Matias do Nascimento Ritter

{Surficial shell accumulations from shallow marine settings are typically averaged over centennial-to-millennial time scales and dominated by specimens that died in the most recent centuries, resulting in strongly right-skewed age-frequency distributions (AFDs). However, AFDs from modern offshore settings (outer shelf and uppermost continental slope) still need to be explored. Using individually dated shells (14C-calibrated amino acid racemization), we compared AFDs along an onshore-offshore gradient across the southern Brazilian shelf, with sites ranging from the inner shelf, shallow-water (\< 40 m) to offshore, deep-water (ġt; 100 m) settings. The duration of time averaging is slightly higher in deeper water environments, and the AFD shapes change along the depositional profile. The inner shelf AFDs are strongly right-skewed due to the dominance of shells from the most recent millennia (median age range: 0–3 ka). In contrast, on the outer shelf and the uppermost continental slope, AFDs are symmetrical to left-skewed and dominated by specimens that died following the Last Glacial Maximum (median age range: 15–18 ka). The onshore-offshore changes in the observed properties of AFDs—increased median age and decreased skewness, but only slightly increased temporal mixing—likely reflect changes in sea level and concurrent water depth-related changes in biological productivity. These results suggest that on a passive continental margin subject to post-glacial sea-level changes, the magnitude of time-averaging of shell assemblages is less variable along the depositional profile than shell assemblage ages and the shapes of AFDs.}

At the beach, death assemblages are constantly reworked by wind and waves. One of the various consequences of this shore dynamic is the constant burial and exhumation of the shells, making them inappropriate for epibionts. However, some gastropod shells collected in the death assemblages arranged on the foreshore of the coastal plain of south Brazil were hardly encrusted. Olivancillaria urceus corresponds to 48.8% of all encrusted taxa, suggesting that some shell species may play a more striking role than others as available bioclasts. Therefore, the research aims to discuss the taphonomic implications for epibionts and bioerosion in gastropod shells. Abandoned gastropod shells were collected on 27 sites along a 150 km coastal strip in southernmost Brazil. Epibionts and bioerosion traces were identified, and their frequency was calculated considering their abundance, which taxa they occurred in, and their settlement on the different parts of the shells. At least 13 of 21 taxa were colonized by epibionts, of which 97% were by bryozoans. Other epibionts recognized were serpulid tubes, bivalves, and balanids. Fifteen taxa were bioeroded, showing traces made by worms (cf. Caulostrepsis), bryozoans (cf. Pennatichnus), balanids (cf. Rogerella), bivalves (cf. Gastrochaenolites), and sponges (cf. Entobia). The results reached in this survey suggest that the bryozoans have an advantage over other epibionts at colonizing the gastropod shells.

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.

Fjords are considered biodiversity hotspots and aquatic critical zones, being extremely sensitive to climate change due to close oceanic, terrestrial, and glacial interactions. These ecosystems have received a great deal of attention in research on current and future anthropic impacts. Despite this, there is no analog in the geological record that presents icehouse-greenhouse biological and climatic changes. Here we present an analog, through a detailed taphonomic survey of the Lontras Shale Lagerstätte (Itararé Group, Paraná Basin, Brazil), related to a climatic optimum of the end of the Late Paleozoic Ice Age (Late Pennsylvanian), in which a temperate outer paleofjord with a rich well-preserved biota was installed. In the monotone layers of black shale, we find subtle variations of the dominant skeletal type, rates of fragmentation and disarticulation, and other taphonomic aspects that define distinct taphofacies. Each of them is the result of distinct time-averaging related to mass mortality events, turbidity, and depositional hiatus periods at different scales and intensities, mixing the ecologic census with short-term and long-term within-habitat assemblages. In addition, the rich paleobiota was reconstructed with autochthonous and allochthonous benthic fauna, many marine nektonic organisms, and intense continental contribution of terrestrial bioclasts, that proliferated and were exceptionally preserved by the establishment of an anoxic temperate outer fjord. The taphofacies show an evolution in a high-frequency sequence within a highstand systems tract, linked to climatic improvement. Furthermore, taphonomic detailing can be used as a comparison of deep marine and deep lacustrine taphofacies, in addition to serving as an analog for the short-time scale biological, biogeochemical, climatic, and stratigraphic changes associated with the icehouse–greenhouse transition in the past, present, and future.

