João Carlos Coimbra

Biostratigraphy of Lower Cretaceous microfossils from the Araripe basin, northeastern Brazil

Abstract A biostratigraphic study was carried out in the Lower Cretaceous Araripe basin, northeastern Brazil, allowing the recognition of several chronostratigraphic units: the Dom Joao (Jurassic?–Lower Cretaceous?), the Rio da Serra (Neocomian) and the Alagoas (Aptian/Albian) local stages. For the first time a large hiatus between the Rio da Serra and Alagoas local stages is carefully documented. The palynomorphs and the ostracode associations throughout the Jurassic?–Aptian/Albian sequence allow the interpretation of the paleoenvironmental evolution of the Araripe basin which otherwise confirms that a polycyclical sedimentation occurred in the basin, being one of the controlling factors on the distribution of ostracodes and palynomorphes.

Zoogeography of Holocene Podocopina (Ostracoda) from the Brazilian Equatorial shelf

Abstract This study reports on the Holocene ostracods of the Brazilian Equatorial shelf from French Guiana to near Natal, almost 1400 km in length. This part of the Western Atlantic Tropical Province, where the mouths of the Amazon and Para rivers separate two zoogeographical units, has distinct oceanographic and sedimentologic features. Three hundred and thirty nine samples were studied from the REMAC (legs 4, 5, 5A and 6) and the GEOMAR projects (legs I, II and III). The ostracod fauna includes 74 species, of which 37 have been previously described (mostly from other areas). The remaining 37 species are left in open nomenclature although 26 of them are probably new. Twelve species are confined to the northwest and 16 to the southeast of the mouths of the Amazon and Para rivers. The inner shelf of the northwestern region is a barren zone resulting from turbid freshwater discharged by the Amazon and Para rivers. Most of the studied species live at water depths of less than 100 m; 28 species inhabit waters shallower than 75 m, and 18 species live in waters shallower than 50 m. Although Brazilian ostracods have many genera and species in common with Holocene ostracods elsewhere in the tropical Atlantic, diversity differs greatly. For example, diversity on the Brazilian Equatorial shelf is lower than elsewhere in the Western Atlantic Tropical Province, but higher than in the Eastern Atlantic Tropical Province. Faunal similarities between these provinces are at the generic rather than species level; exceptions are few and consist of conservative Tethyan species that are cosmopolitan.

Late Cenozoic sea level changes evidenced by ostracodes in the Pelotas basin, southernmost Brazil

Abstract Ostracodes recovered from sediments in seven onshore boreholes within the Pelotas basin, State of Rio Grande do Sul, indicate several continuous nearshore environments and at least four brief transgressive-regressive cycles are present. This interpretation is based on the distribution throughout upper Neogene and Quaternary sequences of species that characterize one or more biofacies depending on the borehole position in the basin. Bradleya pelotensis, Krithe coimbrai, Henryhowella kempfi and H. rectangulata are considered shelf-upper bathyal species whereas the shelf species are represented by Ambostracon crucicostatum, Argenticytheretta variabilis, A. laevipunctata, Brasilicythere reticulispinosa, Caudites posdiagonalis, Costa riograndensis, Coquimba bertelsae, C. tenuireticulata, Cytheretta punctata, Quadracythere eichlerae and Protocytheretta sp. Species with lagoon-estuarine shelf affinities include Callistocythere litoralensis, C. marginalis and Perissocytheridea kroemmelbeini whereas Cyprideis maxipunctata, C. mostardensis, C. posteroinflata, C. salebrosa and C. sparsopunctata represent a lagoon or estuarine environment, and Cypris cassinensis and Limnocythere sp. are freshwater species. Correlation of the ostracode biozones places the four maximum regressive events in the Late Pliocene and Pleistocene (1250-485 ka, 185 ka and 15 ka), whereas the maximum transgressive events occur in the Late Miocene and Pleistocene (1.6 Ma, 423–400 ka and 120 ka), in a barrier-lagoonal depositional system controlled by glacio-eustatic sea level changes.

Taxonomy and ecology of the Family Cytheruridae (Ostracoda) in Recent sediments from the northern Rio de Janeiro coast, Brazil

A study of the family Cytheruridae in Recent sediments from the coast of northern Rio de Janeiro State revealed the presence of four new species: (Hemicytherura auriculata, Oculocytheropteron delicatum, Oculocytheropteron circumcostatum and Semicytherura caudata,) and four previously described species (Semicytherura rugosoreticulata Whatley, Chadwick, Coxill & Toy, 1988, Oculocytheropteron macropunctatum Whatley, Chadwick, Coxill & Toy, 1988, Oculocytheropteron reticulopunctatum Whatley, Chadwick, Coxill & Toy, 1988 and Paracytheridea bulbosa Purper & Ornellas, 1989). A further two species Cytheropteron sp. and Kangarina sp. are left in open nomenclature due to paucity of the material. The ecology and distribution of the fauna suggest that the presence of many of these species, which also occur in colder waters off the coast of Uruguay and Argentina, is probably due to the upwelling of the South Atlantic Central Water in this area.

