Several Ordovician outliers along or near the northern Ottawa-Bonnechere graben are bounded by Precambrian rocks of the Canadian Shield; however, they are remnants of a once expansive Late Ordovician phase of the St. Lawrence Platform extending into the craton interior. Integrating litho-, bio-, and chemostratigraphic evidence, four outliers (Deux Rivières, Brent Crater, Cedar Lake, and Manitou Islands) preserve Turinian strata, whereas Owen Quarry outlier preserves lower Chatfieldian strata. Each outlier documents a unique depositional succession but commonly records shallow-water depositional environments during net transgression. Limestone diagenesis occurs in the surface marine, shallow-burial, and deep-burial zones. Dolomite shows basement-related, stratabound, and fault/fracture-related spatial distributions. Combining petrological and isotopic (C, O, Sr) evidence, early-stage dolomitization may be related to Mg derived from marine or meteoric waters whereas late-stage dolomitization, including hydrothermal saddle dolomite, likely involves brines that migrated along Paleozoic-Precambrian boundary, then refocused along vertical faults and fractures.