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1
Sennikov, N. V., O. T. Obut, N. G. Izokh, R. A. Khabibulina, T. A. Shcherbanenko, and T. P. Kipriyanova. "THE REGIONAL STRATIGRAPHIC CHART FOR THE ORDOVICIAN OF TYVA (NEW VERSION)." Geology and mineral resources of Siberia, no. 9c (2021): 37–60. http://dx.doi.org/10.20403/2078-0575-2021-9c-37-60.
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A new version of the Regional stratigraphic chart for the Ordovician of Tyva and explanatory note, compiled in accordance with the Russian Stratigraphic Code, introduce changes, additional and specified data in comparison with the previous (third edition) chart. The Interdepartmental stratigraphic meeting held at Novosibirsk in 1979 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 1979 meeting, the stages of the Ordovician chart were changed. Volumes of the lower, middle and upper series were also changed. For the present version of the stratigraphic chart the new standard Ordovician stages were used.
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Sennikov, N. V., O. T. Obut, N. G. Izokh, and T. P. Kipriyanova. "THE REGIONAL STRATIGRAPHIC CHART FOR THE ORDOVICIAN OF THE WESTERN SAYAN (NEW VERSION)." Geology and mineral resources of Siberia, no. 9c (2021): 4–14. http://dx.doi.org/10.20403/2078-0575-2021-9c-4-14.
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A new version of the Regional stratigraphic chart for the Ordovician of the Western Sayan and explanatory note, compiled in accordance with the Russian Stratigraphic Code 2006, 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 Ordovician chart were changed. Thus, instead of the traditional British stages (Tremadocian, Arenigian, Llanvirnian, Llandeilian, Caradocian, Ashgillian) the following units were adopted by the International Stratigraphic Chart – Tremadocian, Floian, Dapingian, Darriwilian, Sandbian, Katian, Hirnantian. Volumes of the lower, middle and upper series were also changed. For the present version of the stratigraphic chart the new standard Ordovician stages were used.
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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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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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Normore, Leon, Peter W. Haines, Lidena K. Carr, Paul Henson, Yijie Zhan, Michael T. D. Wingate, Yong Yi Zhen, et al. "Barnicarndy Graben, southern Canning Basin: stratigraphy defined by the Barnicarndy 1 stratigraphic well." APPEA Journal 61, no. 1 (2021): 224. http://dx.doi.org/10.1071/aj20160.
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Funded by Geoscience Australia’s Exploring for the Future initiative and operated by the Geological Survey of Western Australia, the Waukarlycarly 1 deep stratigraphic drillhole was designed to investigate the geology of the little-known Waukarlycarly Embayment and assess the petroleum, mineral, groundwater and CO2 storage potential of the area. Based on consultation with the Western Desert Lands Aboriginal Corporation on the cultural significance of the name, Waukarlycarly, it has been agreed to change the name of the well to Barnicarndy 1 and the tectonic subdivision to the Barnicarndy Graben. This and all future publications will now refer to the Barnicarndy 1 stratigraphic drillhole (previously Waukarlycarly 1) and the Barnicarndy Graben (previously Waukarlycarly Embayment). Drilling commenced on 1 September 2019 and reached a total depth (TD) of 2680.53m on 30 November 2019, recovering more than 2km of continuous core. The cored interval extended from 580m to TD in Neoproterozoic Yeneena Basin dolostone, which was unconformably overlain by a thick, lower Canning Basin Ordovician stratigraphy, including richly fossiliferous marine mudstones with common volcanic ash beds. A major unconformity is located at the top of the Ordovician section where it is overlain by sandstones and muddy diamictites of the Carboniferous–Permian Grant Group, followed by a Cenozoic succession near surface. Ditch cuttings were collected from surface to 580m at 3m intervals. The pre-Grant Group Paleozoic succession is unique within the Canning Basin, indicating that the Barnicarndy Graben’s depositional history is markedly different when compared with adjacent structural subdivisions, such as the Munro Arch and Kidson Sub-basin. Detrital zircon geochronology, biostratigraphy and borehole imaging interpretation assisted in the definition of two new geological units within the Ordovician stratigraphy of Barnicarndy 1: the Yapukarninjarra and Barnicarndy formations. Preliminary routine core analysis data indicates the potential for CO2 storage within the Barnicarndy Formation beneath a Grant Group seal. The well also provides new insights into the structural interpretation of the Barnicarndy Graben.
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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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Moreau, Julien, and Jean-Bernard Joubert. "Glacial sedimentology interpretation from borehole image log: Example from the Late Ordovician deposits, Murzuq Basin (Libya)." Interpretation 4, no. 2 (May 1, 2016): B1—B16. http://dx.doi.org/10.1190/int-2015-0161.1.
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In the Murzuq Basin, the Late Ordovician glaciogenic succession forms a very complex clastic reservoir system. Although the structural setting is simple, the architecture of the stratigraphic succession is particularly intricate, and conventional wireline logs display rather homogeneous signatures. However, when exposed, the glaciogenic sedimentary succession indicates a very large range of depositional environments and clear stratigraphic changes. Based on high-quality processing and interpretation of wireline microresistivity image logs over a single well, our method allows the precise recognition of the internal sedimentary structures and supports the interpretation of the depositional environments within the Late Ordovician succession. During interpretation, it is possible to draw a descriptive sedimentological log, similar to a standard log from cores or outcrops. The image log is interpreted like a regular sedimentary log and compared to an outcrop analog from the nearby outcrop area of Ghat. The success of the well analysis resides in the quality of the borehole image log, permitting the recognition of sandstone grain sizes, textures (facies), and sorting. In addition, crucial information is extracted from the identification of glacial surface and ice-flow orientations, which, combined with the recognition of major transgressive events, allows the recognition and correlation of glacial-type stratigraphy. As in the modern Pleistocene glaciation, stadial/interstadial and glacial/interglacial stages are identified from resistivity imaging of the Libyan Ordovician succession. In addition to the unprecedented potential of correlation between wells within the basin, the sedimentary information extracted from the borehole image log provides important insights on the paleogeographic context of the basin and thus on the exploration potential of the prolific Ordovician-Silurian petroleum system.
