Detailed biostratigraphic sampling of the Lower Ordovician Boat Harbour and Catoche formations in the Boat Harbour - Cape Norman area of western Newfoundland has yielded hitherto unrecorded trilobite faunas so far unparalleled in richness and diversity anywhere in the Appalachians. -- Thirty species are systematically treated. Three new genera are proposed (Randaynia, Magnusnasus and Parapeltabellia). Seventeen species are new (Leiostegium proprium, Randaynia saundersi, R. langdoni, Hillyardina minuspustulata, H. levis, Hystricurus pseudoculilunatus, Magnusnasus proprius, Parahystricurus smithiae, Bolbocephalus stevensi, Jeffersonia angustimarginata, Parapeltabellia boatharbourensis, Peltabellia knighti, P. pseudopeltabella, Strigigenalis brevicaudata, Grinnellaspis newfoundlandensis, Uromystrum forteyi and Benthamaspis hintzei). Hyperbolochilus Ross is a junior synonym of Hillyardina Ross. -- Five new biostratigraphic zones are proposed, three of which are based on trilobites. These zones, in ascending order, are as follows: 1) Barren Interzone I, 2) Randaynia saundersi Assemblage Zone, 3) Barren Interzone II, 4) Strigigenalis brevicaudata Range Zone and 5) Strigigenalis caudate Range Zone. These zones are correlated with the standard trilobite zonation of the proposed Ibexian Series as well as the stages of the classical Canadian Series. -- A major Early Ordovician (Late Tremadoc - Early Arenig) faunal and sedimentological break is documented in western Newfoundland. The disconformity represented by a solution surface and pebble horizon is documented faunally by the absence of Ross-Hintze trilobite zone G1. This break is correlated with comparable breaks in the four major trilobite provinces which then existed, and it is proposed that these breaks are related to a world-wide Late Tremadoc - Early Arenig regressive event followed by a Early Arenig transgressive event.
A new fossil locality within a sequence previously assigned to the Middle Ordovician Baie D'Espoir Group in south-central Newfoundland contains fragmented crinoid columnals and brachiopods. Distinctive, pentastellate crinoid columnals, similar to those assigned to the monobathrid camerate Hexacrinites Austin and Austin by Russian authors, are named Hexacrinites? Pentastellatus n. sp. Nodal(?) columnals of this species have a circular, depressed articular facet, with a conical to bowl-like crenularium, a depressed, circular areola, a raised perilumen and a short, slender axial canal of pentagonal section. The oldest Hexacrinites sensu stricto are Late Silurian, suggesting that the fossiliferous strata have been incorrectly assigned to the Ordovician. Cross-sections of brachiopods from the same locality include an example that resembles several Early Silurian to Late Devonian pentameroid genera including Brooksina Kirk, 1922. Correlation with Late Silurian, bivalve-bearing strata SO km to the northeast would indicate that a major unconformity may occur above the fossiliferous Early and Middle Ordovician strata and the Early Ordovician ophiolite complexes.
RÉSUMÉ
Un nouvel emplacement de fossiles à I'intérieur d'une sequence auparavant attribute au groupe de l'Ordovicien moyen de Baie d'Espoir dans le centre-sud de Terre-Neuve renferme des fragments de columnales et de brachiopodes de crinoldes. Des columnales de crinoldes pentaétoilées caractéristiqucs, semblables à celles attributées à l’Hexacrinites Austin and Austin à loges monobathrides par des auteurs russes, sont baptisées nouvelle espèce pentastellatus d'Hexacrinites?. Les columnales nodales(?) de cette espèce sont pourvues d'une facette articulaire renfoncée et circulaire munie d'un crenularium allant de conique à bombé, d'une aréole circulaire renfoncie, d'un périlumen surélevé et d'un canal axial mince et court de section pentagonalc. Les plus anciens Hexacrinites, au sens strict, remontent au Silurien supérieur, ce qui permet de supposer qu'on a incorrectement attribué la strate fossilifère à l'Ordovicien. Des iéchantillons représentatifs de brachiopodes du même emplacement comprennent un exemple qui ressemble à plusieurs genres de pentaméroides datant du Silurien inférieur au Dévonien supérieur, notamment le Brooksina Kirk, 1922. Leur corrélation avec des strates renfermant des bivalves du Silurien supérieur à 50 km au nord-cst signale qu'une discordance importantc pourrait se présenter au-dessus des strates fossiliferes de l'Ordovicien inférieur ou moyen de même que des complexes d'ophiolites de l'Ordovicien inférieur.
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Faunal assemblages of the autochthonous, shelf carbonate sequences belonging to the St. George and Table Head groups are dominated by shelly macrofossils and conodonts. Rare, usually monotypic graptolitic horizons enable correlation with the allochthonous Cow Head Group, which was deposited on the middle to lower slope, and the shelly, conodont, and graptolitic zonal schemes elsewhere in North America.The Catoche Formation of the St. George Group is of Ibexian (Canadian) age and yields graptolites indicative of the Tetragraptus approximatus and Tetragraptus akzharensis zones (early Arenig). The basal Aguathuna Formation belongs to the Pendeograptus fruticosus Zone, whereas higher parts span the Ibexian–Whiterock boundary. Graptolites suggest that the Table Head Group entirely postdates the Cow Head Group. This is supported by a Whiterock (early Llanvirn) trilobite, conodont, and brachiopod fauna.
The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygids Tulepyge cowiei and T. tesella n. spp., hystricurids Millardicurus and Hystricurus , and several species of Symphysurina. Micragnostus chiushuensis (Kobayashi, 1931) is rare, as are Chasbellus sp., Clelandia sp., and Lunacrania ?. The presence of several Symphysurina species places the Antiklinalbugt Formation within the Symphysurina Zone. Chasbellus indicates the upper (lower Ordovician) part of the Symphysurina Zone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in the Cordylodus intermedius conodont Biozone, the lower upper part in the Cordylodus angulatus conodont Biozone and the uppermost part in the Rossodus manitouensis conodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.
