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An unusually rich and diverse suite of virgianid brachiopods, hitherto poorly known, is systematically described here for the first time from the Ordovician–Silurian boundary interval (late Katian – Aeronian) of North Greenland. The Late Ordovician virgianids comprise typical taxa of the warm‐water Tcherskidium fauna (e.g. Tcherskidium tenuicostatum, Proconchidium schleyi, Holorhynchus giganteus and Deloprosopus dawesi sp. nov.). Among the early Silurian taxa, Virgiana hursti sp. nov. occurs as abundant shell beds, similar to other congeneric species in Laurentia, but has somewhat larger internal skeletal structures, albeit not as extravagantly developed as in the late Katian virgianids; Borealoides balderi gen. et sp. nov. shows extreme thickening of the shell wall and internal structures, approaching the extravagant calcification of Katian virgianids. The highly distinctive mid‐Aeronian stricklandioid brachiopod genus, Kulumbella, characterized by a shell with criss‐cross (divaricate) ribbing, also occurs in North Greenland, represented by K. heimdali sp. nov., which has the largest and most strongly biconvex shells for the genus. Palaeogeographically, the Late Ordovician virgianid fauna of Laurentia was highly distinct, confined to the low–mid tropical latitudes north of the palaeoequator. In comparison, the early Silurian (Rhuddanian) Virgiana and some related taxa in Laurentia spanned the tropics of both hemispheres, forming extensive shell beds in carbonate basins, although Borealis and Borealoides gen. nov. remained confined largely to the northern hemisphere, suggesting a certain level of provincialism extending into the earliest Silurian. A palaeoecological preference for warm‐water carbonate settings would explain the unusual abundance and richness of the virgianid faunas in North Greenland. [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 [summation]REE) show insignificant correlations with the [delta][.sup.18]O and [delta][.sup.13]C values, thus supporting the preservation of at least near-primary geochemical compositions. Among the three lots of shells, the mean [delta][.sup.18]O value is the highest in those from the Lexington Formation (-4.5[per thousand] [+ or -] 0.3[per thousand] VPDB), lowest from the Stony Mountain Formation (-6.8[per thousand] [+ or -] 0.4[per thousand] VPDB), and intermediate from the Sheguindah Shale (-6.0[per thousand] [+ or -] 0.8[per thousand] VPDB). The relative gradient in [delta][.sup.18]O 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 [delta][.sup.13]C value (0.8[per thousand] [+ or -] 0.2[per thousand] VPDB) and relatively high P contents (170 [+ or -] 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 [+ or -] 0.6), which is consistent with blooming organic productivity that likely led to more consumption of oxygen in the water column. Des coquilles de brachiopodes dalmanelloides ont ete recueillies de la Formation de Lexington de l'Ordovicien superieur (Katien inferieur) du Kentucky, du shale de Sheguindah (Katien moyen) de l'ile Manitoulin (Ontario) et de la Formation de Stony Mountain (Katien superieur) de la region de Winnipeg (Manitoba). Elles ont ete examinees pour verifier l'hypothese d'une zonation paleolatitudinale du benthos a coquilles. Une approche faisant appel a plusieurs techniques a ete utilisee pour evaluer la preservation petrographique et geochimique (isotopique et elementaire) de la couche secondaire des coquilles. La microscopie classique preliminaire, la cathodoluminescence (CL) et la microscopie electronique a balayage (MEB) ont confirme la retention d'une ultrastructure primaire dans les coquilles (calcite pauvre en Mg prismatique). Des caracteres geochimiques temoignant de la diagenese (p. ex. Sr, Mn, Fe et [summation]ETR) montrent des correlations significatives avec les valeurs de [delta][.sup.18]O et de [delta][.sup.13]C, appuyant l'interpretation de la preservation de compositions geochimiques au moins quasi primaires. Parmi les trois lots de coquilles, la valeur de [delta][.sup.18]O moyenne est la plus elevee pour celui de la Formation de Lexington (-4,5 [per thousand] [+ or -] 0,3 [per thousand] VPDB), la plus faible pour la Formation de Stony Mountain (-6,8 [per thousand] [+ or -] 0,4 [per thousand] VPDB) et intermediaire pour le shale de Sheguindah (-6,0 [per thousand] [+ or -] 0,8 [per thousand] VPDB). Le gradient relatif d'augmentation du [delta][.sup.18]O concorde avec le gradient paleolatitudinal dans lequel le Kentucky se trouve a des latitudes subtropicales, le sud de l'Ontario, a des latitudes mid-tropicales et le sud du Manitoba, a des latitudes subequatoriales. Les coquilles de la Formation de Lexington presentent egalement le [delta][.sup.13]C moyen le plus eleve (0,8 [per thousand] [+ or -] 0,2 [per thousand] VPDB) et des concentrations de P relativement fortes (170 [+ or -] 27 ppm), ce qui indiquerait une plus grande productivite organique, en accord avec l'interpretation anterieure de remontees frequentes d'eaux froides riches en nutriments le long de la bordure sud-est de la Laurentie au Katien. Les coquilles de la Formation de Lexington ont aussi un rapport Th/U moyen plus faible (0,6 [+ or -] 0,6), ce qui concorde avec une productivite organique fleurissante qui s'est vraisemblablement traduite par une consommation d'oxygene accrue dans la colonne d'eau. [Traduit par la Redaction], Introduction The abundance of planktonic and benthic foraminifers in the Cenozoic marine carbonates provided suitable material for the geochemical studies that reconstructed the environmental variations during that time interval (e.g., [...]

Abstract: 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 [...]

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 [...]