“ORBITAL RECORDS SHAPED BY DEPOSITIONAL ARCHITECTURE IN A CONTINENTAL MARGIN: CYCLOSTRATIGRAPHIC–SEISMIC ANALYSIS OF THE MIOCENE ALBACORA OILFIELD (CAMPOS BASIN, BRAZIL)”

Abstract

This master's dissertation aims to integrate cyclostratigraphy and seismic stratigraphy, together with Integrated Prediction Error Filter Analysis (INPEFA) and the Relative Geological Time (RGT) model, to investigate Miocene deposits in the Albacora Oilfield, Campos Basin, Brazil. Well-log gamma-ray data from six wells, distributed along two dip sections and one strike section, were used as paleoclimatic proxies through spectral analysis to identify periodic components related to Milankovitch cycles. Additionally, 3D seismic data acquired over the Miocene deposits of the Albacora oilfield were used to construct geological sections and to analyze the evolution of the depositional system. Cyclostratigraphic analysis revealed clear evidence of orbital forcing within the records. Spectral and evolutionary harmonic analyses allowed the identification of cycles interpreted as long and short eccentricity, obliquity and precession, most of which exceed the 95–99% confidence levels, consistent with expected orbital ratios for 14 Ma, with long- and short-eccentricity wavelengths of ~145 m and ~47 m. Results from correlation coefficient (COCO) and evolutionary correlation coefficient (eCOCO) analyses confirmed the presence of orbital forcing and indicated maximum sedimentation rates ranging from 30.0 to 45.4 cm/kyr across the wells, consistent with previously reported values (~30 cm/kyr) for the same region. Seismic stratigraphic analysis reveals a mainly progradational system, with better stratigraphic preservation in the mid-slope domain, where thicker successions and up to three long-eccentricity cycles are recorded, in contrast to only one cycle on the shelf and at the base of the slope. These variations in stratigraphic preservation, reflected in differences in the number of long-eccentricity cycles identified along dip-oriented seismic sections, demonstrate that seismic-supported multi-well correlation is a useful tool for assessing stratigraphic completeness and, consequently, for improving 2D/3D cyclostratigraphic correlation. Hypotheses involving discontinuous sedimentation and/or depositional hiatuses associated with erosional processes were explored to account for the absence of these records in the shelf and base-of-slope settings. The RGT model corroborates a progradational pattern and reveals variability in sedimentation rates along strike sectrion, whereas INPEFA delineates key stratigraphic surfaces linked to hiatuses and erosional events. These findings underscore the need to account for depositional system dynamics when interpreting cyclostratigraphic signals and refining geological time estimates. Estimates of depositional duration accounting with variations in stratigraphic preservation were compared with biostratigraphic constraints, reshaping previous estimates of depositional duration. To our knowledge, this study provides the first systematic investigation of the lateral preservation of astronomical cyclicity within a seismic volume as controlled by depositional architecture, and demonstrates how incorporating this variability can substantially modify geological time estimates.