Summary

The predominantly siliciclastic Bylot Supergroup, northern Baffin and Bylot islands, contains >1500 meters of platform, shelf and slope carbonates that are constrained to have been deposited between ~1270 and ~723 Ma. Limited chronostratigraphic resolution has led to the broad correlation of Baffin sediments with predominantly Neoproterozoic successions elsewhere in Laurentia. A chemostratigraphic study of Bylot Supergroup carbonates and genetically related sediments from Somerset Island and the northwest Greenland was undertaken to test proposed interregional correlations. Stratigraphic shifts of up to 4 are not associated with corresponding changes in lithology or depositional environment and are interpreted as recording secular variation in the marine carbon reservoir. In contrast, limited lateral isotopic variability, generally <1, correlates with changes in depositional setting and is interpreted as resulting from recycling of isotopically light organic carbon during microbial degradation.

Carbon isotopic data reveal a pattern of moderately postive values, near 3.5±1, episodically punctuated by negative excursions to -1.0±1. Similar carbon isotopic values obtained from Somerset Island and northwest Greenland suggest regional correlations that support recent lithostratigraphic comparisons. However, isotopic values recorded in these successions are distinctly different from values recorded in sedimentary units of western Laurentia, indicating that these successions are not coeval. Comparison of isotopic values with published data from other successions worldwide indicates that ¹³C values between ~1.0 and 4.0 are characteristic of the interval between ~1300 and ~800 Ma. Isotopic patterns are distinct from those obtained from both younger Neoproterozoic successions (typically recording values in excess of 5) and older Mesoproterozoic successions (values commonly near 0), suggesting that moderately positive values may be useful for broad time-correlation. Recognition of these patterns permits a first-order reconstruction of secular changes in marine carbon isotopic compositions during this period.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah