Structure of a Turbiditic System in Neogene of Guadalquivir Basin (South Spain)

Jaime Suarez, Wenceslao Martinez, Ana Serrano, Gabriel Leret

The Guadalquivir basin constitutes the foreland basin for the Betic Ranges, filled with Neogene marine sediments in which turbidites have been identified. This basin presents a half-graben configuration: a northern passive margin formed by a flexure of the Hercynian basement and a southern active border, an olistostrome that slid northward from the Betics during the Neogene. Turbidites are confined to a narrow area between a nonsedimentation, or bypass, zone and the olistostrome.

The interpretation of the seismic morphologies related to the top of the sand bodies allowed us to identify a sequence of seismofacies: channels, leveed channels, and lobes. The internal structure of each turbiditic sand body shows a gentle downlap to the west and an onlap to the north, interpreted as a progradation and an aggradation, respectively. Six different sand bodies can be individualized by erosive scars, lying one beside the other. The whole turbiditic system exhibits, instead of the classical vertical stacking, an extreme lateral juxtaposition bias with a westward progradation. The younger bodies lie to the north and west of the older ones. Juxtaposition is generated by lateral shifting to the only available area where deposition can progress: the northern bypass zone and t e western frontal part of the former body.

Neither a morphological paleotalus nor a preferential sediment supply zone has been observed. Field studies show these sediments to be high-energy deposits transported by turbiditic currents and grain-flow mechanism related to low-efficiency systems.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.