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Sennikov, N. V., O. T. Obut, N. G. Izokh, R. A. Khabibulina, and T. P. Kipriyanova. "THE REGIONAL STRATIGRAPHIC CHART FOR THE SILURIAN OF THE WESTERN SAYAN (NEW VERSION)." Geology and mineral resources of Siberia, no. 9c (2021): 15–36. http://dx.doi.org/10.20403/2078-0575-2021-9c-15-36.
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A new version of the Regional stratigraphic chart for the Silurian of the Western Sayan and explanatory note, compiled in accordance with the Russian Stratigraphic Code, introduce changes, additional and specified data in comparison with the previous (first edition) chart. The Interdepartmental stratigraphic meeting held at Novosibirsk in 1964 approved the old version of the chart and later it was validated by the USSR Interdepartmental Stratigraphic Committee as the official stratigraphic base for all types of the regional geologic activities. Since 1964 meeting, the stages of the Silurian chart were changed. Thus, former stages Llandovery, Wenlock, Ludlow and Pridoli become series. New stages Rhuddanian, Aeronian, Telychian, Sheinwoodian, Homerian, Gorstian and Ludfordian were adopted for the three former series. For the presented stratigraphic chart the new standard Silurian stages were used.
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Zhang, Shunxin, Khusro Mirza, and Christopher R. Barnes. "Upper Ordovician – Upper Silurian conodont biostratigraphy, Devon Island and southern Ellesmere Island, Canadian Arctic Islands, with implications for regional stratigraphy, eustasy, and thermal maturation." Canadian Journal of Earth Sciences 53, no. 9 (September 2016): 931–49. http://dx.doi.org/10.1139/cjes-2016-0002.
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The conodont biostratigraphy for the Upper Ordovician – Upper Silurian carbonate shelf (Irene Bay and Allen Bay formations) and interfingering basinal (Cape Phillips Formation) facies is established for parts of Devon and Ellesmere islands, central Canadian Arctic Islands. Revisions to the interpreted regional stratigraphic relationships and correlations are based on the stratigraphic distribution of the 51 conodont species representing 32 genera, identified from over 5000 well-preserved conodonts recovered from 101 productive samples in nine stratigraphic sections. The six zones recognized are, in ascending order, Amorphognathus ordovicicus Local-Range Zone, Aspelundia fluegeli Interval Zone, Pterospathodus celloni Local-Range Zone, Pt. pennatus procerus Local-Range Zone, Kockelella patula Local-Range Zone, and K. variabilis variabilis – Ozarkodina confluens Concurrent-Range Zone. These provided a more precise dating of the members and formations and, in particular, the range of hiatuses within this stratigraphic succession. The pattern of regional stratigraphy, facies changes, and hiatuses is interpreted as primarily related to the effects of glacioeustasy associated with the terminal Ordovician glaciation and smaller Early Silurian glacial phases, the backstepping of the Silurian shelf margin, and the geodynamic effects of the collision with Laurentia by Baltica to the east and Pearya to the north. Conodont colour alteration index values (CAI 1–6.5) from the nine sections complement earlier graptolite reflectance data in providing regional thermal maturation data of value in hydrocarbon exploration assessments.
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Sennikov, N. V., N. V. Novozhilova, O. T. Obut, and R. A. Khabibulina. "The Pridoli (Silurian) Lithostratigraphy and Biostratigraphy of Gorny Altai." Russian Geology and Geophysics 62, no. 11 (November 1, 2021): 1269–84. http://dx.doi.org/10.2113/rgg20204232.
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Abstract —The paper presents new data on the upper Silurian litho- and biostratigraphy of the Gorny Altai area. Sediments within this interval store a succession of taxonomically representative middle–upper Ludfordian, lower Pridoli, and Lower Devonian (Lochkovian–Pragian) conodont assemblages. The new fauna constraints made a basis for updated correlations of the local and regional stratigraphic units at the Silurian/Devonian boundary of Gorny Altai with the stages of the International Stratigraphic Chart. The correlation results reveal a mismatch between the boundaries of the local and regional Silurian units and the respective boundaries of stages in the International Stratigraphic Chart.
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Zhang, Lei, Lun Wei Zhu, and Xue Juan Zhang. "High Resolution Sequence Stratigraphy of Silurian Strata in Tazhong Area." Advanced Materials Research 734-737 (August 2013): 111–16. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.111.
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According to the fundamental principles of high resolution sequence stratigraphy, this paper focused on the application of high resolution sequence stratigraphy to Silurian strata in Tazhong area. Based on the comprehensive study of logging, drilling and seismic information, the high resolution sequence boundaries of Silurian strata and two scales of datum level cycles (long-term and intermediate-term) can be recognized in Tazhong area. Seven chronstratigraphic boundaries can be recognized in Silurian strata, including four sequence boundaries, which were the transformation from datum level falling to datum level rising, and three flooding surfaces, which the transformation from datum level rising to datum level falling. The Silurian strata in Tazhong area can be divided into three third-order sequences which correspond to three long-term datum level cycles, and 11 fourth-order sequences (parasequence sets) relating to 11 intermediate-term datum level cycles. The classification aforementioned can much better solved the corresponding problem between the six lithological sections of Silurian strata and sequence formations, finally establishes the high resolution sequence stratigraphic framework of Silurian strata in Tazhong area.
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Vacek, František, Jindřich Hladil, and Petr Schnabl. "Stratigraphic correlation potential of magnetic susceptibility and gamma-ray spectrometric variations in calciturbiditic facies (Silurian-Devonian boundary, Prague Synclinorium, Czech Republic)." Geologica Carpathica 61, no. 4 (August 1, 2010): 257–72. http://dx.doi.org/10.2478/v10096-010-0015-2.
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Stratigraphic correlation potential of magnetic susceptibility and gamma-ray spectrometric variations in calciturbiditic facies (Silurian-Devonian boundary, Prague Synclinorium, Czech Republic)Magnetic susceptibility (MS) and gamma-ray spectrometry (GRS) stratigraphy were used for correlation and characterization of eight Silurian-Devonian (S-D) sections in the Prague Synclinorium (Czech Republic). They represent two different facies developments: lower subtidal to upper slope deposits and slope-to-basin-floor distal calciturbidites. Sections from relatively shallow- and deep-water sections are easy to compare and correlate separately, although the detailed relationship between these two facies is still not entirely clear and correlations between the two settings are difficult. This may be due to sharp facies transitions and presence of stratigraphic gaps. The MS and GRS stratigraphic variations combined with sedimentologic data have been also used for reconstruction of the evolution of the sedimentary environment. The beds close above the S-D boundary show noticeably enhanced MS magnitudes but weak natural gamma-ray emissions. It may correspond to an increased amount of terrigenous magnetic material occurring with short-term shallowing (sedimentological evidence). In deep-water sections the uppermost Silurian is characterized by high MS and GRS values. It corresponds to a supply of recycled sediment to the lower wedge which occurred during the late Pridoli regression phase. The basal Devonian beds correspond to gradual deepening, but the overlying sequences reflect other shallowing episodes which are expressed in increasing MS and gamma ray activity of rocks. The MS and GRS fluctuations are interpreted as a result of local subsidence of the sea bottom along synsedimentary growth-faults and/or a biotic event rather than of eustatic sea-level changes.
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Craigie, Neil W. "Definition of the Hercynian Unconformity in eastern Saudi Arabia using chemostratigraphy in conjunction with biostratigraphy, sedimentology and lithostratigraphy." Petroleum Geoscience 26, no. 4 (December 19, 2019): 568–88. http://dx.doi.org/10.1144/petgeo2019-116.
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The following chemostratigraphy study was conducted on Paleozoic sediments encountered in 14 wells in eastern Saudi Arabia. A total of 1500 samples were analysed by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), with data acquired for 48 elements, ranging from Na to U in the periodic table. The aim was to utilize chemostratigraphy, in conjunction with existing biostratigraphic, lithostratigraphic and sedimentological data, to define the Hercynian Unconformity in each well and to recognize stratigraphic boundaries occurring above and below it. This was necessary as the unconformity eroded to different stratigraphic levels in each well, with Devonian, Silurian and Ordovician sediments found immediately below it in adjacent locations. In the absence of chemostratigraphic, biostratigraphic and sedimentological data, it is often very difficult to define this boundary and others using lithostratigraphy alone as many stratigraphic intervals yield similar gamma-ray (GR) log trends. For example, a low ‘blocky’ GR response is typical of both the Carboniferous Ghazal Member and the Ordovician Sarah Formation. Similarly, both the Silurian Sharawra Member and the Silurian–Devonian Tawil Formation produce a ‘ratty’ GR trend. Each stratigraphic member and formation was found to have distinctive chemostratigraphic, biostratigraphic, sedimentological and/or wireline log signatures.
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Eriksson, Mats. "Silurian Ramphoprionid polychaetes from Gotland, Sweden." Journal of Paleontology 75, no. 5 (September 2001): 993–1015. http://dx.doi.org/10.1017/s0022336000039901.
