Título: Major and Trace Elements in Organic Matter Accumulated in Stylolites by ICP/MS Electron Microprobe Analysis (EPMA)

Autor: Lo Mónaco, S.; L. López; H. Rojas; J. G. Gastiel

Fuente: 8th Latin American Congress on Organic Geochemestry CD-ROM Memorias

Año: 2002

País de publicación: Colombia

Tipo de documento: CD-ROM Memorias

Resumen

Primary migration, the process by which the bitumen is expelled from the source rock, has been considered to cause the differences between the chemical composition of bitumen in the source rock and crude oil in the reservoir (Tissot and Welte, 1984). In carbonate source rock, Sassen et al. (1987) suggested that stylolitization had enhanced the efficiency of petroleum expulsion by concentrating kerogen along stylolites. Leythaeuser et al. (1995) based on geochemical and petrographic studies, show that the pressure solution during carbonate diagenesis exerts major controls on the processes of petroleum generation and migration, and López and Pasquali (1996) report that the bitumen extracted from stylolites from the Querecual Formation shows a deficiency of the light n-alkanes (< C20) and the isoprenoids phytane and pristane, when compared to the bitumen dispersed in the rock. The observed differences suggest the preferential expulsion of light nalkanes and isoprenoids through stylolites, leaving residue enriched in the heavy n-alkanes after the primary migration through stylolites in the source rock. As stylolites serve as a means of migration in carbonate source rocks, the composition of the organic material accumulated in them reflects the composition of the bitumen retained in the rock, and suggests the composition of the migrated bitumen. Also it should be an indication of the distribution of trace elements in the fraction rich in organic material corresponding to stylolites and the organic material dispersed in the rock. In this work the concentration of major and trace elements obtained by ICP/MS are presented, together with the distributions of some relevant elements as recorded in X-rays maps acquired by EPMA, this with the intention of studying the associations of the trace elements with the organic (bitumen and kerogen) and inorganic phases (minerals) in the organic matter accumulated in stylolites and the organic matter dispersed in the whole rock.