ABSTRACT: Factors Controlling Pliocene-Quaternary Sedimentation on the Gulf of Cadiz Continental Slope, Spain

J. Baraza, C. H. Nelson, A. Maldonado

The Pliocene-Quaternary sedimentation on the Gulf of Cadiz continental slope records an interaction between the tectonics responsible for a complex bathymetry, and the Mediterranean outflow undercurrent developed after the opening of the Gibraltar Strait at the end of the Miocene. During periods of low sea level, sedimentation was controlled mainly by changes in the sediment supply from the various rivers that fed the area. During high sea level, periods like the present, deposition is controlled mainly by the Mediterranean undercurrent.

The Mediterranean undercurrent flows out from the Strait of Gibraltar toward the northwest and impinges on the Cadiz continental slope at 300- to 500-m depths. Flows are fastest near the Strait of Gibraltar (as much as 200 m/sec) and slow to 10-20 m/sec westward Portugal. The gradual decrease in undercurrent speed from the Strait of Gibraltar to the center of the Gulf of Cadiz results in a westward change from erosional to depositional characteristics on the upper continental slope. Erosion in the southeastern part of the Gulf is characterized by exposed bed rock on the sea floor and by erosional truncation of reflectors on sea-floor slopes. In contrast, several prograding shelf-break types and slope configurations occur in the west, showing the influence of tectonic subsidence, diapi uplift and sediment supply on the Pliocene-Quaternary sedimentation.

At middle slope depths, high-energy depositional features, such as cut-and-fill structures, are observed in seismic profiles. Energy-decreasing bed-form fields, from east to west, are shown in profiles and sonographs of the most sufficial units on the deep platforms. In addition, sediment drift bodies deposit against basement diapiric ridges near the canyon-ridge central area.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990