Facies analysis of tertiary alluvial fan deposits in the Jundiai region, São Paulo, southeastern Brazil

This article presents an analysis of facies of sedimentary sequences that occur as discontinuous bodies in the Jundiai region, west of the main Tertiary continental basins of the southeastern Brazil continental rift. Nine identified sedimentary facies, grouped into four associations, suggest the existence of an ancient alluvial fan system whose source area was the Japi mountain range (Serra do Japi). The deposits are considered Tertiary in age and chronocorrelated with those identified in the Atibaia region and at other sites up to 100 km east and northeast of Jundiai. The depositional model adopted to explain the filling of the basin proposes that the alluvial fans, which directly derive from the source area, terminated in a braided channel longitudinal to the basin axis that flowed to northwest, in a similar configuration to that of the present day. This basin may have extended to the Atibaia region or formed a set of small basins laterally contiguous to the faults associated with the rift. Such occurrences show that the formation of rift basins was broader than the area presently occupied by the main deposits. (c) 2005 Elsevier Ltd. All rights reserved.

Facies analysis of the Codó formation (Late Aptian) in the Grajaú area, Southern São Luís-Grajaú Basin

Facies descriptions of the Codó Formation in the Grajaú area are provided for the first time, and its sedimentary characteristics compared to those from the Codó area to allow paleoenvironmental reconstructions. Deposits in the Grajaú area include evaporites, limestones and argillites bearing features indicative of a shallow, low energy, subaqueous, saline environment exposed to meteoric and/or capillary conditions. Floodingevaporative concentration-desiccation cycles suggest a saline pan complex surrounded by extensive evaporitic mudflats. The location of the system, whether coastal or inland, is a matter open for debate. However, the later hypothesis is favored considering: 1. Sr isotopic data, with values higher than those expected for Late Aptian marine waters; 2. calcitic composition of limestones (instead of dolomitic and/or magnesitic as expected in coastal settings); and 3. presence of continental ostracods and lack of marine fauna. This interpretation is consistent with that proposed for UpperAptian deposits of the Codó area, but the depositional system there was one dominated by more stable, well-stratified, anoxic waters and evaporite precipitation in central lacustrine areas, while in the Grajaú area the salt pan was more oxygenated and ephemeral, with salt precipitation mainly in marginal areas or along surrounding mudflats.

Shell beds from the Low Head Member (Polonez Cove Formation, early Oligocene) at King George Island, west Antarctica: new insights on facies analysis, taphonomy and environmental significance

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Facies analysis on sediment core CRP-3 from the Ross Sea, Antarctica

Cape Roberts Project drill core 3 (CRP-3) was obtained from Roberts ridge, a sea-floor high located at 77°S, 12 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 939 m long and comprises strata dated as being early Oligocene (possibly latest Eocene) in age, resting unconformably on ~116 m of basement rocks consisting of Palaeozoic Beacon Supergroup sediments. The core includes ten facies commonly occurring in five major associations that are repeated in particular sequences throughout the core and which are interpreted as representing different depositional environments through time. Depositional systems inferred to be represented in the succession include: outer shelf, inner shelf, nearshore to shoreface each under iceberg influence, deltaic and/or grounding-line fan, and ice proximal-ice marginal-subglacial (mass flow/rainout diamictite/subglacial till) singly or in combination. The record is taken to represent the initial talus/alluvial fan setting of a glaciated rift margin adjacent to the block-uplifted Transantarctic Mountains. Development of a deltaic succession upcore was probably associated with the formation of palaeo-Mackay valley with temperate glaciers in its headwaters. At that stage glaciation was intense enough to support glaciers ending in the sea elsewhere along the coast, but a local glacier was fluctuating down to the sea by the time the youngest part of CRP-3 was being deposited. Changes in palaeoenvironmental interpretations in this youngest part of the core are used to estimate relative glacial proximity to the drillsite through time. These inferred glacial fluctuations are compared with the global d180 and Mg/Ca curves to evaluate the potential of glacial fluctuations on Antarctica for influencing these records of global change. Although the comparisons are tentative at present, the records do have similarities, but there are also some differences that require further evaluation.

