Abstract The Arctic Ocean is unique among the world’s oceans because of its perennial ice cover. The geologic and climatologic factors that contributed to development of the Arctic Ocean ice cover are understood in a general way, even though the precise mechanism and time during the Cenozoic that the first ice cover formed are not known. Data concerning climatological processes that encouraged development of an Arctic Ocean ice cover have developed from the general understanding of the paleogeographic sequence of events since the last major time of ice-free conditions during the Cretaceous and early Cenozoic. The lack of facts concerning the precise time, and to some extent the mechanism, of ice cover origin is largely the result of an inadequate data base in the Arctic Ocean. For example, no long sediment core with middle Cenozoic sediment that may represent the time of the initial ice-cover development has been collected. Unfortunately, no research ship with capability for recovery of long sediment cores has been designed for work in the area of year-round Arctic pack ice. Therefore, the only sediment record for the central Arctic Ocean is that recovered from drifting ice stations such as the U.S. T-3 program and the Canadian LOREX and CESAR projects. Offshore drilling on the continental slope of Alaska and Canada has penetrated a more complete Cenozoic section. The sediment is largely non marine and, in the shallow Beaufort Sea area, consists of thick deltaic sediment. Detailed paleoclimato- logic study of this sediment has not been accomplished, but

Abstract High-latitude polar regions of the Earth have experienced cold, cool, and temperature paleoclimates in the course of their geologic history, but they have probably always been colder than low-latitude continents and oceans. Extreme climates leading to development of extensive frozen and ice-covered regions at high latitudes can, however, only be documented for a few, relatively short intervals of the Earth’s history, separated by long time spans with little or no ice (Frakes, 1979). The Cenozoic evolution of glacial-type climates during the past 30 to 40 m.y. is the most recent period of extreme climate, and differs from the preceding ones. During the Cenozoic, plate-tectonic processes generated climatically isolated land areas and ocean basins in both the Southern and Northern Hemispheres, which were repeatedly affected by glaciations. For glacial-type paleoclimates older than the Cenozoic, we have only been able to document unipolar glaciation because the opposite high-latitude area was situated in wide and deep ocean basins and was probably relatively ice free due to advection of warmer surface water from lower latitudes. Despite the apparent similarity of Quaternary high-latitude paleoclimates, the development of glacial-type paleoceanographies of the northern and southern polar oceans have revealed important differences, and they are not easily compared with each other. Our understanding of Cenozoic Southern Hemisphere paleoclimates is much more advanced than it is for the Northern Hemisphere. It is particularly intriguing that the available data appear to indicate that the Southern Hemisphere may have become cold more than 20 m.y. earlier than its northern counterpart.

Most biostratigraphic schemes for conodonts (and other fossils) are based on a combination of geographically separated stratigraphic sequences that contain abundant fossils. In developing biostratigraphy, generally little attention is given to identification of lithofacies that yield the fossils. Many sections in western North America include a mixture of sediments that represent a variety of marine environments. Such a stratigraphic mix of environment types yields a vertical sequence of fossils that represent a range of environments. Geographically separated but chronologically similar sections containing different environmental sequences may produce different sequences of fossils within a similar stratigraphic framework. Because of this, biostratigraphic schemes for similar age sequences may differ. Lower Triassic biostratigraphy in western North America is based on study of rock sequences that represent a variety of transgressional and progradational sediments. The “standard” Lower Triassic conodont zonation that has emerged is real, even usable, but includes conodont species representing a range of environments from shallow inner shelf to deeper basinal. This ecologic mix has utility simply because most comparable Triassic rock sequences are also a mix of lithofacies, and at least some of the conodont species in the “standard” can be found in any other section. Because certain conodont species probably were more sensitive to a narrow set of environmental parameters than has been realized, application of the ecostratigraphy concept may develop actual conodont biofacies biostratigraphy, a different biostratigraphy for each definable position along an environmental gradient.

