Diagenetic history of Ordovician and Devonian oil ... - Geology Ontario

equivalent to the Platteville Group, High Bridge Group and the Plattin Limestone Group to
the south. Trenton terminology varies. It is referred to as Trenton Limestone in northern
and southwestern Indiana and northwestern Ohio, whereas in Michigan it is either Trenton
Group or Trenton Formation. In southwestern Ontario the Trenton and Black River are
termed groups; the Trenton Group consists of the Cobourg, Sherman Fall, and Kirkfield
formations and the Black River Group consists of the Coboconk, Gull River and Shadow
Lake formations. The Trenton and Black River groups are Champlainian to early
Cincinnatian in age and together range up to 280 m in thickness with the top of the Trenton
Group at depths varying from 665 m in the extreme southwest (Malden pool) to 950 m in
Lambton County, just north of Lake St. Clair. Equally extensive Cincinnatian shales and
limestones overlie the limestones of the Trenton Group. In southwestern Ontario these
shales and limestones include the Queenston Shale, Georgian Bay and Blue Mountain
formations and range in thickness from 152 m on the Bruce Peninsula to 549 m under the
eastern end of Lake Erie (Sanford, 1961). Subsurface stratigraphic charts of Russell and
Telford (1983) depict the Cobourg Formation as the Lindsay Formation (outcrop
terminology); but the name Lindsay has never been used in the subsurface and the
uppermost formation of the Trenton Group continues to be termed the Cobourg (Figure 3).
The Trenton Group in the subsurface of southwestern Ontario exhibits a sharp,
irregular contact with the overlying deep-water black shales of the Blue Mountain
Formation (Utica Shale equivalent). Beards (1967) termed this shale unit the Collingwood
Member. Based on lithology, however it was renamed the Blue Mountain Formation by
Russell and Telford (1983). The Trenton-Blue Mountain contact is readily picked in core
and on gamma ray log as a rapid change from limestone to shale. In contrast, to the north
of southwestern Ontario, core, gamma ray log and outcrops exhibit a gradual transition
from limestone to shale due to the presence of the Collingwood Member (Russell and