On the non-existence of a Cadomian basement in southern France (Pyrenees, Montagne Noire): implications for the significance of the pre-Variscan (pre-Upper Ordovician) series

2004 ◽  
Vol 175 (6) ◽  
pp. 643-655 ◽  
Author(s):  
Bernard Laumonier ◽  
Albert Autran ◽  
Pierre Barbey ◽  
Alain Cheilletz ◽  
Thierry Baudin ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Classical Model ◽  
Black Shales ◽  
High Grade ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
Montagne Noire ◽  
Back Arc

Abstract The deepest Hercynian metamorphic terrains in the Pyrenees and in the nearby Montagne Noire are made up of medium-grade orthogneisses and micaschists, and of high-grade, often granulitic, paragneisses. The existence of a granitic-metamorphic Cadomian basement and of its sedimentary Lower Paleozoic cover was advocated from the following main arguments: (i) a supposed unconformity of the Lower Cambrian Canaveilles Group (the lower part of the Paleozoic series) upon both granitic and metamorphic complexes; (ii) a ca. 580 Ma U-Pb age for the metagranitic Canigou gneisses. A SE to NW transgression of the Cambrian cover and huge Variscan recumbent (“penninic”) folds completed this classical model. However, recent U-Pb dating provided a ca. 474 Ma, early Ordovician (Arenigian) age for the me-tagranites, whereas the Vendian age (581 ± 10 Ma) of the base of the Canaveilles Group was confirmed [Cocherie et al., 2005]. In fact, these granites are laccoliths intruded at different levels of the Vendian-Lower Cambrian series. So the Cadomian granitic basement model must be discarded. In a new model, developed in the Pyrenees and which applies to the Montagne Noire where the orthogneisses appear to be Lower Ordovician intrusives too, there are neither transgression of the Paleozoic nor very large Hercynian recumbent folds. The pre-Variscan (pre-Upper Ordovician) series must be divided in two groups: (i) at the top, the Jujols Group, mainly early to late Cambrian, that belongs to a Cambrian-Ordovician sedimentary and magmatic cycle ; the early Ordovician granites pertain to this cycle; (ii) at the base, the Canaveilles Group of the Pyrenees and the la Salvetat-St-Pons series of the Montagne Noire, Vendian (to earliest Cambrian?), are similar to the Upper Alcudian series of Central Iberia. The Canaveilles Group is a shale-greywacke series with rhyodacitic volcanics, thick carbonates, black shales, etc. The newly defined olistostromic and carbonated, up to 150 m thick Tregurà Formation forms the base of the Jujols Group, which rests more or less conformably on the Canaveilles Group. The high-grade paragneisses which in some massifs underlie the Canaveilles and Jujols low- to medium grade metasediments are now considered to be an equivalent of the Canaveilles Group with a higher Variscan metamorphic grade; they are not derived from metamorphic Precambrian rocks. So, there is no visible Cadomian metamorphic (or even sedimentary) basement in the Pyrenees. However, because of its age, the Canaveilles Group belongs to the end of the Cadomian cycle and was deposited in a subsident basin, probably a back-arc basin which developed in the Cadomian, active-transform N-Gondwanian margin of this time. The presence of Cadomian-Panafrican (ca. 600 Ma) zircon cores in early Ordovician granites and Vendian volcanics implies the anatexis of a thick (> 15 km?) syn-Cadomian series, to be compared to the very thick Lower Alcudian series of Central Iberia, which underlies the Upper Alcudian series. Nd isotopic compositions of Neoproterozoic and Cambrian-Ordovician sediments and magmatites, as elsewhere in Europe, yield Paleoproterozoic (ca. 2 Ga) model-ages. From the very rare occurrences of rocks of this age in W-Europe, it can be envisionned that the thick Pyrenean Cadomian series lies on a Paleoproterozoic metamorphic basement. But, if such a basement does exist, it must be “hidden”, as well as the lower part of the Neoproterozoic series, in the Variscan restitic granulites of the present (Variscan) lower crust. So a large part of the pre-Variscan crust was made of volcano-sedimentary Cadomian series, explaining the “fertile” characteristics of this crust which has been able to produce the voluminous Lower Ordovician and, later, Upper Carboniferous granitoids.

