Martin Point Research Articles

LATE CAMBRIAN RADIOLARIAN FAUNAS AND BIOSTRATIGRAPHY OF THE COW HEAD GROUP, WESTERN NEWFOUNDLAND

Abstract Well-preserved Late Cambrian radiolarian faunas were recovered from carbonate rocks of the Cow Head Group of the Great Northern Peninsula of the island of Newfoundland, Canada. Several different faunal assemblages were recognized from three strata at Green Point, one from a stratum at Martin Point, and three from strata at Broom Point South in Gros Morne National Park. The faunas contain nine genera, five of which are new, and 33 species, all but two of which are new. The five new genera are Curvechidnina, Grosmorneus, Pararcheoentactinia, Ramuspiculum, and Subechidnina. Most of the genera belong to the families Archeoentactinidae, Echidninidae, Palaeospiculumidae, and Protoentactiniidae; a few taxa have an uncertain taxonomic position. Echidnina, whose taxonomic identity was uncertain, is shown to be a radiolarian. The diversity of each of these faunas is similar, but the difference in faunal compositions among the faunas examined is distinct. From this analysis, the Late Cambrian strata between...

Rekonstruktion eines unter-bis mittelordovizischen Karbonatschelfrandes: Cow Head Gruppe, West-Neufundland

Lower Ordovician (Arenig) rocks of the Cow Head Group in western Newfoundland represent a well preserved fragment of the continental slope of the early Paleozoic Iapetus Ocean. Cow Head Group strata are characterized by conglomerate beds intercalated with deep water carbonates and minor siliciclastics. Three megaconglomerate units (beds 10, 12 and 14) on Cow Head Peninsula with lateral and distal equivalents exposed at Lower Head, on Stearing Island, at St. Pauls Inlet, Western Brook Pond and Martin Point yield clasts and boulders from shelfedge and upper slope of the Iapetus Ocean. These clasts represent superbly preserved remains of the inner continental margin, a rarely preserved facies around the North American craton. This study comprises a documentation of carbonate lithofacies deduced from fragments of the shelf margin for the purpose of determining nature and evolution of the inner marginal environment through the Arenig interval. Among clasts in the megaconglomerates local (lower slope derived), foreign (shelf-, shelfbreak- and upper slope-derived) and older clasts were distinguished. Study of facies relationships and abundances of the different clast lithologies combined with conodont biostratigraphy enable reconstruction of the upper slope/shelfbreak sedimentary environment.

The proposed Cambrian–Ordovician global Boundary stratotype and point (GSSP) in Western Newfoundland, Canada

