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The Late Ordovician (late Katian) Tcherskidium fauna consisted of large- and thick-shelled virgianid pentamerid brachiopods characterized by large and ribbed shells of Tcherskidium and Proconchidium and usually associated with Holorhynchus, Deloprosopus, and Eoconchidium. This unique fauna was widely distributed across several tectonic plates, largely confined to the paleoequatorial and especially the northern paleotropical zones, such as northern Laurentia, accretionary terranes of Alaska, Kolyma, Baltica, Siberia, Kazakh and adjacent terranes, and South China. In Laurentia, the eponymous genus Tcherskidium was predominant in regions north of the paleoequator and, in sharp contrast, was absent south of the paleoequator. In this study, Tcherskidium lonei n. sp. and Proconchidium schleyi n. sp. are described from Alaska and North Greenland, respectively, adding new data on the Tcherskidium fauna of the Late Ordovician Northern Hemisphere. Shell gigantism, together with the sharp paleobiogeographic division, suggests that the Late Ordovician (late Katian) Northern Hemisphere had a prevailing warm-water mass, probably due to the lack of large landmass beyond the northern tropics. This was in sharp contrast to the Southern Hemisphere, which was frequently influenced by cold-water invasions from the ice-bearing Gondwana supercontinent centered on the South Pole. UUID: http://www.zoobank.org/25d9b772-bd7d-4ad6-bfc6-ba02b1567cf3 [ABSTRACT FROM AUTHOR]

ABSTRACT Middle Ordovician iron ooids in the Upper Yangtze region of South China are composed mainly of hematite and/or chamosite, found in mixed siliciclastic and carbonate successions, with hematitic ooids occurring in the west, and predominantly chamositic ooids in the east of the study area. In the three iron ooid‐bearing Middle–Upper Ordovician successions, 19 microfacies are recognized and grouped into eight facies associations, representing a shallow‐water mosaic comprising restricted and semi‐restricted lagoons, and open marine subtidal deposits interfingering with tidal flat and shoal facies. Hematitic ooids with well‐sorted and well‐rounded quartz grains formed in the transgressive shoal setting when the depositional environments changed from restricted lagoon to bioclast–quartz shoal and open marine subtidal. Episodic stasis and erosional intervals during transgression controlled the formation of hematite‐rich and mixed hematite–chamosite laminae within the cortices of hematitic ooids. In contrast, chamositic ooids formed in a semi‐restricted lagoonal environment, under long‐term transgressive condensation. Alternating episodes of relatively oxic conditions with thriving organisms and eutrophication‐driven anoxia resulted in the alternation of porous and dense laminae consisting mainly of chamosite in chamositic ooids. The stromatolite‐like cauliflower structures associated with chamositic ooids suggest microbial activity that promoted iron concentration, similar to the origin of approximately coeval iron‐rich oncoids in South China. Various iron ooid types demonstrate that these coated grains could form in a range of depositional setting and palaeooceanographic conditions on a generally shallow‐marine platform during the Ordovician. [ABSTRACT FROM AUTHOR]

A Late Ordovician brachiopod fauna from the Black River quadrangle (D-1 1:63,360 scale) of east-central Alaska comprises taxa typical of the Late Ordovician brachiopod fauna in the pericratonic epeiric seas of Laurentia, including Hesperorthis pyramidalis (Twenhofel, 1928), Plaesiomys occidentalis (Okulitch, 1943), Eoplectodonta sp., Holtehdalina sp., Leptaena sp., Brevilamnulella minuta n. sp., Tcherskidium tenuicostatum n. sp., Rhynchotrema iowense Wang, 1949, and Whitfieldella sp. The presence of Plaesiomys occidentalis and Tcherskidium tenuicostata n. sp. indicates a latest Katian age by correlation with similar species in the Mackenzie Mountains, southern Manitoba, Anticosti Island, the American midcontinent, Kolyma, and Siberia. Cluster analysis based on 20 well-studied late Katian brachiopod faunas from various regions within Laurentia and elsewhere in other tectonic plates suggests that the small brachiopod faunule from Alaska has the strongest paleobiogeographic affinity with Laurentia, confirming that the Black River quadrangle of Alaska was part of Laurentia during the Late Ordovician. UUID: http://zoobank.org/6b387856-61d5-4685-a592-faf5287c1e0f [ABSTRACT FROM AUTHOR]

While it is well established that the shapes and sizes of shells are strongly phylogenetically controlled, little is known about the phylogenetic constraints on shell thickness. Yet, shell thickness is likely to be sensitive to environmental fluctuations and has the potential to illuminate environmental perturbations through deep time. Here we systematically quantify the thickness of the anterior brachiopod shell which protects the filtration chamber and is thus considered functionally homologous across higher taxa of brachiopods. Our data come from 66 genera and 10 different orders and shows well‐defined upper and lower boundaries of anterior shell thickness. For Ordovician and Silurian brachiopods we find significant order‐level differences and a trend of increasing shell thickness with water depth. Modern (Cenozoic) brachiopods, by comparison, fall into the lower half of observed shell thicknesses. Among Ordovician–Silurian brachiopods, older stocks commonly have thicker shells, and thick‐shelled taxa contributed more prominently to the Great Ordovician Biodiversification but suffered more severely during the Late Ordovician Mass Extinction. Our data highlight a significant reduction in maximum and minimum shell thickness following the Late Ordovician mass extinction. This points towards stronger selection pressure for energy‐efficient shell secretion during times of crisis. [ABSTRACT FROM AUTHOR]

Dalmanelloid brachiopod shells were collected from the Upper Ordovician Lexington Formation (lower Katian) of Kentucky, Sheguindah Shale (middle Katian) on Manitoulin Island, Ontario, and the Stony Mountain Formation (upper Katian) in the Winnipeg area, Manitoba. They were investigated to test the hypothesis of paleo-latitudinal zonation of the shelly benthos. A multi-technique approach was applied to evaluate the petrographic and geochemical (isotopic and elemental) preservation of the secondary layer of shells. Preliminary conventional microscopy, cathodoluminescence (CL), and scanning electron microscopy (SEM) confirmed the retention of primary shell ultrastructure (prismatic low-Mg calcite). The geochemical diagenesis proxies (e.g., Sr, Mn, Fe, and ΣREE) show insignificant correlations with the δ18O and δ13C values, thus supporting the preservation of at least near-primary geochemical compositions. Among the three lots of shells, the mean δ18O value is the highest in those from the Lexington Formation (–4.5‰ ± 0.3‰ VPDB), lowest from the Stony Mountain Formation (–6.8‰ ± 0.4‰ VPDB), and intermediate from the Sheguindah Shale (–6.0‰ ± 0.8‰ VPDB). The relative gradient in δ18O increase is in agreement with the paleo-latitudinal gradient, with Kentucky in subtropical, southern Ontario in mid-tropical, and southern Manitoba in subequatorial latitudes. The Lexington Formation shells also have the highest mean δ13C value (0.8‰ ± 0.2‰ VPDB) and relatively high P contents (170 ± 27 ppm), suggesting higher organic productivity, which is consistent with previous interpretation of frequent upwelling of nutrient-rich cool waters along the southeastern margin of Laurentia during the Katian. The Lexington shells also have a lower mean Th/U (0.6 ± 0.6), which is consistent with blooming organic productivity that likely led to more consumption of oxygen in the water column. [ABSTRACT FROM AUTHOR]