A computerized file of approximately twenty thousand records of conodont occurrences was used in a quantitative study of conodont provincialism. Although biases in the fossil record, in specimen collection, and in data collection preclude any rigid statistical testing, study of quantitative measures of similarity between faunas, when combined with paleogeographic reconstructions, can give insight into provincial patterns and their possible causes. Conodonts showed strong provinciality three times during Paleozoic time. In each instance, temperature is a plausible control of the provincial distribution. In the Ordovician, one fauna inhabited the low to mid latitudes in Laurentia, China, Siberia, and northern Gondwana. Another fauna inhabited high latitudes in Baltica. Cooler high-latitude temperatures as compared to warmer low-latitude temperatures could have been the factor controlling distribution. In the Early Devonian, the Aurelian-province fauna (in present-day Europe and Turkey) inhabited a semirestricted seaway, while the Tasman-Cordilleran-province fauna (in present-day western North America, Siberia, and Australia) occupied the shores of a larger ocean. Eastern North America had a seemingly transitional fauna. These provinces were all in low to mid latitudes, but reconstructed current patterns suggest a warmer temperature in the Aurelian seaway than in the larger ocean. In the Pennsylvanian and Permian, the fauna in western Pangea (present-day North America) differed from that in eastern Pangea (present-day Eurasia). Again both provinces were in low to mid latitudes, but a stronger westward equatorial current due to the Pennsylvanian-Permian glacial episode could have contributed to a warming of the eastern (Tethyan) coast relative to the western coast.

Modern ecologic models for conodonts were extrapolated principally from experience with North American shallow-water subequatorial faunas. Further evidence can be derived from the calcareous lower part of the Swedish Ordovician. This succession among other things offers uniformity of facies, as well as long-ranging conodont genera. Paleomagnetic data indicate deposition at 60°S, i.e., relatively cool climate and fluctuations in air and shallow-water temperatures. The succession might represent a subantarctic shallow-water carbonate platform. Another interpretation favors depth of 100 to 500 m. The relative frequencies of long-ranging conodont genera were plotted against facies data. All data indicate complexity of interaction of depth, temperature, and current dependent factors that influenced the distribution of conodont genera, in particular during a regressive phase about the Arenigian-Llanvirnian transition. Microzarkodina, Periodon , and Protopanderodus had extended frequency minima during the regression. Paroistodus was abundant before the regression, then apparently disappeared from Europe. In a section at Skövde, formed perhaps in particularly deep water, Baltoniodus has a minimum and Drepanoistodus a maximum that might correspond to the peak of regression, but elsewhere the conditions are either ambiguous or reversed. At least Protopanderodus and Periodon probably were not epibenthic, since they occur with shelly fauna in carbonates as well as with graptolites in dark mudstones and with radiolarians in ophiolite-associated cherts (in Scotland). The importance of sorting by differential transport is stressed throughout the study.

Conodonts are divided into three groups with different histologies: protoconodonts (most primitive), paraconodonts, and euconodonts (most advanced). The first is poorly known, but paraconodonts included a Westergaardodina and a coniform evolutionary lineage, and each was the ancestor of one or more euconodont lineages. Early euconodonts are thus polyphyletic and included the Proconodontus and Tendonitis Lineages, which appeared in the middle Late Cambrian, and the Fryxellodontus and Chosonodina Lineages, which appeared in the Early Ordovician. Major changes in conodont evolution, biofacies adaptation, and development of provincialism coincided with sea-level fluctuations near the end of the Cambrian (here named the Lange Ranch Eustatic Event, or LREE) and similar fluctuations recorded at the Lower/Upper Tremadoc boundary (here named the Black Mountain Eustatic Event, or BMEE). Protoconodonts and paraconodonts were probably pelagic and cosmopolitan. Genera of the Proconodontus Lineage were probably also pelagic. Some genera of the latter lineage are found only in low- to mid-paleolatitude areas; others were cosmopolitan, including Cordylodus . Genera of the Teridontus and Fryxellodontus Lineages may have been nektobenthic. Some were adapted to warm, high-salinity environments that existed during the LREE, but younger genera probably were adapted to normal salinity and were more widely distributed. No apparent provincialism existed until the appearance of euconodonts, after which two broad faunal realms are distinguishable. The warm faunal realm included shallow seas in low to middle paleolatitudes; the cold faunal realm included high-paleolatitude seas and open-ocean areas. Early euconodonts of the Proconodontus Lineage appeared and quickly became dominant in the warm faunal realm during the latest Cambrian. Much of the preexisting protocondont-paraconodont fauna was displaced from the warm faunal realm but continued to dominate the cold faunal realm through the Early Tremadoc. Major faunal changes occurred in the warm faunal realm as a result of the LREE, and after this event conodonts in this ream consisted for the most part of genera from the Teridontus Lineage. During the BMEE a different euconodont fauna of uncertain ancestry became adapted to the cold faunal realm, after which most of the previously dominant primitive fauna became extinct. Cosmopolitan Cordylodus lived in both faunal realms during much of the Tremadoc, but after it became extinct prior to the Arenig, provincialism was extreme because few species were adapted to both faunal realms. Oneotodus tenuis Müller is reclassified as the type species of a new genus, Phakelodus.

