Gilberto A. Albertão

A possible tsunami deposit at the Cretaceous-Tertiary boundary in Pernambuco, northeastern Brazil

Abstract Interdisciplinarry and integrated investigations of a stratigraphic succession spanning the Cretaceous-Tertiary (K-T) boundary in Pernambuco (the Poty Quarry section, near Recife), northeastern Brazil, provides direct evidence for the hypothesis of an extraterrestrial bolide impact event. Discussions on the exact position of the K-T boundary point to an impact event in the earliest Danian. One particular bed at the base of the Maria Farinha Formation shows sedimentary characteristics and exotic (probably impact-derived) material which suggest the action of a tsunami wave. The distribution of iridium concentrations throughout the studied succession records a major peak of iridium (up to 69 times the background levels) at about 15–20 cm above the main tsunami bed.

TSUNAMIITES–CONCEPTUAL DESCRIPTIONS AND A POSSIBLE CASE AT THE CRETACEOUS–TERTIARY BOUNDARY IN THE PERNAMBUCO BASIN, NORTHEASTERN BRAZIL

Abstract An important occurrence of a highly probable impact-derived tsunamiite in the Pernambuco Basin, northeastern Brazil, is discussed in detail. This possible tsunamiite occurs within a sedimentary succession spanning the Cretaceous/Tertiary (K/T) boundary, where interdisciplinary and integrated investigations provide direct evidence for the impact of an extraterrestrial bolide. The bed involved shows sedimentary characteristics and exotic (probably impact-derived) material that suggest the action of tsunami waves. The iridium (Ir) concentration throughout the succession records a major peak (up to 69 times the background levels) at about 60 cm above the base of the interpreted tsunamiite. The controversial exact position of the K/T boundary as well as the implications of the currently different interpretations is discussed.

Petrographic and Geochemical Studies in the Cretaceous-Tertiary Boundary, Pernambuco — Paraíba Basin, Brazil

The stratigraphic record of the Cretaceous-Tertiary (K-T) boundary (the Poty quarry section) in the Pernambuco-Paraiba coastal basin, Northeastern Brazil, provides evidence supporting the interpretation that the impact of a bolide has caused the widespread biotic extinction at the end of the Cretaceous. New considerations relating to the distribution of iridium and fluorine, as well the occurrence of shocked quartz, spherules, tsunamite bed, biotic extinction and other possible impact-related characteristics have been brought together in this report. The relative abundance of 35 chemical elements were analysed and are presented in geochemical profiles. A geochemical break for most of these elements is better expressed in the geological contact than in the K-T boundary, although iridium and fluorine anomalies have been determined exactly at the boundary. Palaeoenvironmental characterisation is determined by micropalaentological considerations, stable isotope data, and the presence of phosphatised fragments. Most of the particular characteristics described here, such as the geochemical anomalies (iridium, total organic carbon and fluorine) and the presence of a tsunami deposit, of possible shocked quartz grains, and of some impact-related spherules, give support to previous preliminary interpretations of this stratigraphic boundary as a sedimentary record of a catastrophic event marking the K-T boundary.

Seismically constrained reservoir quality modeling - an example in Eocenic turbidites of Campos Basin, Brazil.

Summary The integration of seismic data into the reservoir characterization process is very important in cases where the amount of well information is sparse. This is the case for most of the Campos Basin oil fields as well as for the field object of this study. Due to the large well spacing in this field, the use of seismic derived attributes to constrain the reservoir modeling is of paramount importance. For this case, the seismic amplitude, the most common seismic attribute used for reservoir characterization in Campos Basin, shows very weak correlation with the reservoir properties mainly due to strong impedance variations of the overlain beds. The alternative attribute chosen was the acoustic impedance derived from a post-stack seismic inversion. Such attribute showed better correlation with the reservoir properties of interest and it was then incorporated to the reservoir characterization process via geostatistical procedures. Stochastic simulation algorithms were used to generate facies and porosity models: the acoustic impedance was used as a soft constraint for the facies modeling and the facies distribution conditioned the porosity realizations. Based on the geological knowledge of the reservoir, some porosity models were selected to be the basis of the flow simulation model.