'Collingwood' strata in south-central Ontario---a petrophysical chemostratigraphic approach to comparison and correlation using geophysical borehole logs.

摘要

A petrophysical chemostratigraphic comparison and correlation of "Collingwood" strata across central Ontario was conducted using geophysical borehole log data and core produced by the Ontario Oil Shale Assessment Project (OSAP). Outcrop sections were also measured, sampled and described. The resultant geophysical correlation was compared to sections in the Michigan Peninsula. Microfacies analyses and a biostratigraphic review were also conducted. The dark organic rich rocks collectively referred to as the "Collingwood Member, Lindsay Formation", in Ontario were deposited during the progressive drowning of a mid to late Ordovician carbonate ramp. Due to variability in ramp palaeotopography, condensation intensity (sedimentation stress) varied across the region during drowning. This variability resulted in regional differences in Collingwood section thickness and facies. Less condensed carbonate rich "Collingwood" sections are associated with palaeotopographic highs such as the Algonquin Arch in Ontario and grade upwards and outwards (off-arch) from predominantly deep-shelf carbonates (microfacies type SMF 9, FZ 2---open sea shelf---deep undatherm below wave base) to more condensed deeper water shale rich strata (microfacies type SMF 3, FZ1-basin fondotherm below oxygen level)---that contain abundant graptolites and Triarthrus trilobites.