Cytherellid species (Ostracoda) and their significance to the Late Quaternary events in the Santos Basin, Brazil

Four autochthonous cytherellid species (Cytherella serratula (Brady, 1880),C. hermargentinaWhatley et al. 1998,C. pleistocenica sp. nov. andC. santosensis sp. nov.) have been identified from two offshore cores (44 samples) within the Santos Basin. The distribution of these ostracodes is controlled by local hydrological conditions such as the temperature and, possibly, the oxygen minimum zone (OMZ). However, these factors cannot explain completely the species occurrence in the analysed cores, and relative sea level changes and productivity variation driven by climatic changes are proposed as additional explanations for the faunal distribution pattern.

Ostracodes (crustacea) from Cananéia-Iguape estuarine/lagoon system and geographical distribution of the mixohaline assemblages in southern and southeastern Brazil

The ostracode assemblages from Cananeia-Iguape estuarine/lagoon system (southernmost State of Sao Paulo) are here discussed in detail for the first time. Thirty-four sites, approximately 1 km equidistant, were sampled along the system, including the Cananeia Sea, Pequeno Sea, Cubatao Sea, Ribeira de Iguape River and Itapitangui River. The ostracodes throughout this area have poor assemblages, with a total of 662 specimens of dead and living organisms. The majority of the ostracode fauna is composed of euryhaline species, as follows: Cyprideis multidentata Hartmann, 1955 (174 specimens), Minicythere heinii Ornellas, 1974 (54 specimens), Tanella gracilis Kingma, 1948 (96 specimens) and Whatleyella sanguinettiae Coimbra, Carreno & Ferron, 1994 (226 specimens). Although there are few studies on the Brazilian mixohaline ostracode faunas, including the euryhaline marginal marine taxa, the published data show that the group is best known in the south and southeast regions. Based on this review and with the new data presented in this paper, the geographical distribution of eight mixohaline key species in southern and southeastern Brazil is also discussed.

Taxonomy of limnic Ostracoda (Crustacea) from the Alagamar Formation, middle–upper Aptian, Potiguar Basin, northeastern Brazil

Abstract Fifteen limnic ostracodes species have been recorded in the Alagamar Formation, Potiguar Basin: Cypridea araripensis Silva, 1978a; Cypridea? sp., Harbinia sinuata (Krömmelbein and Weber, 1971); Harbinia crepata n. sp., Harbinia dimorphica n. sp., Harbinia alta Antonietto et al., 2012; Paracypria? elongata n. sp., Ilyocyprimorpha berthoui (Colin and Dépêche, 1997); Ilyocypris? sp., Brasacypris subovatum n. sp., Candona? sp., Theriosynoecum colini n. sp., T. guzzoi n. sp., T. silvai (Silva, 1978b) diagnosis emended by Do Carmo et al. (2004b); and Darwinula martinsi Silva, 1978c diagnosis emended by Do Carmo et al. (2004b). Nine of these species have also been recorded outside of the Potiguar Basin, either in other Cretaceous basins in Brazil or coeval strata in western Africa. Despite the controversy about dating the local Alagoas Stage and the relatively large range of the Zone Harbinia spp. 201–218, the material studied in this paper belongs to the interval corresponding to the well-defined palynological zone coded as P-270, which is mid-upper Aptian in age.

The taxonomy and zoogeography of the family Trachyleberididae (Crustacea: Ostracoda) from the Equatorial Continental Shelf of Brazil

A study of the family Trachyleberididae Sylvester-Bradley from the Equatorial Continental Shelf of Brazil (almost 1400 km in length) revealed the presence of five new species, which are described herein. These are: Cletocythereis atlantica, Cativella paratranslucens, Cativella reticulocostata, Henryhowella tuberculoclaviforma and Australimoosella polypleuron. Two sub-species of the genus Costa, C. variabilicostata brasiliensis subsp. nov. and C. variabilicostata aff. recticostata Bold, are placed within the variabilicostata group. The genus Neocaudites is represented by two species, N. subimpressus Edwards and N. triplistriatus Edwards, originally described from the Upper Miocene and Pliocene of the Duplin Marl, North Carolina, USA. The genus Puriana is represented by P. convoluta Teeter and P. variabilis Chukewiski & Purper, described originally from Belize (British Honduras) and the Brazilian coast, respectively. The geographical distribution of the studied fauna, reveals the presence of two assemblages on the Equatorial Continental Shelf of Brazil, a Northwest and a Southwest assemblage, separated by the area of discharge of the Amazon and Pará rivers and each with its distinctive oceanographical and sedimentological characteristics.

A new recent marine Ostracoda species (Hemicytheridae) from Brazil

Ostracods were collected on Sargassum sp. from the littoral of Sao Sebastiao, Sao Paulo State, southeastern Brazil. A new species, Aurila ornellasae, is illustrated and described based on a population with various instars and adult specimens. This is the first living species of this genus described from Brazil. A brief discussion on the systematics of the genus Aurila Pokorný, 1955 and its allied genera is presented.

SPATIAL VARIATION IN THE TEMPORAL RESOLUTION OF SUBTROPICAL SHALLOW-WATER MOLLUSCAN DEATH ASSEMBLAGES

Abstract: 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.