Thermal Maturity and Transformation Ratios of Aptian–Turonian Petroleum Source Rocks in the Pará-Maranhão Basin: Insights from 1D Basin Modeling

One-dimensional (1D) basin modeling was performed for well 1-MAS-26-MA in the Pará-Maranhão Basin (equatorial Atlantic margin, Brazil) using PetroMod, integrating stratigraphic, geochemical, lithological, and thermal data to reconstruct burial history, thermal maturity, and hydrocarbon generation for three petroleum source rock intervals. The stratigraphic column spans from the Aptian (~124 Ma) to the Pleistocene, reaching 4,300 m depth. The three petroleum source rock intervals modeled are the Codó Formation (Aptian, 117–117.5 Ma), the Caju Group (Albian, 100–111 Ma), and the Travosas Formation (Turonian, 89–93 Ma), all assigned Type II kerogen with kinetic parameters from Baur (2019). Boundary conditions were reconstructed through geological time: paleowater depth ranged from 50–100 m during the Early Cretaceous to 400 m at peak rifting, declining to ~250 m at present; sediment-water interface temperatures decreased from 29°C in the Cretaceous to ~20°C today. Heat flow rose from 40–45 mW/m² in the early Aptian to a peak of 80 mW/m² at ~100 Ma, associated with the transform-extensional opening of the Equatorial Atlantic, and declined to 66 mW/m² at present, yielding a geothermal gradient of 33°C/km. Thermal calibration used two bottom-hole temperatures (100°C at 3,000 m; 135°C at 4,100 m) and six vitrinite reflectance measurements in the Travosas Formation (0.43 %Ro at 1,932 m; 0.49 %Ro at 2,094 m; 0.51 %Ro at 2,256 m; 0.51 %Ro at 2,418 m; 0.54 %Ro at 2,562 m; 0.60 %Ro at 3,084 m). The % Ro (Nielsen et al., 2015) was selected over easy%Ro (Sweeney & Burnham, 1990), which overestimates reflectance by up to 0.35 %Ro in the 0.5–1.7 %Ro range covered by this dataset. The Codó Formation reached 10% transformation ratio (TR) at 82.33 Ma and 50% TR at 61.70 Ma, currently exhibiting TR = 83.72%. The Caju Group crossed 50% TR at 35.96 Ma and currently shows TR = 77.13%, with modeled %Ro of 0.76–1.19% and Tmax of 440–464°C, confirming advanced generation and expulsion since the Paleogene. The Travosas Formation initiated significant generation at 26.33 Ma and presents TR = 36.43% at present, consistent with measured %Ro of 0.60% and Tmax of 416–447°C, placing it at peak oil generation to early expulsion. Maastrichtian–Campanian intervals show TR < 10% throughout burial history, with Tmax of 418–430°C, confirming immature to early-mature status. These results identify the Aptian and Albian intervals as the dominant petroleum kitchen in this sector, supporting exploration of deep Albian–Aptian plays in slope and deepwater settings of the Pará-Maranhão Basin.