Late Middle Ordovician Research Articles

Early Ordovician StromatoporoidPulchrilamina spinosafrom South China: Geobiological Significance and Implications for the Early Development of Skeletal-Dominated Reefs

The thin, laminar to low domical, encrusting stromatoporoid Pulchrilamina spinosa is reported from the Tremadocian—Floian in Hubei and Guizhou provinces, South China. The Chinese Pulchrilamina appeared earlier (late Tremadocian—early Floian) than North American equivalents (early Floian), which possess large domical forms and are the main framework-builders. Pulchrilamina appeared much earlier than the observed diversification of other stromatoporoids. These skeletal reef-builders thus provide excellent clues for understanding the initial evolution of the stromatoporoids and the subsequent development of the skeletal-dominated (especially stromatoporoid-dominated) reefs that reached their first acme in the late Middle—Late Ordovician.

The Haraa Gol terrane in the western Hentiyn Mountains (northern Mongolia): geochemistry, geochronology, and geodynamics

According to geological, petrological, geochemical, and geochronological studies, the Haraa Gol terrane in the western Hentiyn Mts. is dominated by two rock assemblages of different ages, associated with the initiation and development of the island arcs and marginal spreading seas of the Mongol–Okhotsk Ocean. The Late Cambrian, Early Ordovician, and Middle Ordovician were marked by the effusion of basalt and basaltic andesite and the formation of gabbro and gabbro-dolerite in back-arc spreading basins. In the Late Silurian–Devonian, after a short pause, tectonomagmatic processes were activated, with the formation of differentiated island-arc volcanics, gabbro, and granitoids. Their absolute 40Ar–39Ar age is given in the paper. The model age of the TNd(DM) protolith of the Haraa Gol igneous rocks corresponds to the composition of the Mesoproterozoic juvenile crust.

The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three-dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal-dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal-dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.

Testing the plateau: a reexamination of disparity and morphologic constraints in early Paleozoic crinoids

Studies of crinoid morphology have been pivotal in understanding the constraints on the range of morphology within a clade as well as the patterns of disparity throughout the Phanerozoic. Newly discovered and described faunas and recent study of early Paleozoic crinoid diversity provide an ideal opportunity to reanalyze Ordovician through Early Silurian crinoid disparity with more complete taxonomic coverage and finer stratigraphic resolution. Using the coarse stratigraphic binning of Foote (1999), the updated morphologic data set has a similar disparity pattern to those previously reported for the early Paleozoic. However, with the more resolved stratigraphic binning used by Peters and Ausich (2008), a significant difference exists between the original and current data sets. Both data sets have a pronounced disparity high during the late Middle Ordovician. However, the updated disparity curve has a much higher initial disparity during the Early Ordovician and a pronounced rise in disparity during the Silurian recovery. Examination of differential sampling, proportions of the crinoid orders through time, and methods of coding characters indicate these factors have little effect on the pattern of crinoid disparity. The Silurian morphospace expansion occurs primarily within disparids and coincides with the origination of the myelodactylids. These findings corroborate the rapid expansion of morphospace during the Ordovician. However, crinoid disparity did not remain static and, although less frequent than during the initial radiation, new body plans evolved following the Ordovician Extinction (e.g., the myelodactylids). These results are consistent with the hypothesis of ecology constraining the limits on morphologic disparity at the class level.

Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana)

• The advent of embryophytes (land plants) is among the most important evolutionary breakthroughs in Earth history. It irreversibly changed climates and biogeochemical processes on a global scale; it allowed all eukaryotic terrestrial life to evolve and to invade nearly all continental environments. Before this work, the earliest unequivocal embryophyte traces were late Darriwilian (late Middle Ordovician; c. 463-461 million yr ago (Ma)) cryptospores from Saudi Arabia and from the Czech Republic (western Gondwana). • Here, we processed Dapingian (early Middle Ordovician, c. 473-471 Ma) palynological samples from Argentina (eastern Gondwana). • We discovered a diverse cryptospore assemblage, including naked and envelope-enclosed monads and tetrads, representing five genera. • Our discovery reinforces the earlier suggestion that embryophytes first evolved in Gondwana. It indicates that the terrestrialization of plants might have begun in the eastern part of Gondwana. The diversity of the Dapingian assemblage implies an earlier, Early Ordovician or even Cambrian, origin of embryophytes. Dapingian to Aeronian (Early Silurian) cryptospore assemblages are similar, suggesting that the rate of embryophyte evolution was extremely slow during the first c. 35-45 million yr of their diversification. The Argentinean cryptospores predate other cryptospore occurrences by c. 8-12 million yr, and are currently the earliest evidence of plants on land.

