Revision of the Zone 13 graptolite biostratigraphy in the Marathon, Texas, standard succession and its bearing on Upper Ordovician graptolite biogeography

One of the long-standing problems in North American graptolite biostratigraphy is the distinct differences in assemblages of post-Climacograptus bicornis age between the classical graptolite sequences in the New York - Quebec and Marathon, west Texas, regions. These have been attributed either to faunal provincialism or to the presence of a major hiatus between the Woods Hollow and Maravillas formations in Texas. New collections from the key Marathon Picnic Grounds section contain diagnostic Late Ordovician graptolites that confirm the existence of a major stratigraphic gap below the Maravillas Formation. The lower Maravillas Formation (Zone 13) has a Late Ordovician, low-diversity Pacific Province graptolite fauna that includes the biostratigraphically diagnostic species Climacograptus nevadensis, C. tubuliferus, Orthograptus fastigatus and Dicellograptus ornatus. Zone 13 graptolite assemblages from the Marathon region correlate with the C. tubuliferus to D. ornatus zones in the Trail Creek, Idaho, succession, the Ea4-Bo2 interval in Victoria, the O. fastigatus Zone in the Canadian Arctic Islands, the O. quadrimucronatus to D. ornatus zones of the Canadian Cordillera, and the D. complanatus to D. anceps zones in Scotland. The hiatus between the Woods Hollow and Maravillas formations spans an interval corresponding to at least the Eal Ea3 interval in Australia, the C. americanus to upper A. manitoulinensis zones in the New York - Quebec succession, and the D. clingani and P. linearis zones in Scotland. These results agree with the magnitude of the hiatus previously indicated by conodont biostratigraphy. Late Ordovician graptolite distribution patterns in North America can be explained by an extension of Cooper, Fortey & Lindholm's (1991; Lethaia 24) Lower Ordovician graptolite biofacies model into the Upper Ordovician, which incorporates both lateral water-mass specificity and depth stratification. Using this model, we recognize in Laurentia two separate biofacies among tropical-zone Late Ordovician Pacific Province graptolite faunas, a cosmopolitan Oceanic biofacies, and a cratonic Laurentian biofacies. The lower Maravillas Formation graptolite fauna is clearly part of the Oceanic biofacies, whereas the coeval Appalachian faunas represent the Laurentian biofacies. □Graptolites, Ordovician, biostratigraphy, Texas, biofacies, biogeography.     

Die Graptolithen des Ordoviziums von Rügen (Norddeutschland, Vorpommern)

Graptolite faunas from theHolmograptus lentus,Pterograptus elegans, Hustedograptus teretiusculus andNemagraptus gracilis Zones are identified in the Ordovician succession of Rügen. The well sections bear incomplete, often fault-bounded successions. Tectonic stacking is present in the Rügen 3h core. A sedimentological gap is expected in the Arenig. About twenty graptolite species are described and their local biostratigraphic ranges are documented. Most of the faunal elements are described for the first time from the Ordovician of northern Germany. The faunal associations belong to the Atlantic Faunal Province.     

The graptolite correlation of the North American Upper Ordovician Standard

The North American Upper Ordovician reference standard, the Cincinnatian Series, contains rich shelly microfossil faunas in its type area in the Cincinnati Region but graptolites are uncommon in most of its shallow-water calcareous sediments. Consequently, the graptolite correlation of this key sequence has remained uncertain, in part, even controversial. A review of both previously published recently discovered graptolite Occurrences in the type Cincinnatian, combined with data from the important graptolite successions in Oklahoma New York-Quebec, has not only clarified the graptolite correlation of the Cincinnatian but also added new data on the morphology taxonomy, the vertical horizontal distribution, of several taxa. The information now at hand indicates that the Edenian Stage correlates with the C. spiniferus Zone, the Maysvillian Stage with the C. pygmaeus lower middle P. manitoulinensis Zone, the Richmondian Stage with the upper P. manitoulinensis , the D. complanatus , possibly part of the C. inuiti Zone. Comparison between graptolite conodont biostratigraphic evidence reveals no apparent conflict. Correlations are proposed between Upper Ordovician North American stages, graptolite conodont zones, successions in Texas, Oklahoma, Sweden, European graptolite zones, British series.     

