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The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ 13 C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ 13 C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ 13 C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ 13 C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin. [ABSTRACT FROM AUTHOR]

The Bambuí Group is a lithostratigraphic unit that comprises a mixed carbonate-siliciclastic platform deposited in a foreland basin. It is a 1st order sequence that filled the São Francisco Basin during the Ediacaran-Cambrian in southeast Brazil. The Lagoa do Jacaré Formation is the second carbonate unit of the Bambuí Group and is related to a 2nd-order regressive hemicycle composed of dark gray shallow water carbonates with high positive ẟ1³C values (>+10‰) related to the upper part of the Middle Bambuí Excursion (MIBE). We described four outcrops in the center-north of Minas Gerais state (Paraopeba, Curvelo, Montes Claros and Ubaí areas) coupled with ẟ13C and ẟ18O, and SEM-EDS analysis in order to support detailed facies analyses. One seismic line and three well logs in the south part of the Januária High were also used to define the stratigraphic framework of the Lagoa do Jacaré Formation in the Bambuí Foreland Basin system. Eight facies were interpreted from the outcrop data and grouped into five facies associations, that represent peritidal zone (FA1), ooidal sand shoals (FA5), tempestites of mid ramp (FA3), fine-grained carbonate of outer ramp (FA4), and fine-grained siliciclastic from offshore (FA2). The strong presence of terrigenous material (quartz, feldspars, muscovite, biotite, apatite) with some authigenic/diagenetic minerals (pyrite, titanite, rutile) in all facies are the main petrographic aspect of the studied carbonate rocks, related to high sedimentary input and some events during early diagenesis. FA1 with lower mean values of ẟ1³C (+9‰) predominates in the north, meanwhile FA3 is the main association in the south with higher ẟ1³C mean values (+12‰). This difference is probably related to the stratigraphic differences between the basal section (at south) and upper section (at north) of the Lagoa do Jacaré Formation. The Januária High was the main controlling element for the deposition of the carbonate ramp in the north sector of the basin, close to the Ubaí and Montes Claros cities. Probably, this structural high also played an important role as source area in the forebulge sector, uplifted by flexure due to the orogeny of the Brasília and Araçuaí (still in development) Belts (∼540-520 Ma). To the east, a N–S carbonate ramp system was developed in the back-bulge sector according to the main paleocurrents measurements. This ramp is related to a 300 m thickness section of the Lagoa do Jacaré Formation that was firstly identified and correlated to the successions on the surface using well logs, possibly registering at the top the decreasing in the ẟ1³C values, after the main stages of the MIBE probably in close association with Ediacaran-Cambrian boundary, related to the assembling of the Gondwana Supercontinent recorded in this region of southeast Brazil. • The Lagoa do Jacaré Formation (LJF) has more than 300 m of thickness. • The LJF deposited in a homoclinal carbonate ramp in the central Bambuí Basin. • The LJF increase in thickness from Januária High to Montes Claros. • a remarkable assemblage of siliciclastic minerals was first identified in the LJF. • The LJF was deposited in the back-bulge and forebulge of a foreland basin system. [ABSTRACT FROM AUTHOR]

The basal units of the Vazante Group, the Santo Antônio do Bonito and Rocinha formations, present different stratigraphic records and younger ages than the rest of the group. These units are characterized by diamictites, sandstones, pelites and rare carbonates originated from subaqueous gravitational sedimentation. U–Pb geochronological data in detrital zircon indicate a Tonian maximum depositional age for both formations. The youngest zircon grains yielded ages ranging from 903 to 935 Ma. The main source for zircon is Paleoproterozoic (mainly Rhyacian and Orosirian) to Mesoproterozoic (Calymmian and Ectasian) areas being probably the São Francisco paleocontinent the main area. Due to the complete absence of ice-rafted debris within fine-grained sediments in the Santo Antônio do Bonito Formation, we interpret a gravitational reworking as the main process of diamictites deposition, probably during a period of ice retreat and sea level rise. The U–Pb data corroborate a lateral correlation between the Santo Antônio do Bonito and Rocinha formations with the glaciogenic Jequitaí Formation (Bambuí Group). From east to west, glacial sediments of the Jequitaí Formation were reworked probably by a slope-apron system during a late-glacial to post-glacial stage on the western margin of the São Francisco paleocontinent. Therefore, the Vazante Group can be divided into two successions: the upper Lagamar-Serra do Garrote formations and the lower Santo Antônio do Bonito-Rocinha formations. The Lagamar-Serra do Garrote sedimentation comprises a late Mesoproterozoic mixed carbonate-siliciclastic deposition in passive margins. The second succession is a gravitational slope-apron resedimentation and probably correlates with the Neoproterozoic glacial rocks of the Jequitaí Formation from the Bambuí Group. Finally, the collisional phase of the Brasília Belt was responsible for stratigraphic inversion, placing the older Lagamar-Serra do Garrote formations over the younger Santo Antônio do Bonito-Rocinha formations. • New regional and local geological mapping of the basal formations of the Vazante Group. • Gravitational sedimentation record in the basal formations of the group, relate to a subaqueous slope-apron system. • New U–Pb data of the Santo Antônio do Bonito and the Rocinha formations and its provenance change during Neoproterozoic. • Lateral correlations between Santo Antônio do Bonito and Jequitaí formations, during final stages of the ice retreatment. [ABSTRACT FROM AUTHOR]