The fossil record of bioerosion on rudists is commonly restricted to brief mentions that mainly use general terms and do not constitute detailed ichnological studies. This contribution comprises a detailed study of the bioerosion structures present on the shells of different species of rudists from the Upper Cretaceous (Maastrichtian) of Cuba. In addition, paleobiological, paleoecological and taphonomic implications of these boring are inferred. Among the studied material, seventeen rudist shells exhibits bioerosion structures. Based on their morphological features the borings have been ascribed to Gastrochaenolites isp. and Entobia isp. Gastrochaenid bivalves and clionaid sponges, respectively, have been proposed as their more likely producers. The modes of occurrence, density, and position of such bioerosion structures rule out a syn-vivo relationship between rudists and boring bivalves and sponges, demonstrating that colonization mainly was postmortem. Furthermore, the combination of these data together with previous paleoecological interpretations and the fact that the most parts of the rudist shells are filled by sediment, provides enough evidence to propose a subsequent process of reworking and reburial of these shells in shallow marine settings.

Anomalocardia flexuosa is a bivalve that inhabits shallow, low hydrodynamics coastal environments of normal to brackish salinity, currently distributed from the Caribbean up to the state of Santa Catarina (∼28°S) in southern Brazil, but its fossil record extends along the southwestern Atlantic up to ∼40°S, in Argentina. Its absence in southern coasts today is attributed to ocean water cooling as a result of Middle-Late Holocene changes in relative influence of the warm waters of the Brazil Current and the cold waters of the Malvinas/Falklands Current, but geomorphologic and stratigraphic data suggest that coastal evolution controlled mainly by glacioeustatic-driven oscillations may have also played a role on the shifts of its distribution. Here we review the past and present distribution of A. flexuosa along southern Brazil, establishing a correlation with the Holocene geological history of this area. The Holocene post glacial marine transgression (PMT) produced a large complex of interconnected coastal lagoons landward of sandy barriers stretching from southern Brazil (state of Rio Grande do Sul) to Argentina, creating a corridor that allowed for the southward dispersion of A. flexuosa. The few available numerical ages indicate that A. flexuosa was established in the northern coastal plain of Rio Grande do Sul around ∼7.1 ka BP, and by ∼5.8 ka BP it had reached the southern plain, facilitated by warmer ocean waters than today and the sea-level highstand of 6–5 ka BP. The combination of cooling, sea-level fall that reduced marine influence, and fluvial inputs of freshwater and sediments, converted most of the lagoon complex into smaller isolated freshwater lakes after ∼4 ka BP, leading to the regional extinction of that species. The fossils of A. flexuosa and other tropical mollusks in middle and late Pleistocene interglacial barrier-lagoon coastal deposits along the southwestern Atlantic suggest that their latitudinal distribution shifted cyclically, driven by glacial-interglacial oscillations of sea-level and temperatures. The understanding of the coastal processes that affected the distribution of A. flexuosa may help assessing how mollusks and other marine species respond to environmental forcings related to sea-level oscillations and climate, thus contributing from a paleobiological perspective for conservation and management efforts under present and future scenarios of changes in coastal ecosystems.

{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.

This paper focuses on high-resolution coastal stratigraphy data, which were revealed by the Ground Penetrating Radar (GPR) system. Surveys performed with GPR on the surface of prograded barriers reveal patterns of reflections that allow the interpretation of the geometry and stratigraphy of coastal deposits in a continuous mode. At the Curumim prograded barrier in southern Brazil (29°30′ S–49°53′ W), a two-dimensional transverse GPR survey revealed, with high precision, a serial of contacts between aeolian deposits of relict foredunes and relict beach deposits that have a strong correlation with sea level. In a 4 km GPR profile, a total of 24 of these contacts were identified. The high accurate spatial positioning of the contacts combined with Optical Stimulated Luminescence dating resulted in the first confident sea-level curve that tells the history of sea-level changes during the last 7 ka on the southernmost sector of the Brazilian coast. The curve shows that sea-level was still rising before 6 ka BP, with a maximum level of 1.9 m reached close to 5 ka BP; after that, sea-level started to falling slowly until around 4 ka BP when fall accelerated.

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.

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.

In this paper, a reinterpretation of the older 14C ages of the Pleistocene substrate of the Holocene barrier-lagoon system of three coastal localities in southern Brazil is presented (Hermenegildo, Cassino, and Curumim). Sedimentological, geochronological, palynological, and diatom analyses of a sedimentary deposit formed in an estuarine/shallow marine environment are examined. This sedimentary deposit is presently found between 22 and 25 m depth below sea level in the Pinheira coastal plain. Results from all studied sites indicate that the deposit was formed under a former sea level of Marine Isotopic Stage 3 (MIS 3) that may have oscillated in the study region between 5 and 23 m depth below present sea level, from 36.2 to 47.7 ka. These results are reinforced by studies of nearby sites, including southeast Brazil. The Pleistocene substrate of the Holocene lagoonal-barrier system, at depths lower than 5 m below sea level, seems to correspond to sedimentary deposits of the Pleistocene barrier formed during MIS 5, while at depths greater than 5 m below sea level, they might correspond to sedimentary deposits that were formed during the relative high sea levels of MIS 3.

