A high-precision global biostratigraphy of myodocope ostracods for the Silurian upper Wenlock Series and Ludlow Series
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Abstract:
The wide, trans-oceanic geographical distribution of myodocope ostracods during the Silurian (especially during the Ludlow and Pridoli epochs), and their widespread preservation in rocks of that age, permits the establishment of a transcontinental biostratigraphy of comparable resolution to coeval graptolite/chitinozoan/conodont biozones. Seven myodocope biozones, extending from the Homerian Stage, upper Wenlock Series Cyrtograptus lundgreni graptolite biozone to the middle part of the Ludfordian Stage of the Ludlow Series, enable a time-resolution for each biozone of circa 1 million years. These biozones can provide high-resolution correlation across Europe into Arctic Russia and Central Asia. There is also the potential for a myodocope biostratigraphy applicable from the uppermost Silurian (Pridoli) to the Carboniferous.Keywords:
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The Kalana quarry in central Estonia is known for its exceptionally well-preserved non-calcified algal and other fossils.The interval with the fossil Konservat Lagerstätte in the Kalana section has previously been tentatively dated as early Aeronian.Recent findings of graptolites now enable more precise dating of these beds.The strata yielding the Lagerstätte are not older than the mid-Aeronian and correspond to the Pribylograptus leptotheca graptolite Biozone.In terms of conodont biostratigraphy they correlate with the middle of the Pranognathus tenuis conodont Biozone.It has also become evident that the uppermost Jõgeva Beds of the Nurmekund Formation, and probably also the uppermost Ikla Member of the Saarde Formation, are younger than previously thought and correlate with the Pribylograptus leptotheca graptolite Biozone.Our data additionally indicate that the conodont genus Aulacognathus had appeared by the mid-Aeronian.
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Zhen, Y.Y. & Percival, I.G. March 2017. Late Ordovician conodont biozonation of Australia—current status and regional biostratigraphic correlations. Alcheringa 41, xxx–xxx. ISSN 0311-5518.Seven conodont biozones are recognized in the Upper Ordovician of Australia. The Pygodus anserinus, Belodina compressa and Phragmodus undatus–Tasmanognathus careyi biozones are successively represented in the Sandbian. Although the Erismodus quadridactylus Biozone of the late Sandbian North America Midcontinent succession was previously recognized in the Stokes Siltstone of the Amadeus Basin and the Mithaka Formation of the Georgina Basin in central-north Australia, we argue for a middle–late Darriwilian age for these two units. Four conodont biozones, from oldest to youngest the Taoqupognathus philipi, T. blandus, T. tumidus–Protopanderodus insculptus and Aphelognathus grandis biozones, are established in the Katian of eastern Australia. Taoqupognathus species are particularly useful in correlation of the lower–middle Katian successions of eastern Australia with contemporary rocks in other parts of eastern Gondwana and peri-Gondwana, such as with the three major terranes of North and South China and Tarim. These regions, together with Sibumasu and eastern Australia, were part of the Australasian Superprovince during the Late Ordovician, with a strong palaeobiogeographic identity signalled by domination of Taoqupognathus, Tasmanognathus and Yaoxianognathus. Longstanding difficulties for precise correlation with the well-established North American Midcontinent or Baltoscandian successions in the Late Ordovician, owing mainly to strong endemism of the Australian faunas particularly from shallow-water settings, have been resolved by integration of regional conodont biostratigraphic schemes. The conodont biozonation of the Australian Upper Ordovician reviewed herein also provides a crucial chronological reference for better constraining the temporal and spatial range of Late Ordovician tectonostratigraphic events across the intracratonic basins of northern and western Australia and orogenic belts of eastern Australia.Yong Yi Zhen* [yong-yi.zhen@industry.nsw.gov.au] and Ian G. Percival [ian.percival@industry.nsw.gov.au], Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry NSW 2753, Australia.
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Abstract Abundant conodont elements have been recovered from the Hwajeol Formation, to allow five zones to be erected: Proconodontus, Eoconodontus notchpeakensis, Cambrooistodus minutus, Cordylodus proavus , and Fryxellodontus inornatus‐Monocostodus sevierensis‐Semiacontiodus lavadamensis zones, in ascending order. More confident biozones are recognized in the Sesong Slate and lower Hwajeol Formation in the Makgol section, a part of the southern limb of the Baekunsan syncline, Taebaeksan Basin, Korea, especially focusing on the conodont biostratigraphic boundary of two units, and the subdivision potential of the previous “ Proconodontus Zone”, lowermost biozone of the Hwajeol Formation. Similarly, only a few conodont elements recovered from upper 14.5 m interval, namely the Furongian portion of the Sesong Slate, in the Makgol section did not allow erection of a biozone. Nevertheless, this part of the unit plus the basal 2.5 m interval of the Hwajeol Formation is characterized by the occurrence of Prooneotodus rotundatus (Druce and Jones), Teridontus nakamurai (Nogami), Phakelodus elongatus (An) and Phakelodus tenuis Müller, This interval marks the early Furongian “ Prooneotodus rotundatus Zone”. The rest of the measured section yielded relatively abundant conodonts, so three conodont biozones are proposed, based on the successive appearance of key species: Proconodontus tenuiserratus, Proconodontus posterocostatus , and Proconodontus muelleri zones, in ascending order, and thus allowing subdivision of the previous “ Proconodontus Zone”. The four conodont biozones are correlated with the relevant biozones of North and South China, and North America.
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Abstract Integrated graptolite, conodont and chitinozoan biostratigraphical data are presented from the Llandovery and Wenlock of the Kolka-54 core, Latvia. Correlations between graptolite and chitinozoan biozones are consistent with those published from other East Baltic sections and the Welsh Basin. While most correlations between graptolite and conodont biozones agree with those presented in previous studies, there are important exceptions. Significantly, we report here the discovery of Distomodus staurognathoides Biozone conodonts in the lowest Aeronian Demirastrites triangulatus graptolite Biozone. The base of the D. staurognathoides Biozone was previously considered to lie much higher in the Aeronian. Also it is shown that Walliserodus survived the late Wenlock Mulde Event, during which it was considered previously to have become extinct.
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The Scottish Carboniferous conodonts described by Hinde and figured by Smith in 1900 are refigured and redescribed. Additional specimens from the John Smith collection and from the writer's own collection are described. Sixteen genera of conodonts are shown to be present in the Scottish Carboniferous and thirty species, of which seventeen are new, are described. Correlation of the Scottish Carboniferous Limestone Series with the Upper Mississippian is indicated by the conodont fauna.
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Based on the preliminary research of the conodonts from the Zitai Formation at Liushuting Section,Shitai County,the conodont biodiversity changes during the Floian and the Dapingian are discussed according to the conodont biozones. The Ordovician conodont radiation in the study area got its first acme during the Oepikodus evae Biozone,which was consistent with the macroevolutionary trend of brachiopods in South China. The brachiopod faunas had their first biodiversification acme in the graptolite Didymograptellus eobifidus Biozone,roughly corresponding to the middle part of the conodont Oepikodus evae Biozone. Trilobites of South China radiated much later and got their first diversity acme in the Exigraptus clavus Biozone (late Dapingian,Mid Ordovician). In contrast,the graptolites had a much earlier biodiversification trend with its first acme in the Acrograptus filiformis Biozone and Didymograptellus eobifidus Biozone on the Yangtze Platform. After the first biodiversification,the conodont diversity on the Yangtze Platform decreased gradually. Through the correlation with the sea-level fluctuation of South China Block,the authors suggest that the conodont diversity changes might be partially controlled by the sea-level fluctuations.
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