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The Arroio do Silva Pluton comprises quartz-rich syenite-monzonite-diorite rocks, with subordinate lamprophyre as enclaves. Compositional and textural variations lead to the identification of three main varieties: (i) quartz monzonite to syenite, (ii) quartz monzonite to monzodiorite and (iii) quartz diorite. The transition between all rock types is gradational and marked mostly by the increase of mafic mineral phases, especially biotite, and by the K-feldspar content, which is characteristically euhedral in the quartz monzonite to syenite variety and becomes subhedral to anhedral towards diorite compositions. Geochemical features corroborate field relations and both point to magma mingling as the main differentiation process. Syenite is considered to be the felsic endmember, whilst the mafic one has dioritic composition. Different degrees of interaction between these magmas result in hybrid varieties represented by quartz monzonite to monzodiorite. A third magma type is observed as ultrapotassic lamprophyric enclaves, but its influence in the mixing processes seems to have been minor. Both mafic and felsic magmas have K 2 O/Na 2 O ratios between 1 and 2, compatible with their shoshonitic affinity, whilst ratios slightly above 2 characterize lamprophyric enclave magmas as ultrapotassic. The source of shoshonitic and ultrapotassic magmas, according to trace element and isotope evidence, is probably a phlogopite-bearing mantle which was affected by previous subduction of Paleoproterozoic or Neoproterozoic age. The variation of ultrapotassic to shoshonitic magmas is probably controlled by variation of phlogopite contents in the mantle source. U Pb zircon crystallization age of 578 Ma (LA-MC-ICP-MS) determined for the ASP quartz monzonite to syenite variety is in agreement with the Neoproterozoic post-collisional period of the Dom Feliciano Belt. This age value is also in agreement with that of other syenitic associations from south Brazil, such as the Piquiri Syenite Massive, that records similar chemical signatures. Therefore, these syenitic associations are taken to represent previously metasomatized mantle sources in late post-collisional setting from the Brasiliano/Pan-African Cycle in southermnmost Brazil. • Syenite-monzonite-diorite association of shoshonitic affinity resulted from magma mingling processes. • Minor volume of lamprophyric ultrapotassic rocks indicates depth mantle sources. • Ediacaran U Pb zircon LA-MC-ICPM-MS age and geological context indicates post-collisional period. • Metasomatized mantle sources contribution at post-collisional period in southern Brazil. [ABSTRACT FROM AUTHOR]

• Re-interpretation of the paleoenvironmental evolution of the São Francisco Basin. • Results indicate a depositional age for the Bambui Group of > 550 Ma, significantly older than recently reported. • Six sequences record the Marinoan and Gaskiers glaciations and track oxygen fluctuations through the Ediacaran. • Loess form most of the siltstones and stimulated photosynthetic oxygen production in surface waters. The Bambui Group is a ca. 2,000 m-thick mixed biochemical-siliciclastic sedimentary succession that accumulated in the Sao Francisco Basin, central Brazil. Its age is contentious, but deposition during the Cryogenian-Ediacaran (ca. 635–550 Ma) is consistent with a new sequence stratigraphic model presented herein and previously published geochemical and structural data. Six stratigraphic sequences are recognized that record depositional evolution from an epeiric sea to foreland basin during the Marinoan snowball glaciation (ca. 635 Ma) to shortly after the Gaskiers (ca. 580 Ma) glaciation. Although this stratigraphic architecture differs from the classic lithostratigraphic and more recent chemostratigraphic and sequence stratigraphic interpretations of the Bambui Group, it is supported by correlation to other Cryogenian-Ediacaran successions globally. Collectively, these six sequences preserve a robust record of seawater redox structure leading up to the oxygenation threshold that triggered the evolution of multicellular animals in the Ediacaran. Sequence 1 is composed of Marinoan glacial deposits and an overlying cap carbonate with aragonite fan pseudomorphs and barite. Sequence 2 is composed of lime-mudstone that changes laterally into loess-rich peritidal phosphorites, suggesting oxygen stratification in shallow paleoenvironments. Sequence 3 is a carbonate succession with abundant stromatolites implying widespread oxygen production. The top of Sequence 3 is marked by a regional subaerial unconformity developed during uplift associated with the onset of the Brasiliano-Pan African Orogeny. Sequence 4 signals a return to loess derived sedimentation. Distal deposits contain abundant organic matter with framboidal pyrite reflecting bacterial sulfate reduction in low sulfate Ediacaran seawater. Sequence 5 is composed of well-developed aggradational parasequences composed of alternating deep subtidal organic-rich siltstones and shallow-water carbonate grainstones. Their well-defined cyclicity is interpreted to record extreme sea level fluctuations during the onset of the Gaskiers glaciation. Stromatolites suggest an oxygen-stratified water column. Sequence 6 marks the change from an epeiric sea to a foreland basin. Interbedded basinal glauconitic siltstone and shale loess-rich are correlative with shoreface sandstones. Authigenic glauconite requires suboxic bottom waters to precipitate and thus reflects oxygenation of distal settings. Most of the deposition ended by ca. 560–550 Ma when the entire Bambui Group was deformed during the assembly of West Gondwana. In sequences 1, 2, 3, 4, 5, and the lower portion of 6, the lateral continuity of lithofacies, predictable layer-cake stratigraphy, and lack of fluvial coarse siliciclastic deposits are characteristics of epeiric sea successions. The appearance of immature sandstone, poorly sorted conglomerate, braided fluvial deposits, and synsedimentary deformation in the upper part of Sequence 6 are interpreted as the onset of foreland basin development. Stacking relationships of redox sensitive, authigenic lithofacies in both the epeiric sea and foreland phases support recent research suggesting seawater redox conditions were in a state of flux during the apex of the purported Neoproterozoic Oxygenation Event. Organic matter and authigenic pyrite in Sequences 4 and 5 reflect increased primary productivity in surface waters fertilized by nutrients such as P and Fe adsorbed on loess particles. This mechanism could be expanded to a global scale and have contributed to the increase in atmospheric and oceanic oxygen levels. These findings redefine and highlight the significance of the Bambui Group for Neoproterozoic Earth history. [ABSTRACT FROM AUTHOR]