Mathematics – Logic
Scientific paper
Jan 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985gecoa..49..145i&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 49, Issue 1, pp.145-151
Mathematics
Logic
3
Scientific paper
The ammonium contents of biotites in Precambrian rocks from Finland have been determined, to examine the possibility that ammonium in biotites represents a chemical fossil. If biologic activity existed in Precambrian sedimentary environments, biotites formed from the sediments should contain distinctly larger quantities of NH 4 + than biotites from igneous rocks. Biotites from Svecokarelidic metasediments, which were originally products of sedimentation about 2400-1900 Ma ago, have high NH 4 + contents (hundreds of ppm), while biotites from Svecokarelidic plutonic rocks of 1800-1900 Ma old and Postsvecokarelian rapakivi granites of 1650-1700 Ma old have low NH 4 + contents (tens of ppm). The results may indicate that biologic activity was plentiful during sedimentation of the Svecokarelian strata. This agrees with evidence for ancient life found in dolomites and greywacke-slates of the Svecokarelides. Biotites from Presvecokarelidic schists of more than 2600-2800 Ma old have only tens of ppm of NH 4 + . This value is at the same level as those of biotites from the rapakivi granites and the Svecokarelidic plutonic rocks. Considering the rarity of fossils in Presvecokarelidic rocks, the low NH 4 + content of biotite from a Presvecokarelidic pelitic schist may indicate less biologic activity during the sedimentation of the original sediments. These data emphasize that ammonium in biotites of Precambrian metasediments may be a useful chemical fossil for identifying the geologic sites of ancient life.
Itihara Yuuko
Suwa Kanenori
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