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Silurian ramphoprionid polychaete annelids, represented by their jaws (scolecodonts), are described from extensive collections from Gotland, Sweden. The family Ramphoprionidae, monotypic at its original description, is sub-divided into four genera; Protarabellites Stauffer, 1933; Ramphoprion Kielan-Jaworowska, 1962; “Pararamphoprion” Männil and Zaslavskaya, 1985; and Megaramphoprion new genus. Identified species include “P.” cf. nordicus Männil and Zaslavskaya, 1985; P. rectangularis new species; P. staufferi new species; P. triangularis new species; and two Protarabellites species left in open nomenclature. Ramphoprion is represented by one new highly plastic species, R. gotlandensis, housing five distinguishable morphotypes showing gradual evolution. Megaramphoprion, which is most closely related to Ramphoprion, is represented by M. magnus new genus and species, a rare but distinctive taxon. Most species have long stratigraphic ranges within which important morphological changes can nonetheless be observed. The stratigraphic range of ramphoprionids includes, at least, the Ordovician to the Silurian. They are fairly rare in the Silurian of Gotland and where present they generally form less than 10 percent of the polychaete faunas, although occasionally reaching as much as 20 to 30 percent. Evolution, paleoecology, and surface structures of the investigated species are briefly discussed.
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Toyos, J. M., and C. Aramburu. "El Ordovícico en el área de Los Barrios de Luna, Cordillera Cantábrica (NW de España)." Trabajos de Geología 34, no. 34 (March 9, 2015): 61. http://dx.doi.org/10.17811/tdg.34.2014.61-96.
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Resumen: El estudio cartográfico y estratigráfico del Ordovícico en el área de Los Barrios de Luna (flanco sur del Sinclinal de Abelgas-Alba), ha permitido reconocer una compleja estratigrafía, condicionada por una tectónica sinsedimentaria, probablemente relacionada con el intenso vulcanismo que se observa algo más al este. Se revisa la estratigrafía de la Fm. Barrios, de edad Cámbrico Medio a Tardío en su mayor parte. Se redenomina una unidad estratigráfica informal (capas de El Ventorrillo), del Ordovícico Temprano?, Medio y Tardío. Se definen formalmente dos formaciones en el Ordovícico Superior-Silúrico basal? (Caliza de La Devesa y Cuarcita de La Serrona), y se precisa la estratigrafía de la unidad informal silúrica capas de Getino. Las costras ferruginosas situadas en la base de las capas de El Ventorrillo y de las capas de Getino se interpretan como originadas por alteración de materiales volcánicos.Palabras clave: Ordovícico, cartografía, estratigrafía, costras ferruginosas, tectónica sinsedimentaria, rifting, Cordillera Cantábrica, Macizo Ibérico.Abstract: The mapping and stratigraphic study of the Ordovician rocks in Los Barrios de Luna area (southern limb of Abelgas-Alba Syncline), allowed us to recognize a complex stratigraphy, conditioned by a synsedimentary tectonics, probably related to the intense volcanism observed further east. The stratigraphy of the Barrios Fm., mostly Middle to Late Cambrian age, is reviewed. An informal stratigraphic unit (El Ventorrillo beds), of Early?, Middle to Late Ordovician age, is renamed. Two Upper Ordovician-basal Silurian? formations are formally defined (La Devesa Limestone and La Serrona Quartzite), and the stratigraphy of the Silurian informal unit Getino beds is refined. The ferruginous crusts at the base of El Ventorrillo beds and Getino beds are interpreted as a result of alteration of volcanic materials.Key words: Ordovician, cartography, stratigraphy, ferruginous crusts, synsedimentary tectonics, rifting, Cantabrian Mountains, Iberian Massif.
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Zuykov, Michael, David A. T. Harper, and Emilien Pelletier. "Revision of the Ordovician brachiopod genus Noetlingia Hall and Clarke, 1893." Journal of Paleontology 85, no. 3 (May 2011): 595–98. http://dx.doi.org/10.1666/10-060.1.
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The enigmatic pentameride brachiopod Noetlingia Hall and Clarke, 1893 is revised and its stratigraphic range corrected. The type species Noetlingia tscheffkini occurs only within the upper Darriwilian (Ordovician) of the East Baltic and not in the Silurian as previously assumed. Thus, presently defined, the superfamily Porambonitoidea does not cross the boundary between the Ordovician and Silurian systems. Two other species occurring in the Lower to Middle Ordovician of South China and North America are assigned to Noetlingia.
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Donovan, Stephen K., and David G. Keighley. "Fossil crinoids from the basal West Point Formation (Silurian), southeast Gaspé Peninsula, Québec, eastern Canada." Atlantic Geology 52 (November 10, 2016): 211. http://dx.doi.org/10.4138/atlgeol.2016.010.
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Silurian strata of Atlantic Canada and southern Québec locally preserve common fossil crinoids, albeit mostly as disarticulated remains. New crinoids from the Chaleurs Group, West Point Formation (Ludlow to Pridoli?; Upper Silurian) of the Gaspé Peninsula include Iocrinus? maennili (Yeltysheva) (otherwise known from the Katian of Estonia), Bystrowicrinus (col.) depressus sp. nov. and Cyclocyclicus (col.) sp. aἀ. C. (col.) echinus Donovan. On the basis of both its gross morphology and stratigraphic position, Iocrinus? maennili is unlikely to be an iocrinid disparid, a family that became extinct at the end of the Ordovician. The trivial name has hitherto been erroneously spelled as männili, mannili and mjannili. Most specimens of the common Bystrowicrinus (col.) depressus appear cyclocyclic because the pentastellate lumen occurs in a deeply sunken claustrum that is commonly occluded by sediment; clean specimens are highly distinctive. Cyclocyclicus (col.) sp. aἀ. C. (col.) echinus is similar to a species known from the Katian of North Wales. Taken together, this assemblage is more reminiscent of Katian strata (Upper Ordovician). Ḁis is problematic given the current mapping of the outcrop as West Point Formation (Upper Silurian), suggesting further stratigraphic studies in the area are required.
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Copper, Paul, and Daniel G. F. Long. "Stratigraphic revisions for a key Ordovician/Silurian boundary section, Anticosti Island, Canada." Newsletters on Stratigraphy 21, no. 1 (January 1, 1988): 59–73. http://dx.doi.org/10.1127/nos/21/1989/59.
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Deline, Bradley, and William I. Ausich. "Testing the plateau: a reexamination of disparity and morphologic constraints in early Paleozoic crinoids." Paleobiology 37, no. 2 (2011): 214–36. http://dx.doi.org/10.1666/09063.1.
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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.
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Barr, Sandra M., and Rebecca A. Jamieson. "Tectonic setting and regional correlation of Ordovician–Silurian rocks of the Aspy terrane, Cape Breton Island, Nova Scotia." Canadian Journal of Earth Sciences 28, no. 11 (November 1, 1991): 1769–79. http://dx.doi.org/10.1139/e91-158.
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Interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of Ordovician to Silurian age are characteristic of the Aspy terrane of northwestern Cape Breton Island. These rocks were affected by medium- to high-grade metamorphism and were intruded by synkinematic granitoid orthogneisses during Late Silurian to Early Devonian times. They were intruded by posttectonic Devonian granitic plutons and experienced rapid Devonian decompression and cooling. The chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic-arc setting. The volcanic rocks of the Aspy terrane differ from many other Silurian and Silurian–Devonian successions in Atlantic Canada, which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within-plate settings, and are somewhat younger than the Aspy terrane sequences. Aspy terrane units are most similar to Ordovician–Silurian volcanic and metamorphic units in southwestern Newfoundland, including the La Poile Group and the Port aux Basques gneiss. Together with other occurrences of Late Ordovician to Early Silurian volcanic-arc units, they indicate that subduction-related compressional tectonics continued into the Silurian in parts of the northern Appalachian Orogen. The complex Late Silurian – Devonian tectonic history of the Aspy terrane may reflect collision with the southeastern edge of a Grenvillian crustal promentory.
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BORYSENKO, Tamara. "CORRELATION OF THE SILURIAN SEQUENCE OF THE 25-KOTYUZHINY STRUCTURAL WELL WITH THE DNIESTER REFERENCE SECTION OF THE SILURIAN IN THE VOLYN-PODILLYA PLATE." Ukrainian Geologist, no. 1-2(44-45) (June 30, 2021): 127–34. http://dx.doi.org/10.53087/ug.2021.1-2(44-45).238962.