AbstractSections exposing the Cambrian–Ordovician Boundary interval at Broom Point in western Newfoundland have been proposed earlier for a global systemic boundary stratotype. These lie within the Cow Head Group, a late Middle Cambrian to early Middle Ordovician allochthonous unit of limestone, shale, and conglomerate deposited at the toe of the ancient continental slope and on the adjacent continental rise. Several recent studies have further investigated the stratigraphy, sedimentology, and palaeontology of the Cow Head Group and others are under way on magnetostratigraphy and chemostratigraphy. These aspects are reviewed for six key boundary sections representing proximal to distal facies: Cow Head Ledge, Broom Point South, Broom Point North, St Pauls Inlet Quarry, Martin Point, and Green Point. In particular, new data are presented from 260 conodont samples that yielded 15500 conodonts. This intense sampling has allowed the discrimination of minor hiatuses in the proximal to intermediate facies where conglomerates have eroded and cannibalized underlying strata. New conodont data from Broom Point North have lowered the base of the C. lindstromi Zone into unit 74 conglomerates, thereby making this section unsuitable as a boundary stratotype. New collections from Green Point have yielded abundant conodonts and over 9400 conodonts have been recovered from 77 samples.The conodont, graptolite, and trilobite biostratigraphy through the boundary interval is documented allowing accurate correlation between sections and more precisely revealing small hiatuses in the proximal and intermediate facies. The sequence of conodont zones is: Eoconodontus notchpeakensis, Cordylodus proavus, C. caboti, C. intermedius, C. lindstromi and C. angulatus. These can be correlated with trilobite zones established from both in situ and clast faunas from the proximal to intermediate facies and with graptolite assemblages (of Cooper 1979) especially in the intermediate to distal facies. Three new species of Cordylodus are described (C. andresi, C. hastatus and C. tortus) and the full apparatus of Iapetognathus preaengensis is illustrated.The criteria for selecting a global boundary stratotype and point (GSSP) are reviewed in terms of the Cow Head sections. The Green Point section is shown to meet, and largely surpass, the prerequisites required of a stratotype. The Green Point section is proposed to be the global boundary stratotype with the base of the Ordovician System defined at the base of unit 23, which is the base of the Broom Point Member, Green Point Formation, at a level coincident with the base of the Cordylodus lindstromi Zone. In addition to an abundant and superbly preserved conodont fauna, this section preserves the best sequence of earliest planktic graptolites through a 40 m interval; the first nematophorous graptolites (of Assemblage 1) occur in unit 25, 6.9 m above the base of the C. lindstromi Zone. This level can be readily correlated into the proximal facies where both deep and shallow water trilobites (in situ and in clasts, respectively) show the base of the C. lindstromi Zone to lie within the Symphysurina brevispicata trilobite Subzone.

The earliest Ordovician nematophorid graptolites: taxonomy and correlation

AbstractThe earliest nematophorid (planktic) dendroid graptolites (Family Anisograptidae) are described and revised from several heterofacial facies sections of the Broom Point Formation, Cow Head Group, western Newfoundland (Broom Point North and St Paul's represent medial to upper continental slope, Martin Point and Green Point distal slope environments). Noting potential conodont recycling in the palaeoslope environments of the proximal Cow Head Group sections, graptolites are the only group of fossils that could not have been subject to post-burial transport. The graptolites belong to an informal group of quadriradiate form-species principally representing two originally related but then diverging phyletic groups: pendent Rhabdinopora Eichwald, 1855 and horizontal to sub-horizontal Staurograptus Emmons, 1855; both being stratigraphically within Assemblage Zone I (emended after Cooper, 1979) of earliest Tremadoc or early Ibexian age (top of Cordylodus intermedius to base of C. lindstromi conodont zones). Assemblage I graptolites offer a higher resolution than coeval conodonts and are a better tool for inter-facies correlations both within the Broom Point Formation and with other graptolitic sequences on a global scale. Form-species of quadriradiate Rhabdinopora rustica (such as ?R. praeparabola and R. parabola) and of Staurograptus dichotomus (e.g. ‘Radiograptus’ or ‘Heterograptus’ flexibilis or ‘Aletograptus’) are interpreted as astogenetic morphs, or as phylogenetically descendant variants of these forms. Upon evidence of late astogenetic insertion of dissepiments in Staurograptus and Anisograptus the names ‘Heterograptus’ and ‘Radiograptus’ are placed into junior synonymy, and ‘Aletograptus’ is regarded a junior synonym of Staurograptus because its post-primary dichotomies are merely delayed distally (or omitted) to be observed exclusively in very mature specimens. The Cow Head Group fauna is compared with earliest nematophorids from Oslo, Norway (Naersnes) and Dayangcha, Jilin, China (Xiaoyangqiao), and a new comprehensive ecostratigraphic zonation for early Tremadoc graptolites is proposed.

