Early Silurian paleopole for redbeds and volcanics of the King George IV Lake area, Newfoundland

1989 ◽  
Vol 26 (10) ◽  
pp. 1904-1917 ◽  
Author(s):  
K. L. Buchan ◽  
J. P. Hodych
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Paleomagnetic Data ◽  
Atlantic Canada ◽  
Lake Area ◽  
Consistent Direction ◽  
Canadian Appalachians

Redbeds and felsic and mafic volcanics of the King George IV Lake area of the Dunnage Zone in southwestern Newfoundland have been studied paleomagnetically. After unfolding, both hematite and magnetite carry a consistent direction of magnetization (D = 29.6°; I = 1.0°; k = 19.3; α95 = 11.3°) corresponding to a near-equitorial paleolatitude (0.5°N ± 6°) and yielding a paleopole at 84.6°E, 35.9°N (dm = 11.3°; dp = 5.6°). A positive fold test shows that the remanence was acquired before Devonian deformation. A positive conglomerate test and a reversal of the magnetization in a continuous redbed sequence demonstrates that the remanence was acquired at the time of formation, which has been assigned to the Early Silurian on the basis of a U–Pb zircon date of 431 ± 5 Ma.No other undisputed primary or pre-fold remanence has been reported from Atlantic Canada for the Late Ordovician – Silurian period. Therefore, from paleomagnetic data it is not yet possible to estimate the amount of post-Silurian movement within the Canadian Appalachians. Pre-fold magnetizations from Late Ordovician and Silurian rocks of cratonic North America predict a paleolatitude of 16°S ± 12 °for Newfoundland. However, further results are necessary to determine whether any significant displacement has occurred between Newfoundland and the craton since the Early Silurian.

A Kinematic Reconstruction of Jurassic ocean spreading from the ophiolites of California, the western U.S. using structural geology and paleomagnetism.

2021 ◽  
Author(s):  
Cemil Arkula ◽  
Nalan Lom ◽  
John Wakabayashi ◽  
Grant Rea-Downing ◽  
Mark Dekkers ◽  
...  
Keyword(s):  
North America ◽  
Relative Position ◽  
North American ◽  
Fault System ◽  
Paleomagnetic Data ◽  
Geochemical Data ◽  
Ophiolite Belt ◽  
The North ◽  
Western Us ◽  
Jurassic Ophiolites

<p>The western edge of the North America plate contains geological records that formed during the long-lived convergence between plates of the Panthalassa Ocean and North America. The geology of different segments along western North America indicates different polarities (eastward and westward) for subducted slabs and thereby various tectonic histories and settings. The western United States (together with Mexico) plays a key role in this debate, many geologic interpretations assume continuous eastward subduction in contrast to observations within proximal geologic segments and tomographic images of the lower mantle below North America and the eastern Pacific Ocean which suggest a more complex subduction history. In this study, we aim to evaluate the plate tectonic setting in which the Jurassic ophiolites of California formed. Geochemical data from these ophiolites suggest that they formed above a nascent intra-oceanic or continental margin subduction zone. We first developed a kinematic reconstruction of the western US geology back to the Jurassic based on published structural geological data. Importantly, we update the reconstruction of the various branches of the San Andreas fault system to determine the relative position of the ophiolite fragments and adopt a previous restoration of Basin and Range extension which we expand northward towards Washington state. We then reconstruct North American margin deformation associated with Cretaceous to Paleogene shortening and strike-slip faulting. We find no clear candidates in the geological record that may have accommodated major subduction between the Jurassic ophiolite belt and the North American margin and consequently concur with the school of thought that considers that the ophiolite belt, as well as the underlying subduction-accretionary Franciscan Complex, likely formed in the North American fore-arc. We collected paleomagnetic data to reconstruct the spreading direction of the Jurassic Californian ophiolites, by providing new paleomagnetic data from sheeted dykes of the Josephine and Mt. Diablo Ophiolites. These suggest a NE-SW paleo-ridge orientation, oblique to the North American margin which may be explained by partitioning of a dextral component of subduction obliquity relative to North America. We used this spreading direction in combination with published ages of the ophiolites and our restoration of the relative position of these ophiolites prior to post-Jurassic deformation to construct a ridge-transform system at which the Jurassic ophiolites accreted. The results will be used to evaluate which parts of the subduction systems that existed in the eastern Panthalassa Ocean may reside in the western US, and which parts may be better sought in the northern Canadian Segment or/and in the southern Caribbean region.</p>

