Pliocene-Quaternary Fault Control of Sedimentation and Coastal Plain Morphology in NE Brazil

Journal of South American Earth Sciences 14 :2001) 61±75 www.elsevier.nl/locate/jsames Pliocene-Quaternary fault control of sedimentation and coastal plain morphology in NE Brazil Francisco H.R. Bezerraa,*, Venerando E. Amaroa, Claudio Vita-Finzib, Allaoua Saadic aDepartamento de Geologia, CCET, Universidad Federal do Rio Grande do Norte, Campus UniversitaÂrio, Natal RN, 59072-970, Brazil bDepartment of Geological Sciences, University College, Gower Street, London WC1E 6BT, UK cDepartamento de Geogra®a, Instituto de GeocieÃncias, Universidad Federal de Minas Gerais, Av. AntoÃnio Carlos 6627, Belo Horizonte MG, 31270-901, Brazil Accepted 18 January 2001 Abstract Although the last major tectonic event in the Brazilian passive margin was the South America±Africa breakup during the Mesozoic, there is pervasive evidence in northeastern Brazil for pronounced faulting since the late Tertiary. The faulting was partitioned between strike-slip and normal-slip and it reactivated Precambrian shear zones as well as generating new structures. A 040±0608 -trending fault set and a 300±3208 -trending set have strongly in¯uenced both the deposition of alluvial and aeolian sediments and coastal evolution. Vertical throws have attained 260 m since the Pliocene, and topographic breaks resulting from cumulative late Tertiary to Quaternary slip have attained 30±40 m. Fault control of sediment deposition and coastal morphology may have affected the entire South American passive margin. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cenozoic; Sedimentation; Coastal plain morphology; Fault control; NE Brazil 1. Introduction region and in shaping the low-elevation coastal plain is also unclear. We addressed the question by analyzing the In eastern South America and West Africa the last major littoral zone between Natal and JoaÄo Pessoa :Fig. 1) in an tectonic event took place during plate separation in the attempt to trace fault evolution since the Pliocene in this part Mesozoic. Several studies :e.g. Popoff, 1988; Chang et al., of the South American passive margin. The evidence comes 1992; Matos, 1992) have shown that the Gondwana breakup from remote sensing, borehole logs, and ®eld mapping of reworked continental shear zones under a transtensional geological and geomorphological features. regime, leading to the formation of passive margin basins in both Africa and South America. Since then, both conti- nents have enjoyed relative tectonic quiescence. Neverthe- 2. Tectonic setting and lithostratigraphic units less, recent studies in South America that have focused on ®ssion track data :e.g. Harman et al., 1998), intraplate The coastal plain is composed of Precambrian crystalline volcanism :e.g.Almeida et al., 1988), the uplift of coastal basement overlain by Cretaceous basins and a Cenozoic deposits :Martin et al., 1986; Bezerra et al., 1998), paleo- sedimentary cover :Fig. 1). The basement consists of drainage patterns :Potter, 1997), and the instrumental seis- Archean and Proterozoic fold belts composed mainly of mological record :AssumpcËaÄo, 1992; Ferreira et al., 1998) volcanic-sedimentary terrains and granite plutons deformed have shown that Precambrian shear zones and major faults by one or more orogenic cycles dating from 2.3±2.15 Ga, were reactivated and new faults generated long after the 1.90±1.95 Ga, and 650±550 Ma :Jardim-de-SaÂ, 1994). The breakup. Even so, it is not clear whether northeastern Brazil basement orogenies indicate strain partitioning between :Fig. 1), the last part of the South American plate to be domains of folding and strike-slip or oblique-slip mylonitic separated from the African plate :FrancËolin and Szatmari, belts. The last of these cycles :Brasiliano/Panafrican 1987; Szatmari et al., 1987), underwent a clearly de®ned, orogeny) strongly deformed and overprinted older struc- widespread tectonic event in the Cenozoic. The role of faults tures throughout the area :Jardim-de-SaÂ, 1994; Amaro, in the deposition of Cenozoic sedimentary units in the 1998). The shear zones are generally marked by strong, pervasive foliation; present sigmoidal shapes :Fig. 1), and * Corresponding author. Tel.: 155-84-215-3831; fax: 155-84-215-3806. their deep roots are indicated by strong gravity anomalies E-mail address: [email protected] :F.H.R. Bezerra). :Jardim-de-SaÂ, 1994; Amaro, 1998). 