C AND O-ISOTOPE STRATIGRAPHY OF ...

4 downloads 0 Views 227KB Size Report
Nascimento Silva, M.V. et al. ... Nascimento-Silva, M.V. 1, Sial, A.N. 1, Neumman, V.H. M.L. 2, Barbosa, J. A. 2, ..... W.W. Norton & Company, New York, 575 pp.
VI South American Symposium on Isotope Geology San Carlos de Bariloche - Argentina - 2008

C AND O-ISOTOPE STRATIGRAPHY OF CARBONATES FROM THE K-T BOUNDARY, PARAÍBA BASIN, NORTHEASTERN BRAZIL Nascimento-Silva, M.V. 1, Sial, A.N. 1, Neumman, V.H. M.L. 2, Barbosa, J. A. 2, and Ferreira, V.P.1 1

LABISE, Department of Geology, Federal University of Pernambuco, Recife, PE, Brazil valberlandiageo@ yahoo.com.br 2 LAGESE, Department of Geology, Federal University of Pernambuco, Recife, PE, Brazil Keywords: isotope geochemistry, K-T boundary, Paraíba basin ABSTRACT The Paraíba basin is characterized by a complete sedimentary sequence deposited in the Maastrichtian and in the Paleocene. The study area is located at the Poty quarry, north of Recife, state of Pernambuco. C and O stable isotopes have been analyzed in 165 carbonate samples from a drill hole at the Poty quarry. In 25 of these samples, major, minor and trace elements have been analyzed by X-ray fluorescence. Chemostratigraphic profiles (δ13C, δ18O, Mg/Ca, Si, Al, Mn/Sr, Rb and Sr) have been prepared and compared with chemostratigraphic profiles described in the literature pertaining the K-T. These limestones were deposited in a period of marine transgression in the Early Maastrichtian, with increasing temperature and bioproductivity, according to the obtained isotopic signals (δ18O varies from -3 to -5 ‰PDB; and δ13C, from 1,2 to 0,1 ‰PDB) reaching its maximum in the Late Maastrichtian, with values of δ13C around +2,3 ‰ PDB. In the early Danian, there was a small positive excursion with values around +2 ‰PDB, falling to values of +1 ‰PDB, right after the Maastrichtian-Danian transition. After the K-T transition, there was an increase of SiO2 and Al2O3 that can be associated to the influence of terrigenous material. Upsection, there was a period of marine regression with a bioproductivity fall as recorded in theδ13C curve (+1 ‰PDB) and carbonate sediments with higher Mg/Ca ratios (dolomitic limestones) possibly deposited in shallow-marine environment. The C- and O-isotope behavior in the Cretaceous-Paleogene boundary registered in the Poty quarry is similar to that observed elsewhere in the world. INTRODUCTION The events relating to the Cretaceous-Paleogene boundary (K-T) are subjects of diverse works in the field of geology and paleontology. Alvarez and et al. (1980) suggested the hypothesis of an impact of a meteorite resulting in environmental changes that could have caused the extinguishing in mass of the species that inhabited the Earth. This hypothesis is based on the anomalous iridium enrichment that is abundant in meteorites, but rare on the terrestrial crust, in section of carbonate rocks of deep marine waters, near Gubbio City, in Italy. These geologic and geochemistry data are subjects of a great number of research and discussion, and consist of geologic and paleontological landmark, for suggesting the causes that would have taken the disappearance in mass of the species in the Cretaceous-Paleogene boundary. Since the work of Alvarez et al. (1980), diverse evidences that corroborate with this theory had been found, for example: iridium anomalies in other localities of the world, and the discovery of a crater in the Peninsula of Iucatan, in Mexico, that would be related to the impact of the meteorite. In the South America these registers of the K-T boundary can be found in the Paraíba coastal basin, Northeastern Brazil (Albertão, 1993; Sial et al. 2001, 2003) and Yacoraite, Neuquen basin, in Argentina (Sial et al., 2001, 2003). The Paraíba basin is characterized for containing a complete carbonate infill, registering the Upper Cretaceous (Gramame Formation-Maastrichtiano) and the Lower Paleogene (Maria Farinha Formation-Paleoceno), including a possible iridium geochemistry anomaly (Albertão, 1993). C and O isotope studies in outcrops of this K-T boundary sequence already had been analyzed previously by researches (Sial et al., 1993; Ferreira et al., 1996; Barbosa et al., 2005; Sabino et al., 2005), however this work had studied well core samples. The study area is located at the Poty quarry, 30 km north of Recife, State of Pernambuco, Northeastern Brazil (Fig. 1).

Nascimento Silva, M.V. et al.: C and O-isotope stratigraphy of carbontes from the K-T boundary, Paraiba Basin. Northeastern Brazil.