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BERGSTRÖM, STIG M., CHEN XU, BIRGER SCHMITZ, SETH YOUNG, RONG JIA-YU, and MATTHEW R. SALTZMAN. "First documentation of the Ordovician Guttenberg δ13C excursion (GICE) in Asia: chemostratigraphy of the Pagoda and Yanwashan formations in southeastern China." Geological Magazine 146, no. 1 (November 5, 2008): 1–11. http://dx.doi.org/10.1017/s0016756808005748.
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AbstractThe only published δ13C data from the Ordovician of China are from the Lower and Upper Ordovician, and only the latter records include a significant excursion, namely the Hirnantian excursion (HICE). Our recent chemostratigraphic work on the Upper Ordovician (Sandbian–Katian) Pagoda and Yanwashan formations at several localities on the Yangtze Platform and Chiangnan (Jiangnan) slope belt has resulted in the recognition of a positive δ13C excursion that has values of ~+1.5‰ above baseline values. This excursion starts a few metres above a stratigraphic interval withB. alobatusSubzone conodonts as well as graptolites of theN. gracilisZone. The distinctive conodontsAmorphognathusaff.Am. ventilatusandHamarodus europaeusfirst occur at, or very near, the excursion interval. Because these conodonts appear in the stratigraphic interval of the Guttenberg δ13C excursion (GICE) in Estonia, we identify the Chinese excursion as the GICE. This is the first record of the GICE in the entire Asian continent. It confirms that GICE is a global excursion and provides an illustration of how δ13C chemostratigraphy, combined with new biostratigraphic data, solves the problem of the previously controversial age of the Pagoda Formation and how this classical stratigraphic unit correlates with the Baltoscandian and North American successions.
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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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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.
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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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Hansheng, Ding. "Cambrian Ordovician sedimentary facies and its evolution in Tadong area." E3S Web of Conferences 329 (2021): 01055. http://dx.doi.org/10.1051/e3sconf/202132901055.
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In order to clarify the sedimentary development law under the Cambrian Ordovician regional stratigraphic framework in Tadong area, and lay a theoretical foundation for further oil and gas exploration in the study area. The distribution, characteristics and evolution of main sedimentary facies belts of Cambrian Ordovician are studied by means of drilling core observation, cast thin section identification, logging curve feature analysis, seismic profile and well connection profile. The results show that the Cambrian middle lower Ordovician in Tadong area is equivalent to a second-order sequence and can be further divided into 12 thirdorder sequences. Each third-order sequence is mainly composed of transgressive and highstand tracts. Carbonate platform margin beach facies and Reef (mound) beach complex facies are favorable reservoir development facies belts in this area; Under the regional stratigraphic framework, three types of sedimentary facies can be identified in Cambrian Ordovician, and a total of 10 subfacies are developed; The evolution of sedimentary facies is mainly controlled by the rise and fall of sea level, which is characterized by the migration of platform margin facies and the change of platform facies.
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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.
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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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Li, Xing, and Mary Droser. "The development of Early Paleozoic shell concentrations: evidence from the Cambrian and Ordovician of the Great Basin." Paleontological Society Special Publications 6 (1992): 183. http://dx.doi.org/10.1017/s2475262200007437.
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Shell concentrations have constituted an important and conspicuous part of the stratigraphic record since the Early Cambrian. The paleontological and stratigraphic significance of shell beds is well understood, primarily from Mesozoic and Cenozoic examples. Lower Paleozoic fossil concentrations, however, have not received much attention. The Cambrian and Ordovician evolutionary radiations were two of the most significant events in the history of life and established the Cambrian and Paleozoic faunas respectively. In order to determine the effect of these radiations on the development of fossil accumulations, a systematic study of early Paleozoic shell beds was conducted in the Great Basin areas of California, Nevada, and Utah.In order to minimize taphonomic variations in original chemical and physical conditions, shell beds were compared from strata deposited in similar depositional environments from similar tectonic settings. Preliminary analysis of the shell beds from relatively pure carbonate facies and mixed carbonate and siliciclastic facies shows: 1) that shell concentrations became a significant stratigraphic feature in the later Early Cambrian; 2) the thickness and lateral extent of the shell beds increase from Early Cambrian to Middle Ordovician; 3) the abundance and internal complexity of the shell beds increase from Early Cambrian to Middle Ordovician; and 4) the Cambrian and Early Ordovician shell beds are primarily, if not exclusively, dominated by trilobites whereas the Middle Ordovician shell beds are dominated by brachiopods and ostracodes.These data show a temporal trend in the development of the early Paleozoic shell beds. The nature of the Cambrian and Ordovician shell beds differs qualitatively and quantitatively. There is an increase in physical scale, abundance, and internal complexity through time. The thickness and abundance of the trilobite beds increase through the Cambrian. Interestingly, although trilobites were still diverse and abundant, they did not commonly generate thick trilobite beds after the Late Cambrian. The early Middle Ordovician is a critical time in the development of early Paleozoic shell beds. A variety of monotaxic and polytaxic shell beds, including 6m thick composite beds, first appeared at this time. While the brachiopods and ostracodes generate laterally extensive, commonly monotaxic, shell beds, the gastropods and bryozoans only formed lenticular concentrations.
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Pu, RenHai, KunBai Li, Machao Dong, ZiCheng Cao, and Pengye Xu. "The 3D seismic characteristics and significance of the strike-slip faults in the Tazhong area (Tarim Basin, China)." Interpretation 7, no. 1 (February 1, 2019): T1—T19. http://dx.doi.org/10.1190/int-2016-0135.1.
