Facies-dependent δ13C variation and diagenetic overprinting at the onset of the Sturtian glaciation in North-East Greenland

• Published in: Precambrian Research
• Main Authors: Klaebe, RM, Smith, MP, Fairchild, IJ, Fleming, EJ, Kennedy, MJ
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2018
• Subjects: Andrée; Ella Ø; Greenland; Kap; Kap Weber; Andrée-Land; East Greenland
• Online Access: https://doi.org/10.1016/j.precamres.2017.12.008; https://ora.ox.ac.uk/objects/uuid:3e91881e-ac81-4c54-b42f-90d048f7d3b7

Time-significant surfaces are used to construct a stratigraphic test of the intrabasinal reproducibility of a 16‰ Neoproterozoic carbon-isotope (δ 13 C) anomaly in the NE Greenland Caledonides. The δ 13 C excursion from +6‰ to -10‰ occurs in the carbonate-dominated Andrée Land Group and lies below glacial diamictites of the Tillite Group commonly correlated as Sturtian in age (~720 Ma) and has been widely interpreted to record a global isotopic event reflecting a perturbation in the carbon cycle preceding the initiation of the snowball ice age. δ 13 C stratigraphic patterns were determined in two strike sections with relatively shallow platform deposits at Kap Weber and slope deposits on Ella Ø preserved directly below the first evidence for glaciation. The top and bottom of the δ 13 C profile was bounded by contiguous chronostratigraphic surfaces including an unconformity (sequence boundary) at the base recognisable in both sections and a subaerial exposure surface with a basinal correlative conformity at the top. The δ 13 C profile at Kap Weber shows δ 13 C values of +6‰ that drop to -8‰ in fine-grained slope deposits before returning to +6‰ in platform carbonates at the base of the glacial diamictite. The slope section on Ella Ø shows similar values for platformal carbonates of +6‰ with a similar drop to -10‰ in slope deposits, but this section lacks the return to platform deposits evident at Kap Weber beneath the diamictite as well as a return to positive δ 13 C values. The absence of the platformal sediments and positive δ 13 C values on Ella Ø cannot be attributed to erosional truncation because the contact in this section shows a conformable, interbedded transition into the glacial deposits indicating that a continuous record is preserved. This disparity in δ 13 C values below the base of the Tillite Group suggests that the most negative δ 13 C values recorded in slope mudstone facies (-10‰) occur near synchronously with values of +6‰ on the platform. Elemental mapping of the mudstone facies indicates ...