Ubiratan Ferrucio Faccini

Sequence stratigraphy of continental Triassic strata of Southernmost Brazil: a contribution to Southwestern Gondwana palaeogeography and palaeoclimate

Abstract The continental Triassic succession of southernmost Brazil comprises two second-order depositional sequences—the Sanga do Cabral (Early Triassic) and the Santa Maria (Middle to Late Triassic) supersequences. The first one includes ephemeral, low-sinuosity fluvial deposits developed on a low gradient plain. Based on fossil tetrapods, especially procolophonids, an Upper Induan age is estimated for this sequence. Facies association of the Santa Maria Supersequence indicates low-sinuosity fluvial rivers, deltas and lakes. This supersequence can be further subdivided into three third-order sequences (age provided by palaeovertebrate biostratigraphic data) as follows: Santa Maria 1 (Ladinian), Santa Maria 2 (Carnian to Early Norian) and Santa Maria 3 (probably Raethian or Early Jurassic) sequences. The Gondwanides paroxysms I and II in the Sierra de la Ventana–Cape Fold Belt are directly related to the development of both supersequences. The source area of the Sanga do Cabral Supersequence was located to the south. It consisted of an uplifted peripheral bulge situated landward of the retro-foreland system, from where older sedimentary rocks were eroded. The source area of the Santa Maria Supersequence was also positioned southwards and related to the uplifted Sul-Rio-Grandense and Uruguayan shields. The Santa Maria Supersequence stratigraphic architecture is comparable to the Triassic rift basins of Western Argentina. Diagenesis, facies and palaeontology of the studied succession suggest a dominantly semiarid climate during the Triassic.

Nonmarine sequence stratigraphy: Updip expression of sequence boundaries and systems tracts in a high-resolution framework, Cenomanian Dunvegan Formation, Alberta foreland basin, Canada

Ten allomembers, labeled J-A, have been mapped in the deltaic Dunvegan Formation using 2340 wells and 63 outcrop sections. Each allomember spans about 200 k.y., is bounded by regional transgressive surfaces, and consists of 3-10 component shingles, apparently of autogenic origin. Allomembers H-E are discussed in this article. Their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences. Sequences H-F have a sigmoidal-prismatic geometry, downlap to the southeast, and thin northwest onto the coastal plain. No differential thickening exists toward the orogen in the southwest. In contrast, sequence E thickens markedly toward the northwest. The tabular geometry of sequences H-F suggests accommodation was controlled by sea level change, whereas the wedge geometry of sequence E suggests significant tectonic tilting. Subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120-330 km updip into outcrop. The base of each sequence is characterized by shoreline backstep of 80-150 km. Transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata. Falling-stage shingles offlap seaward with little or no nonmarine equivalents updip, whereas lowstand shingles show renewed coastal onlap. In outcrop, three nonmarine systems tracts are recognized: (1) A channel-dominated, low-accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract. (Begin page 1968) (2) A lacustrine-dominated, high-accommodation systems tract comprises mudstone enclosing ribbon channel sandstones, blankets interfluves, and forms the bulk of each sequence. It is equivalent to late transgressive and early highstand systems tracts. (3) A paleosol-dominated, low-accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary. It is equivalent to the late highstand systems tract. Sequence-bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation, followed by fluvial entrenchment and clastic bypass, and represent the late highstand, falling-stage, lowstand, and early transgressive systems tracts. Coastal plain deposits record only part (perhaps

Age constraints of the glaciation in the Paraná Basin: evidence from new U–Pb dates

The absence of absolute dating in glacial deposits of the Paraná Basin prevents better understanding of the complete history of the Late Palaeozoic Ice Age in Western Gondwana and the climatic change that took place in the late Carboniferous. In this study, new U–Pb radiometric ages date the topmost glacial deposits of the Itararé Group at 307.7 ± 3.1 Ma (Kasimovian−Moscovian) and the base of post-glacial deposits of the Rio Bonito Formation at 298.8 ± 1.9 Ma (Ghzelian−Asselian). Correlation of glacial and post-glacial deposits of the Paraná Basin with other southwestern Gondwana basins shows that the end of the Late Palaeozoic Ice Age is asynchronous. Supplementary material: Laser ablation inductively coupled plasma mass spectrometry U–Pb zircon data and methods for the ash sample of the Itararé Group and the tonstein sample of the Rio Bonito Formation are available at https://doi.org/10.6084/m9.figshare.c.3278273.

