The Gaspé Belt in the Restigouche area comprises three successions separated by a Late Silurian (Salinic) disconformity and an Early Devonian angular unconformity. The lower, Upper Ordovician to Lower Silurian sequence consists of siliciclastic turbidites of the Boland Brook and Whites Brook formations (Grog Brook Group), overlain by calcareous turbidites of the Pabos and White Head formations (Matapédia Group), and slope and shelf deposits of the Upsalquitch and Limestone Point formations (lower Chaleurs Group). Above the Salinic disconformity, the upper Chaleurs Group and the Dalhousie Group record a transgressive–regressive cycle. The former comprises Pridolian carbonate rocks of the West Point Formation and overlying Pridolian to Lochkovian sedimentary rocks of the Indian Point Formation. The Chaleurs Group is conformably overlain by Lochkovian to early Emsian subaerial volcanic rocks of the Dalhousie Group (Val d'Amour Formation), which is unconformably overlain by alluvial–lacustrine deposits of the late Emsian Campbellton Formation. Acadian orogenesis began during the Emsian and is characterized by open to closed folding, heterogenous cleavage development, and reverse and strike-slip faults. The Salinic orogeny is manifested in extensional block faulting, within-plate volcanism, and uplift and deep erosion of Early Silurian strata. Early Devonian high-level intrusion of the Matapédia Group, White Head clasts in Indian Point conglomerate, and thermal maturation data all indicate an extended period of Late Silurian – Early Devonian uplift in parts of the Restigouche area. Thermal maturities of West Point and Indian Point strata are within the oil and condensate windows and suggest potential for hydrocarbons in the study area.

Four sections of the lower part of the Cape Phillips Formation, two outcrops on northeastern Cornwallis Island and one outcrop and one drill core from Truro Island, Northwest Territories, Canada, provide significant new data on the Ordovician–Silurian boundary. They show evidence of continuous sedimentation through the boundary interval and a continuous sequence of graptolite zones, including the bohemicus and persculptus zones, which have not been previously found in Arctic Canada. Strata yield graptolites, including uncompressed specimens, and conodonts through most of the sections. The ordovicicus conodont Zone occurs within the pacificus to lower persculptus graptolite zones. The nathani conodont Zone contains a "transitional fauna," a mixing of species typical of the preceeding ordovicicus Zone and those generally regarded as Silurian indicators. This conodont zone ranges from the middle of the persculptus graptolite Zone into the lower acuminatus graptolite Zone and, thus, spans the Ordovician–Silurian boundary. The Ordovician–Silurian faunal turnover of the conodonts, therefore, also spans the Ordovician–Silurian boundary and is not coincident with the interval of major graptolite extinction, which occurs earlier, at the end of the pacificus Zone. The base of the kentuckyensis conodont Zone occurs in the acuminatus graptolite Zone. Sedimentologic evidence of the maximum eustatic sea-level drop can be seen within the bohemicus Zone (early Hirnantian) and possibly one or several smaller scale sea-level fluctuations through the underlying zones.

The Potsdam Group is a Cambrian to Lower Ordovician siliciclastic unit that crops out along the southeastern margins of the Ottawa graben. From its base upward, the Potsdam consists of the Ausable, Hannawa Falls, and Keeseville formations. In addition, the Potsdam is subdivided into three allounits: allounit 1 comprises the Ausable and Hannawa Falls, and allounits 2 and 3, respectively, the lower and upper parts of the Keeseville. Allounit 1 records Early to Middle Cambrian syn-rift arkosic fluvial sedimentation (Ausable Formation) with interfingering mudstone, arkose, and dolostone of the marine Altona Member recording transgression of the easternmost part of the Ottawa graben. Rift sedimentation was followed by a Middle Cambrian climate change resulting in local quartzose aeolian sedimentation (Hannawa Falls Formation). Allounit 1 sedimentation termination coincided with latest(?) Middle Cambrian tectonic reactivation of parts of the Ottawa graben. Allounit 2 (lower Keeseville) records mainly Upper Cambrian quartzose fluvial sedimentation, with transgression of the northern Ottawa graben resulting in deposition of mixed carbonate–siliciclastic strata of the marine Rivière Aux Outardes Member. Sedimentation was then terminated by an earliest Ordovician regression and unconformity development. Allounit 3 (upper Keeseville) records diachronous transgression across the Ottawa graben that by the Arenigian culminated in mixed carbonate–siliciclastic, shallow marine sedimentation (Theresa Formation). The contact separating the Potsdam Group and Theresa Formation is conformable, except locally in parts of the northern Ottawa graben where the presence of localized islands and (or) coastal salients resulted in subaerial exposure and erosion of the uppermost Potsdam strata, and accordingly unconformity development.