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The eastern part of Tazhong area in the Tarim Basin consists of three sets of vertical strike-slip faults oriented in north–northeast (36°azimuth), east–northeast (68° azimuth), and west–northwest (126°azimuth) directions that cut the strata from Cambrian to Carboniferous. The fault belts indicate significant horizon upwarp and downwarp deformations and variations in their stratigraphic thickness on seismic profiles. Through detailed interpretation of the 3D seismic data, we consider that these phenomena reflect the different stress properties and active stages of the faults. The horizon upwarp and downwarp within the fault belts correlated respectively to the decrease and increase in stratigraphic thickness within the fault belts in comparison to the coeval counterpart of the bilateral fault blocks. For the same fault, different stratigraphic intervals express different types of horizon deformation and thickness changes. The horizon downwarp and the contemporaneous stratigraphic thickening inside the fault belts suggest the transtensional actions of the fault. The horizon upwarp and the contemporaneous thinning within the fault belts suggest transpressional actions of the fault. Based on this, we inferred the active periods of the three sets of strike-slip faults. The north–northeast-striking faults were formed in the late Ordovician Sangtamu Formation. This set of faults experienced four stages, i.e., sinistral transpression, sinistral transtension, static, and transtension. The east–northeast and west–northwest-striking faults initiated in the mid-Cambrian period as coupled transtension. Activity ceased in the west–northwest faults after the mid-Cambrian and in the east–northeast faults during the late Ordovician. The three sets of strike-slip faults all affect the formation of the hydrothermal dissolution reservoirs that are distributed in the Ordovician carbonate rocks.
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Zhang, Shunxin. "Ordovician conodont biostratigraphy and redefinition of the age of lithostratigraphic units on northeastern Melville Peninsula, Nunavut." Canadian Journal of Earth Sciences 50, no. 8 (August 2013): 808–25. http://dx.doi.org/10.1139/cjes-2013-0009.
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Northeastern Melville Peninsula, Nunavut, Canada, preserves the stratigraphic record of the northwestern margin of the Foxe Basin. The Ordovician sequence on the peninsula includes the Lower Ordovician Ship Point Formation and Upper Ordovician Frobisher Bay, Amadjuak, Akpatok, and Foster Bay formations. Their biostratigraphic ages and correlations are poorly understood; in particular it is unclear whether the organic-rich “Boas River Formation” exists on the peninsula. Following extensive sampling of these stratigraphic units, studies of numerous conodont elements from both outcrops and rubble at about 60 localities have established five conodont assemblages through the five lithostratigraphic units on the peninsula. Oepikodus communis – Jumudontus gananda Assemblage in the Ship Point Formation is correlated to the Reutterodus andinus Zone in the uppermost Ibexian, Lower Ordovician. The other four assemblages from the Upper Ordovician are as follows: Appalachignathus delicatulus – Polyplacognathus ramosus – Belodina confluens in the Frobisher Bay Formation correlated to lower B. confluens Zone in the upper Chatfieldian; Belodina confluens – Periodon grandis in the Amadjuak Formation to the upper B. confluens, Oulodus velicuspis, O. robustus, and lower Aphelognathus grandis zones from Edenian to lowest Richmondian; Amorphognathus ordovicicus – Plegagnathus and Rhipidognathus symmetricus – Aphelognathus cf. A. divergens in the Akpatok and Foster Bay formations to the lower and upper Richmondian. The biostratigraphy is combined with geographical information systems (GIS) and Google Earth technologies in estimating the thickness of Paleozoic strata, which reduces the likelihood of “Boas River Formation” existing on Melville Peninsula to minimum.
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Anderson, Donna, and Mark Longman. "Subsurface Reinterpretation of Ordovician and Devonian Strata in Southwest Wyoming with Implications for Upwarping Across the Transcontinental Arch." Mountain Geologist 55, no. 3 (July 2018): 91–118. http://dx.doi.org/10.31582/rmag.mg.55.3.91.
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A new interpretation of the subsurface geometries of the Ordovician Bighorn Dolomite and overlying Devonian strata across southwestern Wyoming arises from revising the stratigraphy in a core from the Mountain Fuel Supply UPRR #11–19–104–4 well drilled on the crest of the Rock Springs Uplift in 1962. One of only a few wells to penetrate all or part of the Lower Paleozoic succession in the subsurface of southwestern Wyoming, the well was almost continuously cored through the Devonian–Cambrian succession. From a reinterpretation of the stratigraphy in the core, 22 ft of Bighorn Dolomite is recognized based on the characteristic Thalassinoides bioturbation fabric in skeletal dolowackestone typical of Late Ordovician subtidal carbonate facies ranging from Nevada to Greenland along the western margin of the Great American Carbonate Bank. This lithology is in complete contrast with the alternating dolomitic flat-pebble conglomerate and dolomudstone of the underlying Cambrian Gallatin Limestone and the cyclical units of brecciated anhydritic dolomudstone and quartzose sandstone of the overlying Devonian Lower Member of the Jefferson Formation. Stratigraphic re-interpretation yields insights regarding Ordovician–Devonian stratal geometries across southwestern Wyoming. More widespread than previously portrayed, the Bighorn Dolomite pinches out on the eastern flank of the Rock Springs Uplift. Similar to past interpretations, Devonian strata pinch out east of the Rock Springs Uplift at Table Rock Field. A true-geometry multi-datumed stratigraphic cross section yields insights not obtainable by mapping. Regionally, top truncation of stratigraphic units below the base-Madison Limestone unconformity normally progresses stratigraphically deeper eastward. However, in southwestern Wyoming, the Devonian Lower Member of the Jefferson Formation overlaps the older Bighorn Dolomite by marked onlap across the Rock Springs Uplift and then pinches out by top truncation/onlap near Table Rock Field, forming an “abnormal” overlap relationship along the northern margin of the Transcontinental Arch. The underlying Bighorn Dolomite shows little to no onlap onto the underlying Cambrian section, but is markedly top truncated below the Lower Member of the Jefferson Formation. Comparing proportions of onlap versus top truncation for the two formations constrains the timing of two successive upwarping episodes along the northern margin of the Transcontinental Arch across southwestern Wyoming. The first is arguably Middle Devonian, and the second spans the Devonian–Mississippian boundary. Two subtle and different angular unconformities created by these two episodes imply a persistent fold or tilt axis that sequentially was reactivated along the northern margin of the Transcontinental Arch in southwestern Wyoming.
