Alcina Magnólia Franca Barreto

Holocene sea-level history on the Rio Grande do Norte State coast, Brazil

Abstract The Rio Grande do Norte State coast, northeastern Brazil, lies in an intraplate region which displays elevated Holocene shorelines, abandoned tidal flats and other intertidal deposits. A field and chronological investigation, which used 48 radiocarbon dates on unaltered mollusk shells, peats, coral reefs, and vermetids in living position and death assemblages encrusted on beachrock, tidal flat and peat deposits, was carried out along two littoral zones, one trending east–west and the other north–south. The sea-level envelope curve for the region indicates at least one sea-level oscillation after the maximum Holocene highstand, which occurred at ∼5000 cal. yr BP. This curve shows notable deviations from the mean sea-level curve for the Central Brazilian coast in the early and mid Holocene. However, in general, this envelope curve fits a glacio-isostatic prediction for the area. A significant deviation from this prediction, related to a small sea-level oscillation, occurred from ∼2100 to ∼1100 cal. yr BP. The comparison between the glacio-isostatic prediction and the sea-level observation enables us to conclude that local events may have disturbed the sea-level record. Minor Holocene sea-level oscillations, which were mainly associated with climate changes or tectonics and superimposed on a major smooth pattern, were observed in South Africa and Australia. But in northeastern Brazil, neotectonic controlled crustal movements or variation in marine and wind currents could provide the answer. The data indicate that local events may have an important role in the history of coastal progradation and retreat.

Late Pleistocene marine terrace deposits in northeastern Brazil: sea-level change and tectonic implications

Abstract Coastal areas of passive margins are among the best places to examine the reality of sea-level changes. Elevation of marine terraces is central to interpretation of their approximate age in this kind of tectonic setting. The recognition of Pleistocene shorelines on the South American eastern continental margin is becoming increasingly common, but data are commonly imprecise in both time and space, and the resulting chronology is based mainly on geomorphological attributes. Nine thermoluminescence dates and four optically stimulated luminescence dates of 220–206 ka and 117–110 ka were obtained for two marine terrace deposits along 340 km of coast in Rio Grande do Norte State, northeastern Brazil. They are correlated with the highstands of marine oxygen-isotope substages 7c and 5c sea level, respectively. The older deposit occurs mainly on the N–S-trending coast and ranges in elevation between 7.5 and 1.3 m. The latter is found along the E–W-trending coast at altitudes that vary between 1 m and 20 m. It indicates relative downfaulting of the 220–206-ka marine terrace and uplift of the 117–110-ka marine deposit, which is locally about 12 m higher than deposits of similar age described 1000 km to the south. It follows that elevation alone is an unreliable tool for establishing a Quaternary sea-level change chronology also on passive margin coastal areas.

Geologia e geomorfologia do quaternário costeiro do estado do Rio Grande do Norte

O objetivo deste trabalho e a apresentacao de um mapa geologico-geomorfologico preliminar para o Quaternario costeiro do Estado do Rio Grande do Norte, com destaque para os depositos eolicos. O mapa foi elaborado a partir de fotografias aereas, escala 1:70.000, imagens de satelite (P/B, banda 4), escala 1:100.000, mapas topograficos e trabalhos de campo. Foram feitas datacoes 14C em rochas praiais e depositos de paleomangues e datacoes por termoluminescencia em sedimentos eolicos e marinhos. Nos depositos eolicos foram identificados tres dominios geomorfologicos de dunas inativas e um de dunas ativas. Eles formaram-se no Quaternario a partir de retrabalhamento de areias da propria planicie costeira e de sedimentos da Formacao Barreiras. As idades TL de 36 amostras indicam que os depositos eolicos foram formados durante seis intervalos principais: 390.000 - 326.000, 270.000 - 240.000, 210.000 - 150.000, 63.000. - 24.000, 11.000 - 9.000 e, 6.500 anos - presente. Essas idades sugerem sua deposicao tanto durante estagios glaciais como interglaciais, relacionados a niveis relativos de mar baixos e altos respectivamente. Dois terracos marinhos foram identificados, com idades de 210.000 a 214.000 anos e 110.000 a 120.000 anos. O primeiro ocorre entre Natal e Baia Formosa, onde a costa se orienta na direcao N - S; o segundo encontra-se no trecho da costa entre Sao Bento e Zumbi, com orientacao E - W. Extensos depositos de intermare holocenicos, principalmente de arenitos praiais, estao localizados na costa orientada N - S e apresentam idades entre 7.000 - 6.000 anos AP. e 5.500 - 4.500 anos AP.

