Middle Ordovician Conodonts Research Articles

Middle Ordovician (late Dapingian–Darriwilian) conodonts from the Cow Head Group and Lower Head Formation, western Newfoundland, Canada1This article is one of a series of papers published inCJES Special Issue: In honour of Ward Nealeon the theme of Appalachian and Grenvillian geology.

Middle Ordovician (late Dapingian–Darriwilian) conodonts from the Shallow Bay and Green Point formations, Cow Head Group, and the Lower Head Formation are recorded from three sections in Gros Morne National Park. The collection was investigated to clarify local age relationships between the uppermost part of the Cow Head Group and the interbedded to overlying sediments of the Lower Head Formation. Conodonts from St. Pauls Inlet North section indicate a middle Dapingian age for the upper lower Bed 13, latest Dapingian to early Darriwilian age for the upper Bed 13, an early Darriwilian (Dw 1) age for the top beds or Bed 15 of the Shallow Bay Formation at Lower Head, and the Lower Head Formation is referred to the Darriwilian. The uppermost part of the lower Bed 13 contains Periodon hankensis n. sp., Gothodus sp. A , and Diaphorodus delicatus followed by Periodon macrodentatus , Ansella longicuspica , Erraticodon n. sp. A , and Spinodus wardi n. sp. in the lowermost part of upper Bed 13. The fauna with P. macrodentatus is referred to the newly established Periodon macrodentatus conodont (phylo-)Zone, which is used for global correlation. The uppermost fauna in the Cow Head Group, i.e., Bed 15, includes Histiodella holodentata , Nealeodus martinpointensis , Oistodella pulchra , Dzikodus peavyi , and Yangtzeplacognathus n. sp. A , which are included in the Histiodella holodentata conodont (Bio-)Subzone of the Periodon macrodentatus Zone. Nealeodus is a new genus introduced here; Periodon hankensis n. sp. and Spinodus wardi n. sp. are new species described from the beds 13 and 15, respectively, in the Cow Head Group; Drepanodus aff. D. giganteus , Drepanodus aff. D. robustus , Erraticodon n. sp. A, Protopanderodus cf. P. cooperi , P. cf. P. varicostatus , and Yangtzeplacognathus n. sp. A are taxa referred to in open nomenclature.

Lower and Middle Ordovician conodonts from the subsurface of SE Estonia and adjacent Russia

Lower and Middle Ordovician conodonts from the subsurface of SE Estonia and adjacent Russia

Lower and Middle Ordovician conodont diversity of the Yichang Region, Hubei Province, Central China

Lower and Middle Ordovician conodont diversity of the Yichang Region, Hubei Province, Central China

Biodiversification of Early to Middle Ordovician conodonts: a case study from the Zitai Formation of Anhui Province, eastern China

The Lower–Middle Ordovician Zitai Formation of the South China palaeoplate consists of a succession of purple red, nodular argillaceous limestones. Palaeogeographically, it is distributed along the southeastern margin of the Yangtze Platform, and is of late Floian to Dapingian age, correlative with the Dawan Formation of the Middle and Lower Yangtze Platform. In Shitai County, Anhui Province, East China, the Zitai Formation is rich in conodonts, enabling the recognition of four biozones based on first appearance data. Detailed palaeontological and biostratigraphical study of these conodonts reveals that the Ordovician conodont radiation in the Lower Yangtze Platform attained its first diversity peak low in the Oepikodus evae Biozone. This diversification is generally consistent with macroevolutionary trends of brachiopods of South China and graptolites of the Upper Yangtze Platform, but was earlier than that of trilobites and acritarchs of the same palaeoplate. Correlation with the sea-level curve for South China suggests that conodont diversity change during the Ordovician radiation was mainly controlled by regional sea-level fluctuations.

日本最古の堆積岩年代４７２Ｍａ（オルドビス紀前期末）とその意義―飛騨外縁帯一重ケ根層のジルコンＵ‐Ｐｂ年代―

The Hitoegane Formation, with the Middle Ordovician conodont, in the Hida marginal belt, Southwest Japan, represents the oldest sedimentary unit in Japan. In order to date the lowest part of the formation, U-Pb age of igneous zircon from tuff beds was measured by LA-ICP-MS. A felsic tuff bed from the lower part of the Hitoegane Fm was newly dated 472 Ma (latest Early Ordovician) that marks the oldest age for sedimentary unit hitherto reported from Japan. This result suggests that the basement of proto-Japan was probably older than the Ordovician. The Iwatsubodani Formation, an apparently underlying unit below the Hitoegane Fm, however, yielded U-Pb zircon age of 280 Ma (Early Permian). Thus this unit is too young to be the sedimentary basement of the Hitoegane Fm. Newly added also were some pieces of information on the U-Pb ages and stratigraphy of the Paleozoic-Mesozoic sedimentary units of the Hida marginal belt.

