Cape Phillips Formation Research Articles

The Devonian clastic wedge and underlying strata of southwestern Canadian Arctic Archipelago: stratigraphic revisions

The Devonian clastic wedge (DCW) and underlying carbonate platforms and basinal mudrocks of the study area are re-examined using legacy seismic data and X-ray fluorescence surveys of borehole chip samples. The Ordovician–Devonian basinal succession of Melville Island is consolidated under the name Ibbett Bay Group within the Northwest Territories, whereas equivalent strata in Nunavut are grouped into the Cape Phillips Formation. The Kitson Formation black shale is correlative with the upper Ibbett Bay Group. Six horizons with high TOC and high gamma response are traced in the Ordovician–Devonian, with the fourth (4a) approximating the Silurian/Devonian boundary; the upper two (4b, 5) are Emsian and Eifelian. In the direction of progradation, the base of Kitson Formation rises stratigraphically from gamma horizon 4a to 5. The upper Kitson represents basinal toes of westward prograding DCW clinoforms. The Blackley and Cape de Bray formations of Embry and Klovan (Embry, A.F., and Klovan, J.E. 1976. The middle-upper devonian clastic wedge of the franklinian geosyncline. Bulletin of Canadian Petroleum Geology, 24: 485–639. https://pubs.geoscienceworld.org/cspg/bcpg/article/24/4/485/57135) are not traceable enough to warrant their formation rank. We revert to the original usage of Tozer and Thorsteinsson (Tozer, E.T., and Thorsteinsson, R. 1964. Western Queen Elizabeth Islands, Arctic Archipelago. Geological Survey of Canada, Memoir 332: 242 p. doi:10.4095/100556) where these units are members within the Weatherall Formation. The distinctive seismic character of the Cape de Bray in western and central Melville Island warrants its recognition as a formal member; elsewhere, it is informal as it cannot be consistently traced. The Blackey is treated as a formal member in an outcrop area of ∼2000 km 2 where it was defined; it is not recognized in the subsurface. Onset of the DCW is tentatively linked to flexural subsidence and crustal thickening caused by the Romanzof Orogeny in the hinterland.

Correcting Tmax Suppression: A Numerical Model for Removing Adsorbed Heavy Oil and Bitumen from Upper Ordovician Source Rocks, Arctic Canada

A Rock-Eval 6 dataset of 66 samples from the Cape Phillips Formation in the Canadian Arctic region was studied to investigate source rock characteristics and petroleum generation potential. Bulk geochemical characteristics and thermal decomposition behavior of the samples indicate an initial generation potential close to 700 mg HC/g TOC and show an unusually low onset Tₘₐₓ temperature for petroleum generation. This led to an examination of possible Tₘₐₓ suppression due to a large amount of high-molecular-weight heavy oil and bitumen derived from the early breakdown of kerogen in the samples. Application of a numerical method based on kerogen decomposition kinetics allows for the numerical removal of thermal evaporative products of oil and bitumen adsorbed in the sample without requiring additional pyrolysis experiments or solvent extraction treatments of sample replicates. The removal of the adsorbed hydrocarbon from samples increases the Tₘₐₓ value up to 17 °C. The estimated petroleum in the sorption phase varies from 1 to about 9 mg HC/g rock, depending on the total organic content (TOC) and maturity, and is the main form of the total oil yield in this area. The corrected Tₘₐₓ–HI cross-plot suggests an onset of petroleum generation around 435 °C of Tₘₐₓ, consistent with the general consensus for a normal marine source rock in this region. The constructed kinetic model shows a maximum of 75% transformation ratio (TR), and most samples show TR ranging from 10 to 50% in the early oil generation window on Cornwallis Island. This reconstructed source rock thermal decomposition model in a geological time scale indicates the onset of massive petroleum generation at a temperature of 120 °C, and the maximum transformation ratio of 75% corresponds to a temperature of 140 °C over geological time.

