An Edgewood-type Hirnantian fauna from the Mackenzie Mountains, northwestern margin of Laurentia

Silicified brachiopods from Hirnantian strata in three sections of the lower Whittaker Formation, Mackenzie Mountains, northwestern Canada, yielded a moderately diverse, Edgewood-type Hirnantian fauna, consisting of 13 species: Biparetis paucirugosus, Brevilamnulella laevis, Dalmanella edgewoodensis, Drabovia noixella, Eospirigerina putilla, Epitomyonia paucitropida, Epitomyonia sekwiensis, Glyptorthis papillosa new species, Gnamptorhynchos orbiculoidea, Katastrophomena mackenzii new species, K. parvicardinis, Parastrophina cf. P. minor, and Skenidioides sp. Compared to the typical Edgewood fauna of the American Midcontinent, Brevilamnulella laevis has a notably smaller shell than B. thebesensis, and is interpreted as a deeper-water form. The strong faunal affinity of the Mackenzie Mountains fauna to the Edgewood-type Hirnantian fauna is indicated by the occurrence of Biparetis, Brevilamnulella, Eospirigerina, and Gnamptorhynchos. In addition to the Edgewood type area within Laurentia, Biparetis, Eospirigerina, and Gnamptorhynchos are characteristic taxa that also occur in the Ellis Bay Formation (Hirnantian) of Anticosti Island. Multivariate and network analyses strongly support the differentiation between an Edgewood-type Hirnantian fauna in Laurentia and peri-Laurentia and the typical Hirnantia fauna of the Kosov Province in Gondwana, peri-Gondwana, South China, Kazakhstan terranes, Avalonia, and Baltica

Middle Ordovician brachiopods from Tagoat, Co. Wexford, SE Ireland: Dapingian diversity drivers

The Dapingian (Arenig) siltstones and sandstones of the Tagoat Group, County Wexford, SE Ireland, contain a well-preserved and diverse brachiopod fauna including a new genus of alimbellid, Palaeotagoatia (type species: Orthis Bailyana Davidson) together with the plectorthid Ffynnonia costata (Bates) hibernica nov. subsp. Of the 13 forms documented, at least six are conspecific with brachiopods from the upper Arenig (Dapingian-lowest Darriwilian) Treiorwerth Formation on Anglesey and a further two are identified with species occurring in the older Dapingian Carmel Formation. The faunal province affinities of the fauna are with those assemblages assigned to the peri-insular and marginal Celtic province and which occupied positions within the Middle Ordovician Iapetus Ocean between the Laurentian and Baltic platform provinces. More precise correlation of Middle Ordovician units suggests a significant species richness during the Dapingian-earliest Darriwilian and signalling also an early development of the Celtic province. But the shallow-water siliciclastic facies associated with these islands may also have influenced the distribution of some elements of the Celtic brachiopods and promoted the prevalence of coarse-ribbed orthides, such as Paralenorthis

The rise and fall of the Malvinoxhosan (Malvinokaffric) bioregion in South Africa: Evidence for Early-Middle Devonian biocrises at the South Pole

Global reconstructions, inclusive of environments and ecosystems, and biodiversity counts for the Devonian Period are often done so at the expense of high latitude regions given a historical lack of data presented from these areas. This has bearing on the recognition of biocrises (events marked by extinctions and faunal turnovers) at high latitudes as well as their controls and potential correlation with global, regional, and local tempos. The appearance and disappearance of high-latitude endemic Malvinoxhosan (synonymous with the “Malvinokaffric Realm” which it supersedes) marine invertebrate faunas from West Gondwana are often overlooked, in part owing to difficulties in correlating fossil-bearing strata with global frameworks given the absence and rarity of several key index taxa as well as detailed biostratigraphic appraisals in which to draw regional interbasinal correlations and comparisons. The Early to Middle Devonian Series of South Africa (upper Table Mountain, Bokkeveld and lower Witteberg groups) are a classic Malvinoxhosan-bearing section recording the rise of these endemic faunas, as well as their decline and replacement by cosmopolitan faunas. A detailed biostratigraphy of this interval was created following an assessment of fossil material curated at the Council for Geoscience and Iziko South African Museum, Cape Town as well as from literature. These data suggest that the Malvinoxhosan bioregion persisted as a cohesive unit during Rietvlei-Baviaanskloof to Waboomberg deposition (Pragian/Emsian-early Givetian) given that many representative taxa are found in these strata, however showing a trend of decreasing diversity with little origination through time. Above this interval, few representative taxa are known to continue into the upper Bokkeveld and Witteberg groups, disappearing entirely by the deposition of the Blinkberg Formation. The few fossils that are known in these strata and those succeeding it (e.g., the Swartruggens Formation) are entirely cosmopolitan in identity. Using novel multivariate statistical methods (non-metric multidimensional scaling and cluster analysis) in conjunction with network analysis (NA), the data were interrogated to indicate potential groupings of strata according to their fossil content as well as to track faunal changes through time. These analyses suggest the presence of at least seven to eight interval assemblage biozones housed within at least three larger faunal complexes (Eo-Malvinoxhosan, Malvinoxhosan and Post-Malvinoxhosan) based on their constituent faunal makeup. A closer inspection of these faunal complexes and interval assemblage biozones show a stepped decline in biodiversity with little to no origination and recovery through time that may be correlated with local base-level change at varying orders of magnitude. Declines in biodiversity show selectivity for taxa with epifaunal and semi-infaunal habits with respect to infaunal, deep infaunal and nektonic taxa. Environmental conditions associated with the collapse of the Malvinoxhosan bioregion are thought to have been catastrophic as few new (often short-ranging) immigrants are registered in Post-Malvinoxhosan strata. Further to this, those faunas that are prevalent in Post-Malvinoxhosan strata (e.g., Tropidoleptus) those with known high environmental tolerance and were already present in the region prior to the collapse of the Malvinoxhosan bioregion. Lastly, the observed biodiversity changes in South Africa with respect to local base-level show remarkable similarities with several time equivalent locales in South America suggesting that the decline and extinction of the Malvinoxhosan biota was regional and that the biostratigraphy presented herein has regional application. Here, it is thought regional tectonic controls are suggested to have brought on sea-level changes and entrained warmer waters into higher latitudes against the backdrop of overall rising temperatures from the late Givetian onwards. Whilst the decline of the Malvinoxhosan bioregion might associated with global Middle Devonian biocrises (e.g., Kačák; Taghanic) insufficient age constraints for these strata are available at present to make direct comparisons. Furthermore, an adequate driver for global sea-level change during the Devonian Period, needs to be established to tease out global and local signals in constructed local sea-level curves to establish if these changes (and their effects in changes in biodiversity) are truly global in extent