Quaternary paleoenvironments and relative sea-level changes in Marajo Island (Northern Brazil): Facies, delta(13)C, delta(15)N and C/N

The reconstruction of physical environments of Amazonian areas is of great interest to determine the dynamic evolution of the Amazon drainage basin. However. few studies have emphasized the Quaternary deposits in this region. which is mostly due to the lack of natural exposures imposed by the low topography. This work integrates facies analysis. radiocarbon dating, delta(13)C, delta(15)N, and C/N of an 124 m-thick core from an area located at the mouth of the Amazon River. northeastern Amazonia. The study records deposits up to 50.795 (14)C yr B P. in age. which formed in a variety of depositional environments including fluvial channel, tidal flat, outer estuarine basin to shallow marine. inner estuarine basin, estuarine channel and lagoon. Facies interpretation was significantly improved with the inclusion of delta(13)C, delta(15)N, and C/N analyses of organic matter extracted from the sediments The obtained values conform to a transitional. mostly estuarine paleosetting evolved during successive relative sea-level fluctuations. The results suggest fluvial deposition between 40,950 (+/- 590) and 50.795 (14)C yr B P, with a rise in relative sea level that commenced between 35,567 (+/- 649) and 39,079 (+/- 1114) (14)C yr B P. An overall transgression took place until 29,340 (+/- 340) (14)C yr B P., after which the relative sea level dropped, favoring valley rejuvenation and incision. Following this time up to 10,479 (+/- 34) (14)C yr B.P. a rise in relative sea level filled up the valley with estuarine deposits After 10.479(+/- 34) (14)C yr B.P., the estuary was replaced by a lagoon At the end of the Holocene, the coastline prograided approximately 45 km northward, replaci ng the lagoon by a lake system Despite the influence of eustatic fluctuations. regional tectonics played a significant role to create new space where these Late Pleistocene and Holocene sediments accumulated. (C) 2009 Elsevier B V All rights reserved.

Archaeofacies Analysis: Using Depositional Attributes to Identify Anthropic Processes of Deposition in a Monumental Shell Mound of Santa Catarina State, Southern Brazil

In the coast of Santa Catarina State (southern Brazil), a large population of monumental shell mounds characterizes a highly dynamic coastal setting. In this paper, sedimentary facies analysis was adapted for description, sampling, and interpretation of shell mound complex and repetitive archaeostratigraphic successions. Archaeofacies identification in the field, according to depositional attributes, is tested by contrasting field description with multi-element chemical analyses, total carbon and nitrogen determinations, and micromorphological descriptions. Two vertical sequences at the black deposit of Jabuticabeira II shell mound were studied and preliminary results showed that: (1) depositional attributes are a reliable base for archaeofacies identification in the field, (2) the formation process of this site involved a sequence of anthropic depositional processes, where burned refuse was redeposited over the shell mound following a ritual construction pattern, and (3) the black deposit includes a double palimpsest that refers to provenance and meaning of mound construction material. (C) 2009 Wiley Periodicals, Inc.

Stratigrafia fisica ed analisi di facies dei depositi torbiditici della Formazione delle Arenarie del Monte Cervarola tra la Val Secchia e la Val Scoltenna (Aquitaniano-Burdigaliano, Appennino Settentrionale)