Lowstand Turbidites and Delta Systems of the Itararé Group in the Vidal Ramos region (SC), southern Brazil

Turbidites have captioned the attention of sedimentologists during the last decades due their importance as hydrocarbon reservoirs. However, their relationship to delta systems still deserves further studies. This paper presents examples from a late deglacial to early post-glacial deltaic and turbidite strata exposed in the surroundings of Vidal Ramos (Santa Catarina State, Brazil), southern portion of the Parana Basin. There, the uppermost part of the Mafra Formation and the Rio do Sul Formation onlap the Proterozoic basement and comprises an up to 360 m thick package. It includes (base to top) black shales, mass transport deposits (MTD) and sandy turbidites (Mafra Formation) as well as thin bedded turbidites (tbt), including one interval of black shales and sandy turbidites, overlain by proximal delta front sandstones (Rio do Sul Formation). The analysis of the succession shows two more than 150 m thick coarsening-upwards deltaic successions composed of turbidite sand sheets at their base (prodelta), followed by partially collapsed thin bedded turbidites (delta slope wedge) and delta front sandstones. Both turbidite sand-sheets abruptly overlay black shale intervals related to maximum flooding surfaces and therefore record correlative conformities. A detailed stratigraphic section elaborated from the correlation of four logs (1/100) suggests that distal delta front sands includes both thin bedded turbidites and wave reworked sands whereas the proximal delta front was dominated by long-lived underflows (hyperpycnal flows). The succession suggests that the most expressive turbidite beds (base of the delta systems) have resulted from relative sea-level falls (early lowstand) whereas the thin-bedded turbidites were related to the development of the late lowstand wedge. Black shales represent the transgressive systems tract and HST were not deposited or preserved in the area. High sediment supply associated with lowstand tracts could explain the occasional (Vidal Ramos) to common occurrence of slope failures (slumps and diamictites) involving thin bedded turbidites and delta front sandstones. This situation is quite logical in terms of deglacial periods, and resulting high sediment supply, within a long-term icehouse context, with prevalence of lowstand to transgressive settings.

Xylopteris (Frenguelli) Stipanicic & Bonetti in the Middle-Upper Triassic (Santa Maria Formation) of Brazil

Abstract. The fossil genus Xylopteris was conceived for Corystospermales fronds presenting pinnate and basally bifurcate pinnae bearing narrow one-veined segments. Later, the possibility was proposed that some of its forms may include 2–3 bifurcated fronds with lobed pinnules and more complex venation. The fossil record attests to its exclusive occurrence in Middle-Upper Triassic Dicroidium floras from Gondwana. Among these, a significant portion of Xylopteris-related morphotypes was included either in the genus Dicroidium or as its subgenus. Such taxonomic placement was adopted in previous studies in Brazil. The new morphotypes herein described present an unsuspected diversity marked by well-preserved frond impressions accompanied by partially preserved Umkomasia strobili. They were identified in a limited exposure of lacustrine shales, at the top of the main fluvial succession of the Passo das Tropas Member, the lower lithostratigraphic unit of the Santa Maria Formation, in the Paraná Basin succession. Given the absence of anatomical structures, the proposed affinity with Xylopteris is based on the original characteristics assigned in the emended diagnosis and in comparisons with other Gondwana records. The described materials attest to the presence of widely distributed types, such as X. elongata, X. spinifolia, X. remotipinnulia and X. rigida as well as X. densifolia, which is restricted to South America and Africa. X. rotundipinnulia, a new generic combination and new species, is proposed for material from Southern Brazil and is comparable to that found in the Molteno beds. The obtained data expands the paleogeographic distribution of the genus and extends the age of the Dicroidium flora in Southern Brazil to the Carnian.

Divulgação de dados ambientais e socioeconômicos na internet usando um modelo baseado no uso de ferramentas livres

Um modelo baseado no uso de ferramentas livres e apresentado, visando a publicacao de dados socioeconomicos e ambientais e divulgacao de informacoes na internet. A estrutura deste modelo permite que as informacoes sejam apresentadas sob a forma de tabelas, graficos, fotos ou mapas para a web. A escolha de um determinado formato de apresentacao da informacao e determinada de acordo com os objetivos do desenvolvedor. Como resultado do trabalho, o usuario criara um banco de dados geograficos virtual para gerar informacoes estaticas e mapas interativos para a web. As principais ferramentas utilizadas foram o sistema de informacoes geograficas Spring, banco de dados relacional MySQL, PHP script e o servidor Apache HTTP. Palavras-chave: mapeamento via Web, ferramentas livres, Spring Web, Sistema de Informacao Geografica.