Ciclos e seqüências deposicionais das formações Rio da Batateira e Santana (Andar Alagoas), Bacia do Araripe, Brasil

The Rio da Batateira e Santana formations, the latter with Crato, Ipubi and Romualdo members (Alagoas Stage, Aptian), were studied in four cored and logged wells from the eastern portion of Araripe Basin, Northeastern Brazil. The investigated section is 230 m-thick, and PS-14 well is the most representative, because it is the only one which sampled the evaporites of Ipubi Member. Nine facies cycles were identified, being formed by siliciclastics (estuarine, deltaic and lacustrine), mixed lithologies (lacustrine), carbonates, black shales and marls (lacustrine), and gypsum-anhydrite (lacustrine evaporite). The ordering of facies cycles furnished six depositional sequences. They were formed by siliciclastic, regressive-transgressive R-T cycles (S1 and S4, corresponding to Rio da Batateira Formation and to Santana Formation/Romualdo Member), by siliciclastics and carbonates, R-T cycles (S2, S3.1 and S3.2, corresponding to Crato Member), and by siliciclastic-carbonate, R-T cycles followed by evaporitic cycles (S3.3, referred to Ipubi Member). The last cycles correspond to concentration-dilution, C-D cycles of marine brines, which precipitated gypsum in the restricted lacustrine basin.

Facies sedimentares e ambientes deposicionais da Formação Barbalha no vale do cariri, bacia do araripe, nordeste do Brasil

The Aptian Barbalha Formation represents the first unit of the post-rift sequence of the Araripe Basin and crops out at the slopes of the Aranpe plateau in the eastern part ot Aranpe Basin. The unit has also been named Kio da Batateira Formation, but this name is here used in its original definition as Batateira Beds, an interval of great lateral continuity and characterized by the presence of bituminous shales of the Alagoas Stage (P-270 palynological biozone). This paper presents the results of a stratigraphic analysis carried out along the outcrop belt in order to establish the facies architecture and to interpret deposicional environments of the siliciclastic Barbalha Formation. Detailed stratigraphic vertical sections were measured and correlated. They allowed the recognition of two depositional sequences characterized by fining upward arrangement of facies, beginning with fluvial deposits and ending with lacustrine deposits at their tops. The end of the first cycle is represented by black shales and brecciated limestones of the Batateira Beds that record a geologic event of regional magnitude and serve as meaningful long-distance stratigraphic mark. The second deposicional sequence overlies disconformably the Batateira Beds and begins with clast-supported conglomerates, which are covered by a succession of fluvial sandstones and minor intervals of pelitic rocks. The sandstone content diminishes towards the top and the upper part of the unit is characterized by the presence of ostracode-rich green shales. The Barbalha Formation is conformably overlaid by Late Aptian lacustrine limestones belonging to the Crato Member of the Santana Formation.

Estratigrafia das seqüências deposicionais do grupo Guatá, borda leste da Bacia do Paraná

Pós-graduação em Geologia Regional - IGCE

Estratigrafia de seqüências do Grupo Itararé (Neocarbonifero-Eopermiano) na região de Rio Negro (PR) - Mafra (SC)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Heavy mineral as a tool to refine the stratigraphy of kaolin deposits in the Rio Capim Area, Northern Brazil

Estudos de minerais pesados provenientes em depósitos cauliníticos da Formação Ipixuna na região do rio Capim (Brasil) revelaram uma mineralogia matura a supermatura, representada dominantemente por zircão e turmalina e, subordinadamente, rutilo, cianita e estaurolita. Os minerais encontrados não variam muito, entretanto cada unidade caulinítica apresenta uma assinatura particular definida por diferenças nasproporções entre os principais minerais, assim como em suas características texturais. Este trabalho demonstrou que asunidades de caulim soft (inferior) e semi-flint (superior) podem ser consideradas seqüências deposicionais distintas. As altas percentagens de opacos em relação aos minerais transparentes e altos teores de zircão são diagnósticos da unidade caulinítica inferior. O incremento no volume de grãos de zircão e turmalina arredondados a subarredondados na unidade caulinítica superior sugere que esta inclui grãos que foram submetidos a um grau mais elevado de retrabalhamento. O aumento no volume de grãos não alterados de estaurolita e cianita na unidade superior leva a concluir que, além da reciclagem sedimentar, uma fonte distinta deve ser invocada. Estes resultados também mostram que as características da assembléia de minerais pesados da unidade intermediária são comparáveis com aqueles da unidade superior, o que sugere mesmo posicionamento estratigráfico.

