Evolution of sedimentary systems tracts in the Tarfaya Basin (Moroccan Atlantic Margin) from the Cretaceous to the Present: Influence of structural evolution and eustasy
Final Report Abstract
This study provided a regional seismic and sequence stratigraphic interpretation of the Mesozoic and Cenozoic sequences of the Tarfaya margin which is based mainly on a large number of subsurface data (SGY seismic reflection lines and wells) made kindly available by the Moroccan oil company (ONHYM). The definition of sequences was based on seismic sequence boundaries and well logs analysis. The passive continental margin of southern Morocco exhibits the transition between a relative undisturbed passive shelf, governed mostly by thermal subsidence from the rifting phase and a broad, complex structurally margin, reactivated by alpine movements. Three different scales of genetic units are recognized on the Tarfaya basin: transgressive-regressive cycles (T-R cycles), sequences and systems tracts. The analysis of seismic facies allows us to define the sequence boundaries, to interpret the relative sea level changes and to show their organization in space and time. The sedimentary and stratigraphic framework of the Tarfaya margin has been subdivided schematically in five major Transgressive-Regressive cycles (T-R cycles) which are separated by regional unconformities and composed of 10 seismostratigraphic sequences separated by 9 regional unconformities and 8 regional marine flooding surfaces (surfaces of maximum transgression) with combined influence of tectonic movements, eustatic sea level changes and sediment supply. In most cases, the seismo-stratigraphic sequences could be divided into systems tracts. Based on sequence stratigraphic analysis and 3D structural modeling, four main tectonostratigraphic stages have been defined on the Tarfaya margin: the pre-rift (Precambrian-Palaeozoic) corresponds to the NE-SW Zemmour Hercynian thrust faults, the syn-rift (Late Triassic-Early Jurassic) characterized by grabens and half graben structures which are bounded by NE-SW striking listric normal faults and filled with continentally derived shales, sandstone and evaporites, the post-rift (Upper Jurassic-Upper Cretaceous) marked by the installation of the carbonate platform of the Upper Jurassic which underwent variable subsidence. With erosional base level lowered, thick sequence of continental to marine-deltaic clastic sediments was deposited at the Early Cretaceous period and marked by thin-skinned extensional listric growth faults resulting from gravity sliding above a salt and/or shale décollement. The Middle and Upper Cretaceous marked only by a general transgression of eustatic origin and the inversion of the Tertiary expressed by tectonic instability that is linked to the evolution of the Atlas and Rif belts and interferes with glacio-eustacy starting in the Oligocene with the Antarctic and Arctic glaciations. Three factors were found to be responsible for the deposition of sequences in the Tarfaya margin: (1) Sea level fall associated to the tectonic uplift (2) Eustasy and (3) sediment supply. The deposition of the sedimentary systems is controlled by the accommodation space and siliciclastic sediment influx into an area. With an increase in accommodation space and continuing siliciclastic sediment influx into the studied area, aggradational to progradational processes remain active. With a reduction in accommodation space and when the sediment influx is insufficient, the agents of erosion shift the sediment seaward causing the development of unconformity surfaces. The chrono-stratigraphic framework based on T-R cycles for the Tarfaya margin when compared to the framework for the Atlantic margin and the New Jersey basin illustrating the degree of viability of this approach for global correlation.
Publications
- 2006. Diversification and evolution of the sedimentary system tracts on the Tarfaya Offshore (Moroccan Atlantic Margin) from the Lower Cretaceous to the Tertiary: Tectonic-climatic-eustatic interactions. Geophysical Research Abstracts, Vol. 8. 2006, 08900, SRef-ID: 1607-7962/gra/EGU06-A-08900
El Jorfi, L., Suess, M.P., Aigner, T., Mhammdi, N.
- 2006. The influence of synsedimentary tectonics on stratigraphic sequences – Insights from the southern Moroccan continental margin. Sediment 2006, 21th Meeting of SEPM Central European Section, Abstracts, pp. 162
Suess, M.P., Aigner, T. & El Jorfi, L.
- (2007). Diversification and Evolution of the sedimentary systems tracts on the Tarfaya Offshore (Moroccan Atlantic Margin). Moroccan Association of Petroleum Geologist (MAPG) Conference, Marrakech, Morocco)
El Jorfi, M.P. Süss, T. Aigner, N. Mhammdi & M. El Mourabet
- (2008). Sequence and Tectono-Stratigraphy of the Tarfaya Basin (Moroccan Atlantic Margin): the interplay between developing structural evolution, eustasy and sedimentation. Abstracts: 304
El Jorfi, M.P. Süss, T. Aigner, N. Mhammdi & M. El Mourabet