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The paper is devoted to lithostratigraphic and biostratigraphic subdivision of the Silurian deposits of 358 m total thickness in the 25-Kotyuzhiny structural well and its comparison with the stratotypic Dniester section of the Silurian system in accordance with Legend to the geological map of Ukraine, the Volyn-Podolsky series of 1: 200 000 scale, consistent with the latest modernization of Silurian stratigraphic charts. The described section is a parastratotype for Silurian litho-stratons of the Kovel-Khotyn structural and facies zone and a reference one for Silurian deposits in the central part of this zone. The Silurian in the 25-Kotyuzhiny well is represented by the lower (Llandoverian and Wenlockian stages) and upper (Ludlovian and Przhidolian stages) series. According to the lithological-facies composition and sedimetantaion conditions during Silurian times, there are 3 major completed stages of sedimentation as transgressive-regressive cycles, corresponding to the the Yarugian, Malinovetsian and Rukshinian series, which are quite clearly subdivided into 10 suites and 12 sub-suites. In correlation with the Dniester reference section, litho-stratons of the Silurian are characterized mainly by carbonate and clay-carbonate composition, relative stable thickness and facies pattren, diversity of fauna with a predominance of shallow benthic forms. The well is characterized by bituninous manifestations indicating hydrocarbon potential of the area and its prospectivity for shale gas accumualtions in the formations of the upper Silurian in particular.
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Williams, D. Michael, and P. D. O'Connor. "Environment of deposition of conglomerates from the Silurian of north Galway, Ireland." Transactions of the Royal Society of Edinburgh: Earth Sciences 78, no. 3 (1987): 129–32. http://dx.doi.org/10.1017/s0263593300011056.
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ABSTRACTConglomerates from the Lettergesh Formation in the Silurian sequence of N Galway, Ireland, demonstrate palaeocurrents from the NE. Fabric studies demonstrate that the conglomerates were emplaced largely by traction currents and not by down-slope sliding or dispersive currents. Stratigraphic relationships demonstrate that the conglomerates were deposited in an environment which was adjacent to fluviatile, shallow-marine and deeper shelf facies at different times. A fan-delta environment of deposition is suggested, which requires a modification of previous Silurian sea-level curves at, or near, the base of the Wenlock.
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Yochelson, Ellis. "The Decline of The Use of "Lower Silurian" and The Rise of "Ordovician" In U.S. Geologic Literature." Earth Sciences History 16, no. 1 (January 1, 1997): 4–12. http://dx.doi.org/10.17704/eshi.16.1.6844363517t44154.
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During the 1880s and 1890s, the term "Lower Silurian" was in common use in United States geologic literature, whereas use of "Ordovician" was exceedingly rare. The few comments regarding Ordovician which appeared were mostly based on concepts of priority and advocated usage of Lower Silurian. J. D. Dana, author of the most significant textbook of the time, consistently opposed adoption of the term. However, by the early 1900s, Ordovician was widely used in the literature and in 1903 it was adopted for use by the U.S. Geological Survey. There is no record of public discussion of the move away from Lower Silurian. C. D. Walcott, employed by the USGS throughout this interval, may have played a pivotal, but private, role in this change of stratigraphic nomenclature.
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Adrain, Jonathan M., and Lars Ramsköld. "Silurian Odontopleurinae (Trilobita) from the Cape Phillips Formation, Arctic Canada." Journal of Paleontology 71, no. 2 (March 1997): 237–61. http://dx.doi.org/10.1017/s0022336000039160.
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Odontopleurids are a diverse component of rich silicified trilobite faunas recovered from the Wenlock and Ludlow of the Cape Phillips Formation, central Canadian Arctic. Odontopleurinae and Acidaspidinae are common, but Ceratocephalinae and Koneprusiinae are also represented. This work treats all of the Odontopleurinae, with the exception of the genus Acanthalomina Prantl and Přibyl, 1949.New species of Kettneraspis Prantl and Přibyl, 1949, include the upper Sheinwoodian K. wrightae, the lower Homerian K. lindoei, and the Gorstian K. caldwelli. Rare specimens assigned to Odontopleura Emmrich, 1839, and Radiaspis Richter and Richter, 1917, occur in the Sheinwoodian of the central Arctic.Edgecombeaspis (type species E. johansonae new species) is proposed for an odontopleurine clade endemic to Laurentia, and in the Silurian restricted to northern Laurentia. Cladistic analysis yields a hypothesis of ingroup structure that is in general calibrated with stratigraphic sequence. An exception is a group of Telychian species from the Mackenzie Mountains, whose stratigraphic sequence was used to support a previous hypothesis of an ancestral-descendant lineage. The cladistic result indicates that the stratigraphic pattern is the inverse of the phylogenetic pattern: the stratigraphically lowest species in the proposed lineage is the most derived, and the highest is most primitive. In addition to the type, new species of Edgecombeaspis include the mid-Sheinwoodian E. jahansi and the lower Homerian E. soehni. Edgecombeaspis apparently became extinct in the Homerian.The species Kettneraspis lenzi (Chatterton and Perry, 1983) and Radiaspis cf. R. norfordi (Chatterton and Perry, 1983) occur in the central Arctic, and further strengthen previous correlations with strata in the central Mackenzie Mountains, Northwest Territories.
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Sobolevskaya, R. F., and L. V. Nekhorosheva. "THE REGIONAL STRATIGRAPHIC CHART OF THE SILURIAN DEPORTS OF TAYMYR." GEOLOGY AND MINERAL RESOURCES OF SIBERIA, no. 5s (2016): 83–104. http://dx.doi.org/10.20403/2078-0575-2016-5s-83-104.
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Le Hérisse, Alain, Haytham Al-Tayyar, and Hans van der Eem. "Stratigraphic and paleogeographical significance of Silurian acritarchs from Saudi Arabia." Review of Palaeobotany and Palynology 89, no. 1-2 (November 1995): 49–74. http://dx.doi.org/10.1016/0034-6667(95)00041-u.
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Wilson, Reginald A., and Sandra L. Kamo. "The Salinic Orogeny in northern New Brunswick: geochronological constraints and implications for Silurian stratigraphic nomenclature1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology." Canadian Journal of Earth Sciences 49, no. 1 (January 2012): 222–38. http://dx.doi.org/10.1139/e11-041.
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The Salinic Orogeny is defined to encompass tectonic interactions that affect all elements of Ganderia involved in the closure of the Tetagouche–Exploits back-arc basin between the Late Ordovician and Early Devonian. Hence, the D1 and D2 deformations in the Miramichi Highlands and Elmtree Inlier of northern New Brunswick are Salinic events, and onlap of Lower Silurian rocks onto exhumed parts of the Brunswick Subduction Complex represents the earliest (Salinic A) of three Silurian unconformities in the region. Upper Ordovician to Lower Silurian rocks of the Matapédia successor basin contain widespread evidence of Middle Silurian tectonism (e.g., disconformities, angular unconformities, and fold interference patterns) created by Devonian overprinting of Silurian folds lacking axial planar cleavage (Salinic B). Recent U–Pb radioisotopic dating of chemically abraded zircon from rhyolite just above the Salinic B unconformity has yielded an age of 422.3 ± 0.3 Ma; combined with late Early Silurian fossil ages just below the unconformity, this indicates a ca. 5 million year Middle Silurian hiatus. Finally, Upper Silurian (Ludfordian) rocks are locally disconformably overlain by polymictic conglomerates that form the base of the Devonian section (Salinic C). All Silurian rocks in northeastern New Brunswick have historically been included in the Chaleurs Group; however, unconformities and local stratigraphic variations (especially compared with the type locality) support the introduction of new higher rank names in New Brunswick. Hence, the Quinn Point Group is introduced to incorporate Lower Silurian rocks, the Petit Rocher Group to include Upper Silurian sedimentary rocks in the Nigadoo River Syncline, and the Dickie Cove Group for Upper Silurian volcanic rocks in the Charlo – Jacquet River area. Upper Silurian rocks west of Campbellton that are contiguous with the Chaleurs Group in Quebec, will remain part of the Chaleurs Group.
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Jeppsson, L., V. Viira, and P. Männik. "Silurian conodont-based correlations between Gotland (Sweden) and Saaremaa (Estonia)." Geological Magazine 131, no. 2 (March 1994): 201–18. http://dx.doi.org/10.1017/s0016756800010736.
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AbstractCorrelations between the Silurian successions of Gotland and the East Baltic are based on the narrowest stratigraphic units that can be distinguished in both areas. In order further to increase precision, true ends of ranges in measured sections have been used instead of ‘pooled’ formational faunas, where outcrops and collections permit. Some previous correlations are confirmed. In other cases, there are considerable changes both in levels of correlation and in precision. The major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards. At least some of these gaps decrease in magnitude southwards in Estonia. Gaps at these levels are also noted on Gotland, although they are small and probably do not extend across the island. The patterns through time of deposition (during secundo episodes) and gaps (during primo episodes) agree very well with what can be predicted from a model of oceanic and climatic cyclicity.
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Larsen, P., and J. C. Escher. "A stratigraphic section through the Silurian turbidite sequence (Peary Land Group)in northern Nyeboe Land, North Greenland." Rapport Grønlands Geologiske Undersøgelse 151 (January 1, 1991): 1–21. http://dx.doi.org/10.34194/rapggu.v151.8140.