Correlation of zooclast reflectance with Rock-Eval Tmax values within Upper Ordovician Cape Phillips Formation, a potential petroleum source rock from the Canadian Arctic Islands

The lower part of the Cape Phillips Formation (Upper Ordovician, Canadian Arctic) is an ideal unit to test the correlation of graptolite and chitinozoan reflectance, and to compare zooclast reflectance with Rock-Eval pyrolysis Tmax. The Cape Phillips Formation is an organic-rich limestone and shale containing abundant zooclasts, bitumen, and amorphous organic matter, and has biomarker characteristics consistent with a carbonate depositional environment and organic matter derived from marine algae.Random graptolite reflectance on thirty-seven samples in the Rograp range of 0.58%–1.02% (Tmax range of 424–441 °C) were examined. The correlation between random reflectance of graptolite and chitinozoan reflectance was determined to have the following linear model:(Rograp)=0.11+0.814×(Rochi)whereas the linear correlation between Rock-Eval Tmax (converted to vitrinite reflectance equivalent VRoeqv) and Rograp and Rochi were determined to be:VRoeqv(Tmax)=0.232+0.499×(Rograp)for random reflectance of graptolites.VRoeqv(Tmax)=0.231+0.482×(Rochi)for chitinozoan.Graptolite and chitinozoan reflectance are generally greater than vitrinite reflectance equivalent, but the difference between the equations to convert graptolite and chitinozoan reflectance to VRoeqv(Tmax) are so small that the equations could be used interchangeably and may represent a general solution to the conversion of zooclasts reflectance to VRoeqv(Tmax) in Lower Paleozoic rocks.The correlation between zooclast reflectance and Rock-Eval Tmax improves in samples that have undergone solvent extraction, indicating that hydrocarbons affect Tmax. Sample that has asymmetrical S2 peak on Rock-Eval pyrolysis also has very high total extract yield with resins and asphaltenes as the dominant extracted fractions. Rock-Eval analysis of samples before and after solvent extraction demonstrates that some portion of the soluble hydrocarbon is pyrolysed in the temperature range that overlaps the S2 peak. In extracted samples S2 peaks become more symmetrical and the Tmax value shifts compared to the unextracted samples.

Hirnantian (Ordovician) through Wenlock (Silurian) conodont biostratigraphy, bioevents, and integration with graptolite biozones, Cape Phillips Formation slope facies, Cornwallis Island, Canadian Arctic Islands

Cornwallis Island in the Canadian Arctic Archipelago provides one of the world’s best areas for establishing an integrated graptolite–conodont biozonation for the Late Ordovician – Silurian given the well-exposed interfingering relationship of the basinal shale and carbonate platform facies. Building on earlier graptolite work, 180 samples were collected from nine sections of the Cape Phillips Formation, of which 118 yielded approximately 7600 conodont elements representing 54 species in 25 genera, including one new genus and species, Mayrodus melchini; the conodonts are well preserved, with minimal thermal alteration (colour alteration index, CAI 1). Nine conodont zones are recognized and defined for this region, namely the Amorphognathus ordovicicus, Distomodus kentuckyensis, Aspelundia expansa, As. fluegeli, and Pterospathodus celloni Interval zones, Pt. a. amorphognathoides Taxon-range Zone, Pt. pennatus procerus and Kockelella ranuliformis Highest-occurrence zones, and K. ortus absidata Taxon-range Zone. An integration of graptolite and conodont zones is documented. Earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the Silurian ocean–climate system and identified major faunal turnovers or events. Five of these are recognized in the Cornwallis fauna and related to oceanographic and climate changes, in part referring to recent oxygen isotope data from conodonts from the Cornwallis collections: Hirnantian extinction event, Sandvika Event (late Aeronian, Llandovery), Snipklint Primo Episode (early Telychian, Llandovery), Ireviken Event (late Telychian, Llandovery–Sheinwoodian, Wenlock), and Mulde Event (early Homerian, Wenlock).

