Search

Pérez-Arlucea, M., Álvarez-Iglesias, P. and Rubio, B., 2007. Holocene Evolution of Estuarine and Tidal-flat Sediments in San Simón Bay, Galicia, NW Spain. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 163 – 167. Gold Coast, Australia, ISSN 0749.0208 San Simón Bay is located in the inner part of a Galician ría. Three rivers enter the bay from the north, forming shallow estuaries. Tidal range is mesotidal (2 to 4 m with an average of 2.2 m). High productivity ecosystems develop due to upwelling processes, which are common in all the Galician rías. The aim of this paper is the study of fluvial and tidal interactions giving rise to distinctive facies architecture in the context of the Holocene transgression. Vertical facies distributions and architecture show alternating units of well-defined estuarine channel-fill and tidal flat deposits. Two millennial-scale, fining-upward sequences show an initial incision evolving into channel fill and tidal flat deposits. An age model has been developed based on AMS 14C and 210Pb and 137Cs dating to put them in the context of the established climatic and sea-level changes. Older dated deposits give an age of 5.9 ky cal BP close to the last Holocene eustatic maximum. Millennial-scale sedimentation rates are about 1.0-1.6 mm y-1, whereas the last few decades show values 5 to 6 times higher. Differences in sedimentation rates are attributed to increasing human influence over recent decades. Incision stages at the base of the sequences (5.1 to 4.8 cal. ka BP and 2.3 to 2.0 cal. ka BP) followed by aggradation are interpreted in terms of high frequency climatic oscillations and related changes in sediment supply and river activity (incision taking place with a decrease in sediment supply). Meter-scale sequences are developed in channel-fill units, indicating superimposed minor, centennial-scale, climatic instabilities giving way to changes in channel activity. [ABSTRACT FROM AUTHOR]