Brachiopod associations from the Middle Ordovician of the Oslo Region, Norway

Abstract: The marine upper Darriwilian (Middle Ordovician) Elnes Formation of southern Norway contains very rich and diverse invertebrate faunas. Stratigraphically detailed recent collections of these well-preserved faunas have permitted a more thorough description of the various faunal groups and their preferences in the late Middle Ordovician of the Oslo Region, southern Norway, than ever before. The brachiopod faunas are described in the present article, which include a new genus and a new species respectively Wandaasella modheimrensis and Cyclomyonia vikersundi. The brachiopod fauna is largely dominated by linguliformeans although some sections of the formation are dominated by the plectambonitoids Alwynella ildjernensis Spjeldnaes or Cathrynia aequistriata (Hadding) or by orthid brachiopods. Statistical analysis of the brachiopod fauna reveals that the general depositional trend of the Elnes Formation is that of a regressive event from the lower part of the Sjostrand Member to the Hakavik Member. Three main brachiopod associations are recognised: a deep-water, lingulid dominated association associated with quiet and dysoxic bottom conditions, a sowerbyellid dominated association (e.g. Cathrynia and Alwynella) found in muddy to marly deposits formed around maximal storm wave base and an orthid-dominated association representing an environment characterised by a fairly coarse or hard bottom substrate formed well above storm wave base but below fair weather wave base.

Paleozoic structural deformation of Bachu uplift, Tarim basin of Northwest China: Implications for plate drifting

Based on high-resolution 2D seismic profiles, the Paleozoic structural deformation characteristics of Bachu (巴楚) uplift of northwestern Tarim basin, NW China, are exhibited in this article. The deformation happened during three main geological periods: the end of Middle-Late Ordovician (O2–3), the end of Early-Middle Devonian (D1–2), and the end of Late Permian (P2). In the Bachu uplift, there developed a series of NW-trending thrust faults and imbricate structures due to the effect of the NW-SE compression stress towards the end of Middle-Late Ordovician (O2–3) (middle Caledonian movement), and there developed some NNE-trending thrust faults and fault blocks under the control of the NEE-SWW compression stress at the end of Early-Middle Devonian (D1–2) (early Hercynian movement). However, at the end of Late Permian (P2) (late Hercynian movement), some NE-trending thrust faults and associated folds developed as a result of the NE-SW compression stress. The first-stage (O2–3) deformation is obviously more violent than those of the latter two stages (D1–2 and P2), which implies that the Tarim plate drifted quickly to the north at around the same time basin.

A revision of the stratigraphic nomenclature of the Cambrian–Ordovician strata of the Philipsburg tectonic slice, southern Quebec