0

VI South American Symposium on Isotope Geology San Carlos de Bariloche - Argentina - 2008

Figure 1. Study area, Poty quarry, north of Recife Town.

GEOLOGICAL SETTING The area of onshore Paraíba basin is 7.000 km2, and their offshore area is about 31.400 km2, extending itself for the continental platform until 3.000 meters deep. The whole sequence here studied comprises marine carbonate sediments from the Campanian (Itamaracá Formation), Maastrichtian (Gramame Formation), and Danian (Maria Farinha Formation) ages. The Itamaracá Formation was described by Kegel (1955) and defined as a transitional unit from continental to marine phase representing coastal estuary and lagoon deposits. It is composed of carbonate sandstones, shales, and limestones with siliciclastic grains, rich in fossils. A phosphate level was observed in the top of this formation. This phosphate unit was defined as a maximum flooding surface, that is a widespread marine flooding surface that separates the underlying transgressive systems tract from the overlying highstand systems tract (Souza, 1998, 2006; Lima Filho et al., 1998; Barbosa, 2004, 2007). The surface also marks the deepest water facies within a sequence. The maximum flooding surface represents a change from retrogradational to progradational parasequence patterns. It commonly displays evidence of condensation or slow deposition. The Gramame Formation is overlying the Itamaracá Formation, and it is constituted by limestone and marl deposited in a shallow (100 to 150 m deep) carbonate platform (Muniz, 1993). This formation was defined as a highstand system tract, and in its upper part shows an increasing of terrigenous sediments representing an regressive event before the limit of the Danian age. This shallowing upward is in relationship with a forced regression, induced for a tectonic rising up. In the Gramame and Maria Farinha formations boundary there is erosive discordance characterized by carbonate sequence within conglomarate intraclastic breccias, associated to the K-T boundary (Albertão, 1993; Albertão and Martins Jr., 1996; Stinnesbeck and Keller, 1996; Barbosa, 2004; Barbosa et al., 2006). The Maria Farinha Formation is constituted by limestones, marly limestones, and marls in the lower part (Beurlen, 1967a, 1967b). This formation was deposited in a lowstand system tract as being observed in the geochemical data. MATERIAL AND METHODS Hundred sixty five well core samples of carbonate rocks were analyzed for O and C isotope. This well core reached 52 m of the infilling limestone and marl from the Upper Campanian to Lower Paleogene. Twenty five samples analyze XRF (major and traces elements) as meng at determing whether isotopic signal (Mn/Sr ratio, Rb and Sr) was primary or had been influenced by diagenetic processes (Jacobsen and Kaufman, 1999). SiO2, Al2O3 and P2O5 contents have seen also analyzed. Nascimento Silva, M.V. et al.: C and O-isotope stratigraphy of carbontes from the K-T boundary, Paraiba Basin. Northeastern Brazil.

0

VI South American Symposium on Isotope Geology San Carlos de Bariloche - Argentina - 2008

RESULTS An overall variation of δ13C from +2,3 a –1,8 ‰PDB was observed in the isotope curves at the Poty quarry (Fig. 2). Positive values are found in all the Campanian Itamaracá Formation, with δ13C from +1 to +2 ‰ PDB. Negative values (-1,2, -0,3 and 0,1 ‰PDB), however, are seen by the Campanian-Maastrichtian transition. Samples right above this point are enriched in phosphates (3,46 to 5,28 %) and with positive δ13C values (from zero to +1,9 ‰PDB) suggesting an increase of marine bio-productivity. During the Maastrichtian one observes a tendency towards positive values of δ13C until the early Danian, reaching values of +2,3 ‰PDB, with two negative peaks in the midle Maastrichtian (-1,8 % and 0,6 ‰PDB). In the early Danian, there is a small positive excursion with values around +2 ‰PDB followed by a drop to +1 ‰PDB right after the Maastrichtian-Danian transition. The δ18O values vary from -6,6 to 0,8 ‰PDB with a tendency to negative values during the Campanian (0,8 to – 2,7 ‰PDB) and with a negative excursion right after the Campanian-Maastrichtian transition, reaching values from -3 to -5 ‰PDB during all the early Maastrichtian, returning to values around -2 ‰PDB in the middle to upper Maastrichtian. And important negative excursion right after the Maastrichtiaan-Danian, returning to values around -2 to -1 ‰PDB in the Danian. Right after the K-T transition increases SiO2, from 23,0 to 37,6 %, and Al2O3, from 6,8 to 15,2 %. This is associated to an increase of the amount of siliciclastic material in the Basin.

