| Popis: |
In Fe-poor and organic-rich marine sediments, reduced S is mainly organic due to the lack of reactive Fe. These sediments (e.g., carbonates, cherts, phosphates) have high C/S (organic carbon/total reduced sulfur) ratios which are, as a rule, > 3 and may reach 5 or 6 (at times even > 10) in organic-rich rocks. These high ratios are characteristic for these Fe-barren sediments and are very different from those found in marine sediments where pyritic S is the main reduced sulfur species. They may be explained by the escape of H 2 S to the atmosphere. The interpretation of C/1bS plots in these sediments is also quite different. One reason for the S intercept in these plots is the presence of pyritic S and thus, contrary to the conventional plots, this intercept seems to have no environmental significance. On the other hand, the S/C slope appears to be a paleoenvironmental indicator. Low slopes ( 0.2) indicate restricted to normal (aerobic) environments. C/1bS plots have been used to interpret environments of deposition in such sediments from two cycles of organic-rich, Fe-poor Senonian sediments in several basins in central and southern Israel. Both cycles appear to have been deposited in restricted environments. The Campanian (Mishash Formation) environments of deposition appear to be in general more oxic than those of the Maastrichtian (Ghareb Formation). As an independent comparison for the C/S results, the degree of pyritization (DOP) was calculated for some samples. The DOP results confirmed the C/S results. It should be stressed that in such low-Fe environments, even DOP results should be used with caution. |
