Lobal affinity of Late Wisconsin tills at St. Marys in southwestern Ontario, Canada

Abstract

The exposures at the St. Marys Cement Inc. quarry at St. Marys, Ontario, have been studied by geologists since the mid-1950s. This paper summarizes previous and new information collected in 2009, 2010, and 2012 and discusses the record of sediments resting on the bedrock surface that have been exposed during quarry operations. The exposed sediments illustrate the dynamic behavior of the Laurentide Ice Sheet in this area during the Late Wisconsin. Evidence for subglacial meltwater activity, shifting ice-flow directions during till deposition, a local or regional erosion event, possible subaerial exposure, and ice-marginal sedimentation is observed in the sequence of tills and stratified sediments exposed in the quarries. It also highlights how rapid lateral facies changes, complex contact relationships, and steep erosional contacts can prove to be challenging for correlation and extrapolation of subsurface units into three-dimensional stratigraphic models. Fourteen units were identified of which the lower six were deposited during the Nissouri age (Catfish Creek Drift). This included five layers of till deposited by a glacier that alternated from flowing out of the Lake Huron basin to that of a regional flow to the south-southwest. An angular unconformity cuts into these sediments and separates them from a finer-grained sediment sequence (primarily of Port Bruce age) consisting of glaciofluvial gravel, two fine-textured till layers, and rhythmically bedded glaciolacustrine sediments, all overlain by the uppermost till, the Rannoch Till, and Mitchell Moraine ice-marginal fan sediments. Résumé: Les géologues étudient les affleurements à la carrière de la St. Marys Cement Inc., à St. Marys en Ontario, depuis le milieu des années 1950. Le présent article résume des données déjà acquises et de nouvelles informations recueillies durant les années 2009, 2010 et 2012; il traite du profil géologique des sédiments qui reposent sur le socle et qui ont été exposés durant l'exploitation de la carrière. Les sédiments exposés illustrent le comportement dynamique de l'Inlandsis laurentidien dans ce secteur au Wisconsin tardif.Des évidences d'activité d'eau de fonte sous-glaciaire, la variation de la direction de l'écoulement glaciaire, un événement d'érosion local ou régional, une possible exposition subaérienne et une sédimentation en bordure de la glace sont observés dans les séquences de tills et de sédiments stratifiés qui affleurent dans les carrières. Tous ces points soulignent aussi la manière dont les changements latéraux rapides de faciès, les relations complexes de contact et les contacts d'érosion abrupts peuvent poser des défis pour la corrélation et l'extrapolation des unités sous la surface dans des modèles stratigraphiques tridimensionnels. Quatorze unités ont été identifiées dont six unités inférieures qui ont été déposées durant le stade glaciaire Nissouri (drift de Catfish Creek). Ces unités comprenaient cinq couches de till déposées par un glacier qui s'écoulait alternativement entre le bassin Huron et de mani...

Geology and paleoecology of a Middle Wisconsin fossil occurrence in Zorra Township, southwestern Ontario, Canada

“…This unit generally accounts for a significant proportion of the stratigraphic sequence observed within this region with thicknesses ranging between 7 and 25 m in the vicinity of the quarry. Both early and late lobate phases of Catfish Creek Till have been recognized in southwestern Ontario and bracket the main deposits laid down by regional, southerly flowing ice (Hicock 1992;Bajc and Dodge 2011;Dreimanis et al 2014). The observed fluting mentioned earlier in the text may therefore be associated with the late lobate flow of Catfish Creek ice out of the Lake Erie basin.…”

Evaluating the groundwater resource potential of the Dundas buried bedrock valley, southwestern Ontario: an integrated geological and hydrogeological case study

“…Lithologies derived from the north shore of Lake Huron, including Gowganda Formation tillite and jasper conglomerate, are commonly encountered within this northernderived till and aid in its positive identification (Karrow 1988). Both early and late lobate facies of the till, occasionally finer grained and containing fewer clasts, have been recognized further complicating positive identification of the unit based on grain size alone (Hicock 1992;Bajc and Dodge 2011;Dreimanis et al 2014). In addition, interbedding of diamict and fine-grained, waterlain deposits has been observed in the upper and lower parts of Catfish Creek Till in a number of cored boreholes drilled along the interlobate zone as part of regional aquifer mapping projects (Bajc and Dodge 2011).…”