The Philipsburg tectonic slice is bounded to the west by a northeast–southwest-trending thrust fault (Logan’s Line) and preserves 10 formations of Middle (?) to Late Cambrian (Milton, Rock River, and Strites Pond formations), Early Ordovician (Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations), and early Middle Ordovician (Luke Hill, Solomons Corner, and Corey formations) age. The strata were previously assigned to the Philipsburg Group. Early correlations between the Philipsburg succession and coeval strata of the St. Lawrence Platform were mainly based on sparse macrofauna and inferred stratigraphic position. Unconformities at the Cambrian–Ordovician and Early Ordovician – Middle Ordovician boundaries occurring in autochthonous St. Lawrence Platform and the allochthonous Philipsburg succession (Philipsburg tectonic slice) highlight new stratigraphic interpretations between the inner-shelf (St. Lawrence Platform) and the outer-shelf (Philipsburg) successions. The succession in the Philipsburg tectonic slice is divided into three new groups. The Middle (?) to Upper Cambrian Missisquoi Group (new) includes the Milton, Rock River, and Strites Pond formations. The upper boundary of the Missisquoi Group is defined by the upper unconformable contact between the Upper Cambrian Strites Pond Formation and overlying Lower Ordovician Wallace Creek Formation. The Missisquoi Group correlates with the Potsdam Group of the St. Lawrence Platform. The Lower Ordovician School House Hill Group (new) includes the Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations. The upper boundary of this group is marked by a regionally extensive unconformity at the top of the Naylor Ledge Formation and correlates with the younger Beekmantown-topping unconformity. The School House Hill Group is correlative with the lower to upper part of the Beekmantown Group (Theresa Formation and the Ogdensburg Member of the Beauharnois Formation) of the St. Lawrence Platform. The Middle Ordovician Fox Hill Group (new) consists of the Luke Hill, Solomons Corner, and Corey formations. This group correlates with the uppermost part of the Beekmantown Group (Huntingdon Member of the Beauharnois Formation and the Carillon Formation).

Stratigraphic and Structural Framework of Upper Middle Ordovician Rocks in the Head Lake-Burleigh Falls Area of South-Central Ontario

Field investigations in the Head Lake-Burleigh Falls area of south-central Ontario, that focused mainly on the Covey Hill(?), Shadow Lake, Gull River and Coboconk formations along the Paleozoic escarpment, provided clear evidence of faulting. Observed and inferred structural deformation, coupled with faciès changes within the Shadow Lake and lower Gull River, point to a succession of basement movements during the Phanerozoic. These range from Hadrynian-Early Cambrian, through Middle Ordovician to post-late Middle Ordovician times. Some of the earlier movements (Hadrynian-Early Cambrian to late Middle Ordovician) appear to be coincident with, and probably related to, plate tectonic events and the associated Taconian orogeny that were in progress along the southeastern margins of the North American continent. Post-Middle Ordovician block faulting, on the other hand, may have been triggered by any number of epeirogenic events related to late stage Taconian, Acadian or Alleghanian orogenies in Late Ordovician to Carboniferous times, or possibly to rifting associated with continental break-up and initiation of seafloor spreading processes in the early Mesozoic. Manuscrit révisé accepté le 5 août 1993

The LA-ICP-MS zircons U-Pb ages and geochemistry of the Baihua basic igneous complexes in Tianshui area of West Qinling

Baihua meta-igneous complex consists mainly of pyroxenite-gabbro(diorite)-diorite-quartz diorite. They form a complete comagmatic evolutionary series. The geochemical characteristics of basic-intermediate basic igneous rocks indicate that they belong to a tholeiite suite. The REE distribution pattern is nearly flat type and LREE is slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider diagrams are generally similar; the LIL elements (LILE) Cs, Ba, Sr, Th and U are enriched, but Rb, K and the HFSEs Nb, P, Zr, Sm, Ti and Y are relatively depleted. All these show comagmatic evolution and origin characteristics. The tectonics environment discrimination of trace element reveals that these igneous complexes formed in an island-arc setting. The LA-ICP-MS single-zircons U-Pb age of Baihua basic igneous complex is 434.6±1.5 Ma (MSWD = 1.3), which proves that the formation time of the island-arc type magmatite in the northern zone of West Qinling is Late Ordovician or Early Silurian, also reveals that the timing of subduction of paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activities is probably Middle-Late Ordovician to Early Silurian.