Foxe Platform and Basin Tectono-Sedimentary Element

2021 ◽  
pp. M57-2016-27
Author(s):  
Denis Lavoie ◽  
Nicolas Pinet ◽  
Shunxin Zhang
Keyword(s):  
Black Shales ◽  
Coarse Grained ◽  
Hudson Bay ◽  
Precambrian Basement ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Lower Silurian ◽  
The North ◽  
Marine Carbonate ◽  
Single Well

AbstractThe Foxe Platform and Basin Tectono-Sedimentary Element is an ovoid-shaped, predominantly marine basin located in the Canadian Arctic. The Paleozoic sedimentary succession (Cambrian to Silurian) unconformably overlies the Precambrian basement and reaches a maximum measured thickness of slightly over 500 metres in the only exploration well drilled in this basin. The Lower Paleozoic Foxe Platform and Basin Tectono-Sedimentary Element is surrounded by Precambrian basement and by the Paleozoic Arctic Platform to the north and by the Paleozoic-Mesozoic (?) Hudson Bay Strait Platform and Basin to the south. The Paleozoic succession consists of a Cambrian clastic-dominated interval overlain by Ordovician to lower Silurian predominantly shallow marine carbonate. Other than a single well drilled in the northern part of the basin, no subsurface information is available. Thermally immature Upper Ordovician organic matter rich calcareous black shales have been mapped on the onshore extension of the basin to the southeast. Potential hydrocarbon reservoirs consist of Cambrian porous coarse-grained clastics as well as Upper Ordovician dolostones and reefs.

The Developmental Biology of Brachiopods

2001 ◽  
Vol 7 ◽  
pp. 69-88
Author(s):  
Gary Freeman
Keyword(s):  
Developmental Biology ◽  
Life History ◽  
Fossil Record ◽  
Lower Cambrian ◽  
Comprehensive Treatment ◽  
Next Generation ◽  
Lower Paleozoic ◽  
Short Course ◽  
Invertebrate Paleontology ◽  
Lower Ordovician

The chapter on anatomy in the Treatise on Invertebrate Paleontology (Part H, Brachiopoda, revised) (Williams et al., 1997) is the most current and comprehensive treatment that we have of reproduction and development in these animals. My contribution to this short course is a commentary on and addendum to this review. The study of the developmental biology of extant brachiopods describes a large part of their life history and defines several of the parameters that have to be taken into account when thinking about how a given set of genes will make it to the next generation (Havenhand, 1995). Some extant brachiopod genera like Discinisca and Crania (Neocrania) belong to families that first appeared in the fossil record during the Lower Ordovician or, as in the case of Glottidia, to a superfamily that first appeared during the Lower Cambrian. Studies on the development of these extant animals provide a picture of what the development of their Lower Paleozoic ancestors might have been like.

Occurrence and regional geological setting of Paleozoic rocks on the Grand Banks of Newfoundland

1986 ◽  
Vol 23 (4) ◽  
pp. 504-526 ◽  
Author(s):  
Lewis H. King ◽  
Gordon B. J. Fader ◽  
W. A. M. Jenkins ◽  
Edward L. King
Keyword(s):  
Oil And Gas ◽  
Black Shales ◽  
Source Rocks ◽  
Upper Ordovician ◽  
Acoustic Basement ◽  
Lower Paleozoic ◽  
Shallow Marine ◽  
Grand Banks ◽  
Younger Age ◽  
Seismic Reflection Profiles