Modelagem estratigráfica do intervalo cenomaniano-turoniano, formações Açu e Jandaíra, na borda sudoeste da Bacia Potiguar

Pós-graduação em Geociências e Meio Ambiente - IGCE

Evolução tectônica e estratigráfica das bacias da margem continental do Uruguai

Pós-graduação em Geociências e Meio Ambiente - IGCE

Sistemas petrolíferos especulativos da bacia de Pelotas (offshore do Uruguai)

Pós-graduação em Geociências e Meio Ambiente - IGCE

Estratigrafia do Andar Alagoas na sub-bacia do Tucano Norte, Bahia

Pós-graduação em Geociências e Meio Ambiente - IGCE

Estratigrafia do Andar Alagoas na sub-bacia do Tucano Norte, Bahia

Pós-graduação em Geociências e Meio Ambiente - IGCE

Stratigraphy and Palaeontology of the Late Cretaceous Wapiti Formation, west-central Alberta, Canada

A complete stratigraphic assessment and revision of the middle Campanian to upper Maastrichtian Wapiti Formation in north-western Alberta and north-eastern British Columbia is the main aim of this research project. The study area encompasses an area of approximately 200X180 km in the Grande Prairie County (west-central Alberta) and easternmost British Columbia, Canada. Results presented here indicate that the 1300m thick succession currently reported in the literature as “undifferentiated lithostratigraphic unit”, consists of five lithostratigraphic units and four unconformity-bounded depositional sequences; their study and description have been documented integrating several geological disciplines, including sequence stratigraphic methods, well-log signatures, facies analysis, and fossil associations. On the whole, particular attention has been given to 1) age and nature of both basal and upper contacts of the Wapiti Formation, 2) effective mappability of lithostratigraphic units and depositional sequences in western Alberta, and 3) the identification of previously undetermined maximum flooding surface of the Bearpaw seaway and Drumheller Marine Tongue, which are reference marine unit in central and southern Alberta. A second, but not less important, guideline for the project has been the rich paleontological record of the Wapiti deposits. Detailed paleoenvironmental and taxonomical information on old and new finds have been the base for correlation with well known associations of Alaska, southern Alberta, and Montana. Newly discovered rich fossil localities documented an extraordinarily diverse fauna during the latest Cretaceous, including dinosaurs, squamates, and fresh-water fishes and reptiles. Lastly, in order to better characterize the Wapiti Formation, major marker beds were described: these include several bentonites (altered volcanic ash deposits) which have been documented over an area of almost 30.000 km2, as well as four major coal zones, characterized by tabular coal seams with an overall thickness of 2 meters. Such marker beds represent a formidable tool for high-resolution chronology and regional correlations within the Late Cretaceous Alberta foreland basin.

Facies distribution in CRP sediment cores from the Ross Sea, Antarctica

Clasts from the Cape Roberts Project cores CRP-2/2A and CRP-3 provide indications of glacially influenced depositional environments in Oligocene and Miocene strata in the western Victoria Land Basin, Antarctica. CRP-2/2A is interpreted to represent strongly glacially influenced, unconformity bound depositional sequences produced by repeated advance and retreat of floating and grounded ice across the shelf. A similar interpretation is extended to the upper 330 meters of the CRP-3 core, but the lower part of the core records shallow marine deposition with significantly less glacial influence. Clast shape analysis from selected coarse-grained facies throughout the cored interval indicates that most clasts are glacially sourced, with little distinction between diamictite and conglomeratic facies. Three dimensional clast fabric analysis from units immediately above sequence boundaries generally display weak or random fabrics and do not suggest that grounded ice actually reached the drillsite at these intervals. Striated and outsized clasts present in fine-grained lithofacies throughout the cores provide further evidence of sub-glacially transported sediment and iceberg rafting. The distribution of these striated and out-sized clasts indicate that a significant glacial influence persisted through most of the time represented by the cores with glaciers actively calving at sea-level introducing ice-berg rafted glacial debris even in the earliest Oligocene.

