Geologos 15-2.Indd

VIRGÍNIO HENRIQUE NEUMANN ET AL. Geologos, 2009, 15 (2): 103–113 Sedimentary development and isotope analysis of deposits at the Cretaceous/Palaeogene transition in the Paraíba Basin, NE Brazil VIRGÍNIO HENRIQUE NEUMANN1*, JOSÉ ANTÔNIO BARBOSA2, MARIA VALBERLÂNDIA NASCIMENTO SILVA3, ALCIDES NÓBREGA SIAL4, MÁRIO DE LIMA FILHO5 1 LAGESE, Department of Geology, Federal University of Pernambuco, Rua Acadêmico Hélio Ramos, s/n, 5 andar CTG, Cidade Universitária, Recife-PE, Brasil; 1 e-mail: [email protected] 2 e-mail: [email protected] 3 e-mail: [email protected] 4 e-mail: [email protected] 5 e-mail: mfl [email protected] * corresponding author Abstract New data are presented for three formations (Itamaracá, Gramame and Maria Farinha) and two boundaries (Cam- panian/Maastrichtian and Maastrichtian/Danian) in the Olinda Sub-basin of the Paraíba Basin. Currently accepted facies models, sequence stratigraphy characterizations, and stable-isotope data of carbon and oxygen are reviewed. The carbonate cement of the Itamaracá Formation sandstones shows carbon- and oxygen-isotope ratios consistent with a shallow-marine depositional environment: δ18O ranges from -0.8 to –2.7‰ PDB, and δ13C ranges from +1 to +2‰ PDB. Within the Itamaracá Formation, a maximum fl ooding surface at the Campanian/Maastrichtian transition has been identifi ed. During the Maastrichtian, a Highstand System Tract was deposited, which shows an increase in temperature and marine bioproductivity as recorded by stable-isotope values (δ18O from –3 to –5‰ PDB, and δ13C values of –1.2, -0.3, 0.1 and +2.3‰ PDB). Just below the K/Pg boundary, the O-isotope signal indicates three warming phases, alternating with four cooling phases. Keywords: NE Brazil, Cretaceous/Palaeogene boundary, carbon isotopes, oxygen isotopes Introduction was deposited during the Late Campanian, the Maastrichtian and the Palaeocene. The low The Paraíba Basin is located along the At- economic potential of the onshore and offshore lantic margin of NE Brazil, and comprises the continental margin between the Pernambuco coastal area between the Pernambuco Shear Shear Zone (PESZ) and the Touros High (TH) Zone in the south and the Mamanguape Fault implies that it is a poorly studied region. It ap- in the north. The basin is characterized by a pears though that its tectonic characteristics nearly continuous sedimentary succession that differ from those of the neighbouring Potiguar Sedimentary development and isotope analysis of deposits... 104 Virgínio Henrique Neumann et al. and Pernambuco (Mohriak et al., 1995, 1998) According to Lima Filho et al. (1998), Bar- marginal basins (Fig. 1A), as well as from co- bosa et al. (2003), Barbosa (2007), and Souza eval offshore basins along the African conti- (2006), the Beberibe Formation (Santonian?- nental margin along the central segment of the Campanian), the Itamaracá Formation (Cam- South Atlantic Ocean (Moulin et al., 2005). panian-Maastrichtian), the Gramame Forma- We follow here the interpretation that the tion (Maastrichtian), and the Maria Farinha marginal area between the PESZ and the Patos Formation (Palaeocene-Eocene?) are found in Shear Zone (PASZ) corresponds to the coastal the coastal area between the PESZ and the Paraíba Basin and that the area from the PESZ PASZ. to the TH corresponds to the East Platform of In the present contribution, we present the Potiguar Basin (Fig. 1). This interpretation facies models, a sequence-stratigraphic analy- is based primarily on stratigraphical and sedi- sis and C- and O-isotope geochemistry results mentological evidence presented by, among for the upper three of these four sedimentary others, Mabesoone & Alheiros (1993), Feitosa formations of the Paraíba Basin: the Itamaracá et al. (2002), Barbosa et al. (2003) and Barbosa Fm. (calcareous sandstones and limestones), (2007). the Gramame Fm. (limestones and marls) and the Maria Farinha (limestones and marls), and Fig. 1. Location maps. A: Location of the Paraiba Basin in northeastern Brazil. B: Detail of the Paraíba Basin, showing its division into sub-basins, its Maastrichtian-Danian carbonate deposits and locations of investigated quarries. Sedimentary development and isotope analysis of deposits... 105 Fig. 2. Stratigraphy of the onshore Paraíba Basin, showing the distribution of the units over the various sub-basins, the infi ll of which was infl uenced mainly by tectonic events during the Late Cretaceous. for the boundaries that separate the Itamaracá several researchers (Sial et al., 1993; Ferreira et and Gramame Formations (Campanian/Maas- al., 1996; Barbosa et al., 2005; Sabino et al., 2005, trichtian) and the Gramame and Maria Farinha Nascimento-Silva et al., 2008). All these au- Formations (Maastrichtian/Danian = K/Pg) thors have suggested an enrichment of carbon (see Fig. 2). near the K/Pg boundary and a marked break The unconformity that coincides with the after this limit. Also, the C- and O-isotope be- K/Pg boundary is only preserved in the Olinda havior in the Cretaceous-Palaeogene boundary Sub-basin (Fig. 1B). Since the work of Alvarez registered in