Network and frequency distribution analyses of global brachiopod occurrences in the earliest Silurian (Rhuddanian–Aeronian) revealed that brachiopod recovery from the end-Ordovician mass extinction during the early–late Rhuddanian was represented mainly by the reestablishment of Late Ordovician cosmopolitan holdover taxa. Brachiopods nearly doubled their generic diversity from Rhuddanian to Aeronian, owing to the radiation of both endemic and cosmopolitan taxa, associated with an overall post-glacial amelioration of global environment and increased habitat heterogeneity as a result of marine transgressions and expansion of epeiric seas. A drastic turnover from the Ordovician-type to Silurian-type brachiopod faunas took place in the Aeronian, several million years after the terminal Ordovician mass extinction. Compared with the orders of orthides and strophomenides that radiated and predominated in the Ordovician, the atrypides and pentamerides displayed pulses of drastic diversification from the Rhuddanian to Aeronian, mainly in tropically located paleoplates, to become the most abundant and diverse brachiopod orders in the Silurian. Atrypides recovered in the early Rhuddanian, whereas diversification of pentamerides was delayed until the Aeronian and becoming widespread in South China, Kazakhstan terranes, Baltica, Avalonia, and Laurentia. [ABSTRACT FROM AUTHOR]

During the late Sandbian and early to middle Katian, a major marine transgression flooded the intracratonic basins and platforms of eastern North America, allowing brachiopods to disperse into the newly formed epicontinental seas. Two main brachiopod faunas can be differentiated using multivariate analysis of faunal data from localities across Laurentia during this time: a relatively diverse Scoto-Appalachian Fauna confined to the eastern margin of North America and peri-Laurentian terranes, and a less diverse but more widely distributed Epicontinental Fauna that expanded into the remainder of the flooded continent. The Epicontinental Fauna can be divided into four subfaunas with subtle compositional differences that correspond to different paleoenvironmental settings of eastern North America, influenced by such paleoecological factors as nutrient-rich cool-water upwelling onto the continent through the Sebree Trough, a greater range of habitable environments on the continental margin and in the adjacent deep Taconic foreland basin, and the interactions between pericratonic and intracratonic water masses of different physical and chemical properties. The Epicontinental brachiopod faunas dominated basins and platforms of continental interior until the Hirnantian extinction event. [ABSTRACT FROM AUTHOR]

Ziegler's (1965) early Silurian brachiopod community zones and Boucot's (1975) Benthic Assemblages have been instrumental in determining the community structures of early–middle Paleozoic level-bottom communities, but are difficult to apply to reef ecosystems due to the mixing of level-bottom community assemblages in these systems. In this study, Shannon and Simpson diversity levels were calculated for reef-dwelling brachiopod faunas from several North American and one European localities. Reef-dwelling brachiopod diversity collapsed at the end of the Ordovician and did not recover until the mid-Aeronian when modest diversity reef faunas appeared in the higher tropics. Reef-dwelling brachiopods did not achieve high diversity levels until the Telychian when reefs invaded the paleoequatorially located Hudson Bay and Moose River basins. The Attawapiskat Formation (Telychian) contains the earliest known coral-stromatoporoid reef complex with associated high-diversity brachiopod faunas. These faunas were separated into nine community associations through clustering and principal component analyses. These associations can be further grouped into a level-bottom-type and a cryptic-type based on dominant brachiopod taxa, diversity levels, average shell size, and substrate type. Surprisingly, the large species Pentameroides septentrionalis was able to thrive in the relatively flat and open spaces of inter-reef areas and among frame-building corals and stromatoporoids within reef cores. The absence of Stricklandia within the Attawapiskat Formation is due to the high water temperature of the equatorial seas which were too warm to be invaded by this cool-water dependent genus. In addition, the presence of deep-water Clorinda and Gypidula in the shallow-water Attawapiskat reefs is explained by the lack of hurricane-grade storms in the equatorial region, which would be comparable to the quiet-water conditions below storm wave base in higher latitudes. [ABSTRACT FROM AUTHOR]

Karlsorus n. gen. is proposed in this study as a large, smooth-shelled pentameride brachiopod of the family Pentameridae, based on Pentamerus gothlandicus Lebedev, 1892, from the Wenlock (Silurian) Slite beds of Gotland, Sweden. This species is transferred from Pentamerus to the new genus because of the combination of a Pentamerus-like shell shape and the development of a brachiophorium through fusion of the outer hinge plates in the middle portion, like a dorso-ventrally inversed cruralium. The first appearance of brachiophorium in pentamerids is in the late Wenlock, known also in Brooksina, Pentamerifera, and other related pentamerid genera, marking a significant stage in morphological transformation of dorsal internal structures, as part of the Silurian pentameride diversification in both level-bottom and reefal depositional environments. [ABSTRACT FROM AUTHOR]

Pentameroides is a large-shelled pentameride brachiopod, which was widespread throughout Laurentia in the early Silurian (Telychian). Evolving from Pentamerus in the early Telychian, it dispersed from its subtropical - high tropical origin to subequatorial intracratonic seas by the late Llandovery. In this study, large collections of reef-dwelling Pentameroides septentrionalis from the Attawapiskat Formation, Akimiski Island, Nunavut, and level-bottom-inhabiting Pentameroides subrectus from the Fossil Hill Formation, Manitoulin Island, Ontario, and the Jupiter Formation, Anticosti Island, Quebec, were biometrically analyzed for seven external morphological features. Bivariate and ordination analysis (principal components analysis) revealed that P. septentrionalis has a more globose, more biconvex shell with a larger ventral umbo than P. subrectus. These morphological differences, coupled with their excellent preservation in shallow-water reefal environments, suggest that P. septentrionalis was adapted to a relatively low-turbulence, hurricane-free, nutrient-stressed environment near the equator (<10°S) while P. subrectus lived in storm-dominated higher tropical latitudes (∼15°S-25°S). This interpretation is corroborated by the morphology of level-bottom-dwelling Harpidium and Sulcipentamerus from the paleoequatorial lower Silurian of North Greenland, which exhibit morphological features similar to those of P. septentrionalis, even though they did not inhabit a reefal environment. Principal components analysis reveals that P. septentrionalis resembles P. subrectus in early ontogeny, suggesting that P. septentrionalis evolved from P. subrectus as it moved northwards from high tropical to near-equatorial settings. [ABSTRACT FROM AUTHOR]

