CICLOSTRATIGRAPHY OF SEDIMENTARY RECORDS IN SOUTHERN ALBACORA FIELD, CAMPOS BASIN, BRAZIL

Abstract

In this work, we integrate seismic and cyclostratigraphic interpretations carried out in the thinning region of the northern portion of the Campos Basin, Brazil. For this purpose, gamma-ray data from three wells, arranged in a dip profile, and 3D seismic acquisitions located in the Miocene deposits of the Albacora hydrocarbon field were used. Only the most onshore well (1-RJS-297) has chronostratigraphic control through biozones that have been used as tie-points in the generation of the astronomical time scale. The other two wells did not have tie-point records and therefore had floating astronomical time scale. This issue has been addressed by associating ages with seismic reflectors common to all wells. The association between these ages was made through cyclostratigraphy and the biozones present in well 1-RJS-297. The results of cyclostratigraphic analyses have shown that orbital forces modulate the deposition of sediments. Spectral analysis, in conjunction with evolutionary harmonic analysis, revealed sedimentary cycles interpreted as cycles of long and short eccentricity, obliquity, and precession. Sediment accumulation rate analyses confirmed Milankovitch cycle modulation and generated values between 28 and 45 cm/kyr, which corroborate the literature. Thus, seismic interpretation was essential for the correlation between wells and the establishment of Milankovitch cycles in geological time. The integration of these two methods of deposit analysis, sismostratigraphic and cyclostratigraphic, made it possible to perform a high-resolution 2D chronostratigraphy for the study area, comprising a period of 3 Myr. The data series studied comprise the deposits of the middle Miocene and record the Optimal Climate of the Miocene, as well as the significant sea-level falls that define it. The interpretation of these records provided important inferences on the sedimentary and paleoclimatic evolution of the region.