Variability of fluvial architecture in a poorly vegetated Earth: Silurian sheet‐braided and meandering ancestor river deposits recorded in northeastern Brazil

Abstract

Rivers with little to no influence of vegetation and their implications for the architecture of Early Paleozoic and Precambrian fluvial deposits are an important topic of investigation for both clastic sedimentology and Earth System evolution perspectives. Despite the long-held concept of a dominant style of wide, shallow sheet-braided sandy channels, growing evidence for a great variability of architectural elements in pre-vegetation settings point to the predictable occurrence of other fluvial styles, which are possibly related to areas of low-slope alluvial plains. The present work brings sedimentological descriptions and fluvial style interpretations of Silurian fluvial successions of the Serra Grande Group in northeastern Brazil, developed in a glaciated basin margin (therefore with little to no effect of vegetation). The comparison of the resulting channel body architectures integrated to paleocurrent data and a diffusion-based numerical model enabled the evaluation of the controls on fluvial architecture variability in unvegetated alluvial plains. K E Y W O R D S bar surface orientation, clinoform modelling, Early Paleozoic rivers, meandering ancestors, paleocurrents

So close and yet so far: U–Pb geochronological constraints of the Jaibaras Rift Basin and the intracratonic Parnaíba Basin in SW Gondwana

“…The palaeocurrents of the Cariri Formation indicate palaeoflow towards the NW, and subordinately to the NE (Assine, 1994;Batista et al 2012;Silvestre et al 2017), in agreement to that observed for the Tacaratu Formation (Carvalho et al 2018). The palaeocurrent (Cerri et al 2020) and fluvial architecture (Janikian et al 2019) of Ipu and Jaicós formations of Serra Grande Group corroborate the regional sedimentary dispersion pattern and indicate the presence of a marine basin to the west and NW, with a marine transgression (represented by Tianguá Formation) towards the east and SE. It is therefore plausible that this sediment route from the elevated orogenic mountain areas of the Brasiliano/ Pan-African orogens at the south and SE possibly flowed to the oceanic areas located at the west and NW margins of the Gondwana supercontinent (Fig.…”

Luminescence signals of quartz and feldspar as new methods for stratigraphic discrimination and provenance analysis of siliciclastic successions: The case of the Parnaíba Basin (Brazil) of West Gondwana

“…In this case, the colonisation of continents by plants and further periods with expanded forests influenced weathering and sediment storage in source areas and continental depositional systems, creating conditions for longer residence of mineral grains in soils and surface sedimentary deposits. The Early Paleozoic units of the Parnaíba Basin, such as the Serra Grande Group, record pre‐vegetation fluvial systems dominated by unstable bedload channels with faster sediment transport from sources to depositional sinks (Janikian et al., 2020). Appearance of vascular plants during the Devonian and latter diversification during the Pennsylvanian (Giblling & Davies, 2012, and references therein) might have contributed to the impact on the weathering conditions and denudation rates of sediment source areas of the Parnaíba Basin during the Paleozoic.…”

Cross‐strata palaeocurrent analysis using virtual outcrops

“…The deposits in outcrop LL02 (Fig. 3E) comprise part of the basal portion of the Jaicós Formation (Janikian et al., 2019). The older glacio‐fluvial Ipu Formation is exposed in the other four outcrops of the Serra Grande Group, LL01, PC01, PC02 and PC03 (Janikian et al., 2019).…”

“…3E) comprise part of the basal portion of the Jaicós Formation (Janikian et al., 2019). The older glacio‐fluvial Ipu Formation is exposed in the other four outcrops of the Serra Grande Group, LL01, PC01, PC02 and PC03 (Janikian et al., 2019). These units are separated by the transgressive succession of the Tianguá Formation (Caputo & Lima, 1984; Vaz et al., 2007), useful for stratigraphically positioning the studied outcrops in spite of the lack of detail in available geological maps (Fig.…”

“…3D) represents coarser‐grained proximal deposits, whereas PC01, PC02 and PC03 (Fig. 3A, B and C) represent finer‐grained distal successions (Janikian et al., 2019).…”