Abstract
Vitoria Bay is a 20 km long estuary, morphologically narrow, with a microtidal regime and, as other modern estuaries, was formed during the last post-glacial transgression. The estuarine bed morphology is characterised by a main natural channel limited by tidal flats with developed mangroves. Original radiocarbon dates were obtained for the site. Five radiocarbon ages ranging from 1,010 to 7,240 years BP were obtained from two sedimentary cores, which represent a 5 m thick stratigraphic sequence. The results indicate that, until about 4,000 cal. yrs BP, environmental conditions in Vitoria Bay were still of an open bay, with a free and wide connection with marine waters. During the last 4,000 yrs, the bay has experienced a major regression phase, by becoming more restricted in terms of seawater circulation and probably increasing tidal energy. Three main stratigraphic surfaces were recognised, which limit trangressive, trangressive/highstand and regressive facies. The present channel morphology represents a tidal scouring surface or a tidal diastem, which erodes and truncates regressive facies bedding. Foraminiferal biofacies, which change from marine to brackish and mangrove tidal-flat environments, support the seismic stratigraphic interpretation. Absence of mangrove biofacies at one of the two cores is also an indication of modern tidal ravinement.
Highlights
Modern estuaries in Brazil were developed during the last postglacial marine transgression, when downstream river valleys and coastal lowlands were flooded
Original radiocarbon ages ranging from 1,010 cal. yrs BP to 7,240 cal. yrs BP were obtained from two sedimentary cores in Vitoria Bay, representing a 5m thick stratigraphic sequence
The results indicate that, until around 4,000 cal. yrs BP, environmental conditions in Vitoria Bay were still of an open bay, with a free and wide connection with marine waters
Summary
Modern estuaries in Brazil were developed during the last postglacial marine transgression, when downstream river valleys and coastal lowlands were flooded. Estuaries are considered as ephemeral geological features that are infilled by fluvial and marine sedimentary processes, which lead to the development of coastal sedimentary plains. Facies models and resultant estuarine infill sequences have been proposed elsewhere by several authors, either for transgressive and regressive. ALMEIDA ment supply, availability of accommodation space and prevailing hydrodynamic conditions (tides and waves). Time duration for a complete estuarine infill depends on relative sediment supply and creation rates of accommodation space. In Brazil, some estuaries have been studied in order to understand the sedimentary infill processes There are still many unanswered questions in terms of their evolution along the eastern Brazilian regressive coast (Lessa 2005)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
