Matias do Nascimento Ritter

These datasets include the relative abundances of planktonic foraminifera, relative abundances of drilled specimens, stable isotope data and age model results of sediment core SAT-048A.

The paleoecological evolution of a peat bog in the Campos region, Rio Grande do Sul State, Brazil, was determined based on an integrated study of stratigraphy, palynology, and geochronology. The peat bog is constituted of silty-clay material, with high levels of ash (residue on ignition) and organic matter content that was deposited on a sandy substrate. Palynological analysis show that grassland taxa dominated from the base of the core at the early deglacial (∼17.4 cal kyr B.P.) to the Present. Four pollen zones were identified: CCQ I Zone (3.20 m to 2.50 m), covering the deglaciation (Upper Pleistocene), corresponding to dry climate conditions; CCQ II Zone (2.50 m to 1.60 m, latest deglaciation and Early Holocene), associated with a slightly humid climate; CCQ III Zone (1.60 m to 0.50 m, mid to late Holocene), established under very humid climatic conditions; and CCQ IV Zone (0.50 m to 0.00 m, last ∼500 years), representative of a low-humidity period. The floristic composition of grassland communities observed throughout the drill core is very similar to that found in the region where the municipality of Cacequi is located, in which Poaceae, Asteraceae, Fabaceae, and Rubiaceae were identified as the most abundant families. Consequently, although in the last ∼17.4 cal kyr B.P. the humidity oscillated, the grassland vegetation remained predominant, although not being represented by the same families, as indicated by changes in the floristic composition among the four pollen zones. Palynological and geochronological data, when compared with other sectors of the Río de la Plata Grasslands, show a predominance of dry conditions over the studied interval. From the early deglacial until the Present, climatic fluctuations shaped the diversity of plant communities and affected the particularities of each sector of the Río de la Plata Grasslands, including the Campos region. High ash content was detected along the core, similar to what occurs with other peatlands already studied in Brazil. In the peat bog analyzed, Poaceae is the predominant family, being known as a major producer of biomineralized structures, which would explain the high ash content recorded.

{The study of sambaquis (ancient shell mounds) in conservation paleobiology is a complicated subject, especially when comparing body sizes of current and past mollusk valves to observe possible changes. There is a lack of information regarding how ancient fisher-gardeners collected these shellfish. Another obstacle is finding the hypothesis tests and data that can be used to compare current and past body sizes. To this end, we use the t-test (tt), Mann-Whitney (mw), and Bootstrap (bt) analyses to determine data scenarios for yellow clam (Amarilladesma mactroides) shells from two sambaquis units, and from two transects along the beaches of Rio Grande do Sul in southern Brazil. The study finds that the average body size of an Amarilladesma mactroides adult specimen is greater in sambaquis than the current valves across all tests (tt

The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbonate and graphite percent Modern Carbon (pMC) values (m = 0.996; 95% CI [0.991–1.001]). An analysis of differences and a 95% confidence interval on pMC values reveals that there is no significant difference between direct carbonate and graphite pMC values for 76% of analyzed specimens, although variation in direct carbonate pMC is underestimated. The difference between the two methods is typically within 2 pMC, with 61% of direct carbonate pMC measurements being higher than their paired graphite counterpart. Of the 36 specimens that did yield significant differences, all but three missed the 95% significance threshold by 1.2 pMC or less. These results show that direct carbonate 14C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14C dating.