The decimeter-scale 3-D network structure of the Upper Ordovician Pagoda Formation in South China has been an enigmatic sedimentary feature and a case of non-uniformitarian carbonate depositional system, without modern analog. The network bands are developed pervasively throughout the entire Pagoda Formation, superficially resembling desiccation or syneresis cracks, especially in bedding-plane view, with decimeter-scale sub-polygonal to irregularly sinuous patterns. Detailed petrographic analysis, however, shows that the crack-like network bands have the same carbonate matrix, skeletal grains, and overall fabrics as the rock they surround. In this study, we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time-specific lithofacies. It originated from prolonged growth of nodular carbonate, controlled by the convergence of several geological and paleoclimatic factors, including a) a protracted sea-level highstand lasting for about 5 Myr, b) an interval of tectonic quiescence favoring the dominance of carbonate production, with minimal siliciclastic input, and c) location of the South China paleoplate in the hurricane-free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases (normally 15–120 m depths), favoring long-term, uninterrupted growth of CaCO 3 meganodules on a mid-shelf substrate. This study corroborates recent paleogeographic reconstructions that position the South China paleoplate on the Equator during the Late Ordovician. [ABSTRACT FROM AUTHOR]

Paleobiogeographic patterns of the brachiopod faunas before and during the first radiation of the Great Ordovician Biodiversification Event (GOBE) in South China at 6 different localities from the upper Jiangnan Slope to the vast area of the Upper Yangtze Platform show several interesting features. First, the initial brachiopod diversity acme was accompanied by both high origination and extinction rates. Second, no significant changes took place in the taxonomic composition and paleobiogeographic pattern of the brachiopod fauna during the radiation at 5 of the 6 localities studied except the near shore locality, where the first brachiopod radiation was much later than at other localities and was marked by a dramatic increase in endemic constituents. Third, orthides were the predominant brachiopod group during the radiation, and regional brachiopod taxa played a significant role in defining the paleobiogeographic pattern of the radiation. Fourth, the first brachiopod radiation was associated with 3 major pulses of onshore migration from the upper Jiangnan Slope through the central Upper Yangtze Platform to the near shore settings of the platform, with the middle pulse being the most significant. Finally, paleogeographic dispersal took place in both onshore and offshore directions, although the onshore expansion was more prominent; several key brachiopods, such as Paralenorthis, Nocturnellia, Protoskenidioides, Nereidella, Euorthisina and Yangtzeella, first appeared on the upper Jiangnan Slope and later formed distinct, and taxonomically diverse, communities on the Upper Yangtze Platform. The paleogeographic dispersal of brachiopods is considered to be closely related to the tectonic evolution of the Qianzhong Arch. [ABSTRACT FROM AUTHOR]

An exceptionally preserved noncalcified tb.allopb.ytic alga, Menieria minuta gen. nov. et sp. nov. from the uppermost Gun River Formation (middle Aeronian, Lower Silurian) of Anticosti Island, eastern Canada, is characterized by a relatively delicate thallus with a central axis, lateral branches, and helically arranged, regularly and closely spaced, elongate-linguoid appendages. The algae locally constitute an important portion of the biomass in a brachiopod-dominated paleocommunity, forming an algal meadow on a relatively deepwater subtidal setting within the photic zone. This rare fossilization window suggests that such soft algal meadows may have been common during the Early Paleozoic, resembling modern sea grass meadows that are part of the carbon sink. [ABSTRACT FROM AUTHOR]

In modern marine ecosystems, sea-grass and chlorophyte meadows play an important ecological role by serving as a carbon sink. Despite their generally limited areal distribution, the high productivity of sea-grass meadows makes them an efficient assimilator of CO2. During the early Palaeozoic, complex life was virtually confined to the marine environment, with algae being one of the common carbon-fixers, alongside abundant calcifying cyanobacteria, rhodophytes, chlorophytes and charophytes, as well as non-skeletal dinoflagellates and acritarchs. Fossil and molecular data indicate that marine thallophytic algae first appeared in the Early Proterozoic and became widespread in the Palaeozoic, although their fossil record is sporadic because of their soft-bodied nature; in the absence of angiosperm sea grass and mangroves and poorly understood phytoplankton biomass, thallophytic algae were probably major primary producers. In this article, we suggest that thallophytic algae may have played a significant role as a carbon sink in the Early Silurian, analogous to modern sea-grass meadows or kelp forests, based on the well-preserved Early Silurian thallophytic algal meadow from Anticosti Island, eastern Canada. [ABSTRACT FROM AUTHOR]

Late Katian (Late Ordovician) carbonate mudmounds in the Turesø Formation, Peary Land, North Greenland, succeed normal marine faunas dominated by brachiopods, bryozoans, cephalopod and gastropod molluscs, aulaceratid stromatoporoids, corals and receptaculitid algae, in the Børglum River Formation, and are themselves succeeded by organic-rich, largely barren limestones. This peri-Laurentian succession suggests deteriorating environmental conditions from a normal marine to a more restricted basin during the Late Katian and Hirnantian, against a background of gradual marine regression following the peak of the Boda Warming Event. The generally low-energy depositional setting probably lay within the Inter-Tropical Convergence Zone on the equator. [ABSTRACT FROM AUTHOR]

The palaeocontinent Laurentia experienced pulses of major marine transgression during the Late Ordovician (Katian) and was covered by extensive equatorial to subtropical epicontinental seas. Brachiopods that evolved in the newly created habitats showed increasingly strong endemism from the early to late Katian. At the faunal level, the Laurentian epicontinental brachiopod (LEB) fauna became ubiquitous in the epicontinental seas, with a high level of generic homogeneity but little in common with the coeval faunas in other palaeotropically located tectonic plates. At the level of species distribution, there was limited mixing between palaeoequatorial intracratonic basins and higher tropical to subtropical pericratonic shelves within Laurentia by late Katian. This was demonstrated by the palaeogeographical distribution of several species lineages and morphological clines along latitudinal and other ecological gradients. Such a high level of endemism suggests an extreme specialization of the LEB fauna in the tropical epicontinental seas, which made it most vulnerable to the drastic climate change and mass extinction during the Hirnantian glaciation. [ABSTRACT FROM AUTHOR]

The Early Devonian graptolite fauna of the Arctic Islands comprises the highest species content (17 species) in the world. In spite of this richness, no new species have been recognized; instead already-existing species, scattered around the then-known continents, suggest that relatively complete cosmopolitanism held sway for graptolites. Canadian Arctic biozonation is very similar to schemes elsewhere, consisting of the uniformis and hercynicus biozones in the Lochkovian, falcarius in the lower Pragian, and an expanded yukonensis Biozone in the upper Pragian and the lower Emsian. Three genera and 17 species are recognized: ' Monograptus' ( microdon cf. microdon, microdon curvatus); Neomonograptus (cf. atopus, aequabilis, bardoensis, falcarius, notoaequabilis); and Uncinatograptus ( birchensis, craigensis, hercynicus, langgunensis, parangustidens, subhercynicus, telleri, thomasi, uniformis, yukonensis). [ABSTRACT FROM AUTHOR]