Source rocks of western Newfoundland

Studies on the organic geochemistry of natural oil seeps, although not always associated with major economic deposits, offer opportunity to compare chemical characteristics of an oil to a sedimentary depositional environment. One such seep occurs in the geologically well-documented Parsons Pond region of Western Newfoundland. A number of potential sources for the oil, which has been observed for 170 years, have been proposed including shales from the Shallow Bay and Green Point Formations of the Cow Head Group, the Table Head Group and similar sediments from the Curling Group, all which represent deposition along a continental margin in the Cambro-Ordovician. Total organic carbon in the shales ranges from quite low (0.6%) to moderate (5.2%). Gas chromatography-mass spectrometry shows evidence that suggest weathering. Odd predominance prior to C 21 is seen in these oils and is characteristic of most Ordovician oils. The oils contain a slight even predominance in the C 25+ alkanes. Pristane and phytane were both observed to be present yielding a ratio of 1.6. Isotopic compositions from the Green Point Formation extracts are closest to that of the oils (−28.5%). Similar variations in isotope values from one fraction to another are observed in both the oils and Green Point extracts. Nitrogen isotope studies show a large range in the extracts with the best comparison between the Broom Point (0.5%ℵ) and seep oils (0.6%ℵ). The composition of the organic matter from the Broom Point and Martin Point Members of the Cow Head Group reflect the hydrocarbon compositions of the oil The effect of thermal maturation eastward across the Parsons Pond region is observed in increased bitumen contents and heavier carbon isotope compositions.

Crustal structure and velocity anisotropy beneath the Beaufort Sea

Crustal-scale seismic refraction data obtained in the Beaufort Sea during 1976 reveal a 4–5 km thick sedimentary layer overlying an oceanic crust that thickens rapidly as it approaches the continental terrace of Alaska. A synthetic seismogram analysis of multiple reflected, water-wave events indicates that the upper sedimentary layer has a compressional velocity of 1.8 km/s and a shear velocity of about 0.2 km/s. An oceanic layer 2A of 4.3 km/s, a layer 3A of 6.6 km/s, and a layer 3B of 7.6 km/s overlying an anisotropic (3%) upper mantle with a median velocity of 8.3 km/s are interpreted. The direction of maximum upper-mantle velocity appears to be approximately north–south in the area surveyed, suggesting that a rotation of the Northwind Ridge–Chukchi Plateau away from the Barrow–Martin Point sector of Alaska may have occurred.

The Golden Grindstone: The Adventures of George M. MitchellWild Horses and Gold: From Wyoming to the YukonThe Klondike NuggetAlaskans AllThe Reign of Soapy Smith Monarch of Misrule in the Last Days of the Old West and the Klondike Gold RushArctic Night’s Entertainments: Being the Narrative of an A1askan-Estonian Digger, August Masik, as told during the Arctic Night of 1933-34 near

<i>The Golden Grindstone: The Adventures of George M. Mitchell</i><i>Wild Horses and Gold: From Wyoming to the Yukon</i><i>The Klondike Nugget</i><i>Alaskans All</i><i>The Reign of Soapy Smith Monarch of Misrule in the Last Days of the Old West and the Klondike Gold Rush</i><i>Arctic Night’s Entertainments: Being the Narrative of an A1askan-Estonian Digger, August Masik, as told during the Arctic Night of 1933-34 near

The Golden Grindstone: The Adventures of George M. MitchellWild Horses and Gold: From Wyoming to the YukonThe Klondike NuggetAlaskans AllThe Reign of Soapy Smith Monarch of Misrule in the Last Days of the Old West and the Klondike Gold RushArctic Night’s Entertainments: Being the Narrative of an A1askan-Estonian Digger, August Masik, as told during the Arctic Night of 1933-34 near

<i>The Golden Grindstone: The Adventures of George M. Mitchell</i><i>Wild Horses and Gold: From Wyoming to the Yukon</i><i>The Klondike Nugget</i><i>Alaskans All</i><i>The Reign of Soapy Smith Monarch of Misrule in the Last Days of the Old West and the Klondike Gold Rush</i><i>Arctic Night’s Entertainments: Being the Narrative of an A1askan-Estonian Digger, August Masik, as told during the Arctic Night of 1933-34 near