Christopher R. Barnes

Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry

The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earths history. Previous temperature estimates of up to ∼70°C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician–Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.

The strontium isotopic composition of Ordovician and Silurian brachiopods and conodonts: Relationships to geological events and implications for coeval seawater

utilized for strontium isotope measurements. The results document a gradual decrease in 87 Sr/ 86 Sr, from 0.7091 to 0.7087, from Tremadoc to Llandeilo, a sharp decline to 0.7078 during the late Llandeilo-early Caradoc; little change during Caradoc and the Ashgil; and a steady rise to 0.7087 through the Silurian. These long-term (10 7 yr) variations, with magnitudes in the range of 10 23 , are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering. The gradual decrease in 87 Sr/ 86 Sr ratio during the Early Ordovician may record the reduction in uplift and weathering rates due to waning of the Pan-African orogenies. The rapid decline near the Llandeilo/Caradoc boundary suggests a strong hydrothermal flux likely due to increased sea-floor spreading and a possible superplume event. The latter may have caused the prominent transgressive phase, the largest in the Phanerozoic, which would have muted continental flux input. Although the Caradoc was the main interval for the Taconic Orogeny, its impact on the Sr continental flux may have been delayed until the early Llandovery. This effect, complemented by reworking of glacial deposits near the Ordovician-Silurian boundary and enhanced by phases of the Silurian Salinic Orogeny, may have combined to give the progressive increase in the strontium isotope ratio through the Silurian. The scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes. Copyright

The Pattern of Global Bio-Events During the Ordovician Period

The 70 Ma Ordovician Period is characterized by extensive epeiric seas, paleocontinent dispersal, intervals of intense volcanism and black shale deposition, a greenhouse climate state deteriorating to a brief icehouse state, strong faunal provincialism, and profound changes to the biota including the changeover from the Cambrian Fauna to the Paleozoic Fauna. Although many invertebrate phyla diversify during the Ordovician, precise biostratigraphic and global biogeographic data are provided best by conodonts, trilobites and graptolites. These three groups are used in this chapter to recognize five major bio-events four of which correspond closely to Series boundaries: Basal Tremadoc (BTc), Basal Arenig (B’Ag), Basal Llanvirn (B’Ln), Basal Caradoc (B’Cc) and Upper Ashgill (U’Al). Most of these correspond to significant eustatic events and the latter to the terminal Ordovician glaciation. The first four are each characterized by extinctions but these are overshadowed by a rapid innovation event with a radiation of a more diversified fauna; the U’Al is a severe extinction event, second only to the terminal Permian event in the entire Phanerozoic. Compared to many other Phanerozoic systems, the Ordovician is a period of considerable biologic, climatic and oceanographic complexity within which the balance between the forcing processes that produced the major and minor events is still not well understood.

Late Ordovician glaciation under high atmospheric CO2: A coupled model analysis

The analysis of the geologic record has revealed a question concerning how the Late Ordovician glaciation could have occurred simultaneously with high CO2 levels (10–18x). Sensitivity studies using a coupled atmosphere-ocean-sea ice model show that it is possible to maintain a permanent snow cover (which corresponds to 60% of all the glacial deposits found on Gondwana) under 10x CO2 levels, warm fall/cool spring orbital parameters, a 4.5% reduction in solar luminosity, a length of day of 21.5 hours, and an enhanced snow/sea ice albedo of 0.3. A cold summer orbit experiment with 10x CO2 and a reduced snow/sea ice albedo of 0.1 also sustains a permanent (albeit less extensive) snow cover. The geographic configuration of the Late Ordovician results in an up to ∼42% increase in the global ocean poleward heat transport in the Southern Hemisphere relative to present-day and a significant asymmetry relative to the equator.

Late Ordovician–Early Silurian (Ashgillian–Llandovery) sea level curve derived from conodont community analysis, Anticosti Island, Québec

Abstract Earlier workers have established sea level curves for the Ashgillian–Llandovery sequence on Anticosti Island, Quebec, Canada, based on sedimentology and on brachiopod and reef communities. The complete Anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800–1100 m sequence. This paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths. This allows the establishment of a eustatic sea level curve for the sequence. This curve is in general agreement with those of the earlier workers, but is more detailed and better constrained stratigraphically given the large sampling program. The curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier, and different water depths for certain intervals from those established earlier. The curve is valuable given that the Anticosti sequence is one of the most complete in the world for this interval, and its divergence from global eustatic curves for this interval is noted.

