Paleomagnetic study of the Late Ordovician–Early Silurian platform sequence of Anticosti Island, Quebec

1986 ◽  
Vol 23 (12) ◽  
pp. 1880-1890 ◽  
Author(s):  
Maurice K. Seguin ◽  
Allen A. Petryk
Keyword(s):  
Late Ordovician ◽  
Residual Magnetization ◽  
Time Interval ◽  
Reverse Polarity ◽  
Common Component ◽  
Magnetization Component ◽  
Paleomagnetic Study ◽  
Middle Carboniferous ◽  
Component C ◽  
Anticosti Island

Eighteen sites (152 samples, 441 specimens) from the Late Ordovician — Early Silurian sequence of Anticosti Island were studied paleomagnetically. Six sites were collected in the Vauréal Formation, seven in the Ellis Bay Formation, three in the Becscie Formation, and one each in the Gun River and Jupiter formations. The lithologies sampled consisted of limestones, sandy limestones, marls, and sandy calcareous shales drawn from a sedimentary platform sequence of predominantly inter-bedded limestones and shales. The specimens were demagnetized in alternating fields (AF) and thermally and were found to be quite stable. Two components of magnetization were isolated. The memory carrier is fine- to medium-grained magnetite; AF and thermal cleanings are about equally efficient. The average directions of residual magnetization are D = 167°, I = 37°, α95 = 18°; D = 315°, I = −24°, α95 = 17 °for components B and C, respectively. The corresponding paleopoles for the B and C components are 129°E, 19°N (dp = 12°, dm = 21°) and 341°E, 16°S (dp = 10°, dm = 18°).Component A is most probably composed of component C and the present Earth's field (PEF); it was chiefly observed in the more altered Vauréal Formation and in the altered top part of the cored samples. The most common component in the Ellis Bay, Becscie, Gun River, and Jupiter formations is component C. Component B is mainly found in the Becscie and Ellis Bay formations. Both components B and C are isolated in the 300–500 °C and 10–40 mT ranges. Component C is either older than component B or synchronous and of reverse polarity to component B. If this last alternative is correct, then the Ordovician and Silurian formations are overprinted by a pre-Kiaman magnetization. The more plausible scenario is the following: component B is secondary, of pre-Middle Carboniferous age, and overprinted on an older secondary magnetization (component C), the acquisition age of which is confined to the Silurian–Carboniferous time interval.

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.

Paleomagnetism of Carboniferous diabase dykes from Gaspé, Quebec

1987 ◽  
Vol 24 (8) ◽  
pp. 1705-1714 ◽  
Author(s):  
Maurice K. Seguin
Keyword(s):  
Early Carboniferous ◽  
Pole Position ◽  
Common Component ◽  
The North ◽  
Paleomagnetic Study ◽  
Short Period ◽  
Middle Carboniferous ◽  
North American Craton ◽  
Devonian Age ◽  
Geological Units

The reported paleomagnetic study was carried out on 53 oriented samples (156 specimens) at 10 sites in the eastern Gaspé Peninsula. All sampled geological units are composed of sub vertical diabase dykes that cut the sedimentary formations of late Early Devonian – early Middle Devonian age. The radiogenic (whole-rock K/Ar) age of these and similar dykes ranges from Late Devonian to early Middle Carboniferous (mean whole rock K/Ar age = 310 Ma). Two components were isolated. The most common component, A (D = 152°, I = +41°), is normal, whereas the second component, B (D = 315°, I = −44°), is reverse. Both components may be considered as a single one; alternatively, component A may be considered slightly older than component B. Unblocking temperatures, median destructive fields, relative frequency of occurrence of the components, and various degrees of alteration are arguments favouring the first or the second situation. The case of a single component is more probable, representing an Early Carboniferous time of acquisition of remanence (thermoremanent magnetization (TRM) probably corresponding to the time of intrusion and resetting of surrounding sedimentary rocks). The corresponding paleopole position in 148°E, 11°N. This pole position is located some 25 °to the southeast of the cluster of Carboniferous poles (mainly Middle to Late Carboniferous) for the North American craton. The significance of this discrepancy is not well understood, but it is worth noting that very recent paleomagnetic results from western Newfoundland and central New Brunswick are located closer to the paleomagnetic results of this study. The age and direction of the dyke system suggest a short period of extension following the compressive pulse of the Acadian orogeny and preceding the Alleghenian orogeny. For these reasons, the dyke system is unrelated to the initial opening of the present Atlantic Ocean.

