Análises estratigráfica e estrutural da Seção Rifte (Valanginiano ao Barremiano) na área do levantamento sísmico 3D de baixo vermelho, Bacia Potiguar emersa

Baixo Vermelho area, situated on the northern portion of Umbuzeiro Graben (onshore Potiguar Basin), represents a typical example of a rift basin, characterized, in subsurface, by the sedimentary rift sequence, correlated to Pendência Formation (Valanginian-Barremian), and by the Carnaubais fault system. In this context, two main goals, the stratigraphic and the structural analysis, had guided the research. For this purpose, it was used the 3D seismic volume and eight wells located in the study area and adjacencies. The stratigraphic analysis of the Valanginian-Barremian interval was carried through in two distinct phases, 1D and 2D, in which the basic concepts of the sequence stratigraphy had been adapted. In these phases, the individual analysis of each well and the correlation between them, allowed to recognize the main lithofacies, to interpret the effective depositional systems and to identify the genetic units and key-surfaces of chronostratigraphic character. The analyzed lithofacies are represented predominantly by conglomerates, sandstones, siltites and shales, with carbonate rocks and marls occurring subordinately. According to these lithofacies associations, it is possible to interpret the following depositional systems: alluvial fan, fluvio-deltaic and lacustrine depositional systems. The alluvial fan system is mainly composed by conglomerates deposits, which had developed, preferentially in the south portion of the area, being directly associated to Carnaubais fault system. The fluvial-deltaic system, in turn, was mainly developed in the northwest portion of the area, at the flexural edge, being characterized by coarse sandstones with shales and siltites intercalated. On the other hand, the lacustrine system, the most dominant one in the study area, is formed mainly by shales that could occur intercalated with thin layers of fine to very fine sandstones, interpreted as turbidite deposits. The recognized sequence stratigraphy units in the wells are represented by parasequence sets, systems tracts and depositional sequences. The parasequence sets, which are progradational or retrogradational, had been grouped and related to the systems tracts. The predominance of the progradation parasequence sets (general trend with coarsening-upward) characterizes the Regressive Systems Tract, while the occurrence, more frequently, of the retrogradation parasequence sets (general trend with finning-upward) represents the Transgressive System Tract. In the seismic stratigraphic analysis, the lithofacies described in the wells had been related to chaotic, progradational and parallel/subparallel seismic facies, which are associated, frequently, to the alluvial fans, fluvial-deltaic and lacustrine depositional systems, respectively. In this analysis, it was possible to recognize fifteen seismic horizons that correspond to sequence boundaries and to maximum flooding surfaces, which separates Transgressive to Regressive systems tracts. The recognition of transgressive-regressive cycles allowed to identify nine, possibly, 3a order deposicional sequences, related to the tectonic-sedimentary cycles. The structural analysis, in turn, was done at Baixo Vermelho seismic volume, which shows, clearly, the structural complexity printed in the area, mainly related to Carnaubais fault system, acting as an important fault system of the rift edge. This fault system is characterized by a main arrangement of normal faults with trend NE-SO, where Carnaubais Fault represents the maximum expression of these lineations. Carnaubais Fault corresponds to a fault with typically listric geometry, with general trend N70°E, dipping to northwest. It is observed, throughout all the seismic volume, with variations in its surface, which had conditioned, in its evolutive stages, the formation of innumerable structural features that normally are identified in Pendencia Formation. In this unit, part of these features is related to the formation of longitudinal foldings (rollover structures and distentional folding associated), originated by the displacement of the main fault plan, propitiating variations in geometry and thickness of the adjacent layers, which had been deposited at the same time. Other structural features are related to the secondary faultings, which could be synthetic or antithetic to Carnaubais Fault. In a general way, these faults have limited lateral continuity, with listric planar format and, apparently, they play the role of the accomodation of the distentional deformation printed in the area. Thus, the interaction between the stratigraphic and structural analysis, based on an excellent quality of the used data, allowed to get one better agreement on the tectonicsedimentary evolution of the Valanginian-Barremian interval (Pendência Formation) in the studied area

