The Ediacaran Salinas turbidites, Araçuaí Orogen, MG: tectonics and sedimentation interplay in a syn-orogenic basin

ABSTRACT:

The Ediacaran Salinas Formation exposed in the northern Araçuaí 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.

KEYWORDS:
Syn-sedimentary deformation; Araçuaí orogen; Salinas Formation; turbidite; tectonic and sedimentation