Controls on Early Cretaceous desert sediment provenance in south‐west Gondwana, Botucatu Formation (Brazil and Uruguay)

Abstract

The Lower Cretaceous Botucatu Formation records the development of widespread dry–aeolian desert sedimentation throughout the Paraná Basin in south‐west Gondwana. To reconstruct the provenance of the aeolian sediment, petrography, granulometric analysis, U‐Pb detrital zircon ages have been determined from along the southern basin margin in Rio Grande do Sul state (southern Brazil) and Uruguay (Tacuarembó region). The dataset reveals a mean composition Qt89F8L3, comprising very fine to medium‐grained quartozose and feldspatho‐quartzose framework. Heavy mineral analysis reveals an overall dominance of zircon, tourmaline and rutile grains (mean ZTR0.84) with sporadic garnet, epidote and pyrolusite occurrences. The detrital zircon U‐Pb ages are dominated by Cambrian to Neoproterozoic (515 to 650 Ma), Tonian to Stenian (900 to 1250 Ma) and Orosirian to Rhyacian (1.8 to 2.2 Ga) material. The detrital zircon dataset demonstrates a significant lateral variation in sediment provenance: Cambrian to Neoproterozoic detrital zircons dominate in the east, while Tonian to Stenian and Orosirian to Rhyacian ages predominate in the west of the study area. Sandstones are quartz‐rich with dominantly durable zircon, tourmaline and rutile heavy mineral suite, with subtle but statistically significant along‐strike differences in heavy mineral populations and detrital mineralogy which are thought to record local sediment input points into the aeolian system. The similar age spectra of Botucatu desert with proximal Paraná Basin units, the predominance of quartzose, and zircon, tourmaline and rutile components, suggests that recycling is the mechanism responsible for the erg feeding.

Novo Hamburgo Complex formed by hydrothermal, explosive injection of Botucatu erg sand into extensive tracts of Paraná Volcanic Province (S Brazil)

“…Eolian sandstones of the Botucatu Formation are exposed in the southern lowlands of the Herveiras cuesta, covered along the escarpment by basalt, basaltic andesite and rhyodacite of the Serra Geral Group. Description of the paleoerg in the southern portion of the Paraná Basin is in Bertolini et al (2020). Injected sandstones of the Novo Hamburgo Complex are minor, hosted in the volcanic succession.…”

“…1). The Botucatu Formation forms the underburden of the volcanic group and is made up of eolian deposits (e.g., Bertolini et al 2020); the upper part (60 m) is intercalated with the first flows of the volcanic group. Sand injectites occur in all lava flows of the volcanic group from the first to the topmost.…”

Ordination analysis in sedimentology, geochemistry and palaeoenvironment—Background, current trends and recommendations

“…A better option would have been to draw convex hulls (Arreguín‐Rodríguez & Alegret, 2016; Tomašových, 2004) if the groups are known. When they are not known, clustering/machine learning without supervision for unknown groups (Bertolini et al, 2020; Höltke et al, 2016) would be a preferred way of identifying the groups.…”

Sand and mud generation from continental flood basalts in contrasting landscapes and climatic conditions (Paraná–Etendeka conjugate igneous provinces, Uruguay and Namibia)

“…1; O'Connor & Duncan, 1990; Peate, 1997). In the Paraná and Huab basins of South America and Namibia, the volcanic sequences either non‐conformably cover Precambrian basement or stratigraphically overlie, and are locally intercalated with, aeolian quartzarenites of the Botucatu (or Tacuarembó; Waichel et al ., 2012; Bertolini et al ., 2020) and Twyfelfontein (or Etjo) formations (Jerram et al ., 2000), respectively. In the Paraná Basin, volcanic rocks extend for more than 1 million km 2 among southern Brazil, Uruguay, eastern Paraguay and northern Argentina, reaching a thickness of ca 1.7 km in the north.…”