マレーシア・ランカウィ諸島における下部‐中部オルドビス系生層序の確立

Eighteen species of Early and Middle Ordovician conodonts belonging to sixteen genera were discovered in the Kaki Bukit Formation in the Langkawi Islands, northern peninsular Malaysia. These conodonts are classified into faunas A and B, and are contained in the lower and uppermost parts of the study section, respectively. Fauna A including Cooperignathus nyinti, Reutterodus sp. cf. R. andius, and Acodus deltatus indicates the late Floian age, the latest Early Ordovician. Jumodontus gananda and Tropodus laevis in fauna B show that the upper part of the section is of the earliest Middle Ordovician age. Thus, the Lower and Middle Ordovician boundary exists in the middle of the section. It is inferred from lithological analyses that limestones of the Kaki Bukit Formation were deposited on a carbonate platform on a shelf during the Early and Middle Ordovician age. Biogeographical evidence suggests Early Ordovician conodonts from Southeast Asia belong to the Australian province, which was characterized by a tropical climate and a shallow-water environment. Further research on Lower and lower Middle Ordovician limestones in the Langkawi Islands would clarify the conodont biostratigraphy and transitions of paleobiogeography and depositional environments in detail.

Reinterpretation of Early and Middle Ordovician conodonts from the Thong Pha Phum area, western Thailand, in the context of new material from western and northern Thailand

ABSTRACT Early and Middle Ordovician conodonts are described and illustrated from the Thong Pha Phum and Kanchanaburi areas in western Thailand and the Li area in northern Thailand. The Thong Pha Phum fauna consists of 14 species representing ten genera and one unidentified species, and from the Kanchanaburi and Li sections two and five species, respectively, have been recovered. Two conodont zones, the Triangulodus larapintinensis and Aurilobodus leptosomatus zones, are established in the Thong Pha Phum section. The fauna from the T. larapintinensis Zone includes Panderodus nogamii, Triangulodus larapintinensis, and species of Juanognathus, and the A. leptosomatus Zone is characterized by A. leptosomatus, Histiodella holodentata, and Plectodina onychodonta. Two regression events are recorded in a lower part of the Thong Pha Phum section. The conodont biostratigraphy indicates that the regressions took place in latest Early Ordovician and earliest Middle Ordovician.

Morphology, evolution and stratigraphic distribution in the Middle Ordovician conodont genus Microzarkodina

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.

Middle and Upper Ordovician conodonts from the Fågelsång GSSP, Scania, southern Sweden

Based on Haddding's (1913) conodont collection supplemented by much larger recent collections, about 20 conodont taxa have been identified from the Fågelsång GSSP and nearby outcrops, which include a stratigraphic interval from the Eoplacognathus lindstroemi Subzone of the Pygodus serra Zone to the Baltoniodus variabilis Subzone of the Amorphognathus tvaerensis Zone. The base of the global Upper Ordovician Series, and that of the Sandbian Stage, is located in the middle part of the Pygodus anserinus Zone, apparently very close to the base of the Amorphognathus inaequalis Subzone. Each of the nine conodont species introduced by Hadding (1913) is discussed and interpreted in terms of modern multielement taxonomy.

Lower and Middle Ordovician conodonts from the Thung Song and Thung Wa areas, southern peninsular Thailand

ABSTRACT Lower and Middle Ordovician conodonts from the Thung Song Group, in the Thung Song and Thung Wa areas of southern peninsular Thailand, are described and illustrated here for the first time. These conodonts are divided into faunas A, B, and C, which are middle to late Arenigian, middle Arenigian to Darriwilian or Caradocian, and late Arenigian to early Caradocian, respectively. Fauna A resembles faunas in Australia, South China, the Argentine Precordillera, and North America. Fifteen species belonging to twelve genera were studied systematically.

Ordovician conodonts from the Thong Pha Phum area, western Thailand

The Ordovician conodont biostratigraphy of a limestone sequence in the Tha Manao Formation, exposed in the Thong Pha Phum area, western Thailand, comprises four Early to Middle Ordovician conodont zones. These are the Juanognathus variaviris Zone, the Walliserodus comptus Zone, the Juanognathus jaanussoni– Histiodella holodentata Zone, and the Plectodina onychodonta Zone, in ascending order. These conodont faunas are similar to those from the Midcontinent Province, North China, Australia, and Argentina.

