Journal articles: 'Ordovician age'

1

Sun, Weidong. "The age of the Ordovician-Silurian boundary and the End Ordovician Mass Extinction." Solid Earth Sciences 4, no. 4 (December 2019): 199–200. http://dx.doi.org/10.1016/j.sesci.2019.11.007.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Sun, Weidong. "The age of the Ordovician-Silurian boundary and the End Ordovician Mass Extinction." Solid Earth Sciences 5, no. 1 (March 2020): 29–30. http://dx.doi.org/10.1016/j.sesci.2019.11.008.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Smith, M. P., and J. S. Peel. "The age of the Danmarks Fjord Member, eastern North Greenland." Rapport Grønlands Geologiske Undersøgelse 132 (December 31, 1986): 7–13. http://dx.doi.org/10.34194/rapggu.v132.7957.

Full text

Abstract:

Conodonts of late Early Ordovician age (late Canadian, early-middle Arenigian) are identified from the Danmarks Fjord Member of the Wandel Valley Formation at its type locality near the head of Danmark Fjord, eastern North Greenland. The identifications confirm recent suggestions of an Early Ordovician age for the member made on lithostratigraphic grounds, and refute earlier opinions that the dolomite was probably of Early Cambrian age.

APA, Harvard, Vancouver, ISO, and other styles

4

Wynne, P. Jane, E. Irving, Daniel J. Schulze, Douglas C. Hall, and Hewart H. Helmstaedt. "Paleomagnetism and age of three Canadian Rocky Mountain diatremes." Canadian Journal of Earth Sciences 29, no. 1 (January 1, 1992): 35–47. http://dx.doi.org/10.1139/e92-005.

Full text

Abstract:

Paleomagnetic results, and age estimates derived from them, arc presented for three diatremes, using as a basis of comparison the combined apparent polar wander (APW) path for North America and Europe of Van der Voo. The Cross diatreme of the Front Ranges of the Canadian Rocky Mountains has yielded a radiometric age of 241 Ma (earliest Triassic) and is hosted by the flat-lying Pennsylvanian Tunnel Mountain Formation. It has normal polarity magnetization and yields a paleopole correctly placed according to its radiometric age on the APW path. The Blackpool diatreme (for which no radiometric age is available), which is located in the Main Ranges of the Rocky Mountains, is known to be post-Late Ordovician because it is hosted by rocks of that age. It also has magnetization of normal polarity and yields a paleopole that, when calculated with respect to present horizontal, is coincident with the latest Cretaceous to Paleocene paleopole for North America. The paleopole, when calculated with respect to bedding, lies on the Middle Ordovician portion of the combined APW path. A clockwise rotation of 10° brings the paleopole into agreement with the latest Ordovician. Hence, from a paleomagnetic standpoint, a latest Cretaceous to Paleocene or latest Ordovician age is possible. The HP pipe (radiometric age 391 ± 5 Ma or Early Devonian), previously studied by D. T. A. Symons and M. T. Lewchuk, is hosted in limestones of Upper Cambrian to Middle Ordovician age. It has reversed polarity and yields a paleopole that, when compared with the combined APW path, suggests an age of mid-Permian, although errors are such that it could be somewhat younger, roughly coeval with the Cross diatreme. We conclude, therefore, that the radiometric age estimated for the HP pipe could be too old by about 130 million years.

APA, Harvard, Vancouver, ISO, and other styles

5

Pharaoh, T. C., T. S. Brewer, and P. C. Webb. "Subduction-related magmatism of late Ordovician age in eastern England." Geological Magazine 130, no. 5 (September 1993): 647–56. http://dx.doi.org/10.1017/s0016756800020951.

Full text

Abstract:

AbstractDeep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.

APA, Harvard, Vancouver, ISO, and other styles

6

LOPEZ-SANCHEZ, M. A., A. IRIONDO, A. MARCOS, and F. J. MARTÍNEZ. "A U–Pb zircon age (479 ± 5 Ma) from the uppermost layers of the Ollo de Sapo Formation near Viveiro (NW Spain): implications for the duration of rifting-related Cambro-Ordovician volcanism in Iberia." Geological Magazine 152, no. 2 (August 15, 2014): 341–50. http://dx.doi.org/10.1017/s0016756814000272.

Full text

Abstract:

AbstractThe uppermost metavolcanic layer of the Cambro-Ordovician Ollo de Sapo Formation, the largest accumulation of pre-Variscan igneous rocks in the Iberian Peninsula, have been dated in its northernmost part using U–Pb SHRIMP-RG zircon age techniques at 479.0 ± 4.7 Ma. The age obtained is the youngest age found so far in the metavolcanic facies of Ollo de Sapo Formation and represents the cessation of the rifting-related Cambro-Ordovician Ollo de Sapo volcanism at the northernmost tip of the Iberian Peninsula. Our results show that the Cambro-Ordovician volcanism in the NW of the Iberian Peninsula is not as short-lived as previously thought and confirm the correlation between the Cambro-Ordovician volcanic sequences that crop out in the Central Iberian Zone and the French Southern Armorican Massif. Finally, our study suggests that the cessation of the Cambro-Ordovician volcanism along the Ibero-Armorican Arc was synchronic or, less probably, slightly diachronic with younger ages towards the north (in present-day geographical coordinates).

APA, Harvard, Vancouver, ISO, and other styles

7

Peel, John S. "Ordovician gastropods from pebbles in Cretaceous fluvial sandstones in south-east Disko, West Greenland." Bulletin of the Geological Society of Denmark 67 (September 27, 2020): 75–81. http://dx.doi.org/10.37570/bgsd-2019-67-05.

Full text

Abstract:

The gastropods Sinuopea sp. and Lecanospira cf. compacta (Salter 1859) of probable early Ordovician age are described from cherty limestone clasts within fluvial strata of the Cretaceous Atane Formation of south-east Disko, central West Greenland. The record of Sinuopea possibly suggests an earliest Ordovician (Tremadocian) age, slightly older than the Floian–Dapingian age suggested by the oldest known conodont assemblages described from West Greenland. The determinations provide supporting evidence for a former periodic cover of Ordovician strata in the Archaean terrane of south western Greenland, extending deep into the heart of the Laurentian landmass.

APA, Harvard, Vancouver, ISO, and other styles

8

Sweet, Walter C. "Conodonts and biostratigraphy of Upper Ordovician strata along a shelf to basin transect in central Nevada." Journal of Paleontology 74, no. 6 (November 2000): 1148–60. http://dx.doi.org/10.1017/s0022336000017674.

Full text

Abstract:

Conodonts representing 38 species of 26 genera have been identified in samples from Upper Ordovician rocks at three central Nevada localities. Ranges of these species and associated graptolites are used graphically to determine correlation of the strata considered with an evolving composite standard that includes information from Ordovician strata at more than 100 localities in North America. Results indicate that the Hanson Creek Formation at Lone Mountain is latest Edenian through mid-Richmondian in age; that the Ordovician part of the Hanson Creek in the Monitor Range section spans an interval from Maysvillian through Richmondian; and that the upper 29 m of the Vinini Formation at the Vinini Creek locality is of mid-Maysvillian to late Richmondian age. Physical discontinuities in the Ordovician-Silurian boundary interval complicate correlations, but it is now clear that conodonts that range upward into, and have long been considered distinctive of the Lower Silurian, make their debut in central Nevada in an upper segment of the Upper Ordovician Normalograptus persculptus graptolite zone that may be latest Richmondian in age.

APA, Harvard, Vancouver, ISO, and other styles

9

Schmitz, Birger, Kenneth A. Farley, Steven Goderis, Philipp R. Heck, Stig M. Bergström, Samuele Boschi, Philippe Claeys, et al. "An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body." Science Advances 5, no. 9 (September 2019): eaax4184. http://dx.doi.org/10.1126/sciadv.aax4184.

