Insights into the Connaught sequence of the Timiskaming varve series from Frederick House Lake, northeastern Ontario

Abstract

A sub-bottom acoustic profile survey encountered a mass transport deposit (MTD) bed, 5–7 m thick, interbedded within glaciolacustrine deposits of glacial Lake Ojibway at Frederick House Lake, Ontario, Canada. Analysis of the thickness patterns of rhythmic couplets in recovered core samples revealed that the Connaught sequence, the youngest of the Timiskaming varve series, immediately underlie and overlie the MTD. Comparison to regional published varve series reveals two possible interpretations for the varve numbering: varve (v) 2066 to v2115, which requires the inference of a 55 varve year (vyr) disconformity just below the Connaught sequence, while the alternative numbering, v2011a to v2060a (a = alternative), extends continuously from older varves. Circumstantial evidence supporting the alternative numbering is as follows: (i) the uncertainty of applying a common 55 vyr disconformity to three varve series located up to 23 km apart and which otherwise exhibit closely matching thickness plots; (ii) the lack of evidence of an erosive unconformity in the sub-bottom acoustic profiles from Frederick House Lake; and (iii) the uncertain varve count within a key part of the Matagami series, located about 300 km away and from which the 55 vyr disconformity is extrapolated. At Frederick House Lake, the alternative numbering indicates that the maximum position of the Cochrane ice advance and the Connaught varves may be, in effect, contemporary in age. More broadly, the alternative numbering indicates that the youngest known varve that formed before the terminal drainage of glacial Lake Ojibway is v2074a rather than v2129 in the original numbering.