Analyses of seismic reflection profiles supported by lithological and palynological studies of core samples from submarine outcrops indicate that the lower Paleozoic succession of the Avalon Terrane, southeast Newfoundland, is continuous offshore. The succession crops out over an area greater than 30 000 km2 and is approximately 8 km thick. The sequence is dominantly siltstone and is of Late Cambrian to ?Devonian or younger age. It is relatively unmetamorphosed, underlain by Hadrynian acoustic basement, and overlain along its eastern and southern margins by a Mesozoic–Cenozoic succession that is economically important from an oil and gas perspective.Lithofacies studies indicate that in Early Ordovician time restricted shallow-marine conditions probably prevailed over a vast area of the Avalon Terrane. Upper Ordovician and Silurian siltstones show evidence of deposition under more-dynamic and well-oxygenated conditions and probably represent a normal shallow-marine environment. Redbeds of possible Devonian or younger age are interpreted to be of continental origin. Black shales of Ordovician age are potential source rocks for the generation of hydrocarbons.

The Precambrian Shield and the Lower Paleozoic Shelf: The Unstable Provenance of the Lower Paleozoic Flysch Sandstones and Conglomerates of the Appalachians between Beaumont and Bic, Quebec

1974 ◽  
Vol 11 (7) ◽  
pp. 951-963 ◽  
Author(s):  
Jean Lajoie ◽  
Yvon Héroux ◽  
Bernard Mathey
Keyword(s):  
Flow Direction ◽  
Source Area ◽  
Mean Flow ◽  
Lower Paleozoic ◽  
Original Source ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Lower Ordovician ◽  
Shelf Sediments ◽  
A Minor

Three sections of lower Paleozoic flysch in the Quebec Appalachians were sampled at Beaumont, Bic, and Trois Pistoles in order to determine the position, composition, and relief of the source area. At Beaumont, the mean flow direction of sediment transport is east-southeasterly; at Trois Pistoles and Bic it is south-southeasterly. Locally there is strong dispersion of the data but no northerly directions have been observed.Albite is the common plagioclase in all Cambrian sandstones; grains generally show polysynthetic twins, but in a few beds only untwinned albite is present. Oligoclase and andesine are the dominant plagioclases in Lower Ordovician rocks. The accessory suite has few diagnostic species; pink garnet is present in all sections, but absent in the basal unit at Bic. Diopside, sphalerite, and barite are found only in the Lower Ordovician rocks at Beaumont. At the three localities, the feldspar content, grain size, and sand/shale ratio vary up-section.The original source area for the sandstones and conglomerates consisted of an early Paleozoic shelf and a Precambrian land-mass. The oldest sands were derived from Precambrian metasediments, Paleozoic shelf sediments, Precambrian sodic plutons, and to a minor degree from gneisses. In Late Cambrian time the major contributors were sedimentary rocks of the shelf, sodic plutons, and gneisses. By Early Ordovician time most of the sands were derived from Grenvillian gneisses and shelf sedimentary rocks.The relief of the Grenvillian Orogenic Belt was high and denudation rapid from Early Cambrian to Late Cambrian, suggesting continuous, but irregular uplift. Uplift of the shelf began early in Cambrian, with major movements occurring in Late Cambrian when the Grenvillian source was rejuvenated. The source area was stabilized by Early Ordovician time.

Strike-slip terranes and a model for the evolution of the British and Irish Caledonides

1987 ◽  
Vol 124 (5) ◽  
pp. 405-425 ◽  
Author(s):  
Donald H. W. Hutton
Keyword(s):  
North America ◽  
Continental Margin ◽  
Strike Slip ◽  
Slip Zone ◽  
Lake District ◽  
Early Ordovician ◽  
Boundary Fault ◽  
Lower Ordovician ◽  
Major Strike ◽  
Back Arc