New age constraints on the duration and origin of the Late Ordovician Guttenberg δ13Ccarb excursion from high-precision U-Pb geochronology of K-bentonites

2020 ◽  
Author(s):  
J. Garrecht Metzger ◽  
Jahandar Ramezani ◽  
Samuel A. Bowring ◽  
David A. Fike
Keyword(s):  
High Precision ◽  
Carbon Isotopic Composition ◽  
Late Ordovician ◽  
Environmental Drivers ◽  
Time Interval ◽  
Driving Mechanism ◽  
Ionization Mass ◽  
Mass Extinctions ◽  
Carbon Isotopic ◽  
The North

Perturbations to the global carbon cycle as recorded in the isotopic compositions of marine deposits have been commonly associated with major shifts in the climate and/or biologic activity, including mass extinctions. The Late Ordovician Guttenberg isotopic carbon excursion (GICE) is a large, globally correlative positive shift (∼3‰) in the carbon isotopic composition of marine carbonates (δ13Ccarb), but its driving mechanism(s) remains ambiguous. This is in large part due to uncertain correlations among Late Ordovician records, as well as complex and poorly constrained temporal relationships of abundant K-bentonite (altered volcanic ash) marker beds deposited in this time interval. Here, we provide new, high-precision U-Pb zircon geochronology by chemical-abrasion−isotope-dilution−thermal ionization mass spectrometry for K-bentonites bounding the GICE in the North American Midcontinent, including robust 206Pb/238U ages (reported with 2σ analytical uncertainty) for two important regional markers: the Deicke (453.35 ± 0.10 Ma) and Millbrig (453.36 ± 0.14 Ma) K-bentonites. The new data from these K-bentonites directly constrain the duration of the GICE to less than 400 k.y. at two well-studied locations in eastern Missouri, United States. The abruptness of the GICE precludes relatively gradual tectonic mechanisms as possible drivers of the excursion and suggests more rapid environmental drivers, such as changes in eustatic sea level associated with pre-Hirnantian glacial activity.

Anticostia, a distinctive new Late Ordovician "glyptograptid" (Diplograptacea, Graptoloidea) based on three-dimensionally preserved specimens from Anticosti Island, Quebec

1997 ◽  
Vol 34 (2) ◽  
pp. 215-228 ◽  
Author(s):  
Scott Stewart ◽  
Charles E. Mitchell
Keyword(s):  
Late Ordovician ◽  
Type Specimens ◽  
Anticosti Island ◽  
First Time

Three-dimensionally preserved specimens of Late Ordovician graptolites have been isolated from Vauréal Formation limestone samples collected from Anticosti Island, Quebec. The morphology, astogeny, and systematics of Anticostia macgregorae n.gen., n.sp. are described. These specimens show a new astogenetic pattern (pattern K) described for the first time. The similar glyptograptid species Glyptograptus hudsoni Jackson, Glyptograptus tenuissimus Ross and Berry, and Orthograptus fastigatus Davies all possess a pattern K astogeny. These species, along with Glyptograptus lorrainensis, which possesses the less-derived pattern G astogeny, are included within Anticostia n.gen. Anticostia tenuissima (Ross and Berry) is redescribed and Normalograptus? occidentalis (Ruedemann) is refigured based on their type specimens from coeval rocks in Nevada and Idaho.