Full text

Abstract:

The breakup of the L-chondrite parent body in the asteroid belt 466 million years (Ma) ago still delivers almost a third of all meteorites falling on Earth. Our new extraterrestrial chromite and3He data for Ordovician sediments show that the breakup took place just at the onset of a major, eustatic sea level fall previously attributed to an Ordovician ice age. Shortly after the breakup, the flux to Earth of the most fine-grained, extraterrestrial material increased by three to four orders of magnitude. In the present stratosphere, extraterrestrial dust represents 1% of all the dust and has no climatic significance. Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.

APA, Harvard, Vancouver, ISO, and other styles

10

Molyneux, S. G., and F. Paris. "Late Ordovician Palynomorphs." Journal of Micropalaeontology 4, no. 1 (March 1, 1985): 11–26. http://dx.doi.org/10.1144/jm.4.1.11.

Full text

Abstract:

Abstract. ACRITARCHSOrdovician acritarchs have been recorded in five core samples collected between 2520 ft. and 3000 ft. in Well E1-81, and ten cutting samples taken between 12150 ft. and 13240 ft. in Well J1-81A. All the assemblages recovered are of Late Ordovician age; no Early Ordovician or Middle Ordovician assemblages have been identified.Investigations have so far concentrated on the acritarch assemblages from Well El-81. The highest three Ordovician samples from depths of 2520 to 2550 ft., 2552 to 2557 ft., and 2562 to 2567 ft., yielded similar assemblages which include Veryhachium irroratum, V. cf. lairdii, V. oklahomense?, V. subglobosum, V. trispinosum, Villosacapsula setosapellicula and a new species, Striatotheca sp. A. Navifusa similis? is represented by one specimen in the sample from 2552 to 2557 ft. Another specimen from the same sample is tentatively referred to Aremoricanium syringosagis. Specimens of Baltisphaeridium, Peteinosphaeridium, Leiofusa and Eupoikilofusa occur throughout the interval 2520 to 2567 ft. but are rare. Commonly occurring species include V. irroratum and V. setosapellicula. V. irroratum has been recorded from the Middle Ordovician of North America (Loeblich & Tappan, 1969) and the Caradoc of England (Turner, 1984) but Cramer & Diez (1979) maintain that it has its acme in the Ashgill. V. setosapellicula is common in the Sylvan Shale of Oklahoma (Loeblich, 1970) which is generally understood to be of Ashgill age, but is rare in the Eden Shale (Caradoc) of Indiana (Colbath, 1979) and in the type section of the Caradoc Series in Shropshire, England (Turner, 1984). . . .

APA, Harvard, Vancouver, ISO, and other styles

11

Zhang, Shunxin. "Ordovician conodont biostratigraphy and redefinition of the age of lithostratigraphic units on northeastern Melville Peninsula, Nunavut." Canadian Journal of Earth Sciences 50, no. 8 (August 2013): 808–25. http://dx.doi.org/10.1139/cjes-2013-0009.

Full text

Abstract:

Northeastern Melville Peninsula, Nunavut, Canada, preserves the stratigraphic record of the northwestern margin of the Foxe Basin. The Ordovician sequence on the peninsula includes the Lower Ordovician Ship Point Formation and Upper Ordovician Frobisher Bay, Amadjuak, Akpatok, and Foster Bay formations. Their biostratigraphic ages and correlations are poorly understood; in particular it is unclear whether the organic-rich “Boas River Formation” exists on the peninsula. Following extensive sampling of these stratigraphic units, studies of numerous conodont elements from both outcrops and rubble at about 60 localities have established five conodont assemblages through the five lithostratigraphic units on the peninsula. Oepikodus communis – Jumudontus gananda Assemblage in the Ship Point Formation is correlated to the Reutterodus andinus Zone in the uppermost Ibexian, Lower Ordovician. The other four assemblages from the Upper Ordovician are as follows: Appalachignathus delicatulus – Polyplacognathus ramosus – Belodina confluens in the Frobisher Bay Formation correlated to lower B. confluens Zone in the upper Chatfieldian; Belodina confluens – Periodon grandis in the Amadjuak Formation to the upper B. confluens, Oulodus velicuspis, O. robustus, and lower Aphelognathus grandis zones from Edenian to lowest Richmondian; Amorphognathus ordovicicus – Plegagnathus and Rhipidognathus symmetricus – Aphelognathus cf. A. divergens in the Akpatok and Foster Bay formations to the lower and upper Richmondian. The biostratigraphy is combined with geographical information systems (GIS) and Google Earth technologies in estimating the thickness of Paleozoic strata, which reduces the likelihood of “Boas River Formation” existing on Melville Peninsula to minimum.

APA, Harvard, Vancouver, ISO, and other styles

12

Pojeta Jr., John, and Christopher A. Stott. "Nucularcidae: a new family of palaeotaxodont Ordovician pelecypods (Mollusca) from North America and Australia." Canadian Journal of Earth Sciences 44, no. 10 (October 1, 2007): 1479–501. http://dx.doi.org/10.1139/e07-028.

Full text

Abstract:

The new Ordovician palaeotaxodont family Nucularcidae and the new genus Nucularca are described. Included in Nucularca are four previously described species that have taxodont dentition: N. cingulata (Ulrich) (the type species), N. pectunculoides (Hall), N. lorrainensis (Foerste), and N. gorensis (Foerste). All four species are of Late Ordovician (Cincinnatian Katian) age and occur in eastern Canada and the northeastern USA. Ctenodonta borealis Foerste is regarded as a subjective synonym of Nucularca lorrainensis. No new species names are proposed. The Nucularcidae includes the genera Nucularca and Sthenodonta Pojeta and Gilbert-Tomlinson (1977). Sthenodonta occurs in central Australia in rocks of Middle Ordovician (Darriwilian) age. The 12 family group names previously proposed for Ordovician palaeotaxodonts having taxodont dentition are reviewed and evaluated in the Appendix.

APA, Harvard, Vancouver, ISO, and other styles

13

Nielsen, Arne Thorshøj. "A review of Ordovician agnostid genera (Trilobita)." Transactions of the Royal Society of Edinburgh: Earth Sciences 87, no. 4 (1996): 463–501. http://dx.doi.org/10.1017/s0263593300018150.

Full text

Abstract:

ABSTRACTThe definition and scope of Ordovician genera of agnostid trilobites are discussed, and the generic affiliation of Ordovician species and well-illustrated material referred to in open nomenclature is assessed. Some 198 Ordovician species plus 25 species of uncertain latest Cambrian/earliest Ordovician age are enumerated, representing 24 genera and subgenera, of whichGeragnostus (Novoagnostus)n.subg. andLotagnostus (Semagnostus)n.subg. are new.Geragnostellais ranked as a subgenus ofGeragnostus. The species ofArthrorhachisare tentatively divided among atardusspecies group and anelspethispecies group. Species ofDividuagnostusare divided among asensu strictogroup and an early species group.PseudorhaptagnostusLermontova, 1951 is restored as senior synonym ofNeoagnostusKobayashi, 1955. It is concluded that Ordovician agnostids were largely adapted to temperate and colder water habitats.

APA, Harvard, Vancouver, ISO, and other styles

14

Dean, W. T., and O. Monod. "Revised stratigraphy and relationships of Lower Palaeozoic rocks, eastern Taurus Mountains, south central Turkey." Geological Magazine 127, no. 4 (July 1990): 333–47. http://dx.doi.org/10.1017/s0016756800014898.

Full text

Abstract:

AbstractLithostratigraphic terminology is revised for rocks of Ordovician age in the eastern Taurus. The Seydişehir Formation, of late middle Cambrian to early Ordovician age, is shown to be applicable in the eastern and western Taurus as well as in south-eastern Turkey. Near Degˇirmentaş, northeast of Adana, the Seydişehir Formation is overlain, with inferred unconformity, by clastic strata of Ashgill age referred to the Şort Tepe Formation, first defined south of Hakkâri, in the Border Folds of southeastern Turkey. Palaeontological evidence is cited for the early Silurian (Llandovery) age of the unconformably overlying Halityayla Formation farther south, on the coast near Ovacik, where the Şort Tepe Formation is as yet unrecorded. A general model is proposed showing relationships of Cambrian and Ordovician rocks and faunas in southern and southeastern Turkey.

APA, Harvard, Vancouver, ISO, and other styles

15

Rohr, David M., Robert B. Blodgett, and William M. Furnish. "Maclurina manitobensis(Whiteaves) (Ordovician Gastropoda): the largest known Paleozoic gastropod." Journal of Paleontology 66, no. 6 (November 1992): 880–84. http://dx.doi.org/10.1017/s0022336000021004.

Full text

Abstract:

The concept of the Ordovician gastropod genusMacluritesLe Sueur, 1818, at present includes much variation.MaclurinaUlrichinUlrich and Scofield, 1897, is removed as a subjective synonym ofMacluritesand reestablished as a separate genus. Species ofMacluriteswith spiral grooves on the outer whorl surface and a relatively small umbilicus are transferred toMaclurina. Maclurina manitobensis(Whiteaves, 1890) forms a distinctive part of the Late Ordovician-age “Arctic Ordovician fauna.” An unusually large specimen (25 cm in diameter) from the Bighorn Dolomite (Upper Ordovician), Wyoming, is illustrated; this Wyoming specimen is the volumetrically largest Paleozoic gastropod ever reported.

APA, Harvard, Vancouver, ISO, and other styles

16

Lynas, B. D. T., C. C. Rundle, and R. W. Sanderson. "A note on the age and pyroxene chemistry of the igneous rocks of the Shelve Inlier, Welsh Borderland." Geological Magazine 122, no. 6 (November 1985): 641–47. http://dx.doi.org/10.1017/s0016756800032040.

Full text

Abstract:

AbstractGeological survey, electron microprobe analyses of clinopyroxenes and isotopic age determinations have revealed that the intrusive dolerites and basic–intermediate lavas of the Shelve Ordovician Inlier are part of a co-magmatic suite which show transitional affinities between tholeiites and alkali basalts. The ages of most of the intrusives are shown to be mid-Ordovician.

APA, Harvard, Vancouver, ISO, and other styles

17

MILLER, C., M. THÖNI, W. FRANK, B. GRASEMANN, U. KLÖTZLI, P. GUNTLI, and E. DRAGANITS. "The early Palaeozoic magmatic event in the Northwest Himalaya, India: source, tectonic setting and age of emplacement." Geological Magazine 138, no. 3 (May 2001): 237–51. http://dx.doi.org/10.1017/s0016756801005283.

Full text

Abstract:

In the High Himalayan Crystalline Series of Northwest India, numerous peraluminous granites intruded the metasediments of the late Proterozoic to early late Cambrian Haimanta Group. Nd and Sr isotope systematics confirm that they were derived from heterogeneous crustal sources. New geochronological data from two plutons range in age from late Precambrian to early Ordovician: single zircon U–Pb dating yielded an age of 553 ± 2 (2σ) Ma for the Kaplas granite, whereas mineral Sm–Nd isotope systematics define a crystallization age of 496 ± 14 (2σ) Ma for the tholeiitic mafic rocks in the Mandi pluton, where evidence of magma mingling documents a close association between mafic and granitic melts. The end of this period of magmatic activity coincides with the depositional gap below the Ordovician transgression, caused by surface uplift and erosion, that is an important feature in the stratigraphy of the Northwest Himalaya. In Spiti, the transgression of the Ordovician basal conglomerates on a normal fault indicates pre-Ordovician extensional faulting. Therefore, the early Palaeozoic magmatic activities in the Northwest Himalaya could be correlated with a late extensional stage of the long-lasting Pan-African orogenic cycle which ended with the formation of the Gondwana supercontinent.

APA, Harvard, Vancouver, ISO, and other styles

18

Antonuk, R. M., A. A. Tretyakov, K. E. Degtyarev, and A. B. Kotov. "Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation." Доклады Академии наук 484, no. 1 (May 1, 2019): 61–65. http://dx.doi.org/10.31857/s0869-5652484161-65.

Full text

Abstract:

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

APA, Harvard, Vancouver, ISO, and other styles

19

Chen, Ya-Dong, Shoufa Lin, and Cees R. van Staal. "Detrital zircon geochronology of a conglomerate in the northeastern Cape Breton Highlands: implications for the relationships between terranes in Cape Breton Island, the Canadian Appalachians." Canadian Journal of Earth Sciences 32, no. 2 (February 1, 1995): 216–23. http://dx.doi.org/10.1139/e95-018.

Full text

Abstract:

Cape Breton Island has been interpreted as consisting of four zones of pre-Carboniferous rocks, but the relationships among them are controversial. To help resolve the controversy, we have dated detrital zircons from a conglomerate (part of the Cheticamp Lake Gneiss) in the Aspy terrane in the northeastern Cape Breton Highlands using the U–Pb method. The following ages were obtained: 462 ± 2 Ma (Middle Ordovician); ~492–488 Ma (6 ages; Early Ordovician); 552 ± 3 Ma (latest Precambrian–Early Cambrian); 620 ± 13 and 687 ± 4 Ma (Cadomian); and 809 ± 17, 1423 ± 10, 1462 ± 12, 1605 ± 14, 1644 ± 4, and 1911 ± 5 Ma (Proterozoic). The Middle Ordovician age sets a maximum age limit for deposition of the conglomerate, and supports an Ordovician–Silurian age for the Cheticamp Lake Gneiss. The Early Ordovician, latest Precambrian–Early Cambrian, and Cadomian ages match published ages from the Bras d'Or terrane (and its correlatives) and the Mira terrane (and its correlatives), and indicate provenance of the conglomerate from both terranes. They also indicate that the Bras d'Or and Mira terranes had been connected by the time of deposition of the conglomerate. The combination of the Cadomian and the Proterozoic ages is typical of parts of South America, supporting a suggestion that the Avalon Composite Terrane was derived from South America.

APA, Harvard, Vancouver, ISO, and other styles

20

DAVIDEK, K., E. LANDING, S. A. BOWRING, S. R. WESTROP, A. W. A. RUSHTON, R. A. FORTEY, and J. M. ADRAIN. "New uppermost Cambrian U–Pb date from Avalonian Wales and age of the Cambrian–Ordovician boundary." Geological Magazine 135, no. 3 (May 1998): 303–9. http://dx.doi.org/10.1017/s0016756898008711.

Full text

Abstract:

A crystal-rich volcaniclastic sandstone in the lower Peltura scarabaeoides Zone at Ogof-ddû near Criccieth, North Wales, yields a U–Pb zircon age of 491∓1 Ma. This late Late Cambrian date indicates a remarkably young age for the Cambrian–Ordovician boundary whose age must be less than 491 Ma. Hence the revised duration of the post-Placentian (trilobite-bearing) Cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by Ordovician graptolites and Mesozoic ammonites.

APA, Harvard, Vancouver, ISO, and other styles

21

Riva, John, and Michel Malo. "Age and correlation of the Honorat Group, southern Gaspé Peninsula." Canadian Journal of Earth Sciences 25, no. 10 (October 1, 1988): 1618–28. http://dx.doi.org/10.1139/e88-154.

