Sedimentology (2020) doi: 10.1111/sed.12715 Controls on Early Cretaceous desert sediment provenance in south-west Gondwana, Botucatu Formation (Brazil and Uruguay) GABRIEL BERTOLINI*† , JULIANA C. MARQUES† , ADRIAN J. HARTLEY‡ , ATILAA.S.DA-ROSA§ , CLAITON M. S.SCHERER† ,MIGUELA.S.BASEI¶ and JOSE C. FRANTZ† *School of Geosciences, King’s College, University of Aberdeen, Aberdeen, AB24 3FX, UK (E-mail: [email protected]) †Instituto de Geociencias,^ Universidade Federal do Rio Grande do Sul, Porto Alegre 90040-060, Brazil ‡Geology & Petroleum Geology, King’s College, University of Aberdeen, Aberdeen, AB24 3FX, UK §Departamento de Geociencias,^ Universidade Federal de Santa Maria, Av. Roraima, 1000 Predio 17, Santa Maria, RS 97105-900, Brazil ¶Instituto de Geociencias,^ Universidade de Sao~ Paulo, Sao~ Paulo 05508-080, Sao~ Paulo, Brazil Associate Editor – Subhasish Dey ABSTRACT The Lower Cretaceous Botucatu Formation records the development of wide- spread dry–aeolian desert sedimentation throughout the Parana Basin in south- west Gondwana. To reconstruct the provenance of the aeolian sediment, petro- graphy, granulometric analysis, U-Pb detrital zircon ages have been determined from along the southern basin margin in Rio Grande do Sul state (southern Bra- zil) and Uruguay (Tacuarembo 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, epi- dote 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 Parana Basin units, the predominance of quartzose, and zircon, tourmaline and rutile components, sug- gests that recycling is the mechanism responsible for the erg feeding. Keywords Botucatu desert, Cretaceous Parana Basin, desert accumulation, detrital zircon, heavy minerals, provenance analysis. INTRODUCTION understanding how and why large accumula- tions of aeolian sediment are developed and Determining the origin and transport paths of preserved (Dickinson & Gehrels, 2003; Rahl sediment in aeolian systems is important for et al., 2003). Provenance studies of dune field © 2020 The Authors. Sedimentology © 2020 International Association of Sedimentologists 1 2 G. Bertolini et al. sediment supply and erg sand-delivery systems input from the south. In addition, the close reveal a range of desert sand supply mecha- proximity of the Botucatu to basement highs (for nisms. For example, sands in the Namib Desert example, the Rio-Grandense and Uruguayan are sourced by longshore drift from the Orange shields), may allow establishment of a direct River delta (Garzanti et al., 2014), sands in the ‘source to sink’ connection. Sediment prove- Taklamakan Desert are supplied by fluvial sys- nance studies from the southern part of the tems draining the surrounding mountain ranges basin will therefore be important in reconstruct- (Rittner et al., 2016), and the Rub‘ Al Khali erg ing sediment routing systems, understanding (Arabian Desert) is derived from a mix of sand controls on sediment supply and assessing the sources including aeolian transport and defla- potential for first cycle input direct from tion as well as fluvial, alluvial and coastal basement terranes. inputs (Garzanti et al., 2017; Farrant et al., The primary objective of this study is to con- 2019). In the rock record, a study of the Jurassic strain and clarify the nature of the sediment ergs of the Colorado Plateau was able to recon- source for the Botucatu dunes along a transect struct a transcontinental south-east/north-west of the southern Parana Basin margin (south-east palaeoriver and palaeowind system responsible Brazil and Uruguay). Due to the continental for transportation and dispersal of sediment in scale of the aeolian system, the Botucatu Forma- Laurentia (Dickinson & Gehrels, 2009). When tion covers a number of distinct geological ter- studying the sedimentary record, however, it is ranes providing a wide range of potential often difficult to properly reconstruct aeolian sediment source areas and pathways. Prove- sediment supply systems due to the incomplete- nance analysis utilizing U-Pb detrital zircon ness of the succession and post-depositional dia- geochronology, heavy mineral analysis, petrogra- genetic modification of the original mineralogy phy and granulometric analysis has been under- (Mcbride, 1985; Cardenas et al., 2019). As a taken to ascertain whether significant