The Cervarola Sandstones Formation (CSF), Aquitanian-Burdigalian in age, was deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the CSF, in the same way of other Apennine foredeep deposits, records the progressive closure of the basin due to the propagation of thrust fronts toward north-east, i.e. toward the outer and shallower foreland ramp. This process produce a complex foredeep characterized by synsedimentary structural highs and depocenters that can strongly influence the lateral and vertical turbidite facies distribution. Of consequence the main aim of this work is to describe and discuss this influence on the basis of a new high-resolution stratigraphic framework performed by measuring ten stratigraphic logs, for a total thickness of about 2000m, between the Secchia and Scoltenna Valleys (30km apart). In particular, the relationship between the turbidite sedimentation and the ongoing tectonic activity during the foredeep evolution has been describe through various stratigraphic cross sections oriented parallel and perpendicular to the main tectonic structures. On the basis of the high resolution physical stratigraphy of the studied succession, we propose a facies tract and an evolutionary model for the Cervarola Sandstones in the studied area. Thanks to these results and the analogies with others foredeep deposits of the northern Apennines, such as the Marnoso-arenacea Formation, the Cervarola basin has been interpreted as a highly confined foredeep controlled by an intense synsedimentary tectonic activity. The most important evidences supporting this hypothesis are: 1) the upward increase, in the studied stratigraphic succession (about 1000m thick), of sandstone/mudstone ratio, grain sizes and Ophiomorpha-type trace fossils testifying the high degree of flow deceleration related to the progressive closure and uplift of the foredeep. 2) the occurrence in the upper part of the stratigraphic succession of coarse-grained massive sandstones overlain by tractive structures such as megaripples and traction carpets passing downcurrent into fine-grained laminated contained-reflected beds. This facies tract is interpreted as related to deceleration and decoupling of bipartite flows with the deposition of the basal dense flows and bypass of the upper turbulent flows. 3) the widespread occurrence of contained reflected beds related to morphological obstacles created by tectonic structures parallel and perpendicular to the basin axis (see for example the Pievepelago line). 4) occurrence of intra-formational slumps, constituted by highly deformed portion of fine-grained succession, indicating a syn-sedimentary tectonic activity of the tectonic structures able to destabilize the margins of the basin. These types of deposits increase towards the upper part of the stratigraphic succession (see points 1 and 2) 5) the impressive lateral facies changes between intrabasinal topographic highs characterized by fine-grained and thin sandstone beds and marlstones and depocenters characterized by thick to very thick coarse-grained massive sandstones. 6) the common occurrence of amalgamation surfaces, flow impact structures and mud-draped scours related to sudden deceleration of the turbidite flows induced by the structurally-controlled confinement and morphological irregularities. In conclusion, the CSF has many analogies with the facies associations occurring in other tectonically-controlled foredeeps such as those of Marnoso-arenacea Formation (northern Italy) and Annot Sandstones (southern France) showing how thrust fronts and transversal structures moving towards the foreland, were able to produce a segmented foredeep that can strongly influence the turbidity current deposition.

Marine influence in the Barreiras Formation, State of Alagoas, northeastern Brazil

Tidal processes were important for deposition of the Barreiras Formation located in northern Brazil, while correlatable deposits in northeastern Brazil have been traditionally related to continental environments. Facies analysis in southern Alagoas revealed that the Barreiras Formation consists of cross-stratified conglomerates and sandstones (facies Sx and Cgx), compound cross-stratified sandstones (facies Cx), and heterolithic beddings (facies H). A significant portion of these deposits occurs within channel morphologies displaying fining and thinning upward successions. An abundance of sedimentary features is comparable to those from the northern Brazilian counterpart. These include: tidal bundles; herringbone cross-stratification; heterolithic beddings with sandstone and mudstone beds in sharp contacts; and ichnofossils mostly consisting of Ophiomorpha nodosa, Skolithos and Planolites. Altogether, these features point to a marginal marine depositional setting dominated by tidal processes, which are related to an estuarine system, an interpretation also provided for the Barreiras Formation in northern Brazil. The widespread occurrence of deposits with unambiguous evidence of tidal processes in the Barreiras Formation of northern Brazil, and now in the State of Alagoas, leads to argue that the early/middle Miocene worldwide marine transgression might have left a much more widespread sedimentary record along the Brazilian coast than currently regarded.

Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

In West Timer, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratigraphic investigation integrating field observations and facies analysis, allowed the reconstruction of a synthetic lithostratigraphic succession for the Upper Triassic, a stratigraphic transition from Carnian shales to Upper Norian-Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphic Units A-E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indicative of a distal slope to basin environment. The ammonite rich condensed limestone of Unit H was deposited on a `pelagic carbonate plateau' exposed to storms and currents. The organic facies have been used as criteria for biostratigraphy, palaeoenvironmental interpretation, and sequence stratigraphy. The palaeontological analysis of the Triassic succession of West Timer is based on the investigation of radiolaria and palynomorphs, in the marls and limestones of Units A-E, and also on ammonites and conodonts in the condensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus, associated with `Lueckisporites' cf. singhii, Vallasporites ignacii, Patinosporites densus and Partitisporites novimundanus. Unit C is considered as Norian, on the basis of a relatively high percentage of Gliscopollis meyeriana and Granuloperculatipollis rudis. Unit D contains significant palynomorphs and radiolaria; the organic facies, characterized by marine elements, is dominated by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeata; the radiolaria confirm the Norian age. They range from the lowermost Norian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis salinaria. For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera; the upper part is Upper Norian to Rhaetian based on the presence of Livarella valida. Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic succession of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tectonic melange of the accretionary prism of the island Arc of Banda. is a tectonically dismembered part of a Triassic lithostratigraphic succession. (C) 2000 Elsevier Science B.V. All rights reserved.

Determination of controls on Holocene barrier progradation through application of OSL dating: The Ilha Comprida Barrier example, Southeastern Brazil

Barrier development during the Holocene is studied using the example of the Ilha Comprida, Southeastern Brazil. Aerial photos, facies analysis, and optically stimulated luminescence dating are used to define the barrier emergence and evolution. Optically stimulated luminescence ages and facies successions indicate that the Ilha Comprida probably began as a Holocene transgressive barrier island 6000 years ago, just before the last relative sea-level maximum. Since then the barrier has progradated through the addition of curved beach ridges. Based on beach ridge alignments, six units of growth are identified with two growth directions, transverse and longitudinal. Rates of progradation with transverse growth vary from 0.13 to 4.6 m/year. Rates of longitudinal growth to NE range from 5.2 to 30 m/year. Variation in coastal progradation rates and sediment retention during the last 6000 years is compared with climate, physiography and relative sea-level changes. The physiography, represented by pre-Cenozoic hills, is the major control on sediment retention and alternation between longitudinal and transverse growth. Climate variations, such as the Little Ice Age event, apparently control the formation of ridges types: beach ridges, foredunes, and blowouts. These results allow the use of the Ilha Comprida Barrier as an example to analyze the major controls on barriers progradation. (C) 2011 Elsevier B.V. All rights reserved.

Caracterização tectono-estratigráfica da sequência transicional na sub-bacia de Sergipe