Upper Ordovician – Upper Silurian conodont biostratigraphy, Devon Island and southern Ellesmere Island, Canadian Arctic Islands, with implications for regional stratigraphy, eustasy, and thermal maturation

The conodont biostratigraphy for the Upper Ordovician – Upper Silurian carbonate shelf (Irene Bay and Allen Bay formations) and interfingering basinal (Cape Phillips Formation) facies is established for parts of Devon and Ellesmere islands, central Canadian Arctic Islands. Revisions to the interpreted regional stratigraphic relationships and correlations are based on the stratigraphic distribution of the 51 conodont species representing 32 genera, identified from over 5000 well-preserved conodonts recovered from 101 productive samples in nine stratigraphic sections. The six zones recognized are, in ascending order, Amorphognathus ordovicicus Local-Range Zone, Aspelundia fluegeli Interval Zone, Pterospathodus celloni Local-Range Zone, Pt. pennatus procerus Local-Range Zone, Kockelella patula Local-Range Zone, and K. variabilis variabilis – Ozarkodina confluens Concurrent-Range Zone. These provided a more precise dating of the members and formations and, in particular, the range of hiatuses within this stratigraphic succession. The pattern of regional stratigraphy, facies changes, and hiatuses is interpreted as primarily related to the effects of glacioeustasy associated with the terminal Ordovician glaciation and smaller Early Silurian glacial phases, the backstepping of the Silurian shelf margin, and the geodynamic effects of the collision with Laurentia by Baltica to the east and Pearya to the north. Conodont colour alteration index values (CAI 1–6.5) from the nine sections complement earlier graptolite reflectance data in providing regional thermal maturation data of value in hydrocarbon exploration assessments.

A new Gorstian radiolarian fauna from the upper Silurian of the Cape Phillips Formation, Cornwallis and Bathurst islands, Canadian Arctic

This study provides a taxonomic treatment and comparison of lower Gorstian (Silurian) radiolarians recovered from two sections of the Cape Phillips Formation in the Canadian Arctic that accumulated in two different paleoenvironmental settings. Twilight Creek is more basinal, located ∼100 km from the paleo-shelf margin, whereas Snowblind Creek is located within 1 km of the paleo-shelf break, on Cornwallis Island. The fauna, like other material from the Cape Phillips Formation, is extremely well preserved and was recovered from four samples at two localities, all from the Lobograptus progenitor graptolite Zone, an interval that has few published studies regarding radiolarians. A total of 28 species are recognized, of which two are new and described herein (Fusalfanus bilateralis n. sp. and Pseudospongoprunum parvispina n. sp.), belonging to the Haplotaeniatidae, Inaniguttidae, “Sponguridae”, Ceratoikiscidae, Entactiniidae, Palaeoscenidiidae, and Secuicollactidae. Based on these new data, the stratigraphic ranges of some taxa are extended. The species concepts of several closely related inaniguttid species are re-evaluated. As a result, Inanihella tarangulica Nazarov and Ormiston, 1984 is transferred to the genus Fusalfanus Furutani, 1990 based on cortical shell structure, and Inanihella duroacus, Inanihella legiuncula, and Inanihella perarmata are synonymized under Fusalfanus tarangulica sensu lato. Aciferopylorum admirandum is transferred to Fusalfanus and considered a junior synonym of Fusalfanus osobudaniensis. The comparative analysis of taxonomic richness and composition reveals that the more distal sample from Bathurst Island exhibits a slight, but statistically significant, higher alpha diversity at the species rank than the more proximal basin/platform samples from Snowblind Creek. Biodiversity indices at the genus rank produced mixed results, indicating that differences between sites are at best slight. There is also a strong taxonomic separation between the fine and coarse size radiolarian fractions recovered during the sieving of each sample. The siliceous sponge spicule assemblages from these faunas show an inverse diversity relationship to the radiolarians in that Snowblind Creek contains greater alpha diversity than Twilight Creek. This study provides the first documentation of facies-controls in Silurian radiolarian diversity and is useful in evaluating the role of taxa used in biostratigraphy.