Poty Quarry Maria Farinha Fm

0 0

(LST)

1 0 0 0 10

K-T

(HST)

Gramame Fm

2 0 0 0 20

3 0 0 0 30

Itamaraca Fm

4 0 0 0 40

(TST)

5 0 0 0 50

-6

-3 18

Ωδ O

0

-2

0

Ωδ 13C

2

0

0.4

Mn/Sr

0

0.4

Mg/Ca

0

400

Sr

800

0

40

80

Rb

Figure 2. O and C isotopes, and Mn/Sr, Mg/Ca, Sr and Rb at Poty Quarry sections, Paraíba Basin, NE Brazil.

CONCLUSIONS The O isotope signature suggests a cold climate during the Upper Campanian, and a heating phase during the Lower Maastrichtian, following a gradual decrease of the temperature during the Middle and Upper Maastrichtian to the Paraíba basin. However, it was observed a succession of negative and positive peaks in the Upper Maastrichtian. These peaks could be related to climatic variations as like those suggested by Keller (2001, 2005) and Keller et al. (2003, 2004) referring to multiple impacts before the biggest one. The C isotope signatures are related to the marine productivity and show that the organic productivity fall down after the Campanian-Maastrichtian boundary. But, also shows a gradual recovery during the whole Maastrichtian. An enrichment of C was observed near the K-T boundary, showing a marked break after this limit.

Nascimento Silva, M.V. et al.: C and O-isotope stratigraphy of carbontes from the K-T boundary, Paraiba Basin. Northeastern Brazil.

0

VI South American Symposium on Isotope Geology San Carlos de Bariloche - Argentina - 2008

After the K-T transition, there was an increase of SiO2 and Al2O3 that can be associated to the influence of terrigenous material. Upsection, there was a period of marine regression with a bioproductivity fall as recorded in theδ13C curve (+1 ‰PDB) and carbonate sediments with higher Mg/Ca ratios (dolomitic limestones) possibly deposited in shallow-marine environment. The C- and O-isotope behavior in the Cretaceous-Paleogene boundary registered in the Poty quarry is similar to that observed elsewhere in the world. ACKNOWLEDGEMENTS MVNS is grateful CNPq Agency for doctoral scholarship. We would like to thank Gilsa Maria Santana and Vilma Sobral Bezerra for assistance with the stable isotope analyses in the LABISE. LAGESE. This study was supported by the Paraíba Drill Project/UFPE/CNPq/Princeton University for the samples of the well cores. REFERENCES Albertão, G.A. Martins Jr., P. P. 1996. A possible tsunami deposit at the Cretaceous-Tertiary boundary in Pernambuco, Northeastern Brazil. Sedimentary Geology. 104: 189-201. Albertão, G. A. 1993. Abordagem Interdisciplinar e Epistemológica sobre as Evidências do Limite Cretáceo-Terciário, com Base em Leituras Efetuadas no Registro Sedimentar das Bacias da Costa Leste Brasileira. Dissertação de Mestrado, Departamento de Geologia daEscola de Minas da Universidade Federal de Ouro Preto, 255 pp. Alvarez, L.W., Alvarez, W., Asaro, F., and Michael, H.V. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science. 208: 1095-1108. Barbosa, J. A. 2007. A deposição carbonática na faixa costeira Recife-Natal: aspectos estratigráficos, geoquímicos e paleontológicos. Tese de Doutorado, Centro de Tecnologia e Geociências, Universidade Federal de Pernambuco, 270 pp. Barbosa, J.A., Viana, M.S.S. e Neumann, V.H. 2006. Paleoambientes e icnofácies da seqüência carbonática (Cretáceo e Paleogeno) da Bacia da Paraíba, NE do Brasil. Revista Brasileira de Geociências. 36(3): 73-90. Barbosa J.A, Sial, A.N Ferreira, V.P, Neumann, V.H. 2005. Isótopos de Carbono e Oxigênio a través do Maastrichtiano e Paleoceno da bacia da Paraíba, Ne do Brasil. X Congresso Brasileiro de Geoquímica e II Simpósio de Geoquímica dos Países do Mercosul. Barbosa, J.A. 2004. Evolução da Bacia da Paraíba durante o Maastrichtiano-Paleoceno: formações Gramame e Maria Farinha, NE do Brasil. Dissertação de Mestrado, Centro de Tecnologia e Geociências, Universidade Federal de Pernambuco, 230 pp. Barbosa, J.A. and Neumann, V.H. 2004. The Poty quarry conglomeratic bed: the record of a tsunami triggered by an impact?. 67th Meeting of the Meteoritical Society, Rio de Janeiro. Meteoritics and Planetary Sciences.39: 33-33. Barbosa, J.A., Souza, E.M., Lima Filho, M.F., Neumann, V.H. 2003. A estratigrafia da Bacia Paraíba: uma reconsideração. Estudos Geológicos. 13: 89-108. Universidade Federal de Pernambuco. Beurlen K. 1967a. Estratigrafia da faixa sedimentar costeira Recife-João Pessoa. Bol. Geol. 16(1): 43-53. São Paulo, SP. Beurlen K. 1967b. Paleontologia da faixa sedimentar costeira Recife-João Pessoa. Bol. Geol.: 16(1): 73. São Paulo, SP. Ferreira, V.P., Sial A.N., and Menor, E.A. 1996. Carbon and Oxigen Isotopes in offshore and continental Mesozoic and Tertiary limestones, NE Brasil: the K-T boundary and Tertiary climatic variations. Acta Geologica Hungarica. 39: 43-46. Jacobsen, S.B. and Kaufman, A.J. 1999. The Sr, C and O isotopic evolution of Neoproterozoic seawater. Chemical Geology. 161: 37-57. Kegel, W. 1955. Geologia do fosfato de Pernambuco. Div. Geol. Min. DNPM. Boletim 157, 54 pp. Keller, G. 2005. Impacts, volcanism and mass extinction: random coincidenceor cause and effect? Australian Journal of Earth Science. 52: 725-757. Keller, G., Adatte, T., Stinnesbeck, W., Stüben, D., Berner, Z., Kramar, U., and Harting, M. 2004. More evidence that the impact predates the K-T mass extinction. Meteoritics and Planetary Science. 39: 1127-1144. Keller, G., Stinnesbeck, W., Adatte, T., and Stüben, D. 2003. Multiple impacts across the Cretaceous-Tertiary boundary. Earth-Science Rewiews. 62: 327-363. Keller, G. 2001. The end-cretaceous mass extinction in the marine realm: year 2000 assessment. Planetary and Space Science. 49: 817–830. Lima Filho, M. F., Monteiro, A. B., and Souza, E. M. 1998. Carbonate sections of the Paraiba and Pernambuco Basins, Northeastern Brazil: Implications for the late stages of opening of Southern Atlantic Ocean. 15th. International Congress of Sedimentology, Alicante. Abstracts: 504-505.