This thesis deals with the tectonic-stratigraphic evolution of the Transitional Sequence in the Sergipe Sub-basin (the southern segment of the Sergipe-Alagoas Basin, Northeast Brazil), deposited in the time interval of the upper Alagoas/Aptian stage. Sequence boundaries and higher order internal sequences were identified, as well as the structures that affect or control its deposition. This integrated approach aimed to characterize the geodynamic setting and processes active during deposition of the Transitional Sequence, and its relations with the evolutionary tectonic stages recognized in the East Brazilian Margin basins. This subject addresses more general questions discussed in the literature, regarding the evolution from the Rift to the Drift stages, the expression and significance of the breakup unconformity, the relationships between sedimentation and tectonics at extensional settings, as well as the control on subsidence processes during this time interval. The tectonic-stratigraphic analysis of the Transitional Sequence was based on seismic sections and well logs, distributed along the Sergipe Sub-basin (SBSE). Geoseismic sections and seismic facies analysis, stratigraphic profiles and sections, were compiled through the main structural blocks of this sub-basin. These products support the depositional and tectonic-stratigraphic evolutionary models built for this sequence. The structural analysis highlighted similarities in deformation styles and kinematics during deposition of the Rift and Transitional sequences, pointing to continuing lithospheric extensional processes along a NW trend (X strain axis) until the end of deposition of the latter sequence was finished by the end of late Aptian. The late stage of extension/rifting was marked by (i) continuous (or as pulses) fault activity along the basin, controling subsidence and creation of depositional space, thereby characterizing upper crustal thinning and (ii) sagstyle deposition of the Transitional Sequence at a larger scale, reflecting the ductile stretching and thinnning of lower and sub crustal layers combined with an increasing importance of the thermal subsidence regime. Besides the late increments of rift tectonics, the Transitional Sequence is also affected by reactivation of the border faults of SBSE, during and after deposition of the Riachuelo Formation (lower section of the Transgressive Marine Sequence, of Albian age). It is possible that this reactivation reflects (through stress propagation along the newlycreated continental margin) the rifting processes still active further north, between the Alagoas Sub-basin and the Pernambuco-Paraíba Basin. The evaporitic beds of the Transitional Sequence contributed to the development of post-rift structures related to halokinesis and the continental margin collapse, affecting strata of the overlying marine sequences during the Middle Albian to the Maastrichtian, or even the Paleogene time interval. The stratigraphic analysis evidenced 5 depositional sequences of higher order, whose vertical succession indicates an upward increase of the base level, marked by deposition of continental siliciclastic systems overlain by lagunar-evaporitic and restricted marine systems, indicating that the Transitional Sequence was deposited during relative increase of the eustatic sea level. At a 2nd order cycle, the Transitional Sequence may represent the initial deposition of a Transgressive Systems Tract, whose passage to a Marine Transgressive Sequence would also be marked by the drowning of the depositional systems. At a 3rd order cycle, the sequence boundary corresponds to a local unconformity that laterally grades to a widespread correlative conformity. This boundary surface corresponds to a breakup unconformity , being equivalent to the Pre-Albian Unconformity at the SBSE and contrasting with the outstanding Pre-upper Alagoas Unconformity at the base of the Transitional Sequence; the latter is alternatively referred, in the literature, as the breakup unconformity. This Thesis supports the Pre-Albian Unconformity as marker of a major change in the (Rift-Drift) depositional and tectonic setting at SBSE, with equivalent but also diachronous boundary surfaces in other basins of the Atlantic margin. The Pre-upper Alagoas Unconformity developed due to astenosphere uplift (heating under high lithospheric extension rates) and post-dates the last major fault pulse and subsequent extensive block erosion. Later on, the number and net slip of active faults significantly decrease. At deep to ultra deep water basin segments, seaward-dipping reflectors (SDRs) are unconformably overlain by the seismic horizons correlated to the Transitional Sequence. The SDRs volcanic rocks overly (at least in part) continental crust and are tentatively ascribed to melting by adiabatic decompression of the rising astenospheric mantle. Even though being a major feature of SBSE (and possibly of other basins), the Pre-upper Alagoas Unconformity do not correspond to the end of lithospheric extension processes and beginning of seafloor spreading, as shown by the crustal-scale extensional structures that post-date the Transitional Sequence. Based on this whole context, deposition of the Transitional Sequence is better placed at a late interval of the Rift Stage, with the advance of an epicontinental sea over a crustal segment still undergoing extension. Along this segment, sedimentation was controled by a combination of thermal and mechanical subsidence. In continuation, the creation of oceanic lithosphere led to a decline in the mechanical subsidence component, extension was transferred to the mesoceanic ridge and the newly-formed continental margin (and the corresponding Marine Sequence) began to be controlled exclusively by the thermal subsidence component. Classical concepts, multidisciplinary data and new architectural and evolutionary crustal models can be reconciled and better understood under these lines