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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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Waldron, John W. F., and Glen S. Stockmal. "Mid-Paleozoic thrusting at the Appalachian deformation front: Port au Port Peninsula, western Newfoundland." Canadian Journal of Earth Sciences 28, no. 12 (December 1, 1991): 1992–2002. http://dx.doi.org/10.1139/e91-181.
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Structures exposed on Port au Port Peninsula in western Newfoundland record the nature of the Appalachian deformation front, which forms the western boundary of the Humber tectono-stratigraphic zone. The major structures affect the Late Ordovician to Late Silurian Long Point – Clam Bank succession, but not the unconformably overlying Carboniferous rocks; they are probably of Devonian age.At the west coast of the peninsula, Long Point and Clam Bank strata are affected by both east-vergent and west-vergent structures. The basal surface of the succession is interpreted as an east-vergent thrust, forming the upper detachment of a "triangle zone," and correlates with a similarly located contact seen in offshore multichannel seismic profiles. Within the succession, east-vergent deformation zones locally duplicate the stratigraphy. West-vergent structures, including a map-scale overturned fold north of Round Head mountain, are probably younger.Farther south, Middle Ordovician foreland basin sediments are also affected by east-vergent thrusts, which have been variably rotated by west-vergent folds. In the underlying Cambrian–Ordovician platform carbonate succession, east-vergent thrusts duplicate the stratigraphy.These structures are related to telescoping of the carbonate platform and the overlying Humber Arm Allochthon during Devonian westward wedging of the structural triangle zone beneath the Long Point – Clam Bank succession. The platform succession must therefore be allochthonous, and the Humber Arm Allochthon has been transported to the west of its Late Ordovician position.
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Sobolevskaya, R. F., and L. V. Nekhorosheva. "THE REGIONAL STRATIGRAPHIC CHART OF THE ORDOVICIAN OF TAYMYR." GEOLOGY AND MINERAL RESOURCES OF SIBERIA, no. 5s (2016): 58–82. http://dx.doi.org/10.20403/2078-0575-2016-5s-58-82.
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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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Hersi, O. Salad, G. S. Nowlan, and D. Lavoie. "A revision of the stratigraphic nomenclature of the Cambrian–Ordovician strata of the Philipsburg tectonic slice, southern Quebec." Canadian Journal of Earth Sciences 44, no. 12 (December 1, 2007): 1775–90. http://dx.doi.org/10.1139/e07-041.
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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).
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Löfgren, Anita, and Tatiana Tolmacheva. "Morphology, evolution and stratigraphic distribution in the Middle Ordovician conodont genus Microzarkodina." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 99, no. 1 (March 2008): 27–48. http://dx.doi.org/10.1017/s1755691008007056.
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ABSTRACTMicrozarkodina is a genus of mainly Middle Ordovician conodonts that has its centre of distribution in Baltoscandia, and much less commonly occurs in southern China, Australia, Argentina and Laurentia. In Baltica a series of species, Microzarkodina russica n. sp., M. flabellum, M. parva, M. bella, M. hagetiana and M. ozarkodella, established themselves successfully. The succession of species ranges from just below the base of the Middle Ordovician (M. russica) to the upper part of the Middle Ordovician (M. ozarkodella). The species are frequently used for biostratigraphical purposes. The largely contemporaneous species Microzarkodina bella and M. hagetiana probably both evolved from M. parva and mostly occurred in separate areas. Microzarkodina ozarkodella probably evolved from M. hagetiana. This present investigation is based on a total of 94,208 elements, collected from 20 sections and one drill-core site in Sweden, one drill-core site and one outcrop in Estonia and two sections in the St Petersburg area in Russia. The Microzarkodina apparatus probably consisted of 15 or 17 elements: four P, two or four M and nine S elements. The S elements include different Sa, Sb1, Sb2, and Sc element types.
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Voldman, Gustavo G., Juan L. Alonso, Luis P. Fernández, Gladys Ortega, Guillermo L. Albanesi, Aldo L. Banchig, and Raúl Cardó. "Tips on the SW-Gondwana margin: Ordovician conodont-graptolite biostratigraphy of allochthonous blocks in the Rinconada mélange, Argentine Precordillera." Andean Geology 45, no. 3 (June 6, 2018): 399. http://dx.doi.org/10.5027/andgeov45n3-3095.
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The Rinconada Formation is a mélange that crops out in the eastern margin of the Argentine Precordillera, an exotic terrane accreted to Gondwana in Ordovician times. Its gravity-driven deposits have been studied by means of conodont and graptolite biostratigraphy, and complemented with stratigraphic analyses. 46 rock samples (85 kg total weight) were obtained from blocks of limestones and of carbonate-cemented quartz-arenites, and from limestone clasts included in conglomerate blocks and debrites. 16 of these samples were productive after standard laboratory acid procedures, yielding 561 conodont elements. The specimens occur in variable number per sample and are frequently fragmented, but they reveal the occurrence of phantom stratigraphic units in the Darriwilian of the Precordillera. Lithological and fossil evidence from the Rinconada Formation provide new constraints on the biostratigraphy, palaebiogeography and tectonostratigraphic history of the southwestern margin of Gondwana during the Ordovician to Lower Devonian times.
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Parnell, John, Natalie Salter, and Peter West. "A micrometeorite record in Ordovician Durness Group limestones, Isle of Skye." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 106, no. 2 (June 2015): 81–87. http://dx.doi.org/10.1017/s1755691016000037.
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ABSTRACTSamples of mid-Ordovician Durness Group limestone from Skye yield micrometeorites in the magnetic fraction after dissolution in acid. The micrometeorites are concentrated in the upper part of the sequence, in the Arenig Balnakeil and Croisaphuill formations. This finding is consistent with their stratigraphic distribution determined previously in the Durness district. A single sample of contemporaneous limestones from the Highland Border Fault Zone also yielded a micrometeorite. These observations suggest an elevated flux of meteoritic matter, shortly before the greatest concentration of meteorites in the geological record in the mid-Ordovician of Sweden.