Luminescence dated Late Pleistocene wave-built terraces in northeastern Brazil

This study presents field and chronological investigations along the coast of northeastern Brazil from � 4 ◦ S to 9 ◦ S latitude, which corresponds to � 700 km of coastline under a semi-diurnal mesotidal regime. We investigated wave-built terrace deposits and dated sediments using the optically stimulated luminescence and thermoluminescence methods on quartz grains. The wave-built terraces yielded two main age groups: 200-230 ka and 100-130 ka, which we interpreted as depositional ages. We correlated these age groups with oxygen-isotope stages 7c and 5e, respectively. These events correspond to the antepenultimate and penultimate transgressions along the Brazilian coast. The deposits occur mainly in patches on low-lying flat plateaus along the littoral zone and incision valleys that cut across coastal tablelands. The altitude of the base of the 200-230 ka terraces ranges from 10 m above mean sea level (asl) to –2m asl, whereas the base of the 100-130 ka varies from 12 m asl to –2 m asl. Both terraces were deposited in the foreshore and upper shoreface zones. We noted a coincidence between sea-level highstand chronologies in northeastern Brazil and those in the Bahamas and Bermuda.

ESR dating of teeth from Brazilian megafauna

The study of radiation defects created in biomaterials, such as bone and teeth, can be used in dating with importance to palaeontology and archaeology. Two Stegomastodon teeth (AL1 and AL2) from north-eastern Brazilian megafauna were studied by electron spin resonance (ESR) spectroscopy. The samples were collected in Fazenda Ovo da Ema, (913349 / 3714965) UTM, Alagoas state, Brazil. The dating of these samples can contribute to the better knowledge of megafauna presence in this region as well as to the events associated to the extinction of these species.

Tafonomia dos Invertebrados do Sítio Canastra, Formação Romualdo, Cretáceo Inferior, Bacia do Araripe, Araripina, Pernambuco, Brasil

The Romualdo Formation, Araripe Basin, corresponds to sedimentary rocks of shallow marine to transitional environment deposited during the late Aptian-early Albian. In the Sitio Canastra section, municipality of Araripina, Pernambuco State, are observed mudstones grading to calcarenites at the base of the outcrop. Calcareous nodules bearing fossil fishes are frequently found in the mudstones. The paleoenvironment is interpreted as transitional with fluctuating energy, suggesting successive transgression cycles. Towards the top the section, there are calcareous sandstones with fossils molluscs and echinoids, allowing the stablishment of different taphofacies, supporting the paleoenvironmental interpretation of the area. Through the taphonomic analysis, three taphofacies (T.I, T.II, T.III) were identified. The presence of marine organisms in the taphofacies, such as the echinoids of the species Pygurus tinocoi and Bothryopneustes araripensis in association cassiopid gastropods and mitilid bivalves, suggest a deposition in a of the species marine environment. Well preserves articulated equinoid shells ocurring in association to articulated and closed bivalves in T.I indicate a mostly biogenic living community generated by obrution deposits. In T.II and T.III, fragmentation is frequent, with bioclasts of several sizes. The fossil concentrations are poorly sorted with complex and chaotic packing, both in plant and vertical section, the above features are typical of tempestitic events in proximal areas. We concluded that the Canastra fossil site, represents the evolution of the Araripe paleolagoon, with an initial transgression gradating to a shallow marine environment with transport and burial of macrobenthic organisms between the beach and the platform (Araripina), through the action of storms, in agreement with data obtained in other areas of the basin.

Creation of museums as strategy for preservation of the fossil heritage of Araripe sedimentary basin in Pernambuco, NE, Brazil

Agradecemos ao Conselho Nacional de Desenvolvimento Cientifico e Tecnologico do Brasil/CNPq, pela bolsa de produtividade de pesquisa 303071/2014-1 e o projeto de pesquisa 401748/2010, a Pro-reitora de Extensao- PROEXT-UFPE e a FUNCULTURA, Processo 0756/2014. Sinceros agradecimentos tambem sao devidos a prefeitura do Municipio de Exu, ao Departamento Nacional de Producao Mineral-DNPM e ao Sindicato da Industria do Gesso de Pernambuco/SINDUGESSO, pelo apoio no desenvolvimento da pesquisa.