Preliminary results and documentation of sediment cores CRP2 and CRP-2A from the Ross Sea off Cape Roberts, Antarctica

The site for CRP-2, 14 km east of Cape Roberts (77.006°S; 163.719°E), was selected to overlap the early Miocene strata cored in nearby CRP-1, and to sample deeper into the east-dipping strata near the western margin ofe he Victoria Land Basin to investigate Palaeogene climatic and tectonic history. CRP-2 was cored from 5 to 57 mbsf (metres below the sea floor) (core recovery 91 %), with a deviation resulting in CRP-2A being cored at the same site. CRP-2A reached down to 624mbsf (recovery 95%), and to strata with an age of c. 33-35 Ma. Drilling took place from 16 October to 25 November 1998, on 2.0-2.2 m of sea ice and through 178 m of water. Core fractures and other physical properties, such as sonic velocity, density and magnetic susceptibility, were measured throughout the core. Down-hole logs for these and other properties were run from 63 to 167 mbsf and subsequently from 200 to 623 mbsf, although density and velocity data could be obtained only to 440 mbsf because of hole collapse. Sonic velocity averages c. 2.0 km S-1 for the upper part of the hole, but there is an sharp increase to c. 3.0 km s-1 and also a slight angular unconformity, at 306 mbsf, corresponding most likely to the early/late Oligocene boundary (c. 28-30 Ma). Velocity then increases irregularly to around 3.6 km s-1 at the bottom of the hole, which is estimated to lie 120 m above the V4/V5 boundary. The higher velocities below 306 mbsf probably reflect more extensive carbonate and common pyrite cementation, in patches, nodules, bedding-parallel masses and as vein infills. Dip of the strata also increases down-hole from 3° in the upper 300 in to over 10° at the bottom. Temperature gradient is 21° k-1. Over 2 000 fractures were logged through the hole. Borehole televiewer imagery was obtained for the interval from 200 to 440 mbsf to orient the fractures for stress field analysis. Lithostratigraphical descriptions on a scale of 1:20 are presented for the full length of the core, along with core box images, as a 200 page supplement to this issue. The hole initially passed through a layer of muddy gravel to 5.5 mbsf (Lithological Sub-Unit or LSU 1.1), and then into a Quaternary diatom-bearing clast-rich diamicton to 21 mbsf (LSU 2. l), with an interval of alternating compact diamicton and loose sand, and containing a rich Pliocene foraminiferal fauna, to 27 mbsf (LSU 2.2). The unit beneath this (LSU 3.1) has similar physical properties (sonic velocity, porosity, magnetic susceptibility) and includes diamictites of similar character to those of LSU 2.1 and 2.2, but an early Miocene (c. 19 Ma) diatom assemblage at 28 mbsf (top of LSU 3.1) shows that this sub-unit is part of the older section. The strata beneath 27 mbsf, primary target for the project, extend from early Miocene to perhaps latest Eocene age, and are largely cyclic glacimarine nearshore to offshore sediments. They are described as 41 lithological sub-units and interpreted in terms of 12 recurrent lithofacies. These are 1) mudstone, 2) inter-stratified mudstone and sandstone, 3) muddy very fine to coarse sandstone, 4) well-sorted stratified fine sandstone, 5) moderately to well-sorted, medium-grained sandstone, 6) stratified diamictite, 7) massive diamictite, 8) rhythmically inter-stratified sandstone and mudstone, 9) clast-supported conglomerate, 10) matrix-supported conglomerate, 11) mudstone breccia and 12) volcaniclastic sediment. Sequence stratigraphical analysis has identified 22 unconformity-bounded depositional sequences in pre- Pliocene strata. They typically comprise a four-part architecture involving, in ascending order, 1) a sharp-based coarse-grained unit (Facies 6,7,9 or 10), 2) a fining-upward succession of sandstones (Facies 3 and 4), 3) a mudstone interval (Facies l), in some cases coarsening upward to muddy sandstones (Facies 3), and 4) a sharp-based sandstone dominated succession (mainly Facies 4). The cyclicity recorded by the strata is interpreted in terms of a glacier ice margin retreating and advancing from land to the west, and of rises and falls in sea level. Analysis of sequence periodicity awaits afirmer chronology. However, apreliminary spectral analysis of magnetic susceptibility for a deepwater mudstone within one of the sequences (from 339 to 347 mbsf) reveals ratios between hierarchical levels that are similar to those of the three Milankovitch orbital forcing periodicities. The strata contain a wide range of fossils, the most abundant being marine diatoms. These commonly form up to 5% of the sediment, though in places the core is barren (notably between 300 and 412 mbsf). Fifty samples out of 250 reviewed were studied in detail. The assemblages define ten biostratigraphical zones, some of them based on local or as yet undescribed forms. The assemblages are neritic, and largely planktonic, suggesting that the sea floor was mostly below the photic zone throughout deposition of the corcd sequence. Calcareous nannofossils, representing incursions of ocean surface waters, are much less common (72 out of 183 samples examined) and restricted to mudstone intervals a few tens of metres thick, but are important for dating. Foraminifera are also sparse (73 out of 135 samples) and represented only by calcareous benthic species. Changing assemblages indicate a shift from inshore environments in the early Oligocenc to outer shelf in the late Oligocenc, returning to inshore in the early Miocene. Marine palynomorplis yielded large numbers