Ordovician paleomagnetic results from the St. George and Table Head carbonates of western Newfoundland

1987 ◽  
Vol 24 (9) ◽  
pp. 1785-1796 ◽  
Author(s):  
Ernst R. Deutsch ◽  
Jagat N. Prasad
Keyword(s):  
Thermal Treatment ◽  
Geomagnetic Field ◽  
Late Paleozoic ◽  
Middle Ordovician ◽  
Viscous Component ◽  
Head Groups ◽  
Anticlockwise Rotation

We have studied 85 limestone and dolostone samples from 21 sites of the St. George and Table Head groups (Lower and Middle Ordovician) on Port au Port Peninsula (Humber Zone). Their gentle (~15°) tilt is probably Devonian. A steep viscous component dominant in the natural remanence is removed by thermal and (less efficiently) alternating-field demagnetization. In about 60% of all samples, the thermal treatment yielded a southeasterly reverse component ("A"), which typically remained blocked to 450–500 °C and then decayed to noise. Mean A component directions calculated from Zijderveld plots and referred to bedding are D, I = 148.5°, +33.6 °for N = 9 St. George sites and D, I = 150.0°, I = +40.7 °for N = 5 Table Head sites. Corresponding antipoles are 17.5°N, 152.3°E, dp, dm = 2.8°, 4.9 °and 13.4°N, 149.2°E, dp, dm = 2.9°, 4.7°, respectively. We interpret these results as representative of the geomagnetic field in the Early and mid-Ordovician. In 14 samples, mainly from the older St. George strata, thermal treatment yielded a reverse ("B") component with mean direction D, I = 167.9°, −9.2°, corresponding to an antipole at 44.9°N, 138.2°E, dp, dm = 3.6°, 7.1°. We interpret this as a late Paleozoic overprint in diagenetic hematite. The 30° anticlockwise rotation of Newfoundland proposed by Wegener is not supported by our data.

The amalgamation of Pangea: Paleomagnetic and geological observations revisited

2020 ◽  
Author(s):  
Lei Wu ◽  
J. Brendan Murphy ◽  
Cecilio Quesada ◽  
Zheng-Xiang Li ◽  
John W.F. Waldron ◽  
...  
Keyword(s):  
Selection Criteria ◽  
Late Paleozoic ◽  
Geological Data ◽  
High Quality ◽  
Early Devonian ◽  
Polar Wander ◽  
Middle Ordovician ◽  
Oblique Convergence ◽  
Q Factors ◽  
European Variscides

The supercontinent Pangea formed by the subduction of the Iapetus and Rheic oceans between Gondwana, Laurentia, and Baltica during mid-to-late Paleozoic times. However, there remains much debate regarding how this amalgamation was achieved. Most paleogeographic models based on paleomagnetic data argue that the juxtaposition of Gondwana and Laurussia (Laurentia-Baltica) was achieved via long-lasting highly oblique convergence in the late Paleozoic. In contrast, many geology-based reconstructions suggest that the collision between the two continents was likely initiated via a Gondwanan promontory comprising the Iberian, Armorican, and Bohemian massifs, and parts of the basement units in the Alpine orogen during the Early Devonian. To help resolve this discrepancy, we present an updated compilation of high-quality paleopoles of mid-to-late Paleozoic ages (spanning Middle Ordovician and Carboniferous times) from Gondwana, Laurentia, and Baltica. These paleopoles were evaluated with the Van der Voo selection criteria, corrected for inclination error where necessary, and were used to revise their apparent polar wander (APW) paths. The revised APW paths were constructed using an innovative approach in which age errors, A95 ovals, and Q-factors of individual paleopoles are taken into account. By combining the resulting APW paths with existing geological data and field relationships in the European Variscides, we provide mid-to-late Paleozoic paleogeographic reconstructions which indicate that the formation of Pangea was likely initiated at 400 Ma via the collision between Laurussia and a ribbon-like Gondwanan promontory that was itself formed by a scissor-like opening of the Paleotethys Ocean, and that the amalgamation culminated in the mostly orthogonal convergence between Gondwana and Laurussia.

Graptolites from the Lower–Middle Ordovician St. George and Table Head groups, western Newfoundland, and their correlation with trilobite, brachiopod, and conodont zones

1987 ◽  
Vol 24 (3) ◽  
pp. 456-470 ◽  
Author(s):  
S. Henry Williams ◽  
W. Douglas Boyce ◽  
Noel P. James
Keyword(s):  
Head Group ◽  
Middle Ordovician ◽  
Faunal Assemblages ◽  
Head Groups ◽  
Brachiopod Fauna ◽  
Lower Slope

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.

