DISTAL EVIDENCE (?) OF THE LATE TRIASSIC (NORIAN) MANICOUAGAN IMPACT, NORTHEASTERN QUEBEC: NEW DATA FROM THE FUNDY GROUP (CANADIAN MARITIMES)

Preliminary petrographic analysis (optical and scanning electron microscopy) was conducted on samples from selected horizons in the nonmarine Upper Triassic Blomidon and Middle (?) Triassic Quaco formations (Fundy Group) from three Bay of Fundy coastal localities: Five Islands/Red Head and Houston Beach/Delhaven, Nova Scotia; and St. Martins, New Brunswick. Results to date from the Blomidon Formation reveal the presence of multiple sand-grade intragranular fracture sets potentially indicative of high magnitude Late Triassic (Norian) paleoseismicity consistent with the Manicouagan (distal) impact causal model proposed previously. Samples of particular interest include fluvial and eolian sandstones collected from the formation’s White Water Member ‘synsedimentary’ deformation zones (‘DH1’ and ‘DH2’) exposed on the Blomidon Peninsula (Nova Scotia) previously attributed, in an alternative model, to basin-wide, meter-scale subsurface evaporite dissolution and stratal collapse effects. These chaotically deformed units contain (rare) transported quartz grains displaying open microfracture (radial and spallation) styles considered to be diagnostic genetically of dynamic concussion (i.e., rapid seismic shock) origin. However, precise controls on, and the timing of, this microdeformation still remain uncertain due to the paucity of unequivocal associated distal ejecta material (e.g., shocked quartz, microspherules, PGE anomalies and/or heavy minerals) from the Manicouagan impact. Similarly fractured, dominantly quartzite cobbles comprise the Middle (?) Triassic fluvial conglomeratic Quaco Formation at the third locality, St. Martins, New Brunswick on the western Fundy coastline (Stonehammer Geopark). These rudites have also been interpreted tentatively as in situ evidence of a major regional (post-?Carnian) paleoseismic event, possibly synchronous with that considered responsible for the lower Blomidon Formation synsedimentary deformation observed in the Minas Subbasin approximately 100 km to the east.