Applications of clay minerals and other proxies to study the actual sedimentary dynamic in the Ria de Aveiro (Portugal Centre) (original) (raw)

Th is work aims to study recent climatic oscillations and their infl uence on sedimentation in the Ria de Vigo, a coastal embayment in Galicia, NW Spain. It is based on the study of clay mineral assemblages, in conjunction with other proxies (granulometric, geochemical, geochronological and microfaunal), in the core KSGX 24. A Benthic Foraminifera High Productivity (BFHP) proxy was used to determine changes in the fl ux of organic matter (OM) at the bottom of the study area. Total organic carbon (TOC) content is not a suitable proxy to estimate changes in the past supply of OM due to diagenetic processes. Th e sedimentation was fi nest in 3 sections: ~ 230-214 cm, ~ 185-73 cm and ~ 20-0 cm. Th ese muddy sections are characterised, in general, by higher proportions of detrital minerals, concentrations of several chemical elements related to lithogenic sources and BFHP values. In addition, these sections are impoverished in carbonates, Ca, Sr and La when compared with the layers with the highest sand content. Th e clay mineral assemblage of the studied site, characterised by the dominance of illite, intermediate concentrations of kaolinite and minor amounts of smectite and chlorite, reveals the prevalence of a typical temperate humid climate in the last 3 ka BP, the estimated age for the core base. However, the quantities of illite and chlorite increase in the muddy layers. Th e characteristics of these muddy layers were interpreted as representing relatively cold climatic oscillations associated with the strengthening of northerly winds and the prevalence of an upwelling regime corresponding to wellknown periods, such as the fi rst cold period of the Upper Holocene (~ 2.9 ka cal BP), the Dark Ages (between ~ 2.2-1.2 ka cal BP) and the Little Ice Age (~ 0.6 ka cal BP).