Symposium Program - Precambrian Research Office - McGill ...

Abstracts – Posters
Refined stratigraphy and regional correlation of the early Neoproterozoic Wynniatt Formation, Shaler
Supergroup, Victoria Island, NWT
Danielle Thomson 1 and Robert Rainbird 2
1 Department of Earth Science, Carleton University, Canada, dthomso2@connect.carleton.ca
2 Geological Survey of Canada, Ottawa, Canada
The early Neoproterozoic (late Tonian-Cryogenian) Shaler Supergroup of the Amundsen Basin is well
exposed in the Minto Inlier, Victoria Island, NWT. It is correlated with the Mackenzie Mountains
Supergroup (Mackenzie Mountains) and Fifteenmile Group (Ogilvie Mountains).
The Wynniatt Formation (middle Shaler Supergroup) is composed of >900 meters of sediment
deposited on a broad, distally steepened carbonate ramp within a shallow intracontinental basin
that was periodically restricted from an exterior ocean. Study of the Wynniatt Formation supports
division into: 1) lower-carbonate member, an upward-deepening succession of supra- to sub-tidal
carbonates; 2) black-shale member, a recessive interval of dark-grey siltstone and silty shale deposited
on a pro-delta; 3) stromatolitic-carbonate member, comprising stacked upward-shallowing cycles of
sub- to supratidal carbonates and, 4) upper-carbonate member, an upward-shallowing succession
from sub-tidal black calcareous shale to resistant benches of peritidal, cross-bedded grainstone and
stromatolitic limestone. Facies stacking patterns reveal cyclical, upward-shallowing parasequences that
define at least six third-order sequences. Harmonious sets of third-order base-level rise and fall define
three, second-order sequences (supersequences). Correlative strata in the northern Cordillera start
to record northwest-facing rift basins during this time, however our work in the Amundsen Basin
suggests relatively stable tectonics, supporting multi-stage, non-correlative breakup of Rodinia along
the northwestern margin of Laurentia.
A negative δ 13 C excursion was recognized in a Wynniatt section from the northeastern Minto Inlier
and has been correlated with similar excursions in the Mackenzie and Ogilvie mountains, as well as the
global Bitter Springs isotopic stage. The Wynniatt anomaly was recorded in rocks collected adjacent to
a thick diabase intrusion. We re-sampled this stratigraphic interval from a locality in southwestern
Minto Inlier, away from any intrusions, to test its validity. Our data confirms the presence of a negative
anomaly over the same stratigraphic interval, supporting the validity of the excursion and intrabasinal
and extrabasinal correlations.
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