Palaeoecology of transported brachiopod assemblages embedded in black shale, Cape Phillips Formation (Silurian), Arctic Canada

Brachiopod communities have been widely used for palaeoecological studies and reconstruction of sea-level changes in Earth history. Previous studies of brachiopod communities emphasised sampling benthic shelly fossils preserved in situ to avoid preservation bias. Silurian (Wenlock) brachiopod assemblages are well preserved as debris-turbidity flows, including calcareous concretions, embedded in thick sequences of black shale of the Cape Phillips Formation, with a mixture of deep-water brachiopods and transported shallow-water forms. In this study, the first attempt is made to use the transported assemblages to reconstruct Silurian brachiopod communities that once lived along a palaeogradient from the shallow-water Arctic Platform to the deep-water Franklinian Basin. Seven transported brachiopod assemblages were recognised using multivariate analyses (cluster analysis and principal components analysis), with varying ratios of shallow- versus deep-water shells, segregated according to their known palaeobathymetric ranges in other regions. The Wenlock–early Ludlow sea-level fluctuations in the study area, reconstructed using the percentage values of shallow- and deep-water brachiopod specimens as a proxy, have a high degree of agreement with the Arctic Silurian sea-level curve and moderate agreements with global sea-level histories of other regions such as the British Isles and Gotland interpreted from graptolite abundance and diversity changes, and sequence and event stratigraphical methods, respectively.

Complex noncalcified macroalgae from the Silurian of Cornwallis Island, Arctic Canada

Thin beds of silty limestone within a Ludlovian (Ludfordian) section of the Cape Phillips Formation on Cornwallis Island, Arctic Canada, contain numerous specimens of noncalcified macroalgae in association with dendroid and graptoloid graptolites, brachiopods, and trilobites. The algal material, preserved as carbonaceous compressions, represents three new taxa, each characterized by a central axis surrounded by laterals. Laterals ofEocladus xiaoin. gen. n. sp. are thin and branch to the fifth order whereas those ofChaetocladus captitatusn. sp. are undivided and form a distinctive capitulum. Thalli ofPalaeocymopolia nunavutensisn. gen. n. sp. have a branched, serial-segmented form and a corticated structure. On the basis of thallus architecture, all three taxa are assigned to the extant green algal order Dasycladales. Parallels exist between this macroalgal assemblage and a modern macroalgal association in Florida Bay.

Palaeocope ostracods from the Silurian Wenlock Series of Arctic Canada

Silurian Wenlock Series deposits of the Cape Phillips Formation on Baillie-Hamilton Island and Cornwallis Island, Arctic Canada, have yielded a silicified ostracod assemblage that spans the late Sheinwoodian and Homerian stages. Sixteen palaeocope ostracod species are recorded, including the new species Beyrichia ( Beyrichia ) marssae , Gabrielsella ? copelandi , and Platybolbina ( Abruptobolbina ) adraini . The ostracod faunas can be linked into local trilobite, microvertebrate, and graptolite zonal schemes, and a few of the ostracod species offer potential for local and perhaps wider biostratigraphical correlation. The ostracods are mostly known only from the Cape Phillips Formation, but also include two taxa found in the Wenlock Series of the Avalanche Lake area, Northwest Territories, Canada. Other ostracod species suggest links with Silurian successions in northern Canada and the Baltic. Low-diversity ostracod faunas characterize the level of a marked positive carbon isotope excursion and coeval mid-Homerian regression at the level of the regional Pristiograptus dubius – Gothograptus nassa graptolite Biozone. Comparison with the pattern of distribution of coeval ostracod faunas elsewhere in Canada suggests that diversity changes in the Cape Phillips Formation ostracod faunas are controlled by local palaeoenvironmental factors perhaps linked to global sea-level change.

