In this paper,present research situation of metalloporphyrin geochemistry, including metalloporphyrin types, chemical structure series of porphyries, highly dealkylated porphyries, and high carbon number porphyrins, and their origins and distributions in sediments(e. g. oil shales, coals and recent sediments), was summarized based on the research data from previous scientists and recent resalts from the authors of this paper. In oil and source rock samples, nickel and vanadyl porphyrins are the major metalloporphyrin types. Iron porphyrins, however, also exist in oil shales and coals.Copper complex was found in recent soft sediments. Metalloporphyrin distributions in coals are different from those in oils, shales and source rocks. So far, only iron, gallium, manganese and nickel porphyrins have been detected in coals, without copper and vanadyl types. Evidences for cobalt and zinc complexes occurring in sediments were obtained from ICP-MS and probe MS data,etc., but they need further confirmation. Geoporphyrins belong mainly to cycloalkanporphyrin and aetioporphyrin structure series. The other three series, di-CAP, Rhod-Aetio and Rhodo-CAP, are the minor ones. Usually, the carbon numbers of geoporphyrins are from C26-C33. Highly dealkylated porphyrins (HDP, <C26) and high carbon number porphyins(HCNP,>C33)with small amounts, however, have been discovered with nickel, copper and vanadyl complexes. The HDP and HCNP have special geological and geochemical significances.
In the paper, the authors pointed out that further work on metalloporphyrin studies should be carried out in some areas, such as finding new metalloporphyrin types in sediments and determining chemical structures of porphyrins.
Applications of porphyrin compounds to geological exploration were summarized in this paper. Porphyrin is an important indicator for estimating source rock. Source rock with a high amount of porphyrin may be a high quality oil-generating rock. In general, samples with type I-II kerogen contain more porphyrins, those with type II kerogen contain medium amount of porphyrins, and those with type III contain relatively less porphyrins. Porphyrins are stable biomarkers and often used for correlative comparisons between oils; between source rocks; and between oil and source rock. During oil migration, porphyrins in oil may be absorbed by clay minerals; therefore, with increasing migrating distance, concentration of porphyrin in oil decreases gradually. In addition, aetio series are less polar than CAPs, and the former migrates faster than the latter, so, the CAP/(CAP+aetio) ratio is an oil-migrating index. One of the main applications of porphyrins to geology is the study of palaeo-environment of deposition. Nip/(Nip+V)=Op value is a useful indicator for marine-terrestrial environment determination, because terrestrial organic matter provides more nickel porphyrins, while marine organic matter produces relatively more vanadyl porphyrins. CAP/(CAP +aetio ), average carbon number, minimum carbon number and maximum carbon number of porphyrins are useful indices for determining maturity of organic matter. With increasing maturity, all of these indices decrease.