Full text

Abstract:

The Honorat Group of southern Gaspé consists of two formations: the Arsenault and the Garin. The Arsenault Formation, heretofore considered barren, has yielded a graptolite faunule indicative of a Llanvirn–Llandeilo age (early Middle Ordovician), suggesting a correlation with the lower Mictaw Group of Gaspé as revised by de Broucker. A hiatus of indeterminate magnitude, corresponding to the Taconic unconformity, probably separates the Arsenault Formation from the overlying Garin Formation. The Garin has yielded graptolites ranging from the upper Climacograptus spiniferus Zone to the Paraclimatograptus manitoulinensis Zone (late Middle to early Late Ordovician). The C. spiniferus Zone graptolites are identical to those of the upper γ sequence of the Cloridorme Formation of northern Gaspé and the Blind Brook Formation of the Munsungun Anticlinorium of Maine but differ somewhat from those from the upper Tetagouche Group of New Brunswick, which are closer to those from the Summerford and Exploits groups of north-central Newfoundland. The C. spiniferus zone has a wide distribution in eastern North America. It correlates with the Orthograptus amplexicaulis Zone of the southwestern United States and with the Climacograptus baragwathi Zone (Ea2) of the Pacific faunal province.The Matapédia Group, stratigraphically above the Honorat Group, has yielded both shelly fossils and a few graptolites. The ages of the graptolites now date it as Late Ordovician to late Early Silurian (Dicellograptus complanatus Zone – Monograptus sedgwickii Zone).

APA, Harvard, Vancouver, ISO, and other styles

22

LANDING, E., S. A. BOWRING, K. L. DAVIDEK, A. W. A. RUSHTON, R. A. FORTEY, and W. A. P. WIMBLEDON. "Cambrian–Ordovician boundary age and duration of the lowest Ordovician Tremadoc Series based on U–Pb zircon dates from Avalonian Wales." Geological Magazine 137, no. 5 (September 2000): 485–94. http://dx.doi.org/10.1017/s0016756800004507.

Full text

Abstract:

Two thin volcaniclastic sandstone beds in the Bryn-llin-fawr road section in North Wales overlie an apparent sequence boundary within the uppermost Cambrian Acerocare Zone and are overlain by lowest Ordovician (lower Tremadoc) Rhabdinopora faunas. U–Pb geochronology of zircons from these sandstones yields a maximum Cambrian–Ordovician boundary age of 489±0.6 Ma. This age indicates both that the Tremadoc Series (lowest Ordovician) may be shorter in duration than was previously thought and that the duration of the Middle and Late Cambrian (c. 22 Ma) was much less than that of the Early Cambrian (c. 33 Ma). Cambrian trilobite zones locally had an average duration as short as 1 Ma.

APA, Harvard, Vancouver, ISO, and other styles

23

Kusky, T. M., J. S. Chow, and S. A. Bowring. "Age and origin of the Boil Mountain ophiolite and Chain Lakes massif, Maine: implications for the Penobscottian orogeny." Canadian Journal of Earth Sciences 34, no. 5 (May 1, 1997): 646–54. http://dx.doi.org/10.1139/e17-051.

Full text

Abstract:

The Boil Mountain ophiolite complex of west-central Maine is widely interpreted to mark the Lower Ordovician Penobscottian suture between the Dunnage, Chain Lakes, and Gander terranes. The ophiolite consists of two distinct volcanic groups, including a lower island-arc tholeiite sequence and an upper mid-ocean-ridge basalt sequence. A new Middle Ordovician 477 ± 1 Ma U–Pb age on a tonalite sill that intrudes the lower volcanic–gabbroic sequence is younger than other ca. 500 Ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the Chain Lakes massif. A comparison of ages and paleogeography of the Boil Mountain ophiolite with ophiolitic sequences in Quebec and Newfoundland indicates that the Taconian and Penobscottian orogenies and ophiolite obduction occurred simultaneously, although on different margins of the Iapetus Ocean. The Taconian ophiolite sequences were obducted onto the Appalachian margin of Laurentia during its collision with the Notre Dame – Bronson Hill belt in the Middle Ordovician, whereas the Boil Mountain ophiolite was obducted onto the Gander margin of Gondwana during its collision with the Exploits subzone – Penobscot arc of the Dunnage terrane in the Lower – Middle Ordovician. We suggest that the lower volcanic–gabbroic sequence of the Boil Mountain ophiolite represents the fore-arc ophiolitic basement to the Penobscot arc. Middle Ordovician rifting of the Penobscottian orogenic collage on the Gander margin formed a new volcanic sequence (Popelogan arc) in front of a growing back-arc basin, and erupted the upper tholeiitic sequence of the Boil Mountain ophiolite in a back-arc-basin setting. The tonalité sill formed during this event by partial melting of the lower volcanic–gabbroic sequence. Spreading in this back-arc basin (Tetagouche basin) brought a fragment of the Gander margin (Chain Lakes massif), along with an allochthonous ophiolitic cover (Boil Mountain complex) across Iapetus, where it collided with the Taconic modified margin of North America in the Late Ordovician and was then intruded by the Ashgillian Attean pluton.

APA, Harvard, Vancouver, ISO, and other styles

24

Dix, George R., Osman Salad Hersi, and Godfrey S. Nowlan. "The PotsdamBeekmantown Group boundary, Nepean Formation type section (Ottawa, Ontario): a cryptic sequence boundary, not a conformable transition." Canadian Journal of Earth Sciences 41, no. 8 (August 1, 2004): 897–902. http://dx.doi.org/10.1139/e04-040.

Full text

Abstract:

There are two unreconciled interpretations for the age and character of the boundary separating the CambrianOrdovician Potsdam and Beekmantown groups that underlie the Ottawa Embayment in eastern Ontario. These stratal groups consist of interior facies of the central Laurentian Platform. As exposed in the type section of the Nepean Formation (upper Potsdam Group), located in the City of Ottawa, the boundary was previously interpreted to be conformable and of Early Ordovician age. This intepretation was of enormous impact on subsequent regional geology compilations that showed a diachronous boundary across the platform interior. From recent subsurface analysis across eastern Ontario, the contact was interpreted to be disconformable, a sequence boundary separating Late Cambrian and Early Ordovician strata. This paper reexamines the type section. Lithologically, the group boundary should be repositioned downsection by ~1.5 m. The contact now lies coincident with a disconformity that has a paleorelief of < 10 cm. The proposed revision is geologically significant. Previous collections of Early Ordovician conodonts from the type section, used to define the age of what had been interpreted to be upper Potsdam strata, now fall entirely within the lower Beekmantown Group. Nepean (Potsdam) strata exposed in the type section remain undated. Regional correlation of the disconformity across the Laurentian platform suggests that Nepean strata at the type section are likely of Late Cambrian age. There now exists a regionally coherent separation of Cambrian and Ordovician sedimentation patterns in the Ottawa Embayment.

APA, Harvard, Vancouver, ISO, and other styles

25

Trettin, H. P. "Pearya: a composite terrane with Caledonian affinities in northern Ellesmere Island." Canadian Journal of Earth Sciences 24, no. 2 (February 1, 1987): 224–45. http://dx.doi.org/10.1139/e87-025.

Full text

Abstract:

In Ellesmere Island, the Canadian Shield and Arctic Platform are flanked on the northwest by the lower Paleozoic Franklinian mobile belt, which comprises an unstable shelf (miogeocline) and a deep-water basin, divisible into an inner sedimentary belt and an outer sedimentary–volcanic belt. Both are tied to the shelf by interlocking facies changes, but additional exotic units may be present in the outer belt.Pearya, bordering the deep-water basin on the northwest, is divisible into four successions. Succession I comprises sedimentary and(?) volcanic rocks, deformed, metamorphosed to amphibolite grade, and intruded by granitic plutons at 1.0–1.1 Ga. Succession II consists mainly of platformal sediments (carbonates, quartzite, mudrock), with smaller proportions of mafic and siliceous volcanics, diamictite, and chert ranging in age from Late Proterozoic (Hadrynian) to latest Cambrian or Early Ordovician. Its concealed contact with succession I is tentatively interpreted as an angular unconformity. Succession III (Lower to Middle Ordovician?) includes arc-type and ocean-floor volcanics, chert, mudrock, and carbonates and is associated with fault slices of Lower Ordovician (Arenig) ultramafic–mafic complexes–possibly dismembered ophiolites. The faulted contact of succession III and the ultramafics with succession II is unconformably overlapped by succession IV, 7–8 km of volcanic and sedimentary rocks ranging in age from late Middle Ordovician (Blackriverian = early Caradoc) to Late Silurian (late Ludlow?). The angular unconformity at the base of succession IV represents the early Middle Ordovician (Llandeilo–Llanvirn) M'Clintock Orogeny, which was accompanied by metamorphism up to amphibolite grade and granitic plutonism. Pearya is related to the Appalachian–Caledonian mobile belt by the Grenville age of its basement, the age of its ultramafic–mafic complexes, and evidence for a Middle Ordovician orogeny, comparable in age and character to the Taconic. By contrast, the Franklinian mobile belt has a Lower Proterozoic (Aphebian) – Archean basement and was not deformed in the Ordovician. Stratigraphic–structural evidence suggests that Pearya was transported by sinistral strike slip as three or more slices and accreted to the Franklinian deep-water basin in the Late Silurian under intense deformation. The inferred sinistral motion is compatible with derivation from the northern Caledonides.