One of the most essential and valuable applications of high-resolution sequence stratigraphy is reservoir zonation and characterization. Establishing a hierarchical chronostratigraphic framework comprising sequences at multiple scales is crucial to identify main reservoir heterogeneities that compartmentalize the fluid flow in the subsurface. In this context, this paper proposes a workflow that integrates different signal analysis techniques to identify sequences of multiple hierarchies from a series of stratigraphic data. The Continuous Wavelet Transform (CWT), Detrend Error Log (DTEL), and Integrated Detrend Error Log (INDTEL) techniques are utilized to process gamma-ray data obtained from outcrops of the Yacoraite Formation, which are conventionally employed as analogs for reservoir characterization. Our results suggest that CWT fits better with higher frequency cycles, while INDTEL shows a good fit with medium frequency cycles. In addition to these techniques, Hidden Markov Models were also applied, predicting T-R cycles as hidden states from the facies transition matrix and possible occurrence of missed beats. All these methods were scripted in the Python programming language, enabling the generation of fast and interactive outputs. This approach brings parameters that can guide the construction of stratigraphic models by automated processes. • Multifrequency transgressive-regressive cycles were obtained from spectral decompositional techniques on Gamma-Ray proxies. • High-Frequency output curve from Continuous Wavelet Transform has direct relationship with high-frequency transgressive-regressive cycles. • INDTEL method is a powerful tool to detect hidden trends and well correlation. • Hidden-Markov Models show high-frequency transgressive-regressive cycles as hidden states from facies transition • The integrated aplication of the methods proves to be a promising tool to help detect missed-beats. [ABSTRACT FROM AUTHOR]

• Extensive new Ba isotopic survey of modern barites. • First Proterozoic Ba isotopic results. • Provides genetic model for enigmatic post-Marinoan barite formation. • Provides evidence for stratified post-Marinoan ocean. • Provides arguments for why barite horizons are confined to Marinoan and not Sturtian or Paleoproterozoic strata. Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or 'marine'), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO 4 -poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record. [ABSTRACT FROM AUTHOR]

The Serra da Saudade Formation is part of the Bambuí Group, a cratonic cover from the western São Francisco craton. It is composed by siliciclastic sediments deposited in a foreland basin during a transgressive event. The Serra da Saudade Formation is mainly represented by rhythmites, siltstones (locally glauconitic) and rare sandstones. The glauconitic siltstone was deposited during a maximum flooding surface and sediment starvation, which allowed high concentrations of probable volcanic-sourced potassium. The interpretation of the depositional age of the Bambui Group had multiple turnovers in the last decades. Finding and dating synsedimentary volcanic rocks is essential to solve this conundrum. This paper presents the first U-Pb direct dating of the Bambuí Group from zircon grains recovered from a volcaniclastic layer interbedded with glauconitic siltstones from the upper Serra da Saudade Formation. A total of 107 U-Pb ages were obtained by LA-ICP-MS and plotted into a Concordia diagram. The provenance signature comprises a wide range of detrital zircon ages (1.0–2.8 Ga). These data represent inherited zircon grains incorporated into the magma during magmatic activity that produced the volcanic sediment, or to dilution and reworking of volcanic ashes that mixed to fine-grained clastic sediments prior to deposition. A significant amount of 10 highly concordant, prismatic zircon grains clustered into a well constrained age of 520.2 ± 5.3 Ma, which represent the explosive volcanic eruption age, and by extent, the depositional age of the upper Serra da Saudade Formation. Since the currently final thrust stacking ages from the Brasilia Belt and the Araçuaí Belt are dated ca. 600 and 540 Ma, respectively, one must carefully look for the real age of the deformation event that affected the Bambuí Group over the São Francisco craton. Image 1 • Stratigraphy, petrography and geochronology of Serra da Saudade Formation, Bambuí Group. • The glauconitic siltstone was deposited in a foreland basin during low sedimentation rates and related to volcanic processes. • The volcanoclastic layer described in the upper Bambuí Group reveals a sedimentation age of 520.2 ± 5.3 Ma. • The Bambuí Group spanned the Ediacaran-Cambrian boundary and was deformed during the Cambrian Period. [ABSTRACT FROM AUTHOR]