Geochemistry of crude oil from Bent Horn field (Canadian Arctic Archipelago) and its possible Paleozoic origin

Geochemical analysis shows that oil from Devonian reservoirs at Bent Horn field in the Canadian Arctic Archipelago is non-biodegraded and has a maturity corresponding to the mid-late part of the oil window. It is characterized by a smooth n-alkane profile, low concentration of acyclic isoprenoids and saturated hydrocarbon biomarkers, with some variability in sterane composition. Compared with oil from Mesozoic strata of the Canadian Arctic Islands, the Bent Horn oil shows higher paraffin indices and aromatic hydrocarbon maturity indicators (MPI, MDR), dominant tricyclic terpanes and different distribution of regular steranes. Geological evidence suggests a Paleozoic source rock for the oil. Rock–Eval pyrolysis and total organic carbon (TOC) data indicate good source rock potential for the Silurian basinal facies and Upper Silurian–Lower Devonian clastics of the Boothia Uplift. These intervals are enriched in Type II oil-prone organic matter (commonly 2.0–5.0% TOC, maximum 13.6%) and are mature with respect to petroleum generation. Based on preliminary biomarker analysis, maturity, and stratigraphic and geographic proximity to the Bent Horn oil field, the Cape Phillips Formation appears to be the most likely source rock for the hydrocarbon accumulation at Bent Horn.

UPPER WENLOCK CERATOIKISCIDAE (RADIOLARIA) FROM THE CAPE PHILLIPS FORMATION, ARCTIC CANADA

Abstract Taxa belonging to the Ceratoikiscidae are described in detail from two measured sections of Member C of the Cape Phillips Formation exposed along Rookery Creek, Cornwallis Island, Arctic Canada. The sections encompass uppermost Sheinwoodian (top lower Wenlock) to the base of the Gorstian (base Ludlow) and are dated by graptolites assigned to the Cyrtograptus perneri–Monograptus opimus Zone (upper Sheinwoodian), the Cyrtograptus lundgreni Zone (lower Homerian), and the Colonograptus praedeubeli–Colonograptus deubeli Zone (upper Homerian). Radiolarians are found in great abundance throughout the lower Homerian, allowing for the establishment of the first appearance of the genus Helenifore Ormiston and Nazarov. Helenifore is emended to accommodate the Silurian species H. quadrispina n. sp. and H. speciosus (Furutani 1990). One new genus, Kappaforma, including the new species, K. insecta, is described, as is the new species H. quadrispina. Ceratoikiscum octapleura Renz and C. armiger Furutani are syn...

Sheinwoodian (uppermost Lower Silurian) Radiolaria from the Cape Phillips Formation, Nunavut, Canada

Radiolarians from the C. perneri-M. opimus graptolite Zone (Sheinwoodian; Wenlock) are described from a section in the Cape Phillips Formation, Nunavut, Canada, with a focus on the spherical radiolarian component (Archaeospicularia, Entactinaria, and Spumellaria). Three new genera, Involutentactinia, Perforentactinia, and Franklinia are described and the genera Labyrinthospahera, Gyrosphaera, and Haplotaeniatum are emended. Ten new species are described: Involutentactinia eccentra n. sp., containing two varieties; Involutentactinia eccentra n. sp. sensu strictu , and I. eccentra cupressa n. var.; Magnentactinia ostentata n. sp., Perforentactinia excepta n. sp., Plussatispila aethra n. sp., Franklinia tricae n. sp., F. dipulvisphaera , n. sp., Haplotaeniatum vertigospongum , n. sp., Gyrosphaera cavea n. sp., Labyrinthosphaera lancia , n. sp., and Labyrinthosphaera ? lenzi n. sp. Haplotaenitaumiids and entactiniids are dominant and respectively, comprise as much as 35% and 20% percent of the fauna in some samples. Secuicollactines represent a small but persistent component. Inaniguttids, formerly thought to be a dominant portion of upper Sheinwoodian faunas, are represented by only one inaniguttid species, P. aethra , which makes up between 0.5 to 18% of the fauna. This first detailed glimpse at the upper Shein-woodian revises the ranges of two biostratigraphically important taxa: the first appearance of Inanihella tarangulica group taxa occurs above the C. perneri-M. opimus Zone and the last appearance of Haplotaeniatum is within the C. perneri-M. opimus Zone. Revisions to the existing radiolarian biozonation of Noble and Aitchison are proposed; the Long-spined inaniguttid 2 zone now extends through the C. perneri –M. opimus Zone encompassing this fauna, and the base of the Long-spined inaniguttid 3 Zone is redefined and moved to the base of the Homerian.

