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Morphology, biostratigraphy, and evolution of PliocenePleistocene diatoms Proboscia barboi..

Publication . Andrade, J.; Legoinha, P.; Stroynowski, Zuzanna; Abrantes, Fatima

Proboscia barboi and Proboscia curvirostris are two important diatom biostratigraphic markers from the high latitudes of the North Pacific and North Atlantic Oceans, dating back to the Pliocene-Pleistocene time. This study analyzes the biostratigraphic events and describes the morphology of P. barboi and P. curvirostris, particularly the morphologic variations of the latter species, based on observations of samples of Core U1340A from the IODP Expedition 323 in the Bering Sea. In Site U1340, the First Occurrence of P. curvirostris is observed at 1.52Ma and its First Common Occurrence at 1.39Ma, where morphologic variations were found abundantly. The Last Occurrence of P. curvirostris was found at 0.33Ma, while P. barboi's Last Occurrence is found at 0.67Ma. Based on the morphological similarity and known biostratigraphic distribution, previous authors have assumed that P. curvirostris descends from P. barboi, although this hypothesis is still in debate. At 1.39Ma P. curvirostris shows an increased size and thickness, which is typical of P. barboi, and some specimens display an incipient structure characteristic of P. curvirostris - the secondary spine. This morphology is intermediate between the two species and suggests an evolutionary transition from P. barboi to P. curvirostris. However, P. curvirostris already existed since 1.9Ma in the subarctic indicating that its speciation happened much earlier than 1.39Ma. Furthermore, since P. barboi co-occurs with P. curvirostris in the North Pacific, this evolutionary process was cladogenetic. Besides being evidence for a phylogenetic relationship, the abundant occurrence of intermediate forms at 1.39Ma may constitute a bioevent for a short time interval in the Bering Sea.

2019Journal article

Open access

Geochemistry, luminescence and innovative dose rate determination of a Chalcolithic calcite-rich negative feature

Publication . Rodrigues, A. L.; Dias, M., I; Carlos Valera, António; Rocha, F.; Prudencio, M., I; Marques, R.; Cardoso, G.; Russo, D.

An interdisciplinary approach comprising archaeological, chemical, mineralogical, and luminescence data was applied to a better understanding of the fill dynamic and chronologies of a calcite-rich negative archaeological feature from Southern Portugal. This work aims to contribute to the assessment of the human involvement in the backfilling actions of a negative archaeological feature from a Chalcolithic site, thus better defining the moments of its destruction and/or abandonment. There are well-known limitations of luminescence dating of calcite-rich materials, particularly in the dose rate determination. In this work, a proposal of two innovative protocols to determine the dose rate of calcite-rich contexts is discussed. A clear improvement of the dose rate estimation was obtained by using the "radionuclide weighed" protocol. The comprehensive used methodologies enabled to define the infill phases and the sources of the infill materials. The luminescence profiling studies were also useful to describe the infill processes, highlighting their discontinuity and pointing to different deposition rates. The luminescence ages obtained, when using the "radionuclide weighed" protocol proposed in this work, are closer to the archaeological evidence of a Chalcolithic occupation.

2019-08Journal article

Restricted access

Comparison between the dead and living benthic foraminiferal assemblages in Aveiro lagoon (Portugal)

Publication . Martins, Maria Virgínia Alves; Hohenegger, Johann; Frontalini, Fabrizio; Miranda, Paulo; Rodrigues, Maria Antonieta da Conceição; Dias, João Manuel Alveirinho

This work provides a comparison between living (LAs) and dead (DAs) benthic foraminiferal assemblages in 53 sampled sites located in intertidal and subtidal areas of Ria de Aveiro (Portugal). The results of multivariate statistical analysis provide evidence for the main factors that control the distribution of DAs and LAs, which seems to correspond to different gradients of marine/continental influence, conditioned by differences in the hydrodynamics of tidal currents. In addition to these factors, the LAs are clearly influenced by the total organic carbon, biopolymers and pollutants. The main factor that however drives the high level of agreement or the degree of disorder between the DAs and the LAs seems to be the hydrodynamics. The highest level of agreement between the DAs and the LAs is found in sheltered inner lagoon areas, out of the tidal currents strongest influence. This study shows an interesting application of advanced statistical analysis to study the similarity between LAs and DAs aiming to identify the zones or conditions of a coastal system in which the DAs can potentially be a better record of Las. Through similar studies conducted in coastal systems it is possible to select the most suitable sites to collect cores in view of the development of paleoenvironmental studies. (c) 2016 Elsevier B.V. All rights reserved.

2016-08Journal article

Restricted access

Publication . Alves Martins, Maria Virgínia; Hohenegger, Johann; Frontalini, Fabrizio; Dias, João Manuel Alveirinho; Geraldes, Mauro Cesar; Rocha, Fernando

This study compares living (LA) and dead (DA) benthic foraminiferal assemblages and identifies different factors that possibly cause differences in the distribution of both assemblages in the Aveiro Continental Shelf (Portugal). A total of 44 sediment samples was collected during summers of 1994 and 1995 along transects (east-west direction) and between 10 and 200 m water depth. Complex statistical analyses allow us to compare the abundance and composition of the LAs and DAs in function of depth, grain-size and total organic matter in all studied stations even in those where the numbers of individuals were rare in one or both assemblages. The highest densities and diversities of the LAs are found in the middle continental shelf on gravel deposits (coarse and very coarse sands) mostly due to the substrate stability, reduced deposition of fine sedimentary particles, availability of organic matter with high quality related to oceanic primary productivity likely induced by upwelling events, and oxygenated porewaters conditions. The DAs have, in general, higher densities and diversities than the LAs. In the outer continental shelf, the dissimilarity between both assemblages is higher due to the accumulation of tests, low dilution by sedimentary particles and scarcity of living foraminifera. Based on the comparison of LAs and DAs and considering the characteristics of the study area and the species ecology, it has been possible to understand the cause of temporal deviation between the LAs and DAs of benthic foraminifera. This deviation is much more pronounced in the inner shelf where the energy of the waves and the currents induce very dynamic sedimentary processes preventing the development of large LAs and the preservation of DAs. Some deviation also occurs in the middle shelf due to the seasonal loss of empty tests. The most well-preserved time-averaged DAs were found in the outer continental shelf.

2019Journal article

Open access