FAR-REACHING SEISMIC EFFECTS OF THE MANICOUAGAN IMPACT: EVIDENCE FROM THE FUNDY BASIN
The Quaco Formation (Fundy Group) comprises mostly clast-supported cobble conglomerate of probable Carnian age cropping out in coastal New Brunswick. The most distinctive feature of this formation is the pervasive occurrence of cm-scale circular to elliptical markings on the cobble surfaces. Although smooth-surfaced depressions on some cobbles are consistent with a pressure-solution origin, hackly markings, radial fracturing of the clasts, grain fracturing within the clast fabric, and spalling are explained as the result of concussion fracturing at points of clast contact during the passage of a strong shock wave. Elsewhere in the basin, the Norian-Hettangian-age Blomidon Formation, exposed along the Nova Scotia coast, contains a 10-m-thick zone of intensely deformed strata that is characterized by rubblization and step-wise faulting near the formation base. This zone, which correlates basin-wide, is interpreted as the result of a strong synsedimentary seismic event during the early Norian. No distinct ejecta layer has been found in the Fundy basin, but quartz grains with multiple sets of planar features, which appear partially annealed, and glassy spherulitic grains occur at the top of the deformed zone. Paleomagnetic data suggest that this zone correlates with established age of the Manicouagan impact. Stratigraphic constraint of the age of the impact allows an accurate assessment of the biotic effects of this event, which does not coincide with any major extinctions.