A preliminary radiolarian biozonation for the Lower Silurian of the Cape Phillips Formation, Nunavut, Canada

Radiolaria from the Lower Silurian of the Cape Phillips Formation, Nunavut, Canada allow the definition of four biostratigraphic assemblages. The Haplotaeniatum assemblage extends from the basal Llandovery to topmost Coronograptus cyphus graptolite Biozone. The base is taken as the first occurrence of Haplotaeniatum nunavutensis; no samples were collected below the Ordovician–Silurian boundary. The top of the assemblage is defined by the first occurrence of Orbiculopylorum. The Orbiculopylorum assemblage is marked by the first occurrence of Orbiculopylorum. The boundary between this assemblage and the overlying Plussatispila assemblage is unclear because of a break in stratigraphy (upper Spirograptus turriculatus through Monograptus crispus graptolite biozones). The last occurrence of Orbiculopylorum defines the top of the assemblage. The base of the Plussatispila assemblage is defined by the last occurrence of Orbiculopylorum. A barren interval (Cyrtograptus insectus to lower Monograptus instrenuus – Cyrtograptus kolobus graptolite biozones) separates the Plussatispila assemblage and subsequent Ceratoikiscum assemblage. The first occurrence of Ceratoikiscum is taken as the boundary between these assemblages. The top of the Ceratoikiscum assemblage is not established, but is taken as the first occurrence of Inanihella tarangulica Group radiolarians. This zonation is comparable to, and a modification from, the global radiolarian biozonation of Noble and Aitchison (2000).

HAPLOTAENIATUMIDAE AND INANIGUTTIDAE (RADIOLARIA) FROM THE LOWER SILURIAN OF THE CAPE PHILLIPS FORMATION, CORNWALLIS ISLAND, NUNAVUT, CANADA

Radiolaria of the families Haplotaeniatumidae Won, Blodgett, and Nestor, 2002 and Inaniguttidae Nazarov and Ormiston, 1984 were recovered from the Llandovery and lower Wenlock of the Cape Phillips Formation on Cornwallis Island, Nunavut, Canada. Three new species of haplotaeniatumids are described. Haplotaeniatum fissura n. sp. is diagnosed by a densely constructed outer layer around a less dense interior; Haplotaeniatum nunavutensis n. sp. has small, circular pores separated by wide lattice bars; and Orbiculopylorum granti n. sp. possesses robust external spines. Haplotaeniatumids described in open nomenclature are Haplotaeniatum labyrintheum?, Haplotaeniatum aff. cathenatum, Haplotaeniatum cf. raneatela, Haplotaeniatum species A, Orbiculopylorum aff. adobensis, Orbiculopylorum cf. marginatum and Orbiculopylorum species A. Gyrosphaera Noble and Maletz, 2000 is synonymized with Haplotaeniatum. The Inaniguttidae are assigned to Plussatispila n. gen. The genus is diagnosed by two, well-spaced lattice shells and at least seven main spines; additional shells may be present. Plussatispila magnilimax n. sp. has a total of four shells, and P. cornwallisensis n. sp. a total of three. Plussatispila delicata n. sp. has only the two fundamental shells of the genus and is slightly more delicate than the other inaniguttids. Plussatispila pellicia n. sp. possesses weakly developed spines and may have additional irregular layers.

