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Living, dead and fossil benthic foraminifera on a river dominated shelf (northern Gulf of Cadiz) and their use for paleoenvironmental reconstruction

Publication . Mendes, Isabel; Dias, J. A.; Schönfeld, J.; Ferreira, Óscar; Rosa, F.; Lobo, F. J.

Same-area comparison between patterns of Recent (living) and Holocene benthic foraminiferal assemblage composition is essential to validate their utility as proxies for paleoenvironmental reconstructions. Such reconstructions have scarcely been attempted in shelf environments. In this study, we compared living (stained), dead and Holocene benthic foraminiferal assemblages from the Gulf of Cadiz continental shelf off the Guadiana River. On average, 99% of the living benthic foraminiferal species were preserved in the dead assemblage and 95% in the fossil record. Several common species were assessed as indicators for certain environmental factors, including river discharge, supply of terrestrial organic matter, heavy metal concentrations, oxygen levels, substrate properties, hydrodynamic energy levels, sea-level rise and human impact. The paleoenvironmental reconstruction depicted five stages of Holocene environmental evolution of the Guadiana shelf over the last 11500 Cal yr BP. The characteristics of the stages, and the transitions between them, were in particular driven by changes in sea-level, influx of terrestrial organic matter and limits of productivity.

2013Journal article

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Inner shelf paleoenvironmental evolution as a function of land–ocean interactions in the vicinity of the Guadiana River, SW Iberia

Publication . Mendes, Isabel; Rosa, F.; Dias, J. A.; Schönfeld, J.; Ferreira, Óscar; Pinheiro, J. P.

This study investigates the land-ocean interactions along the northern margin of the Gulf of Cadiz in the vicinity of the Guadiana River. Benthic foraminifera and sedimentological characteristics were analysed in a sedimentary sequence spanning ca. 5000 years (core 8, 22 m water depth) retrieved from the inner shelf prodeltaic wedge. The analyses were integrated in a temporal framework based on accelerated mass spectrometry radiocarbon dating. Paleoenvironmental changes and sediment transfer mechanisms from the continent to the shelf were investigated and related to climatic oscillations and anthropogenic impact in the region. The results allowed the identification of two main periods of deposition. The first period, from ca. 5150 cal. BP (core base) to 1500-1200 cal. BP, is characterised by a mix of fine and coarse sediments, relatively constant percentages of terrigenous and bioclasts, and benthic foraminifera species characteristic of coastal environments. These features indicate an environment strongly influenced by discharge from the Guadiana River. The second period, from ca. 1500-1200 cal. BP to ca. 200 cal. BP (core top), is characterised by silt-clay fraction dominated sediments, an increase in terrigenous sediment towards the top, and benthic foraminifera species characteristic of environments with low levels of energy. An increase in the level of human occupation associated with changes in climate led to widespread erosion and soil loss to the continental shelf during this period, with possible silting up of the Guadiana eastern distributary, allowing the transport of high amounts of sediment to the shelf by the western distributary that led to the enhancement of fine sedimentation and the formation of the prodeltaic wedge in the area of the studied core.

2010Journal article

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