The Ellis Bay Formation on Anticosti Island, Quebec, is subdivided into six members and is composed of calcareous shale and argillaceous limestone and varies in thickness from 53 m in the west to about 96 m in the east. Member 6 accounts for about half the total thickness of the formation and near its base small bioherms are developed widely across the island. Lateral variation in lithology represents a gradual transition from a nearshore facies (east) to an offshore, shallow subtidal facies (west) . The members may reflect eustatic changes produced by the Ashgillian glaciation in North Africa. Conodont samples were collected from three composite stratigraphic sections, at Ellis Bay, and the Vaureal and Salmon Rivers, over a distance of about 140 km. Thirty-five multielement species representing 18 multielement genera are recogni zed in the fauna of 14 665 conodont elements from 183 samples. New species are Oulodus? nathani , Panderodus clinatus andStaufferel/a inaligera. Eighteen form species , ten of which are new and unnamed, are also present, as is one new, unnamed form genus. Panderodus is the major component of the Ordovician fauna and is represented by seven multielement and four form species. Two species of Gamachignathus comprise about 45 per cent of the Ordovician conodont fauna of the Ellis Bay section. An almost complete faunal replacement occurs in the Silurian with only three species of Panderodus and one species each of Decoriconus and Pseudooneotodus continuing across the systemic boundary. Other than these taxa, the Silurian fauna contains 5 multielement genera and 8 multielement species. Panderodus graci/is (Branson and Mehl) dominates the Silurian fauna; Ozarkodina and Oulodus? are the most abundant ramiform conodont genera. The Ordovician fauna, although including many taxa from the underlying Richmondian Vaureal Formation, is characterized by Gamachignathus. The strata containing this fauna are regarded as representing a latest Ordovician time interval bearing a fauna referred to as Fauna 13 and for which the re-introduction of the Gamachian Stage is advocated. An Ordovician-Silurian transition zone, about 1.5 m thick, is present with species from both periods co-occurring. The Silurian fauna is similar to that of the Distomodus kentuckyensis Zone, the oldest conodont zone of the North American Llandoverian. However, the new species appear to represent an earlier, new, Llandoverian zone, the Ou/odus? nathani Zone. The Ordovician-Silurian boundary is herein drawn at the first appearance of species of Ozarkodina and this occurs about 2 - 3 m above the base of Member 6 of the Ellis Bay Formation. The distribution of the Ordovician conodonts indicates the presence of three laterally segregated communities corresponding to the offshore subtidal, intermediate and nearshore environments. The offshore community (Community A) is dominated by Gamachignathus and Panderodus. The intermediate community (Community B) includes several species of Panderodus , Oulodus, Amorphognathus and Aphelognathus. Community C, the nearshore community, is characterized by large and robust elements belonging to Aphe/ognathus and Panderodus. In Silurian strata, Community D is characterized by the presence of Ozarkodina oldhamensis (Rexroad) and Oulodus? nathani n.sp. and is developed in an intermediate subtidal facies. Ozarkodina hassi (Pollock, Rex.road and Nicoll) and Ou/odus? kentuckyensis (Branson and Branson) dominate within Community E and reflect a shallow subtidal environment.

The Upper Ordovician graptolite facies of the northern Canadian Cordillera is divided into two biostratigraphic units, the Dicellograptus ornatus Zone and the Pacificograptus pacificus Zone. Interbedded limestone yielded conodont Fauna 12. The uppermost Ordovician equivalents to the graptolite Climacograptus extraordinarius Zone and conodont Fauna 13 are absent, signifying a widespread stratigraphic hiatus probably attributable to the effects of glacially induced regression.The lowest Silurian graptolite fauna, of the Glyptograptus persculptus Zone, is tentatively identified in some sections, although it is absent in others. Conodonts from the zone, although present, are not diagnostic.Thicknesses of the lowest Silurian G. persculptus Zone sediments are anomalously high in comparison with average thicknesses of the zone elsewhere in the world.