Organic Matter: Concepts and Definitions

The concept of sedimentary organic matter, as well as the definitions and meanings of different organic facies have become an important tool in paleoenvironmental characterization, basin analysis and fossil fuel exploration. The application of this concept is the best way to integrate the techniques of microscopy to the study of kerogen contained in sedimentary rocks. The present chapter aims to provide a general view of sedimentary organic matter in relation to the techniques used for its application in the field of geosciences, with special emphasis on its contribution to both fundamental and applied scientific knowledge. Organic petrology is a branch of Earth Science that studies the organic matter present in sedimentary sequences, particularly in coal (concentrated organic matter) and finely disseminated in sedimentary rocks (dispersed organic matter - DOM) by using a set of petrographic methods generally in combination with various geochemical analytical techniques. The parameters obtained from petrological studies are important for defining the organic facies, geothermics and paleogeography of sedimentary basins, for investigating the geological structure, the present and past thermal regimes of the earth's crust as an aid to basin analysis, for assessing the mining and utilization of coal, and for the exploration of fossil fuel resources. All this explains the rapid development of organic petrology [1]. Thus, organic petrology studies based on the presence and concentration of sedimentary organic matter in both conventional and unconventional hydrocarbon systems have become, in recent years, a powerful tool for the characterization of the depositional paleoenvironment as well as for the evaluation of sedimentary sequences with oil and gas potential. Although the scope of organic petrology is broad, it employs just a few fundamental principles, one example of which is organic content characterization that is used to assess the type and quality, and thermal maturity of kerogen.

Keywords: Organic matter, Thermal maturity, Kerogen, Organic petrology, Optical microscopy.