Paleomagnetic study of the Ordovician Table Head Group, Port au Port Peninsula, Newfoundland

1988 ◽  
Vol 25 (9) ◽  
pp. 1407-1419 ◽  
Author(s):  
Stuart A. Hall ◽  
Ian Evans
Keyword(s):  
North America ◽  
Geomagnetic Field ◽  
Head Group ◽  
Time Interval ◽  
Reverse Polarity ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Stable Component ◽  
Paleomagnetic Study ◽  
Two Component

A paleomagnetic study of the Ordovician Table Head Group in the Port au Port Peninsula of western Newfoundland reveals a simple two-component magnetization history comprising a reversely magnetized, stable southeasterly remanence with a, shallow to moderate inclination, and an unstable present-day overprint. Pole positions for the stable component, both with and without tectonic tilt correction, correspond with the Early to middle Ordovician pole positions for North America, suggesting this remanence is early. Although the nature of the geomagnetic field in the Ordovician is not well known, the polarity observed is consistent with that reported from other mid-Ordovician studies and appears to reflect a predominance of reverse polarity for this time interval. Evidence of significant rotation of any of the sites studied is absent, indicating that the continental margin in this region acted in an integral rather than a fragmented fashion during deformation.Previously published and new, but preliminary, results from the Early Ordovician St. George Group indicate the presence of two stable components of remanence. These components have similar south-southeasterly declinations but differ in inclination. The shallow to intermediate positive inclination component has a direction that is broadly compatible with Early Ordovician poles from North America. The shallow negative inclination component observed in rocks of similar age from other parts of western Newfoundland appears to be consistent with a later remagnetization of this unit.

Integrated chitinozoan, conodont, and graptolite biostratigraphy from the upper part of the Cape Cormorant Formation (Middle Ordovician), western Newfoundland

2001 ◽  
Vol 38 (3) ◽  
pp. 387-409 ◽  
Author(s):  
Roberto Albani ◽  
Gabriella Bagnoli ◽  
Jörg Maletz ◽  
Svend Stouge
Keyword(s):  
Early Stage ◽  
Foreland Basin ◽  
Black Shales ◽  
Head Group ◽  
Middle Ordovician ◽  
Head Groups ◽  
Taconic Orogeny ◽  
Low Diversity ◽  
Conodont Fauna ◽  
Abundance And Diversity

The Cape Cormorant Formation of the Table Head Group exposed on the Port au Port Peninsula, western Newfoundland, is composed of dark-brown to black shales with interbeds of thin calcareous silty and sandy distal turbidites. Distinctive carbonate conglomerates and breccias derived from the foundering shelf are occasionally found in the formation. The sediments accumulated in the foreland basin formed during the early stage of the Taconic orogeny. The faunas from the upper part of the Cape Cormorant Formation include graptolites, conodonts, and chitinozoans. The graptolites are well preserved, but are of low diversity and are referred to the Darriwil Pterograptus elegans Zone. Conodonts recorded from the distal turbidites are rare and fragmented. The faunas include taxa that are known from the St. George and Table Head groups. The conodont fauna is tentatively assigned to the Histiodella kristinae Phylozone and to the younger, unzoned interval. The chitinozoans are well preserved and the yield is high. The fauna is assigned to the Cyathochitina jenkinsi Zone and to an undefined interval. The abundance and diversity of the chitinozoan assemblages display a cyclic pattern, which is related to changes of the oceanic watermass in the foreland basin. The new chitinozoan species Belonechitina nevillensis n. sp., Belonechitina uniformipunctata n. sp., and Cyathochitina cormorani n. sp. are described.

Ordovician Sphinctozoan Sponges from the Eastern Klamath Mountains, Northern California

1986 ◽  
Vol 60 (S20) ◽  
pp. 1-47 ◽  
Author(s):  
J. Keith Rigby ◽  
A. W. Potter
Keyword(s):  
New Species ◽  
North America ◽  
Growth Form ◽  
Late Ordovician ◽  
Late Paleozoic ◽  
Late Devonian ◽  
Northern California ◽  
New Genera ◽  
Klamath Mountains ◽  
Middle Ordovician

Extensive silicified faunules of Middle and Late Ordovician sphinctozoan sponges have been assembled from the northern part of the eastern Klamath Mountains in northern California. The sponges are from eugeosynclinal rocks that are the westernmost Middle Ordovician to Late Devonian rocks at that latitude in North America. Seventeen new species occur in the assemblages, including 10 porate and 7 aporate forms. New genera of porate forms areAmblysiphonelloidesandCorymbospongia, and new porate species include:Amblysiphonella grossa, Amblysiphonelloides tubula, A. reticulata, Imperatoria mega, I. media, I. minima, I. irregularis, Corymbospongia adnata, C. mica, andC.(?)perforata.These are the first reported occurrences ofAmblysiphonellaandImperatoriain the Ordovician. New aporate genera areCystothalamiellaandPorefieldia, and new aporate species include:Cystothalamiella ducta, C. craticula, C. tuboides, Porefieldia robusta, Girtyocoelia epiporata, andG. canna.This is the oldest known occurrence ofGirtyocoelia, which is generally considered a Late Paleozoic form.Cliefdenella obconican. sp. is characterized by an obconical growth form in contrast to other species of the genus that are more massive or explanate.Cliefdenellais considered here as an imperforate sphinctozoan.Minor isolated hexactines and hexactine-derived spicules of Hexactinellida were associated with the sphinctozoans. No particular taxa within the class can be distinguished from these individual elements.