the Poty quarry is similar to that et al. (1980) on the origin of the Cretaceous/Pal- observed elsewhere in the world. aeogene boundary event, much additional evi- The objective of the present contribution is dence that corroborates their impact theory has a short reconstruction of the geological devel- been found. For example: iridium anomalies in opment of the study area just before, during the K/Pg contact layer elsewhere in the world, and just after the K/Pg transition. This is done and the discovery of a large-scale impact cra- on the basis of a combination of changes in the ter in the subsurface of the Yucatan Peninsula sedimentological development and analysis of (Mexico). In South America, preserved suc- the carbon and oxygen isotopes. cessions that include the actual K/Pg boundary are known from the Paraíba coastal basin (Albertão, 1993; Sial et al., 2001, 2003; Barbosa Characteristics of the Paraíba & Neumann, 2004) and the Yacoraite region of Basin the Neuquen Basin, Argentina (Sial et al., 2001, 2003). C- and O-isotope studies of the K/Pg bound- The Paraíba Basin (Fig. 1) is subdivided into ary layers have previously been analyzed by three sub-basins: Olinda (South), Alhandra 106 Virgínio Henrique Neumann et al. (middle) and Miriri (Morth). The Olinda Sub- interpreted by previous researchers to have basin is bounded in the South by the PESZ, and formed in shallow lagoons that experienced in the North by the Goiana High (a NE–SW some estuarine infl uences. This unit represents trending basement high that strikes toward the a rapid transgressive pulse over the basin. This coast, north of Goiana City). It has a semicir- transgressive event was driven mainly by tec- cular form, and it contains the area where the tonic subsidence, which affected this region of basin is widest. Only in this sub-basin, a rela- north-eastern Brazil during the Late Campa- tively continuous Maastrichtian-Palaeocene nian (Barbosa & Lima Filho, 2006; Barbosa et carbonate succession has been preserved. Little al., 2004, 2007). At the top of this succession, a work, though, has been done on these depos- phosphate-rich, sandy carbonate bed is present. its, with the exception of exposures in the Poty Based on gamma-ray logs and sedimentologi- Quarry and at Ponta do Funil. The Poty Quarry cal profi les that indicate the end of the trans- (outcrops and cores) contains the best studied gressive cycle and the beginning of a carbonate K/Pg transitional beds in South America. domain, this phosphate-rich level is interpreted as a maximum fl ooding surface (MFS). Within the basin, the thickness of this phosphatic bed Material and methods varies between 50 cm and 6 m. This phosphatic layer (Maastrichtian) marks the Campanian/ For the present study, four quarries (Poty, Maastrichtian boundary. Itapessoca, Cipasa and Cimepar) and one drill The Campanian/Maastrichtian boundary core (Poty Quarry) were studied and sampled has been studied mainly in cores. In cores, these (Fig. 1B). Fifty-three thin sections were made easily weathered, silty, carbonate-rich phos- from selected samples collected in these quar- phate deposits are easily observed; in outcrops, ries; they were studied petrographically to the phosphatic bed is rarely well-exposed. It identify the sedimentary lithofacies and micro- represents the MFS of the transgressive system facies. In addition, cathodoluminescence (CL) tract (Barbosa & Lima Filho, 2006; Barbosa et analysis was done on the thin sections to evalu- al., 2004, 2007). ate authigenic cement types. Additionally, 165 samples, spaced 30 cm apart, from a 52 m drill core made at the Poty Quarry, were analyzed Gramame and Maria Farinha for C and O isotopes, using McCrea´s (1950) Formations method. The sampled core includes Late Cam- panian, Maastrichtian and Danian carbonates. Based on the stable-isotope results, 25 sam- Both formations consist of shoaling-upward ples were chosen for major and trace chemis- cycles that consist of dark- to light-grey to try analyses by XRF. The elements that were yellowish, fi ne- to medium-grained, marly analyzed include Sr, Mn, Mg, Ca and Rb. These limestones alternating with marl beds (Fig. 3). elemental analyses were carried out in order to These lithologically monotonous deposits are strengthen the interpretation of the isotope re- characterised by even, laterally continuous, sults and to verify that the stable-isotope signal planar bedding that clearly extends beyond the was not signifi cantly altered by diagenesis. scale of the outcrops (Fig. 3). These carbonate deposits were deposited on a shallow carbonate platform that was domi- Formations under investigation nated by low-energy carbonate muds. Bioclasts are common and some terrigenous infl ux was also present. In some intervals, reworked bio- Itamaracá Formation clasts are concentrated, which is inferred to represent bottom winnowing during storms. The Itamaracá Formation consists of carbon- These tempestite layers also contain burrows ate-cemented sandstones and shales that were dominated by the genus Thalassinoides.

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