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.

Studies of conodonts from the North American Lower Ordovician have concentrated on taxonomy and biostratigraphy. These objectives will continue to have high priority in the near future; however, sequences of conodonts now known in the Lower Ordovician of central and western United States allow preliminary assessment of the geographic distributions of the faunas. By earliest Ordovician time, conodonts had differentiated into a population that inhabited the shallow seas of the craton and another population that was adapted to the deeper conditions of the marginal basins. The conodonts of younger Ibexian rocks were segregated into biofacies whose regional distributions suggest concentric belts around the central craton. Present knowledge of occurrences of these conodonts permits recognition of associations of genera and species that are characteristic of deposits that accumulated on (1) intertidal and shallow subtidal carbonate banks and flats, (2) shelf areas in the open ocean, and slope-rise regions in marginal basins. The possibility of further paleobiogeographic subdivision of shelf faunas is suggested by the evidence at hand, but greater geographic control will be needed to verify it. The factors that controlled the distribution of these conodonts along a probable bathymetric gradient are not known.

Many conodont lineages that appear in the Ludlovian on Gotland and elsewhere have no known earlier record anywhere. The closest relatives are found not in the earliest Ludlovian but in the latest Llandoverian-earliest Wenlockian or in still older beds. Ordinary biofacies and lithofacies models fail to explain the observed distribution, since such lineages appear in all of the different facies identified. Either these lineages evolved in an as yet unsampled province, the isolation of which broke down gradually during the Ludlovian, or their appearance reflects changes in the chemistry of the seawater. If the latter interpretation applies, then it indicates that conodonts can be used as sensitive indicators of fluctuations in the marine realm.

Several species of conodonts in the Columbus and Delaware limestones of north-central Ohio are segregated stratigraphically and form associations that correspond fairly well to lithofacies in which they occur. Polygnathus linguiformis , P. angusticostatus , P. angustipennatus , P. intermedius , and Panderodus sp. appear to have been benthic creatures sensitive to substrate texture and energy levels. Other species of Polygnathus may have been benthic, but a nektonic habit is possible for some. Prioniodina tortoides preferred deep-water conditions but was likely nektonic. Simple-cone taxa other than Panderodus and species of Icriodus are ubiquitous and considered to have been shallow-pelagic plankton or nekton. Icriodus orri shows some preference for near-shore environments. Associations similar to some in this area occur in New York, central Ohio, and southwestern Ontario. Endemic forms appear to define a faunal realm limited to the Illinois, Appalachian, and southeastern Michigan basins that is distinct from a realm extending westward and northwestward from the northern to westernmost Michigan Basin. Barriers to intermixing of endemics involved tectonic elements but also hypersalinity and other environmental factors.

Analysis of the distribution of conodonts in sample sets measured down discrete beds exposed in the depositionally steeply dipping marginal-slope facies of the Upper Devonian reef complex of the Canning Basin has been undertaken in order to test the Seddon and the Druce interpretations of conodont biofacies. Each of the 14 sample sets was taken at measured intervals down single beds. The maximum difference in elevation between top and bottom samples was 65 m, indicating the water depth of the bottom sample to have been in excess of 65 m. Analysis of conodont distribution in the 53 sample points of the 14 sample sets does not indicate any clear depth segregation of conodont species that would correspond to the biofacies recognized by Seddon and Druce.

