Organic geochemical investigation of cretaceous source rocks with varying thermal maturity levels in the East Andes (Boyacá, Colombia)

Abstract

This study encompasses a geochemical investigation of Cretaceous source rocks from the Eastern Cordillera (Colombia). This basin represents an interesting area for geochemical studies due to its abundance of organic matter-rich levels, some of which exhibit mild to extremely high thermal maturities, enabling discussion on long-term carbon sinks. This research work focuses on the study of organic-rich shaly sediments of Barremian to Campanian age from seven (7) outcrop locations in two areas of the Boyacá Department. A set of seventy (70) rock samples have been analysed using several organic geochemical techniques and have shown to cover thermal maturity ranges from the early oil window to the metagenesis stage (measured reflectance values from 0.6% to 2.1%). The OAE2 event was identified based on a 2.5‰–3‰ carbon isotopic excursion in the distal Guaguaquí Group from the section along the Guaquaquí River. Maturity was not found to correlate with depositional burial depths in the so-called distal study area, suggesting that other tectonic events may have played an important role in the genetic history of hydrocarbons particularly in this part of the Boyacá Department. During the mid-to late Cretaceous times, the two study areas consisted of a marine margin with a terrestrial input from the east, which is reflected in a higher terrestrial character of sediments in the eastern foothills (V/Ni < 0.7) compared to the others. Finally, fluorene- and diamondoid-based components were used for enhancing the characterization of the mid-to late Cretaceous organic matter in terms of source in the study sub-region (three-fluorenes and dimethyl-/trimethyl-adamantanes ratios above or below 0.25 and 0.85).