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Stratigraphy of the Roraima Supergroup Along The DOI: 10.1590/2317‑4889201720160139 ARTICLE Stratigraphy of the Roraima Supergroup along the Brazil‑Guyana border in the Guiana shield, Northern Amazonian Craton – results of the Brazil‑Guyana Geology and Geodiversity Mapping Project Estratigrafia do Supergrupo Roraima ao longo da fronteira Brasil‑Guiana no escudo das Guianas, norte do Cráton Amazônico – Resultados do Projeto Mapeamento Geológico e da Geodiversidade Brasil‑Guiana Nelson Joaquim Reis1*, Serge Nadeau2, Leda Maria Fraga1, Leandro Menezes Betiollo1, Maria Telma Lins Faraco1, Jimmy Reece2, Deokumar Lachhman2, Randy Ault2 ABSTRACT: The Geological and Geodiversity Mapping binational RESUMO: O programa binacional de Mapeamento Geológico e da program along the Brazil‑Guyana border zone allowed reviewing and in‑ Geodiversidade na fronteira Brasil‑Güiana possibilitou a revisão e inte‑ tegrating the stratigraphy and nomenclature of the Roraima Supergroup gração da nomenclatura estratigráfica do Supergrupo Roraima ao longo along the Pakaraima Sedimentary Block present in northeastern Brazil do Bloco Pacaraima nas regiões extremo norte brasileira e ocidental guia‑ and western Guyana. The area mapped corresponds to a buffer zone of nense. A área corresponde a um buffer de aproximados 25 quilômetros a approximately 25 km in width on both sides of the border, of a region partir da fronteira, em um trecho definido pelo Monte Roraima (região extending along the Maú‑Ireng River between Mount Roraima (the tri‑ de tríplice fronteira) e vizinhanças da vila Mutum, no Brasil, e serra ple‑border region) and Mutum Village in Brazil and Monkey Mountain Monkey, na Guiana, ao longo do rio Maú ou Ireng. O flanco sul da bacia in Guyana. The south border of the Roraima basin is overlain exclusively assenta exclusivamente em rochas efusivas e vulcanoclásticas dos correlatos by effusive and volcaniclastic rocks of the Surumu Group of Brazil and its grupos Surumu e Burro‑Burro. correlated equivalent the Burro‑Burro Group of Guyana. PALAVRAS‑CHAVE: Supergrupo Roraima; Fronteira Brasil‑Guia‑ KEYWORDS: Roraima Supergroup; Brazil‑Guyana border; stratigraphy. na; estratigrafia. 1Serviço Geológico do Brasil – Superintendência Regional de Manaus – Manaus (AM), Brazil. E‑mails: [email protected]; [email protected]; [email protected]; [email protected] 2Guyana Geology and Mines Commission (GGMC) – Georgetown, Guiana. E‑mails: [email protected]; [email protected]; [email protected]; [email protected] *Corresponding author. Manuscript ID: 20160139. Received in: 12/09/2016. Approved in: 02/03/2017. 43 Brazilian Journal of Geology, 47(1): 43‑57, March 2017 Stratigraphy of the Roraima Supergroup along the Brazil-Guyana border INTRODUCTION of Brazil with Guyana, based on the work performed during the Geological and Geodiversity (land‑use) Mapping The Pakaraima Sedimentary Block (PSB) (Reis & Carvalho of the Brazil‑Guyana Project, carried out by geologists of 1996, Reis & Yánez 2001) represents a stratigraphical land‑ the CPRM — Geological Survey of Brazil and the GGMC — mark of the Roraima Supergroup, being the register of a Guyana Geology and Mines Commission. The area of geo‑ Paleoproterozoic sedimentary basin in the northern portion logical mapping includes the three main villages of Uiramutã of the Amazon Craton (Fig. 1). Of unparalleled scenic beauty, and Mutum on the Brazilian side and Orinduik on the it gathers a dozen tepuys, which stand out Mount Roraima, Guianese side, all of them located within that buffer zone a triple frontier between Brazil, Venezuela and Guyana of 25 kilometers on both sides of the frontier (Fig. 2). (Reis 2009). The basin register a historical gold and diamond In spite of the bad weather conditions and the impossibility mining activity in a stratigraphic framework poorly investi‑ to drive along the dirt roads between Karasabai Village and gated and deserving attention at the application of sequence Monkey Mountains, it was possible to reach Orinduik by stratigraphy, tectonic setting and geochronological studies. plane. During the flight, it was possible to observe an inter‑ This paper discusses the correlation of the stratigraphy esting area of the Roraima Supergroup where the first sedi‑ of the Roraima Supergroup on both sides of the border mentary rocks form cliffs overlying the Iwokrama volcanics 60º00´W 60º00´W Atlantic Ocean GUYANA Venezuela Guyana Suriname French Guiana BRAZIL Colombia Guiana Shield 00º00´ 5º00´N PacificEquador Ocean 500 km Orinduik Taiano Dolerite Avanavero Dolerite Uiramutã Matauí Formation Roraima Uaimapué Formation Supergroup Suapi Group Mutum 25 km Monkey Arai Formation Surumu and Burro-Burro Groups Figure 1. The PSB along the Venezuela, Brazil and Guyana border and the regional geological setting of the Guiana Shield. 