The paradox of the global standard Late Ordovician–Early Silurian sea level curve: Evidence from conodont community analysis from both Canadian Arctic and Appalachian margins

Relative sea level fluctuations in the Late Ordovician–Early Silurian were largely driven by Gondwana deglaciation, three possible short-lived ice readvances, and the closure of the Iapetus Ocean. This study establishes and compares sea level events on the Canadian Arctic and Appalachian margins of Laurentia based on the pattern of conodont communities, and demonstrates that sea level events were not synchronous on the two margins. Conodont data were compared for a) the Arctic margin from the Cape Phillips Formation (Richmondian, Upper Ordovician through lower Sheinwoodian, Lower Silurian), Cornwallis Island, Canadian Arctic Islands, and b) the Appalachian margin from the upper Ellis Bay, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations (Richmondian, Upper Ordovician, Rhuddanian, Aeronian, and most of Telychian, Lower Silurian), Anticosti Island, Quebec. The pattern of Late Ordovician–Early Silurian conodont communities is established based on three cluster analyses on conodonts from Cornwallis Island (4967 specimens representing 54 species from 77 samples, Cape Phillips Formation) and Anticosti Island (1980 specimens representing 21 species from 25 samples, upper Ellis Bay Formation; 24,839 specimens representing 42 species from 123 samples, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations). Overall, the sea level curves inferred from the distribution of the conodont communities from Cornwallis and Anticosti exhibit gradual and rapid oscillating patterns, respectively. Specifically, during the time interval of the latest Ordovician and the Early Silurian (Rhuddanian), the sea level behaved differently in these two regions: 1) during the latest Ordovician, conodont community changes show the different patterns in the two regions, which reflects a transgression on Cornwallis, but a regression on Anticosti; 2) during the earliest Rhuddanian, similar conodont communities arose in both regions, but they indicate a regression on Cornwallis and a transgression on Anticosti; 3) in the early Rhuddanian, these communities were replaced by a deeper water community on Cornwallis and a shallower water community on Anticosti, which suggest a transgression on Cornwallis and a regression on Anticosti; 4) a highstand drove out almost all conodonts from Anticosti by the end of Rhuddanian, which is not seen on Cornwallis; 5) a deep-water conodont community remained almost unchanged on Cornwallis from the late Rhuddanian to the early Aeronian, whereas a shallow water conodont community returned to Anticosti in the early Aeronian. However, the sea level dropped on both Cornwallis and Anticosti during the late Telychian, and the sea level curves show a similar pattern. The difference in the sea level pattern during the late Richmondian, Rhuddanian and Aeronian on both the northern and southern margins of Laurentia reflected by conodont communities is supported by the studies on Quaternary glaciation/deglaciation events, where the melting of an ice sheet was accompanied by sea level change but with variable regional isostatic effects that do not generate a uniform global eustatic signal.

The brachymetopid trilobite Radnoria in the Silurian (Wenlock) of New York State and Arctic Canada

Radnoria bretti n. sp., from the Wenlock (Sheinwoodian) Rochester Formation of western New York State, is the best preserved and most completely known member of its genus. It provides the first definitive information on Radnoria's hourglass-shaped rostral plate, the first known hypostome of a Silurian member of the genus, demonstrates that Radnoria engaged in sphaeroidal enrollment, and reveals that early holaspid individuals had tubercles on the posterior thoracic axes and pygidial axial rings that were effaced with maturity. Three new species from the Wenlock of the Cape Phillips Formation of Nunavut are known from sparse material and are reported in open nomenclature. Together, the species greatly increase knowledge of Laurentian Silurian brachymetopids, which have until now been known from a single cranidium from the Wenlock of Arkansas.

Early Silurian (Wenlockian) δ13C profiles from the Cape Phillips Formation, Arctic Canada and their relation to biotic events

Geochemical data from the Cape Phillips Formation, Arctic Canada, are examined in association with three Silurian biotic crises in the graptolite community; the early Wenlockian Ireviken, mid Wenlockian Cyrtograptus lundgreni, and end Wenlockian Colonograptus ludensis extinction events. Positive δ13Corg excursions are associated with the Ireviken and C. lundgreni events, but not the Co. ludensis Event. The Ireviken and C. lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea-level drop. The C. lundgreni excursion is of greater magnitude in the more proximal basin margin section at Abbott River, Cornwallis Island, and is explained by the amplification of a more strongly positive δ13C signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf. Excursion C5, within the C. praedeubeli – C. deubeli Zone, is also of regional significance, as it occurs in both the Abbott River section and Twilight Creek section on Bathurst Island, and is also recognized in Estonia, Poland, and England. Excursion C6 is recognized in the Gorstian Stage, yet its regional significance remains equivocal. There is a reasonable general agreement between the shape of the δ13Corg and δ13Ccarb curves, yet the δ13Ccarb curve is largely a record of detrital carbonate derived from the shelf. The δ13Corg curve represents extraction of dissolved inorganic carbon by plankton and thus is more indicative of ambient paleoceanographic conditions. These data are valuable in that they provide a detailed secular marine δ13C curve for the Wenlockian of Arctic Canada from relatively unaltered sections of varying facies whose ages are well constrained by graptolite biostratigraphy.