Middle Ordovician (Darriwilian) conodonts from allochthonous limestones in the Oakdale Formation of central New South Wales

Twenty species of late Middle Ordovician conodonts including two new forms, Erraticodon bellevuensis sp. nov. and Ansella? haustra sp. nov., are described and illustrated from allochthonous limestone blocks in the Oakdale Formation of the Bell River Valley, N.S.W. The co-occurrence of Paroistodus horridus, Histiodella kristinae and Appalachignathus delicalulus in the fauna suggests the limestone was originally deposited in late Darriwilian (most likely early-mid Da3) time, providing a maximum age constraint on its inclusion in the Oakdale Formation. Some faunal similarities are apparent between this conodont fauna and that from (1) allochthonous limestone clasts within the Fairbridge Volcanics below the Wahringa Limestone Member and (2) contemporaneous deep-water cherts in basinal turbidite facies of the Adaminaby Group. The latter similarity suggests that prior to downslope displacement into the Oakdale Formation, the original depositional environment of the limestone was on an unstable outer shelf edge rather than in shallow water depths.

Early to early Middle Ordovician conodont biostratigraphy of the Gillberga quarry, northern Öland, Sweden

The Gillberga quarry in northern Öland provides a c. 16 m thick sequence through middle Volkhov to upper Kunda (mid-Arenig to early Llanvirn) beds. The section has been sampled for conodonts and its temporal faunal changes have been investigated on the basis of fiftynine samples yielding over 300,000 conodont elements. Conodont zones earlier recognized in south-central Sweden and ranging from the middle of the Baltoniodus navis Zone to the middle or upper part of the Microzarkodina ozarkodella Subzone of the Eoplacognathus pseudoplanus Zone were encountered at Gillberga. The temporal changes in relative frequencies of the most abundant conodont genera were calculated throughout the sequence and are presented in frequency diagrams. A new species, Microzarkodina bella, from the lower Kunda has been identified and is described.

Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

Middle Ordovician (late Arenigian - early Caradocian) conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the Pinney Hollow Formation in the Eastern Cover sequence near West Bridgewater, Vermont. These are the first reported fossils from the metamorphic cover sequence rocks east of the Green Mountain, Berkshire, and Housatonic massifs of western New England. The conodonts are recrystallized, coated with graphitic matter, thermally altered to a color alteration index (CAI) of at least 5, and tectonically deformed. The faunule is nearly monospecific, consisting of abundant Periodon aculeatus Hadding? and rare Protopanderodus. The preponderance of Periodon and the absence of warm, shallow-water species characteristic of the North American Midcontinent Conodont Province suggest a slope or basin depositional setting. The conodont-bearing carbonaceous schist is traceable 3 km southeast to the Plymouth area, where it had been designated the uppermost member of the Plymouth Formation, previously regarded as Early Cambrian in age. The age and structural position of the carbonaceous schist above dolostones of the Plymouth Formation but below the Pinney Hollow Formation (upper Proterozoic and Lower Cambrian?) suggest that this unit may be correlative or time transgressive with the Ira Formation, which underlies the Taconic allochthons in the Vermont Valley. Such a correlation supports the concept of placing the western limit of the root zone of the Taconic allochthons beneath the Pinney Hollow Formation. An approximate absolute age assignment for the conodont-bearing rock is between 470 and 454 Ma. This suggests that dynamothermal metamorphism during the Taconian orogeny on the east flank of the Green Mountains was younger than early Caradocian, which is in accord with the middle Caradocian age of the Ira Formation west of the Green Mountain massif.

Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

Aserian and Lasnamägian (Middle Ordovician) conodont biostratigraphy and lithology at Kullstaberg and Lunne in Jämtland, central Sweden

About 17,500 conodont specimens referred to 21 genera and 33 species were obtained in Middle Ordovician sections at Kullstaberg and Lunne in Jämtland. The correlation between the two sections is based on conodont biostratigraphy, however, the lithologies follow the conodont zones rather clearly. Stromatolites (“Lunne facies”) are present at two stratigraphic levels, the upper one in the top part of the Pygo-dus anitae Subzone and the bottom of the Eoplacognathus foliaceus Subzone, and the lower one in the bottom part of the P. anitae Subzone. On the basis of conodonts, the upper stromatolite is in an interval coeval with the Skärlöv Limestone in the Siljan region.

