Tectonic activation, source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil)

Abstract

Changes in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn-rift successions composition.

Comments on paper by M. Arai "Aptian/Albian (Early Cretaceous) paleogeography of the South Atlantic: a paleontological perspective"

“…According to the hypothetical paleogeographic scenario proposed by Arai (2014), the seawaters advanced towards the continental interior in a complete opposite direction of the contemporaneous flowing rivers of the Araripe and Tucano basins. Hundreds of paleocurrent data measured from distinct outcrops in the Aptian fluvial deposits of the Barbalha Formation, Araripe Basin (Assine 1994, Chagas et al 2007, Scherer et al 2015, and in the Marizal Formation, Tucano Basin (Rolim & Mabesoone 1982, Figueiredo et al 2015, indicate a consistent paleoflow towards south and southeast. Considering that the sea transgressions are constrained by the continental drainage, the paleocurrents of Aptian fluvial deposits strongly suggest that the marine transgression advanced towards the continent throughout fluvial valleys, from the Recôncavo-Tucano basin back to the watersheds located at north and northwest (Assine 1994).…”

Upper Aptian mixed carbonate-siliciclastic sequences from Tucano Basin, Northeastern Brazil: Implications for paleogeographic reconstructions following Gondwana break-up

“…After a long erosional period during the entire early Aptian, the resumption of subsidence due to the reactivation of faults generated in the rift phase (Figueiredo et al, 2015) allowed the preservation of the late Aptian sedimentation in the Tucano Basin. The lower sandstone-dominated succession with minor conglomerate was thereby generated, and its facies association is typical of deposition in rivers with braided channel patterns, which were associated with alluvial fan deposits right above the erosive paleosurface developed in the early Aptian (Freitas, 2014;Figueiredo et al, 2015;Almeida et al, 2016). The progradational pattern of the fluvial bedforms is typical of the Lowstand System Tract (LST) stratigraphic architecture.…”

“…The Gondwana rifting and the opening of the South Atlantic Ocean created Cretaceous sedimentary basins that basically consist of rift (continental) and drift (marine) megasequences separated by an evaporitic transitional post-rift megasequence of late Aptian age (Chang et al, 1988(Chang et al, , 1992. Although considered as a sag basin generated from thermal subsidence, several studies have found evidences of continued rifting tectonics during the transitional sequence (e.g., Karner et al, 2003;Chaboureau et al, 2013;Figueiredo et al, 2015).…”

“…The Marizal Formation is considered as late Aptian in age (Viana et al, 1971), based on palynomorphs positioned in the P-270 palynological zone, P-270.2 subzone (Sergipea variverrucala biozone) (Regali, 2000). This unit consists mainly of sandstones and conglomerates, attributed to be deposited in fluvial and alluvial fan systems, with localized exposures of finegrained siliciclastic deposits and lacustrine carbonates (Magnavita et al, 1994;Lima and Vilas Boas, 2000;Figueiredo et al, 2015).…”

Heterogeneidades em multiescala da Formação Marizal (Aptiano, Bacia do Tucano, BA) como análogo de reservatórios fluviais em bacias distensionais

“…Desta forma a região de estudo compreendeu a Formação Marizal (Aptiano, Bacia do Tucano, BA) que apresenta ótimas exposições de arenitos fluviais, recentemente estudadas por Freitas (2014), Carrera (2015) e Figueiredo et al (2015).…”