occurrence and distribution of the observed sediment drifts and the underlying topography, and thus of the Mozambique Ridge’s basement structure (Fig. 2). Based on our observations, published paleoceanographic data (e.g. Uenzelmann-Neben et al., 2016) and a recent paleobathymetric model by Castelino et al. (2016) we propose a pelagic deposition under partly euxinic conditions in the area of the Mozambique Ridge until ~100 Ma (Fig. 3a). The onset of a strong circulation affecting deposition at the Mozambique Ridge is inferred by the Late Cretaceous ~25 Myr hiatus reported by drilling results and documented in the seismic records, whereas black shales deposited in the nearby Transkei Basin indicate the absence of a deep circulation at least until ~85-80 Ma (Fig. 3b; Simpson et al., 1974; Schlüter and Uenzelmann-Neben, 2008a; Fischer et al., 2016). We propose that the observed hiatus might be a consequence of two factors: the uplift of the Mozambique Ridge (Girdley et al., 1974), and the Falkland Plateau clearing the tip of Africa therefore enabling circulation through the Agulhas Passage (Dingle et al., 1983). The circulation affecting the Mozambique Ridge seems to have weakened in Campanian times, which is documented by the occurrence of sediment drifts in seismic unit S2a (Fig. 3c). We suggest that the onset of current controlled sedimentation was accompanied by further paleogeographic (e.g., opening of Equatorial Atlantic Gateway) and paleoclimate changes (e.g. Southern Hemisphere cooling). An unconformity on top of seismic unit S2a terminates the current controlled sedimentation in Maastrichtian times indicating the onset of another episode of strong current circulation, which according to Leclaire (1974) might be related to the vortical circulation of the Agulhas-Mozambique system.



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Inbook
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Published
Eprint ID
44037
Cite as
Fischer, M. and Uenzelmann-Neben, G. (2017): SO232 – Late Cretaceous onset of current controlled sedimentation in the African–Southern Ocean gateway , In: Statusseminar Meeresforschung mit FS Sonne, Schriftenreihe Projektträger Jülich, Jülich, Forschungszentrum Jülich GmbH, 221 p., ISBN: 978-3-95806-207-8 .


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