Morphology, accumulation and preservation of draa systems in a Precambrian erg (Galho do Miguel Formation, SE Brazil)

A Mesoproterozoic hybrid dry-wet aeolian system: Galho do Miguel Formation, SE Brazil

“…All these surfaces were restored with respect to the original palaeohorizontal. Palaeowind orientations have been previously deduced by Abrantes et al (2020) and Mesquita et al (2021) to be towards N-NE; we used these data, corroborated by measurements underpinning this research, to describe the exposures of the architectural elements. The following sedimentary structures were used as reliable indicators of palaeohorizontal: (i) thin layers of irregular horizontal beds, (ii) vortex-rippled layers and (iii) erosional bounding surfaces atop compound or single sets of cross-strata when overlain by planar-parallel sandstone strata.…”

“…Low-grade metamorphism transformed the original quartzarenites of Galho do Miguel Formation into metaquartzarenite. Cross-stratified sets, 0.1 to 6 m thick, and planar parallel stratification sets, 0.1 to 6.5 m thick, are peculiar characteristics of this unit (Abrantes et al, 2020;Mesquita et al, 2021). The base of the unit is composed of marine deposits that are transgressive on the Sopa Brumadinho Formation (Dossin et al 1987;Santos et al 2013); the top is overlain by coastal and marine deposits (Conseilheiro Mata Group) (Santos et al, 2015).…”

“…The base of the unit is composed of marine deposits that are transgressive on the Sopa Brumadinho Formation (Dossin et al 1987;Santos et al 2013); the top is overlain by coastal and marine deposits (Conseilheiro Mata Group) (Santos et al, 2015). Based on detailed sedimentological study (Abrantes et al, 2020;Mesquita et al, 2021) the Galho do Miguel Formation was interpreted as the preserved record of a complex aeolian system, characterised by megadunes (draas), simples dunes and sand sheets subjected to climate-driven water-table variations, which caused temporal alternations of aeolian dune fields (ergs) and sands sheets. Based on dip-azimuth measurements of isolated transverse dune foresets, a general palaeowind direction towards E-NE has been tentatively inferred (Abrantes et al, 2020;Mesquita et al, 2021).…”

“…This study examines and discusses the apparently limited architectural complexity of Precambrian aeolian depositional systems, compared to what would be expected for a Precambrian, "bare-surface" Earth, where the action of the wind acting on plentiful source of loose and dry sediment should have been more effective at inducing complex aeolian system development (Bose et al, 2012;Rodríguez-López et al 2014;Mesquita et al, 2021, see their Supplementary Material 1 and 2).…”

“…This paper examines the possible factors that led to the construction, accumulation and preservation of the Galho do Miguel Formation, produces a depositional model for this unit and seeks to explain the common occurrence of aeolian systems in humid climate setting and only the rare preservation of complex and large aeolian bedforms in Proterozoic sedimentary successions (cf. Mesquita et al, 2021; their Supplementary Material 1 and 2 ).…”