Abstract: The early Katian (Late Ordovician) was marked by a major greenhouse episode and the early stage of a first-order marine transgression that led to the flooding of much of North America during the middle–late Katian. Multivariate analyses of 33 brachiopod faunas of early Katian (Trentonian, Chatfieldian, late Caradoc) age, including 252 rhynchonelliform genera, demonstrate that the “Trentonian brachiopod faunas” of Laurentia were already clearly differentiated into a Scoto-Appalachian fauna and an epicontinental fauna. Globally, four distinct faunal clusters are identified: Kazakhstan, Avalonia, epicontinental Laurentia, and Scoto-Appalachia. The Scoto-Appalachian fauna, which originated during the Sandbian, persisted into the early Katian and became most closely related to the brachiopod faunas along the western margins of Laurentia. The early Katian epicontinental faunas of Laurentia were more closely related to the coeval brachiopods of the Lithuanian–North Estonian confacies belts of Baltica than to the Scoto-Appalachian fauna. Palaeoecological control on the faunal endemism within Laurentia was attributable to isolation of Appalachian foreland basin by faulting and peripheral bulging during the early Taconic Orogeny, palaeolatitudinal faunal gradient from the subtropical Appalachia to mid-tropical epicontinental Laurentia, as well as different water depth, water temperature, and substrate types between the two palaeogeographical settings of Laurentia. [Copyright &y& Elsevier]

Multivariate analysis of 197 well-preserved specimens among 11 species of late Late Ordovician (Katian and Hirnantian) plaesiomyid brachiopods from North America revealed two trends of morphological changes: (1) increasing globosity and dorsal convexity from the early to late Katian, and (2) coarser, but fewer ribs in species from the paleoequatorial intracratonic seas compared with species from the mid- to high-tropical pericratonic shelves and platforms. Another notable change, albeit not quantified, was the enlargement of cardinal process in plaesiomyids from early to late Katian, characterized by a predominantly trilobed cardinal process in the intracratonic species versus a bilobed cardinal process in pericratonic species. Increases in dorsal convexity and shell globosity are interpreted to have allowed for development of a larger lophophore, improving the capacity and efficiency of filter feeding and gas exchange. Smaller but more frequently bifurcating ribs would have led to more numerous setae near the margin of the shell, resulting in increased sensitivity to environmental stimuli. Increased size and number of lobes of the cardinal process would have allowed for larger diductor muscles to open a larger, heavier shell. In this study, two new species, Plaesiomys periosa sp. nov. and Plaesiomys lenzi sp. nov., are proposed, and two existing species are transferred from Dinorthis to Plaesiomys. [ABSTRACT FROM AUTHOR]

Tangshanaspis Zhou and Zhang, 1978 (Family Missisquoiidae), has been reported widely from western North America and has been assigned invariably to a single species, T. depressa (Stitt, 1971 b). The base of the T. depressa Subzone as defined in Oklahoma is an important biostratigraphic datum for inter-regional correlation of uppermost Cambrian strata. Study of previously undescribed material in collections from Oklahoma shows that T. depressa is, in fact, a composite of cranidia and pygidia that belong to two stratigraphically segregated species in the Signal Mountain Formation. Tangshanaspis silveri n. sp. includes the pygidial morph originally attributed to T. depressa. Revision of the species from Oklahoma allows definition of a new biostratigraphic unit, the Tangshanaspis Zone, which is divided into a lower T. silveri Fauna and an overlying T. depressa Fauna; in addition to the eponymous species, the T. depressa Fauna includes pygidia that represent two additional species of Tangshanaspis that are placed in open nomenclature. Correlation with other areas suggests that the ' Missisquoia' mackenziensis Fauna of northern Canada may be equivalent to the T. silveri Fauna of Oklahoma, rather than a pre- Tangshanaspis interval that is unrepresented elsewhere in Laurentian North America. [ABSTRACT FROM AUTHOR]

Multivariate analysis based on nine biometric characters of 171 Late Ordovician rhynchonellide specimens from nine upper Sandbian-upper Katian localities in North America supports the hypothesis that one of the diagnostic taxa of the North American epicontinental brachiopod fauna, Hiscobeccus, evolved from Rhynchotrema, which lived predominantly in peri-cratonic settings. The oldest known Hiscobeccus, H. mackenziensis of early Katian age, exhibits transitional characteristics between Rhynchotrema and Hiscobeccus, and it clusters more closely with Rhynchotrema than with younger species of Hiscobeccus of mid-late Katian (Maysvillian-Richmondian) age. Diversification of the Hiscobeccus lineage in epicontinental seas was characterized by drastic increase in shell size, globosity and lamellosity, especially in palaeoequatorially located inland basins. Such morphological trends are interpreted as adaptation to relatively shallow, muddy substrates, moderate water turbulence, relatively low oxygen content and unstable supply of nutrients in generally overheated epicontinental seas with sluggish circulation. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Massive-bedded Thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast Upper Ordovician carbonate platforms along the palaeoequator of Laurentia, from the Børglum River Formation in North Greenland, through the Red River Formation and Bighorn Dolomite of the Williston Basin (Manitoba, Canada to Wyoming, USA), to the Ely Springs Dolomite and equivalent strata of the eastern Great Basin (Utah and Nevada, USA). The Late Ordovician Thalassinoides is characterised by complex, three-dimensional, anastomosing or multi-level galleries that are consistent in size, pattern and density, with preserved depth of 1m or greater. In addition to the similar Thalassinoides burrows, the ichnofacies across the palaeocontinent also contains typical taxa of the Red River biota, such as the soccer-ball sized receptaculitid Fisherites, large-shelled, diverse and abundant nautiloids, the distinctively planispiral gastropod Maclurina, as well as diverse tabulate and rugose corals. The consistent characteristics of the Red River biofacies and Thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of Laurentia during the pre-Hirnatian Late Ordovician. The Thalassinoides ichnofacies marked the first phase of mega-scale invasion of burrowers into relatively deep-water platform and shelf environments by successively creating a well-oxygenated deep burrow system for protection and deposit feeding. Such substrate tiering expansion constituted an important aspect of the Great Ordovician Biodiversification Event. [Copyright &y& Elsevier]

