Published:January 01, 1995
1995. "Pletmos Basin", Sequence Stratigraphy in Offshore South African Divergent Basins: An Atlas on Exploration for Cretaceous Lowstand Traps by Soekor (Pty) Ltd., L. F. Brown, Jr., J. M. Benson, G. J. Brink, S. Doherty, A. Jollands, E. H. A. Jungslager, J. H. G. Keenan, A. Muntingh, N. J. S. van Wyk, G. J. Brink, N. J. S. van Wyk, L. F. Brown, Jr., K. R Barton, K. J Bate, S. R Carney, A. A. Fraser, N. Fraser, H. J. Gouws, M. G. Guest, K. A. Kitchin, H. W. Pferdekämper, J. Turner, V. H. Valicenti, G. W. J. Beamish, D. S. Broad, P. J. Buck, P. L. A. Burden, C. P. N. Davies, J. Fouché, C. E. Gilbert, K. Hodges, J. J. Maier, S. P. Petrie, S. H. Robson, J. Roux, G. J. Smit, J. Turner, V. H. Valicenti, D. Van Der Spuy, T. Webb, S. J. Winters, H. T. Buhrmann, R. D. P. Noble, P. J. Strauss
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The Pletmos Basin lies beneath the Indian Ocean offshore from the southern coast of South Africa between Mossel Bay and Cape St. Francis (Figure 13). The basin covers about 10,000 km2 and is filled with postrift Cretaceous rocks (Figure 14). It is bounded on the northeast by the St. Francis Arch and on the southwest by the Infanta Embayment. The faulted northern boundary of the Pletmos Basin closely follows the present shoreline, and the southern boundary is approximately at the 200-m isobath, south of which is the deep southern Outeniqua Basin extending southward to the Agulhas-Falkland Fracture Zone (Figures 13, 15). The Pletmos Basin comprises the Plettenberg, northeastern, northern, southern, and Southeastern subbasins. The subbasins are mostly grabens, bounded all or in part by the Plettenberg, Superior, and Pletmos faults (Figure 13). Although the fault systems were initiated during rift onset, they continued to impose significant structural control on the basin complex during most of its postrift Cretaceous history.
Exploration of the Pletmos Basin by Soekor (Pty) Ltd. began in the 1970s when drilling targeted Upper Jurassic and Lower Cretaceous synrift sandstone reservoirs and rift structural traps. This initial phase included the drilling of about 20 boreholes and resulted in discoveries of some subcommercial gas. A second phase of drilling began in 1989, when prospecting shifted to postrift Cretaceous reservoirs within low-stand basin floor fans, slope fans, prograding wedges, and incised valley fills (Table 2). To date, eight wildcat wells (Table 3) have targeted stratigraphic or combined structural-stratigraphic traps based
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Sequence Stratigraphy in Offshore South African Divergent Basins: An Atlas on Exploration for Cretaceous Lowstand Traps by Soekor (Pty) Ltd.
“Sequence Stratigraphy in Offshore South African Divergent Basins” is the result of an offshore exploration and drilling program by Soekor (Pty) Ltd in the Republic of South Africa beginning in 1987. Seismic stratigraphic data and borehole information were incorporated and released in what was one of the first detailed and comprehensive published examples of the new field of sequence stratigraphy. The project was conducted over a South African offshore area of 175,000 km2, in the Pletmos, Bredasdorp, and Orange basins, which are examples of divergent basins associated with the breakup of Gondwana. Thirty-four third-order Cretaceous sequences between 126 and 67 Ma were recognized and correlated. The book is published in an oversized 11” × 24” landscape format, which works well for the numerous seismic lines and cross sections in this heavily illustrated volume. Each basin is examined in detail, including discussion of the tectonic, paleogeographic, and depositional settings, and the sequence stratigraphy based in large part on regional seismic interpretation. The application of the sequence stratigraphic interpretations to generation of petroleum prospects and evaluation of drilling results is the end result, provided in a manner that is far more open and enlightening than is the case for typical petroleum industry publications.