Chitinozoan zonation of the Late Ordovician and the Early Silurian of the island of Anticosti, Québec, Canada

A reappraisal of chitinozoan distribution across the Ordovician-Silurian boundary on the Island of Anticosti has led to the recognition of a new zone, the Ancyrochitina ellisbayensis biozone, in the uppermost part of the Ellis Bay Formation. This biozone lies between the well defined Upper Ordovician Spinachitina taugourdeaui biozone and the lowest Silurian (Rhuddanian) Plectochitina nodifera biozone of the Becscie Formation. The occurrence of such diagnostic species as P. nodifera, Belonechitina postrobusta, Conochitina electa and Ancyrochitina ramosaspina in the Lower Silurian of Anticosti points to a close similarity to faunas in Estonia and north Latvia and indicates an age ranging from the Parakidograptus acuminatus to the Coronograptus cyphus in terms of graptolite zones. The chitinozoan biozonation harmonizes with that based on conodonts and, to a lesser extent, with the known graptolite faunal succession. Five new species: Ancyrochitina ellisbayensis sp. nov., Clathrochitina postconcinna sp. nov., Conochitina gunriveris sp. nov., Clathrochitina perexilis sp. nov., Bursachitina basiconcava sp. nov. and three species in open nomenclature are described.     

MIDDLE LLANDOVERY (AERONIAN) GRAPTOLITES OF THE WESTERN MURZUQ BASIN AND AL QARQAF ARCH REGION, SOUTH-WEST LIBYA

Abstract:  The taxonomy and biostratigraphy of the Aeronian graptoloid graptolites of the Tanezzuft Formation (Murzuq Basin and Al Qarqaf Arch area) is presented and discussed with respect to their palaeoenvironmental setting and palaeobiogeographical links. The gregarius-libycus , ' leptotheca ', convolutus and sedgwickii assemblage biozones and tenuis Subzone are recognized and correlated with the generalized zonal scheme and with graptoloid successions in peri-Gondwanan Europe. The Rhuddanian/Aeronian boundary is tentatively placed at the base of the gregarius-libycus Biozone. Telychian faunas have not been identified. Fourteen of the 23 species recorded herein belong to the middle Aeronian convolutus Biozone assemblage. The overall low diversity may be the result of inhabiting unstable, occasionally turbulent and/or oxic environments. The lowest diversity, but with abundant graptoloid rhabdosomes, is observed in proximal silty and sandy deposits. The presence of ' Paraclimacograptus' libycus suggests biogeographical links to Aeronian graptolite faunas of Jordan and South America. The convolutus Zone assemblage is very similar to the coeval faunas of the Saudi Arabian Qusayba shales. The occurrence of several species endemic to northern and north-western Gondwana and peri-Gondwana provides further evidence for a distinct palaeoclimatic/palaeolatitudinal control on graptolite distribution.     

内蒙古中部新近纪动物群的演替与生物年代

内蒙古中部地区陆相新近系出露广、含化石丰富。对这一地区新近纪的研究,可以追溯到20世纪初期瑞典地质学者安特生(J．G．Andersson)、法国古生物学者德日进(P．Teilhar de Chardin)和以美国探险家安德鲁斯(R．C．Andrews)为首的美国自然博物馆中亚考察团分别对二登图、高特格和通古尔的考察与化石采集。他们的开拓性工作使这些地方成为中国十分重要的新近纪经典地点。特别是通古尔,由于其产出的化石丰富、具有中中新世动物群的特征, 已引入中国地质年表,作为新生代中一个“阶”的名称。最近20多年对这一地区新近纪生物地层学的研究又取得了很大的进展,新发现了数个不同时代的化石地点和层位,同时采集到大批哺乳动物化石标本。内蒙古中部各地点化石层的厚度一般不大,但所含的哺乳动物化石种类多、材料丰富。由于具有这一特点,使其化石组合能比较接近地反映短期内动物群体的结构面貌,较客观地指示沉积时期的生态环境。利用这些组合进行动物群相对时代的确定,以及对其生态环境的恢复无疑都会很有意义。但是,这里的地层缺乏测试绝对年龄的材料,化石组合间少见有直接的叠置关系,使得在这一地区建立独立的动物群时间顺序,确定动物群的演替序列和生物年代只能更多地依赖于对动物系统发育和动物群体变化的研究。本文对这一地区各地点发现的哺乳动物化石组合进行了审定,提供了最新的动物群名单;根据默尔根地点上部层位产出的化石组合特征,提议把该组合命名为铁木钦动物群;通过对哺乳动物系统发育关系的分析,将动物群进行先后排序,并阐述了这些动物群在各生物年代的演替特征;同时展示了各动物群与有关岩石地层和磁性地层的关系。文中进一步认定了苏尼特左旗的嘎顺音阿德格动物群为内蒙古中部地区现知新近纪动物群中的最早代表,其后依次为推饶木动物群、默尔根动物群、铁木钦动物群、阿木乌苏动物群、沙拉动物群、宝格达乌拉动物群、二登图动物群、哈尔鄂博动物群、比例克动物群、高特格动物群。内蒙古中部被认为是新近纪生物年代学研究的重要地点,在地质时代上这一哺乳动物群系列跨越了新近纪中新世至上新世的大部分时段。其中的嘎顺音阿德格动物群具有中国陆生哺乳动物年代山旺期的典型持征;推饶木动物群、默尔根动物群、铁木钦动物群构成的广义通古尔动物群,正是定义东亚中中新世陆生哺乳动物年代的依据;阿木乌苏动物群、沙拉动物群、宝格达乌拉动物群和二登图动物群符合保德期动物群的含义;比例克动物群和高特格动物群具有榆社期动物群的性质。虽然目前还无法根据这些动物群对我国陆生哺乳动物年代的时限进行精确界定, 但依某些动物阶元(主要为科和属一级)的最早迁入或在该区的最早出现,以及在该区地层中的最后出席,概述了内蒙古中部地区新近纪动物群所指示的哺乳动物年代特征,并分别把通古尔期和保德期细分为3个和4个非正规亚期。深入的研究,包括在这一地区发现新的化石层位和材料,不仅会为内蒙古中部地区生物年代的厘定提供更多的资料,而且有助于完善中国新近纪地质年代的内涵。     

