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Geological Society, London, Special Publications; 2005; v. 244; p. 7-25;
DOI: 10.1144/GSL.SP.2005.244.01.02
© 2005 Geological Society of London

Stratigraphic Development of Submarine Slope Systems

Late Quaternary shelf-margin wedges and upper slope progradation in the Gulf of Cadiz margin (SW Iberian Peninsula)

F. J. Lobo1,2, J. M. A. Dias1, F. J. Hernández-Molina3, R. González1, L. M. Fernández-Salas4 & V. Díaz Del Río4

1 CIACOMAR-CIMA, Universidade do Algarve, Avenida 16 de Junho s/n, 8700-311 Olhão, Portugal
2 Instituto Andaluz de Ciencias de la Tierra, CSIC-Univ. Granada, Facultad de Ciencias, Campus de Fuentenueva, s/n. 18002 Granada, Spain pacolobo{at}ugr.es
3 Departamento de Geociencias Marinas y Ordenación del Territorio, Facultad de Ciencias, Universidad de Vigo, 36200 Vigo, Spain
4 Instituto Español de Oceanografía (IEO), Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640 Fuengirola, Spain

The distribution patterns and internal geometries of recent shelf-margin wedges off the Guadiana River, Gulf of Cadiz margin, were studied in order to discern the effects of varying trends of falling sea-level and lowstand on upper slope progradation. A seismic-sequence stratigraphic analysis was conducted, based on the interpretation of a dense grid of high-resolution seismic profiles.

Five major shelf-margin wedges deposited during late Quaternary sea-level fall and lowstand periods were documented. Most of the studied shelf-margin wedges produce upbuilt-outbuilt upper slopes. The analysis of their internal geometries reveals two distinct types of configuration: the four older shelf-margin wedges are mainly composed of forced regressive deposits developed during stepped sea-level falls. The scarceness of lowstand deposits suggests abrupt sea-level fall to rise transitions; and the most recent shelf-margin wedge shows both forced regressive deposits and low-stand deposits significantly preserved. This architecture probably resulted from the occurrence of a long-lived sea-level lowstand after a prolonged period of gentle sea-level fall.

Two types of shelf-margin wedges have been recognized: wedges with elongate parallel depocentres, laterally constant thickness and uniform seaward shelf-break migration, related to linear source supply and high lateral sediment redistribution during gently falling sea level; and wedges with (multi) lobate depocentres with laterally variable thickness, leading to uneven shelf-break migration during periods of faster sea-level fall, due to delta lobe switching and significant shelf valley incision.





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[Abstract] [PDF]