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

Pteropoda (Gastropoda, Thecosomata e Gymnosomata) coligidos ao largo dos arquipélagos de São Pedro e São Paulo, costa nordeste, Brasil Pteropoda (Gastropoda, Thecosomata and Gymnosomata) collected along the northeast coast of the archipelago of São Pedro and São Paulo, Brazil

<abstract language="eng">Pteropoda studies were carried out offshore São Pedro and São Paulo Archipelago (0º56'2"N e 29º20'6"W) to assess biodiversity and spatial distribution. A Bongo net (mesh size 300 micrometer) was hauled obliquely from a depth between 0 and 50 m and Oand 100 m by the REVIZEE-SCORE/NE I oceanographic expedition on board of the Brazilian Navy Oceanographic Ship Antares. Samples were collected at 16 stations from September to October 1995. A total of 880 organisms distributed in 20 species, 14 genera and 9 families were identified. At the layer 0-50 m, Creseis virgula (Rang (828) was the most frequent species (71.43%), followed by Limacina inflata (Orbigny, (836) and Cavolinia inflexa (Lesueur, 18(3) (64.28%, each). ln terms of relative abundance outranked L. inflara (varying between 57.5 and 92.24%) and C. virgula (varying between 60.0 and 72.73%). At the layer 0-100 m, C. virgula was very frequent (80%), L. inflata (70%) and Cuvierina columnella (Rang (827) (40%) were frequent, other species had less than 30% of frequency. L. inflata varied from 37.5 to 100% and C. virgula from 42.42 to 100% of relative abundance. Species diversity varied from medium to low ( < 2.0 bits.ind-1) in both layers. At the layer 0-50 m C. virgula was directly correlated to temperature and salinity, while at the layer 0-100 m L. inflata was correlated to these parameters, showing that these species are Tropical Water indicators