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Proterozoic First-Order Sedimentary Sequences of the Sao Francisco

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Proterozoic First-Order Sedimentary Sequences of the Sao Francisco Marine and Petroleum Geology 33 (2012) 127e139 Contents lists available at SciVerse ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo Proterozoic first-order sedimentary sequences of the São Francisco craton, eastern Brazil Fernando F. Alkmima,*, Marcelo A. Martins-Netob a Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, Morro do Cruzeiro, 35.400.000 Ouro Preto, MG, Brazil b Vicenza Mineração, Av. Agulhas Negras, 580, Mangabeiras, 30210-340 Belo Horizonte, MG, Brazil article info abstract Article history: The São Francisco craton in eastern Brazil hosts sedimentary sequences deposited between the Paleo- Received 4 May 2010 archean (w3300 Ma) and Late Neoproterozoic (w580 Ma). Proterozoic successions occurring in this Received in revised form region comprise five 1st-order sedimentary sequences, which besides episodes of global significance 15 August 2011 record major basin-forming events. The ca. 8000 m-thick Minas-Itacolomi 1st-order sequence, exposed Accepted 18 August 2011 in the Brazilian mining district of the Quadrilátero Ferrífero and containing as marker bed the Lake Available online 5 September 2011 Superior-type Cauê Banded Iron Formation, tracks the operation of a Wilson cycle in the Paleoproterozoic Era. The quartz-arenite dominated Espinhaço I and II sequences record at least two major rift-sag basin- Keywords: First-order sequences forming events, which affected the host continent of the São Francisco craton at around 1.75 Ga and Proterozoic 1.57 Ga. The Macaúbas sequence and its correlatives in the extracratonic domains witness the individ- São Francisco craton ualization of a São Francisco-Congo plate in synchronicity with the break-up of Rodinia in the Cryogenian Brazil period. The São Francisco-Congo plate together with various fragments derived from Rodinia reas- sembled to form Gondwana in the Ediacaran period. In the course of the Gondwana amalgamation, orogenic belts developed along the margins of the craton; its interior, converted into foreland basins, received the shallow water carbonates and pelites of the Bambuí 1st-order sequence and its correlatives. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction accretionary material (Brito Neves et al., 1999; Almeida et al., 2000; Alkmim et al., 2001). The best preserved and most intensively studied Precambrian We selected for discussion in this paper five Proterozoic 1st- sedimentary record of South America is exposed in a relatively order sequences exposed in the São Francisco craton region. The small area of eastern Brazil, which corresponds to the São Francisco sequences chosen for discussion record not only the Proterozoic craton and its margins (Fig. 1). The São Francisco craton (Almeida history of the São Francisco craton, but also tectonic and climatic et al., 2000) hosts sedimentary successions accumulated in the events of global significance. Archean sedimentary successions, time interval between the Neoarchean (w2800 Ma) and Late although present in many sectors of the craton, are tectonically Neoproterozoic (w580 Ma). dismembered and demand further detailed studies. For this reason The Precambrian nucleus of the South American continent, they will be not addressed in this paper. consisting essentially of Archean to Paleoproterozoic rocks with As a consequence of its previous residence in Gondwana, the São minor additions of Meso- and Neoproterozoic juvenile material, Francisco craton has an African counterpart (Fig. 1), which is rep- comprises cratons and Neoproterozoic orogenic belts (Fig. 1). The resented by the Congo craton. The link between the São Francisco São Francisco together with three other cratons of South America and Congo cratons is made by a crustal bridge that connects the corresponds to the internal portions of the plates involved in the Paleoproterozoic Eastern Bahia orogenic domain in Brazil to the assembly of West Gondwana by the end of the Proterozoic Era. The Paleoproterozoic Francevillian or West Central African belt in Neoproterozoic or Brasiliano orogenic belts, on the other hand, Gabon (Fig. 1). This piece of crust remained intact from the middle encompass the margin of those plates and the intervening Paleoproterozoic until the beginning of the Cretaceous, when West Gondwana started to split apart (Porada, 1989; Trompette, 1994; Ledru et al., 1994; Feybesse et al., 1998; Pedrosa-Soares et al., * Corresponding author. Tel.: þ55 31 3559 1849; fax: þ55 31 3559 1600. 1992, 2001). For this reason, correlatives of the focused Brazilian E-mail addresses: [email protected], [email protected] (F.F. Alkmim). 