Biotic invasion, niche stability, and the assembly of regional biotas in deep time: comparison between faunal provinces

Paleobiology ◽  
2016 ◽  
Vol 42 (3) ◽  
pp. 359-379 ◽  
Author(s):  
Mark E. Patzkowsky ◽  
Steven M. Holland
Keyword(s):  
Late Ordovician ◽  
Niche Shift ◽  
Time Interval ◽  
Natural Experiments ◽  
Deep Time ◽  
Taconic Orogeny ◽  
Ecological Parameters ◽  
High Level ◽  
Biotic Invasion ◽  
Rank Abundance

AbstractBiotic invasions in the fossil record provide natural experiments for testing hypotheses of niche stability, speciation, and the assembly and diversity of regional biotas. We compare ecological parameters (preferred environment, occupancy, median abundance, rank abundance) of genera shared between faunal provinces during the Richmondian Invasion in the Late Ordovician on the Laurentian continent. Genera that spread from one faunal province to the other during the invasion (invading shared genera) have high Spearman rank correlations (>0.5) in three of four ecological parameters, suggesting a high level of niche stability among invaders. Genera that existed in both regions prior to and following the invasion (noninvading shared genera) have low correlations (<0.3) and suggest niche shift between lineages that diverged at least 8 Myr earlier. Niche shift did not accumulate gradually over this time interval but appears to have occurred in a pulse associated with the onset of the Taconic orogeny and the switch from warm-water to cool-water carbonates in southern Laurentia.

Late Ordovician sand-wave complexes on Anticosti Island, Quebec: a marine tidal embayment?

1987 ◽  
Vol 24 (9) ◽  
pp. 1821-1832 ◽  
Author(s):  
D. G. F. Long ◽  
Paul Copper
Keyword(s):  
Local Community ◽  
Late Ordovician ◽  
Sand Wave ◽  
Sand Waves ◽  
The North ◽  
Sand Ridges ◽  
Tidal Embayment ◽  
Tidal Modification ◽  
Global Sea Level ◽  
Anticosti Island

Laterally discontinuous, mixed carbonate–siliciclastic sandstones in the upper Vaureal and lower Ellis Bay formations of Anticosti Island were deposited on an equatorial carbonate ramp with a slope of less than 1°. The 10–18 m thick sandstones are interpreted as subaqueous sand-wave complexes analogous to detached parts of modern shoreface-connected sand ridges. These record storm-enhanced, tidal modification of a northerly derived shoal retreat massif that may have formed in response to recovery from global sea-level lowstands in the Late Ordovician (Ashgill: late Rawtheyan – Hirnantian). The sand-wave complexes formed within a tidal embayment that was confined by the Precambrian Shield to the north and northwest by rising tectonic highlands of the Humber Zone in Newfoundland to the east, and by active tectonic highlands in the Quebec Appalachians (Gaspésie) to the south. Paleocurrent distributions, parallel to the western margins of the Strait of Belle Isle, suggest that the north end of the embayment was closed in Late Ordovician time. Low-diversity faunas within the sand units consist mostly of sowerbyellid, strophomenid, and rhynchonellid brachiopods, bivalves, gastropods, large aulacerid stromatoporoids, and large, domed favositid corals. These "sandy fades" faunas belong to communities significantly different from those found in the laterally interfingering and overlying carbonates and shales, suggesting that the sand waves played an important role in local community modification.

scholarly journals Sedimentology and paleoecology of Upper Ordovician mounds of Anticosti Island, Quebec

1981 ◽  
Vol 18 (10) ◽  
pp. 1562-1571 ◽  
Author(s):  
John H. Lake
Keyword(s):  
Late Ordovician ◽  
Calcareous Algae ◽  
Upper Ordovician ◽  
Salmon River ◽  
Shallow Subtidal ◽  
Anticosti Island ◽  
Primary Porosity

Relatively thin organic buildups in the Ellis Bay Formation of Anticosti Island developed in a shallow subtidal regressive marine shelf environment during the Late Ordovician. The Ellis Bay Formation has been subdivided into six members by Bolton. Two buildups, one in each of members 4 and 6, were studied in detail. The member 6 mud mound on the Salmon River (8 m thick) is bound by calcareous algae, stromatoporoids, and corals, and consists of a micritic bafflestone core capped by crinoidal lime grainstone. Early marine cementation permeated nearly all of the primary porosity. Cathodoluminescence indicates at least five stages of cementation of the mound. Constructive mound development was terminated by progressively shallowing, agitated marine conditions.The member 4 mound is a small coral (ecological) reef exposed on the Vaureal River.

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