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A stratigraphic section is presented through the 6330 m thick Silurian turbidite sequence of the Peary Land Group at Hand Bugt in northern Nyeboe Land, North Greenland. Thickness, age and sediment characteristics of the Merqujoq, Lauge Koch Land, Wulff Land and Nyeboe Land Formations, the Castle Ø Member of Nordkronen Formation and the Chester Bjerg Formation are described.
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Bultynck, Pierre, and Léon Dejonghe. "Preface." Geologica Belgica 4, no. 1-2 (April 15, 2002): 3–4. http://dx.doi.org/10.20341/gb.2014.041.
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The lithostratigraphic guide of Belgium is subdivided into ten chapters dealing respectively with Cambriam-Ordovician-Silurian formations, Devonian formations, Lower Carboniferous formations, Upper Carboniferous formations, Permian formations, Triassic and Jurassic formations, Cretaceous formations, Paleogene and Neogene formations, Quaternary formations. The different chapters have been prepared by the respective national stratigraphic subcommissions set up by the Belgian National Committee for Geological Sciences.
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Beznosova, Tatiana, and V. Matveev. "Regional carbon isotope curve and biotic events in the Silurian of the Western slope of the Subpolar Urals and Chernov Uplift." Vestnik of geosciences, no. 9 (November 28, 2022): 31–36. http://dx.doi.org/10.19110/geov.2022.9.4.
Full textAbstract:
We present a new regional event scale based on a generalized analysis of results of determination of event-stratigraphic boundaries of biotic events of various levels and 13C isotope anomalies in studied reference sections of the Subpolar Urals and the Chernov Uplift.
The combined regional curve of carbon isotopic composition allows finding out several isotopic events in the Silurian.
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žigaitė, živilė, Valentina Karatajūtė-Talimaa, and Alain Blieck. "Vertebrate microremains from the Lower Silurian of Siberia and Central Asia: palaeobiodiversity and palaeobiogeography." Journal of Micropalaeontology 30, no. 2 (September 1, 2011): 97–106. http://dx.doi.org/10.1144/0262-821x11-016.
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Abstract. The biostratigraphic and palaeogeographical distributions of early vertebrate microfossils from a number of Lower Silurian localities in northwestern Mongolia, Tuva and southern Siberia were reviewed. Vertebrate microremains showed high taxonomic diversity, comprising acanthodians, chondrichthyans, putative galeaspids, heterostracans, mongolepids, tesakoviaspids, thelodonts and possible eriptychiids. The majority of taxa have lower stratigraphic levels of occurrence compared to other Silurian palaeobiogeographical provinces, such as the European-Russian or Canadian Arctic. Vertebrate microremains are numerous within the samples, which may indicate warm-water low-latitude palaeobasins with rich shelf faunas. This disagrees with the recent interpretations of the territory as a northern high-latitude Siberian palaeocontinent. The palaeobiogeographical distribution of vertebrate taxa indicates an endemic palaeobiogeographical province of connected epeiric palaeoseas with external isolation during the early Silurian. In previous works separation between Tuvan and Siberian palaeobiogeographical provinces has been suggested. After careful revision of the vertebrate microfossil record of the region, we find that differences in a few vertebrate taxa do not provide not strong enough evidence to reliably distinguish these provinces. We therefore dispute the hypothesis of two biogeographical provinces in the early Silurian of the Siberian palaeocontinent, and propose a single unified Siberian–Tuvan palaeobiogeographical province.
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Edgecombe, Gregory D. "Encrinurine trilobites from the Silurian Brownsport Formation of Tennessee." Journal of Paleontology 64, no. 6 (November 1990): 961–67. http://dx.doi.org/10.1017/s0022336000020035.
Full textAbstract:
Encrinurinae from the Ludlovian Brownsport Formation in west central Tennessee include Balizoma ramskoeldi n. sp., Fragiscutum glebale Campbell, 1967, and Mackenziurus sp. Balizoma ramskoeldi is most similar to Ludlovian species in England and Gotland. The discovery of F. glebale in Tennessee extends the geographic range of this species, known also from the correlative Henryhouse Formation in Oklahoma. Fragiscutum is an eastern/southern Laurentian endemic; Balizoma is of Wenlockian–Přidolían range, with its most widespread Euramerican distribution in the Ludlow. The stratigraphic range of Mackenziurus is extended into the Ludlow.
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Mauviel, Alain, and André Desrochers. "A high-resolution, continuous δ13C record spanning the Ordovician–Silurian boundary on Anticosti Island, eastern Canada." Canadian Journal of Earth Sciences 53, no. 8 (August 2016): 795–801. http://dx.doi.org/10.1139/cjes-2016-0003.
Full textAbstract:
One of the best-exposed and most complete stratigraphic records from paleotropical areas spanning the Ordovician–Silurian (O–S) boundary is located on Anticosti Island, eastern Canada. Our study is the first one to sample strata superbly exposed at low tide along the west coast of Anticosti Island, thus providing a previously unexploited, nearly complete stratigraphic interval (∼300 m) at the O–S boundary for δ13C chemostratigraphy. A new high-resolution δ13C curve with more than 500 data points spaced at every ∼0.5 m has been produced, rectifying important pitfalls of previously published δ13C curves (i.e., low sampling resolution, variable sampling intervals, stratigraphic gaps). This new high-resolution δ13C curve displays a lower and an upper positive Hirnantian Isotope Carbon Excursion (HICE) recognized elsewhere around the globe. The ascending limb of the lower HICE starting from baseline values of +0.5‰ corresponds to the upper 20 m of the late Katian Vauréal Formation, but δ13C peak values of +2.5‰ occur in the lower part of the Hirnantian Ellis Bay Formation. In spite of a δ13C record segmented by a few stratigraphic hiatuses, the upper HICE, with its peak values of +4.5‰, is well recorded in the upper part of the Hirnantian Ellis Bay Formation. When compared with sections from around the globe, our δ13C curve displays a distinct long-term trend with a long sustained lower HICE followed abruptly by the upper HICE and return to baseline values of +0.5‰ prior to the Rhuddanian. The continued descending isotopic trend well into the Becscie Formation suggests that the O–S boundary may occur at a higher stratigraphic level (up to 30 m) than previously interpreted. Active subsidence combined with moderate initial water depths prior to the Hirnantian were key factors controlling the deposition of a thick O–S sedimentary succession with a few hiatuses on Anticosti Island and capturing a comprehensive, reliable δ13C record across this interval.
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Lavoie, Denis, and Esther Asselin. "A new stratigraphic framework for the Gaspé Belt in southern Quebec: implications for the pre-Acadian Appalachians of eastern Canada." Canadian Journal of Earth Sciences 41, no. 5 (May 1, 2004): 507–25. http://dx.doi.org/10.1139/e03-099.
Full textAbstract:
The post-Taconian units in the Quebec and northern New Brunswick Appalachians constitute the Gaspé Belt and geological studies have mostly focussed on its eastern Quebec segment. Biostratigraphic data indicate that the succession in southern Quebec is no older than Late Silurian and extends into the Early Devonian. Two distinct stratigraphic assemblages are present. The first assemblage (Saint-Luc, Cranbourne, and Lac Aylmer formations, and Glenbrooke Group) unconformably overlies the Humber and Dunnage zones. The units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection, which have recorded a post-Late Silurian transgressive event. The second assemblage (Saint-Francis Group and Frontenac Formation) is faulted against either Dunnage units or autochthonous post-Taconian units. It locally unconformably overlies units of the Dunnage Zone; the succession shows progressively deeper marine conditions upsection and also has recorded a post-Late Silurian transgressive event. The biostratigraphic framework suggests that some of the units that were assumed to be vertically stacked are rather laterally equivalent. Independant evidence supports the hypothesis that the Gaspé Belt in southern Quebec formed after the collapse of the Taconian orogen in Late Silurian time. This event is ascribed to the Salinian Orogeny. The framework from southern Quebec is incorporated in a regional scenario. The Gaspé Belt experienced a PridolianLochkovian sea-level rise. In Pragian time, shallower marine conditions were established in southern Quebec, whereas in the Gaspé Peninsula, the shallower conditions only occurred in early Emsian time.
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Suchy, Daniel R., and Colin W. Stearn. "Evidence of a continent-wide fault system on the Attawapiskat River, Hudson Bay Platform, northern Ontario." Canadian Journal of Earth Sciences 30, no. 8 (August 1, 1993): 1668–73. http://dx.doi.org/10.1139/e93-145.
Full textAbstract:
The grouping of areas of outcrop of Lower Silurian reefs along a stretch of the Attawapiskat River west of James Bay (northern Ontario, Canada) is controlled by a conjugate set of faults striking approximately 60 and 280°. The faults are evident in disturbed outcrops along the river and in subtle lineaments revealed in aerial photographs and Landsat imagery in the surrounding marshland topography. Slumping of large blocks from a reef crest in Silurian time and stratigraphic relationships within the Hudson Basin indicate a major episode of movement in late Llandovery time. Movements on the fault set have been traced back to Proterozoic time and, to affect the present subdued topography recently emerged from marine inundation, must have been renewed in rapid recent postglacial uplift of this area.