Patterns, processes and likely causes of the Ordovician trilobite radiation in South China

AbstractThe Ordovician genus‐diversity trajectories of trilobites and the radiation patterns previously proposed in South China are reviewed on the basis of an extensive and intensive study of 32 representative collections assigned respectively to the suecicus, hirundo and clavus graptolite‐zone intervals and made along shelf environment gradients from 15 re‐measured representative early‐Middle‐Ordovician sections. Analyses of new data indicate that components of the Whiterock Fauna (Paleozoic Evolutionary Fauna) spread across the whole of the environmental spectrum and in general increased steadily through the Ordovician. The major faunal innovations appeared first in the inner shelf during the Early Ordovician and the novelties then expanded seawards into the outer shelf. The Whiterock Fauna first exhibited a higher representation in shallow outer‐shelf faunas and made its early appearance in deep outer‐shelf habitats during the early Middle Ordovician. However, it was not until the clavus interval (late early Middle Ordovician) that the onset of the major Ordovician radiation or the radiation of the Whiterock Fauna as a whole commenced in deep outer‐shelf environments. From the Darriwilian onwards, members of the Whiterock Fauna had further developed and dominated all environments, but it was not until the Hirnantian that they comprised the whole fauna. The beginning of the radiation in South China was dominated by the expansion of reedocalymenine calymenids, trinucleids and cyclopygids. All of these three trilobite clades had their early diversification centred in high latitude zones of Gondwana. In terms of the macroevolution of trilobites, these specialized trilobites were only diagnostic of a regional Ordovician radiation. All of them represented a subset of the Paleozoic Evolutionary Fauna, which became extinct before or during the latest Ordovician mass extinction and bore no relationships to the Silurian Fauna. Therefore, the Whiterock Fauna of South China only played a minor role in the global macroevolution of the Paleozoic Evolutionary Fauna. As revealed by close investigations, the Ordovician radiation in South China may have been directly triggered by two major transgressive‐regressive cycles during the Tremadoc/Arenig and Lower/Middle Ordovician. The increase of oxygen levels in oceans during the early Middle Ordovician may have provided an essential condition for the radiating fauna to eventually inhabit the new ecological niches of the deep outer shelf. Copyright © 2007 John Wiley & Sons, Ltd.

Macroevolutionary interplay between planktic larvae and benthic predators: COMMENT: COMMENT

[Peterson (2005)][1] has hypothesized that planktotrophic larvae originated between the Late Cambrian and Middle Ordovician as a consequence of benthic predation operating on lecithotrophic ancesters. The evidence used to support this viewpoint is based on an extrapolation of larval trophic mode (

Sedimentary and tectonic environment of the Ordovician Föllinge Greywacke, Storsjön area, Swedish Caledonides

The Middle to Upper Ordovician Föllinge Greywacke occupies about 4 500 km2 of the easternmost overthrust terrain in the Caledonides of central Sweden. Its outcrop area around lake Storsjön can be divided into two realms in which turbidites are preserved from the two principal stages of development of a basin that was characterized by a western facies of sand-rich fans and an eastern basin plain with dark mud. The eastern, Föllinge Realm, represents an early stage of the basin, with lithic greywackes, with feldspar and detrital carbonate among the clasts. The western, Mörsil Realm is characterized by quartz wackes to lithic greywackes with a high clay content and little carbonate or feldspar, and transport from the southwest and west. The heavy-mineral suite of both realms is dominated by zircon and minerals derived either from old granitic terrains or reworked sediments derived from the erosion of such terrains. The Cr and Ni content is relatively high and increased in late stages of basin evolution, as did the chlorite content. The basin was at first situated between a western tectonic rise, deformed between the Middle Cambrian and the Middle Ordovician, and an eastern starved carbonate facies to the east. Subsidence of the rise in late Middle Ordovician to early Late Ordovician led to westward migration of the deepest part of the basin, which was subsequently fed from an elevated terrain still farther to the west, but also from rises to the north and south.

