Mid to late Holocene constraints for continental shelf mud deposition in association with river input: the Guadiana Mud Patch (SW Iberia) |
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| Authors: | Francisca Rosa J A Dias I Mendes ?? Ferreira |
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| Institution: | (1) CIMA, University of Algarve, Campus de Gambelas, Edif?cio 7, 8005-139 Faro, Portugal;(2) CIMA/FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal |
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| Abstract: | This study correlates Holocene sedimentation with regional environmental changes for the Guadiana middle shelf, SW Iberia,
based on a detailed sedimentological analysis combined with radiocarbon and amino acid racemization dating. The sedimentary
record of vibrocore CRIDA16 (307 cm) from the mud patch off the Guadiana River is characterized by a transgressive signature.
Terrigenous sand–gravel dominates the core base up to ca. 5,000 cal. years b.p., enriched in schist/greywackes and non-reworked quartz. The shelf area was under the direct influence of Guadiana bed load
discharges, as sea level was lower than today but rising, favouring the entrapment of fines during the Guadiana estuary infilling
in the early Holocene. Core upwards, fines dominate the record. Sea-level stabilization at ca. 5,700–3,700 cal. years b.p. led to estuary infilling by coarser sediments and export of suspended sediment to the middle shelf. After ca. 900–700 cal.
years b.p., the formation of the Guadiana Mud Patch signifies deposition in a marine environment dominated by suspended material from
the Guadiana River. Comparison with earlier publications showed that a similar evolutionary mechanism of middle shelf mud
deposition occurred in other parts of the Iberian Margin, pointing to a generalized establishment of this type of sedimentary
body in Iberia since the mid to late Holocene. This suggests that the formation of mud belts on the north and south Iberian
Margin was to a large extent synchronous. It is likely that the evolution of the Guadiana Mud Patch on the shelf was controlled
foremost by the overall climate trends identified for several parts of Iberia during the Holocene (i.e. increased aridity
punctuated by significant humidity stages), and less by human occupation of the region. Enhanced humidity stages led to higher
rainfall and intensified floods, with a consequent increase of discharges to the shelf which ultimately were responsible for
the Guadiana Mud Patch formation. It is expected that this pattern of sedimentary dynamics has been strongly disturbed since
2002, when the closing of the Alqueva Dam (the biggest on the Iberian Peninsula) was completed in the Guadiana River basin. |
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