Ordovician rocks in the Eastcan et al. Freydis B-87 and other wells in offshore Atlantic Canada

1984 ◽  
Vol 21 (7) ◽  
pp. 864-868 ◽  
Author(s):  
W. A. M. Jenkins
Keyword(s):  
Late Ordovician ◽  
Atlantic Canada ◽  
Grand Banks ◽  
Exploratory Wells

Acritarchs and Chitinozoa from the lower 1300 ft (400 m) of the Eastcan et al. Freydis B-87 well, Labrador Shelf, indicate that these strata accumulated in a marine setting during Late Ordovician time. Five or more other exploratory wells on the Labrador Shelf and the Grand Banks of Newfoundland also have encountered Ordovician rocks.

Paleoenvironmental Reconstruction Based on Horn Corals, with an Example from the Late Ordovician of North America

Palaios ◽  
1988 ◽  
Vol 3 (1) ◽  
pp. 22 ◽  
Author(s):  
Robert J. Elias ◽  
Ronald G. Zeilstra ◽  
Thomas N. Bayer
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Paleoenvironmental Reconstruction

scholarly journals The Palearctic species Bembidion femoratum and Amara communis (Coleoptera: Carabidae): new records and notes on modes of introduction to North America

2005 ◽  
Vol 137 (5) ◽  
pp. 532-538 ◽  
Author(s):  
Christopher G. Majka
Keyword(s):  
North America ◽  
New Records ◽  
Atlantic Canada ◽  
Marine Traffic ◽  
Nursery Stock ◽  
Palearctic Species ◽  
The Many ◽  
Sizeable Number

AbstractThe Palearctic species Amara communis (Panzer) and Bembidion femoratum Sturm were both first reported from North America in 1992. Since that time a sizeable number of additional specimens of both species have been found, which substantially expands their known range on the continent. These records are summarized herein. The possible modes of introduction of both species are discussed within the context of other introduced insects, particularly those first found in Atlantic Canada. In the case of A. communis, the many coastal localities where it occurs would seem to indicate that it was introduced in association with transatlantic marine traffic, possibly the shipment of dry ballast. In the case of B. femoratum, the mode of introduction is less clear. Possible associations with nursery stock, dry ballast, and the movement of aircraft are all discussed.

Lake ice phenology changes in the northern hemisphere

2021 ◽  
Author(s):  
Yubao Qiu ◽  
Xingxing Wang ◽  
Matti Leppäranta ◽  
Bin Cheng ◽  
Yixiao Zhang
Keyword(s):  
Remote Sensing ◽  
North America ◽  
Northern Hemisphere ◽  
Ice Cover ◽  
Passive Microwave ◽  
Lake Area ◽  
Lake Ice ◽  
Northern Tibetan Plateau ◽  
Break Up ◽  
Ice Phenology

<p>Lake-ice phenology is an essential indicator of climate change impact for different regions (Livingstone, 1997; Duguay, 2010), which helps understand the regional characters of synchrony and asynchrony. The observation of lake ice phenology includes ground observation and remote sensing inversion. Although some lakes have been observed for hundreds of years, due to the limitations of the observation station and the experience of the observers, ground observations cannot obtain the lake ice phenology of the entire lake. Remote sensing has been used for the past 40 years, in particular, has provided data covering the high mountain and high latitude regions, where the environment is harsh and ground observations are lacking. Remote sensing also provides a unified data source and monitoring standard, and the possibility of monitoring changes in lake ice in different regions and making comparisons between them. The existing remote sensing retrieval products mainly cover North America and Europe, and data for Eurasia is lacking (Crétaux et al., 2020).</p><p>Based on the passive microwave, the lake ice phenology of 522 lakes in the northern hemisphere during 1978-2020 was obtained, including Freeze-Up Start (FUS), Freeze-Up End (FUE), Break-Up Start (BUS), Break-Up End (BUE), and Ice Cover Duration (ICD). The ICD is the duration from the FUS to the BUE, which can directly reflect the ice cover condition. At latitudes north of 60°N, the average of ICD is approximately 8-9 months in North America and 5-6 months in Eurasia. Limited by the spatial resolution of the passive microwave, lake ice monitoring is mainly in Northern Europe. Therefore, the average of ICD over Eurasia is shorter, while the ICD is more than 6 months for most lakes in Russia. After 2000, the ICD has shown a shrinking trend, except northeastern North America (southeast of the Hudson Bay) and the northern Tibetan Plateau. The reasons for the extension of ice cover duration need to be analyzed with parameters, such as temperature, the lake area, and lake depth, in the two regions.</p>

scholarly journals Origin of the Late Ordovician Lepidocyclus brachiopod fauna in North America and its biogeographic significance