First Middle Ordovician biota from southern New Brunswick: stratigraphic and tectonic implications for the evolution of the Avalon continent

A limestone boulder in the Triassic Lepreau Formation near Saint John, New Brunswick, has yielded the first diverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the first Arenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Association of the conodonts Drepanoistodus and Baltoniodus and the trilobites Neseuretus, Nileus, and Stapeleyella emphasizes the faunal dissimilarity of Avalon and Laurentia through the late Middle Ordovician. Extension of the ranges of Neseuretus cf. Neseuretus parvifrons and Stapeleyella from Britain into New Brunswick further emphasizes that "eastern" and "western" Avalon were confluent parts of a unified, insular Avalon continent that originated in the latest Precambrian. This fauna correlates with the lower Amorphognathus (Lenodus) variabilis Zone (Kundan Stage) of Baltica and the terminal Arenig (upper Middle Ordovician; lower Darriwilian Stage) of Avalonian Britain. Available evidence suggests that an Arenig cover sequence with local shallow-water hematitic iron ore, quartz arenite, and rare limestone extended across the Avalonian marginal and inner platforms from eastern Newfoundland to the Boston, Massachusetts, region. This "western" Avalonian Arenig shows the greatest similarity with the Arenig of the Welsh Borderlands. Phosphatic fossils from the boulder have a thermal alteration index much lower than that of nearby lower Paleozoic outcrops and suggest derivation of the boulder from a weakly heated Avalonian succession brought into the Bay of Fundy region by post-Ordovician transcurrent faulting.

Ordovician organic-walled microphytoplankton (acritarch) distribution: the global scenario

A number of palaeobiogeographical models for Ordovician organic-walled microphytoplankton (acritarchs, prasinophytes, and related groups) have been published during the past 30 years. A modern synthesis of Ordovician acritarch palaeobiogeography, based on previously published acritarch ‘provinces’ and global distribution models, as well as new plots on recently compiled palaeogeographical maps is presented. Review of the literature and new plots indicate that a number of preliminary conclusions can be drawn. Following minor biogeographical differentiation of acritarch assemblages during the Cambrian, ‘provincialism’ started at the Cambrian–Ordovician boundary. In the late Tremadocian a warm-water assemblage, containing the genera Aryballomorpha, Athabascaella and Lua, but no diacrodians, seems to be limited to low-latitude localities such as Laurentia and North China. From the late Tremadocian and throughout most of the Arenig a peri-Gondwana acritarch assemblage with the easily recognisable taxa Arbusculidium filamentosum, Coryphidium, and Striatotheca is present on the southern margin of Gondwana, and its distribution corresponds almost exactly with that of the Calymenacean–Dalmanitacean trilobite fauna. It seems reasonable to consider the acritarchs of Baltica as belonging to a temperate-water ‘province’, which was probably not restricted to the palaeocontinent of Baltica but had a wider distribution at about the same latitude, as some of the elements recorded from Baltica also occur in South China and Argentina. The maximum separation of the continents during the Arenigian, reflected by a pronounced biogeographical differentiation of most Ordovician fossil groups, led to the development of geographically distinct acritarch assemblages. Data from the late Middle Ordovician and the Late Ordovician remain too poor to elucidate global palaeobiogeographical patterns. The biogeographical distribution of Ordovician acritarchs appears similar to that of the resting cysts of modern dinoflagellates, primarily controlled by latitude but also following the continental margins.

Ordovician accretion of the Argentine Precordillera terrane to Gondwana: a review

The Precordillera terrane of Argentina was rifted as a lithospheric block from the Ouachita embayment of southeastern Laurentia and accreted to western Gondwana. In various interpretations, the time of rifting of the Precordillera terrane from Laurentia ranges from Early Cambrian to Late Ordovician, and the time of accretion to Gondwana ranges from Middle–Late Ordovician to Silurian–Devonian. This review of available data and previous interpretations, leads to the conclusion that rifting from the Ouachita embayment of Laurentia occurred in the Early Cambrian, and collision with the Famatina arc on the western margin of Gondwana occurred in the Middle–Late Ordovician. In that context, Silurian–Devonian deformation reflects the accretion of the Chilenia terrane on the outboard side of the Precordillera terrane.

Middle to early Late Ordovician hydrothermal veining in the Molong Volcanic Belt, northeastern Lachlan Fold Belt: Sedimentological evidence

Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite.