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Ausich, William I., and Mario E. Cournoyer. "New taxa and revised stratigraphic distribution of the crinoid fauna from Anticosti Island, Québec, Canada (Late Ordovician-early Silurian)." Journal of Paleontology 93, no. 06 (May 31, 2019): 1137–58. http://dx.doi.org/10.1017/jpa.2019.36.
Full textAbstract:
AbstractEnd-Ordovician extinctions had a profound effect on shallow-water benthic communities, including the Crinoidea. Further, recovery after the extinctions resulted in a macroevolutionary turnover in crinoid faunas. Anticosti Island is the most complete Ordovician-Silurian boundary section recording shallow-water habitats. Both new taxa and changes in Anticosti Island stratigraphic nomenclature are addressed herein. New taxa includeBecsciecrinus groulxin. sp.,Bucucrinus isotaloin. sp.,Jovacrinus clarkin. sp.,Plicodendrocrinus petrykin. sp.,Plicodendrocrinus martinin. sp.,Thalamocrinus daoustaen. sp., andLateranicrinus saintlaurentin. gen. n. sp. The status ofXenocrinus rubusas a boundary-crossing taxon is confirmed, range extensions of several taxa are documented, and the distribution of crinoids with the revised stratigraphic nomenclature is documented.UUID:http://zoobank.org/19613a44-ec69-47d7-88ab-fcf88ba771f0.
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Cramer, Bradley D., Thijs R. A. Vandenbroucke, and Gregory A. Ludvigson. "High-Resolution Event Stratigraphy (HiRES) and the quantification of stratigraphic uncertainty: Silurian examples of the quest for precision in stratigraphy." Earth-Science Reviews 141 (February 2015): 136–53. http://dx.doi.org/10.1016/j.earscirev.2014.11.011.
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Al-Hadidy, Aboosh H. "Paleozoic stratigraphic lexicon and hydrocarbon habitat of Iraq." GeoArabia 12, no. 1 (January 1, 2007): 63–130. http://dx.doi.org/10.2113/geoarabia120163.
Full textAbstract:
ABSTRACT The crystalline Proterozoic Basement does not crop out in Iraq, but is interpreted from seismic and geophysical potential data to range in depth from about 6–10 km in western Iraq, to 12–15 km in the Zagros Mountains, in eastern Iraq. The Cambrian and Lower Ordovician sedimentary successions of Jordan and Saudi Arabia (including the Middle Cambrian Burj carbonates) are interpreted to extend into Iraq based on seismic data and regional correlations. The entire Paleozoic succssion is about 3–4 km thick. The Ordovician-Permian succession in Iraq consists of ten formations that are here described in a lexicon format. For each formation, the type and reference sections in outcrop or/and subsurface are reviewed (as defined by the original authors or herein), and further documented by including subsurface data (electrical logs and biostratigraphic studies). The Ordovician-Permian formations (and their members) are here placed chronostratigraphically according to the “Geological Time Scale GTS 2004” (and standard global Ordovician stages) and the Arabian Plate sequence stratigraphic framework. The ten formations are: (1) the Early?, Middle and Late Ordovician Khabour Formation (with from base-up seven informal members K7 to K1); (2) the Silurian Akkas Formation (with the proposed lower Hoseiba and upper Qaim members); (3 and 4) the Late Devonian Pirispiki Red Beds Formation and enclosed Chalki Volcanics; (5) the Late Devonian (Famennian) and early Carboniferous (early Tournaisian) Kaista Formation; (6) the Carboniferous (Tournaisian) Ora Formation; (7) the Carboniferous (Tournaisian-Visean) Harur Limestone Formation; (8) the Visean-Serpukhovian Raha Formation (proposed here); (9) the late Carboniferous-early Middle Permian Ga’ara Formation; and (10) the late Middle and Late Permian Chia Zairi Formation (in outcrop consisting from base-up of the informal Dariri, Satina Anhydrite and Zinnar members). The Late Devonian-early Carboniferous succession, comprising the Pirispiki, Chalki, Kaista, Ora, Harur and Raha formations, is here proposed to comprise the Khleisia Group. The Paleozoic succession of Iraq is hydrocarbon-prospective in the western part of the country, and particularly in the Western Desert near Jordan, Saudi Arabia and Syria. The source-rock component of the petroleum system consists of several potential organic-rich shales including the regionally widespread Silurian Akkas “hot shale”. In the Akkas-1 well, two hot shale units have a combined thickness of 61 m (210 ft) and total organic carbon (TOC) values that reach 16.6%. Several reservoirs and seals present exploration targets in the Western Desert of Iraq. In the Akkas field, light (specific gravity of 42° API), sweet oil and gas (no H2S) were discovered in 1993 in the Akkas and Khabour formations, respectively. The Akkas reservoir occurs in the upper Qaim Member of the Silurian Akkas Formation and consists of sandstones that have a porosity of 6.5% and permeability of 0.2 mD. The Khabour reservoir occurs in the Upper Ordovician K1–K4 members and consists of sandstones with a fracture porosity of up to 7.6% and permeability of 0.13 mD. In North Iraq the carbonates of the Permian Chia Zairi and Triassic Mirga Mir formations correlate to gas reservoirs in the Khuff Formation of Arabia and the Dalan and Kangan formations of Iran, and may therefore be prospective. Southern Iraq, along the Kuwait and Saudi Arabian border, may also be prospective; however, no wells have been drilled into the deep Paleozoic succession in this vast region.
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Machulina, S. O., and O. P. Oliinyk. "BLACK SHALES OF SILURIAN AND DEVONIAN DEPOSITS OF THE FORE-DOBROGEA TROUGH." Geological Journal, no. 4 (December 28, 2021): 90–103. http://dx.doi.org/10.30836/igs.1025-6814.2021.4.238357.
Full textAbstract:
The article discusses the structural features of the Paleozoic (Silurian and Devonian) deposits of the Fore-Dobrogea Trough, a promising oil and gas region of Ukraine, with the aim of identifying black shale strata enriched with organic matter in them. Such strata under certain geological-thermobaric conditions obtain oil and gas generating properties and can be sources of hydrocarbons. This study included analysis of the core data and geophysical logs of deep wells and the cyclostratigraphic division of the Silurian and Devonian deposits. Within the sedimentation cycles of the Silurian and Devonian, the stratigraphic levels of the black-shales strata have been identified. Features of their lithological composition, the facies-geochemical conditions of accumulation, and spatial distribution have been determined. Carbonate-terrigenous strata of the Skal horizon of the Lower Silurian and clay strata of the Upper Silurian developed in the depressions of the Fore-Dobrogea Trough and island Zmiinyi, are classified as strata of the black shale type. They are characterized by a high content of sapropel organic matter. In the Middle-Upper Devonian sedimentary complex, the most significant black-shale strata is the Middle Devonian (Givetian), composed of alternating marls and pyritized argillites, accumulated in the reducing conditions of the aquagenic basin, which was favorable for the formation of petroleum bitumoids. Based on these studies, the prospects for the oil and gas content of the Fore-Dobrogea Trough have been substantiated.
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West Jr, David P., Charles V. Guidotti, and Daniel R. Lux. "Silurian orogenesis in the western Penobscot Bay region, Maine." Canadian Journal of Earth Sciences 32, no. 11 (November 1, 1995): 1845–58. http://dx.doi.org/10.1139/e95-142.
Full textAbstract:
New 40Ar/39Ar mineral ages from rocks collected west of Penobscot Bay, Maine, indicate this region was regionally deformed, metamorphosed to amphibolite facies conditions, and intruded by plutons in Silurian times rather than in the Devonian as previously assumed. Disturbed hornblende age spectra, along with the presence of some Devonian felsic plutons and extensive retrograde metamorphic textures do suggest, however, that these rocks were subsequently affected by low-grade Devonian thermal events. In sharp contrast, rocks west of the Sennebec Pond thrust fault, a major tectono-stratigraphic boundary in this region, lack a significant Silurian tectono-thermal signature, and instead record the effects of intense Devonian deformation and high-grade regional metamorphism. The data suggest the two regions experienced very different pre-Devonian histories and were most likely juxtaposed by the Sennebec Pond thrust fault in latest Silurian to Early Devonian time. Rocks now exposed east of the Sennebec Pond fault probably occupied much higher structural levels during Devonian orogenesis and were not subjected to the same intense Devonian deformation and metamorphism as those rocks now found to the west of this structure. The Silurian tectonism now recognized in this region bears striking resemblance to events of similar age recorded along the northwest margin of the Avalon composite terrane throughout much of Atlantic Canada. This greatly extends the zone of Silurian orogenesis in the northern Appalachians and requires that previous models of New England middle Paleozoic tectonism be significantly revised.