Life mode of in situ Conularia in a Middle Devonian epibole

Exceptionally abundant specimens of Conularia aff. desiderata Hall occur in multiple marine obrution deposits, in a single sixth-order parasequence composed of argillaceous and silty very fine sandstone, in the Otsego Member of the Mount Marion Formation (Middle Devonian, Givetian) in eastern New York State, USA. Associated fossils consist mostly of rhynchonelliform brachiopods but also include bivalve molluscs, orthoconic nautiloids, linguliform brachiopods and gastropods. Many of the brachiopods, bivalve molluscs and conulariids have been buried in situ. Conulariids buried in situ are oriented with their aperture facing obliquely upward and with their long axis inclined at up to 87degree to bedding. Most specimens are solitary, but some occur in V-like pairs or in radial clusters consisting of three specimens, with the component specimens being about equally long or (less frequently) substantially different in length. The compacted apical end of Conularia buried in situ generally rests upon argillaceous sandstone. With one possible exception, none of the examined specimens terminates in a schott (apical wall), and internal schotts appear to be absent. The apical ends of specimens in V-like pairs and radial clusters show no direct evidence of interconnection of their periderms. The apical, middle or apertural region of some inclined specimens abuts or is in close lateral proximity to a recumbent conulariid or to one or more spiriferid brachiopods, some of which have been buried in their original life orientation. The azimuthal bearings of Conularia and nautiloid long axes and the directions in which conulariids open are nonrandom, with conulariids being preferentially aligned between 350 and 50degree and with their apertural end facing north-east, and nautiloids being preferentially aligned between 30 and 70degree. Otsego Member Conularia were erect or semi-erect, epifaunal or partially infaunal animals, the apical end of which rested upon very fine bottom sediment. The origin of V-like pairs and radial clusters remains enigmatic, but it is probable that production of schotts was not a regular feature of this animal's life history. Finally, conulariids and associated fauna were occasionally smothered by distal storm deposits, under the influence of relatively weak bottom currents. © The Palaeontological Association.

Análise estratigráfica da sequência mesodevoniana-eocarbonífera da Bacia do Parnaíba, nordeste do Brasil

The Middle Devonian-Early Carboniferous sequence of the Parnaíba Basin, lithostratigraphically defined as Canindé Group, has been reinterpreted using the basic model of sequence stratigraphy. Therefore, lithology and gamma ray well-logs and seismic lines of central portion of the basin were analyzed, producing up from there diagrams 1D, isochore maps and stratigraphic sections. As results of this study, were defined two depositional cycles of second order, referred as Depositional Sequence 1 (SEQ1) and the Depositional Sequence 2 (SEQ2). The SEQ1, with interval about 37 Ma, is limited below by Early Devonian Unconformity and is equivalent to the formations Itaim, Pimenteiras and Cabeças. The SEQ2, which follows, comprises a range of about 15 Ma and is equivalent to the Longá Formation The SEQ1 starts with the lowstand systems tract, consisting of progradational parasequence set in the basal part, predominantly pelitic, deposited on a prodelta under influence of storms and the upper part consists in sandstones of deltaic front, with the maximum regressive surface on the upper limit. The transgressive systems tract, deposited above, is characterized by retrogradacional parasequence set composed of shallow shelf mudstones, deposited under storm conditions. The maximum flooding surface, upper limit of this tract, is positioned in a shale level whose radioactivity in gammaray well-log is close to 150 API. The highstand systems tract presents progradational parasequence set, comprising mudstones and sandstones deposited in shelf, fluvial-estuarine or deltaic and periglacial environments, with the upper limit the Late Devonian Unconformity. The SEQ2 was deposited in shelf environment, starting with the lowstand systems tract, that is characterized by a progradational parasequence set, followed by the transgressive systems tract, with retrogradational character. The upper limit of the tract corresponding to the fusion between maximum flooding surface with the upper limit of this sequence, which is the Early Carboniferous Unconformity, where the overlapping section was eroded. This section, which corresponds the highstand systems tract is restricted to portions at which the erosion that generate the Early-Carboniferous Unconformity was less effective, preserving the records of this unit.