Middle Ordovician conodonts from the Buchans Group, central Newfoundland, and their significance for regional stratigraphy of the Central Volcanic Belt: Discussion

Nowlan and Thurlow have recently reported a conodont fauna of latest Arenig early Llanvirn age from the Buchans Group, central Newfoundland, and have suggested that this demonstrates that all volcanogenic massive sulfide deposits and, hence, associated volcanism in the Canadian Appalachians are of Caradocian or older Ordovician age. They go on to state that this requires substantial revisions of models for the northern Appalachians. We welcome this important contribution to the knowledge regarding the age of Roberts Arm Volcanic Belt (which includes the Buchans Group; Dean 1977) but find their suggestion that current models for central Newfoundland are inadequate or erroneous to be somewhat misleading. Perhaps this is the case if the tectonic models they are referring to are those, for instance, of Dean (1977, 1978), Strong (1977), or Dean and Kean (1980). However, their results strongly support the models set out by Kidd et al. (1977),

Middle Ordovician conodonts from the Buchans Group, central Newfoundland, and their significance for regional stratigraphy of the Central Volcanic Belt: Reply

Conodonts have been recovered from carbonate clasts within breccia units in the Buchans Group of central Newfoundland. The assemblage is characterized by specimens of Cordylodus horridus Barnes and Poplawski and Histiodella holodentata Ethington and Clark. These and other species recovered suggest a Whiterockian (latest Arenig–early Llanvirn) age for the clasts. This is somewhat older than the whole-rock Rb–Sr age of 447 ± 18 Ma on volcanics of the Buchans Group. The carbonate clasts are considered to be derived from the area of deposition of the Buchans Group rather than from some exotic source. This interpretation is based on knowledge of local tectonics, inferred paleogeogaphy, and geographic distribution of the conodont assemblage. All other clasts in the breccia units are considered of local origin. If the conodonts are of local Buchans Group origin then they indicate a Whiterockian age for the unit. In view of this, current regional models for the Central Volcanic Belt may require substantial revi...

Middle Ordovician conodonts from the Buchans Group, central Newfoundland, and their significance for regional stratigraphy of the Central Volcanic Belt

Conodonts have been recovered from carbonate clasts within breccia units in the Buchans Group of central Newfoundland. The assemblage is characterized by specimens of "Cordylodus" horridus Barnes and Poplawski and Histiodella holodentata Ethington and Clark. These and other species recovered suggest a Whiterockian (latest Arenig–early Llanvirn) age for the clasts. This is somewhat older than the whole-rock Rb–Sr age of 447 ± 18 Ma on volcanics of the Buchans Group. The carbonate clasts are considered to be derived from the area of deposition of the Buchans Group rather than from some exotic source. This interpretation is based on knowledge of local tectonics, inferred paleogeogaphy, and geographic distribution of the conodont assemblage. All other clasts in the breccia units are considered of local origin. If the conodonts are of local Buchans Group origin then they indicate a Whiterockian age for the unit. In view of this, current regional models for the Central Volcanic Belt may require substantial revision. A Whiterockian age for the Buchans Group is consistent with the observation that all significant volcanogenic massive sulphides of the Canadian Appalachians are of Caradoc or older Ordovician age. It is suggested that the Buchans Group is thrust southeastwards over the Victoria Lake Group, which is a probable distal facies equivalent.

Conodonts from the Davidsville Group, north-eastern Newfoundland: Discussion

Stouge (1980) has reported a new record of a Middle Ordovician conodont fauna from the basal part of the Davidsville Group at Weir's Pond, north of Gander. This occurs on the east side of the Reach Fault, which has been considered (McKerrow and Cocks 1977) to represent the suture along which the Iapetus Ocean finally closed. To the west of the Reach Fault, on New World Island, the Cobbs Arm Limestone has yielded similar conodonts (Bergstrom et al. 1974), though some additional taxa are present in this limestone. Stouge (1980, p. 270) has concluded that the similar conodont faunas on either side of the suture implies that that boundary was insignificant. However, it has long been known that the North Atlantic conodont province was present on both sides of the Iapetus Ocean (Bergstrom 1971, Fig. 12): similar faunas are present in the Appalachians and Scotland (both northwest of the suture) and Scandinavia (east of the suture). Indeed, many of the Davidsville species recorded by Stouge were originally described from Scandinavia. During the Middle and Late Ordovician Epochs, only benthic faunas (like trilobites and brachiopods) were clearly distinct on either side of the Iapetus Ocean (McKerrow and Cocks 1976). As Bergstrom and Cooper (1973) have shown, many pelagic conodonts and graptolites were able to cross the Iapetus Ocean from Llanvirn and Llandeilo times onwards. As Middle Ordovician conodont distributions do not distinguish either side of the Iapetus Ocean, Stouge's criticisms of our conclusions are unfounded. The benthic faunas still indicate that the Reach Fault marks the site of the Iapetus suture.