The fossil molluscan assemblages found on the shores of Mirim Lake, in southern Brazil and Uruguay, provide information about the environmental changes and geological evolution of that water body. The storm-generated shell deposits at Latinos Spit on the Brazilian shore are dominated by the estuarine bivalve Erodona mactroides, represented mostly by juveniles, and the gastropod Heleobia australis. Species previously unrecorded in this site include the marine gastropods Cylichnella bidentata, Buccinanops cochlidium and Pachycymbiola brasiliana, and the bivalves Tagelus plebeius, Ostrea puelchana, Crassostrea cf. praia, Mactra isabelleana, Anomalocardia flexuosa and Cyrtopleura costata. The two latter currently inhabit tropical areas to the north of Rio Grande do Sul, and their presence in Mirim Lake indicates average coastal water temperatures about 2–3 °C warmer than today. This condition promoted the precipitation of calcium carbonate from dissolved shells, thus cementing together sand and shells in the form of coquinas. The stratigraphic succession, OSL ages obtained in quartz sand from one coquina, radiocarbon dated shells, and δ13C and δ18O of five E. mactroides and five marine species indicate that Mirim Lake became a brackish lagoon around 7.6 ka ago, in response to the postglacial marine transgression (PMT), followed by fully marine conditions during the sea-level highstand of 6–5 ka BP. Marine influence was reduced after ∼4 ka BP as the result of sea-level fall and the closure of the connection with the ocean, related to the evolution of the sandy barrier that originated the modern shoreline. The environmental changes recorded in Mirim Lake help understand how coastal lagoons and their associated ecosystems respond to sea-level oscillations, which may be relevant to address future responses of these water bodies to the ongoing climate change.

Key Points: For the first time, drill holes in planktonic Foraminifera from the western South Atlantic were compared with paleoceanographic proxies. Paleoproductivity of the western South Atlantic was reconstructed using assemblage and geochemical indexes for the last 46 kyr. Paleoproductivity estimates and bioerosion rates of planktonic foraminiferal tests show a strong relation during late Quaternary.

The dynamic physical interval where postmortem alteration of biological remains takes place is widely known as the taphonomically active zone (TAZ). In benthic systems, the TAZ is conventionally considered to be delimited by an upper boundary at the sediment-water interface and a lower boundary corresponding roughly to the deepest sediment layer influenced by bioturbation. However, this definition was developed in the context of marine or continental environments inhabited by benthic fauna and disregards the modifications that pelagic remains undergo while sinking through the water column. Indeed, long before the skeletal remains of planktonic organisms reach the sediment-water interface, they may suffer significant taphonomic damage, primarily due to dissolution. The magnitude of dissolution depends on the composition of the skeletal remains, seawater properties, and the nature and intensity of biological processes in the water column. In open ocean environments, siliceous remains (e.g., diatoms, radiolarians) suffer enhanced dissolution in the upper water column, where seawater is undersaturated in silica, whereas pelagic carbonate remains (e.g., foraminifers, coccolithophores) experience higher dissolution below the lysocline (the depth where there is a sharp increase in dissolution rate) until they reach the carbonate compensation depth (CCD), where dissolution is complete. Therefore, we argue that the TAZ concept for pelagic organisms should be extended to include the water column through which they settle after death. Furthermore, the extent of taphonomic damage of pelagic microfossils can be used as a potential proxy for past changes in seawater chemistry and circulation related to oceanographic conditions. © 2018, SEPM (Society for Sedimentary Geology).

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The operator effect is a well-known analytical bias already quantified in some taphonomic studies. However, the influence of operator bias in the replicability on taphonomic studies has still not been considered. Here, we quantified for the first time this bias using different multivariate statistical techniques, testing if the operator effect is related to the replicability. We analyzed the results reported by 15 operators working on the same dataset. Each operator analyzed 30 bioclasts (bivalve shells) by site, from a total of five sites, considering the following taphonomic attributes: shell fragmentation, edge rounding, corrasion, bioerosion, and color alteration. The operator effect followed the same pattern reported in previous studies, characterized by a worse correspondence for those attributes having more than two levels of damage categories. However, the effect did not appear to have relation to replicability, because nearly all operators found differences among sites. The binary attribute bioerosion exhibited 83{%} of correspondence among operators, but at the same time, it was the taphonomic attribute that showed the highest dispersion among operators (28{%}). Therefore, we concluded that binary attributes, despite indicating a reduction of the operator effect diminishes replicability, result in different interpretations of concordant data. We found that a variance value of nearly 8{%} among operators was enough to generate a different taphonomic interpretation, in a Q-mode cluster analysis. The results reported here showed that the statistical method employed influences the level of replicability and comparability of a study and that the availability of results may be a valid alternative to reduce bias.