Tectonic evolution and significance of Silurian – Early Devonian hinterland-directed deformation in the internal Humber zone of the southern Quebec Appalachians

In the southern Quebec Appalachians, the early tectonic history of the Laurentian margin (Humber zone) comprises foreland-propagating, northwest-directed thrust faulting, nappe emplacement, and regional prograde metamorphism in response to the obduction of large ophiolitic nappes during the Taconian orogeny. In the internal Humber zone, this event is dated at 462 ± 3 Ma (late Middle Ordovician), which is interpreted to represent the timing of near-peak Taconian metamorphism. Superimposed hinterland-directed structures are accompanied by retrograde metamorphism and consist of back thrusts and normal faults, which respectively delimit the northwestern and southeastern limbs of the Sutton and Notre-Dame mountains anticlinoria, both salient structures of the internal Humber zone of southern Quebec. Geochronologic data on the timing of hinterland-directed deformation vary from 431 to 411 Ma. Two tectonic models are presented and discussed, which may account for the Silurian – Early Devonian evolution of the Laurentian margin: (1) back thrusting and syn- to post-compressional crustal extension in response to the tectonic wedging of basement-cored duplexes inducing delamination of supracrustal rocks; (2) tectonic exhumation of the internal Humber zone by extensional collapse. Evidence for Silurian – Early Devonian extensional tectonism in the Humber zone provides the basement infrastructures necessary for the creation and the onset of sedimentation in the Gaspé Belt basins (e.g., Connecticut Valley – Gaspé synclinorium). Several structural, metamorphic features in the internal Humber zone of the northwestern New England Appalachians yield analogous characteristics with those of southern Quebec and may have shared a similar Silurian – Early Devonian tectonic evolution.

Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation?

Research Article| January 01, 2003 Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation? Michael C. Pope; Michael C. Pope 1Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Search for other works by this author on: GSW Google Scholar Jessica B. Steffen Jessica B. Steffen 1Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Michael C. Pope 1Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Jessica B. Steffen 1Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Publisher: Geological Society of America Received: 08 Jun 2002 Revision Received: 16 Sep 2002 Accepted: 23 Sep 2002 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2003) 31 (1): 63–66. https://doi.org/10.1130/0091-7613(2003)031<0063:WPLMTL>2.0.CO;2 Article history Received: 08 Jun 2002 Revision Received: 16 Sep 2002 Accepted: 23 Sep 2002 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael C. Pope, Jessica B. Steffen; Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation?. Geology 2003;; 31 (1): 63–66. doi: https://doi.org/10.1130/0091-7613(2003)031<0063:WPLMTL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Late Middle to Late Ordovician subtidal ramp carbonates of New Mexico, Texas, and Oklahoma contain abundant spiculitic chert (to 70% chert by volume) and phosphate (1–5 wt%), indicating that these rocks formed in an extensive upwelling zone. Upwelling began in the late Middle Ordovician (ca. 454 Ma) and persisted until the end of the Ordovician. Late Ordovician cherty carbonates also occur along the U.S. Cordilleran margin, in board of organic-rich graptolitic shale and chert. The widespread occurrence of Late Ordovician cherty and phosphatic carbonates on southern and western Laurentia, in addition to phosphate-rich, cool-water carbonates over much of the North American Midcontinent, suggests vigorous thermohaline circulation related to prolonged (10–14 Ma) Gondwana glaciation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Middle Ordovician (Llandeilan) radiolarians from West Junggar, Xinjiang, China

A distinctive long-spined Inaniguttid dominated radiolarian fauna is present in cherts of the Kekesayi terrane in west Junggar, Xinjiang Province, China. This fauna contains moderately well preserved specimens of Protoceratoikiscum clarksoni on which the presence of caveal ribs and patagial tissue can be observed. Characteristics of the fauna are similar to others of correlative late Middle Ordovician (Llandeilan) age known from Scotland (U.K.) suggesting that Protoceratoikiscum clarksoni may be biostratigraphically useful.