52´W SIMPLIFIED GEOLOGICAL MAP Phanerozoic Cover OF GUIANA SHIELD LATE OROSIRIAN CALIMIAN Atlantic Ocean Pakaraima Sedimentary Block – PSB (> 1.78 Ga) 10´N Undifferentiated (1.90 – 1.43 Ga) South America EARLY OROSIRIAN Rio Urubu Igneous Belt – RUIB (1.94 – 1.93 Ga) Orocaima Volcano-Plutonism – OVP (1.98 – 1.95 Ga) Cauarane-Coeroeni Belt – CCB (~2.00 Ga) Trairão-Anauá Arc (2.04 – 2.02 Ga) RHYACIAN Andes Belt Granulites/Charnockites Bakhuis – B (2.06 Ga) Braziliano Belts Granite-Greenstone Belt (and gneisses) (2.21 – 2.07 Ga) Cratons Amazonian Craton ARCHEAN 1-Guiana Shield Imataca (IB) and Amapá Block (AB) 2-Brazil-Central Shield 200 km Figure 2. Simplified geological map of the Pakaraima Sedimentary Block along the Brazil and Guyana border and the location of the Guiana Shield, north of the Amazon Craton. 44 Brazilian Journal of Geology, 47(1): 43‑57, March 2017 Nelson Joaquim Reis et al. and where tuffs of the Uaimapué Formation are forming of magmatism during the Avanavero event (Santos et al. hills and plateaus. Another landscape feature observed was 2003, Reis et al. 2013). The main sources of sediments of the rainforest distribution developed over the hills of basic the Arai Formation were rocks of Trans‑Amazonian age rocks, occurring as dyke and sill intrusions of the Avanavero (2.26 – 2.01 Ga), as indicated by the main population of Dolerite. The interpretation of the landscape was an import‑ detrital zircons at 2123 ± 14 Ma. The second source was ant tool to identify the units of the Roraima Supergroup in rocks with an age of 1958 ± 19 Ma (Santos et al. 2003), Guyana, once the stratigraphy has been defined by previous probably related to the Orocaima Event which included and detailed mapping work on the Brazilian side. Surumu calc‑alkaline volcanic rocks and its plutonic equiv‑ alents of the Pedra Pintada Suite granitoids (Reis et al. 2000a) and from Iwokrama volcanic rocks and its plu‑ REGIONAL GEOLOGICAL SETTING tonic equivalents. The Roraima basin along the southern border of the The Roraima Supergroup is part of the Pakaraima PSB unconformably overlies volcanic rocks of the Surumu Sedimentary Block, forming a continuous area of sedi‑ Group and Iwokrama Formation (Burro‑Burro Group) mentary rocks covering some 73,000 km2 of the Guiana in the Brazilian and Guyanese terranes, respectively, Shield in parts of Venezuela, Brazil and Guyana (Fig. 1). forming an elongated E‑W trending belt. These rocks Using the geochronological provinces subdivisions defined show a prominent mylonitic foliation, which has been by Tassinari and Macambira (2004), the PSB will be part of attributed to the regional deformation of the crust during the Maroní‑Itacaiúnas Province with ages ranging between the K’Mudku episode around 1.2 Ga. No contacts were 2.2 and 1.9 Ga. On the other hand, it will belong to the observed between the sedimentary rocks of the Roraima Tapajós‑Parima Province proposed by Santos et al. (2006), Supergroup with the comagmatic granitoids of the volca‑ with ages varying between 2.03 and 1.88 Ga. nic rocks of the Surumu and Burro‑Burro Groups. At the The Roraima Supergroup, whose sediments have base of the Roraima Supergroup, where the sedimen‑ been deposited throughout the Orosirian period of the tary rocks were locally tightly to gently folded, they only Paleoproterozoic Era, has maximum and minimum ages present traces of low‑grade metamorphism in the zeolite of 1.95 and 1.78 billion years, respectively (Tab. 1). facies. Thermal metamorphism is always present along the Zircons from tuffs within the Uaimapué Formation contact of the Avanavero intrusive bodies (Pinheiro et al. yielded a U‑Pb SHRIMP age of 1873 ± 3 Ma (Santos et al. 1990). Swarm of dolerite dykes dated at around 200 Ma 2003). The minimum age of the Roraima Supergroup is (Nomade et al. 2007) cut all of these older rocks, mainly 1795 ± 2 Ma and 1782 ± 3 Ma and was determined by U‑Pb in a NE‑SW direction, extending over more than 70 km geochronology using baddeleyite and zircon from two mafic for the Tumong Dyke located near the Brazil‑Guyana bor‑ sills (Avanavero magmatism) possibly suggesting two pulses der, to the southeast of Orinduik village. Table 1. Stratigraphy of Roraima Supergroup proposed by Reis and Yánez (2001) along the Brazil – Venezuela border and it extension to Guyana. Compilation of ages of the volcanic rocks underlying the Roraima Supergroup along the border between Brazil and Guyana (Surumu Group and Iwokrama Formation), of a pyroclastic rock unit of the Uaimapué Formation in Brazil and of intruding sills of the Avanavero Dolerite in Brazil. Brazil‑Venezuela Stratigraphy as proposed Keats (1973) Main U‑Pb and Pb‑Pb Ages by Reis and Yanez (2001) Avanavero Magmatism 11787 ± 14 (bd); 11782 ± 3 (zr); 21795 ± 2 (bd); Matauí Formation Unit X Uaimapué Formation Unit IX 11873 ± 3 Ma Quinô Formation Unit VII and VIII Cuquenán Formation Unit VI Suapi Group Pauré Formation Verde Formation Unit V Roraima Supergroup Uiramutã Formation Arai Formation Unitn I to IV 1detrital zircons: 2123 ± 14 (main); 1958 ± 19 (younger) Pakaraima/Surumu Group Iwokrama Fm. 11984 ± 9; 31989 ± 10; 41966 ± 7; 41964 ± 7; 51982 ± 3 References: 1Santos et al. (2003); 2Reis et al.
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