1992 ◽  
Vol 6 ◽  
pp. 149-149
Author(s):  
Jisuo Jin
Keyword(s):  
North America ◽  
Sea Level ◽  
North American ◽  
Plate Tectonics ◽  
Late Ordovician ◽  
Sea Level Changes ◽  
Stepping Stones ◽  
Shell Size ◽  
Larval Stages ◽  
The North

Three rhynchonellid brachiopod genera, Hiscobeccus, Lepidocyclus, and Hypsiptycha, are the most diagnostic elements of the Lepidocyclus fauna of North America in Late Ordovician time. These are characterized by relatively large, strongly biconvex to globular shells with coarse imbricating growth lamellae and, internally, with septiform cardinal processes in brachial valves. Among the three genera, Hiscobeccus appears the earliest, now known from rocks of late Trentonian-Edenian age in the Canadian Rocky Mountains and Mackenzie Mountains. Morphologically, Hiscobeccus is distinguished from the other two genera by its open delthyrium in the pedicle valve. Early forms of Hiscobeccus show close morphological similarity to Rhynchotrema in their non-globular biconvex shells covered by strong growth lamellae only in the anterior portions. It has been suggested that Hiscobeccus evolved from the Rhynchotrema wisconsinense stock through increase in shell size, globosity, and strength of growth lamellae. Earliest species of Rhynchotrema has been documented convincingly from rocks of early Trentonian age, and the derivation of Hiscobeccus most likely took place during the mid-Trentonian. Lepidocyclus and Hypsiptycha evolved from either Rhynchotrema or Hiscobeccus by developing a pair of deltidial plates covering the delthyrium.Rhynchotrema and other rhynchonellids that evolved before mid-Trentonian time are common to the North American (Laurentian) and the Siberia-Kazakhstan paleocontinents. In contrast, Hiscobeccus, Lepidocyclus, and Hypsiptycha that evolved after the mid-Trentonian are virtually restricted to Laurentia. Therefore, Rhynchotrema marked the last successful intercontinental migration of rhynchonellids during their Llandeilian-Caradocian cosmopolitanism. The pronounced provincialism of the North American Lepidocyclus fauna may have been caused by a number of factors. Facies control is not likely the explanation because these rhynchonellids occur in nearly all the inland and marginal platform seas of Laurentia and commonly are found together in the same types of rocks. Plate tectonics and sea-level changes are considered major causes. The Ordovician rhynchonellids lived in shallow marine (intertidal-subtidal) environments and were incapable of crossing vast, deep oceanic barriers because of their sedentary mode of life and short-lived motile larval stages. The widening of the ocean between North America and Siberia, coupled with high sea-level stand, may have created a sufficiently wide oceanic barrier to interrupt faunal mixing between the two paleocontinents by late Trentonian time. Moreover, the rise in sea level would have resulted in the disappearance of island faunas, which could have served as stepping stones for intercontinental migration of shallow-water benthic faunas during low sea-level stand.

Flexible crinoids from the Upper Ordovician Maquoketa Formation of the northern midcontinent and the evolution of early flexible crinoids

2001 ◽  
Vol 75 (2) ◽  
pp. 370-382 ◽  
Author(s):  
James C. Brower
Keyword(s):  
New Species ◽  
North America ◽  
Late Ordovician ◽  
Upper Ordovician ◽  
Middle Ordovician

