FORMATION HISTORY AND OCEANOGRAPHIC CONTROL OF LATE HOLOCENE MUD DEPOCENTERS IN THE NORTHEASTERN GULF OF CADIZ, SOUTHERN SPAIN

The interplay between sediment supplied by several rivers, a complex ocean current system and a fluctuating sea level control the depositional architecture of transgressive and highstand sediment depocenters (“mudbelts”) on the continental shelf in the northeastern portion of the Gulf of Cadiz. Previous investigations relied almost exclusively on subbottom echosounder data. With the high demand of sedimentary facies identification as a response to environmental changes during the late Holocene, this study utilizes an extensive seismo-acoustic data set and sediment cores to determine the formation history of confined shelf mud depocenters produced from the Guadalquivir River and surrounding sources. Through correlation of these data sets, the identification of transport pathways, a budget calculation, the localization of centers of deposition, and a reconstruction of the depocenters’ growth structure will be illustrated.

Sediment samples are analyzed by radiography, magnetic susceptibility, porosity, density, XRF element distribution, grain size, and age. The combination of these methodological approaches will lead to detailed insight of annual through centennial changes in continental runoff and oceanographic forcing mechanisms.

The study area is mainly confined to the northeastern area of the Gulf of Cadiz at water depths ranging from 15 to 200 m. Preliminary results depict a sediment rich environment with Holocene sediment thicknesses up to 20 m close to the Guadalquivir River prodelta at water depths of 15 to 50 m. Further off the prodelta, hard sub-bottom structures are covered by a 2 m thick sediment drape with up to 22 m of sediment filling between them. Close to the shelf edge, the internal reflection horizons pinch out indicating the seaward limit of the depocenters. The core most proximal to the Guadalquivir River mouth shows internal sediment structures on a millimeter scale recording its history of flash floods in high temporal resolution. A tentative sediment budget estimate links continental discharge, sediment storage on the shelf and material export into the open ocean.

This study is a collaboration between Coastal Carolina University, MARUM–University of Bremen, and CSIC–University of Granada as part of the CADISED (Cadiz Shelf Sediment Depocenters) project.