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Sennikov, N. V., O. T. Obut, E. V. Lykova, A. V. Timokhin, R. A. Khabibulina, and T. A. Shcherbanenko. "EVENT STRATIGRAPHY AND CORRELATION PROBLEMS OF THE ORDOVICIAN STRATA OF GORNY ALTAI AND SALAIR." Geodynamics & Tectonophysics 12, no. 2 (June 23, 2021): 246–60. http://dx.doi.org/10.5800/gt-2021-12-2-0523.
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Study of the Ordovician sedimentary sequences of Gorny Altai and Salair has revealed lithological and paleontological features correlating with global sedimentary events:(1) The Acerocare Regressive Event (an initial event in the Early Tremadocian);(2) Black Mountain Transgressive Event (Early Tremadocian);(3) Peltocare Regressive Event (Tremadocian);(4) Kelly Creek Regressive Event (Late Tremadocian);(5) Ceratopyge Regressive Event (Late Tremadocian);(6) Billingen Transgressive Event (Early Floian);(7) Stein Lowstand Event (Middle Darriwilian);(8) Vollen Lowstand Event (Sandbian);(9) Arestad Drowning Event (Middle Sandbian);(10) Frognerkilen Lowstand Event (Early Katian);(11) Linearis Drowning Events 1 and 2 (Middle Katian);(12) Terminal Husbergoya Lowstand Event (Hirnantian); and(13) Hirnantian Lowstand Event (HICE) (Late Ordovician).The chronostratigraphic levels with traces of the global sedimentary events in the Uymen-Lebed structural-facies zone (SFZ) (Gorny Altai) differ from those in the Charysh-Inya and Anui-Chuya SFZ (Altai). In the Ordovician, the Altai basin located in the Charysh-Inya and Anui-Chuya SFZ was a marine area separated from both the Uymen-Lebed basin and the coeval Salair basin. The traces of the global sedimentary and/or biotic events in the Altai and Salair sections can be used as a precise basis for direct correlation of the local stratigraphic units with the units of the International Stratigraphic Chart.
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Clark, David L., John K. Sorenson, Andrea N. Ladd, and James R. Freiheit. "Probable microvertebrates, vertebrate-like fossils, and weird things from the Wisconsin Ordovician." Journal of Paleontology 73, no. 6 (November 1999): 1201–9. http://dx.doi.org/10.1017/s0022336000031085.
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Phosphatic microfossils including probable microvertebrates occur in the Early and Middle Ordovician rocks of Wisconsin. The eight types described here include the probable ostracoderm Anatolepis, and six unidentified but possible vertebrate fragments as well as the palaeoscolecid worm Milaculum. These fossils are rare, but at two localities several specimens per kg were recovered over significant stratigraphic intervals. The high concentration of certain fossils in the lower part of the Galena Group suggests that there is stratigraphic value in their description. Identification of similar material or of articulated assemblages of these fossils may eventually lead to identification of biologic affinities.
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Sanford, Bruce V. "Stratigraphic and Structural Framework of Upper Middle Ordovician Rocks in the Head Lake-Burleigh Falls Area of South-Central Ontario." Géographie physique et Quaternaire 47, no. 3 (November 23, 2007): 253–68. http://dx.doi.org/10.7202/032956ar.
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ABSTRACT 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
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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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Marquis, Robert, and Godfrey S. Nowlan. "Stratigraphic position and conodonts of the early Middle Ordovician Melbourne Formation, Quebec." Canadian Journal of Earth Sciences 28, no. 5 (May 1, 1991): 816–21. http://dx.doi.org/10.1139/e91-070.
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A new fossil locality yielding rare conodonts of probable late Arenig to early Llanvirn age in the previously unfossiliferous Melbourne Formation of the Appalachian Humber Zone has been discovered in the Eastern Townships of Quebec. The presence of a continental-margin fauna at the northeast end of the Sutton Mountains Anticlinorium suggests a continuity of sedimentation, and this contradicts previous suggestions of a major disconformity between the Lower and Middle Ordovician rocks in this part of the Quebec Reentrant. Moreover, recent geological mapping shows that the contact between the conodont-bearing Melbourne Formation and the underlying Sweetsburg Formation of the Oak Hill Group is conformable and gradational. Consequently, it is proposed that the graphitic limestone of the Melbourne Formation represents the youngest unit of the Cambro-Ordovician Oak Hill Group.
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Delano, John W., Steven J. Tice, Charles E. Mitchell, and Daniel Goldman. "Rhyolitic glass in Ordovician K-bentonites: A new stratigraphic tool." Geology 22, no. 2 (1994): 115. http://dx.doi.org/10.1130/0091-7613(1994)022<0115:rgiokb>2.3.co;2.
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Amorim, Paula, and Helena Couto. "Geological Mapping of Rates and São Félix of Laúndos Region (Northern Portugal)." IOP Conference Series: Earth and Environmental Science 906, no. 1 (November 1, 2021): 012120. http://dx.doi.org/10.1088/1755-1315/906/1/012120.
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Abstract The Rates and São Félix of Laúndos region is located in the NW extension of the Valongo Anticline (Northern Portugal), comprising Palaeozoic formations with ages ranging from the Cambrian to the Carboniferous, locally overlaid by Plio-Pleistocene beach deposits and dunes. Detailed geological mapping was developed. The fieldwork allowed distinguishing different lithostratigraphic units, some of them fossiliferous. The study under optical microscope and Scanning Electron Microscope (SEM) allowed noting the presence of volcanic rocks along the Palaeozoic succession. A rhyolite in the Cambrian - Ordovician transition, a likely ignimbrite in the Upper Ordovician, and the existence of a porphyry in the Carboniferous, were for the first time identified in this region. The palaeontological study focuses on the samples collected in the field, essentially belonging to the Middle Ordovician (Valongo Formation), but also to Silurian and Carboniferous. The Devonian formations are largely covered by agricultural fields and by urbanization, not allowing the collect of fossils, so the Devonian fossils studied belong to the Stratigraphical and Palaeontological Collection of the Department of Geosciences, Environment and Spatial Planning, Faculty of Sciences, University of Porto. The geological mapping previously developed in this region goes back to the XX century. In the present work a detailed geological mapping at a scale of 1:15 000 was developed, with reinterpretation of the stratigraphic succession.