1st-order sequences in the Congo craton are indicated in the text. 0264-8172/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpetgeo.2011.08.011 128 F.F. Alkmim, M.A. Martins-Neto / Marine and Petroleum Geology 33 (2012) 127e139 Figure 1. The São Francisco craton together with its African counterpart, the Congo craton, in the tectonic scenario of West Gondwana. Cratons of South America and Africa: A Amazonian; P Rio de la Plata; WA West Africa; SFC São Francisco-Congo; K Kalahari. Cities: S Salvador and V Vitória (Brazil); Luanda (Angola); LB Lebreville (Gabon). Special emphasis is given to the correlations between the Neo- Proterozoic and Phanerozoic sedimentary units. The ca. 2.1 Ga proterozoic successions exposed on both cratons. Mineiro belt (Teixeira and Figueiredo, 1991; Teixeira et al., 2000) The concept of 1st-order sequence adopted in the present paper that bounds the Archean block to the south involves the Archean was postulated by Martins-Neto et al. (2001) and Catuneanu et al. basement, Paleoproterozoic passive margin to foreland basin units, (2005). Since Precambrian basins are often characterized by poor and voluminous granitoids emplaced between 2.25 and 2.02 Ga stratal preservation and by a general lack of time control, an (Machado et al., 1996; Teixeira et al., 2000; Noce et al., 2000; Ávila approach based on the stratigraphic hierarchy is considered the et al., 2010). The famous Brazilian mining district known as the best way to interpret the stratigraphic framework. Stratigraphic Quadrilátero Ferrífero (“Iron Quadrangle”)(Dorr, 1969) is located in hierarchy involves the separation of different orders of sequences the foreland domain of the Mineiro belt and corresponds to the and bounding surfaces based on their relative importance. In this type area of the Paleoproterozoic Minas-Itacolomi sequence, dis- context, changes in the tectonic setting provide the key criterion for cussed in the next section. the basic subdivision of the rock record. Thus, a first-order The Proterozoic cover units of the São Francisco craton occur in sequence corresponds to an entire sedimentary basin-fill succes- two distinct tectonic domains: the São Francisco basin and the sion, regardless of the origin and life span of each particular basin. Paramirim aulacogen (Fig. 2). The poly-historic São Francisco basin This first-order basin-fill succession can be in turn subdivided into extends over ca. 800 km along the NS-trending lobe of the craton second- and lower-order sequences, based on the steps involved in and is bounded by emergent thrusts of the adjacent Neoproterozoic the tectonic evolution of the basin, irrespective of the time span orogenic belts, except to the south and northeast (Dominguez, between two same-order consecutive events. 1993; Alkmim and Martins-Neto, 2001; Zalán and Romeiro-Silva, 2007). The southern limit is erosional. To the northeast the basin 2. The São Francisco craton is bounded by the Paramirim corridor, a Neoproterozoic intra- cratonic deformation zone, which affects the neighboring Para- In the continent interior, the São Francisco craton is bounded by mirim aulacogen (Alkmim and Martins-Neto, 2001; Cruz and the Neoproterozoic Brasília, Araçuaí, Rio Preto, Riacho do Pontal Alkmim, 2006). The Precambrian basin-fill units comprise the and Sergipano orogenic belts (Fig. 2)(Almeida et al., 1981). Along Espinhaço and São Francisco supergroups, of Paleo/Mesoproter- the eastern Brazilian coast, the craton boundary is made up by ozoic and Neoproterozoic ages, respectively. The Phanerozoic Cretaceous passive margin basins, developed on the cratonic bridge section contains the glacial sediments of the Permo-carboniferous that once linked the São Francisco and Congo blocks. Santa Fé Group (Campos and Dardenne, 1994), as well as the The basement of the São Francisco craton consists of an Archean Cretaceous rift-sag succession of the Areado, Urucuia, and Mata da nucleus and two segments of a Paleoproterozoic orogen (Alkmim Corda Groups (Sgarbi et al., 2001). and Marshak, 1998; Teixeira et al., 2000; Barbosa and Sabaté, The Paramirim aulacogen (sensu Cruz and Alkmim, 2006) 2004)(Fig. 1). The Archean block, which corresponds to the NS- encompasses two morphotectonic domains of the São Francisco elongated segment of the craton, is almost entirely covered by craton: the northern Espinhaço range and a large plateau referred F.F. Alkmim, M.A. Martins-Neto / Marine and Petroleum Geology 33 (2012) 127e139 129 Figure 2. Geological map of the São Francisco craton showing the bordering Neoproterozoic Brasiliano belts, the Proterozoic cover sequences (younger than 1.8 Ga), the São Francisco basin, and the Paramirim aulacogen. Morphotectonic domains of the Paramirim aulacogen: NE Northern Espinhaço range; CD Chapada Diamantina. The box indicates the area of Fig. 5; the dotted line the location of the seismic section
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