Abstract A composite standard (CS), assembled graphically through consideration of the ranges of more than 300 conodont species in measured sections at 127 localities, will apparently be adequate as the backbone for a conodont-based chronostratigraphic framework for the Ordovician System of North America. The SRS is a 374-m core through Middle and Upper Ordovician rocks drilled at a site in north-central Kentucky. Relations between the SRS and additional Ordovician sections have been determined graphically following a compilation strategy that involves extension of the network of correlated sections into older and younger rocks by use of overlapping control sections. The weakest link is currently between Ibexian and lower Whiterockian rocks and the well-controlled upper Whiterockian-Mohawkian-Cincinnatian part of the CS. An undescribed composite section through Whiterockian and lower Mohawkian rocks in east-central Nevada is cited as a promising bridge between these two parts of the Ordovician System. It is not certain if the CS extends to the top of the system, because it is not yet possible to add described North American sections through the Ordovician-Silurian boundary to the network of correlated sections anchored by the SRS described here.

R- and Q-mode cluster analysis of data on the occurrence and distribution of 43 conodont species enables delineation in North America of warm-water Red River and Ohio Valley provinces during the Late Ordovician Velicuspis Chron, and suggests recognition of six major biofacies that represent a continuum from nearshore, shallow-water biotopes with numerous endemics to offshore, deeper-water biotopes characterized by more cosmopolitan species. Approximately coeval conodonts from Great Britain, Baltoscandia, and continental Europe are assignable to at least 36 taxa, which are less well known than those of equivalent age in North America but represent cold-water faunas whose Late Ordovician distribution and frequency of occurrence may be used to characterize British, Baltoscandic, and Mediterranean provinces, within which we recognize only three distinct biofacies. Only a third of the taxa in the Late Ordovician cold-water region are also represented in warm-water areas, where they characterize relatively deeper-water biofacies or have a distribution that indicates they were eurythermal cosmopolites. Late Ordovician conodonts are treated as components of warm- and cold-water pelagic faunas, not because their distribution demands that interpretation, but because the pelagic model is simpler than a benthic or nektobenthic one and squares readily with available distributional data.

Abstract Abstract—Throughout the Ordovician, two well-distinguished provinces were delineated by distribution of conodonts in the northern hemisphere. One, the North Atlantic Province, includes all of northwest Europe, much of the British Isles, and a tract in the eastern Appalachians that stretches from Newfoundland on the north to Georgia and Alabama on the south. A second, the North American Midcontinent Province, embraces all of interior North America, the western belts of the Appalachians, and at least part of the Canadian Arctic Archipelago. Although there was limited and episodic exchange between North Atlantic and North American Midcontinent conodont faunas, and vicarism is evident between some elements, the two were strikingly different and apparently largely unrelated through the Ordovician. Limited information suggests that Midcontinent faunas were also characteristic of at least part of the Siberian Platform and elements of these faunas are also known from the Ordovician of New Zealand, Australia, and probably South Korea. Elements of North Atlantic type have been recorded from western Nevada, the Yukon, east-central Alaska, and northwest Argentina. Lithologic associates of Midcontinent conodonts suggest that the Midcontinent fauna developed at low latitudes, perhaps astride the Ordovician equator, and that the North Atlantic fauna was characteristic of higher latitudes. Water temperature was probably the most important factor in defining boundaries between the two conodont provinces.

Distribution of Middle and Upper Ordovician conodonts in North America is marked by provincialism at many levels. Thus, although zonal sequences can be established in several regions, none is completely continental in scope. Conodonts in the eastern Appalachians are closely related to those of northern Europe and both are discussed by Bergström in another report in this volume. Synthesis of regional sequences west of the Appalachians permits recognition of 12 distinct faunas, composed largely of species known best or exclusively from North America. The lower four, in the Whiterock Stage, have been reported only from Cordilleran, Marathon, and Arbuckle sections. Faunas 5 and 6 are represented in Cordilleran, Midcontinent, and southern Appalachian sections, and six ranges to the top of the Chazy in Quebec; 7 through 9, in the Black River-Trenton, are best known in the eastern United States and the Midcontinent, but are also represented in the Cordilleran region. The distribution of faunas 10 through 12, in the Cincinnatian Series, has been most thoroughly established in the eastern Midcontinent, but representatives of these faunas are known from Hudson Bay to Texas and Nevada. As yet, this sequence of 12 faunas cannot be correlated very closely with that of the Anglo-Scandinavian-Appalachian Province.

Conodonts have been described from Jurassic rocks in Japan and from Upper Cretaceous rocks in western Africa. However, both occurrences might also be interpreted as reworked faunas. Arguments in favor of the reported ages include independent interpretation of the age of the enclosing rock and apparent lack of source rocks for reworking. Opposing arguments include well-established Triassic occurrences of conodonts that appear to be identical with most of the species reported as post-Triassic.