variations consequence, with the exception of the Per- in sediment provenance signatures across the mian–Jurassic Colorado Plateau ergs (Dickinson southern basin margin can be identified. & Gehrels, 2003, 2009, 2010; Rahl et al., 2003), there is a lack of studies that address the recon- struction of sediment source terranes, pathways, GEOLOGICAL CONTEXT mixing, recycling and transport distance in ancient large-scale ergs. To address this gap, this The Botucatu Formation forms part of the study has undertaken a provenance analysis of intracratonic Parana Basin fill succession – an the Botucatu Formation, a Cretaceous aeolian 8 km thick (Zalan et al., 1990) sedimentary- unit deposited across south-west Gondwana. magmatic package of Late Ordovician to Early The Cretaceous Botucatu dune field extended Cretaceous age (Fig. 2). In the south (Brazil, continuously across 1.5 million km2 of the inte- Argentina, Uruguay and Paraguay), the basin-fill rior of the south-west Gondwana Supercontinent is divided into six supersequences (Milani et al., and represents part of what was probably the 1998): Rio Ivaı (Ordovician–Silurian), Parana most voluminous continuous dune field in Earth (Devonian), Gondwana I (Carboniferous to Lower history (Scherer & Goldberg, 2007; Fig. 1). The Triassic), Gondwana II (Triassic), Gondwana III Botucatu sand sea forms part of the intracratonic (Early Jurassic to Lower Cretaceous) and Bauru Parana Basin-fill succession and represents the (Early Cretaceous). The Rio Ivaı, Parana and last phase of sedimentation in the Parana Basin Gondwana I supersequences represent marine prior to break-up of the South American and and shoreline deposits. The Gondwana II, Gond- African continents. The Parana Basin developed wana III and Bauru supersequences comprise ter- across a wide range of different pre-Mesozoic restrial sediments and associated volcanic strata. basement terranes (Palaeoproteorozoic to Cam- The Botucatu Formation and the Serra Geral For- brian) with differing ages and compositions. mation form part of the Gondwana III superse- Consequently, when combined with previous quence, also known as the Sao~ Bento Group work on palaeowind directions, it should be (Schneider et al., 1973). The Botucatu palaeoerg possible to distinguish different provenance sig- is overlain by 700 to 1700 m of lava-flows from natures in the Botucatu Formation. Previous the Parana–Etendeka Large Igneous Province studies of the formation (e.g. Bigarella & Sala- (Serra Geral Formation). Interbedded basaltic muni, 1961) show that coarser sediment prevails lava flows and aeolian sediments indicate co- in the southern part of the basin suggesting existence between, and a transition from, aeolian © 2020 The Authors. Sedimentology © 2020 International Association of Sedimentologists, Sedimentology Controls on desert sediment provenance 3 Fig. 1. Botucatu desert extent in South America within the Parana and Chaco-Parana Basins with sample locations. The desert had a bimodal wind pattern, with southerly directions in low latitudes and north-east/east directions in the study (Scherer, 2000; Scherer & Goldberg, 2007). sedimentation to lava emplacement (Scherer, Formation (Amarante et al., 2019). The Botucatu 2002). Formation also has equivalent units in Argen- The age of the top of the Botucatu Formation tina (San Cristobal Formation), Paraguay (Mis- is constrained by overlying lavas of the Serra siones Formation), Bolivia (Ichoa Formation) Geral Formation, which have yielded ages of ca and Namibia (Twyfelfontain Formation) (Scherer 134 Ma (Valagininan) by Ar/Ar (whole-rock & Goldberg, 2007). Outcrops in Rio Grande do grains/plagioclase) and U-Pb methods (Zircon Sul State and Uruguay likely represent the and Badeleeite) (Ernesto et al., 1999; Thiede & upwind margin of the erg as illustrated by: (i) Vasconcelos, 2010; Janasi et al., 2011; Pinto variations in thickness from 0 to 100 m along et al., 2011; Baksi, 2018; Rossetti et al., 2018). the southern margin to up to 400 m thickness in The determination of the onset of Botucatu the basin centre (Milani et al.,1998); and (ii) deposition is imprecise due to a lack of dated palaeocurrent data demonstrating a consistent interbedded volcanics and/or palaeontological north-east/east palaeowind direction along