Taxonomy, Evolution, and Biostratigraphy of Conodonts from the Kechika Formation, Skoki Formation, and Road River Group (Upper Cambrian to Lower Silurian), Northeastern British Columbia

Conodonts, the tiny, phosphatic, toothlike remains of an extinct group of early vertebrates, are the most important fossil group for biostratigraphy throughout their stratigraphic range from Late Cambrian to Late Triassic. The monograph presents the results of a significant project in remote regions of northeastern British Columbia. It extends the knowledge of the stratigraphic framework and conodont faunas into a region where information of this kind is largely unknown. Complete stratigraphic sections exposed in the high alpine of the Northern Rocky Mountains allowed examination of strata across a platform-shelfbreak-basin transect. The conodont faunas from the Kechika Formation, Skoki Formation, and Road River Group are described from an extensive collection of nine stratigraphic sections (over 9000 m measured) that yielded abundant conodont elements (38 600 total). This monograph represents a benchmark study of these important zonal fossils. The detailed paleontological work not only provides a taxonomic basis for future studies on early Paleozoic conodonts but also focuses on the evolution of conodonts in the early Ordovician, a time of extraordinary adaptive radiation. The taxonomic work provides detailed descriptions and illustrations of 185 species representing 69 genera. Seven new genera and 39 new species are described. The high diversity of taxa across the platform-to-basin transect shows the biogeographic differentiation and spatial ecological partitioning of conodonts through time. The taxonomy permits the refinement to the biostratigraphic zonation within two faunal realms for British Columbia that can be correlated with schemes elsewhere in North America and also internationally.

A NEW LLANDOVERY (EARLY SILURIAN) CONODONT BIOZONATION AND CONODONTS FROM THE BECSCIE, MERRIMACK, AND GUN RIVER FORMATIONS, ANTICOSTI ISLAND, QUÉBEC

Abstract An abundant conodont fauna was recovered from 202 samples taken from the Becscie, Merrimack, and Gun River formations of early Llandovery (Early Silurian) age on Anticosti Island, Québec. From the collection of 22,409 identifiable specimens, 28 species and four associations representing 12 genera and one group of drepanodontiform elements are documented and their stratigraphic ranges established. One new genus, Rexroadus, is established for two species earlier assigned with question to Oulodus. New species described are Icriodella dicrana, Oulodus sigmoideus, Ozarkodina strena, and Pterospathodus? originalis. The fauna is dominated by species of Ozarkodina and Oulodus; many species have a first appearance that is slightly older than elsewhere suggesting that the Anticosti Basin may have been an important evolutionary radiative center in the early Silurian. There is a slow and progressive diversity increase in conodonts through this interval after the initial appearance of many new taxa in the basal Silurian following the mass extinction in the terminal Ordovician. The Anticosti Llandovery sequence represents one of the few highly fossiliferous, continuous successions in the world and a new conodont biozonation based on conodonts for the Llandovery is proposed with the following interval zones in ascending order: Ozarkodina hassi (new), Ozarkodina strena (new) [subdivided into Oulodus jeannae (new) and Oulodus panuarensis (new) subzones], Ozarkodina clavula (new), Ozarkodina aldridgei (new), Pterospathodus celloni, and Pterospathodus amorphognathoides zones.

