MANICOUAGAN IMPACT STRUCTURE – FUNDY RIFT BASIN

STRATIGRAPHIC RECORD IN THE FUNDY RIFT BASIN OF THE MANICOUAGAN IMPACT

The impact did trigger a powerful seismic event as Lawrence Tanner from Bloomsburg University recently discovered in a deformed zone of the Fundy Rift Basin. “There have been previous reports attempting to link paleoseismicity, as recorded by soft-sediment deformation features, to impacts,” Tanner explained. “But this is the first instance of linking the Manicouagan impact to the stratigraphic record. The Fundy rift Basin experienced a substantial period of volcanic activity at the time of the Manicouagan impact.

Cape Spit, Bay of Fundy Nova Scotia, the craggy escarpment which rings this immense gulf was formed during a critical juncture in Earth history called the Triassic-Jurassic boundary, 200 million years ago (Thurston, 1994). Image by the author from C-GOZM.
Late Triassic outcrop maps of key Fundy Group coastal localities interpreted to contain potential distal Manicouagan impact evidence. (a) Regional setting showing the present-day location of the Manicouagan impact structure. (b) Shaded-relief map of the Minas Subbasin, highlighting major structural elements including the Cobequid-Chedabucto (C-CF) master fault (part of the ‘Minas Fault Zone’ = MFZ), an historically active continent-microplate boundary that separates the northern Avalon terrane from the Meguma terrane to the south. (c) Late Triassic Fundy Group stratigraphic column. (d) Regional geology map showing key coastal outcrops and locations of pertinent onshore/offshore subsurface and industry well control (i.e. N-37 and P-79). (Modified from USGS I-2781, Thomas 2006, Withjack et al. 2009, 2012, and Sues and Olsen 2015)

ABSTRACT
The terrestrial redbeds of the Blomidon Formation were deposited in the Fundy rift basin during Norian to Hettangian time. A 10-m-thick zone of intensely deformed strata that occurs near the base of the formation is characterized by rubblization and step-wise faulting. Correlation of this zone basin-wide indicates that it is a record of a very powerful paleoseismic event. The greater thickness of the deformed zone in proximity to the border fault, the Minas Fault Zone (MFZ), indicates that movement of the MFZ was the immediate cause of this paleoseismicity. The presence in strata just above the deformed zone of quartz grains displaying features of shock metamorphism raises the intriguing possibility that reactivation of the MFZ was triggered by a bolide impact. (Tanner 2002)

 

Location and geologic map of the study area in the Fundy basin. Samples analyzed in this study were collected from Partridge Island, near Parrsboro, Nova Scotia (adapted from [12]). MSB=Minas sub-basin; CSB=Chignecto sub-basin; FSB=Fundy sub-basin. (Tanner 2005)

The ~100 km-wide Manicouagan impact structure in northeastern Canada, 700 km from the Fundy rift basin, is one of the largest well-documented impact sites. Once considered a candidate for the cause of the end-of-Triassic extinctions, U-Pb zircon dating of the impact melt establishes the age of the impact as much earlier Norian, approximately coeval with the seismic deformation of the Blomidon Formation. Stratigraphic constraint of the age of the impact allows an accurate assessment of the effects of this event on biota.  (see – David E. Brown ET AL 2018 and Onoue 2012 above)The impact did trigger a powerful seismic event as Lawrence Tanner from Bloomsburg University recently discovered in a deformed zone of the Fundy Rift Basin. “There have been previous reports attempting to link paleoseismicity, as recorded by soft-sediment deformation features, to impacts,” Tanner explained. “But this is the first instance of linking the Manicouagan impact to the stratigraphic record. I made the association between the impact and paleoseismicity in the Fundy Rift Basin, a sedimentary basin 700 km away from the impact site, and went looking for shocked quartz grains. Finding them allows us to place this impact into a stratigraphic context and look elsewhere to see if there are any significant biotic effects. So far, there don’t seem to be any.” The Fundy rift Basin experienced a substantial period of volcanic activity at the time of the Manicouagan impact. (GEOLOGICAL SOCIETY OF AMERICA 2002)

Back to MANICOUAGAN IMPACT STRUCTURE main page