Eospirifer, the oldest known genus of the spiriferide group (Brachiopoda), first appeared on the Zhe-Gan Platform of South China paleoplate during late Katian (Late Ordovician) represented by E. praecursor. It survived the end-Ordovician mass extinction, and reappeared on the Upper Yangtze Platform of South China paleoplate by the end of Ordovician near the upper part of the Normalograptus persculptus Biozone. Starting from the beginning of Silurian, Eospirifer experienced some morphological innovations and expanded its geographical distribution substantially. It reached its species diversity acme and the widest geographic distribution in Wenlock (middle Silurian), with the diversity hotspots in Laurentia, Avalonia, and Baltica. Various shell size frequency curves of E. praecursor under different paleogeographic settings suggest that this pioneer species of Eospirifer, with several macroevolutionary novelties, adopted a range of life strategies to adapt to the changing environments during early spiriferide evolution. There are also some morphological macroevolutionary trends during the evolutionary history of Eospirifer from Late Ordovician to the end of Silurian, such as the ever enlarging shell sizes and the width/length ratios from late Katian to Wenlock, but decreasing apparently of both parameters from Wenlock to Pridoli. [ABSTRACT FROM AUTHOR]

The most common forms of Late Ordovician dalmanellid brachiopods from the Cincinnatian type area, previously treated as either Dalmanella or Onniella, are assigned to Cincinnetina gen. nov. The new genus differs from Dalmanella and Onniella in having a consistently developed primary medial costa in the dorsal valve, a larger cardinal process that tends to develop a trilobed myophore, strongly differentiated fine and coarse punctae, and sparse aditicules. Cincinnetina can be distinguished from the closely related Paucicrura and Diceromyonia in its smaller trilobed cardinal process (when developed) that does not have a dominant medial lobe and does not extend into the delthyrial cavity of the ventral valve. Globally, Dalmanella and Onniella occur most commonly in deposits of relatively deep- or cool-water palaeoecological settings, whereas in North America, Cincinnetina, Paucicrura and Diceromyonia are found mainly in carbonate-rich deposits in warm-water depositional environments, with Cincinnetina and Paucicrura most common in pericratonic settings and Diceromyonia in palaeoequatorial inland seas. [ABSTRACT FROM AUTHOR]

Four species of olenelloid trilobites characterized by advanced or robust genal spines are described from the lower Cambrian Rabbit Point Formation (Cambrian Series 2, Stage 4) of eastern Devon Island, representing the most diverse assemblage of olenelloids yet described from Arctic Canada. New taxa: n. sp., n. sp., n. gen. and n. sp. [ABSTRACT FROM AUTHOR]

The genus represents one of the earliest taxa of axonophoran graptolites with geniculate thecae, but its current status and evolutionary relationships are difficult to access even after a number of cladistic analyses have been executed. (Ruedemann), a poorly known little species from the lower Darriwilian of eastern North America is interpreted as a possible member of the genus. The species belongs to a group of axonophorans with highly asymmetrical proximal end and pattern C astogeny, characterized by the lack of an apertural spine on th12, ranging from the Biozone (Darriwilian) to the Biozone (Sandbian). Specimens are common in North America and the Argentinian Precordillera, but have not been reported from any Atlantic Faunal Realm localities. The distribution of the group indicates a restriction to the Pacific Faunal Realm, providing the earliest indication of a developing biogeographic differentiation of axonophoran graptolites after their origin in the oceanic biofacies during the Upper Dapingian to lower Darriwilian time interval. is described as a new species. [ABSTRACT FROM AUTHOR]

Examination of topotype material of the type species of Dalmanella, D. testudinaria, from the Hirnantian strata of Borenshult, southern Sweden, revealed several diagnostic characters that distinguish the type species from some common North American species assigned previously to the genus. The typical Dalmanella testudinaria has a consistently developed, primary medial interspace in the dorsal valve, a cardinal process with an invariably bilobed myophore, punctae of two distinctly different sizes, and a lack of aditicules. In contrast, many Late Ordovician species from North America, such as 'Dalmanella' meeki and 'Dalmanella' multisecta from the Cincinnati type area, consistently have a dorsal medial costa, with a strong tendency to develop aditicules and a trilobate cardinal process. This study confirms the previous notion of many authors that true Dalmanella testudinaria, or the genus as a whole, is either rare or entirely absent in North America. Typical Dalmanella was predominant in cool-water depositional environments (such as the Hirnantia Fauna), whereas the North American dalmanellids (e.g. Cincinnati-type 'Dalmanella', Paucicrura, and Diceromyonia) were most abundant and diverse in tropical, epicontinental sea settings. A clear definition of the true Dalmanella, therefore, has important implications for the study of Late Ordovician-Early Silurian brachiopod evolution, paleoecology, and paleobiogeography. [ABSTRACT FROM AUTHOR]

Late Ordovician strophomenide brachiopods (superfamilies Strophomenoidea and Plectambonitoidea) from the upper Changwu Formation (mid Ashgill, late Katian) of Jianglütang, Chun’an County, western Zhejiang Province, consist of ten genera and 12 species. Five new species of three new genera are recognized: Chunanomena triporcata, Chunanomena sembellina, Cheramomena subsolana, Lateriseptomena modesta, and Lateriseptomena rugosa. The strophomenide brachiopods from the upper Katian strata described in this study and those from the border region of Zhejiang and Jiangxi provinces reported in previous work contain 16 strophomenoid and 12 plectambonitoid genera, and most of the strophomenoids are endemic to South China. Numerical analysis of well-documented late Katian strophomenide brachiopod faunas indicates a strong provincialism, characterized by the highly distinct North American province (Laurentia), the South China-Kazakhstan province, and the Avalonia-Baltica province (Wales, Belgium and Sweden). Surprisingly, the Girvan district of Scotland, which was a peri-Laurentian terrane during the Ordovician, contains a late Katian brachiopod fauna that is more closely related to the contemporaneous brachiopods of Avalonia-Baltica than to those of North America. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue, including one by Kathy A. Hollis and William I. Ausich on the functional morphology of a top-tier crinoid and another by Renbin Zhan and Jisuo Jin on the migration of brachiopod.

Brachiopods from the lower Tonggao Formation (Floian, late Early Ordovician) of Sandu, southeastern Guizhou Province, represent a deep-water benthic shelly fauna from the Jiangnan Slope facies of the South China paleoplate. The fauna contains 16 brachiopod taxa, with orthides, lingulates, and pentamerides being the common groups. Concurrent graptolites confine the brachiopod fauna to the Tetragraptus approximatus and the Acrograptus filiformis biozones (early Floian). The first appearance datum (FAD) of several brachiopod genera, such as Paralenorthis, Protoskenidioides, and Nereidella, in the Sandu slope facies is one or two graptolitic biozones lower than their FAD in shallower water facies on the Yangtze Platform. Later in the late Floian, these genera became major components of the Sinorthis fauna that flourished over much of the Yangtze Platform, suggesting a migration of the benthic shelly fauna from slope to platform facies during the Floian radiation in South China. Compared to the platform fauna, the deep-water brachiopod fauna of the Sandu area has a lower level of richness, diversity, and community organization. Three brachiopod associations are recognized: the Paralenorthis–Nereidella, the Palaeoglossa longa, and the Lingulella–Protoskenidioides associations. An upsection decrease in shell size, faunal richness, and species diversity in the Tonggao Formation indicate a deteriorating environment towards hypersalinity in the Sandu area, resulting in the ultimate disappearance of the deep-water brachiopod fauna. [ABSTRACT FROM AUTHOR]