of well-preserved forms from most of the 116 samples examined. The new in situ assemblagc found last year in CRP-1 is extended down into the late Oligocene and a further new assemblage is found in the early Oligoccnc. Many taxa are new, and cannot us yet contribute to an improved understanding of chronology or ecology. Marine invertebrate macrofossils, mostly molluscs and serpulid tubes, are scattered throughout the core. Preservation is good in mudstones but poor in other lithologies. Climate on land is reflected in the content of terrestrial palynomorphs, which are extremely scarce down to c. 300 mbsf. Some forms are reworked, and others represent a low growing sparse tundra with at least one species of Nothofagus. Beneath this level, a significantly greater diversity and abundance suggests a milder climate and a low diversity woody vegetation in the early Oligocene, but still far short of the richness found in known Eocene strata of the region. Sedimentary facies in the oldest strata also suggest a milder climate in the oldest strata cored, with indications of substantial glacial melt-water discharges, but are typical of a coldcr climate in late Oligocene and early Miocene times. Clast analyses from diamictites reveal weak to random fabrics, suggesting either lack of ice-contact deposition or post-depositional modification, but periods when ice grounded at the drill site are inferred from thin zones of in-situ brecciated rock and soft-sediment folding. These are more common above c. 300 mbsf, perhaps reflecting more extensive glacial advances during deposition of those strata. Erosion of the adjacent Transantarctic Mountains through Jurassic basalt and dolerite-intruded Beacon strata into basement rocks beneath is recorded by petrographical studies of clast and sand grain assemblages. Core below 310 mbsf contains a dominance of fine-grained Jurassic dolerite and basalt fragments along with Beacon-derived coal debris and rounded quartz grains, whereas the strata above this level have a much higher proportion of basement derived granitoids, implying that the large areas of the adjacent mountains had been eroded to basement by the end of the early Oligocene. There is little indication of rift-related volcanism below 310 mbsf. Above this, however, basaltic and trachytic tephras are common, especially from 280 to 200 mbsf, from 150 to 46 mbsf, and in Pliocene LSU 2.2 from 21 to 27 mbsf. The largest volcanic eruptions generated layers of coarse (up to 1 cm) trachytic pumice lapilli between 97 and 114 mbsf. The thickest of these (1.2 m at 112 mbsf) may have produced an eruptive column extending tens of km into the stratosphere. A source within a few tens of km of the drill site is considered most likely. Present age estimates for the pre-Pliocene sequence are based mainly on biostratigraphy (using mainly marine diatoms and to a lesser extent calcareous nannofossils), with the age of the tephra from 112 to 114 mbsf (21.44k0.05 Ma from 84 crystals by Ar-Ar) as a key reference point. Although there are varied and well-preserved microfossil assemblages through most of the sequence (notably of diatoms and marine palynomorphs), they comprise largely taxa either known only locally or as yet undescribed. In addition, sequence stratigraphical analysis and features in the core itself indicate numerous disconformities. The present estimate from diatom assemblages is that the interval from 27 to 130 mbsf is early Miocene in age (c. 19 to 23.5 Ma), consistent with the Ar-Ar age from 112 to 114 mbsf. Diatom assemblages also indicate that the late Oligocene epoch extends from c. 130 to 307 mbsf, which is supported by late Oligocene nannofossils from 130 to 185 mbsf. Strata from 307 to 412 mbsf have no age-diagnostic assemblages, but below this early Oligocene diatoms and nannofossils have been recovered. A nannoflora at the bottom of the hole is consistent with an earliest Oligocene or latest Eocene age. Magnetostratigraphical studies based on about 1000 samples, 700 of which have so far undergone demagnetisation treatment, have provided a polarity stratigraphy of 12 pre-Pliocene magnetozones. Samples above 270 mbsf are of consistently high quality. Below this, magnetic behaviour is more variable. A preliminary age-depth plot using the Magnetic Polarity Time Scale (MPTS) and constrained by biostratigraphical data suggests that episodes of relatively rapid sedimentation took place at CRP-2 during Oligocene times (c. 100 m/My), but that more than half of the record was lost in a few major and many minor disconformities. Age estimates from Sr isotopes in shell debris and further tephra dating are expected to lead to a better comparison with the MPTS. CRP-2/2A has recorded a history of subsidence of the Victoria Land Basin margin that is similar to that found in CIROS-170 km to the south, reflecting stability in both basin and the adjacent mountains in late Cenozoic times, but with slow net accumulation in the middle Cenozoic. The climatic indicators from both drill holes show a similar correspondence, indicating polar conditions for the Quaternary but with sub-polar conditions in the early Miocene-late Oligocene and indications of warmer conditions still in the early Oligocene. Correlation between the CRP-2A core and seismic records shows that seismic units V3 and V4, both widespread in the Victoria Land Basin, represent a period of fluctuating ice margins and glacimarine sedimentation. The next drill hole, CRP-3, is expected to core deep into V5 and extend this record of climate and tectonics still further back in time.