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Holland, Charles Hepworth, and Paul Copper. "Ordovician and Silurian nautiloid cephalopods from Anticosti Island: traject across the Ordovician–Silurian (O–S) mass extinction boundary." Canadian Journal of Earth Sciences 45, no. 9 (September 2008): 1015–38. http://dx.doi.org/10.1139/e08-048.
Full textAbstract:
Well-preserved shells of Ashgill (Katian–Hirnantian) and Llandovery nautiloids from Anticosti Island include the type species of 10 genera. From a diversity high of some 40 described nektic and nektobenthic species during the deeper water, distal shelf facies of the Vaureal Formation (late Katian, Richmondian), the succeeding Hirnantian shows a decline to ca. 19 species in the shallower water Ellis Bay Formation. A number of Katian species possessed very large orthoconchs (>1 m in length), but Hirnantian species were less than half that size. The initial earliest Silurian (Rhuddanian, Becscie Formation) recovery nautiloid fauna is impoverished, with low diversity (one sp.?), and generally dwarfed, to shells with diameters of <1 cm. Nautiloid diversity expanded and progressed to some 22 species in the late Aeronian through Telychian Jupiter and Chicotte formations, with an apparent peak in the Goéland Member of the Jupiter Formation. Three new species, Actinoceras lesperancei , Eridites barnesi , and Diestoceras macgilvrayoceras , are described. The distribution of shells within the succession defines the fauna’s stratigraphic and paleobiogeographic significance, with a changing mix of Baltic and Laurentian taxa.
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Benachour, Houcine B., Kaddour Mebarki, Mustapha Bensalah, David M. Kroeck, Navid Navidi-Izad, Sylvie Régnier, and Thomas Servais. "Lower Palaeozoic acritarchs from the Traras Mountains – First evidence of Ordovician sediments in northwestern Algeria." Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 297, no. 1 (July 1, 2020): 113–23. http://dx.doi.org/10.1127/njgpa/2020/0917.
Full textAbstract:
The oldest sediments of the Traras Mountains in northwestern Algeria have been analyzed palynologically. Several levels of the 'Formation des Psammites bioturbés' provide few specimens of poorly preserved acritarchs, that nevertheless allow a stratigraphic attribution of the investigated section to the Middle to Upper Ordovician, due to the presence of specimens that can be tentatively attributed to the acritarch species Orthosphaeridium bispinosum and Villosacapsula setosapellicula. This is the first biostratigraphic age assignment for pre-Silurian sediments of northwestern Algeria.
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Huang, Yizhou, Zhenxue Jiang, Kun Zhang, Yan Song, Shu Jiang, Weiwei Liu, Ming Wen, et al. "Effect of Hydrothermal Activity on Organic Matter Enrichment of Shale: A Case Study of the Upper Ordovician and the Lower Silurian in the Lower Yangtze, South China." Minerals 8, no. 11 (November 1, 2018): 495. http://dx.doi.org/10.3390/min8110495.
Full textAbstract:
The effect of organic matter on hydrocarbon potential, storage space, and gas content of shale is well-known. Additionally, present-day content of sedimentary organic matter in shale is controlled by depositional and preservation processes. Therefore, a study of the enrichment mechanisms of sedimentary organic matter provides a scientific basis for the determination of favorable areas of shale gas. In this study the Upper Ordovician Xinkailing Fm. and the first member of the Lower Silurian Lishuwo Fm. were examined. Stratigraphic sequences were identified through conventional logs and elemental capture spectrum data. Oxygen isotope analysis was applied to recover paleotemperature of seawater in the study area. The excess silicon content was calculated and the origin of the silica was determined by the Fe-Al-Mn ternary plot. The enrichment mechanism of organic matter was analyzed by two aspects: redox conditions and paleoproductivity. As a result, the stratigraphic interval was divided into two 3rd-order sequences. Through oxygen isotope, the paleotemperature of seawater was 62.7–79.2 °C, providing evidence of the development of hydrothermal activity. Analysis of excess siliceous minerals identified two siliceous mineral origins: terrigenous and hydrothermal. It also revealed an upwards decreasing tendency in hydrothermal activity intensity. Strong hydrothermal activity during the Late Ordovician, recognized as TST1, formed a weak-oxidizing to poor-oxygen environment with high paleoproductivity, which promoted organic matter enrichment. During the Late Ordovician to the Early Silurian, identified as RST1, TST2, and RST2, weakening hydrothermal activity caused the decline of paleoproductivity and increased oxidation of bottom waters, leading to a relative decrease of organic matter content in the shale. Therefore, favorable areas of shale gas accumulation in the Upper Ordovician and Lower Silurian are determined stratigraphically as the TST1, with a high total organic carbonate content. Geographically, the hydrothermally-active area near the plate connection of the Yangtze and the Cathaysian is most favorable.
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Fordham, Barry G. "Chronometric calibration of mid-Ordovician to Tournaisian conodont zones: a compilation from recent graphic-correlation and isotope studies." Geological Magazine 129, no. 6 (November 1992): 709–21. http://dx.doi.org/10.1017/s001675680000844x.
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AbstractThree available graphic-correlation analyses are used to calibrate mid-Palaeozoic conodont zonations: Sweet's scheme for the mid- to Upper Ordovician; Kleffner's for the mid- to Upper Silurian; and Murphy & Berry's for the lower and middle Lower Devonian. The scheme of Sweet is scaled by applying the high-precision U-Pb zircon date of Tucker and others for the Rocklandian and linked with that of Kleffner by scaling the graptolite sequence of the Ordovician-Silurian global stratotype section to fit two similarly derived dates from this sequence. The top of Kleffner's scheme, all of Murphy & Berry's, as well as standard zones to the Frasnian are calibrated by using tie-points of the latest Cambridge-BP time-scale (GTS 89). However, the recent microbeam zircon date by Claoué-Long and others for the Hasselbachtal Devonian-Carboniferous auxiliary stratotype is used to calibrate the standard Famennian zones. Also the similarly derived but preliminary determination reported by Roberts and others from the Isismurra Formation of New South Wales is tentatively taken as the top of the Tournaisian and so used to calibrate Tournaisian zones. Despite the considerable extrapolation required to compile these schemes and their inherent errors, the resultant time-scale closely agrees with other dates of Tucker and others from the Llanvirn as well as the GTS 89 Homerian-Gorstian tie-point. This suggests that stratigraphic methods can be usefully applied to geochronometry. The Llandovery appears to have lasted longer (16 m. y.) than usually envisaged and the Ordovician-Silurian boundary may need to be lowered to approximately 443.5 Ma. Certainly, chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high-resolution dating for their calibration will be crucial to more accurate biochronometries.
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Lykova, Elena V., and Nikolay V. Sennikov. "GRAPTOLITES FROM THE UPPER ORDOVICIAN SECTION «VERKHNYAYA KARASU» IN THE CENTRAL PART OF GORNY ALTAI." Interexpo GEO-Siberia 2, no. 1 (May 21, 2021): 125–29. http://dx.doi.org/10.33764/2618-981x-2021-2-1-125-129.
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Taxonomic complex of graptolites from the «Verkhnyaya Karasu» section have been studied. This section is located in the central part of Gorny Altai Mountains. The section covers a large stratigraphic interval: from upper Ordovician (Sandbian Stage) to Middle Silurian (Telychian Stage). For the Ordovician, the Bugryshikha, Khankhara and Tekhten' formations are distinguished. For the Silurian, the Vtorye Utyosy, Syrovaty, Polaty, Chesnokovka and Chesnokovka formations are distinguished. Previously, in this section no graptolites were found in the upper part of the Bugryshikha formation. There is a large and diverse complex of taxa collected in 2020. The graptolites assemblage from the upper part of the Bugryshikha formation consists of Reteograptus uniformis Mu et Zhang, Reteograptus geinitzianus Hall, Eoglyptograptus euglyphus Mitchell, Orthograptus apiculatus Elles et Wood, Orthograptus whitfieldi (Hall), Rectograptus truncatus (Lapworth), Rectograptus ex.gr. truncatus (Lapworth), Hustedograptus sp., Callograptus sp.
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Watkins, Rodney, Kathleen A. Walsh, and Jeffrey J. Kuglitsch. "Silurian (Llandovery/Wenlock) foraminiferida in carbonate environments of southeastern Wisconsin." Journal of Paleontology 73, no. 3 (May 1999): 540–46. http://dx.doi.org/10.1017/s0022336000028043.