PALAEOSCENIDIIDAE (RADIOLARIA) FROM THE LOWER SILURIAN OF THE CAPE PHILLIPS FORMATION, CORNWALLIS ISLAND, NUNAVUT, CANADA

Abstract Spicular radiolarians of the family Palaeoscenidiidae were recovered from the Llandovery to lower Wenlock of the Cape Phillips Formation, Nunavut, Canada. Several changes are made to the classification of these radiolarians. Goodbodium rarispinosum (Goodbody, 1986) was previously placed with Palaeoscenidium Deflandre, 1953. Insolitignum MacDonald, 1999 is emended to allow for additional apical rays. Insolitignum cancellatum (Goodbody, 1986) includes species which were previously assigned to Palaeoscenidium, Palaeotripus Goodbody, 1986, and Palaeoephippium Goodbody, 1986, owing to the variable development of one ray. Insolitignum peranima MacDonald, 1999 is synonymized with I. dissimile (Goodbody, 1986). Palaeodecaradium apertum (Goodbody, 1986) was previously placed with Palaeoscenidium; Palaeotripus nudus Goodbody, 1986 is considered a synonym of P. apertum. Palaeoephippium is rediagnosed based on the branching of the basal rays; the new diagnosis also allows for more than six rays and in orient...

Validity and composition of the Silurian trilobite genera Borealarges and Dicranogmus, with new species from the Canadian Arctic

New silicified material from Arctic Canada demonstrates that the lichid trilobite genera Borealarges and Dicranogmus, recently claimed to be synonyms, are independent groups with no close phylogenetic connection to one another. Dicranogmus has been known mainly from cranidia alone; prior association of librigenae and pygidia with the Arctic Canadian species D. skinneri has been queried. This association is correct beyond reasonable doubt, based on description of new material of both D. skinneri and a new species. Three new species of Borealarges are related to B. tuckerae Adrain 1994. Cladistic analysis supports the monophyly of this species group. Pending further new information, however, the group is retained within the genus Borealarges. The stratigraphic range of the species group is extended from the lower Wenlock (Sheinwoodian) to upper Ludlow (Ludfordian) by the discovery of a rare species in the Douro Formation of Cornwallis Island, Arctic Canada. New taxa from the Wenlock of the Cape Phillips Formation, Arctic Canada, include Dicranogmus wynni, Borealarges nicoae, B. warholi, and B. yulei.

Stable Carbon-Isotope Compositions of Compression Fossils from Lower Paleozoic Konservat-Lagerstatten

Abstract Taxon-specific stable carbon-isotope ratios were determined for 7 graptolite (consumer) and 4 alga (primary producer) taxa preserved as thin organic compressions within North American Silurian Konservat-Lagerstatten. Values range from −26.6‰ for a graptolite from the Goat Island Formation, New York, to −32.3‰ for an alga from the Cape Phillips Formation, Arctic Canada. Co-occurring graptolite taxa display nearly identical δ13C compositions (within 0.2‰). Algal taxa co-occurring with graptolite taxa have δ13C compositions which are 1–2‰ more negative than those of associated graptolites. The observed isotopic offset between associated graptolites and macroalgae, both of which are common sources of organic matter in Paleozoic strata, holds implications for the interpretation of time-series δ13Corg curves, and suggests that stable carbon-isotope composition could serve as a chemosystematic tool for discerning the affinities of organic macrofossil problematica.