Sources of organic matter elucidated through Pyr-CG-MS, and relation to basin scale events in the Pimienta Formation (Central Mexico)

Abstract

The study of organic matter is essential for understanding the sedimentary and diagenetic processes that have occurred in a certain area. Sediments rich in organic matter with a vocation for producing hydrocarbons are of particular importance. Studies of organic matter in these environments help not only to determine their potential as hydrocarbon generators, but also contribute to the understanding of the processes that have occurred in the basin over time. In this study, the use of pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS) is proposed to analyse the diversity of organic molecules contained in the sediments of the Pimienta Formation. This technique is versatile and, although destructive, allows rapid analysis of organic matter, in addition to the minimal quantities required for the study. Pyr-GC-MS allows functional groups to be determined; in this study 34 different moieties were identified. The use of this technique is perfectly complemented by Rock-Eval-pyrolysis and fluid inclusion studies, which allows greater detail of the origin of the molecules. The results of the Rock Eval Pyrolysis suggested that there were two types of kerogen: continental (Type III) and marine (Type II)]. Some samples contained organic matter of continental origin , while others contained organic matter of marine origin. Analysis of fluid inclusions suggested sedimentary-diagenetic and meteoric sources for fluids, as well as different types of interaction between them and the surrounding rocks.