APA, Harvard, Vancouver, ISO, and other styles

26

Frey, Robert C. "The paleoecology of a Late Ordovician shale unit from southwest Ohio and southeastern Indiana." Journal of Paleontology 61, no. 2 (March 1987): 242–67. http://dx.doi.org/10.1017/s0022336000028444.

Full text

Abstract:

The Treptoceras duseri shale unit within the Waynesville Formation of Late Ordovician (early Richmondian) age in southwest Ohio and the equivalent Trilobite shale unit in the same formation exposed in adjacent portions of Indiana represent an Ordovician shallow marine mud-bottom epeiric sea facies. These fine-grained elastics contain a moderately diverse mollusk-trilobite assemblage dominated by vagrant epifaunal detritus-feeding calymenid and asaphid trilobites, large endobyssate and infaunal filter-feeding pelecypods, and nektonic nautiloids. Articulate brachiopods, ectoprocts, and pelmatozoan echinoderms form only minor elements of this fauna.This mollusk-trilobite assemblage was common in Late Ordovician shallow marine clastic environments where mobility was an asset and there was an abundance of oxygen and food resources. Such assemblages are characteristic of the Lorraine Fauna of Late Ordovician (Edenian to Richmondian) age that occurs from the Ohio Valley north and east into New York, Ontario, Quebec, and Ireland. These early Paleozoic mud-bottom assemblages were considerably modified by the Late Ordovician extinction event and were replaced in the Silurian and Devonian by distinctly different assemblages dominated by large epifaunal strophomenid and spiriferid brachiopods, crinoids, and phacopid trilobites.

APA, Harvard, Vancouver, ISO, and other styles

27

KOBAYASHI, Teiichi. "On the Pacific biogeography of the Cambro-Ordovician age." Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences 62, no. 10 (1986): 373–76. http://dx.doi.org/10.2183/pjab.62.373.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Lefebvre, Bertrand, Juan C. Gutiérrez-Marco, Oliver Lehnert, Emmanuel L. O. Martin, Hendrik Nowak, Mustapha Akodad, Khadija El Hariri, and Thomas Servais. "Age calibration of the Lower Ordovician Fezouata Lagerstätte, Morocco." Lethaia 51, no. 2 (September 19, 2017): 296–311. http://dx.doi.org/10.1111/let.12240.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Trythall, R. J. B., C. Eccles, S. G. Molyneux, and W. E. G. Taylor. "Age and controls of ironstone deposition (Ordovician) North Wales." Geological Journal 22, S1 (April 1987): 31–43. http://dx.doi.org/10.1002/gj.3350220505.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Ilyin, D. А., T. E. Elshina, and S. Yu Katsko. "Development of a Methodology for Geoinformation Support for Geological Research of Ordovician Rocks of Gorny Altai." Interexpo GEO-Siberia 6 (May 18, 2022): 68–75. http://dx.doi.org/10.33764/2618-981x-2022-6-68-75.

Full text

Abstract:

The relevance of the topic is determined by the fact that many rocks of the Ordovician age have been found in the Altai Mountains, which may be of interest to scientists studying the geology and paleontology of this period. The problem is connected that at the moment there are no maps with outcrops of Ordovician rocks in the public domain, there are only diagrams and schematic maps without a coordinate reference. The aim of the work is to develop a methodology for geoinformation support for geological research of Gorny Altai. To achieve this goal, it is necessary to solve the following tasks: geological survey and mapping of the territory of Gorny Altai; study of geological sections of the Ordovician age with consideration of their lithological specificity and taxonomic composition of faunal groups; prepare a multiscale cartographic framework. In the future, it is planned to create a geoportal that will display outcrops of Ordovician rocks and contain information on lithology and taxonomic composition.

APA, Harvard, Vancouver, ISO, and other styles

31

Kim, Dong Hee, and Duck K. Choi. "Jujuyaspis and associated trilobites from the Mungok Formation (Lower Ordovician), Yongwol, Korea." Journal of Paleontology 74, no. 6 (November 2000): 1031–42. http://dx.doi.org/10.1017/s0022336000017595.

Full text

Abstract:

The trilobite genus Jujuyaspis Kobayashi, 1936, an index fossil of earliest Ordovician age, is recorded from the Yosimuraspis Zone of the Mungok Formation (Lower Ordovician) for the first time in Korea. The Yosimuraspis Zone comprises Yosimuraspis vulgaris Kobayashi, 1960; Jujuyaspis sinensis Zhou in Chen et al., 1980; Elkanaspis jilinensis Qian in Chen et al 1985; and pilekid genus and species indeterminate. Closely comparable faunas to the Yosimuraspis Zone are well represented in North China. The occurrence of Jujuyaspis allows the correlation of the Yosimuraspis Zone with the earliest Ordovician faunas of North America, South America, and Scandinavia, and suggests that the Cambrian-Ordovician boundary in Korea be placed at the base of the Yosimuraspis Zone.

APA, Harvard, Vancouver, ISO, and other styles

32

Schofield, David I., John W. F. Waldron, Chris E. White, and Sandra M. Barr. "Discussion of the reply by R.L. Romer and U. Kroner on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” 1Appears in Canadian Journal of Earth Sciences, 49(6): 775–780, 10.1139/e2012-006." Canadian Journal of Earth Sciences 49, no. 11 (November 2012): 1372–77. http://dx.doi.org/10.1139/e2012-049.

Full text

Abstract:

In their article ‘Reply to the discussion by J.W.F. Waldron and C.E. White on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”’, R.L. Romer and U. Kroner reinterpret geochronological data presented by J.W.F. Waldron, D.I. Schofield, C.E. White, and S.M. Barr to imply an Ordovician, not a Cambrian, depositional age for the succession of the Harlech Dome, North Wales, and Meguma Supergroup, Nova Scotia. However, an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally Cambrian. Waldron et al. used the U–Pb zircon laser-ablation – multicollector – inductively coupled plasma – mass spectrometry technique primarily to provide information on sediment provenance and not depositional age. Investigation of anomalously young 206Pb/238U ages showed evidence of Pb loss. These data provide little constraint on depositional age and cannot be used to infer that the Harlech Grits Group is Ordovician.

APA, Harvard, Vancouver, ISO, and other styles

33

Loydell, David K., Andrew Mallett, Donald G. Mikulic, Joanne Kluessendorf, and Rodney D. Norby. "Graptolites from near the Ordovician-Silurian boundary in Illinois and Iowa." Journal of Paleontology 76, no. 1 (January 2002): 134–37. http://dx.doi.org/10.1017/s0022336000017418.

Full text

Abstract:

The Wilhelmi Formation of Illinois and the Mosalem Formation of Iowa contain monospecific assemblages of the stratigraphically important species Normalograptus parvulus Lapworth. This species is confined elsewhere to the uppermost Ordovician Normalograptus persculptus Biozone and the lower part of the lowermost Silurian Parakidograptus acuminatus Biozone. The presence of this graptolite raises the possibility that the lowermost parts of the Wilhelmi and Mosalem formations are of late Ordovician age rather than of early Silurian age as previously thought.

