ORGANIC MATTER PRESERVATION IN CHERT: MESOPROTEROZOIC ANGMAAT FORMATION, BAFFIN ISLAND, CANADA

Microfossiliferous chert is a common component of Proterozoic peritidal carbonate strata. Chert precipitated during early diagenesis and commonly records textural evidence of both organic and mineral precursors. The exceptional preservation of microbial elements has great potential to inform our understanding of Earth’s earliest ecosystems, although even exceptional microfossil preservation provides limited physiological data. Information regarding microbial processes, however, can be obtained from the biochemistry of the preserved organic matter associated with early diagenetic chert.

Carbonate strata of the 1.1 Ga Angmaat Formation, Baffin Island, Canada record deposition within an evaporative, intertidal to supratidal microbial flat. Abundant chert nodules within the succession preserve exceptional examples of microbial mats (cf. Knoll et al., 2013), as well as mat features associated with growth and decomposition of both coccoidal and filamentous communities. Taphonomically well-preserved mat fabrics are inferred to represent silicification during mat growth, whereas fabrics dominated by compaction and taphonomically degraded materials are inferred to have been silicified during mat decomposition.

Chert from the Angmaat Formation have an average of 1.5 wt% TOC (Kah et al., 2001) and have experienced only low-grade thermal alteration. Here we present n-alkane, hopane, and sterane data from these samples, all of which were absent in the procedural blank. An even-over-odd carbon preference, typical for marine organisms in hypersaline carbonate environments, was observed in the long n-alkanes of each sample. Both hopanes and steranes were observed in each sample. The presence of eukaryotic steranes, in particular, is supported by petrographic evidence for the red alga Bangiomorpha. This preliminary data indicate that organic matter preserved in the Angmaat Formation is well-suited for detailed organic geochemistry, and suggests that silicified samples that exquisitely preserve microfossil morphology might also have a higher potential for molecular preservation.