Journal of South American Earth Sciences ( IF 1.704 ) Pub Date : 2020-10-16 , DOI: 10.1016/j.jsames.2020.102929 Luis C. Escobar-Arenas; Maria I. Marín-Cerón; José M. Jaramillo; Sergio A. Restrepo-Moreno; Robert E. Márquez-Romero; Nestor A. Gamba; Ángel Barbosa-Espitia; Kyoungwon Min
The mineralogical characterization of dark green cements of intraclast 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 in 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 and they are cemented by ankerite as a product of replacement of early calcite through hydrothermal alteration. Solid hydrocarbons analysis together with new apatite (U–Th)/He data, available low-temperature thermochronology (AFT), 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. 5-4 Ma, caused complete hydrocarbon biodegradation and seepage, and increased the effects of meteoric water inflow during the telogenetic stage.