Análise estratigráfica da sequência mesodevoniana-eocarbonífera da Bacia do Parnaíba, nordeste do Brasil

The Middle Devonian-Early Carboniferous sequence of the Parnaíba Basin, lithostratigraphically defined as Canindé Group, has been reinterpreted using the basic model of sequence stratigraphy. Therefore, lithology and gamma ray well-logs and seismic lines of central portion of the basin were analyzed, producing up from there diagrams 1D, isochore maps and stratigraphic sections. As results of this study, were defined two depositional cycles of second order, referred as Depositional Sequence 1 (SEQ1) and the Depositional Sequence 2 (SEQ2). The SEQ1, with interval about 37 Ma, is limited below by Early Devonian Unconformity and is equivalent to the formations Itaim, Pimenteiras and Cabeças. The SEQ2, which follows, comprises a range of about 15 Ma and is equivalent to the Longá Formation The SEQ1 starts with the lowstand systems tract, consisting of progradational parasequence set in the basal part, predominantly pelitic, deposited on a prodelta under influence of storms and the upper part consists in sandstones of deltaic front, with the maximum regressive surface on the upper limit. The transgressive systems tract, deposited above, is characterized by retrogradacional parasequence set composed of shallow shelf mudstones, deposited under storm conditions. The maximum flooding surface, upper limit of this tract, is positioned in a shale level whose radioactivity in gammaray well-log is close to 150 API. The highstand systems tract presents progradational parasequence set, comprising mudstones and sandstones deposited in shelf, fluvial-estuarine or deltaic and periglacial environments, with the upper limit the Late Devonian Unconformity. The SEQ2 was deposited in shelf environment, starting with the lowstand systems tract, that is characterized by a progradational parasequence set, followed by the transgressive systems tract, with retrogradational character. The upper limit of the tract corresponding to the fusion between maximum flooding surface with the upper limit of this sequence, which is the Early Carboniferous Unconformity, where the overlapping section was eroded. This section, which corresponds the highstand systems tract is restricted to portions at which the erosion that generate the Early-Carboniferous Unconformity was less effective, preserving the records of this unit.

Location and ages of terrestrial peatlands located on continental shelves and in coastal sediments

This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

Sea-level control on the connection between shelf-edge deltas and the Bourcart canyon head (western Mediterranean) during the last glacial/interglacial cycle

A dense grid of high- and very high resolution seismic data, together with piston cores and borehole data providing time constraints, enables us to reconstruct the history of the Bourcart canyon head in the western Mediterranean Sea during the last glacial/interglacial cycle. The canyon fill is composed of confined channel–levee systems fed by a series of successively active shelf fluvial systems, originating from the west and north. Most of the preserved infill corresponds to the interval between Marine Isotope Stage (MIS) 3 and the early deglacial (19 cal ka BP). Its deposition was strongly controlled by a relative sea level that impacted the direct fluvial/canyon connection. During a period of around 100 kyr between MIS 6 and MIS 2, the canyon “prograded” by about 3 km. More precisely, several parasequences can be identified within the canyon fill. They correspond to forced-regressed parasequences (linked to punctuated sea-level falls) topped by a progradational-aggradational parasequence (linked to a hypothetical 19-ka meltwater pulse (MWP)). The bounding surfaces between forced-regressed parasequences are condensed intervals formed during intervals of relative sediment starvation due to flooding episodes. The meandering pattern of the axial incision visible within the canyon head, which can be traced landward up to the Agly paleo-river, is interpreted as the result of hyperpycnal flows initiated in the river mouth in a context of increased rainfall and mountain glacier flushing during the early deglacial.