HR: 1340h
AN: GP53B-1222    [Abstracts]
TI: Tracing Late Holocene Warm Periods in the Galician Continental Margin (NW Spain): Detrital Control vs. Early Diagenetic Modulation.
AU: * Mohamed, K
EM: kmohamed@uvigo.es
AF: Dept. Marine Geosciences and L. M., University of Vigo. Lagoas-Marcosende., Vigo, 36310, Spain
AU: Rey, D
EM: danirey@uvigo.es
AF: Dept. Marine Geosciences and L. M., University of Vigo. Lagoas-Marcosende., Vigo, 36310, Spain
AU: Rubio, B
EM: brubio@uvigo.es
AF: Dept. Marine Geosciences and L. M., University of Vigo. Lagoas-Marcosende., Vigo, 36310, Spain
AU: Vilas, F
EM: fvilas@uvigo.es
AF: Dept. Marine Geosciences and L. M., University of Vigo. Lagoas-Marcosende., Vigo, 36310, Spain
AB: The sediments of the Galician continental margin (NW Spain) exhibit great but variable degrees of early diagenetic dissolution of magnetic minerals. This process completely erases any detrital magnetic signal at time-scales that range from about 1,000 years to less than 50 years in the highly productive estuarine-like environment of the Galician Rias Baixas. The more open marine conditions encountered in the adjoining continental shelf exhibit however a significantly different behavior. The singular balance between early diagenetic dissolution and lower sedimentation rates allows partial and variable preservation of the also variable detritally controlled magnetic inputs. In this context it is possible to reconstruct the recent environmental history of the area attending to the changes in the concentration of magnetically-interesting iron oxides. High-resolution magnetic and geochemical measurements carried out in 6 cores from the continental self evidenced the occurrence of correlatable peaks of magnetic mineral concentration that were interpreted as periods of enhanced detrital input. Magnetically depleted sediments were related to lower detrital input and/or to enhanced productivity that intensified the reductive conditions. The magnetic concentration peaks occurred within the Medieval (MWP) and Roman Warm Periods. Similar concentrations of hematite in the MWP and the RWP suggest that the lower concentration-dependent magnetic properties in the RWP are most likely caused by a greater degree of dissolution of magnetic detrital oxides due to a longer exposure to reducing conditions. These features could be traced over all the studied area, despite the great heterogeneity of the shelf sediments. This highlights the potential of magnetic properties as proxies of paleoenvironmental conditions in areas of similar complexity. This approach can be used as a rapid and cost-effective tool to screen large areas in the search for suitable settings for more precise, but time-consuming analysis, as well to extrapolate results through correlation of the appropriate magnetic features. We thank Prof. T. von Dobeneck and Dr. M. Dekkers for their kind support and advice during the stays of K. Mohamed in Bremen and Utrecht. The research of K. Mohamed in Bremen was funded by the EU Paleostudies program.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting