Molecular geochemical indicators

Galimberti R., Ghiselli C., and Chiaramonte M. A. (2000) Acidic polar compounds in petroleum a new analytical methodology and applications as molecular migration indices. Org. Geochem. 31, 1375-1386. 

Compared to the well defined structures and interrelationships of the discrete molecular blomarkers and geochemical indicators discussed above, relatively little is known about marine humic substances. Whether the major source of input to dissolved and sedimentary marine humic substances is of terrigenous or marine origin is still occasionally debated in the literature, although most Interpretations point towards marine planktonic sources. (12-lA). based most convincingly on isotopic ratios, GC-MS, H and C NMR and infrared sj ctra (15-17). Stuermer et d l2) propose a combination of C and H/C ratios as a... 

Raymond A. C. and Murchison D. G. (1992) Effect of igneous activity on molecular-maturation indices in different types of organic matter. Org. Geochem. 18, 725-735. 

In geochemically reversible reactions, environmental conditions determine the final ratio of starting material to end product if conditions in the environment change, this ratio adjusts to the change. In cases of slow equilibration a molecular ratio of starting material to end product may be preserved, which is indicative of past environmental conditions. More data are needed to test this idea, but it is conceivable that analyses of aromatic and hydroaromatic hydrocarbons and pigments might be interpreted in terms of a fossil environment. 

Benner, R., and Opsahl, S. (2001). Molecular indicators of the sources and transformations of dissolved organic matter in the Mississippi river plume. Org. Geochem. 32,597-611. 

Pancost R. D., Freeman K. H., Patzkowsky M. E., Wavrek D. A., and Collister J. W. (1998) Molecular indicators of redox and marine photoautotroph composition in the late Middle Ordovician of Iowa USA. Org. Geochem. 29, 1649-1662. 

Gas geochemical surveys of light molecular-weight hydrocarbons (C1-C5) and Hg have proved to be useful methods of detecting oil and gas fields in the Ordos Basin of northern China and of indicating potential oil or gas fields in the Lixian Depression of southern China. The annular anomaly is the type most usually found in these regions, although apical and linear anomalies occur under particular conditions. 

There are two main types of geochemical proxy used to identify former life. These are biomarker molecules and isotopic fractionations. Biomarker molecules are specific molecules preserved in sediments as molecular fossils, which are unambiguous indicators of their biological precursors. Some of the most successful... 

---