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Ripperdan, R. L., M. Magaritz, and J. L. Kirschvink. "Carbon isotope and magnetic polarity evidence for non-depositional events within the Cambrian-Ordovician Boundary section near Dayangcha, Jilin Province, China." Geological Magazine 130, no. 4 (July 1993): 443–52. http://dx.doi.org/10.1017/s0016756800020525.
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AbstractCarbon isotope and magnetic polarity stratigraphic results from the Cambrian-Ordovician Boundary section at Xiaoyangqiao, near Dayangcha, Jilin Province, China, in comparison to a contemporaneous section at Black Mountain, Australia, indicate strata equivalent to major portions of the Australian sequence are either absent or are restricted to highly condensed intervals. These intervals are correlative with regressive sea level events identified in Australia and western North America, suggesting regional or eustatic sea level changes strongly influenced deposition of the Xiaoyangqiao sequence. These results also suggest the Xiaoyangqiao section is unfavourable as the site of the Cambrian-Ordovician Boundary Global Stratotype Section and Point.
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Berry, William B. N. "Late Ordovician environmental changes in Carnic Alps and central Nevada : a comparative study." Bulletin de la Société Géologique de France 174, no. 3 (May 1, 2003): 211–16. http://dx.doi.org/10.2113/174.3.211.
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Abstract Correlation of the late Ordovician stratigraphic and faunal successions in the Carnic Alps, which lay in a mid-latitude site at the time, with those in Nevada, which was in the tropics at the time, reveal certain similarities. During much of the late Ordovician glacial interval, deep shelves in both areas were sites of carbonate debris flow accumulations. The debris was derived from inner or shallow shelf environments. Karst topographies developed in inner or shallow shelves in both areas during the later phase of glaciation and sea level drawdown. A quartz sand spread widely at the end of the glacial interval on deep shelf-slope environments in both areas. Perhaps coincidently, shelves in both areas were uplifted and exposed by tectonism after the late Ordovician glacial episode.
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Staal, C. R. Van, J. A. Winchester, and J. H. Bédard. "Geochemical variations in Middle Ordovician volcanic rocks of the northern Miramichi Highlands and their tectonic significance." Canadian Journal of Earth Sciences 28, no. 7 (July 1, 1991): 1031–49. http://dx.doi.org/10.1139/e91-094.
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A detailed geochemical study of Middle Ordovician volcanic rocks, undertaken in the northern Miramichi Highlands of New Brunswick, shows that 10 basaltic suites can be distinguished. These suites are assigned to the Tetagouche and Fournier groups. The contact between these two groups is a major thrust zone, marked for over 70 km by a prominent blueschist zone. All the Tetagouche Group volcanic rocks have chemistries consistent with extrusion in a continental rift, but most Fournier Group basalts in the Miramichi Highlands have chemistries suggestive of an oceanic back-arc setting. The chemical signatures, stratigraphic variations, and structural data indicate that the northern Miramichi Highlands preserve a section across a telescoped Middle Ordovician back-arc basin that initially opened as a result of asthenospheric injection near the rear part of a Lower Ordovician ensialic arc.
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Norford, B. S. "Introduction to papers on the Cambrian–Ordovician Boundary." Geological Magazine 125, no. 4 (July 1988): 323–26. http://dx.doi.org/10.1017/s0016756800013005.
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AbstractThe Working Group has the responsibility of recommending a specific level within a suitable stratigraphic section to serve as the global stratotype for the Cambrian–Ordovician Boundary. Commencing in 1974, comprehensive studies culminated in a plenary session in Calgary in 1985 resulting in decisions on the ‘golden-spike’ principle of selecting the boundary at a horizon just below the first influx of nematophorous graptolites. Conodonts are to be used as the primary guide for the selection of the specific horizon and the global stratotype section must have potential for studies using paleomagnetism, geochemistry and other non-biological correlation tools. The specific horizon will correspond approximately to the base of the Tremadoc Series of Wales and slightly higher than the base of Canadian Series as used in western North America.The Calgary meeting considered the Broom Point and Green Point sections in Newfoundland, Canada, and the Xiaoyangqiao section at Dayangcha, China, as prime candidates to serve as the global stratotype. A delegation from the Working Group inspected the Dayangcha sections in 1986. For this visit, comprehensive documentation and description of the sequence were prepared and published and are briefly summarized in the present issue.Specific uncertainties remain to be resolved for the Dayangcha and Newfoundland stratigraphic sections before the Working Group will be ready to recommend selection of a global stratotype.
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Repetski, J. E., M. E. Taylor, D. S. Collins, A. R. Palmer, G. D. Wood, and R. C. Tobin. "Integrating paleontology, geothermometry, and sedimentology in determining the history of the Reelfoot Basin, southern midcontinent, U.S.A." Paleontological Society Special Publications 6 (1992): 243. http://dx.doi.org/10.1017/s2475262200008030.