Benthic ostracods and deep water-masses in the Atlantic Ocean

Ostracod faunas at six locations are compared, and related to distributions in an Atlantic Ocean-wide data base. Five, widely developed, vertical faunal sequences are recognised at particular levels within deep water-masses: Henryhowella Fauna (lower part of Antarctic Intermediate Water); Krithe Fauna (Upper North Atlantic Deep Water); Poseidonamicus-Bosquetina Fauna (upper part of Lower NADW); Dutoitella Fauna (lower part of Lower NADW); Legitimocythere Fauna (Antarctic Bottom Water). These faunas are correlated with previously established deep water benthic foraminiferal assemblages, and their possible palaeo-oceanographic use is discussed.     

New insights into the paleobiogeography of the Early Ordovician graptolite fauna of northwestern Argentina

A multivariate analysis was used to determine the faunistic relationships of the northwestern Argentinean graptolite faunas of Floian age to faunas from Baltica, Avalonia, Laurentia and SW China. A statistical analysis at the species level of the five geographic regions for the Lower Floian was performed with the classic Jaccard's index. The resulting affinity dendrogram shows stronger relationships between Early Floian graptolite faunas of northwestern Argentina and those from Baltica, with less obvious similarities to Great Britain (Avalonia) faunas and only weak affinities to North American (Laurentia) and Chinese (SW China) graptolite faunas. The statistical analysis confirms the paleobiogeographic relationships previously observed in other areas of the Cordillera Oriental, and supports the hypothesis that during the Early Ordovician, northwestern Argentina was located at middle to high latitudes, corresponding to the Atlantic Faunal Realm of cold water graptolite biofacies. The studied graptolite material from the Quinilicán and Agua Chica sections is preserved in shales and siltstones interbedded with fine to medium-grained sandstones corresponding to the lower part of the Acoite Formation. The biostratigraphic implications of the associated graptolites are briefly discussed, and Trichograptus dilaceratus (Herrmann), Acrograptus gracilis (Törnquist), Expansograptus latus (T.S. Hall) and Corymbograptus v-fractus tullbergi (Monsen) are described from the Argentine Cordillera Oriental for the first time.     

Famennian conodonts from the Hongguleleng Formation at the Bulongguoer stratotype section,western Junggar,Northwest China

The Hongguleleng Formation, the highest and most important Devonian marine carbonate horizon in western Junggar, contains an endemic shallow-water Icriodus–Polygnathus conodont fauna with rare palmatolepids and other genera. The conodont faunas from the Bulongguoer and the Wulankeshun sections are similar, with high abundance (about 40%) of endemic taxa (13 taxa), indicating isolation of the Junggar Basin during early Famennian. Non-endemic species in the faunas suggest that the Lower Member of the Hongguleleng Formation is assignable to the Pa. rhomboidea Zone to the Pa. marginifera marginifera Zone of early Famennian, not including the Frasnian–Famennian boundary. The Upper Member may be of late Famennian–early Tournaisian in age on the basis of our preliminary faunal analysis.     

