Preparative Procedures for End Permian Kerogens

Following the HF/HCl demineralization steps, the organic components in the carbonate-rich SD55 limestone could be identified by transmitted light microscopy. Irregular degraded light and dark brown plant tissue dominate the kerogen. Non-cellular sheets, which may represent plant cuticle, are also present. Figure 1a represents the Py-GC analysis of the HF/HCl residue of SD55 used to make the petrographic observations mentioned above. The organic pyrolysis products appear to be overwhelmed by the by-products of the demineralization procedure. These by-products are likely to be neoformed inorganic fluorides formed by reactions between the carbonate matrix and HF. It has been stated that in some cases it is impossible to avoid the formation of at least some fluorides during the HF/HCl demineralization procedure (Durand and Nicaise 1980). Hence, although appropriate for petrographic analysis the standard HF/HCl residue is unsuitable for chemical analysis. Figure 1b shows a Py-GC analysis of the same HF/HCl residue following repeated treatments with excess concentrated HCl. The organic pyrolysis products are now clearly recognizable as a mixture of «-alkene/«-alkane doublets produced from

Fig. 1. Gas chromatograms of flash pyrolysates (Cu-temperature 610°C) of the residue from the HF/HCl demineralization procedure of the Val Badia organic-rich limestone (SD55) both a) before, and b) after multiple treatments with excess concentrated HCl to remove neoformed fluorides. Numbers indicate the retention times of «-alkene/«-alkane doublets. From left to right the other identified peaks are toluene (C1 alkylbenzene), C2 alkylbenzenes, naphthalene, C1 alkylnaphthalene, C1 alklydibenzofuran, C2 alklydibenzofuran.

Fig. 1. Gas chromatograms of flash pyrolysates (Cu-temperature 610°C) of the residue from the HF/HCl demineralization procedure of the Val Badia organic-rich limestone (SD55) both a) before, and b) after multiple treatments with excess concentrated HCl to remove neoformed fluorides. Numbers indicate the retention times of «-alkene/«-alkane doublets. From left to right the other identified peaks are toluene (C1 alkylbenzene), C2 alkylbenzenes, naphthalene, C1 alkylnaphthalene, C1 alklydibenzofuran, C2 alklydibenzofuran.

aliphatic biomacromolecules and aromatic hydrocarbons and furans from more condensed organic structures. Therefore, it appears that a refined demineralization procedure involving final multiple treatments of excess concentrated HCl, renders the HF/HCl residues of carbonates suitable for kerogen studies by combined petrographic and chemical techniques.

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