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The northeast-trending Reelfoot basin, extending from northeast Arkansas and westernmost Tennessee into southeastern Missouri, southernmost Illinois, and westernmost Kentucky, is geologically, and socioeconomically, significant because it is co-extensive with the New Madrid Seismic Zone, one of the most seismically active areas of the central and eastern United States. The basin has been periodically active from its inception as a rift basin in the Proterozoic to the present and has accumulated up to at least 5,000 m of sediment, including up to at least 1 km of Cretaceous and Tertiary sedimentary strata near the head of the Mississippi Embayment. Structural and stratigraphic interpretations within the subsurface pre-Mesozoic part of the basin have been based almost entirely on geophysical and physical stratigraphic criteria; these interpretations have been loosely constrained due to an extreme sparsity of drillhole data through the Paleozoic sequence. Recent analysis of Cambrian and Ordovician fossils (conodonts, palynomorphs, brachiopods, and trilobites) from cuttings and core from a very few drillholes allows establishment of the beginnings of a verifiable stratigraphy for this part of the sequence. The paleontological data also provide (1) biofacies evidence for interpretations of the depositional setting during part of the Late Cambrian and Early Ordovician interval and (2) thermal maturation data pertaining to the post-depositional geothermal history of these strata.Upper Cambrian phosphatic brachiopods and trilobites provide improved correlations between strata in the basin, the Ozark shelf to the northwest, and the Upper Mississippi River Valley. Cold-water-realm palynomorphs and trilobites from siliciclastic rocks of turbiditic origin in the central part of the Reelfoot basin support an interpretation, based on sedimentary structures in a short interval of core, of a deep-water basinal origin for these strata.Lower Ordovician conodonts provide a biostratigraphy for the carbonate rocks of this part of the sequence; correlations can be made with the shallow-water sequences of the Knox, Prairie du Chien, and Arbuckle Groups, and the Ozark sequence of the adjacent shelf areas to the east, north, and west. The uppermost Lower Ordovician strata in the basin record a short-term incursion of cooler water environments, reflected by the character of both the conodont fauna and the lithofacies. The youngest Paleozoic dates known from the basin south of the Pascola arch are latest Ibexian (Early Ordovician).Thermal alteration indices of both the Cambrian palynomorphs (organic-walled microphytoplankton) and Ordovician conodonts in the deeper parts of the basin, corroborated by fluid inclusion thermometry, vitrinite reflectance, and other geochemical techniques, are of higher values than predicted using any published estimates of overburden burial. These maturation values most likely reflect burial enhanced by the passage of hydrothermal fluids on a regional scale; they place constraints on interpretations of the tectonothermal evolution of the basin.
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Zhang, Shunxin, and John F. Riva. "The stratigraphic position and the age of the Ordovician organic-rich intervals in the northern Hudson Bay, Hudson Strait, and Foxe basins—evidence from graptolites." Canadian Journal of Earth Sciences 55, no. 8 (August 2018): 897–904. http://dx.doi.org/10.1139/cjes-2017-0266.
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Graptolites recovered from the organic-rich intervals, previously named the Boas River Formation in the Upper Ordovician succession on Southampton, Akpatok, and southern Baffin islands provide a reliable age assessment for the Upper Ordovician petroleum source rocks in the northern Hudson Bay, Hudson Strait, and Foxe basins. They are characterised by Anticostia lata and Anticostia hudsoni in the lower Red Head Rapids Formation on Southampton Island; Anticostia decipiens and Rectograptus socialis in the lower Foster Bay Formation on Akpatok Island; and Diplacanthograptus spiniferus and Amplexograptus praetypicalis in the lower Amadjuak Formation on southern Baffin Island. These data suggest that the organic-rich intervals in the northern Hudson Bay and Hudson Strait basins can be correlated to the Dicellograptus anceps and Paraorthograptus pacificus zones of the upper Katian, and the horizon in the Foxe Basin to the Diplacanthograptus spiniferus Zone of the lower Katian. The Boas River Formation is not deemed appropriate to use as it occurs as an organic-rich interbed in different stratigraphic units in different basins; therefore, it is suggested to abandon it as a stratigraphic term.
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Wagner, Peter J. "Stratigraphic tests of cladistic hypotheses." Paleobiology 21, no. 2 (1995): 153–78. http://dx.doi.org/10.1017/s009483730001318x.
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Cladograms predict the order in which fossil taxa appeared and, thus, make predictions about general patterns in the stratigraphic record. Inconsistencies between cladistic predictions and the observed stratigraphic record reflect either inadequate sampling of a clade's species, incomplete estimates of stratigraphic ranges, or homoplasy producing an incorrect phylogenetic hypothesis. A method presented in this paper attempts to separate the effects of homoplasy from the effects of inadequate sampling. Sampling densities of individual species are used to calculate confidence intervals on their stratigraphic ranges. The method uses these confidence intervals to test the order of branching predicted by a cladogram. The Lophospiridae (“Archaeogastropoda”) of the Ordovician provide a useful test group because the clade has a good fossil record and it produced species over a long time. Confidence intervals reject several cladistic hypotheses that postulate improbable “ghost lineages.” Other hypotheses are acceptable only with explicit ancestor-descendant relationships. The accepted cladogram is the shortest one that stratigraphic data cannot reject. The results caution against evaluating phylogenetic hypotheses of fossil taxa without considering both stratigraphic data and the possible presence of ancestral species, as both factors can affect interpretations of a clade's evolutionary dynamics and its patterns of morphologic evolution.
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Norford, B. S., and M. G. Mihalynuk. "Evidence of the Pacific Faunal Province in the northern Alexander Terrane, recognition of two Middle Ordovician graptolite zones in northwestern British Columbia." Canadian Journal of Earth Sciences 31, no. 9 (September 1, 1994): 1389–96. http://dx.doi.org/10.1139/e94-122.
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The Middle Ordovician Pseudoclimacograptus decoratus Zone (Llanvirn) and Climacograptus bicornis Zone (early Caradoc) of the Pacific Faunal Province are documented from the Tatshenshini River map area in the northern Alexander Terrane. Graptolites were collected from three separate localities of uncertain stratigraphic position within the informal unit 1Pza. The ages of the collections are critical to dating the stratigraphic succession of the Lower Paleozoic rocks within the highly deformed terrane.Regionally, unit 1Pza can be correlated with the Descon Formation of Prince of Wales Island, southeastern Alaska, which also forms part of the Alexander Terrane. The original position of the Alexander Terrane is uncertain, but there are broad similarities between the Paleozoic stratigraphic package of the terrane and those of the Sierra Nevada of the western United States, southeastern Australia, and eastern Siberia.
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Keller, M., F. Cañas, O. Lehnert, and N. E. Vaccari. "The Upper Cambrian and Lower Ordovician of the Precordillera (Western Argentina): Some stratigraphic reconsiderations." Newsletters on Stratigraphy 31, no. 2 (October 26, 1994): 115–32. http://dx.doi.org/10.1127/nos/31/1994/115.