AbstractEvidence is presented that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period. Some, such as the Highland Boundary Fault, moved in this way at an earlier stage in the Ordovician. These data allow the Caledonian rocks lying between the Laurentian miogeocline (whose basement is represented by the Lewisian, Moine and possibly the Dalradian) and the Gondwanaland miogeocline (Midland Platform and Welsh Basin) to be re-analysed as a group of disorganized terranes which originated to the southwest in North America and southwest Europe/Africa prior to the Silurian. The Highland Border Terrane and Northern Belt Terrane are interpreted as duplicated pieces of a mid-Ordovician sequence which was a back are to northwest subduction. The Midland Valley Terrane is interpreted as a slice of Laurentian foreland onto which ophiolites were obducted in the lower Ordovician but which became the basement of a continental margin arc to northwest subduction in the mid-Ordovician. The Cockburnland Terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip. The Connemara Terrane is regarded as an allochthonous piece of the Dalradian miogeocline and the South Mayo Terrane as a remnant of an early Ordovician arc and fore arc which in mid-Ordovician times became a back arc/marginal basin to northwest subduction. The Lake District-Wexford Terrane is part of an arc to southeast subduction under Gondwanaland whose activity climaxed in the mid-Ordovician. The Central Terrane is interpreted as a Silurian overstep assemblage which blankets the junction between Laurentian- and Gondwanaland-derived oceanic terranes, and therefore Iapetus is regarded as an Ordovician ocean which closed prior to the Silurian. The model suggests that at the end of the Silurian, a clockwise-rotating Gondwanaland, having carried Laurentia into collision with Baltica, broke free and created a major sinistral strike-slip zone which disrupted the Ordovician palaeogeography in the British Isles/North American sector of Iapetus.

An aglaspidid arthropod from the Upper Ordovician of Morocco with remarks on the affinities and limitations of Aglaspidida

2005 ◽  
Vol 96 (4) ◽  
pp. 327-350 ◽  
Author(s):  
Peter Van Roy
Keyword(s):  
Czech Republic ◽  
Lower Cambrian ◽  
New Combination ◽  
Upper Ordovician ◽  
Filter Feeding ◽  
Feeding Mode ◽  
The Czech Republic ◽  
Lower Ordovician ◽  
Mode Of Life

ABSTRACTA new aglaspidid arthropod, Chlupacaris dubia gen. et sp. nov., is described from the Pusgillian (lower Ashgill, Upper Ordovician) Upper Tiouririne Formation near Erfoud, southeastern Morocco. Although disarticulated, careful documenting of the tergites allows a reconstruction of the exoskeleton to be made. Although somewhat trilobite-like in appearance, the lack of facial sutures, a well-defined axis with articulating half-rings and a pygidium clearly prove Chlupacaris gen. nov. is not a trilobite. An interesting feature is the presence of a hypostome in this non-trilobite arthropod. In contrast to other aglaspidids usually considered to be carnivorous, a filter-feeding mode of life is proposed for Chlupacaris gen. nov., based on the strongly vaulted cephalon, subvertical orientation of the hypostome and less strongly vaulted trunk. Chlupacaris gen. nov. is probably most closely related to the atypical aglaspidid Tremaglaspis unite from the Tremadoc (Lower Ordovician) of the U.K., but it can also be tentatively linked to the problematic Lower Cambrian arthropods Kodymirus vagans and Kockurus grandis from the Czech Republic. The relevance and validity of previous definitions and of possibly significant characters used for identifying aglaspidids are evaluated, and as a result, a new combination of characters diagnosing Aglaspidida is proposed. Contrary to previous reports, it is suggested that aglaspidids are probably more closely related to trilobites than they are to chelicerates. This notion may be supported by the shared possession of a mineralised cuticle, a possibly similar number of cephalic appendages, and the presence of a hypostome in some forms, although this last character may alternatively be homoplastic.