Depósitos quaternários no Parque Nacional Serra da Capivara e circunvizinhanças, Sudeste do Piauí, Brasil

Serra da Capivara National Park and surrounding areas in Southeastern Piaui State (Brazil) were subjected to morphostratigraphical, sedimentological, and geochronological studies about superficial deposits in order to interpret quaternary paleoenvironmental events. The following sedimentary deposits associated with morphostructural units were identified: colluvial fans at Serra Branca Valley and Structural Staircases, and eluvial-colluvial deposits at Reverse of the Cuesta. There are also colluvial and alluvial deposits outside Serra da Capivara National Park. Many colluvial and alluvial deposits are contemporaneous and indicate a semiarid climate. According to luminescence dating (thermoluminescence and optically stimulated luminescence), the present landscape evolution began around 436 ± 51.5 ka when the Piaui River deposited clayey sediments. From 296.55 ± 46.95 ka to 116.3 ± 19.52 ka, the fluvial channel likely exhibited a braided pattern and deposited sand and gravel bars. Penecontemporaneous sands and muds with ages ranging from 202.75 ± 32.81 ka, 135 ± 16.4 ka to 117 ± 14.5 ka were deposited on Serra da Capivara National Park hillslopes. A colluviation episode occurred between 84.7 ± 13.4 ka to 76.2 ± 9.35 ka, which lacks correlatable alluvial deposits. In the Northern hemisphere last glacial maximum, the colluviation and alluviation processes intensified. These depositional processes likely occurred between 15.8 ± 1.9 and 10.35 ± 1.76 ka, during the Holocene-Pleistocene transition.

Tafonomy of macroinvertebrates and Albian marine ingression as recorded by the Romualdo Formation (Cretaceous, Araripe Basin, Brazil)

The Romualdo Formation, Araripe Basin, crops out in the municipality of Exu, Pernambuco State, exposing coquinas. Fauna survey, taphonomic analysis of the macrobenthos, and identification of sedimentary facies of the outcrop were carried out to contribute to paleoenvironmental understanding of the Romualdo Formation. The association of molluscs (Cerithium sp., Tylostoma ranchariensis, Aguileria dissita, Brachidontes araripensis and unidentified cassiopids) and echinoids of the species Bothryopneustes araripensis suggests sedimentation in the marine environment. The taphonomic similarities made possible the grouping of coquinas into two types. Coquinas type 1 exhibit characteristics of transport and reworking of bioclast generated by storms in proximal setting. Coquinas type 2 demonstrates echinoids in situ and articulated with spines connected to shells, suggesting a fast sedimentation by distal tempestite. Regarding sedimentary facies, the concentrations of invertebrates would have been formed in the transitional offshore zone of siliclastic platform. The results presented here evidence a broader distribution of echinoids and expand the geographic limits of the shallow marine environment in the Romualdo Formation.

New Holocene pollen records from the Brazilian Caatinga

We present two pollen diagrams from the semi-arid Caatinga of the Catimbau National Park, in Pernambuco and from a Mauritia palm forest in the Caatinga/Cerrado ecotone of southern Piauí, NE Brazil, spanning the last 10,000 cal. yrs BP and the last 1,750 cal yrs BP, respectively. These two records contain a signature of the local vegetation and permit the correlation of the pollen signal with regional climatic changes. The Catimbau record shows Zizyphus sp., a typical Caatinga taxon, in all three pollen zones indicating regional Caatinga vegetation and the predominance of local arboreal taxa adapted to high humidity from 10,000 to ca. 6,000 cal. yrs BP with a gradual tendency towards drier conditions revealed by a deposition hiatus between 6,000 to ca. 2,000 cal. yrs BP. This abrupt loss of sediments in both localities is interpreted as a consequence of the establishment of modern semi-arid climates. The subsequent return of humidity is signaled by increased sedimentation rates and 14C date inversions in agreement with high precipitation, revealed by σ18O ratios in speleothems from NE Brazil. Modern sediments deposited in the last 500 years reflect local conditions with the maintenance of humidity by geological faulting and surfacing water tables.