APA, Harvard, Vancouver, ISO, and other styles

34

Fortey, Richard A., Alan P. Heward, and C. Giles Miller. "Sedimentary facies and trilobite and conodont faunas of the Ordovician Rann Formation, Ras Al Khaimah, United Arab Emirates." GeoArabia 16, no. 4 (October 1, 2011): 127–52. http://dx.doi.org/10.2113/geoarabia1604127.

Full text

Abstract:

ABSTRACT The Rann Formation occurs as unique ‘exotic’ rafts in front of the Semail Ophiolite in the northern Oman Mountains. Its Ordovician age has been poorly constrained and it is often associated with the Ayim rock unit, which has been considered Devonian, Carboniferous or Ordovician by different workers. Here we present new trilobite and conodont evidence for the Ordovician ages of the three members of the Rann Formation, which includes the Ayim. The members are readily distinguishable on sedimentological and faunal grounds. The Lower Member comprises shales, quartzitic sandstones and thin fossiliferous shell beds. Large Cruziana are common, as is lingulacean debris and, at several horizons, possible hyolithids. Assemblages of graptolites, acritarchs, trilobites (Neseuretus cf. arenosus and Taihungshania cf. miqueli) and conodonts (Baltoniodus sp., Drepanodus arcuatus, Drepanoistodus sp. and Protopanderodus sp., Scolopodus sp.) are considered to range in age from Floian to early Dapingian, late Early Ordovician. The Ayim Member (previously formation) consists of fossiliferous shales and griotte-like nodular bioclastic limestones. The member is distinguished by its red colour and by numerous orthoconic nautiloids. Conodont faunas (Complexodus cf. originalis, Eoplacognathus protoramosus, Dapsilodus sp., Cornuodus sp. and Panderodus sp.) imply a late Darriwilian, Middle Ordovician age. The Upper Member consists of siltstones and sandstones generally lacking bioturbation and with rare shell beds and faunas. Trilobites (Deanaspis goldfussii seftenbergi, Vietnamia teichmulleri and Dreyfussina taouzensis) and chitinozoans are interpreted to indicate an early-middle Katian, Late Ordovician age. The three members represent shallow-marine deposits on a continental shelf subject to changing sand supply, storm-wave activity and sea-bottom oxygenation. The three periods of deposition, Floian – early Dapingian, late Darriwilian and early – middle Katian, correspond to highstands of Paleo-Tethys that also flooded interior Oman and Arabia. The limited burial and lack of metamorphism of the Rann is remarkable given its proximity to the Semail Ophiolite and to subduction related metamorphic rocks occurring nearby.

APA, Harvard, Vancouver, ISO, and other styles

35

Evans, J. A. "Resetting of the Rb–Sr whole-rock isotope system of an Ordovician microgranite during Devonian low-grade metamorphism." Geological Magazine 126, no. 6 (November 1989): 675–79. http://dx.doi.org/10.1017/s0016756800006968.

Full text

Abstract:

AbstractThe Bwlch y Cywion microgranite intrudes an Ordovician sedimentary sequence in northeast Snowdonia, North Wales. Its age is recorded by hornfelses within its metamorphic aureole which give an Ordovician age of 454 ± 20 Ma. The whole-rock Rb–Sr isotope systems of the intrusion, however, and of an associated ash-flow tuff and a rhyolite of the Llewelyn Volcanic Group (Caradoc), were reset during low-grade metamorphism and give Devonian ages of 392±11 Ma, 392±5 Ma, and 405 ± 6 Ma, respectively.

APA, Harvard, Vancouver, ISO, and other styles

36

Rasmussen, Christian M. Ø., Björn Kröger, Morten L. Nielsen, and Jorge Colmenar. "Cascading trend of Early Paleozoic marine radiations paused by Late Ordovician extinctions." Proceedings of the National Academy of Sciences 116, no. 15 (March 25, 2019): 7207–13. http://dx.doi.org/10.1073/pnas.1821123116.

Full text

Abstract:

The greatest relative changes in marine biodiversity accumulation occurred during the Early Paleozoic. The precision of temporal constraints on these changes is crude, hampering our understanding of their timing, duration, and links to causal mechanisms. We match fossil occurrence data to their lithostratigraphical ranges in the Paleobiology Database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high-resolution time slices. In addition, we apply capture–recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates. Our method reveals a stepwise biodiversity increase with distinct Cambrian and Ordovician radiation events that are clearly separated by a 50-million-year-long period of slow biodiversity accumulation. The Ordovician Radiation is confined to a 15-million-year phase after which the Late Ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years. Based on a first-differences approach on potential abiotic drivers controlling richness, we find an overall correlation with oxygen levels, with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present-day levels during the Middle Ordovician Darriwilian Age. Contrary to the traditional view of the Late Ordovician extinctions, our study suggests a protracted crisis interval linked to intense volcanism during the middle Late Ordovician Katian Age. As richness levels did not return to prior levels during the Silurian—a time of continental amalgamation—we further argue that plate tectonics exerted an overarching control on biodiversity accumulation.

APA, Harvard, Vancouver, ISO, and other styles

37

Vandenbroucke, Thijs R. A., Sarah E. Gabbott, Florentin Paris, Richard J. Aldridge, and Johannes N. Theron. "Chitinozoans and the age of the Soom Shale, an Ordovician black shale Lagerstätte, South Africa." Journal of Micropalaeontology 28, no. 1 (May 1, 2009): 53–66. http://dx.doi.org/10.1144/jm.28.1.53.

Full text

Abstract:

Abstract. Isolated chitinozoans from the Soom Shale Member of the Cedarberg Formation, SW South Africa are described and provide a date of the latest Hirnantian–earliest Rhuddanian. The recovered chitinozoans are typical of the latest Ordovician Spinachitina oulebsiri Biozone, although an earliest Silurian age is possible. They indicate a very short time span (less than 1 Ma) across the Ordovician–Silurian boundary. This is currently the highest biostratigraphical resolution attainable for the Soom Shale Lagerstätte. Correlation of the Soom Shale chitinozoans with identical assemblages in post-glacial, transgressive deposits of Northern Africa is possible; both faunas occur in shales that overlie glacial diamictites of the Hirnantian glaciation. A new species, Spinachitina verniersi n. sp. is described.

APA, Harvard, Vancouver, ISO, and other styles

38

Gallagher, V., P. J. O'Connor, and M. Aftalion. "Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite." Geological Magazine 131, no. 5 (September 1994): 669–84. http://dx.doi.org/10.1017/s0016756800012450.

Full text

Abstract:

AbstractThe Croghan Kinshelagh alkali granite intrudes a cleaved volcano-sedimentary sequenceon the border of counties Wicklow and Wexford in southeast Ireland. U-Pb dating of zircons fromthe granite indicate a mid-Caradoc emplacement age of 454 ± 1 Ma. The Duncannon Group hostrocks form the southwestern end of the Avoca Volcanic Belt, a Mid-Ordovician (Caradoc) sequenceof acid and intermediate lavas and volcaniclastics. Dolerite dykes intrude the granite; elsewhere in theregion dolerites are generally associated with volcanic rocks. The main, Dl deformation within theDuncannon Group rocks is manifest as a steep Dl cleavage generally regarded as a product of LateCaledonian regional deformation in southeast Ireland. The Croghan Kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the Caradoc volcanic rocks; relativelyhigh Th, Y, Nb and REE contents set it apart from any other known granite type in southeastIreland. Together with the geochemical evidence, the age determination of 454 Ma indicates that theCroghan Kinshelagh granite was generated and emplaced during Ordovician volcanism in southeastIreland. Volcanism was closely followed by penetrative deformation and emplacement of the granite.The intra-Ordovician deformation may have been a consequence of closure of the Iapetus Ocean ormore localized events such as accretion on the hanging wall of the subduction zone. The age of theCroghan Kinshelagh granite provides an important datum for Ordovician volcanism and subductionin southeast Ireland.