What is Mitrocrinus wetherbyi S. A. Miller and Gurley, 1894?

1995 ◽  
Vol 69 (6) ◽  
pp. 1188-1190
Author(s):  
William I. Ausich
Keyword(s):  
A Priori ◽  
Late Paleozoic ◽  
Middle Ordovician ◽  
Phylogenetic Classification ◽  
Constructional Design

Phylogenetic classification is dependent upon confident ordering of character states that can be greatly facilitated if the earliest members of a clade are known and well understood. Unfortunately, one of the oldest known representatives of the camerate crinoid order Monobathrida is the problematic Mitrocrinus wetherbyi S. A. Miller and Gurley, 1894. It is problematic because it is a teratologic specimen with hexamerous symmetry and because its basic constructional design is more typical of middle to late Paleozoic monobathrids than of a Middle Ordovician monobathrid. A more advanced-looking construction does not preclude this crinoid from being the most primitive monobathrid a priori, but these two problems have relegated this taxon to an addendum in most classifications. Bather (1900, p. 203) included Mitrocrinus as an “incorrect or indeterminable name” by stating that it was “based on a six-rayed individual, probably abnormal, and a Periechocrinid or Carpocrinid” and Ubaghs (1978, p. T518) designated it as order, suborder, superfamily, and family uncertain.

MAGNETIC ORIENTATION OF BOREHOLE CORES

Geophysics ◽  
1969 ◽  
Vol 34 (5) ◽  
pp. 772-774 ◽  
Author(s):  
M. Fuller
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Standard Procedure ◽  
Natural Remanent Magnetization ◽  
Core Sample ◽  
The Core ◽  
Viscous Component ◽  
Late Tertiary ◽  
Geomagnetic Pole ◽  
Orientation Method

The use of natural remanent magnetization (NRM) to orient boreholes was reported at least thirty years ago (e.g., Lynton, 1938). The method depends upon determining the direction of remanent magnetization of the sample and relating it to the geomagnetic field in which the rock was presumed to have been magnetized. If the NRM faithfully records the relevant geomagnetic field and the field is known, the orientation of the core sample is available. Unfortunately, the ancient geomagnetic pole positions are not, in general, sufficiently well known to make this method particularly successful for rocks that are older than late Tertiary. Moreover, the presence of a weak, viscous component of magnetization parallel to the present geomagnetic field at a given site may produce erroneous results unless it is recognized and eliminated. However, the existence of this component provides another means of orienting the core sample. Isolation of this component might initially appear to be difficult, but it is actually a standard procedure of paleomagnetism; and, in fact, many studies have implicitly demonstrated that the direction of the present geomagnetic field at the sample site is recoverable (e.g., As and Zijderveld, 1958; Zijderveld, 1967). Indeed a number of people have recognized the possibility of using this component to orient borehole samples (e.g., Hargraves, 1969—private communication). The use of this soft viscous component has been advocated recently to distinguish between normal and reversely magnetized rocks in connection with tests of the sea floor spreading hypothesis (Irving and Roy, 1968). Nevertheless, no explicit demonstration of the technique of orienting borehole cores has been published. In the course of paleomagnetic surveys, our demagnetization studies have revealed a number of examples of behavior which makes the orientation method possible. This note describes such behavior and explains how the orientation might be recovered.

Brachiopod biostratigraphy of the middle Ordovician Cow Head and Table Head groups, western Newfoundland

1987 ◽  
Vol 24 (1) ◽  
pp. 70-95 ◽  
Author(s):  
Reuben J. Ross Jr ◽  
Noel P. James
Keyword(s):  
Shallow Water ◽  
Water Table ◽  
Deep Water ◽  
Head Group ◽  
Middle Ordovician ◽  
Head Groups

Brachiopods from shallow-water limestone boulders in beds 12, 13, and 14 of the allochthonous Cow Head Group belong in the earliest Whiterockian Orthidiella Zone. Brachiopods of the autochthonous intertidal to deep-water Table Head Group are equivalent to those of the younger Whiterockian Anomalorthis Zone. The Cow Head is older than the Table Head.Integration of the brachiopod data from western Newfoundland with those from the type Whiterockian in Nevada, combined with the evidence of graptolites from both areas, indicates that the Orthidiella Zone spans the Australian Castlemainian, Yapeenian, and lower Darriwilian Dal zones.

Late Paleozoic geomagnetic-field estimates from studies of Permian lavas in northeastern Kazakhstan

2014 ◽  
Vol 55 (1) ◽  
pp. 108-117 ◽  
Author(s):  
M.L. Bazhenov ◽  
R. Van der Voo ◽  
J.G. Meert ◽  
N.M. Levashova ◽  
I.S. Ipat’eva
Keyword(s):  
Geomagnetic Field ◽  
Late Paleozoic
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