A newly discovered fossiliferous horizon within sediments belonging to the Coy Pond Complex of the Exploits Subzone in central Newfoundland yields the graptolite Undulograptus austrodentatus s.l. and cyclopygid trilobite Cyclopyge grandis brevirhachis. This late Arenig faunule constrains the upper age limit of the ophiolite complex and is the first record of an Early Ordovician cyclopygid trilobite in North America. This is consistent with a paleogeographic affinity for south-central Newfoundland with the northern oceanic margin of Avalonia in a peri-Gondwanan position during the Early Ordovician and contrasts with coeval shelly and graptolitic faunas from the Notre Dame Subzone of central Newfoundland, which show marked Laurentian affinities. The Exploits Subzone is generally considered equivalent to the region of Scotland lying south of the Southern Upland Fault. The Newfoundland discovery, which is supported by faunal data from elsewhere in Newfoundland and in Ireland, suggests that the region around the Southern Upland Fault, rather than the Solway Firth, represents the location of the "Iapetus suture" in Britain in Lower Ordovician rocks.
Fossiliferous clasts occur in Carboniferous conglomerate in the Horton Group on western Isle Madame and in the Mabou Group on eastern Isle Madame. Most of the clasts (21 of 23 examined) are calcareous siltstone and sandstone that contain Silurian Lower Devonian faunas comparable to those in the Arisaig area, northern mainland Nova Scotia, although the lithologies are coarser grained and less calcareous than those of the Arisaig section. These middle Paleozoic faunas are well constrained to the Silurian (uppermost Llandovery through Pridoli) and lowest Devonian and are characteristic of those known from shallow siliciclastic-dominated platforms of the Avalon microcontinent in Wales and England. The remaining two clasts have abundant inarticulate brachiopod shells that indicate provenance from Middle Cambrian proximal marine facies on the Avalonian marginal platform. No clasts were found that are likely to have been derived from the Torbrook Formation, and thus from the Meguma terrane in southwestern Nova Scotia, as has been previously reported. The association of relatively large, reworked fossiliferous clasts in Carboniferous conglomerate on Isle Madame suggests local derivation from lower and middle Paleozoic units not presently exposed, although probably present as subcrop under the Carboniferous units, in southwestern Cape Breton Island and adjacent mainland Nova Scotia.
Differentiation of Ordovician faunal groups into provinces in the North Atlantic Region is not strictly comparable with palaeogeographical models and does not relate clearly to criteria for recognizing continental margins and separation across the Iapetus Ocean. Recently published and unpublished stratigraphic and palaeoecological evidence from Laurentia is reviewed. The approach of faunal dynamics, that is, changes of faunas in time and space is used. The cyclic interchange between faunal associations between platform and slope environments is evaluated during early and middle Ordovician time. The study is based on trilobites and conodonts from western Newfoundland and compared with evidence from Scotland, Norway, Greenland and Spitsbergen. The distribution of faunal associations along the edge of the craton suggests a pattern of concentric perhaps depthrelated facies belts. Cyclic appearance of deeper water marginal faunas onto the platform characterized Tremadoc and early Arenig time, but interrupted by an extinction event at the Tremadoc/ Arenig Series boundary. The lower Boat Harbour faunal associations were replaced by the upper Boat Harbour/ Catoche faunal associations. Platform uplift in middle to late Arenig forced faunas to migrate to other areas such as Greenland and Spitsbergen. Foundering of the platform in late Arenig and early Llanvirn allowed the Table Head fauna not only to migrate across the platform, but also the lapetus Ocean, and the taxa appeared in Baltica. However, some taxa associations that were earlier adapted to cool, normal marine waters were able to cross the lapetus Ocean at the time of its presumed maximum extent. The palaebiographical migration-immigration pattern is governed by relative sea level changes and tectonics. The model gives an understanding of the faunal dynamics within the North Atlantic Region and helps to constrain the definition of continental margins using faunal evidence.
The symmetrical, cap-shaped mollusc, Archinacella instabilis (Billings, 1865) is redescribed from a chert horizon within the Uromystrum validum trilobite zone and the Histiodella tableheadensis conodont zone in the Middle Ordovician (Whiterockian) Table Point Formation. The considerable variation in the shell shape is interpreted to be intraspecific. Some of the other thirty North American species of Archinacella Ulrich and Scofield, 1897, are likely junior synonyms of the Newfoundland species.
The Great American Carbonate Bank (GACB) comprises the carbonates (and related siliciclastics) of the Sauk megasequence, which were deposited on and around the Laurentian continent during Cambrian through earliest Middle Ordovician, forming one of the largest carbonate-dominated platforms of the Phanerozoic. The Sauk megasequence, which ranges upwards of several thousand meters thick along the Bank's margin, consists of distinctive Lithofacies and fauna that are widely recognized throughout Laurentia. A refined biostratigraphic zonation forms the chronostratigraphic framework for correlating disparate outcrops and subsurface data, providing the basis for interpreting depositional patterns and the evolution of the Bank. GACB hydrocarbon fields have produced 4 BBO and 21 TCFG, mostly from reservoirs near the Sauk-Tippecanoe unconformity. The GACB is also a source of economic minerals and construction material and, locally, serves as either an aquifer or repository for injection of waste material. This Memoir comprises works on biostratigraphy, ichnology, stratigraphy, depositional facies, diagenesis, and petroleum and mineral resources of the GACB. It is dedicated to James Lee Wilson who first conceived of this publication and who worked on many aspects of the GACB during his long and illustrious career.