APA, Harvard, Vancouver, ISO, and other styles

39

Zhang, Shunxin. "Upper Cambrian and Lower Ordovician conodont biostratigraphy and revised lithostratigraphy, Boothia Peninsula, Nunavut." Canadian Journal of Earth Sciences 57, no. 9 (September 2020): 1030–47. http://dx.doi.org/10.1139/cjes-2020-0006.

Full text

Abstract:

The strata exposed along Lord Lindsay River on southern Boothia Peninsula were previously named the Netsilik Formation, and then recognized as the Turner Cliffs Formation; the interpretation of the age and correlation was based on limited data. New detailed field investigation at 23 localities along the section resulted in the discovery of over 640 identifiable conodont specimens, with 35 species representing 16 genera, among which a new species, Rossodus? boothiaensis sp. nov., is recognized. Five North American standard conodont zone/subzone-equivalent faunas are documented from the section, namely the Hirsutodontus hirsutus Subzone-equivalent, Cordylodus angulatus, Rossodus manitouensis, Acodus deltatus/Oneotodus costatus and Oepikodus communis Zone-equivalent faunas. These faunas enable a new understanding of the age and stratigraphic position of the Netsilik and Turner Cliffs formations on southern Boothia Peninsula. The Netsilik Formation can be correlated with the lower member (except for the lowest part) and upper member of the Turner Cliffs Formation; the previously unmeasured upper part of the section can be associated with the lower Ship Point Formation. Based on the new conodont data, these three units are dated as early Age 10, late Cambrian to middle Tremadocian, Early Ordovician; late Tremadocian, Early Ordovician; and early Floian, Early Ordovician, respectively. This study fills a gap in upper Cambrian and Lower Ordovician biostratigraphy on Boothia Peninsula, and links the regional biostratigraphy to that of Laurentia.

APA, Harvard, Vancouver, ISO, and other styles

40

Luo, Liang, Lianbo Zeng, Kai Wang, Xiaoxia Yu, Yihang Li, Chenxi Zhu, and Shuning Liu. "Provenance investigation for the Cambrian–Ordovician strata from the northern margin of the western Yangtze Block: implications for locating the South China Block in Gondwana." Geological Magazine 157, no. 4 (October 25, 2019): 551–72. http://dx.doi.org/10.1017/s0016756819001110.

Full text

Abstract:

AbstractWe report new U–Pb isotopic data for detrital zircons from Cambrian–Ordovician strata on the northern margin of the western Yangtze Block, which together with published U–Pb isotopic data for coeval strata in the South China Block, provide critical constraints on the provenance of these sediments and further shed light on the early Palaeozoic position of the South China Block in the context of Gondwana. Detrital zircons in this study yield four major age peaks in the early Palaeoproterozoic, early Neoproterozoic, middle Neoproterozoic and late Neoproterozoic – early Palaeozoic. The dominant age population of 900–700 Ma matches well with magmatic ages from the nearby Panxi–Hannan Belt, which indicates that Cambrian–Ordovician sedimentary rocks in the western Yangtze Block were mainly of local derivation. However, compilations of detrital zircon ages for the Cambrian–Ordovician strata from the Cathaysia Block and the eastern Yangtze Block show that both blocks are dominated by late Mesoproterozoic- and early Neoproterozoic-aged detrital zircons, which suggests a remarkable exotic input with typical Gondwana signatures. According to the integrated detrital zircon age spectra of the Cambrian–Ordovician sedimentary rocks from the entire South China Block and palaeocurrent data, the South China Block should have been linked with North India and Western Australia within East Gondwana. Specifically, the Cathaysia Block was located adjacent to Western Australia, while the Yangtze Block was connected with North India.

APA, Harvard, Vancouver, ISO, and other styles

41

Pigage, L. C., J. L. Crowley, L. J. Pyle, J. G. Abbott, C. F. Roots, and M. D. Schmitz. "U–Pb zircon age of an Ordovician tuff in southeast Yukon: implications for the age of the Cambrian–Ordovician boundary1Yukon Geological Survey Contribution 013.2Geological Survey of Canada Earth Science Sector (ESS) Contribution 20110362." Canadian Journal of Earth Sciences 49, no. 6 (June 2012): 732–41. http://dx.doi.org/10.1139/e2012-017.

Full text

Abstract:

Three conodont fossil occurrences stratigraphically above and below a rhyolitic tuff in the Lower Ordovician Crow Formation, southeast Yukon, constrain the tuff to the early Tremadocian Rossodus manitouensis Zone and possibly the Rossodus tenuis Zone. U–Pb dates were obtained from zircon from the tuff that was imaged with cathodoluminescence and chemically abraded to reduce the likelihood of dating grains that contain older components or suffered Pb loss, respectively. Six dates from grains with oscillatory parallel zoning are equivalent, with a weighted mean 206Pb/238U date of 491.04 ± 0.13 Ma. These grains are interpreted as being primary volcanic crystals, and the date is therefore taken as the depositional age of the tuff. Four other dates from grains with sector zoning are slightly older, up to 492.0 Ma, and are interpreted as inherited or recycled from earlier volcanics. The currently defined Cambrian–Ordovician boundary is inferred to be below the tuff and separated from it by at least two conodont biostratigraphic zones that are estimated to span at least 2.25 Ma based on the top of the Rhabdinopora flabelliformis parabola graptolite zone being older than the base of the Rossodus tenuis conodont zone. We interpret the evidence in southeast Yukon to suggest that the global Cambrian–Ordovician boundary is older (>493.3 Ma) than previous estimates of ∼488 and 491 Ma based upon legacy 207Pb/206Pb zircon ages.

APA, Harvard, Vancouver, ISO, and other styles

42

Robson, Sean P., and Graham A. Young. "Late Ordovician conulariids from Manitoba, Canada." Journal of Paleontology 87, no. 5 (September 2013): 775–85. http://dx.doi.org/10.1666/12-0370.

Full text

Abstract:

Six species of conulariids, assigned to four genera, were recovered from the type locality of the Cat Head Member of the Red River Formation in southern Manitoba, Canada. These are middle Katian (Late Ordovician) in age. The most abundant conulariid species from this locality, Conularia porcella, is new, and is represented by 21 specimens. Additionally, 28 three-dimensionally preserved micromorphic conulariids, assigned to Eoconularia aff. loculata, were recovered using acetic acid preparation from limestone samples of late Katian (Late Ordovician) age. These samples had been collected from Churchill, northern Manitoba, by the Geological Survey of Canada's J. B. Tyrrell in 1894. These taxa are unusually abundant for conulariids, which are normally represented by only a few specimens from any given locality, and this abundance may be a reflection of the exceptional preservation at these two localities.

APA, Harvard, Vancouver, ISO, and other styles

43

Hints, O., J. Nõlvak, and V. Viira. "AGE OF ESTONIAN KUKERSITE OIL SHALE – MIDDLE OR LATE ORDOVICIAN?" Oil Shale 24, no. 4 (2007): 527. http://dx.doi.org/10.3176/oil.2007.4.04.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Williams, Harold, and M. A. J. Piasecki. "The Cold Spring Melange and a possible model for Dunnage–Gander zone interaction in central Newfoundland." Canadian Journal of Earth Sciences 27, no. 8 (August 1, 1990): 1126–34. http://dx.doi.org/10.1139/e90-117.

