Stratigraphic and Structural Framework of Upper Middle Ordovician Rocks in the Head Lake-Burleigh Falls Area of South-Central Ontario

Abstract

Field investigations in the Head Lake-Burleigh Falls area of south-central Ontario, that focused mainly on the Covey Hill(?), Shadow Lake, Gull River and Coboconk formations along the Paleozoic escarpment, provided clear evidence of faulting. Observed and inferred structural deformation, coupled with faciès changes within the Shadow Lake and lower Gull River, point to a succession of basement movements during the Phanerozoic. These range from Hadrynian-Early Cambrian, through Middle Ordovician to post-late Middle Ordovician times. Some of the earlier movements (Hadrynian-Early Cambrian to late Middle Ordovician) appear to be coincident with, and probably related to, plate tectonic events and the associated Taconian orogeny that were in progress along the southeastern margins of the North American continent. Post-Middle Ordovician block faulting, on the other hand, may have been triggered by any number of epeirogenic events related to late stage Taconian, Acadian or Alleghanian orogenies in Late Ordovician to Carboniferous times, or possibly to rifting associated with continental break-up and initiation of seafloor spreading processes in the early Mesozoic. Manuscrit révisé accepté le 5 août 1993Des levés de terrain faits dans la région de Head Lake-Burleigh Falls, portant surtout sur les formations de Covey HiII (?), Shadow Lake, Gull River et Coboconk ont fait ressortir la présence de failles. Les déformations tectoniques observées et supposés, ainsi que les changements de faciès dans le Shadow Lake et le cours inférieur de la GuII River, montrent qu'il y a eu une succession de mouvements du socle pendant le Phanérozoïque. Ces mouvements se sont produits de l'Hadryanien-Cambrien inférieur à l'Ordovicien moyen, puis jusqu'après l'Ordovicien moyen supérieur. Certains des premiers mouvements (Hadryanien-Cambrien inférieur à l'Ordovicien moyen) semblent coïncider avec la tectonique des plaques, et y être reliés, et avec l'orogenèse du Taconique qui s'est manifestée sur les marges sud-ouest du continent nord-américain. La formation de failles dans les blocs après l'Ordovicien moyen, d'autre part, a pu être provoquée par un ou plusieurs événements épirogénétiques liés aux orogenèses du dernier étage du Taconique, de l'Acadien et de l'Alléghanien de l'Ordovicien supérieur au Carbonifère pendant la formation des fossés d'effondrement lié à la séparation des continents et le début de l'expansion océanique au Mésozoïque inférieur.FeIdforschungen im Head Lake-Burleigh FaIIs-Gebiet, sùdliches Zentrum von Ontario, die sich hauptsàchlich auf die Bildungen von Covey Hill(?), Shadow Lake, Gull River und Coboconk entlang des palàozoischen Steilabfalls konzentrierten, ergaben ein klares BiId der Verweiiung. Die beobachteten und vermuteten strukturellen Verformungen weisen zusammen mit Fazies-Ànderungen im Shadow Lake und dem unteren Lauf des GuII River auf eine Aufeinanderfolge von Untergrundbewegungen wàhrend des Phanerozoikums. Dièse reichen vom frùhhadrynischen Kambrium durch das mittlere Ordovizium bis zu Zeiten nach dem spàt...

Seismites within Ordovician–Silurian carbonates and clastics of Southern Ontario, Canada and implications for intraplate seismicity

“…An earthquake-related interpretation is supported by previous investigations of the regional structural setting of Southern Ontario during the Ordovician-Silurian. Sanford (1993) showed that block faulting, uplift and arching were a common process in what is now Southern Ontario during that time span and which he related to several episodes of far-field stresses from late stage Taconic and Acadian orogenies. This resulted in the re-activation of Precambrian basement structures and block faulting of overlying Paleozoic strata at different times.…”

“…This work is needed to identify underlying basement structures that might have a persistent record of reactivation during Paleozoic basin formation and which may provide insights into modern intracratonic seismic activity. Sanford (1993) showed that platformal Paleozoic strata that rest on Precambrian basement in Southern Ontario are extensively block faulted as a consequence of far field stresses during successive Appalachian orogenies and propagation of structures upwards into overlying sedimentary strata. Our work complements these findings by identifying prominent deformation structures interpreted as seismites in strata broadly synchronous with Appalachian deformation and faulting.…”

A Reconnaissance Geophysical Survey of the Kawartha Lakes and Lake Simcoe, Ontario

“…Local dips of Paleozoic rocks are greater where they are draped over Precambrian relief. The Paleozoic rock section thickens downdip towards the Appalachian and Michigan Basins south of Lake Ontario and west of Lake Huron respectively (Liberty, 1969;Johnson era/., 1992;Sanford, 1992).…”

“…1). Deer Bay is floored by upper Middle Ordovician sedimentary rocks (Sanford, 1992). The eastern shore of the bay is marked by a cliff of sedimentary rocks reaching 10 m above lake level.…”

Pop-Up Structures and the Fracture Pattern in the Balsam Lake Area, Southern Ontario

“…dipping (15°-30°) seismic reflectors within the crystalline basement across the CMBBZ/NPLZ below Lake Ontario have been interpreted as ductile thrust faults (Milkereit et al, 1992). Brittle faulting in Precambrian rock and vertical displacements of upper Middle Ordovician rocks along major NNE-oriented lineaments within the CMBBZ provide evidence of post-upper Middle Ordovician reactivation of the CMBBZ (Wallach and Mohajer, 1990a;Wallach, 1991;Sanford, 1993). However, seismic data collected across the NPLZ below Lake Ontario indicate that a shale-limestone marker is undisturbed at the data resolution scale and that this zone has been relatively stable since the Ordovician period (Milkereit et al, 1992).…”