Stable carbon isotope record of Bahama Bank sediments

The carbon-isotopic composition (d13C) of bulk carbonates, obtained from a transect of sites drilled through platform and periplatform sediments of Holocene to Early Miocene age, has been compared to ascertain whether changes in the d13C can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the d13C of the dissolved inorganic carbon in the oceans over this time period. Five of the sites were drilled during Leg 166 of the Ocean Drilling Project (1003-1007) in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of Holocene to Oligocene age that are contained in 17 depositional sequences (A-Q). Two shallow-water sites, Clino and Unda were situated on a extension of the same transect on Great Bahama Bank in a water depth of 10-15 m. With the exception of Unda and Clino, the d13C of the carbonates ranges from +5 per mil in the younger sequences to +1 per mil in the Early Miocene. In each of the sites, the d13C is strongly positively correlated with the percentage of aragonite. As a consequence, the d13C of sequences A through F is strongly correlated, reflecting the decreasing amount of aragonite with increasing depth. In the two platform sites, the d13C is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the Pleistocene. Although the d13C of the individual sequences can be correlated in most instances between the ODP holes, the changes are not related to global changes in the d13C of the oceans which in contrast to the d13C of the platform sediments become isotopically lower towards the present day. Instead variations in the d13C appear to be related to varying mixtures of d13C-rich banktop sediments and pelagic material.

Characteristic directions and polarity ratings and polarity chron assignments of ODP Leg 171B sites

The full suite of magnetic polarity chrons from Subchron M''-2r'' (early Albian) through Chron C13r (latest Eocene) were resolved at one or more Ocean Drilling Program sites on the Blake Nose salient of the Florida continental margin. These sediments preserve diverse assemblages of calcareous and siliceous microfossils; therefore, the composite suite provides a reference section for high-resolution correlation of biostratigraphic datums to magnetic polarity chrons of the Late Cretaceous and Paleogene. Relative condensation or absence of polarity zones at different sites along the transect enhance the recognition and dating of depositional sequences and unconformities within the margin succession. A stable paleolatitude of ~25°N was maintained from the late Aptian through Eocene.