In the Southern Brazil ShelfSouthern Brazil Shelf (SBS), surface bioclastic concentrationsBioclastic concentrations are associated with putative paleo-shorelines formed where wave ravinement surfaces are probably present. From the late Last Glacial Maximum, the SBS can be considered a sediment-starved passive margin continental shelf, with its morphostructural development fairly known. There, fourteen molluscan shell samples from near shelf-break deposits (“distal shell-rich”), eleven from proximal, low depth bioclastic deposits (“proximal shell-rich”) and ten samples from sandy substrate (“shell-poor”) were evaluated for taphonomic damage accordingly to updated protocols. Multivariate statistical analysis showed significant differences between the three groups of shelly samples. Low-intensity damage states (such as natural bright and ornamentation) dominate samples from the distal shell-rich deposit, whereas the inverse occurs in the proximal deposit (samples from the shell-poor locations present an intermediate damage pattern). This pattern is consistent either with onlap/toplap and backlap shell bedShell bed formation, according to characteristics determined in the literature. The condition of these three areas may reflect degrees of exposure at the taphonomically-active zone, the magnitude of time averagingTime-averaging and duration of shell accumulation, and even the lack of shelf accommodation space, which in turn is related to glacioeustatic sea-level oscillations.

In the marine realm, the interpretation of taphofacies relies heavily on how oceanographic and sedimentary conditions affect the preservation state of fossils. Several taphonomic variables either covary with depth or are directly influenced by depth. Facies-level factors rather than broad, basin-scale parameters influence the taphonomic profile of mollusc death assemblages according to actualistic and experimental evidence. To determine the possible relation between depth and the taphonomic conditions of multiple species of bivalve remains, we used seven samples gathered over a comprehensive bathymetric gradient (from 7 to 150 m below mean sea level; topmost 10- to 20-cm layer, roughly corresponding to the taphonomically active zone). We selected samples from predominantly muddy facies on the southern Brazilian shelf (SBS). The taphonomic damage profile (TDP) was measured using site samples based on a standard taphonomic analysis (categorical scoring system) of shells and fragments larger than 4 mm, to identify site damage patterns. Restricting the sedimentary grain size (samples from fine sediments) enabled the determination of the variation in damage with depth among the samples. Constrained analysis of proximities (CAP) revealed that up to 46% of the taphonomic variation observed was related to variation in depth (with approximately 28% unexplained by environmental factors). Part of the unexplained fraction was due to the effect of temporal mixing, which is predictable along large-scale patches but is inversely linked to the TDP. Our results show that taphonomic analysis, considering large spatial scales in recent environments, can explain the variations present in shell beds that formed during distinct time periods of the evolution of a Quaternary sedimentary basin. © 2018 Lethaia Foundation. Published by John Wiley & Sons Ltd

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).

The R codes provide Bayesian model fitting procedures for AAR-\^{}14\^{}C datasets. These codes are updated versions of the analytical scripts published by Allen et al. (2013). \\ Based on the ages derived from the models fitted, it is possible then to account for the time-averaging (temporal resolution of the fossil record). The time-averaging estimates are based on empirical posterior distributions, accounting for dating uncertainty, as in Ritter et al. (2017).\İn addition, the R codes implements the figures produced both the cited dissertation and its derived manuscripts, like the best models fitted, age-frequency distribuitions (Histograms), its relations with sea-level oscilation in the Southern Brazilian shelf etc.

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Fossil assemblages are expected to be time-averaged as a result of biological and physical processes that mix skeletal remains. Our quantitative understanding of time-averaging derives primarily from actualistic studies, in which direct numerical dating of individual specimens is used to assess the scale and structure of age mixing in death assemblages (incipient fossil assemblages). Here we examine the age, and the time-averaging of Mactra shells (Bivalvia: Mollusca) gathered from surface mixed siliciclastic-bioclastic sands at three sites on a passive-margin subtropical shelf (the Southern Brazilian Shelf; ∼ 33°S). Sixty Mactra specimens were individually dated using amino acid racemization (AAR) calibrated using radiocarbon ages (n=15). The time-averaging and the total age variability was based on a Bayesian approach that integrates the estimation errors and uncertainties derived from the posterior distribution associated with the AAR calibration average model. The 14C-calibrated AAR ages, pooled across all three sites, are strongly right-skewed with 97% of the individual mollusk shell age estimates ranging from 0 to 6 cal kyr BP. The magnitude of time-averaging varied inversely with the water depth, from < 15 yr at the deepest site (21 m) up to 1020-1250 yr at the shallowest site (7 m). The substantial variation in the temporal resolution across nearby sites, which are located in a seemingly homogenous depositional setting, indicates the presence of notable (if cryptic) spatial heterogeneities in local sedimentation, production, and exhumation, all increasing with water depth. Copyright © 2017, SEPM (Society for Sedimentary Geology).