Navegando por Autor "RUDNITZKI, Isaac Daniel"

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Fácies e isótopos de carbono e oxigênio da Formação Nobres, Neoproterozóico da Faixa Paraguai Norte, Mato Grosso.
(Universidade Federal do Pará, 2011-06-16) RUDNITZKI, Isaac Daniel; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The lastest stages of orogenic evolution of the Northern Paraguay Belt, south of the Amazon Craton, are related to a closure of a passive margin in the Neoproterozoic-Cambrian transition. In this basin, the predominant carbonate sedimentation of the Araras Group was succeeded by siliciclastic deposits of the Alto Paraguay Group. Events that led to the inhibition of carbonate sedimentation were partially recorded in the Nobres Formation, uppermost unit of the Araras Group. In the southern part of the Northern Paraguay Belt, in the Cáceres region, state of Mato Grosso, Central Brazil, the Nobres Formation overlies in unconformity the dolostones of the Serra do Quilombo Formation, and is overlain unconformably by coastal siliciclastic deposits of the Raizama Formation of the Alto Paraguai Group. The Nobres Formation consists of shallowing / brining upward small-scale arid peritidal cycles subdivided into two members: (i) lower member, composed of massive dolostone, intraclastic dolopackstones with enterolithic and megaripple bedding, wavy lamination with mud drapes, dolostone with silicified evaporite molds and domic to stratiform stromatolites, interpreted as tidal flat/sabkha deposits; and (ii) upper member, consisting of massive dolostone, dolomitic sandstone with megaripple bedding, wavy lamination with mud drapes, domic to stratiform and wrinkled stromatolites, dolostones with silicified evaporates molds, sandstones with low angle and climbing ripple cross lamination and mudstones with even parallel and wavy lamination, interpreted as mixed tidal flat deposits. The chemostratigraphic framework of Nobre Formation includes values of 13C and 18O between -2.19 and 0, 27‰VPDB and -7.42 and -4.25‰VPDB, respectively. The δ13C values are primary and representative of the original composition of Neoproterozoic seawater. The analysis of the δ13C stratigraphic curve in combination with the facies interpretation and following the Ediacaran stratified ocean model, allowed the identification of four isotopic patterns of the studied succession: type I, related to the storm wave to storm influenced shallow platform of Serra do Quilombo, with δ13C values near zero ranging from -0.27 to 0.4 ‰VPDB interpreted as a mixing of stratified waters of the ocean; type II, which refers to the transition between Serra do Quilombo and Nobres formations, with δ13C values ranging from -0.12 to 0.41 ‰VPDB, whose positive trend is interpreted as the fixation of 12C by biological activity; type III, defined as the typical isotopic signal of the Nobres Formation, trending and ranging from uniform values δ13C from -1.80 to -0.13‰VPDB related to changes in sea level; and type IV, that consist of crinkled pattern with δ13C values from -2.19 to -0.73‰VPDB indicative of isotopic reequilibrium of peritidal waters. The stacking of peritidal cycles, up to 200 m thick, suggests continuous and recurrent generation of accommodation with probably linked to tectonic subsidence. The siliciclastic inflow in the end of the deposition of the Nobres Formation, hindered the carbonate sedimentation, and it is attributed to uplift of source areas linked to the initial phase of the closure of Clymente Ocean, during the Pampean-Araguaia orogeny at the Neoproterozoic-Cambrian limit.
Acesso aberto (Open Access)
Paleoambiente e quimioestratigrafia da porção superior do Grupo Araras, neoproterozoico da faixa Paraguai Norte, estado do Mato Grosso.
