Low-temperature thermochronology and diagenesis of the Amagá Basin: insights into hydrocarbon generation and its relationship with tectonothermal and hydrothermal processes

• Published in: Journal of South American earth sciences 2021-01, Vol.105, p.102929, Article 102929
• Main Authors: Escobar-Arenas, Luis C., Marín-Cerón, Maria I., Restrepo-Moreno, Sergio A., Jaramillo, José M., Márquez-Romero, Robert E., Gamba, Nestor A., Barbosa-Espitia, Ángel, Min, Kyoungwon
• Format: Article
• Language: English
• Subjects: Ankerite; Apatite uranium-thorium/helium (U-Th)/He thermochronology; Authigenic cements; Bitumen; Paragenesis of sandstones; Pyrite
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2020.102929

The mineralogical characterization of dark green cements of intraclasts and their host sandstones, developed using optical petrography, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and organic petrography, provides new insights about the diagenetic evolution and depositional conditions of the late Oligocene-middle Miocene Amagá Formation, northwestern Colombia. Dark green intraclasts are found as medium-grained, slightly feldspathic sandstones, in which the main authigenic mineral is pyrite that formed during a mesogenetic (burial diagenesis) stage. The host sandstones of the dark green intraclasts were deposited in a meandering river environment and are related to point bar deposits over swampy areas. These strata are medium-grained quartzose sandstones cemented by ankerite as a product of replacement of early calcite through hydrothermal alteration. Solid hydrocarbons analysis together with new low-tempereture thermocronology apatite (U–Th)/He data, available apatite fission-track (AFT), zircon fission-track (ZFT) and vitrinite reflectance (%Ro) data, indicate maximum burial temperatures of ca., 100°C for the deeper parts of the basin. Solid hydrocarbons were emplaced in the late stages of the diagenetic history and occur in a porous system where fractures played an important role. They constitute the first evidence of migration and accumulation of hydrocarbons in the Amagá Basin. However, the latest event of fracturing during a major cooling event associated with basin inversion at ca., 4 Ma, caused complete hydrocarbon biodegradation and seepage, and increased the effect of meteoric water inflow during the telogenetic stage. •AHe thermochronology and mineralogical (XRD, SEM, EDS) analysis for Amagá Formation, Colombia.•Paragenetic sequence which honors petrography and geochronology (AHe, AFT, ZFT).•Low-temperature hydrothermal alteration in the sequence occurred at 23 Ma.•Late petroleum generation associated with Combia magmatic event at 9–12 Ma.•Hydrocarbon biodegradation and intense fracturing at 6-3 Ma.