Recognition of differences in the habitats, apparatuses, and ranges of Late Devonian Icriodus and Pelekysgnathus permits refinement of their biofacies interpretations and construction of an alternate icriodontid zonation. Icriodus is a euphotic genus that predominated in most environments during the early Late Devonian (Frasnian) but died out during the early Famennian. Its apparatus consists of platform (I) elements; four larger, acodiniform cones; and two smaller, oneotodiform, scolopodiform, or drepanodiform cones. Pelekysgnathus is a shallow-water genus, which shortly after Icriodus died out, produced somewhat deeper water taxa with triple-rowed I elements that are homeomorphs of Icriodus I elements. Apparatuses for both single-rowed taxa ( Pelekysgnathus ) and triple-rowed taxa ( “Icriodus”) contain oistodiform cones, apparently in place of one or more of the acodiniform cones. Biofacies models for southern Belgium and Utah show that Icriodus lived not only in nearshore environments but ranged into the pelagic palmatolepid-bispathodid (I) and palmatolepid-polygnathid (II) biofacies. Younger “Icriodus”, however, inhabited mainly the deeper subtidal polygnathid-“icriodid” (III) and polygnathid-pelekysgnathid (IV) biofacies. Pelekysgnathus inhabited mainly the polygnathid-pelekysgnathid biofacies and ranged shoreward into the shallow-subtidal clydagnathid (V), scaphignathid (VI), patrognathid (VII), and pandorinellinid (VIII) biofacies, but has not yet been found in the hypersaline antognathid (IX) biofacies (new). The Late Devonian, subdivided by 28 mainly Palmatolepis -based zones from the Lower (Polygnathus) asymmetricus to Upper (Siphonodella) praesulcata Zones in the standard conodont zonation for pelagic biofacies, can be subdivided into nine icriodontid-based zones in nearshore biofacies. In ascending order, these are the Icriodus symmetricus; Lower and Upper Pelekysgnathus planus; Lower, Middle, and Upper “ I .” cornutus ; and Lower, Middle, and Upper “ I .” costatus Zones. Taxonomic revisions involve mainly relegating several previously described species to subspecies and morphotypes and raising some subspecies to species. Two new biostratigraphically significant subspecies, I. iowaensis ancylus n. subsp. and I. alternatus helmsi n. subsp., are recognized to occur both in the western United States and in Europe. Pelekysgnathus brevis n. sp. is described as new on the basis of a Middle Devonian occurrence in Utah.

The standard Late Devonian conodont zonation between the top of the Upper marginifera Zone and the earliest Carboniferous Siphonodella sulcata Zone is revised to replace the former velifer , styriacus , and costatus zonal groups, which were based primarily on genera other than Palmatolepis , and to eliminate a hiatus above the Upper costatus Zone. The changes were enabled by a new phylogenetic model of Palmatolepis , by range extensions that bridge former gaps between the records of some Palmatolepis taxa, and by further taxonomic revisions of some double-rowed Bispathodus taxa. Basing the standard zonation on conodonts of primarily pelagic biofacies permits construction of parallel, alternative zonations for shallower water biofacies and estimation of phylogenetically more precise zonal timespans.

Extensive new collections from the Dinantian rocks of the British Isles confirm previously published opinions concerning the relationships between conodont distribution and facies. Conodonts from time-equivalent rocks, representative of numerous environments from the supratidal through the shelf into the open basin, indicate that Cavusgnathus and related genera are typical of near-shore environments whereas Siphonodella and Gnathodus characterise deeper water environments. This relationship is also demonstrated within vertical rock sequences through the Dinantian Subsystem, although the change is commonly accentuated by unconformable contacts. A limited number of Dinantian biofacies are recognised. Comparisons are made between conodont associations from the south and north of Britain through the Courceyan-Brigantian interval of time. Conodonts from South Wales and the Mendip region are documented including a new discovery of Scaliognathus anchoralis . The absence, or near-absence, of conodonts from a significant portion of the Chadian to Asbian sequence is attributed to extreme water shallowness over very broad areas of the Dinantian shelf. It is suggested that lack of competition in unfavourable shallow-water environments resulted in the success of long-ranging species. Correlations based on these species are only of local relevance. Only conodont zones based on evolutionary lineages are likely to be of international application. The boundary stratotypes for the six stages of the Dinantian Subsystem recognised in the British Isles have been selected at outcrops in different parts of the region. The rocks at the stratotype sections represent different lithofacies. Where present in the stratotypes, the conodonts are a reflection of the local lithofacies. They provide only limited information concerning the evolutionary sequence of Dinantian conodonts.

The Pearson product moment coefficient and the Baroni-Urbani-Buser binary similarity coefficient were used to test the relationship between lithofacies and conodont biofacies in the Beaver Bend Limestone in Indiana. This lower Chesterian limestone includes a variety of lithotopes, but no associations were readily recognizable. Possibly this failure resulted from collecting techniques, a factor that we plan to test with further study.