The Early Silurian carbonate succession of Anticosti Island, eastern Canada, contains a rich and diverse pentameride brachiopod fauna. Multivariate analyses of 91 samples (total 17 230 specimens) confirm a high degree of temporal segregation but only moderate spatial differentiation of the Virgiana, Pentamerus, Stricklandia, Ehlersella, Microcardinalia, and Clorinda communities. Most pentameride communities show a wider range of water depth than previously believed. The V. barrandei Community occupied a substrate setting from lower BA2 to upper BA3, whereas the V. mayvillensis Community lived mainly in BA4. The P. oblongus Community preferred a BA3 setting, comparable to the classic Pentamerus Community, but the P. palaformis Community was predominantly BA4. The stricklandiid communities have a high β diversity, dominated by various species of Stricklandia, Ehlersella, Microcardinalia, and Kulumbella, and occurred most commonly in BA4, but could extend to BA3 environments. The Clorinda Community of Anticosti Island preferred deep and quiet water settings, comparable to its widely accepted BA5 assignment elsewhere. At the generic level, the Virgiana, Pentamerus, and the stricklandiid communities have a largely overlapping BA range, but a clear stratigraphical separation. Thus, their temporal alternations were not likely controlled by water depth, water turbulence, or substrate conditions, but by fluctuating ocean water temperature, as suggested by chemostratigraphical and paleobiogeographical evidence. [ABSTRACT FROM AUTHOR]

Abstract: The Ordovician radiation is the earliest and most important biodiversification event in the evolution of the Paleozoic Evolutionary Fauna (PEF), when the basic framework of PEF was established. The radiation underwent a gradual, protracted process spanning more than 40 million years and was marked by several diversity maxima of the PEF. Case studies conducted on the Upper Yangtze Platform (South China Palaeoplate) showed that the Ordovician radiation was characterized by drastic increases in α- and β-diversity in various groups of organisms. During the radiation, brachiopods, trilobites, and graptolites of the PEF became more diverse to dominate over the Cambrian Evolutionary Fauna (CEF) in all marine environments. At either global or regional scales, however, the Ordovician radiation was highly heterogeneous in time and space, and the rate and pattern of radiation exhibited by different major fossil groups were also variable. [Copyright &y& Elsevier]

Sixteen species from the Lower Silurian (mostly Aeronian and rarely Telychian) of South China have been assigned previously to the brachiopod family Pentameridae, mainly to the genus Pentamerus. Study of intrapopulation variation suggests that 13 species from the upper Aeronian Lojoping Formation of the Yichang area, western Hubei Province, can be synonymized with Sulcipentamerus dorsoplanus, the most abundant pentamerid species of South China but confined to the Yichang area. The conspicuously high and obtuse ventral umbo, strong ventribiconvexity and a sulcate anterior commissure warrant genus status for Sulcipentamerus, independent of Pentamerus. True Pentamerus is rare in South China, known only from upper Aeronian rocks of Guizhou Province. Multivariate analyses indicate that Aeronian pentameride brachiopods of South China are characterized by a high level of provincialism, distinct from those of Laurentia. Also, the Aeronian pentamerides of South China or Laurentia have a low degree of similarity to those of Baltica, Siberia, Avalonia, Kazakhstan and other palaeotropically located plates or terranes. Besides South China and Laurentia, the pentamerides of other palaeotropical regions constituted a relatively tight cluster. This suggests that the palaeogeographical positions of South China and Laurentia only allowed limited or periodic faunal exchange of these generally large-shelled brachiopods adapted to living in relatively shallow, warm waters. [ABSTRACT FROM AUTHOR]

Systematic and statistical study of brachiopods from the Dawan Formation of the Yichang area, western Hubei Province, central China, indicates that, at generic and specific levels, the α diversity of Early to Mid Ordovician brachiopods in the study area reached the first acme at the beginning of the Corymbograptus deflexus Biozone, marked by the diverse Sinorthis typica Community. This diversity maximum of brachiopods occurred approximately one biozone later than that of the Upper Yangtze Platform. In taxonomic constituents, the main contributors to the diversity maximum were orthoids, which experienced a major increase in the number of genera in the upper Didymograptellus eobifidus Biozone and the lower C. deflexus Biozone. In brachiopod communities or associations, orthoids and pentameroids were the dominant elements. Analyses of Early–Mid Ordovician brachiopods from the Upper Yangtze Platform indicate that a high level of brachiopod community organization, with temporal and spatial stability, was achieved by the Sinorthis Community, which persisted from the D. eobifidus to the Azygograptus suecicus biozones (early Arenig). In the D. eobifidus Biozone, the Sinorthis Community thrived across a wide ecological range (BA3 to upper BA4) in the siliciclastic facies of the central part of the Upper Yangtze Platform and, by the latest D. eobifidus interval, invaded more carbonate-rich substrates in more offshore settings in the northeastern part of the platform (the present Yichang area). [ABSTRACT FROM AUTHOR]

Gypidula was a common pentameride brachiopod in the Silurian and Devonian periods and its oldest-known form, Gypidula akimiskiformis new species, occurs as a common component of a distinct Gypidula Association of the rich and diverse reef-dwelling brachiopod fauna in the Lower Silurian (upper Telychian) Attawapiskat Formation of the Hudson Bay Basin. This pioneer species has a high degree of morphological plasticity, with several infraspecific variations significant for the study of gypiduloid taxonomy and early evolution: 1) the sparsely costate shells may have strong to faint medial ribs, with some shells being quasi-smooth and 2) the inner hinge plates are commonly basomedially inclined toward the dorsal valve floor (not united to form a cruralium), but may also be subparallel or slightly basolaterally divergent toward the valve floor (similar to those in Clorinda). This implies that the basomedially inclined inner hinge plates were not a stable character at the initial stage of evolution of Gypidula during the late Telychian. Another gypiduloid from the Attawapiskat Formation, Erilevigatella euthylomata new genus and species, is characterized by a shell lacking fold or sulcus but having Clorinda-type, basolaterally divergent inner hinge plates and double-flanged crura. Compared to Levigatella, which has been regarded as an intermediate between Clorinda and Gypidula because of its Gypidula-type dorsal sulcus and Clorinda-type inner hinge plates, the rectimarginate shells of Erilevigatella make the distinction between Clorinda and Gypidula even more blurred at the early stage of their evolution. [ABSTRACT FROM AUTHOR]