0895-9811/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0895-9811:01)00009-8 62 F.H.R. Bezerra et al. / Journal of South American Earth Sciences 14 :2001) 61±75 Fig. 1. Tectonic framework of northeastern Brazil :modi®ed from Schobbenhaus et al., 1984; Matos, 1992) showing the location of study area. Insert: the South American continent. The historical and instrumental seismic record indicates Several basins that formed during the South Atlantic an important level of seismicity in the region when opening overlie the Precambrian basement. To the north compared with other areas in Brazil :Fig. 2). It occurs within of the study area, the Potiguar basin, whose age ranges the ®rst 1±12 km of the upper crust :Ferreira et al., 1998) from Early to Late Cretaceous, lies along the east-trending and has been known since 1808, when an earthquake of coast. Its structural framework comprises half-grabens sepa- estimated magnitude mb 4:0 and intensity MM . VI rated by intrabasinal highs related to the Early Cretaceous occurred near AcËu :Ferreira and AssumpcËaÄo, 1983). Many rifting episode of the Brazilian marginal basins :Araripe and earthquake swarms, lasting for at least six months, have FeijoÂ, 1994) :Fig. 1). The stratigraphic column of the Poti- been described :e.g. Ferreira et al., 1998). The most impor- guar basin consists of continental rift sediments and marine tant of them was the JoaÄoCaÃmara earthquake swarm from post-rift sediments. Deposition was controlled by NE-trend- 1986 to 1989, when nearly 4,000 building were damaged ing structures during the rift phase in the mid-and Late and more than 40,000 events were recorded. Two main Cretaceous :Matos, 1992). To the south of the study area, events of 5.0 mb and 5.1 mb and their aftershocks were the Pernambuco-ParaõÂba basin is divided into several faulted concentrated along the 30 km long, 0408 -trending Samam- blocks :Rand and Manso, 1990). It occupies a narrow zone baia fault :Takeya et al., 1989), but no surface offset has along the coastal plain, which crops out to the south of JoaÄo been detected so far. Pessoa and near Recife :Fig. 1); it also occurs offshore :Fig. 1). F.H.R. Bezerra et al. / Journal of South American Earth Sciences 14 :2001) 61±75 63 Fig. 2. Historic and instrumental seismicity and secondary ground failure :liquefaction and landslide) in northeastern Brazil :modi®ed from Ferreira, 1983; Ferreira et al., 1998; Bezerra, 1998). Stratigraphic studies based mainly on outcrop data indicate of debate. Relative dating by palaeomagnetism and micro- that it includes a rift clastic sequence capped by marine post- pollen indicates that it dates from Miocene to Pliocene rift sediments :FeijoÂ,1994). times. A peat layer found in the Barreiras Formation at Eocene±Oligocene magmatic activity is represented by Natal, described by Salim et al. :1975), yielded angiosperm the Macau volcanism :Fig. 1) of 44.6 ^ 6.6±29.0 ^ 0.9 Ma pollen of Zonocostites ramonae. Although this species :Mizusaki, 1989) and consists of ma®c volcanic rocks such ranges form the Eocene to the Holocene, it is abundant in as basalt, basanite, and ankaratrite that occur as plugs, dikes late Miocene sedimentary rocks. More recently, a palyno- and necks :Sial, 1976; Almeida et al., 1988). The Macau logical study of the upper Barreiras Formation in the Poti- Formation is also encountered in boreholes and is indicated guar basin yielded Retisteplanocolpites gracilis, indicative by geophysical studies :e.g. Salim et al., 1975). of a Pliocene age :Lima et al., 1990). In Bahia state, The late Tertiary sedimentary rocks of northeastern 1000 km to the south of the study area, a Pliocene age Brazil formed late in the history of Atlantic opening was proposed for the base of the Barreiras Formation by and are represented mostly by a sedimentary sequence Suguio et al. :1986) on the basis of palaeomagnetic dating. called the Barreiras Formation, which crops out along The dates they obtained range from 4.5 to 5.0 Ma :early to more than 4,000 km of the Brazilian littoral zone from middle Pliocene) near the base of the deposit to 3.0±3.4 Ma the Amazon delta to the Rio de Janeiro coast :Mabesoone :late Pliocene) near the top. For the purpose of the present et al., 1972). study, the age of the top of the local Barreiras Formation is The age of the Barreiras Formation has long been a source therefore taken to be Pliocene. 64 F.H.R. Bezerra et al. / Journal of South American Earth Sciences 14 :2001) 61±75 Fig. 3. Geological map of the coastal plain and adjacent crystalline basement between Natal and Canguaretama, showing the location of geological cross- sections. The city of Natal is omitted for clarity. Quaternary sedimentary rocks overlie the Barreiras 362 of 06 August 1994) which were normalized for haze Formation and are composed of alluvial and aeolian removal according to the method of Chavez :1988). The sediments and beachrock. The deposits range in age digital images were processed on ER-Mapper 5.5 run on a from Pleistocene to Holocene :e.g.Mabesoone and unix workstation. Digital manipulation included principal Campos-e-Silva, 1972). Silva :1991) obtained an age of component 1 :PCl), using a high-pass ®lter for edge 30,190 ^ 370 yr for post-Barreiras Formation deposits enhancement after Schowengerdt :1983). Equalizing trans- t200 km northwest of the study area, but this must be forms were also applied to the above image in order to considered a minimum value.

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