The isotopic structures of geological organic compounds

Abstract

Organic compounds are ubiquitous in the Earth's surface, sediments and many rocks, and preserve records of geological, geochemical and biological history; they are also critical natural resources and major environmental pollutants. The naturally occurring stable isotopes of volatile elements (D, 13C, 15N, 17,18O, 33,34,36S) provide one way of studying the origin, evolution and migration of geological organic compounds. The study of bulk stable isotope compositions (i.e. averaged across all possible molecular isotopic forms) is well established and widely practised, but frequently results in non-unique interpretations. Increasingly, researchers are reading the organic isotopic record with greater depth and specificity by characterizing stable isotope ‘structures’ – the proportions of site-specific and multiply substituted isotopologues that contribute to the total rare-isotope inventory of each compound. Most of the technologies for measuring stable isotope structures of organic molecules have been only recently developed and to date have been applied only in an exploratory way. Nevertheless, recent advances have demonstrated that molecular isotopic structures provide distinctive records of biosynthetic origins, conditions and mechanisms of chemical transformation during burial, and forensic fingerprints of exceptional specificity. This paper provides a review of this young field, which is organized to follow the evolution of molecular isotopic structure from biosynthesis, through diagenesis, catagenesis and metamorphism.

Geochemical applications in petroleum systems analysis: new constraints and the power of integration

“…Similarly, three independent techniques have been developed to measure the 13 C positionspecific signatures of propane (Gao et al 2016;Gilbert et al 2016, Piasecki et al 2016. Eiler et al (2017), in this volume, review published and unpublished work on the isotopic anatomy of organic molecules larger than methane, and outline potential future constraints offered by clumped isotope and site-specific analysis of organic molecules (e.g. biosynthesis, maturation, and the environmental conditions of hydrocarbon generation and storage).…”

“…Gilfillan et al 2009). Finally, the isotopic approaches described in Eiler et al (2017), Gao et al (2017), Pedentchouk & Turich (2017) and Stolper et al (2017) all have the capability to elucidate the origin of hydrocarbons in the environment.…”

A fluorination method for measuring the 13C‐13C isotopologue of C2 molecules

“…Notably, when a isotope exchange reaction is in equilibrium, the Δ value reflects temperature and thus is used as a geothermometer. 2,3 This approach was originally developed from the study of 13 C- 18 O clumped species in CO 2 and carbonates, 4,5 and was then applied to 18 O- 18 O clumped species in O 2 , 13 C-2 H in CH 4 , 15 N-18 O in N 2 O, 13 C-13 C in C 2 H 6 and 15 N-15 N in N 2 . [6][7][8][9][10] The analysis of clumped species in CH 4 , N 2 O, C 2 H 6 and N 2 has been made possible thanks to the development of high-resolution mass spectrometry (HRMS) and laser spectroscopy.…”

“…8,12 Despite the potential of the clumped isotope analysis, the measurement is still limited to a few molecules. 2,[4][5][6][7][8][9][10][11][12] Notably, 13 C- 13 C bonding exists in a wide range of organic compounds, although it has seldom been studied owing to the technical difficulty. Clog et al 9 first reported the measurement of the 13 C-13 C isotopologue of the C 2 compound ethane by using HRMS.…”

“…They reported over 4‰ variation in the Δ 13 C 2 H 6 value from several natural gas samples. 9 In theory, the abundance of the 13 C-13 C isotopologue of a C 2 compound can be viewed from the following homogeneous isotope exchange reaction, as exemplified with ethane: 2 12…”