Stegerhynchus was perhaps the most common rhynchonellide brachiopod in the Early Silurian (Llandovery) postextinction brachiopod fauna of North America. In shell morphology, it closely resembles the Late Ordovician rhynchonellide Rhynchotrema in having a rostrate shell posterior and simple, strong costae. It differs internally from Rhynchotrema primarily in having a much-reduced septalium (=cruralium). Superficially Stegerhynchus has a conservative, typically simple, rhynchonellide morphology, but detailed biometric analysis of large samples from the >400 m-thick Llandovery (mid-Aeronian to mid-Telychian) tropical carbonate succession of Anticosti Island reveals that the genus underwent significant evolutionary and ecophenotypic changes over about five million years. The shell length/width ratios of Stegerhynchus peneborealis from sediments of a low-energy, muddy substrate tend to be lower than those of S. deltolingulatus new species from high-energy, reef or inter-reef settings. A wider shell and hingeline probably had a greater stability on the soft seafloor. Also a wider shell appears to be associated with a larger (relative to shell size) sulcus size at the anterior margin. The changes in relative sulcus size either represent ecophenotypic variation in response to environmental conditions, or a random effect of evolutionary selection through time. Both multivariate and single-character analyses demonstrate that two important biometric features, the apical angle and shell flank rib number, separate all forms of Anticosti Island Stegerhynchus (middle Aeronian to middle Telychian) from the widely cited European species Stegerhynchus borealis (latest Telychian-Wenlock) from the type area of Gotland, Sweden. The temporal changes of these two characters are interpreted to be evolutionary modifications. [ABSTRACT FROM AUTHOR]

Eocoelia akimiskii sp. nov. from the Lower Silurian (upper Telychian) Attawapiskat Formation of Akimiski Island, James Bay, Nunavut, is the first and oldest Eocoelia to be described from the Hudson Bay Basin, one of three largest inland basins of North America. The new species lacks dental plates, dental cavities, and marginal deflection or lip, which indicates a post-Aeronian form of the well-known Eocoelia lineage. In rib numbers, Eocoelia akimiskii falls between E. curtisi and E. sulcata, being closer to E. sulcata. In rib strength, however, the new species is more closely allied to E. curtisi. Although Eocoelia is currently assigned to the Rhynchonellida because of its lack of spiralia, several features (particularly the lack of a septalium, the presence of a unique notothyrial platform and cardinal process, and dense, free-hanging fibrous growth frills) of the genus and other leptocoeliids are distinctly atypical of the rhynchonellides. The new species occurs in an inter-reef, shelly packstone facies within the Attawapiskat Formation, which is characterized by coral-stromatoporoid reefs with abundant, diverse, reef-dwelling brachiopods and other shelly organisms. The close association of Eocoelia akimiskii with the Attawapiskat reefs supports a shallow subtidal (BA2) setting generally assigned to the Eocoelia Community. The reefs themselves, however, host an extremely abundant brachiopod fauna dominated by Pentameroides, Trimerella, Septatrypa, and Gypidula. Four species of Clorinda are also common elements of the reef-dwelling brachiopods. This demonstrates that the concept of the classic Early Silurian level-bottom brachiopod communities cannot be directly applied to reef-dwelling brachiopod communities. [ABSTRACT FROM AUTHOR]

The earliest rhynchonellid brachiopods were small-shelled and preferred cool-water conditions in both siliciclastic and carbonate environments. Relatively large shells of Rhynchotrema evolved in mid-Caradoc time and rapidly became widespread in Laurentia. Hiscobeccus probably evolved from Rhynchotrema during the late Caradoc by developing a large, globular, strongly lamellose shell. The earliest form of Hiscobeccus shows transitional characteristics between Rhynchotrema and typical Hiscobeccus, most notably in its nonglobular shell that is wrinkled by growth lamellae only on the anterior two thirds of the shell. By early Ashgill time, Hiscobeccus became widespread in North American inland basins, although it remained common in marginal carbonate platforms and basins. During the Ashgill, Hiscobeccus, Lepidocyclus, and Hypsiptycha represented a distinct North American fauna, characterized by large, globular, and completely wrinkled shells. These morphological features were adaptations to the shallow, well-circulated, epicontinental, tropical seas with a soft muddy substrate. The gigantism exhibited by the Hiscobeccus Fauna is also shown by orthid and strophomenid brachiopods, gastropods, nautiloids, and trilobites. Extinction of the Hiscobeccus Fauna was probably related to its narrow range of environmental tolerance, especially during the Gondwana continental glaciation, which brought a major global sea-level drawdown and lowered ocean temperature. The cool-water Rostricellula and Rhynchotrema were uncommon in inland seas during the Ashgill and were represented by several opportunistic species in the Anticosti Basin during the Hirnantian and Llandovery, and most of these preferred siliciclastic-rich or deep-water shelf carbonate environments.Les plus précoces brachiopodes de la sous-famille des Rhynchonellidae avaient de petites coquilles et préféraient des conditions d'eau fraîche dans des environnements silicoclastiques ou carbonatés. Les coquillages relativement larges des Rhynchotrema ont évolué au milieu du Caradocien et se sont rapidement répandus à travers la Laurentie. Hiscobeccus a probablement évolué de Rhynchotrema durant le Caradocien tardif en développant une grande coquille globulaire fortement lamellée. La forme du Hiscobeccus la plus précoce montre des caractéristiques de transition entre Rhynchotrema et le Hiscobeccus typique, surtout par sa coquille non globulaire qui est plissée par les lamelles de croissance seulement sur les deux tiers antérieurs de la coquille. À l'Ashgillien précoce, Hiscobeccus était répandu dans les bassins intérieurs de l'Amérique du Nord, bien qu'il soit resté fréquent dans les plates-formes et bassins marginaux carbonatés. Au cours de l'Ashgillien, Hiscobeccus, Lepidocyclus et Hypsiptycha représentaient une faune nord-américaine distincte, caractérisée par des larges coquilles globulaires et complètement plissées. Ces caractéristiques morphologiques étaient des adaptations aux mers tropicales peu profondes à bonne circulation et épicontinentales dont le fond était composé de boues non consolidées. Le gigantisme démonté par la faune Hiscobeccus est aussi démontré par les Brachiopodes Orthida et Strophomenida, des Gastéropodes, des Nautiloidae, et des Trilobites. L'extinction de la faune Hiscobeccus était probablement liée à sa faible plage de tolérance environnementale, surtout au cours de la glaciation continentale du Gondwana où il y eut un grand abaissement global du niveau de la mer et de la température de l'océan. Les brachiopodes d'eau fraîche Rostricellula et Rhynchotrema étaient peu communs dans les mers intérieures au cours de l'Ashgillien et ils étaient représentés par plusieurs espèces opportunistes dans le bassin de l'Anticosti au cours de l'Hirnantien et du Llandovérien ainsi que dans la plupart de ces environnements de choix riches en silicoclastiques ou de plate-forme carbonatée d'eau profonde.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Presents a study conducted on the ribbing designs of pentamerid shells from the Stricklandiid brachiopods. Indepth look at three designs in several genera; Methodology used to conduct the study; Results of the study.

