In:
Canadian Journal of Earth Sciences, Canadian Science Publishing, Vol. 56, No. 10 ( 2019-10), p. 1017-1026
Abstract:
Stable carbon isotope geochemistry is a well-established and reliable tool for studying metabolisms of microbial communities in the Precambrian record; however, the isotopic effects of high-temperature alteration from igneous intrusions (i.e., contact metamorphism) have not been thoroughly explored. The Mesoproterozoic (∼1.4 Ga) Middlebrun Bay Member of the Rossport Formation, Sibley Group, in Ontario, Canada, is composed of carbonaceous stromatolites and microbial laminites preserved in an evaporitic, lacustrine chert–carbonate deposit and is cross-cut by an intrusive mafic sill at the studied locality. Sedimentary organic matter (kerogen) was investigated along two vertical stratigraphic transects to determine the spatial variability of its geochemical preservation. Thermal alteration of the preserved kerogen (as measured by Raman spectroscopy) increased toward the mafic sill, but the alteration was greater for kerogen preserved in carbonate mineralogies compared to that preserved in quartz (chert). Bulk δ 13 C org values fluctuate throughout each vertical section, with a total average of −28.2‰ ± 0.8‰; however, values are unexpectedly lower for samples near the mafic sill, approaching −30‰, inconsistent with previously reported patterns. These measurements indicate that thermal alteration of sedimentary rocks does not universally result in 13 C enrichment and increased δ 13 C org values and suggests that ancient kerogen may be preferentially shielded from postdepositional heating effects due to micrometre-scale differences in mineralogy.
Type of Medium:
Online Resource
ISSN:
0008-4077
,
1480-3313
DOI:
10.1139/cjes-2018-0309
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
2019
detail.hit.zdb_id:
417294-2
detail.hit.zdb_id:
1491201-6
SSG:
16,13
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