Lower Ordovician (Arenig–Llanvirn) graptolites from the Notre Dame Subzone, central Newfoundland

1992 ◽  
Vol 29 (8) ◽  
pp. 1717-1733 ◽  
Author(s):  
S. Henry Williams
Keyword(s):  
Long Island ◽  
Middle Part ◽  
Black Shales ◽  
Head Group ◽  
Sedimentary Sequence ◽  
Lower Paleozoic ◽  
Lower Ordovician ◽  
The World ◽  
Paleozoic Rocks ◽  
Limestone Breccia

Many lower Paleozoic rocks in the Notre Dame Subzone of central Newfoundland are of unknown or imprecise age. Several new Lower Ordovician graptolite occurrences are here reported and earlier records revised. New graptolite localities in the Balsam Bud Cove Formation at Snooks Arm on the Baie Verte Peninsula, previously recorded as "early Ordovician (Arenig)" have yielded an assemblage identical to that found in the middle part of Bed 11 of the Cow Head Group, western Newfoundland, indicating a probable lower Didymograptus bifidus Zone age. At Corner Pond, southeast of Corner Brook, an abundant, diverse fauna from the Corner Pond formation indicates a marginally older age for the black shales than those at Snooks Arm (Pendeograptus fruticosus Zone, equivalent to lower Bed 11). Black shales associated with felsic volcanics and limestone breccia belonging to the Cutwell Group at Lushes Bight, on Long Island, western Notre Dame Bay, which were previously assigned to the widespread black shales of the Lawrence Harbour Formation and equivalents in the Exploits Subzone, contain a rich lower Llanvirn (Paraglossograptus tentaculatus Zone) graptolite assemblage. This agrees with ages established using other macrofossils and conodonts from the associated limestones. In contrast, a lower shale unit from older strata at Southern Head on the eastern end of the island yields a late Arenig Isograptus victoriae maximus Zone assemblage. These newly discovered graptolite faunas provide precise ages for the upper and lower parts of the volcano-sedimentary sequence on Long Island. Interestingly, all four graptolite assemblages discussed here are of open-ocean affinity, permitting accurate correlation with localities not only in western Newfoundland but also elsewhere in the world.

Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation

2002 ◽  
Vol 93 (4) ◽  
pp. 393-401 ◽  
Author(s):  
Daniel Vizcaïno ◽  
J. Javier Álvaro
Keyword(s):  
Statistical Analysis ◽  
Specific Level ◽  
Diversity Patterns ◽  
Early Ordovician ◽  
Fine Grained ◽  
Lower Ordovician ◽  
Montagne Noire ◽  
Bottom To Top

ABSTRACTThe litho- and biostratigraphical subdivisions of the Tremadocian-Arenigian succession of the southern Montagne Noire are hereby revised. The Lower Ordovician diversity patterns are estimated through statistical analysis of 27 families, 64 genera and 132 species of trilobites across nine interval zones; from bottom to top: the Proteuloma geinitzi, Shumardia (Conophrys) pusilla, Euloma filacovi, Taihungshania miqueli, Taihungshania shui landyranensis, Colpocoryphe maynardensis, Neseuretus (Neseuretus) arenosus, Apatokephalus incisus and Hangchungolithus primitivus zones. Maximum trilobite diversity occurred within the E. filacovi and A. incisus zones, alternating with two sharp declines (S. (C.) pusilla and T.shui landyranensis zones), in both cases drastically related to transgressive-regressive trends. Trilobites attained their highest diversity in muddy outer-platform settings, decreasing in fine-grained sandstones and siltstones of shoreface environments, where trilobites could still be numerically abundant. Four major trilobite turnovers are recognised at the bottom of the P. geinitzi, S.(C.)pusilla, E. filacovi and T. shui landyranensis zones, in which survivors from previous intervals are not reported at specific level, and important generic replacements took place. Despite the relative incompleteness of the Lower Ordovician trilobite record, envisaged after analysing the high proportion of monotypic taxa and discontinuous ranges of some families, the trilobite record is representative enough to estimate diversity patterns, although a better understanding of the palaeoenvironmental control will greatly enhance biodiversity resolution.

