An overview on Callovian-Cenomanian intracratonic basins of Northeast Brazil : onshore stratrigraphic record of the opening of the southern Atlantic

A number of small Callovian-Albian sedimentary basins occur in the NE-trending Araripe-Potiguar topographic lowlying area. These basins developed in a fairly narrow zone of Precambrian supracrustal rocks from the Middle Jurassic onwards, as a consequence of the reactivation of ancient fault lines. The basin formation and subsidence took place during five tectonic stages related with the opening of the Southern Atlantic Ocean and the split of South America from Africa. The tectonic-sedimentary sequences that fill these basins record successive evolutionary stages. 1) Proto-rift stage, with minor episodes of a) pre-rift (Callovian -Tithonian) with basin formation and deposition of coarse to conglomeratic sandstones in alluvial fan and braided river systems; (b) tectonic quiescence with continuing subsidence, resulting in hundreds of meters of pelites accumulated mainly in lacustrine and foodplain environments (Tithonian-Berriasian). 2) Syn-rift stage: a) tectonic reactivation with erosion and deposition of sandstones in alluvial fan and braided to low-sinuosity river systems; (b) during more quiet periods, accumulation of fine-grained deposits in lacustrine, palustrine and foodplain environments took place (Berriasian-early Barremian). 3) Erosional stage that would correspond to a transitional proto-oceanic gulf phase in the southern Atlantic and a shift of rifting to the equatorial Atlantic area, causing erosion in the study area (late Barremian-early Aptian). 4) Post-rift stage: (a) related to the beginning of drift in the Atlantic Ocean. This stage is characterised by deposition in the area of shallow lacustrine fine-grained siliciclastics, limestones and gypsum under dry climate (late Aptian-early Albian); (b) two short marine transgressions affected the area and, as a consequence, shallow marine limestones were deposited (late Aptian and Albian); (c) a marine regression resulted in a return to continental conditions with deposition of coastal and lagoonal limestones, lacustrine rhythmites and fluvial sandstones (Albian-early Cenomanian?). Some of the lacustrine to fluvial dominated sequences as well as the marine deposits in these basins include highly fossiliferous units (i.e. Crato and Romualdo Fms. of the Santana Group), with very diverse, exceptionally well preserved fossil assemblages (insects, fishes and reptiles, among others), although they are mainly endemic. 5) Uplift stage: last stage of tectonic calm and slow uplift and erosion (since Cenomanian). On the basis of our proposals further sedimentological and paleontological studies have been undertaken, which confirm the existence of an alternative connection between the equatorial and southern parts of the Atlantic Ocean in Aptian-Albian times. Moreover, the last break-up stages between Brazil and Africa took place probably in the Campanian

An overview on Callovian-Cenomanian intracratonic basins of Northeast Brazil : onshore stratrigraphic record of the opening of the southern Atlantic

A number of small Callovian-Albian sedimentary basins occur in the NE-trending Araripe-Potiguar topographic lowlying area. These basins developed in a fairly narrow zone of Precambrian supracrustal rocks from the Middle Jurassic onwards, as a consequence of the reactivation of ancient fault lines. The basin formation and subsidence took place during five tectonic stages related with the opening of the Southern Atlantic Ocean and the split of South America from Africa. The tectonic-sedimentary sequences that fill these basins record successive evolutionary stages. 1) Proto-rift stage, with minor episodes of a) pre-rift (Callovian -Tithonian) with basin formation and deposition of coarse to conglomeratic sandstones in alluvial fan and braided river systems; (b) tectonic quiescence with continuing subsidence, resulting in hundreds of meters of pelites accumulated mainly in lacustrine and foodplain environments (Tithonian-Berriasian). 2) Syn-rift stage: a) tectonic reactivation with erosion and deposition of sandstones in alluvial fan and braided to low-sinuosity river systems; (b) during more quiet periods, accumulation of fine-grained deposits in lacustrine, palustrine and foodplain environments took place (Berriasian-early Barremian). 3) Erosional stage that would correspond to a transitional proto-oceanic gulf phase in the southern Atlantic and a shift of rifting to the equatorial Atlantic area, causing erosion in the study area (late Barremian-early Aptian). 4) Post-rift stage: (a) related to the beginning of drift in the Atlantic Ocean. This stage is characterised by deposition in the area of shallow lacustrine fine-grained siliciclastics, limestones and gypsum under dry climate (late Aptian-early Albian); (b) two short marine transgressions affected the area and, as a consequence, shallow marine limestones were deposited (late Aptian and Albian); (c) a marine regression resulted in a return to continental conditions with deposition of coastal and lagoonal limestones, lacustrine rhythmites and fluvial sandstones (Albian-early Cenomanian?). Some of the lacustrine to fluvial dominated sequences as well as the marine deposits in these basins include highly fossiliferous units (i.e. Crato and Romualdo Fms. of the Santana Group), with very diverse, exceptionally well preserved fossil assemblages (insects, fishes and reptiles, among others), although they are mainly endemic. 5) Uplift stage: last stage of tectonic calm and slow uplift and erosion (since Cenomanian). On the basis of our proposals further sedimentological and paleontological studies have been undertaken, which confirm the existence of an alternative connection between the equatorial and southern parts of the Atlantic Ocean in Aptian-Albian times. Moreover, the last break-up stages between Brazil and Africa took place probably in the Campanian

