The Cretaceous–Tertiary boundary in southern low-latitude regions: preliminary study in Pernambuco, northeastern Brazil |
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| Authors: | Gilberto A Albertão Eduardo AM Koutsoukos Marília PS Regali Moses Attrep Jr Paulo P Martins Jr |
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| Institution: | PETROBRÁS-DESUD, Rua Elias Agostinho, 665, Imbetiba, 27913-350 Macaé, RJ, Brazil;;PETROBRÁS-CENPES, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil, and Geologisch-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany;;PETROBRÁS-CENSUD, Rio de Janeiro, RJ, Brazil;;Los Alamos National Laboratory, INC-11, MS: J514, 87545 Los Alamos, NM, USA;;Universidade Federal de Ouro Preto, Departamento de Geologia, Campus do Morro do Cruzeiro, 35400-000 Ouro Preto, MG, Brazil |
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| Abstract: | A preliminary integrated study of a Cretaceous-Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non-graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea-level lowstand, the former possibly generated by the K/T boundary Yucatán impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm-thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis ) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock-metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite-like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact-derived material has not been found in the uppermost Cretaceous beds. |
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