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Sennikov, Nikolay, Alexandr Kanygin, Alexandr Timokhin, Nadezhda Izokh, Olga Obut, and Yuri Philippov. "NEW STRATIGRAPHIC UNITS OF THE UPPER ORDOVIKIN THE FUNDAMENTAL OF THE WESTERN SIBERIAN GEOSINELCLYSIS." Interexpo GEO-Siberia 2, no. 1 (2019): 177–82. http://dx.doi.org/10.33764/2618-981x-2019-2-1-177-182.
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Recent data on the Ordovician biostratigraphy of the West-Siberian Geosyncline are discussed. The new Regional unit - Pavlov Horizon and two new local sequences – Zapadno-Novogodnyaya Unit and Lekosskaya Unit were defined.
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MANGE, MARIA A., JOHN F. DEWEY, and DAVID T. WRIGHT. "Heavy minerals solve structural and stratigraphic problems in Ordovician strata of the western Irish Caledonides." Geological Magazine 140, no. 1 (January 2003): 25–30. http://dx.doi.org/10.1017/s0016756802007100.
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Heavy minerals in Ordovician successions in western Ireland record, in the Upper Arenig Sheeffry Formation, the erosion of an ophiolite/island arc complex. The appearance of staurolite and garnet at a basin-wide horizon in the Lower Llanvirn Upper Derrylea Formation signals the unroofing of the Dalradian metamorphic complex. Parts of the Ordovician sequence on Inishturk and in two small inliers are correlated with the standard sequence with unexpected results. The garnet-, sillimanite-, and staurolite-bearing Letter Formation correlates with the Upper Derrylea Formation and, on Inishturk, heavy minerals in south-younging turbidites reveal a sinistral ramp zone, that places the Sheeffry Formation structurally above and to the south of the younger Derrylea Formation.
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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.
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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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Al-jubori, Falah H. Khalaf, Akram K. Youkhana, Srood F. Naqshabandi, and Dyana A. Bayz. "BIOSTRATIGRAPHIC CORRELATION OF PALEOZOIC ROCKS IN NORTHERN AND WESTREN IRAQ." International Journal of Research -GRANTHAALAYAH 8, no. 3 (May 26, 2020): 315–23. http://dx.doi.org/10.29121/granthaalayah.v8.i3.2020.163.
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The Paleozoic rocks outcropped in northern Iraq (Ora, Chia Zairi section) are biostratigraphically investigated for their microfossils content. Benthonic foraminifera and algal genera characterize the upper part of the section while palynomorphs (Miospores & Acritarchs) dominated the lower part the section which is consist of clastic sediments. The study also include the stratigraphic succession of the section and its correlation to the subsurface sections penetrated in oil and water wells drilled in the western desert of Iraq in order to determine the regional distribution of the economically important formations, either as reservoir or as source rocks for hydrocarbons. Index palynomorphs including many types of Acritarch genera are identified in the Khabour Formation indicate lower Ordovician time (Tremadocian? Arenigian –Llanvirnian: age) The Perispik Formation has been found barren of any type of microfossils and is composed of red clastic rocks.
Pollen and Spores are recorded from the "Ore Group" (Kaista, Ora and Harur Formations ) indicate that these rocks are of Upper Devonian – Lower Carboniferous (Famennian – Tournaisian age ) .A Large number of foraminifera and Algal genera are identified in the Chiazairi rocks,these genera and species are indicated the Upper Permian rocks of Thuringian age.
The stratigraphic succession of the Paleozoic section studied in northern Iraq indicate that there is a stratigraphic break represents by missing of the Ga'ara Formation (late Carboniferous –early Permian) and Akkas Formation (Silurian) and the upper part of the Khabour Formation (Upper Ordovician).
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Zhang, Shunxin. "Upper Ordovician conodont biostratigraphy and revised lithostratigraphy and geological map, Akpatok Island, Ungava Bay, Nunavut." Canadian Journal of Earth Sciences 55, no. 1 (January 2018): 52–69. http://dx.doi.org/10.1139/cjes-2017-0145.
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Stratigraphic units exposed on Akpatok Island, Ungava Bay, Nunavut, were previously recognized as Boas River and Akpatok formations; their biostratigraphic ages and correlations, in particular the stratigraphic position and age of the organic rich “Boas River” Formation, were largely based on limited data. New detailed field observations have recognized three stratigraphic units, namely the Amadjuak, Akpatok, and Foster Bay formations, in which extensive microfossil sampling recovered over 22 000 conodont elements from 66 productive samples from both outcrops and rubble at over 20 localities in four areas. Four Upper Ordovician conodont zones and one unzoned interval are established for the three redefined formations: Belodina confluens and Oulodus velicuspis Interval zones are confined to the exposed Amadjuak Formation and correlated to Edenian and Maysvillian; Amorphognathus ordovicicus – Plegagnathus dartoni Concurrent-range Zone occurs with the Akpatok Formation and correlated to lower Richmondian; Rhipidognathus symmetricus Taxon-range Zone is retained in the Foster Bay Formation and correlated to upper Richmondian; and an “Unzoned Interval” is defined between the last two zones in the lower Foster Bay Formation. The conodont Amorphognathus ordovicicus occurs in both Akpatok and lower Foster Bay formations, and it is also recovered from the bituminous, argillaceous limestone rubble, based on which the stratigraphic position of the previously named “Boas River” Formation is most likely positioned within the lower Foster Bay Formation. The biostratigraphy and lithostratigraphy are combined with geographic information systems (GIS) to establish the thicknesses of the three formations and revise the geologic map of the island.
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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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Ariunchimeg, Ya. "Stratigraphic and paleogeographic distribution of the Upper Ordovician bryozoans of Mongolia." Paleontological Journal 43, no. 11 (December 2009): 1432–38. http://dx.doi.org/10.1134/s0031030109110082.
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ERIKSSON, MATS E., and CHARLES E. MITCHELL. "STRATIGRAPHIC ORIGIN OF HINDE'S (1879) ORDOVICIAN SCOLECODONTS INFERRED FROM ASSOCIATED GRAPTOLITES." Journal of Paleontology 80, no. 2 (March 2006): 396–99. http://dx.doi.org/10.1666/0022-3360(2006)080[0396:soohos]2.0.co;2.
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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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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.
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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.