Orbital Pacing of Sedimentation and Reservoir Architecture in Pre-Salt Carbonates

Cyclostratigraphic methods provide an effective framework for resolving temporal organization and stratigraphic architecture in sedimentary systems affected by complex depositional processes. In this study, spectral analysis of gamma-ray logs from two wells (A and B) drilled into Cretaceous pre-salt carbonate reservoirs of the Santos Basin, offshore Brazil, is used to investigate orbital-scale sedimentary cyclicity. The objective is to improve temporal resolution and to evaluate the implications of astronomically forced signals for reservoir characterization and exploration-focused stratigraphic models. Well-defined orbital signals are identified, characterized by persistent cyclicities between ~21 and 28 m and statistically significant spectral peaks above the 95% confidence level. These cycles are interpreted as expressions of the long-eccentricity (405 kyr) orbital cycle. Eight 405 kyr cycles are recognized in well A, whereas seven cycles are identified in well B, corresponding to time intervals of ~3.2 Myr and ~2.8 Myr, with average sedimentation rates of ~6.7 cm/kyr and ~9.05 cm/kyr, respectively. Independent sedimentation rate estimates derived from the TimeOpt method (~6–8 cm/kyr) support these results, while comparison with evolutionary harmonic analysis (EHA) reveals a stable low-frequency spectral pattern throughout the studied interval. The persistence of these cycles across different lithologies highlights the dominant role of astronomical forcing on sedimentation processes, even within complex carbonate systems. In addition, maxima in long-eccentricity cycles are systematically associated with maximum regressive surfaces. These findings demonstrate the value of cyclostratigraphy as a robust tool for refining stratigraphic correlations in pre-salt carbonate reservoirs, constraining sedimentation rates, improving chronostratigraphic frameworks, and supporting reservoir development and future exploration strategies.