Examines the three types of Parastrophinella, Pentamerus reversus, one of the earlier Canadian brachiopod species named by Billings (1857) and based on specimens collected by James Richardson. Features of species; How species have developed; Where species have been discovered; Species excluded from the Parastrophinella family.

This issue of the Canadian Journal of Earth Sciences is dedicated to Professor Glen Caldwell in honour of his extensive contributions to the field of paleontology and scientific publishing. After receiving his Ph.D. degree from the University of Glasgow in 1957, Dr. Caldwell joined the Department of Geological Sciences at the University of Saskatchewan, where he stayed for more than 30 years. During his tenure, he led the way in launching a new integrated curriculum, including paleobiology, geochemistry, and geophysics, and in organizing and equipping a vigorous research program. Dr. Caldwell also organized two international symposia on Cretaceous rocks of the Western Interior Basin of North America. Over the years he served on and made distinctive contributions to a wide variety of national and international professional organizations, including the American Commission on Stratigraphic Nomenclature, GAC, NSERC, and the International Union of Geological Sciences. Dr. Caldwell served as Vice-President (Research) of The University of Western Ontario from 1988 to his retirement in 1996. He continues to teach and serve various scientific organizations, and he remains a strong advocate for basic research grants.Ce numéro du Journal canadien des sciences de la Terre est consacré au professeur Glen Caldwell en l'honneur de ses très grandes contributions à la paléontologie et aux publications scientifiques. Après avoir reçu son doctorat (Ph.D.) de l'Université de Glasgow en 1957, le Dr Caldwell s'est joint au Département des sciences géologiques de l'Université de la Saskatchewan, où il a œuvré durant plus de 30 ans. Durant sa titularisation, il a été l'instigateur d'un nouveau curriculum intégré, incluant la paléobiologie, la géochimie et la géophysique en plus d'organiser et de doter en équipement un programme de recherche dynamique. Le Dr Caldwell a aussi organisé deux symposiums internationaux sur les roches du Crétacé du bassin intérieur ouest de l'Amérique du Nord. Au cours des années, il a été membre de diverses organisations professionnelles nationales et internationales dont l'American Commission on Stratigraphic Nomenclature, l'AGC, le CRSNG et l'Union internationale des sciences géologiques; la contribution qu'il leur a apportée revêt un caractère distinct. Le Dr Caldwell a été vice-président (recherche) pour l'Université de Western Ontario de 1988 jusqu'au moment de sa retraite en 1996. Il enseigne toujours et continue à siéger au sein de divers organisations scientifiques et, de plus, il défend vigoureusement les subventions à la recherche de base. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including conodont biostratigraphy, conodont fauna of Xiushan Formation in South China; and morphological modifications and clines of pentamerid shells.

The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well‐enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Paleozoic deposits. From the Cambrian to the middle Ordovician, this region was characterized by geographically extensive, flat‐bedded siliceous mudstone, indicating the existence of a large ocean basin. The oceanic plate entered the convergence phase in terms of the Wilson Circle during the Middle Ordovician, when numerous magmatic arcs formed along two opposite sides of the ocean. The magmatic arcs became the widest during the Silurian, suggesting that the Hongliuhe‐Niujuanzi‐Xichangjing Ocean (HNX; a southern branch of the Paleo Asian Ocean) was reduced to a small residual ocean in the central Beishan region by that time, and probably lasted till the Carboniferous or later by newly published data. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue which includes thorough and useful synopsis of previously published data on Silurian acritarchs from China and study of clay mineralogy and chemistry to interpret the changing climatic conditions related to the rise of the Caledonide mountains.

Introduces a series of articles regarding the impact of the mass extinction of rare and exotic species on global environment and evolution, published in the 1999 issue "Canadian Journal of Earth Sciences."

One of the best-exposed and most complete stratigraphic records from paleotropical areas spanning the Ordovician-Silurian (O-S) boundary is located on Anticosti Island, eastern Canada. Our study is the first one to sample strata superbly exposed at low tide along the west coast of Anticosti Island, thus providing a previously unexploited, nearly complete stratigraphic interval (∼300 m) at the O-S boundary for δ13C chemostratigraphy. A new high-resolution δ13C curve with more than 500 data points spaced at every ∼0.5 m has been produced, rectifying important pitfalls of previously published δ13C curves (i.e., low sampling resolution, variable sampling intervals, stratigraphic gaps). This new high-resolution δ13C curve displays a lower and an upper positive Hirnantian Isotope Carbon Excursion (HICE) recognized elsewhere around the globe. The ascending limb of the lower HICE starting from baseline values of +0.5‰ corresponds to the upper 20 m of the late Katian Vauréal Formation, but δ13C peak values of +2.5‰ occur in the lower part of the Hirnantian Ellis Bay Formation. In spite of a δ13C record segmented by a few stratigraphic hiatuses, the upper HICE, with its peak values of +4.5‰, is well recorded in the upper part of the Hirnantian Ellis Bay Formation. When compared with sections from around the globe, our δ13C curve displays a distinct long-term trend with a long sustained lower HICE followed abruptly by the upper HICE and return to baseline values of +0.5‰ prior to the Rhuddanian. The continued descending isotopic trend well into the Becscie Formation suggests that the O-S boundary may occur at a higher stratigraphic level (up to 30 m) than previously interpreted. Active subsidence combined with moderate initial water depths prior to the Hirnantian were key factors controlling the deposition of a thick O-S sedimentary succession with a few hiatuses on Anticosti Island and capturing a comprehensive, reliable δ13C record across this interval. [ABSTRACT FROM AUTHOR]

The Kettle Point Formation of southwestern Ontario consists of intervals of organic-rich interlaminated black shale interbedded with organic-poor greyish green mudstones and rare red beds, separated by metre-scale sequences of non-interlaminated black shale. The formation shows a largely consistent background value for the black shales around −20‰ δ34S, punctuated by a substantial positive excursion of ∼32‰ (up to +12.87‰) that coincides with a significant interval of greyish green mudstone and red beds. Lithological and geochemical data indicate that the black shales were deposited during periods of anoxia, with thick intervals of non-interlaminated black shales recording the peak of anoxia, whereas the greyish green mudstones record deposition in more oxygenated environments. Relative water depth is interpreted as the key control on the vertical and lateral distribution of the Kettle Point lithofacies. Interbedded black shales and greyish green mudstones were deposited in relatively shallow waters, where minor, short-lived falls in relative sea level promoted dysoxic to oxic conditions and the deposition of organic-poor lithologies. Non-interlaminated black shales are indicative of substantial rises in relative sea level, resulting in widespread anoxia and the deposition of thicker and more laterally extensive packages of organic-rich sediment. The formation of black shales in relatively shallow waters in southwestern Ontario implies that the extensive deposition of organic-rich sediment across eastern North America during the Late Devonian was a product of widespread anoxia related to restricted circulation in intracratonic and foreland basin depositional centers. [ABSTRACT FROM AUTHOR]