Chitinozoan biostratigraphy of the Upper Ordovician Fågelsång GSSP, Scania, southern Sweden

In the Fågelsång section, the new Global Stratotype Section and Point (GSSP) for the base of the Upper Ordovician Series, 22 samples from the E14 (a, b and c) and E15 outcrops have been studied for chitinozoans. They yield rich and rather diverse species assemblages of this microfossil group. The approximately 16-m-thick sampled part of the section can be subdivided, from bottom to top, into two biozones and a subbiozone: the Laufeldochitina stentor zone, the Eisenackitina rhenana subzone and the Lagenochitina dalbyensis zone. The boundary between the lowest biozone and the subzone is situated 1.7 m below the marker “Fågelsång Phosphorite” bed, thus only slightly lower (0.3 m) than the base of the Nemagraptus gracilis graptolite biozone, which defines the base of the Upper Ordovician Series. The base of the L. dalbyensis zone is located just above the Fågelsång Phosphorite, remarkably low compared to the graptolite biostratigraphy. It is evident that the chitinozoan biozonation provides an additional tool to recognise the base of the Upper Ordovician in this section. Furthermore, a distinct faunal change is shown across the phosphorite bed, possibly indicating a hiatus.     

Didymograptus bifidus and the trans-Atlantic correlation of the Lower Ordovician

Bergström, S. M. & Cooper, R. A.: Didymograptus bi'us and the trans-Atlantic correlation of the Lower Ordovician.
The co-occurrence of Didymograptus bifidus (Hall) and Prioniodus mae Lindstrom, and other conodonts of the middle Arenigian P. mae Zone in the upper part of the Marathon Limestone, Texas, provides the first non-graptolitic evidence that at least part of the D. bifidus Zone, as recognized in the reference area for the standard graptolite zonal succession of the Ordovician of North America, is as old as the BritisK D. nitidus Zone. This has important implications for the correlation of Early Ordovician rocks within North America and across the Atlantic. A regional review of the available evidence from conodonts and shelly megafossils indicates that the D. bifidus—D. artus graptolite assemblage widely used for identification of the D. bifidus Zone in North America ranges in age from the middle Arenigian to, probably, the lower Llanvirnian, and hence is of relatively limited use for precise local and regional correlations. It is also noted that the base of the North American Middle Ordovician falls within hograptus 'caduceus' Zone strata that apparently correspond to an interval in the middle to upper part of the British D. hirundo Zone.     

Tremadocian (Ordovician) biostratigraphy and graptolites at Dayangcha (Baishan,Jilin, NE China)

Based on a systematic study of Tremadocian graptolites from the Early Ordovician Yehli Formation at Dayangcha, Baishan of Jilin, NE China, a revised graptolite zonation is proposed for the Tremadocian rocks in the area. In ascending order, the graptolite zones include theRhabdinopora flabelliformis parabola Zone, theAnisograptus matanensis Zone, thePsigraptus jacksoni Zone and theAorograptus victoriae Zone. The first three zones are discussed with their definitions and durations clarified, whereas the last zone is introduced for the first time as a replacement of the formerAdelograptus-Clonograptus Zone. The entire Yehli Formation is considered to be older than the late Tremadocian Hunneberg Substage of Scandinavia, the latter being represented by the carbonate-dominated basal part of the overlying Liangchiashan Formation where no graptolites have so far been discovered. The Tremadocian succession in the Dayangcha area is regarded as being representative of the North China (Sino-Korea) Palaeoplate, and a correlation of the Tremadocian graptolite sequence with those of other continents is suggested. Nine species belonging toDendrograptus, Aspidograptus, Callograptus andAirograptus of the family Dendroidae, and eight species ofPsigraptus, Adelograptus, Aorograptus andKiaerograptus of the family Anisograptidae are described and some are revised in the present paper. Among the important revisions are the reconstructed proximal development ofPsigraptus jacksoni based on partially three-dimensional specimens from the area, and the complex thecal structures ofAspidograptus.      

The Ecology of Temporary Streams I. The Faunas of Two Canadian Streams

This, the first of two papers on the ecology of temporary streams, describes, in detail, the faunas of two such habitats in southeastern Canada. The adaptive mechanisms for coping with the summer drought are documented for a variety of species and faunal succession is shown to occur from the stream stage (fall-winter) through the pool stage (spring) to the terrestrial (summer).     

Faunal turnovers and trilobite morphologies in the upper Cambrian Leptoplastus Zone at Andrarum, southern Sweden

The Furongian (upper Cambrian) Leptoplastus Zone marks a time of critical changes in the evolution of olenid trilobites. This zone, unexposed at Andrarum in Skåne, southern Sweden, has been re-excavated and the sequence of faunas and sediments logged in detail. The faunal succession accords with that previously described from borehole cores by Westergård, and the subzones of L. paucisegmentatus, L. raphidophorus, L. crassicornis, L. ovatus, L. angustatus, and L. stenotus have been recognized. In the first two subzones the olenid assemblages are monospecific. At the base of the L. crassicornis Subzone more than one species is present and morphotypes with long genal spines appear for the first time. Faunal turnover is rapid, but the incoming of new species is invariably linked to an abrupt change in sedimentation, or follows an unfossiliferous interval; species either arose or migrated in after a time of environmental perturbation. Particular faunal associations are often confined to discrete sedimentary packages though some species may range through a succession of sedimentary changes. Leptoplastus crassicornis has very long genal spines, adapted for resting on the sea floor; it may have competed with the coeval, and very similar, L. angustatus. Subsequently, L. angustatus is accompanied by the stout-bodied, short-spined L. ovatus, which presumably occupied a different niche within the same environment. Leptoplastus stenotus is convergent on the much earlier L. paucisegmentatus, and likewise is found as a monospecific assemblage, presumably being adapted to a similar niche.     

Palaeontologic and biogeochemical characterization of the Cyrtograptus lundgreni event in the black shales of eastern Mid-Sardinia, Italy

A succession of biotic and geochemical changes that occurred during the Cyrtograptus lundgreni Event (Late Wenlock) have been recorded from the 'pelagic' black-shales in the Goni section, eastern mid-Sardinia, Italy. The studied interval encompasses the Cyrtograptus rigidus to Pristiograptus dubius-Gothograptus nassa zones. The fossil association includes graptolites, chitinozoans and microplankton i.e. probable linings of agglutinated foraminifera and radiolaria capsular membranes. Analysis of the chitinozoan distribution revealed a succession of several chitinozoan associations with low species diversity and dominated by opportunistic species. Three chitinozoan faunal turnovers and three extinction events have been recorded. Two of them coincide with graptolite extinctions whereas one probably is of local significance. Disappearance of the chitinozoan and microplankton associations occurred during four consecutive graptolite zones. Geochemical data (trace elements analysis) showed significantly higher (up to c. 100%) values for Co and Cd in the sedimentary organic matter (SOM) than in the whole rock samples. Possible relationships between peaks of metal enrichment, the major faunal changes among chitinozoans, extinction events among chitinozoans and graptolites and, to a certain extent, oceanic events may be inferred. The first extinction datum is older that those occurring in Gotland, Sweden and Thüringen, Germany and is so far considered to be of local significance. The second extinction datum of Sardinia can be matched with Datum 1 of Gotland and Thüringen. A close correlation between the third extinction datum of Sardinia and Datum 2 of Thüringen and Gotland reinforces the importance of these events at global scale.     

Proposal for adoption of the base of the Undulograptus austrodentatus Biozone as a global Ordovician stage and series boundary level

The base of the Undulograptus austrodentatus Biozone appears to be a synchronous event that is widely recognizable within graptolitic facies around the world. It occurs within an interval in which graptolite species ranges are now well known and in which there is a rapid turnover in the composition of graptolite faunas. This turnover reflects the rapid evolutionary radiation of the Diplograptacea simultaneously with the appearance of several distinctive pseudisograptid and glossograptid species. These events provide the basis for the recognition of two thin but widely applicable subzones; a lower Arienigraptus zhejiangensis Subzone and an upper U. sinicus Subzone. The occurrence of the lower boundary of the U. austrodentatus Biozone within a succession of first appearances also permits accurate and reliable identification of the boundary as well as assessment of stratigraphic completeness across the boundary interval in correlated sections. Diverse graptolite faunas of late Yapeenian and early Darriwilian age occur in association with the Histiodella altifrons Biozone of the North American midcontinent conodont zonation and the Paroistodus originalis and Microzarkodina parva biozones of the North Atlantic conodont zonation. They also occur in association with the shelly-fossil zonations developed for several different continents. These features of the base of the U. austrodentatus Biozone make it a suitable level for use as the boundary level for a global stage. Its stratigraphic position within the Ordovician System relative to other likely global stages as well as its coincidence with one of the major events in graptolite evolutionary history suggest that this level also may be a suitable level for the base of a global Middle Ordovician Series.Ordovician System, Ordovician stages, graptolite zonation, chronostratigraphy, international correlation. Charles E. Mitchell and Jörg Maletz, Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260-1550, USA; 13th July, 1994; revised 22nd May, 1995.     

Geopalaeontological setting,chronology and palaeoenvironmental evolution of the Baccinello-Cinigiano Basin continental successions (Late Miocene,Italy)

The Latest Miocene succession of the Baccinello-Cinigiano Basin in southern Tuscany (Italy) recorded a faunal turnover documenting the extinction of an older, insular, endemic faunal complex characterised by the extinct ape Oreopithecus bambolii and the setting of a new, continental, European faunal complex including the colobine monkey Mesopithecus. A similar turnover pattern (Late Miocene ape/Latest Miocene Cercopithecidae) is generally observed in Late Miocene continental successions of Eurasia, from Spain to central Europe, Southwest Europe, the near East, and Southwest Asia. Abundant literature reports that the Late Miocene Eurasian hominoid primate distribution closely tracks the climatic/environmental changes occurring during the 12–9 Ma interval, until their extinction in western Europe. In the primate record, the dispersion of Cercopithecidae and the contraction of hominids is interpreted as an event depicting a pattern of “continentalisation” in the Old World. The sedimentary succession of the Baccinello-Cinigiano basin, one of the longest continuous vertebrate-bearing continental successions in the Neogene Italian record, contributes to the debate on this hypothesis. This paper provides an overview of the main characteristics of the sedimentary succession, the chronological constraints (biochronology, radiometric datings, magnetostratigraphy), and the palaeoenvironmental evolution as derived from palaeobiological approaches and from the study of stable carbon and oxygen isotope contents along the entire sedimentary succession. The 2 myr geological history of the Baccinello Cinigiano Basin, which documents the evolutionary history of Oreopithecus and associated faunas, does not have a direct relation with the event of the Messinian Salinity Crisis. The evolutionary history of Baccinello-Cinigiano Basin and its palaeontological record have been mainly driven by the regional tectonism and palaeogeographic changes that affected the northern Tyrrhenian regions in Late Miocene (Latest Tortonian–Messinian) times.     

Goniatites du Namurien des Pyrénées occidentales Françaises. Implications stratigraphiques et paléogéographiques

New outcrops discovered in detrital ante-Stephanian sequences of the Southwestern Pyrenean Axial Zone (Béarn and Basque Country), yield abundant and varied faunas and floras. Among these the goniatite faunas are of particular interest. In a detailed palaeontological study, 9 species of Namurian age are recognized characterizing 3 levels of different age: the levels R_1a2 (Reticuloceras circumplicatile Subzone) and R_1a3 (Reticuloceras todmordenense Subzone) belong in the lower R₁ Zone (Kinderscoutian, Reticuliceras inconstants Zone), Namurian B; the third level is Upper Namurian in age (Yeadonian, lower Gastrioceras Zone), Namurian C. These goniatite associations are palaeogeographically linked with those of the rest of Europe and North Africa, but their stratigraphical succession is not continuous.     

Glass sponges (Porifera, Hexactinellida) of the northern Mid-Atlantic Ridge

Glass sponges (Hexactinellida) collected under the framework of the MAR-ECO project on the G.O. Sars cruise to the northern Mid-Atlantic Ridge, between the Azores and the Reykjanes Ridge, and on the 49th cruise of Akademik Mstislav Keldysh to the Charlie-Gibbs Fracture Zone are described. Fourteen species were identified in the material. This relatively rich fauna includes several novel findings, indicating that the hexactinellid fauna of the northern Mid-Atlantic Ridge is poorly investigated. One genus, Dictyaulus, has never before been reported from the Atlantic Ocean. Two species belonging to the genera Heterotella and Amphidiscella are new to science. Two other species, Rossella nodastrella Topsent, 1915 and Doconestes sessilis Topsent, 1928, have been collected just one other time. Finally, a probable new genus of Euplectellidae, which unfortunately cannot be adequately described because of how small the specimens are, is represented among these collections. A large portion of dead, rigid skeletons of Euretidae and spicule mats of Rossellidae are also reported but not described in detail. Representation of some genera in the Charlie-Gibbs Fracture Zone, coupled with recent observations from elsewhere along the Mid-Atlantic mountain chain, suggests that this fauna is as similar to those of the Indian Ocean and Indo-West Pacific as it is to West or East Atlantic faunas.