Anelídeos poliquetas do nordeste do Brasil: I - poliquetas bentônicos da costa de Alagoas e Sergipe

Num trabalho anterior (NONATO & LUNA, 1969) discutimos as espécies de poliquetas de escama que fazem parte de uma coleção proveniente de dragagens executadas pelo Laboratório de Ciências do Mar da Universidade Federal de Pernambuco, no Nordeste do Brasil. No atual, são tratadas as espécies desprovidas de escamas, em número de 71. Informações sobre a área amostrada estão contidas nos trabalhos de CAVALCANTI & colab. e de MABESOONE & TINOCO, 1967. Espécies pequenas e delicadas que constituem parte ponderável das populações bentônicas foram muito raras nesta área. Isto pode ser devido a condições eventualmente adversas ou, muito mais provavelmente, é conseqüência de sua destruição durante a coleta e triagem. Os fundos duros predominantes, com superfície irregular e constituídos em grande parte por blocos ou cascalho de algas calcárias e corais, tornam particularmente árdua a amostragem biológica. Nessas condições é difícil preservar a integridade de seres de corpo delicado como os poliquetas, da ação trituradora, dentro dos aparelhos de coleta. Devemos ter em conta essa circunstância ao avaliar a densidade aparente da fauna. Os poliquetas não devem ser tão pouco freqüentes como indica o resultado da prospecção atual. Acreditamos que o uso de melhores técnicas permitirá apreciar a sua verdadeira densidade e conhecer melhor sua distribuição. A pesca noturna, com luz submersa, por exemplo, poderá ser um excelente método para atrair espécies do substrato ou de habitats de outra forma inaccessíveis. Das 71 espécies, apenas uma foi considerada como nova para a ciência. Scoloplis agrestis sp. nov. assemelha-se a S. robustus Rullier e a S. madagascarensis Fauvel, diferindo de ambas pelo número de setígeros torácicos e pelo número reduzido de cerdas aciculares dos neuropódios torácicos. Os Eunicea são o grupo melhor representado, com 26 espécies, das quais a mais comum é Eunice longicirrata Webster (108 exemplares em 19 estações). Diopatra spiribranchis Augener e Hypsicomus elegans Webster são consideradas boas espécies. Somente dois Flabelligerideos foram capturados em toda a área; um deles é um espécimem bem conservado de Pherusa scutigera (Ehlers) e o outro um Piromis sp. A maior parte das espécies desta coleção é constituída por formas semelhantes às encontradas na região das Antilhas, como, aliás, seria de se esperar. Porém, algumas aproximam-se de espécies do Pacífico e do Indico, como é o caso de Glycera longipinnis Grube, Onuphis litoralis Monro e Vermiliopsis acanthophora Augener, cujas características concordam perfeitamente com as descrições a que tivemos acesso.This is the second report dealing with the oenthic Polychaeta collected on the continental shelf of the north-eastern Brazil (approximately between 9.º and 11.º of latitude south), by the Laboratorio de Ciencias do Mar (formerly Institute Oceanográfico) of the Universidade Federal de Pernambuco. In the first one we discussed only the scale-bearing species tNonato & Luna. 1969). Data concerning the area sampled by the Laboratorio de Ciencias do Mar can be found in the papers of Cavalcanti et al. and Mauksoonk & Tinoco, 1967. The present paper is about the scale-free species, in number of 71. Almost all the smaller species we can expect to find in similar areas, seem to be absent here. This may be due to their actual rarity or, most probably, to their destruction during sampling and sorting. The hard bottom prevailing in the area, which has a very rough surface, shaped by blocks and pebbles of calcareous algae and corals make the biological sampling a hard enterprise. It is particularly difficult to preserve the integrity of soft-bodied animals, such as the polychaetes, against the grinding action of the material inside the sampling devices. We must remember this exceptional condition when judging the apparent scarceness of the polychaetes. If the worm fauna of that region seems, at the first approach, very poor, in reality it may be not. In consequence we hope the use of improved methods of sampling will give far better results. The night fishing, with a submerged light, for example, may be a choice method to attract many species from the ground or from the otherwise unaccessible hide-outs. From the 71 species, only one has been considered as new for the science. Scoloplos agrestis sp. nov, approaches S. robustus Rullier and S. madiiguscarensis Fauvel, but differ from them by the number cf the thoracic sctigers (only 15) and by the number of accicular setae of the thoracic neuropodia (only 5 or 6). The Eunicea is the best represented group, with 26 species; the commonest being Eunice longicirrttia Webster (108 specimens, in 19 stations). Diopatra spiribmnchis Augener and also Hypsieomus elegans Webster are considered as good species. Only two flabelligerids were caught in the whole area; one of them is a well preserved specimen of Pherusa scutigera (Fhlersi and the other a damaged specimen of Piromis sp. The greatest part of the present species is believed to be similar to I hose-found in the Caribbean area, as we should expect. But a few show a great similarity with Pacific and Indian species. Some of them, as Glycera longipinnis Grube, Onuphis litorttlis Monro and Vermiliopsis acanthophora Augener, agree closely with the available descriptions