The stratigraphy and depositional environment of the Aphebian Snyder Group, Labrador

• Published in: Canadian Journal of Earth Sciences
• Main Author: Speer, J. Alexander
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1978
• Subjects: General Earth and Planetary Sciences; Snyder; North Atlantic
• Online Access: http://dx.doi.org/10.1139/e78-005; http://www.nrcresearchpress.com/doi/pdf/10.1139/e78-005

The Snyder Group is an Aphebian sedimentary sequence unconformably overlying Archean rocks that has undergone deformation and a medium to high grade contact metamorphism as the result of the emplacement of the Elsonian Kiglapait intrusion. Five lithostratigraphic units totaling 239 m in thickness have been recognized; in ascending order they are: (1) a lower quartz arenite with local arkosic arenites, pelites, conglomerates and a discontinuous basal conglomerate; (2) a manganiferous silicate iron formation; (3) a marble with associated calc-silicates and quartzites; (4) a sphalerite- and pyrrhotite-bearing quartz-rich, graphitic siltstone; and (5) an upper quartzite. The several intrusive rocks are largely basic and intermediate in composition and are grouped as being emplaced either before or after the contact metamorphism by the Kiglapait intrusion. Collectively, their sills and dikes have expanded the section to 355 m.The lower and upper quartzites with their high maturity; poly modal festoon, trough crossbedding; reactivation surfaces; flaser and lenticular bedding; ripple marks; graded bedding; and conglomerates were probably deposited on a shallow, subtidal, tide- and current-dominated sand flat dissected by tidal channels. The few metapelites record deposition during an occasional less turbulent environment. The fine grain size, intraformational conglomerates, cross-laminations, and thin laminations of the intermediate formations indicate that they were deposited in a quiet, probably shallow water environment disturbed only by occasional storms. The sedimentary structures, lithologies and thin, sheet geometries of the beds suggest that the Snyder Group represents a siliciclastic sea shelf sedimentation, which, if reconstructions of the North Atlantic craton are correct, was epicontinental.