A quantitative analysis of conodont distributional patterns in the Middle Pennsylvanian (Atokan and Desmoinesian) Morgan Formation of northeastern Utah and northwestern Colorado supports previous empirically derived Pennsylvanian conodont biofacies models. R-mode factor analysis and stepwise discriminant analysis both demonstrate strong facies-dependence for the platform conodonts Adetognathus and Idiognathodus . The Adetognathus biofacies, which may also include Hindeodus and Diplognathodus , characterizes nearshore marine deposits in which salinity and/or temperature fluctuated considerably. The Idiognathodus biofacies, which also includes Neognathodus , characterizes slightly offshore, normal-marine deposits. The environmental significance of Idioprioniodus is uncertain because of its sporadic distribution; Gondolella , its normal faunal associate, was not observed, because its habitat is probably far offshore from those in which Morgan limestones were deposited. Even at the generic level, Pennsylvanian conodonts are environmentally sensitive; hence, they are useful for both sedimentologists and paleontologists. Sedimentologists can use conodont distributional data as an independent test of their paleoenvironmental interpretations. Paleontologists can identify conodonts that are strongly facies-dependent, and differentiate conodonts best suited for biostratigraphy.

Relative abundances of conodonts stem from abiotic or biotic causes. High frequencies can result from: 1) biotic positive = high standing crop; 2) biotic negative = lethality (mass mortality); 3) abiotic positive = lag concentrates; 4) abiotic negative = starved sedimentation. Neither abiotic cause should substantially affect the taxonomic composition of the fauna, although either biotic cause—good or bad environmental responses—can and must. Pennsylvanian conodont biofacies are clearly established and evidence of their interrelationships and complexity has continued to mount. We currently recognize no fewer than five levels of conodont biofacies: Ia - Primary generic-level biofacies (examples: Cavusgnathus, Aethotaxis) Ib - Secondary generic-level (“nested”) biofacies (examples: Ellisonia with Cavusgnathus, Hindeodus with Aethotaxis) II - Species-level microbiofacies (examples: Idiognathodus delicatus with Missourian Idioprioniodus / Gondolella , Streptognathodus elegantulus with Missourian Aethotaxis ) III - Apparatus-level biofacies (examples: scottognathoid apparatuses least complete with Cavusgnathus, intermediate with Aethotaxis, most with Idioprioniodus in the Missourian) IV - Ecophenotype variant-level biofacies (examples: perhaps two “species” of Ellisonia with contrasting apparatus plans and morphologies in the Desmoinesian, possible Cavusgnathus morphotypes from the Cavusgnathus- to the Streptognathodus -biofacies).

Five marine biofacies based on conodont distributions are recognized for the Permian Phosphoria Formation and related rocks. They are: (1) facies with no conodonts, (2) facies with Hindeodus only, (3) facies with Hindeodus and (or) Neostreptognathodus and (or) Stepanovites and (or) Merrillina, (4) a transitional facies containing any of the components of biofacies 3 with either Neogondolella or Xaniognathus, (5) facies dominated by Neogondolella and Xaniognathus. These biofacies (1–5) represent progressive shore or nearshore to offshore differentiation of the conodont faunas. Intervals of phosphate deposition within the Phosphoria Formation correspond to shoreward encroachment of offshore biofacies during trasgressive events. Elements of these conodont faunas, including the new species Neostreptognathodus newelli , are described.

The Lower Triassic (Smithian) Thaynes Formation represents a broad spectrum of paleoenvironments. Samples collected along a depth-related gradient from tidal flats to a relatively deep, commonly dysaerobic, basin yielded an abundant conodont fauna. Simple chi-square tests and multivariate analyses using six conodont entities indicate the presence of three distinctive biofacies related to the general environmental gradient. The restricted inner shelf is characterized by Parachirognathus . The outer shelf is distinguished by a diverse conodont fauna including Furnishius . Basinward, the low diversity conodont fauna is dominated by species of Neogondolella. Some Early Triassic conodonts such as Neospathodus are ubiquitous and provide the best foundation for inter-basinal conodont zonation. Correlation of assemblages with corresponding position along an environmental gradient defined on lithologic criteria indicates that quantitative measures of conodont faunas are potentially useful in the analysis of paleogeography and changes in relative position of sea level.