Combined micropalaeontological, geochemical and sedimentological studies of the mid-Cretaceous (upper Aptian to Turonian) succession of the Sergipe Basin, northeastern Brazil, indicate that intermittent dysoxic-anoxic events occurred in the basin, most likely associated with the interplay of processes such as restricted physiography in the deep basin, salinity-stratified water masses, increased epipelagic primary productivity and high sea levels. Three maxima in oxygen depletion are recorded in the succession from middle neritic to upper bathyal environments: the late Aptian-earliest Albian, the early Cenomanian, and the latest Cenomanian-earliest Turonian. Improving oxidizing conditions (dysoxic to oxic) are apparent during middle-late Albian and early-middle Turonian times. The existence of a rich and diverse planktonic biota throughout the mid-Cretaceous succession suggests widespread oxygenated epipelagic layers of variable thickness in space and time in the basin.
CYCLOSTRATIGRAPHY OF LOWER PERMIAN -CASE STUDY IN ITARARE GROUp, PARANA BASIN (PART II): EVIDENCES OF ASTRONOMIC FORCING (ORBITAL AND SOLAR) IN CLIMATE AND SEDIMENTATION -The existenceand natureof possibleastronomicforcingof cyclicityin glacialsedimentsof the ItarareGroup,Parana Basin,duringthe Eopermian,were studied in core and gamma ray log data from two wells drilled by CPRM (Companhiade Pesquisa de Recursos Minerais) to coal research,one in Santa Catarina and other in Rio Grande do SuI. The distancebetween the originallocation of the cores (about 380 km) made it possibleto test the astronomicforcing in this deposits in differentlocations of the basin.Two methodsof data sampling were used, accordingto data scaleand the possibleforcing: the gammaray logs were digitizedand sampledat I em intervals, in order to test the presence of orbital forcing (20,000 to 400,000 years) or other forcing phenomena (3,000 to 10,000years), andthe cores were scanned in the intervalswith rhythmites and transformed in gray scale data sampled equally (0,2538 mm), in order to search for annual to centennialcycles.The harmonicanalysis showed cyclicity in both scales: orbital cycles ranging from about 17,000to 100,000years and solar cyclesranging from about 22 to 1,000years. The accumulation time calculatedfor one well in log and core data (about 9,400years for the scannedintervaland about 12,600years for the same intervalin log data) showeda very high correlation. The accumulation rates calculatedfor the log data, ranging from 5,2 to 9,3 cm/ka, are very similarto the Pleistoceneones. The analysisalso showedthat the completesedimentaryrecord of the ItarareGroup for one of the wells corresponds to about half precession cycle (12,342years).As both astronomicforcingphenomenadetected, the solar and the orbitalcycles, affectclimate on a global scale, certainlytheir influence on sedimentation occurred in other locations of the basin.Keywords: cyclostratigraphy, Itarare Group, Lower Permian.Resumo A inducaoastronomica no clima da regiao da Bacia do Parana,durante0 Eopermiano, foi testada com 0 intuito de determinara naturezada ciclicidade presenteem sedimentos do Grupo Itarare,de origem glacial. Utilizaram-se dadosde testemunhos e de perfisde raios gama de dois pOyOS, urn em Santa Catarinae outro no Rio Grandedo Sui,perfuradospela CPRM.A distanciaentre as locacoesdos pOyOS (cerca de 380 km) possibilitou testar a influencia da inducaoastronomicaem localidades distintas. Dois metodos de amostragem foramutilizados, de acordocom a escalados dadose com a possivelinducao: perfisde raios gamaforam digitalizados e amostradosem intervalosde I em, para testara presencados ciclosorbitaisna escalade 20 mil a 400 mil anos, ou fenomenos indutores na escalade 3 mil a 10 mil anos, e os testemunhosforam escaneados nos intervalos com ritmitos e transformados em dados em escala de cinzaequiespacados (0,2538 mm), objetivando a busca por ciclos anuais a centenarios, A analise cicloestratigrafica sugere a presenca dos ciclos orbitais, com perfodosde cerca...
Tectonic reconstructions made across the southern South Atlantic Ocean indicate a diversity of rift and drift basin characteristics on the conjugate margins that define them as different stratigraphic and structural entities. In terms of petroleum systems, the basins are not as unlike as some characteristics suggest. Given the lack of significant hydrocarbon discoveries to date south of the Walvis Ridge, doubts have been cast on the presence in this area of the prolific Lower Cretaceous lacustrine and marine source rock systems, which are well known in the Greater Campos Basin and offshore Angola. Oils and condensates from the basins south and north of the Walvis Ridge exhibit geochemical similarities suggesting that comparable source rock systems are present in both areas. The condensate geochemical analysis results from the Kudu Field in Namibia are compared with oils from marine and lacustrine sources in Brazil, indicating that the Kudu condensates are derived from at least two different source rocks. These results suggest that the underexplored basins offshore Namibia contain thermally mature Lower Cretaceous lacustrine and marine source rocks, offering a new frontier for petroleum exploration in Africa's southern South Atlantic.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.