Full text

Abstract:

Structural relationships at Cold Spring Pond and the recognition of ophiolitic melange bear on the important questions of timing and style of structural superpositioning of Dunnage Zone rocks above Gander Zone rocks in central Newfoundland. The latest models emphasize ductile shear boundaries and orogen-parallel movements. Previous models proposed west-to-east or head-on obduction of Dunnage ophiolitic rocks across the Gander Zone.At the Dunnage (Exploits Subzone) – Gander (Meelpaeg Subzone) boundary at Cold Spring Pond, discrete, outcrop-size ultramafic blocks and smaller quartzite blocks are randomly distributed, and they are surrounded by, or are embedded in, homogeneous black graphitic shale or phyllite. The ultramafic blocks are typical of nearby Early Ordovician Dunnage ophiolite suites, the quartzite blocks are typical of adjacent Early Ordovician or earlier Gander clastic rocks, and the matrix black shales are similar to those of Middle or Early Ordovician age that occur throughout central Newfoundland. This chaotic mixture of almost coeval lithologies at Cold Spring Pond is interpreted as an olistostromal melange; the Cold Spring Melange. It resembles melanges that are dated as Ordovician elsewhere in Newfoundland.The Cold Spring Melange is overprinted by the full range of structures and metamorphic effects evident in adjacent rocks of the Exploits (Dunnage) and Meelpaeg (Gander) subzones. These include the development of lineations, cleavages, schistosities, zones of ductile shearing, regional metamorphism, and contact metamorphism. The oldest of these effects are interpreted as Silurian, based on isotopic dating in southern Newfoundland.The formation of olistostromal, ophiolitic melange implies disruption of the oceanic tract (Exploits Subzone of the Dunnage Zone), and in the case of the Cold Spring example, juxtapositioning or transport of Exploits Subzone ophiolite suites against or across the supracrustal rocks of the Meelpaeg Subzone (Gander Zone). The age and provenance of Cold Spring components, lack of post-Ordovician components, overprinting structural relationships, and comparison with other Newfoundland melanges all support an Ordovician age of formation. Overprinting relationships indicate that major ductile shears at other Dunnage–Gander zone boundaries postdate initial Dunnage–Gander superpositioning.

APA, Harvard, Vancouver, ISO, and other styles

45

King, Lewis H., Gordon B. J. Fader, W. A. M. Jenkins, and Edward L. King. "Occurrence and regional geological setting of Paleozoic rocks on the Grand Banks of Newfoundland." Canadian Journal of Earth Sciences 23, no. 4 (April 1, 1986): 504–26. http://dx.doi.org/10.1139/e86-052.

Full text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

46

Brower, James C. "Carabocrinid crinoids from the Ordovician of northern Iowa and southern Minnesota." Journal of Paleontology 70, no. 4 (July 1996): 614–31. http://dx.doi.org/10.1017/s0022336000023593.

Full text

Abstract:

Four species of carabocrinids from the Ordovician of northern Iowa and southern Minnesota are described, namelyCarabocrinus radiatusE. Billings,C. vancortlandtiE. Billings,C. magnificusSardeson from the Middle Ordovician Dunleith Formation andC. slocomiFoerste from the Upper Ordovician Maquoketa Formation.Carabocrinus radiatusandC. vancortlandtiare also known from the Middle Ordovician of Ontario and Quebec. In addition,C. magnificusandC. vancortlandtiare recorded from the Decorah of the Twin Cities area and the Curdsville Limestone of Kentucky, respectively. Biogeographically, the Middle Ordovician carabocrinids from Iowa and Minnesota are most similar to those from rocks of similar age in the northern Appalachians.Development of the cup and its component plates inC. slocomiis almost entirely isometric so that the its shape is largely constant regardless of size. This species exhibits ridge canals on the shoulders of the radial plates in the cup. The ridge canals probably served for respiration. As expected, the number of ridge canals and their length increase with positive allometry compared to the size and volume of the cup. Growth of the ridge canals restricts the width of the radial facets.

APA, Harvard, Vancouver, ISO, and other styles

47

Fortey, R. A. "Early Ordovician trilobites from the Wandel Valley Formation, eastern North Greenland." Rapport Grønlands Geologiske Undersøgelse 132 (December 31, 1986): 15–25. http://dx.doi.org/10.34194/rapggu.v132.7959.

Full text

Abstract:

A small trilobite fauna is described from the Wandel Valley Formation of Kronprins Christian land, eastern North Greenland. It has a specific composition identical to the fauna from the Catoche Formation, western Newfoundland, which is typical of the shallow water bathyurid biofacies of the eastern part of the Ordovician Laurentian palaeocontinent. The fauna is of early Ordovician age, trilobite Zone H, equivalent to the early Arenig.

APA, Harvard, Vancouver, ISO, and other styles

48

Swami, Narendra K., Andrej Ernst, Satish C. Tripathi, Prasenjit Barman, S. K. Bharti, and Y. P. Rana. "A new cryptostome bryozoan Ptilotrypa from the Upper Ordovician Yong Limestone Formation: Tethyan sequence of Kumaun Higher Himalaya, India." Journal of Paleontology 93, no. 3 (February 12, 2019): 585–91. http://dx.doi.org/10.1017/jpa.2018.94.

Full text

Abstract:

AbstractA new species of the Paleozoic bryozoan genus Ptilotrypa of the order Cryptostomata is described from the lower part of the Yong Limestone Formation, Katian, Upper Ordovician of the Kumaun Tethys Himalaya: Ptilotrypa bajpaii new species. The presence of the genus Ptilotrypa in the Tethyan Himalaya suggests paleogeographic connections to the Upper Ordovician of North America and, consequently, Upper Ordovician age for the lower part of the Yong Limestone Formation. This species displays a reticulate colony shape, which suggests an efficient filtering capacity in an environment with a high primary production. Morphological peculiarities and systematic assignment of the genus Ptilotrypa are discussed.UUID: http://zoobank.org/898276c8-2924-4da2-ae96-3392cb2ebbc3

APA, Harvard, Vancouver, ISO, and other styles

49

Okulitch, Andrew V. "Paleozoic plutonism in southeastern British Columbia." Canadian Journal of Earth Sciences 22, no. 10 (October 1, 1985): 1409–24. http://dx.doi.org/10.1139/e85-148.

Full text

Abstract:

U–Pb dates from zircons indicate that plutonic events occurred during the Paleozoic in the Omineca Crystalline Belt in southeastern British Columbia. In the Kootenay Arc, granitoid cobbles in conglomerate of the Carboniferous Milford Group were derived from quartz monzonite and diorite plutons of probable Ordovician age. Near Little Shuswap Lake, gneissic granitoid units have yielded Cambro-Ordovician ages. At least one episode of deformation affected country rocks of unknown age before intrusion. In the Monashee Complex south of Thor–Odin Nappe in South Fosthall Creek, lineated quartz monzonite is of probable Ordovician age. Comparison of fabrics suggests that at least one episode of metamorphism and deformation occurred prior to intrusion. No clear relationship between the cobbles and these plutons can be demonstrated because major faults lie between them, but substantial revision to accepted models of Paleozoic paleogeography of this region will have to be made. In the Clachnaeudainn tectonic slice east of the Monashee Complex, granitic gneiss is of Paleozoic, possibly Siluro-Devonian, age. This pluton appears to be involved in all phases of deformation that affected its country rocks. Near Quesnel Lake, parts of a composite gneissic granitoid pluton appear to be of Devonian or earliest Carboniferous age.

APA, Harvard, Vancouver, ISO, and other styles

50

Dean, W. T., and O. Monod. "A new interpretation of Ordovician stratigraphy in the Bahçe area, northern Amanos Mountains, south central Turkey." Geological Magazine 122, no. 1 (January 1985): 15–25. http://dx.doi.org/10.1017/s001675680003404x.

Full text

Abstract:

AbstractLower Ordovician rocks in the Bahçe–Fevzipaşa district of the northern Amanos Mountains, previously divided into three separate formations, are referred to the Seydisehir Formation. Shaly strata that crop out southeast of Bahçe and have been termed Kizlaç Formation, Ayran Series or Bahçe Formation, described variously as being of Ordovician or Silurian age, are referred to the lower shale member of the Bedinan Formation; their sparse fauna includes the trilobites Colpocoryphe, Kloucekia and Nobiliasasphus and is of Caradoc age. A single locality containing Kloucekia phillipsii (Barrande, 1846) is shown to be that recorded by Frech in 1916 and subsequently lost sight of.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Ordovician age'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles