Paltodus Deltifer Research Articles

New data on the Cambrian–Ordovician (Tremadocian) conodont biostratigraphy of Guizhou Province, Southwest China

This report documents conodont biostratigraphic successions from the Sandu and Honghuayuan sections located in the southeastern and northern parts of the Guizhou Province. The Sandu section, palaeogeographically located close to the inner margin of the Jiangnan Slope, contains two proto-and paraconodont assemblages of the Miaolingian to early Furongian age recovered from the Sandu Formation and latest Furongian to early Tremadocian Cordylodus lindstromi and Cordylodus angulatus zones recovered from the overlying Guotang Formation. The Honghuayuan section, located within the Sichuan Basin in the central part of the Yangtze Platform, contains middle Tremadocian conodonts of the Rossodus manitouensis and Paltodus deltifer zones. This conodont zonation permits biostratigraphic correlation with the Miaolingian to Tremadocian successions in other parts of South China and biozonal successions across the world.

Upper Cambrian–Lower Ordovician conodonts from the southern margin of the Kopet-Dagh Basin, Saluk Mountains, Iran

A detailed Furongian to Tremadocian conodont biostratigraphy is established from the Saluk Mountains located in southern Kopet-Dagh, northeast Iran. Thirty species assigned to 17 genera were recovered from decimetre-scale limestone beds in a fine-grained siliciclastic succession, deposited in an intraplate rift system. The following biozones are established for the region, in ascending order: Proconodontus muelleri, Eoconodontus, Cordylodus intermedius, Cordylodus lindstromi, Cordylodus angulatus, Paltodus deltifer and Acodus triangularis interval zone. This low-to medium-richness conodont fauna comprises cosmopolitan euconodont species of Proconodontus, Eoconodontus, Cordylodus, Teridontus nakamurai, Semiacontiodus nogamii and a few long- ranging proto- and paraconodont species, which inhabited a narrow marine basin flanked by landmasses and formed by active rifting. It lacks shallow water tropical taxa and probably belongs to the Cold Domain of the Shallow Sea Realm. The occurrence of conodonts of the Paltodus deltifer Biozone in the uppermost part of the Qyzlar Formation in the Ghelli section suggests that the major episode of flood basalt volcanism in south Kopet-Dagh commenced in the late Tremadocian. Hadi Jahangir [Jahangir.hadi@nigpas.ac.cn] and Guanzhou Yan [gzyan@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, PR China.

Carbon isotope (δ13Ccarb) stratigraphy of the Lower-Upper Ordovician of the Yangtze Platform, South China: Implications for global correlation and the Great Ordovician Biodiversification Event (GOBE)

We present new high-resolution carbonate carbon isotope data (δ13Ccarb) from four sections in the Yangtze Platform, South China, ranging in age from Tremadocian to early Katian. The data have five distinct characteristics: 1) A prominent δ13Ccarb increase from −2.79‰ to 0.13‰ at the base of the Ordovician within the Tremadocian Cordylodus angulatus-Rossodus manitouensis Zone. 2) A positive δ13Ccarb excursion from −2.56‰ to 0.58‰ in the Paltodus deltifer Zone during the late Tremadocian. 3) A gradual increase in δ13Ccarb from −1.16‰ at the top of the Oepikodus communis Zone to a peak of ~0.74‰ in the Baltoniodus triangularis Zone at the Floian-Dapingian boundary. 4) A moderate rise in δ13Ccarb from 0.59‰ to 1.24‰ in the middle Darriwilian Dzikodus tablepointensis Zone. 5) A distinct positive δ13Ccarb excursion from 0.86‰ to 2.32‰ at the base of the Amorphognathus superbus-Hamarodus europaeus Zone during the early Katian. These excursions can be correlated with C-isotopic trends identified in age-equivalent successions in South China, Argentine Precordillera, North America, and Central Sweden, demonstrating their potential for global correlations and providing a composite, high-resolution chemostratigraphic framework for sedimentary records of the Lower-Upper Ordovician in South China. Besides, our data demonstrate a temporal coincidence between the long-term rise in δ13Ccarb and the Great Ordovician Biodiversification Event, suggesting that enhanced organic matter burial and accompanied climatic cooling and oxygenation may have played an important role in promoting the increases in biodiversity during the Ordovician.

Conodont biostratigraphy and correlation of the San Juan Formation at the Cerro La Silla section, middle Tremadocian-lower Dapingian, Central Precordillera, Argentina

This study deals with the conodont biostratigraphy from the uppermost part of La Silla Formation (9.6 m) and the overlying San Juan Formation (264.7 m), at the Cerro La Silla section, Central Precordillera of San Juan, Argentina. The 41 samples of carbonate rocks that were digested for microfossils yielded 11,388 conodont elements corresponding to 78 species. The Paltodus deltifer deltifer Subzone of the Paltodus deltifer Zone from the Baltic biostratigraphic scheme is represented at the top stratum of the La Silla Formation and the basal part of the San Juan Formation (28.4 m), which correlates with the Macerodus dianae Zone (middle Tremadocian) of the Precordilleran and North American schemes. Following upwards, the Paroistodus proteus, Prioniodus elegans, Oepikodus evae, Oepikodus intermedius and Baltoniodus triangularis-Tripodus laevis zones (middle Tremadocian-lower Dapingian) are recorded in the San Juan Formation. The Baltoniodus triangularis-Tripodus laevis Zone is recognized from the second reef level (177.3 m from the base of the San Juan Formation) up to the top stratum in the section, in contrast to previous interpretations that assigned the referred interval to the Baltoniodus navis, Paroistodus originalis and Microzarkodina parva zones of the Baltic biostratigraphic scheme. The division of the Oepikodus evae Zone in subzones, according to its original definition for the Precordillera, is not applicable at the Cerro La Silla section due to the particular species distribution. The conodont elements show a brown alteration color (CAI 2-2.5), which indicates a burial paleotemperature of 60-155°C for the bearer strata.

ACRITARCHS AND CONODONTS FROM THE CAMBRO - ORDOVICIAN FURUHÄLL (KÖPINGSKLINT) SECTION (ÖLAND, SWEDEN)

Cambrian to Lower Ordovician acritarchs and Lower Ordovician conodont species have been recorded from the Furuhäll Section at Köpingsklint on Öland, Sweden. The acritarchs are represented by three different microfloras. The first is found at the base of the section investigated and is characterized by the association of Cristallinium cambriense with Eliasum llaniscum, Retisphaeridium dichamerum and R. howellii. This microflora has been recorded in strata previously referred to the Paradoxides paradoxissimus trilobite Superzone.
 The second microflora includes Timofeevia lancarae, T. pentagonalis and T. phosphoritica and it has been found in layers dated to the Upper Cambrian Agnostus pisiformis trilobite Zone.
 The third microflora comprises Of several species among which Aremoricanium ? grootaertii, Athabascaella playfordii, Dasydiacrodium tremadocum, Stelliferidium furcatum which are indicative of a Tremadocian age. This association includes taxa which usually occur in different bioprovinces, thus it allows transprovincial correlations. This microflora has been recorded in Lower Ordovician (Tremadocian) strata Of the Dictyonema flabelliforme s.l. - Clonograptus heres graptolite Zones.
 The new species Adara (Middle Cambrian) and Cristallinium aciculatum (Upper Cambrian) are described.
 The conodont species are referable to Tremadocian Paltodus deltifer Zone and Paroistodus proteus, Prioniodus elegans and Oepikodus evae conodont Zones Of the Arenigian. The fauna is typical Baltic, but includes elements of Tropodus and Tropodus sweeti which otherwise are known from the midcontinent conodont faunal province.
 The composition of the multielement species Baltonidius ? deltatus, B. crassulus, Oistodus aff. O. lanceolatus, Paltodus deltifer, P. peracutus and P. subaequalis is revised.
 The sequence of Furuhäll is characterized by several hiata, some of which can be related to eustatic sea level lows. The most extensive hiatus is from the Upper Cambrian Leptoblastus trilobite Zone into the early Tremadocian Dictyonema flabilliforme s.l. Zone. Barren interzones have been recorded at the base and at the top of Hunnebergian Substage. The lower barren inter-zone corresponds to the Tremadocian - Arenigian stage boundary or the Paltodus deltifer - Paroistodus proteus zonal boundary. The upper barren interzone coincides With Paroistodus proteus and Prioniodus elegans zonal boundary.

Terminal Cambrian and Early Ordovician (Tremadocian) conodonts from Eastern Alborz, north-central Iran

Hadi Jahangir, Mansoureh Ghobadi Pour, Alireza Ashuri & Arash Amini, December 2015. Terminal Cambrian and Early Ordovician (Tremadocian) conodonts from Eastern Alborz, north-central Iran. Alcheringa ##, ###-###. ISSN 0311-5518.Uppermost Cambrian (Furongian) and Lower Ordovician (Tremadocian) deposits of eastern Alborz in northern Iran contain several successive low- to moderate-diversity conodont associations including 13 genera and 19 species of euconodonts, paraconodonts and protoconodonts, which define six biozones: 1, the Proconodontus muelleri; 2, Eoconodontus notchpeakensis; 3, Cordylodus andresi; 4, Cordylodus proavus; 5, Paltodus deltifer; and 6, Paroistodus proteus zones. With the exception of Cordylodus andresi, which is otherwise known from Baltoscandia and from the Oaxaquia terrane (Mexico), all index-taxa are geographically widespread, allowing long-range correlation within the Cold Domain or the North Atlantic Province, and in particular with Baltica. Invasion of euconodonts in the Alborz region, defined by the first occurrence of Proconodontus muelleri, coincides closely with a steady rise in sea level and termination of carbonate sedimentation, whereas the transition from the Proconodontus muelleri to Eoconodontus notchpeakensis zones occurs during a highstand interval unlike in Laurentian sequences. The interval corresponding to the Cordylodus andresi and Cordylodus proavus zones, and the transition from the Paltodus deltifer to Paroistodus proteus zones coincided with unstable sea levels and the formation of shoal complexes. The lower boundary of the Floian Stage can be provisionally placed slightly below the first documented occurrence of Acodus sp. cf. A. kechikaensis, somewhat below the second unit of andesitic lava flows in the Simeh-Kuh section.Hadi Jahangir [jahangir.hadi@gmail.com] and Alireza Ashuri [ashouri2001@yahoo.com] Department of Geology, Faculty of Sciences, Ferdowsi University, Azadi Square, Mashhad 91775-1436, Iran; Mansoureh Ghobadi Pour* [mghobadipour@yahoo.co.uk; m.ghobadipour@gu.ac.ir] and Arash Amini [a.amini@gu.ac.ir], Department of Geology, Faculty of Sciences, Golestan University, Gorgan 49138-15739, Iran. *Also affiliated with Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, UK.

Early Ordovician conodonts from Zhejiang Province, southeast China and their biostratigraphic and palaeobiogeographic implications

Forty-two conodont species are documented from the Liuxia, Shijiatou and Jingshan formations in Zhejiang Province of southeast China, located palaeogeographically on the Jiangnan Slope offshore to the Yangtze Platform. From these faunas, eight successive conodont biozones of Tremadocian to middle Floian (Early Ordovician) age are recognized, including the Cordylodus lindstromi Biozone, Cordylodus angulatus Biozone, Chosonodina herfurthi Biozone, Paltodus deltifer Biozone, Paroistodus proteus Biozone, Triangulodus bifidus Biozone, Serratognathus diversus Biozone and Prioniodus elegans Biozone. Several zonal index species of the Baltoscandian succession—Paltodus deltifer, Paroistodus proteus and Prioniodus elegans—are described and illustrated in detail for the first time from South China. Co-occurrence of P. proteus and Serratognathus bilobatus in several samples below the appearance of P. elegans also confirms correlation of the S. diversus Biozone (basal Floian) with the upper P. proteus Zone of the Baltoscandian succession. These Zhejiang faunas are dominated by pandemic forms, and are similar to those of the Open-Sea Realm elsewhere, inhabiting deep, offshore environments.

An Early Ordovician conodont fauna from the Santa Rosita Formation at its type area in the Santa Victoria Range, Cordillera Oriental, Northwestern Argentina

The Cambrian - Lower Ordovician stratigraphic units from the Cordillera Oriental were originally defined in the Santa Victoria Range, Salta Province, northwestern Argentina, however, the extensive outcrops of this region lack detailed biostratigraphic studies. We describe and analyse the first reported conodont fauna from the Santa Rosita Formation at its type area, which produced significant biostratigraphic information. Over 4,500 well-preserved conodont elements were recovered from outcrops of the Santa Rosita Formation at the southern margin of the Santa Victoria River, near the homonymous locality. Collected specimens exhibit a CAI 3 and correspond to the Paltodus deltifer deltifer Subzone of the P. deltifer Zone (middle Tremadocian, Tr2). A number of species are described for the genera Acanthodus, Acodus, Decoriconus, Drepanodus, Drepanoistodus, Filodontus, Granatodontus, Hammannodus, Iapetonudus, Kallidontus, Paltodus, Paroistodus, Teridontus, Tilcarodus, Utahconus, Variabiloconus, Gen. and sp. indet., the protoconodont Phakelodus and the paraconodont Coelocerodontus. Two new conodont species, Drepanoistodus andinus Voldman, Zeballo and Albanesi and Filodontus carolinae Voldman, Albanesi and Zeballo, are diagnosed herein. The studied assemblages include conodont species of wide intercontinental distribution as well as endemic forms from the Central Andean Basin, which characterize a faunal province with a particular signature from the Shallow Water Realm.

New conodont species and biostratigraphy of the Santa Rosita Formation (upper Furongian–Tremadocian) in the Tilcara Range, Cordillera Oriental of Jujuy, Argentina

A new conodont collection from the Alfarcito area of the Tilcara Range, Cordillera Oriental of northwestern Argentina, has been studied. The Santa Rosita Formation exposed in this area consists of the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members, which have a combined total thickness of ca. 1100 m. The sequence is composed of interbedded shales and sandstones, including calcarenites and coquinas, mostly appearing in the upper parts of the units. An abundant fauna of conodonts (ca. 11 000 elements), associated with graptolites and trilobites, was recorded. The biostratigraphic analysis allows for the identification of the Cordylodus intermedius and C. lindstromi sensu lato zones at the base of the Alfarcito Member. The C. angulatus Zone spans the upper part of the latter unit, and the Paltodus deltifer Zone (Paltodus deltifer pristinus and P. deltifer deltifer subzones) is identified in the Rupasca and Humacha members. The new species Acanthodus raqueli, A. humachensis, Utahconus tortibasis, U. scandodiformis, U. purmamarcensis, Variabiloconus crassus, Kallidontus gondwanicus and Acodus primitivus are recorded from the two latter biozones and they are described herein. The genera Acanthodus and Variabiloconus are emended, and a new genus Tilcarodus is created to include T. humahuacensis (Albanesi and Aceñolaza). Copyright © 2012 John Wiley & Sons, Ltd.

Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana

Research Article| April 01, 2009 Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana Gustavo G. Voldman; Gustavo G. Voldman * 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina *E-mail: gvoldman@efn.uncor.edu Search for other works by this author on: GSW Google Scholar Guillermo L. Albanesi; Guillermo L. Albanesi 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Search for other works by this author on: GSW Google Scholar Víctor A. Ramos Víctor A. Ramos 2CONICET—Laboratorio de Tectónica Andina, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Gustavo G. Voldman * 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Guillermo L. Albanesi 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Víctor A. Ramos 2CONICET—Laboratorio de Tectónica Andina, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina *E-mail: gvoldman@efn.uncor.edu Publisher: Geological Society of America Received: 27 Sep 2008 Revision Received: 10 Nov 2008 Accepted: 14 Nov 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (4): 311–314. https://doi.org/10.1130/G25540A.1 Article history Received: 27 Sep 2008 Revision Received: 10 Nov 2008 Accepted: 14 Nov 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gustavo G. Voldman, Guillermo L. Albanesi, Víctor A. Ramos; Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana. Geology 2009;; 37 (4): 311–314. doi: https://doi.org/10.1130/G25540A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract An Ordovician metamorphic event is recorded by means of conodont paleothermometry in the slope sedimentary sequences of the Western Precordillera. Allochthonous conodonts from reworked deposits of the eastern carbonate platform with CAI 4.5–5 and autochthonous conodonts from the olistostrome matrix with CAI 3 allow for constraining the metamorphic age within the Paltodus deltifer and Lenodus variabilis zones (i.e., ca. 480–465 Ma). The conodont data support an Ordovician instead of an alternative Devonian collision for the Cuyania terrane with the proto-Andean margin of Gondwana, which is consistent with the earlier proposed, but still contentious, microcontinent model. In the latter scenario, the collision of the Cuyania terrane caused unroofing and cannibalism of the leading edge of the carbonate succession and basement rocks. The erosion of these rocks supplied detritus and metamorphosed conodonts to the deeper basinal settings of the Western Precordillera. As the deformation front migrated into the peripheral foreland of the Eastern and Central Precordillera, nonmetamorphosed conodonts were eventually incorporated into the west-prograding synorogenic clastic wedge. The occurrence of allochthonous and autochthonous conodonts in the slope facies of the Western Precordillera provides a time constraint for the early accretion of the Cuyania terrane and its transition to an evolving foreland mountain system in the Ordovician period. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Horizon of the oldest known bryozoans (Ordovician)

Among the six species of fossil bryozoans described by Xia et al. [Xia, F.S., Zhang, S.G., Wang, Z.Z., 2007. The oldest bryozoans: new evidence from the late Tremadocian (Early Ordovician) of East Yangtze Gorges. Journal of Paleontology 81 (6), 1308–1326] from the Fenghsiang Formation of the Chenjiahe section of Yichang and the Guanzhuangping section, Liujiachang Town of Songzi, the Yangtze Gorges, Nekhorosheviella nodulifera occurs in the pristinus Conodont Subzone (lower Subzone of deltifer Conodont Zone) and the five other species are associated with the conodont Paltodus deltifer deltifer and the graptolites Acanthograptus sinensis and A. erectoramus. Based on the conodonts and graptolites, this bryofauna stratigraphically corresponds to the A. sinensis Graptolite Zone or P. deltifer Conodont Zone. The bryofauna is of Tremadocian Age (Early Ordovician) and represents the oldest bryozoans so far as known.

New late Tremadocian (Early Ordovician) conodont and graptolite records from the southern South American Gondwana margin (Eastern Cordillera, Argentina)

New late Tremadocian (Early Ordovician) conodont and graptolite faunas from the eastern and central belts of the Eastern Cordillera (Jujuy Province, northwestern Argentina) are reported. The conodont fauna includes the guide species Paltodus deltifer pristinus, Paltodus deltifer deltifer, and Acodus deltatus (sensu lato), in association with other taxa, and the graptolites Aorograptus victoriae, Ancoragraptus cf. bulmani, and Adelograptus cf. altus. Overlapping ranges of the recorded species allow for a partial correlation between the Acodus deltatus- Paroistodus proteus and Aorograptus victoriae zones, and the Notopeltis orthometopa trilobite Zone. The conodont fauna includes a mixture of forms typical of the Baltoscandian and Laurentian provinces, respectively. The Early Ordovician basin of northwestern Argentina may correspond to the Shallow-Sea Realm and Cold Domain and probably records the development of a differentiated conodont province in the southern South American margin of Gondwana.

A NEW EARLY ORDOVICIAN CONODONT GENUS FROM THE SOUTHERN MONTAGNE NOIRE, FRANCE

Abstract: Two species of a new Tremadocian (Early Ordovician) conodont genus from the Saint Chinian Formation of the southern Montagne Noire, France, are erected: Hammannodus sarae gen. et sp. nov. and Hammannodus juliae gen. et sp. nov. They were found within a single storm‐induced limestone nodule interbedded with offshore shales belonging to the regional Shumardia (C.) pusilla (trilobite) Biozone, and to the Paltodus deltifer deltifer (conodont) Subzone. This conodont record is associated with the episodic development of carbonate productivity in temperate waters of the Montagne Noire platform, a process absent in neighbouring platforms of north‐west Gondwana. The apparatus is composed of five coniform pyramidal elements occupying P and S positions and one bicostate element in the M position, having three or two sharp costae, respectively, with a subtriangular basal outline.

Conodont biostratigraphy and sedimentary history in the upper Tremadoc at Uuga, Cape Pakri, NW Estonia

The upper Tremadocian boundary beds at Cape Pakri, NW Estonia, consist of an extremely friable glauconitic sandstone, which presents a challenge to detailed biostratigraphy. A combination of sedimentological and biostratigraphical criteria has served to clarify the tempo and mode of the processes that formed the sandstone and explain its relationships to strata immediately below and above it. Apatitic conodont elements, which abound in all these sediments, are particularly well suited to tracing the geological history of the surrounding sediment, since they can be repeatedly included in the sediment, eroded and redeposited, often leaving telltale marks on the elements which are nevertheless identifiable. By separating the indigenous elements from those that had been redeposited, we could place the local upper boundary of the Tremadocian at slightly more than 1 m above the base of the c. 4 m-thick sandy deposit. We showed that the sandstone, where 58-97% of the conodont elements have been redeposited, had been formed during four successive phases of sand deposition. The entire sandstone unit belongs to the Paroistodus proteus Zone. In the sandy and clayey Varanguan beds of the Paltodus deltifer Zone that underlie the sandstone, less than 50% of the conodont elements had been redeposited. The upper part of the section consists of limestone beds belonging to the Oepikodus evae Zone, where the redeposited portion of the conodont elements decreases upwards.