Nascimento Silva, M.V. et al.: C and O-isotope stratigraphy of carbontes from the K-T boundary, Paraiba Basin. Northeastern Brazil.

0

VI South American Symposium on Isotope Geology San Carlos de Bariloche - Argentina - 2008

Muniz, G.C.B. 1993. Novos moluscos da Formação Gramame, Cre áceo Superior dosEstados da Paraíba e de Pernambuco, Nordeste do Brasil. Departamento de Geologia, Universidade Federal de Pernambuco. Publicação Especial. 1: 202 pp. Sabino, I., Sial, A.N., Ferreira, V.P., Marquillas, R.A. y de Papa, C. 2005. Características estratigráficas e isotópicas del limite K-T em las Cuencas de Pernambuco-Paraíba (Brasil) y Salta (Argentina). Porto de Galinhas. X Congresso Brasileiro de Geoquímica e II Simpósio de Geoquímica dos Países do Mercosul (CD-ROM). Sial, A. N., Alonso, R.N., Toselli, A.J., Acenolaza, F.G., Parada, M. A., and Rossi de Toselli, J. 2003. C Minimum in the Late Cretáceous-Paleocene Yacoraite Carbonate Sequence, NW Argentina. IV South American Symposium on Isotope Geology. Extended Abstracts: 345 – 348. Sial, A.N., Ferreira, V.P., Chaves, N.S. 1993. Isótopos de Carbono e a Transição Cretáceo-Terciário no Nordeste do Brasil. XV Simpósio de Geologia do Nordeste, Natal, RN. Sociedade Brasileira de Geologia, Núcleo Nordeste. Boletim.13: 44. Souza, E.M. 1998. Levantamento radiométrico das unidades estratigráficas da Bacia Paraíba. Dissertação de Mestrado, Centro de Tecnologia e Geociências, Universidades Federal de Pernambuco. 152 pp. Souza, E.M. 2006. Estratigrafia da seqüência clástica inferior (andares Coniaciano- Maastrichtiano Inferior) da Bacia da Paraíba, e suas implicações paleogeográficas. Tese de Doutorado, Centro de Tecnologia e Geociências, Universidade Federal de Pernambuco, 350 pp. Stinnesbeck, W. and Keller, G. 1996. Environmental changes across the Cretaceous-Tertiary Boundary in Northeastern Brazil. In MacLeod, N. and Keller, G. (Eds): Cretaceous-Tertiary mass extinctions: biotic and environmental changes. W.W. Norton & Company, New York, 575 pp.

Nascimento Silva, M.V. et al.: C and O-isotope stratigraphy of carbontes from the K-T boundary, Paraiba Basin. Northeastern Brazil.

0