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This note presents the first stratigraphic, paleoenvironmental, and systematic account of Silurian foraminifers in Wisconsin, which include nine previously described species of Ammodiscus, Glomospirella, Hemisphaerammina, Hyperammina, Lagenammina, Psammosphaera, Stomasphaera, Thurammina, and Webbinelloidea (Appendix 1). Early Silurian carbonates in this area (Fig. 1) were deposited in shelf and ramp environments in the western part of the Michigan Basin (Harris et al., 1998), and the foraminifers are associated with macrofaunal communities that represent Benthic Assemblages BA3 to BA5 of Brett et al. (1993).Silicified agglutinated foraminifers were obtained from acidinsoluble residues processed for conodonts, sponge spicules, and macrofauna (Watkins et al., 1994; Kuglitsch, 1996; Watkins and Kuglitsch, 1997; Watkins and Coorough 1997a, 1997b). Silicification of the specimens, rather than a composition of agglutinated siliceous grains, is indicated by lack of detrital silica in enclosing dolostones, variable detail of preservation, and association with other silicified fossils.
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Gray, Jane, A. J. Boucot, Yngve Grahn, and Gregory Himes. "A new record of early Silurian land plant spores from the Paraná Basin, Paraguay (Malvinokaffric Realm)." Geological Magazine 129, no. 6 (November 1992): 741–52. http://dx.doi.org/10.1017/s0016756800008463.
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AbstractThe first conclusive evidence for Silurian rocks in the Paraná Basin, Brazil, was reported in 1985. This evidence was based on organic-walled microfossils, principally spore tetrads, and associated phytoplankton (‘acritarchs’ and prasinophytes), the first recovered from the Vila Maria Formation on the northeastern rim of the Basin. The spore assemblage was typical of Gray's Microfossil Assemblage Zone I; size-frequency data for the tetrads suggested an early Silurian (early Llandovery; Rhuddanian) age. We now document a new MA Zone I occurrence of spore tetrads together with a few single trilete spores, from the southwestern rim of the Paraná Basin, Paraguay. The single spores are among the earliest known to have normally dissociated from a tetrahedral tetrad. Size-frequency data for the tetrads suggest a late Llandovery, pre-C5(mid-Telychian) age. These spores, together with phytoplankton and chitinozoans, were recovered from beds laterally equivalent to the Vargas Peña Shale at the type locality from which Llandovery diplograptids and monograptids are known. Llandovery age rocks on the southwesternandnortheastern borders of the Paraná Basin,c. 1400 km apart, suggest that early Silurian rocks were extensively distributed throughout southern Brazil and adjacent Paraguay. Close conformity between the age reference obtained with graptolites and spore tetrads again demonstrates the stratigraphic utility of early Silurian spores in providing reliable age determinations for otherwise unfossiliferous rocks. Spore tetrad assemblages available from the Malvinokaifric Realm (South America, Africa, Arabia) represent a distinct phytogeographic unit contrasted with spore tetrad assemblages from the North Silurian Realm of North America and parts of Europe.
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Beznosova, T. M., and V. A. Matveev. "Manifestation of the Late Aeronian event in the Silurian section on the western slope of the Subpolar Urals." LITHOSPHERE (Russia) 22, no. 5 (November 4, 2022): 599–611. http://dx.doi.org/10.24930/1681-9004-2022-22-5-599-611.
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Research subject. The article presents the results of studying traces of the global Late Aeronian biotic and isotopic (δ13Ccarb) events preserved in a new reference section of the Lower Silurian in the Subpolar Urals.Materials and methods. The samples of sedimentary rocks and microfauna, the results of isotope analysis, as well as the collections with remains of benthic fauna collected by the authors in different years during fieldwork were investigated. The studies were confirmed by sedimentological, biostratigraphic and chemostratigraphic data obtained by the authors.Results. The The event-stratigraphic interval, established in the upper part of the Lolashor stage (Aeronian) of the Silurian, is characterized by increasing regressive tendencies, decreasing biodiversity, disappearance of Pranognathus tenuis conodonts and brachiopods of the genus Pentamerus, as well as by δ13Ccarb anomalies in the upper strata of the Lolashor stage.Conclusions. The obtained data indicate a eustatic drop in the sea level, a major ecosystem restructuring, and a sedimentation gap at the end of the Lolashor time. The boundary between the Lolashor and Philippel stages (Aeronian and Telychian) records a sharp negative isotopic shift of δ13Ccarb, which was first observed in the Lower Silurian section in the European Northeast of Russia.
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Anastas, A. V. "ANALYSIS OF THE TAXONOMIC COMPOSI TION OF THE LLANDOVERIAN AND WENLOCKIAN FOSSILS OF MOLDAVIAN PRIDNESTROVYE ENTERED IN THE ELECTRONIC DATABASE “THE PALAEONTOLOGY OF PRIDNESTROVYE”." Odesa National University Herald. Geography and Geology 26, no. 1(38) (September 4, 2021): 169–91. http://dx.doi.org/10.18524/2303-9914.2021.1(38).234710.
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Problem statement and purpose. In geological surveys of the territory of the Moldavian SSR from the 1960th to the 1990th, deep horizons of Palaeozoic sedimentary rocks were discovered, the leading place among which belongs to the Silurian deposits. At that time, several dozen species and genera of fossils were identified in the Silurian of Moldavian Pridnestrovye. In 2020, as part of the work financed from the state budget on the theme of the creation of GIS “The Geology of Pridnestrovye”, the laboratory “The Geological Resources” developed an electronic database called “The Palaeontology of Pridnestrovye”. The fauna included in the database of palaeontology was divided into groups corresponding to their palaeontological classes and stratigraphic horizons: “Ordovician brachiopods”, “Silurian tabulates”, “Palaeogene foraminifers”, “Neogene bivalves”, etc. Species and genera of the fauna were linked to specific formations and locations, which provides good opportunity for palaeontological analysis of individual formations, horizons, cores of drilling and outcrops. The purpose of this article is to compile lists of fauna from the Llandoverian and Wenlockian formations of Moldavian Pridnestrovye and to compare their chronology with fossil fauna data on the sameage rocks of Podillia, Estonia and Lithuania. Material and methods. Four survey reports deal that on sheets L‑35-V and L‑35-XII were used as the material. The goal was concerning the sedimentary rocks of Llandovery and Wenlock Series. In the local scheme it corresponds to the Marasesti, Step-Soci, Cioc-Maidan (all in Llandovery), Balti formations and Lower Puhoi subformation (Wenlock). The intervals of the formations in boreholes are composed of organogenic limestones, silty, argillaceous stones, argillites and dolomites. The species and genera of the fauna from these intervals are compared with the biostratigraphic data from Podillia, Estonia and Lithuania. Results. In the stratigraphic sequences of Llandovery and Wenlock of the Moldavian Pridnestrovye, (in most cases) species and genera unique to those divisions of brachiopods, tabulates, stromatoporoids, ostracods, rugosans, and trilobites were identified by specialists; a smaller part of the taxa pass between the lowest formations of the Silurian and the overlying Balti formation. Most taxa have correspondences in the Podillian and Baltic basins; however, in these regions, the species and genera identified in Llandovery or Wenlock of Moldavian Pridnestrovye are mostly transitive between Silurian divisions, up to the Ludlow and Pridoli Series. There is practically no identified fauna in the Lower Puhoi sub-formation of Moldavian Pridnestrovye because of its facial specifics. The species Acidolites lateseptatus (Lindstroem), Altha modesta Neckaja, Longiscula caudalis (Jones) in Llandovery and Pentamerus oblongus Sowerby, Halysites catenularius Linnaeus = Halysites priscus Klaamann in Llandovery and Wenlock Series were the only guideing fauna for the first two Silurian series of Moldavian Pridnestrovye. Due to the attribution of the Muksha sub-formation of Podillia to Ludlow Series, no guiding species of the Wenlock stage was identified in the Balti formation of Moldavian Pridnestrovye.
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Ciurca, Samuel J. "New occurrences of Silurian eurypterids (Carcinosomatidae) in Pennsylvania, Ohio and New York." Paleontological Society Special Publications 6 (1992): 57. http://dx.doi.org/10.1017/s2475262200006171.