(Universidade Federal do Pará, 2015-06-22) RUDNITZKI, Isaac Daniel; ADER, Magali; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
In the central portion of the South-America Platform occurs the carbonate succession of the Araras Group, that register an extensive carbonate platforms of the Neoproterozoic, developed along a passive margin at S-SW portion of the Amazon Craton. These sedimentary basins were submitted to a compressional collisional event at Ediacaran-Cambrian transition, resulting in the origin of the Paraguay Belt. While the lower Araras Group are recognized as a post-glacial record of the Marinoan event (~635 Ma), the final paleoceanographic and sedimentary events that led the end of carbonate deposition are discussed, for the first time, in this thesis. The upper Araras Group, represented by Serra do Quilombo and Nobres formations, are the last stage of Araras carbonate platform sedimentation. These units are covered by siliciclastic deposits of Alto Paraguay Group, Middle Ediacaran, which the basal deposits are related to the glacial Gaskiers event (~580 Ma), reported only on the eastern portion of the Belt. Stratigraphy, sedimentology and carbon isotope studies were performed on carbonate rocks exposition in Cáceres and Nobres regions, respectively the western and eastern portion of the belt, Mato Grosso state, Brazil. The Serra do Quilombo and Nobres formations are a unique carbonate ramp in a homoclinal system composed by: i) deep ramp with massive thin dolostone of offshore. ii) Middle ramp with massive thin dolostone, intraclastic and sandy dolostone with hummocky and swaley cross stratification, planar and wave lamination, oncolitic dolostone with wavy bedding and massive oolitic dolostone, from shoreface, oolitic bar complex, and foreshore/shallow subtidal zones; and iii) inner ramp comprising in massive thin dolostone, intraclastic dolostone and dolomitic sandstone with megaripple bedding, microbialites, chert, evaporite molds, laminated sandstone mudstone, deposited in tidal flats. These deposits were developed during highstand conditions after the Marinoan transgressive event , and preceding the implantation of siliciclastic platform from Alto Paraguay Group during the Ediacaran-Cambrian transition. The palinomorphs assemblages from Nobres Formation are represented by spheroidal forms, such as Leiospharidia, rare filamentous and acanthomorphous acritarchs represented mostly by Tanarium correlated to biozone ECAP (Ediacaran Complex Acantomorph Palynoflora) that suggest an age between 600-550 Ma. The High frequency stratigraphy appoint to orbital force as the principal mechanism responsible to accommodation space generation and peritidal cycles composition, and secondarily influenced by tectonic. The patters of carbon isotopes from carbonate (δ13Ccarb), organic matter (δ13Corg) and the coupling of carbon isotope composition (Δ13Ccarb-org = δ13Ccarb - δ13Corg) associated with low TOC suggests an oxidant ocean in equilibrium with atmosphere, with minimal redox variation on sediment/water interface, that includes: i) anoxic layer with δ13Ccarb around ~0‰ and δ13Corg <-28‰, restrict to the distal zone of deep ramp with early organic diagenesis conduct by chemosynthetic organism; ii) oxic layer with δ13Ccarb around ~0‰ and δ13Corg between -28 a -25‰ in open sea system of deep and middle ramp, with primary photosynthetic activities; iii) oxic layer with low pCO2 associates to positives signal of δ13Ccarb (+3‰) and δ13Corg (>-25‰) in shallow middle ramp associated with high ration of inorganic carbonate precipitation; and iv) oxic layer restrict features by negative δ13Ccarb (-2‰) and δ13Corg between -31 to -25‰, exclusive to inner ramp, related to primary photosynthetic production and effective organic early diagenesis drive by sea level changes. These data define the upper Araras Group as the record of a carbonate ramp with restrict coastal environments, on an oxidant ocean, tropical zones with warm waters, high evaporation rate and photosynthetic biomass, during the Middle Ediacaran. The pre-glacial influence indicated by carbon cycles anomalies or glacioeustasy they were not documented to the upper Araras Group. The final sedimentation stage of Araras carbonate platform was influenced by initial continental uplift source areas responsible for the siliciclastic input on carbonate coastal zone, preceding a progradation of continental-coast systems from Alto Paraguay Group at Middle Ediacaran.
Acesso aberto (Open Access)
Reavaliação paleoambiental e estratigráfica da Formação Nobres do Grupo Araras, Neoproterozóico da Faixa Paraguai, região de Cáceres (MT)
(2012-12) RUDNITZKI, Isaac Daniel; NOGUEIRA, Afonso César Rodrigues
Outcrop-based facies and stratigraphic studies in the region of Cáceres, State of Mato Grosso, Brazil, subdivided the Nobres Formation into: lower member, composed of dolostone, intraclastic dolopackstones, sandy dolostones, stratiform stromatolites and evaporitic molds, interpreted as tidal flat/sabkha deposits; and upper member, constituted of dolostone, dolomitic sandstone, stratiform to domal and wrinkled stromatolites, evaporite molds, sandstones and mudstones, interpreted as mixed tidal flat deposits. The stacking of these deposits up to 200 m thick is composed by meter-thick shallowing/brining upward cycles related to a hot arid climate. The peritidal cycles also suggest continuous and recurrent generation of accommodation linked to tectonic subsidence. The siliciclastic inflow at the end of the deposition of the Nobres Formation that hindered the carbonate sedimentation and is attributed to the uplift of source areas linked to the initial phase of closure of the Clymene Ocean, during the Pampean-Araguaia Orogeny, at the limit Neoproterozoic-Cambrian.