Abstract
The Ediacaran Salinas Formation exposed in the northern Aracuai orogen is made up of syn-orogenic turbidites deposited between 580 and 560 Ma. Aiming to investigate how tectonic and sedimentary processes interact during the development of a flysch basin, we carried out a detailed field-based sedimentological and stratigraphic investigation of the Salinas Formation in its type-area located in northern Minas Gerais. Lithofacies and lithofacies assemblages recognized in the unit represent proximal to distal turbidite fan deposits, all of them affected by soft-sediment deformation. Based on the amount of lateral displacement and sediment volume involved, we distinguished four classes of soft-sediment deformation structures. The vertical facies changes of the whole Salinas Formation characterizes a coarsening-upward 1st-order sequence that record a general southwest-south progradation of a turbidite fan system fed from the north. The overall organization of the 25-60 m-thick fining-up cycles are especially elucidative of the interplay between tectonic and sedimentary processes during the accumulation of the Salinas turbidites. They initiate with thick sandstone beds deposited on top of intensively deformed strata, continuing with various sandy turbidite pulses, and ending with fine-grained sediments. In our view, they record the retraction and reorganization of the basin fill system after a sequence of seismic events.
Highlights
Two categories of syn-orogenic basins, namely, foreland and remnant ocean, are sites in which thick packages of turbidites can accumulate and be incorporated in the evolving orogenic edifice (e.g., Ingersoll 2012, Allen et al 2015)
Because of the geological setting and sedimentary processes associated with these successions, the term flysch was used in the past to denote a tectofacies of the geosyncline cycle and, for a while, as synonymous of turbidites
The Ediacaran Salinas Formation, made up of muddy, sandy and conglomeratic turbidites metamorphosed under greenschist to amphibolites facies conditions, occupies a relatively large area of the Araçuaí orogen located between the towns of Taiobeiras, Salinas, and Minas Novas in northern Minas Gerais (Pedrosa-Soares et al 2001, 2008, Lima et al 2002, Santos et al 2009) (Fig. 1)
Summary
Two categories of syn-orogenic basins, namely, foreland and remnant ocean, are sites in which thick packages of turbidites can accumulate and be incorporated in the evolving orogenic edifice (e.g., Ingersoll 2012, Allen et al 2015). Having this question in mind we performed a detailed sedimentological and stratigraphic study in a representative section of the formation, which is exceptionally well exposed in a series of road cuts and quarries located between the towns of Taiobeiras, Salinas and Rubelita in northern Minas Gerais, the type area of the unit This particular section comprises turbidites that preserve their typical sedimentary features, constituting the best site for the purpose of our investigation. In the remaining portions of its occurrence, the formation is separated from glacial and post-glacial units of the Macaúbas Group by a regional unconformity, and intruded by post-collisional granites of the G4-Supersuite (Pedrosa-Soares et al 2001, Alkmim et al 2007, Santos et al 2009, Peixoto et al 2018). The Macaúbas gulf was converted into the Salinas basin, a remnant ocean basin sensu Ingersoll (2012)
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