Caracterização da geometria de depósitos sedimentares na borda sudoeste da Bacia`Potiguar

This study focuses on the potential of several techniques used to identify depositional geometries and paleogeographical investigation on the SW border of the Potiguar Basin. Three areas were selected for an integrated geological, geophysical and geochemistry study. The main used techniques were facies analysis, remote sensing,ground penetrating radar (GPR) and gamma-ray in outcrops, as well as petrographic microscope observations and the using of scanning eletronic microscopic (SEM), and Carbon and Oxygen Isotopic study in the carbonate tufa. These methodological approaches were very efficient in the facies analysis of 2D geometries. The GPR profiles carried out in Quixeré identified important geological reflectors which allowed to the identification of depositional geometries of tufa. However, GPR profiles were not able to identify geological reflectors in the Apodi and Olho d´Água da Bica outcrops. Gammaray profiles also presented good results, which justify their use in 1D and 2D geometric analysis. Carbon and Oxygen Isotopic analyses were also used to investigate paleoenvironmental setting of tufa deposits. It is important to remark the excellent resultsof GRP using in the identification of deposition al geometries of tufa and their contact relationships with the underlying rocks. Field analysis of faults indicate a vertical sigma-1 orientation which was associated to normal faults

Diagênese e proveniência dos arenitos da tectonossequência Rifte na bacias do Rio do Peixe Araripe, NE do Brasil

This thesis presents diagenetic and provenance studies of sandstones belonging to the Rift Tectonosequence of the Rio do Peixe and Araripe basins. These basins are located in the interior of Northeast Brazil aligned along the Trend-Cariri Potiguar. Their origin is related to the Early Cretaceous rifting event. In terms of lithostratigraphy, the studied section corresponds to the Antenor Navarro, Sousa and Rio Piranhas formations of the Rio do Peixe Basin, and the Missão Velha and Abaiara formations of the Araripe Basin, outcropping in the central-west Cariri Valley. A facies analysis was performed and identified nine distinct sedimentary facies for the Rio de Peixe Basin and ten sedimentary facies for the Araripe Basin, individualized according to the different rock types and their sedimentary structures. These facies associations to led paleoenvironments interpretations and their vertical succession allowed understanding the evolution of the depositional setting during the cronostratigraphic interval studied in these basins. Based on petrographic and diagenetic studies it was possible to characterize the texture and mineralogy of these sandstones, identifying their diagenetic stage and the grain framework provenance. The petrographic study allowed to classify the lithotypes studied in both basins as quartzarenites. Such quartzarenites, in general, are rich in quartz, feldspar and lithic fragment grains, and at accessory levels tourmaline, sphene, zircon, epidote and other mineralogy. The diagenetic history of the studied rocks proved to be very complex, being characterized by a variety mineral of phases that succeeded each other during the eo, meso and telodiagenetic stages. According to the studied formation and the textural and compositional aspects of the rocks, some processes were more or less active, while others were even absent. The eodiagenetic stage is marked by mechanical infiltration of clays and early mechanical compactional processes. The mesodiagenetic phase is characterized by continuity of the mechanical compaction and the beggining of chemical compaction, with quartz and feldspar overgrowths, precipitation of kaolinite, alteration of framework grains to chlorite and illite, and finally, precipitation of opaque minerals. The telodiagenetic stage is represented by the oxidation of some grains, matrix and cements. For the provenance analysis of the studied sandstones were used ternary diagrams whose vertices correspond to the percentage of quartz, feldspar and lithic fragments. This study allowed identifies the source area of these rocks as continental blocks. It was also possible, based on the chemical stability and mineralogical maturity of the rocks, recognize that the Antenor Navarro Formation of the Rio do Peixe Basin, and the upper section of the Missão Velha Formation of Araripe Basin have less maturity and stability when compared with the other studied formations