The pre-Mississippian "Neruokpuk Formation," northeastern Alaska and northwestern Yukon: review and new regional correlation

1991 ◽  
Vol 28 (10) ◽  
pp. 1521-1533 ◽  
Author(s):  
Larry S. Lane
Keyword(s):  
Lower Cambrian ◽  
Small Scale ◽  
Lower Paleozoic ◽  
Lower Silurian ◽  
Rock Types ◽  
Upper Proterozoic ◽  
Regional Correlation ◽  
Arctic Alaska ◽  
Lower Ordovician ◽  
Paleozoic Rocks

Since the early 1900's, regional reconnaissance in Alaska and the Yukon has failed to resolve the stratigraphy and structure of the pre-Mississippian Neruokpuk Formation. Its age and distribution have been defined and redefined as new data have slowly accumulated. In most recently published reconnaissance maps of the Yukon, the "Neruokpuk" includes nearly all of the pre-Mississippian strata in the British Mountains and is assigned a Precambrian age. In contrast, approximately half of contiguous strata in adjacent Alaska are interpreted as early Paleozoic in age and are excluded from the Neruokpuk. Recent detailed studies in the Firth River area of the Yukon have documented intense small-scale imbrication of fossiliferous Lower Cambrian to Devonian(?) units that were previously mapped as Precambrian Neruokpuk.A remarkable similarity between the lithologies of lower Paleozoic rocks in the British Mountains and the Selwyn Basin 1000 km to the southeast is strengthened by biostratigraphic ties in Lower Cambrian, Lower Ordovician, and Lower Silurian strata. This correlation between basin facies suggests that shelf and slope facies of upper Proterozoic through lower Paleozoic strata may also be correlatable between the two areas. The paleogeographic implications of these correlations indicate that pre-Mississippian strata in Arctic Alaska and the Yukon are part of a single Arctic–Pacific continental margin.The Neruokpuk Formation name should be restricted in Canada to the quartzite-dominant unit, contiguous with similar strata to which the restricted Neruokpuk definition applies in Alaska. The current broad definition, based on an assumed Proterozoic age but including many rock types, should be discontinued.

Ordovician emplacement of the Mount Dingley Diatreme, Western Ranges of the Rocky Mountains, southeastern British Columbia

1994 ◽  
Vol 31 (10) ◽  
pp. 1491-1500 ◽  
Author(s):  
B. S. Norford ◽  
M. P. Cecile
Keyword(s):  
Late Ordovician ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Fine Grained ◽  
The North ◽  
Lower Ordovician ◽  
Intrusive Rocks ◽  
Volcaniclastic Rocks ◽  
Host Rocks ◽  
Early Late

External and internal morphologies are well shown by a newly discovered diatreme that is exceptionally well exposed in a cirque within the north face of Mount Dingley. The diatreme contains abundant brecciated host rocks mixed with highly altered, fine-grained, light-green igneous fragments (minerals include muscovite, chlorite, quartz, carbonate, and some remnant K-feldspar). The diatreme cuts Lower Ordovician rocks of the McKay Group. Olistostromes and other volcaniclastic rocks that are directly associated with the diatreme are bevelled beneath a regional unconformity below the Upper Ordovician Beaverfoot Formation. Lower Ordovician gastropods are present just below the volcaniclastic rocks and within what appears to be a lens of sediment within one of the olistostrome beds. These occurrences indicate a mid-Early Ordovician time of intrusion, but there is the possibility that the pipe was emplaced later within the interval mid-Early to early Late Ordovician. In the Western Ranges, three other episodes of emplacement of diatremes have been documented previously as within the intervals early Middle to early Late Ordovician, latest Early Silurian to early Middle Devonian, and Late Permian. Many of the diatremes are broadly contemporaneous with widespread, but volumetrically small, Ordovician and Lower Paleozoic volcanic and intrusive rocks found throughout the Canadian Cordillera. These volcanic and intrusive rocks have been interpreted as evidence of continued Lower Paleozoic extensional tectonism and some are associated with large base-metal deposits.

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