Tremadocian Graptolite-Conodont Biostratigraphy of the South American Gondwana margin (Eastern Cordillera, NW Argentina)

The Tremadocian graptolite and conodont faunas of the Gondwana Margin recorded at the Eastern Cordillera (EC) of Salta and Jujuy provinces (northwestern Argentina) are studied. The previous data and the new provided information indicate that a “no nominated interval” and several graptolite zones (Anisograptus matanensis, Rhabdinopora flabelliformis anglica, Bryograptus, Kiaerograptus, Kiaerograptus supremus, Araneograptus murrayi, and Hunnegraptus copiosus zones), as well as several conodont zones (Iapetognathus, Cordylodus angulatus, Paltodus deltifer, and Acodus deltatus - Paroistodus proteus zones) occur in the Ordovician successions studied. New or reappraised data from sections such as Angosto del Moreno, Angosto de Lampazar, Parcha-Incamayo-Incahuasi area, and Cajas range (EC western margin), and Alfarcito area and Mojotoro range (EC eastern margin), provide new information on the composition of the fossil faunas. A composite graptoliteconodont biostratigraphic framework, including records of key trilobites as external control group, is proposed for the Tremadocian of the South American margin of Gondwana. Both fossil groups are generally recorded from outer platform to ocean basin environments, showing significant similarities with the Baltoscandian faunas. Nevertheless, particular shallow-water facies include either specific forms or species associations that are common to the epeiric shallow-water seas of Laurentia. This fact demonstrates an important interplay between faunas of different regions of the Iapetus Ocean during the Tremadocian.

Arenig (Lower Ordovician) conodonts and biozonation in the eastern Siljan district, central Sweden

Based on biostratigraphic investigations in the eastern Siljan district, central Sweden, and combined with earlier studies at Hunneberg, south-central Sweden, it is shown that the early post-Tremadoc-ageParoistodus proteusconodont Zone can be divided into four successive subzones. These are, in ascending order: theDrepanoistodusaff.D. amoenusSubzone; theTripodusSubzone; theParacordylodus gracilisSubzone; and theOelandodus elongatus-Acodus deltatus deltatusSubzone. The lowermost of the subzones is a concurrent range zone, with its reference section at Storeklev, Hunneberg, and the other three interval zones with the reference section at Sjurberg in the eastern Siljan district. Correlations between these two areas, as well as with the Flåsjö area, Jämtland, the Finngrundet core, and some other areas, are discussed, and it is concluded that theDrepanoistodusaff.D. amoenusSubzone and theTripodusSubzone together correspond to theMegistaspis(Ekeraspis)armatatrilobite Zone, and occur below theHunnegraptus copiosusgraptolite Zone. TheParacordylodus gracilisSubzone is equivalent with the lower part of theMegistaspis(Varvaspis)planilimbatatrilobite Zone, and may correspond to theHunnegraptus copiosusZone. The uppermost subzone, theOelandodus elongatus-Acodus deltatus deltatusSubzone, equals the upper part of theM.(V.)planilimbataZone, and the local base of theTetragraptus phyllograptoidesgraptolite Zone is close to the base of this conodont subzone. The last occurrences ofT. phyllograptoidesare close to the top of this conodont subzone. Also included in the investigation are the uppermost part of the uppermost TremadocPaltodus deltiferZone and the conodont zones overlying theP. proteusZone in the eastern Siljan district, thePrioniodus elegansZone and theOepikodus evaeZone; the latter zone corresponds to the trilobite zones ofMegalaspides(M.)dalecarlicusandMegistaspis(Varvaspis)estonica.A few samples from the superimposedBaltoniodus triangularis, B. navis, andParoistodus originalisZones have been investigated and are described as well. The correlation of these conodont zones and subzones with those of areas outside Baltoscandia, particularly North America, is also discussed.

Tremadocian Ceratopyge Limestone identified by means of conodonts, in Jämtland, Sweden

Abstract A section through the autochthonous Ordovician limestone to the east of Brunfloviken, Jamtland, central Sweden, yielded conodonts from the upper Ceratopyge and Latorp limestones. The Tremadocian Ceratopyge Limestone is represented by a 5 cm thick bed with abundant phosphorite and glauconite. It contains the following conodont species: Proconodontus notchpeakensis, Cordylodus prion, C. rotundatus, C. pararotundatus, C. angulatus, C. proavus, Paroistodus numarcuatus and Paltodus varanguensis. The fauna characterizes the upper Tremadoc Paltodus deltifer Zone. This is the first demonstration of the existence of Tremadocian beds in the autochthon of Jamtland.