Three flexible crinoids occur in the Upper Ordovician Maquoketa Formation of Illinois, Iowa, and Minnesota:Protaxocrinus girvanensisRamsbottom, 1961,Clidochirus anebosnew species, andProanisocrinus oswegoensis(Miller and Gurley, 1894).Protaxocrinus girvanensisis also found in the Upper Ordovician of Scotland which indicates that the ocean was narrow enough to allow at least one crinoid species to cross the barrier. The Upper Ordovician of North America and Scotland also share many common crinoid genera. Both phenetic and cladistic methods result in similar phylogenies of flexible crinoids.Protaxocrinuswas derived from a cupulocrinid ancestor during the Middle Ordovician.Clidochirusevolved fromProtaxocrinusor its ancestral stock prior to the Richmondian of the Late Ordovician. The RichmondianProanisocrinusand later anisocrinids are most closely related toClidochirusor its immediate predecessor. Thus, three major lineages of flexible crinoids,Protaxocrinus(taxocrinid group),Clidochirus(icthyocrinid), andProanisocrinus(anisocrinids and homalocrinids), appeared during the Ordovician. Despite their rarity during the Ordovician, all three flexible lineages survived the Latest Ordovician extinction, whereas their more abundant and successful cupulocrinid ancestors were eliminated.

Geomorphic Expression of Abrupt Climate Change in Southwestern North America at the Glacial Termination

2002 ◽  
Vol 57 (3) ◽  
pp. 371-381 ◽  
Author(s):  
Roger Y. Anderson ◽  
Bruce D. Allen ◽  
Kirsten M. Menking
Keyword(s):  
North America ◽  
North Atlantic ◽  
Climate Changes ◽  
Lake Area ◽  
Lake Surface ◽  
Atlantic Region ◽  
Beach Ridges ◽  
The North ◽  
Lake Floor ◽  
Lake Surface Area

AbstractEolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern North America. Drying of pluvial Lake Estancia, central New Mexico, occurred after ca. 12,000 14C yr B.P. Thereafter, eolian landforms on the old lake floor, constructed of gypsum sand, were overridden by rising lake water, modified by subaqueous processes, and organized into beach ridges along the lake's eastern shore. Preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate. Available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the Younger Dryas (YD) stade. The beach ridges provide information about lake surface area, which was 45% of the lake area reached during the maximum highstands of the late Pleistocene. A similar proportional response has been reported for YD climate changes outside the North Atlantic region.

scholarly journals Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation?: Comment and Reply

Geology ◽  
2003 ◽  
Vol 31 (1) ◽  
pp. e28-e29 ◽  
Author(s):  
Stephen A. Leslie ◽  
Stig M. Bergström
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Proxy Record

An enigmatic blastozoan echinoderm fauna from central kentucky

2009 ◽  
Vol 83 (5) ◽  
pp. 739-749 ◽  
Author(s):  
Colin D. Sumrall ◽  
Carlton E. Brett ◽  
Troy A. Dexter ◽  
Alexander Bartholomew
Keyword(s):  
North America ◽  
Northwest Territories ◽  
Middle Devonian ◽  
Fossil Record ◽  
Foreland Basin ◽  
Late Ordovician ◽  
Upper Devonian ◽  
Range Extension ◽  
First Report ◽  
Appalachian Foreland

A series of small road cuts of lower Boyle Formation (Middle Devonian: Givetian) near Waco, Kentucky, has produced numerous specimens of three blastozoan clades, including both “anachronistic” diploporan and rhombiferan “cystoids” and relatively advanced Granatocrinid blastoids. This unusual assemblage occurs within a basal grainstone unit of the Boyle Limestone, apparently recording a local shoal deposit. Diploporans, the most abundant articulated echinoderms, are represented by a new protocrinitid species, Tristomiocystis globosus n. gen. and sp. Glyptocystitoid rhombiferans are represented by isolated thecal plates assignable to Callocystitidae. Three species of blastoids, all previously undescribed, include numerous thecae of the schizoblastid Hydroblastus hendyi n. gen. and sp., the rare nucleocrinid Nucleocrinus bosei n. sp., and an enigmatic troosticrinid radial. The blastoid Nucleocrinus is typical for the age; however, the callocystitid, schizoblastid, and protocrinitid are not. Hydroblastus is the oldest known schizoblastid. Middle and Upper Devonian callocystitids have been previously reported only from Iowa and Michigan USA with unpublished reports from Missouri USA and the Northwest Territories, Canada. This occurrence is thus the first report of a Middle Devonian rhombiferan from the Appalachian foreland basin. Tristomiocystis is the first known protocrinitid in North America and the only protocrinitid younger than Late Ordovician. This occurrence thus represents a range extension of nearly 50 million years for protocrinids. This extraordinary sample of echinoderms in a Middle Devonian limestone from a well-studied area of North America highlights the incompleteness of the known fossil record, at least in fragile organisms such as echinoderms.

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