Upper Ordovician conodonts from the Bowan Park Succession, Central New South Wales, Australia

Some 2379 conodont specimens have been recovered from 50 samples through the 560 m thick BowanPark Group and the basal part of the Malachis Hill Beds of Late Ordovician age, from the western side of the Molong high, in central New South Wales. These have been assigned to 32 species including three new species, Panderodus nodus nov. sp., Paroistodus? nowlani nov. sp. and Yaoxianognathus ani nov. sp., and a revised multielement apparatus of the species, Yaoxianognathus? tunguskaensis (Moskalenko). Two stratigraphically distinct conodont assemblages characterised by the first appearances of T. blandus and T. tumidus, respectively, are recognised. They are correlated with similar faunas in the mid-upper part of the Cliefden Caves Limestone Group and the lower Malongulli Formation of the eastern Molong High in central New South Wales. The Bowan Park fauna as a whole is dominated by Panderodus gracilis (Branson & Mehl), Yaoxianognathus ani nov. sp., Belodina confluens Sweet, Protopanderodus liripipus Kennedy, Barnes & Uyeno and Drepanoistodus suberectus (Branson & Mehl) (72% of total fauna), and shows a mixture of North American Midcontinent and North China affinities. However, influx of some species of North Atlantic Realm aspect mainly occurs in the T. tumidus assemblage which, exhibiting a significant increase in diversity, is preserved in a relatively deeper water facies.

CONODONTS FROM A PLATFORM-TO-BASIN TRANSECT, LOWER ORDOVICIAN TO LOWER SILURIAN, NORTHEASTERN BRITISH COLUMBIA, CANADA

Abstract The conodont fauna from nine sections across a platform-to-basin transect in northeastern British Columbia includes species of Early Ordovician (Tremadocian) to Early Silurian (Llandovery) age. A collection of 9,110 conodont elements was recovered from 205 samples taken from nine stratigraphic sections that preserve the platform succession of the Kechika, Skoki, Beaverfoot, McCusker and Nonda Formations and their off-shelf equivalents, the Ospika, Robb, Kenny and Laurier Formations of the Road River Group. The fauna is assigned to 106 species representing 67 genera; the Ordovician species are representative of two faunal realms. One new genus, left in open nomenclature, is described. Five new species include Drepanoistodus latus and four new species left in open nomenclature assigned to the following genera: Walliserodus, Multioistodus?, Pseudooneotodus, and Belodina. The Midcontinent Realm zones recognized include, in ascending order, the Acodus kechikaensis, Oepikodus communis, Jumudontus gananda, Tripodus laevis to Plectodina aculeata zones, Phragmodus undatus and Gamachignathus ensifer? zones. Zonal species of the Atlantic Realm are Microzarkodina flabellum, Eoplacognathus suecicus, Baltoniodus variabilis, Pygodus anserinus, and Amorphognathus tvaerensis. The Silurian fauna, of lower diversity than the Ordovician fauna, is representative of the Distomodus staurognathoides and Pterospathodus amorphognathoides zones.

Challenges, Benefits, and Opportunities in Installing and Operating Cabled Ocean Observatories: Perspectives From NEPTUNE Canada

The first cabled ocean observatories demonstrate the challenges, benefits, and opportunities for ocean science and commercial applications. NEPTUNE Canadas 800-km subsea infrastructure and 130 diverse instruments established the worlds first regional cabled ocean observatory, northeast Pacific Ocean, off Canadas coast. Introducing abundant power and high bandwidth communications into coastal to abyssal environments allows discrimination between short- and long-term events, interactive experiments, real-time data and imagery, and multidisciplinary teams interrogating a vast database over 25 years. The principal scientific themes addressed through the NEPTUNE Canada infrastructure are: plate tectonic processes and earthquake dynamics; dynamic processes of seabed fluid fluxes and gas hydrates; regional ocean/climate dynamics and effects on marine biota; deep-sea ecosystem dynamics; and engineering and computational research. Resulting data can be applied to important science issues such as ocean/climate change, ocean acidification, natural hazards, and nonrenewable and renewable natural resources. Socioeconomic benefits include many applications in sovereignty, security, transportation, data services, and public policy. The Data Management and Archive System has largely been developed internally. It controls the observatory network and gives transparent access using interoperability techniques within a Web 2.0 environment. The principal challenges encountered during design, installation, and operations involve technical innovations, enlarging the user base, management, securing funding, maximizing educational/outreach, and commercialization opportunities. Cabled ocean observatories are progressively wiring the oceans. Expandable in footprint, nodes, instruments, and scientific questions, they provide testing technology facilities and generate new research opportunities and socioeconomic benefits.