Sedimentary, Geochemical and Micropaleontological Responses to Sea Level Variations in the Vitoria Estuary, Espírito Santo

Abstract

Marine insertion indicators in the Vitoria estuary (ES) revealed relative variations in sea level during the Holocene in three sediment cores. Sedimentological, geochemical (C/N ratio), and paleontological (shells and palynomorphs) analysis and 14C dating associated five sedimentary facies to different estuarine deposits. A C/N ratio <10 at the core base indicated organic matter of marine origin. Moving up the cores to 110–150 cm, an abrupt increase in C/N to 26–63 in every core suggests the sudden entry of higher plants into the estuary, potentially the moment sea level retreated. High continental (10,743 palynomorphs/g) and low marine palynomorph concentrations (323 palynomorphs/g) suggest a primarily continental source even during transgression and at high sea level. Around 8973 cal BP, an open bay already existed in the region of Vitoria. Sea level potentially exceeded the current level around 7110 cal BP. The transgressive maximum was at 5567 cal BP. Marine insertion indicators, such as marine shells, low C/N ratios and foraminiferal linings, did not always respond directly to sea level oscillations. These discrepancies probably result from lateral variations in sedimentary deposits from transport patterns and from variations in organic matter and palynomorph preservation due to differences in river and obstacle proximity.

Dinocysts as a Tool for Palaeoenvironmental Reconstruction in Vitória Bay, Brazil

“…However, although the T_A core contains finer particles that the T_D core, cyst preservation was better from a depth of 90 cm, and this is associated with the low preservation of Vitória Bay: Palaeoenvironmental Evolution 307 foraminiferal test linings and significant preservation of Pseudoschizaea (incertae sedis). These facts taken together could indicate that even in a transgressive period, this could characterize a tidal plain environment, since the sample location is in a more sheltered area of the bay (Machado et al 2018). The foraminiferal test linings as a salinity indicator in the environment (Stancliffe 1996) together with the presence of incertae sedis Pseudoschizaea (common in wetland or flooded environments) lends weight to the current interpretation.…”

“…It was possible to verify the absence of dinocysts along this zone, together with the occurrence of sandy sediment and low TOC values. Machado et al (2018) point out that the grain size from medium to coarse sand in this sediment core may indicate a geological heritage. In general, continental palynomorphs (pollen and spores) and marine organisms (dinocysts) are highly preserved in reducing environments and at finer particle size (Traverse 2008).…”

“…The decrease in the frequency of O. centrocarpum together with the low preservation of foraminiferal test linings could indicate a decrease in local salinity, even in a period of marine transgression (Figure 8). The decrease in the accumulation of dinocysts in this core (T_A) could be associated with the sample collection point, inside the most sheltered part of the bay, under the strong influence of inflowing continental waters and in particular mangrove vegetation (Machado et al 2018). The reduction in the transparency of the water column due to the presence of suspended sediment was highlighted as one of the indicators for low primary production and subsequent deposition of dinocysts in an estuarine region of Bangladesh (Hoq et al 2006).…”

“…proximity to the source area). Machado et al (2018) point out that this sediment core is in the most dynamic part of the estuary, associated with high accumulation of bioclasts, the presence of shell fragments and almost total absence of organic matter, suggesting that deposition was strongly influenced by the marine environment. The preservation of dinocysts and foraminiferal test linings throughout the T_D core was the lowest compared to the other two cores (T_A and T_C).…”