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Carcinosomatids are rare among the Silurian eurypterid faunas of northeastern United States. New discoveries, discussed below, extend the geographic and stratigraphic ranges of two important types:Paracarcinosoma, known primarily from the Bertie Group of western New York, andRhinocarcinosoma, known only from the Illion Shale of eastern New York. PENNSYLVANIA: The very distinctive Rhinocarcinosoma was obtained from rocks of the McKenzie Fm., below Bloomsburg redbeds, just east of Lock Haven. Remains consist of a well preserved carapace with characteristic 'shovel’ developed as an extension of the anterior portion of the carapace. This occurrence is analogous to the occurrence in the New York stratigraphic sequence 185 miles (285 km) to the northeast in the type area of the Illion Shale. At the New York localities, the eurypterid-bearing beds are overlain by the redbeds of the Vernon Fm. (Salina Group).OHIO: The Maumee Quarry east of Toledo has been studied extensively by many geologists. The stratigraphic sequence exposed consists of “Niagaran reefs” overlain by the Greenfield Fm. (Bass Islands Group) but with an impressive array of stromatolitic beds transitionally developed between the two units.In the transitional beds occur the scattered remains of Paracarcinosoma. Specimens are fragmentary, but a small well preserved carapace was obtained showing the intramarginal position of the compound eyes characteristic of this carcinosomatid. The specimens were obtained from fine-grained dolostone with no evidence of other fossils.NEW YORK: The original discovery of Rhinocarcinosoma, as described in 1912 by Clarke and Ruedemann, is here supplemented by new finds in the Illion Shale east of the type area and particularly by the discovery of this eurypterid in rocks of the Lockport Group near Sodus Center, N.Y. Exposures of the Sconondoa Fm. in the Sodus Quarry and in the streambed just to the north yielded numerous specimens. Particularly noteworthy is an operculum of the size and structure illustrated by Clarke and Ruedemann. The new occurrences in the Sodus Center area extend the geographic range of Rhinocarcinosoma westward about 100 miles (160 km).The carcinosomatid occurrences just described are intimately associated with stromatolitic or thrombolitic biostromes or “reefs.” It would appear that both types of eurypterids, Paracarcinosoma and Rhinocarcinosoma, preferred a niche in backreef areas in peculiar algal-lagoonal settings little understood today. Eurypterus, the common form in the Bertie Group, is generally found in rocks having much evidence of hypersalinity (salt hopper structures, etc.), presumably a more supratidal setting.
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Ludman, Allan. "Pre-Silurian stratigraphy and tectonic significance of the St. Croix Belt, southeastern Maine." Canadian Journal of Earth Sciences 24, no. 12 (December 1, 1987): 2459–69. http://dx.doi.org/10.1139/e87-230.
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The St. Croix Belt of southeastern Maine and southwestern New Brunswick is part of a distinctive terrane situated between the Avalon platform and Miramichi arc—two important physiographic components of the Late Precambrian – early Paleozoic Iapetus Ocean. It bears lithologic and stratigraphic similarities to both of those tracts but is identical to neither. Formerly mapped entirely as the Cookson Formation, it is now divided into four formations of Cambrian through Early Orodovician age assigned to the Cookson Group. These rocks record periodic influxes of terrigenous debris into a deep anoxic basin and may have been part of the west-facing continental slope of the Avalonian continental block. The St. Croix Belt has been strongly affected by both pre-Silurian and Early Devonian (Acadian) folding. Facies changes rather than tectonic sutures are used to explain the relationships between the St. Croix Belt and its neighbouring pre-Silurian tracts.
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Sansom, I. J., R. J. Aldridge, and M. M. Smith. "A microvertebrate fauna from the Llandovery of South China." Transactions of the Royal Society of Edinburgh: Earth Sciences 90, no. 3 (1999): 255–72. http://dx.doi.org/10.1017/s0263593300002595.
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AbstractThe late Llandovery (early Silurian) of South China has yielded a locally abundant and diverse microvertebrate fauna. This includes scales of the little-known mongolepids, sinacanthid spines and a whole host of as yet unassigned forms. The material recovered provides a considerable amount of new information about the diversity of fish in the South Yangtze biome during the early Silurian, and suggests that ichthyoliths have a future role to play in Lower Palaeozoic stratigraphic correlation across China and into Mongolia and Siberia. A new family of mongolepids, the Shiqianolepidae, is erected, accommodating the new genus Shiqianolepis with the type species S. hollandi. The description of Shiqianolepis enables the identification of a differentiated squamation in mongolepid fish, a feature which has not previously been recognised. Two further taxa, Rongolepis cosmetica gen. et sp. nov. and Chenolepis asketa gen. et sp. nov., of, as yet, uncertain affinities are also erected.
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BERGSTRÖM, STIG M., WARREN D. HUFF, and DENNIS R. KOLATA. "The Lower Silurian Osmundsberg K-bentonite. Part I: stratigraphic position, distribution, and palaeogeographic significance." Geological Magazine 135, no. 1 (January 1998): 1–13. http://dx.doi.org/10.1017/s0016756897007887.
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A large number of Lower Silurian (Llandovery) K-bentonite beds have been recorded from northwestern Europe, particularly in Baltoscandia and the British Isles, but previous attempts to trace single beds regionally have yielded inconclusive results. The present study suggests that based on its unusual thickness, stratigraphic position and trace element geochemistry, one Telychian ash bed, the Osmundsberg K-bentonite, can be recognized at many localities in Estonia, Sweden and Norway and probably also in Scotland and Northern Ireland. This bed, which is up to 115 cm thick, is in the lower–middle turriculatus Zone. The stratigraphic position, thickness variation and geographic distribution of the Osmundsberg K-bentonite are illustrated by means of 12 selected Llandovery successions in Sweden, Estonia, Norway, Denmark, Scotland and Northern Ireland. In Baltoscandia, the Osmundsberg K-bentonite shows a trend of general thickness increase in a western direction suggesting that its source area was located in the northern Iapetus region between Baltica and Laurentia. Because large-magnitude ash falls like the one that produced the Osmundsberg K-bentonite last at most a few weeks, such an ash bed may be used as a unique time-plane for a variety of regional geological and palaeontological studies.
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Aqrawi, Adnan A. M. "Paleozoic Stratigraphy and Petroleum Systems of the Western and Southwestern Deserts of Iraq." GeoArabia 3, no. 2 (April 1, 1998): 229–48. http://dx.doi.org/10.2113/geoarabia0302229.
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ABSTRACT A stratigraphic scheme for the Paleozoic of the Southwestern Desert of Iraq is proposed based upon the review of recently published data from several deep wells in the western part of the country and from outcrops in other regions in Iraq. The main formations are described in terms of facies distribution, probable age, regional thickness, and correlations with the well-reported Paleozoic successions of the adjacent countries (e.g. Jordan and Saudi Arabia), as well as with the Thrust Zone of North Iraq. The Paleozoic depositional and tectonic evolution of the Western and Southwestern Deserts of Iraq, particularly during Cambrian, Ordovician and Silurian, shows marked similarity to those of eastern Jordan and northern Saudi Arabia. However, local lithological variations, which are due to Late Paleozoic Hercynian tectonics, characterize the Upper Paleozoic sequences. The Lower Silurian marine “hot” shale, 65 meters thick in the Akkas-1 well in the Western Desert, is believed to be the main Paleozoic source rock in the Western and Southwestern Deserts. Additional potential source rocks in this region could be the black shales of the Ordovician Khabour Formation, the Upper Devonian to Lower Carboniferous Ora Shale Formation, and the lower shaly beds of the Upper Permian Chia Zairi Formation. The main target reservoirs are of Ordovician, Silurian, Carboniferous and Permian ages. Similar reservoirs have recently been reported for the Western Desert of Iraq, eastern Jordan and northern Saudi Arabia. In addition, two main regional seals (Lower Silurian shales and Permian evaporites) of northeastern Arabia extend over most of the Southwestern Desert, together with several other local seals. These considerations render the unexplored Paleozoic Southwestern Desert of Iraq prospective.
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Kotik, Ivan S., Tatyana V. Maidl, Olga S. Kotik, and Natalia V. Pronina. "Petroleum source rocks of the Silurian deposits on the Chernov swell (Timan‑Pechora basin)." Georesursy 22, no. 3 (September 30, 2020): 12–20. http://dx.doi.org/10.18599/grs.2020.3.12-20.
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Silurian source rocks are among the least studied in the Timan-Pechora basin. This is mainly due to their occurrence at great depths (3.0–4.5 km) and the limited penetration of this stratigraphic interval by wells. Another source of information is the outcrops of the Silurian, which are known in the eastern and northeastern parts of the Timan-Pechora basin. The studied section of the Silurian deposits is exposed on the Padimeityvis River, located on the Chernov swell in the northeastern part of the basin. This article is devoted to the study of Silurian source rocks based on the results of lithological, coal petrographic studies and geochemistry of organic matter. The studied section is composed of carbonate and clay-carbonate deposits formed in shallow-water shelf conditions. Most of the section, composed of microcrystalline and microcrystalline with bioclasts limestones, is characterized by low concentrations of organic matter (Corg is generally less than 0.3 %). Elevated Corg contents (up to 1.16 %) are characteristic of clay-carbonate rock varieties, which make up about 20 % of the section. Sediments with increased concentrations of organic matter were formed in isolated and deepened areas of the bottom of the shallow-water basin as a whole. Assessment of the catagenetic transformation based on Rock-Eval pyrolysis data, coal petrographic studies, and conodont color indices showed that organic matter reached the conditions of the middle-end of the main oil generation zone (gradation MC2‑MC3). The obtained geochemical characteristics (Corg, S2, HI), taking into account a certain level of organic matter maturity, indicate that the Silurian source rocks had an average hydrocarbon potential.
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Pyle, L. J. "Ordovician-Silurian stratigraphic framework, Macdonald Platform to Ospika Embayment transect, northeastern British Columbia." Bulletin of Canadian Petroleum Geology 49, no. 4 (December 1, 2001): 513–35. http://dx.doi.org/10.2113/49.4.513.
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