A Cambrian–Ordovician boundary section in the Rafnes–Herøya submarine tunnel, Skien–Langesund District, southern Norway

Rock specimens and contained fossils collected in 1976 from a submarine tunnel driven between Herøya and Rafnes in the Skien–Langesund area of southern Norway, have been restudied. The contained fossils include olenid and agnostoid trilobites, graptolites and brachiopods, groups described in detail for the first time from the area and documenting a Cambrian–Ordovician boundary section unique in the district where the upper Cambrian Alum Shale Formation is elsewhere overlain by the Middle Ordovician Rognstranda Member of the Huk Formation (Kundan in terms of Baltoscandian chronostratigraphy). The hiatus at the base of the Huk Formation is thus smaller in the section described herein, beginning at a level within rather than below the Tremadocian. Estimated thickness of the Alum Shale includes 10–12 m of Miaolingian and 20–22 m of Furongian strata with trilobite zones identified, and a Tremadocian section of 8.1 m identified by species of the dendroid graptolite Rhabdinopora in the basal 2.6 m and Bryograptus ramosus at the top. The Tremadocian section is preserved in a postulated zone of synsedimentary subsidence along the Porsgrunn–Kristiansand Fault Zone, while at the same time there was extensive erosion across an emergent, level platform elsewhere in the Skien–Langesund District and the southern part of the Eiker–Sandsvær District to the north. Aspects of stratigraphy and tectonics are highlighted together with a discussion on the Cambrian– Ordovician boundary locally and worldwide

Ordovician successions in southern-central Xizang (Tibet), China—Refining the stratigraphy of the Himalayan and Lhasa terranes

The Ordovician stratigraphy of southern-central Xizang (Tibet) has been revised based on new conodont data recovered from 43 samples in four stratigraphic units and their integration with existing nautiloid and graptolite data. The Histiodella holodentata and Pygodus serra biozones have been identified respectively in the Alai and Jiaqu formations of the Chiatsun Group exposed near Alai village in Nyalam County within the Himalayan terrane, and the Yangtzeplacognathus foliaceus Subbiozone (lower part of the Pygodus serra Biozone) in the Sangqu Formation exposed at the Guyu section within Zayu County in the Lhasa terrane. Recognition of these biozones has increased the precision of correlation of the middle-upper Darriwilian strata in the region. Regional reassessment of the Ordovician stratigraphy permitted by new biostratigraphic data has allowed revised definitions for the Chiatsun and Keerduo groups and the Sangqu and Xainza formations. The Chiatsun Group is defined herein to include three lithologically distinctive formations in descending order, the Jiaqu, the Alai and the Adang formations. The stratigraphic age for the Jiaqu and Alai formations in the type area ranges from the middle Darriwilian (Histiodella holodentata Biozone) to middle Katian (Hamarodus brevirameus Biozone), but the age of the Adang Formation remains less certain

The Sirius Passet Lagerstätte of North Greenland—A geochemical window on early Cambrian low‐oxygen environments and ecosystems

The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water‐column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR/FeT), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ15N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea‐level change, and where this early Cambrian biota was established in conditions with very low oxygen

The latest Ordovician Hirnantia brachiopod fauna of Myanmar: Significance of new data from the Mandalay Region

A new, latest Ordovician brachiopod fauna is systematically described from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group of the Pa-thin area, Mandalay Region, Myanmar, revealing one of the most diverse representatives of the typical Hirnantia Fauna. Rhynchonelliformean, craniiformean and linguliformean brachiopods studied belong to 23 genera and a few indeterminate taxa, among which the most abundant genus Kinnella, along with the four common genera (Paromalomena, Pseudopholidops, Fardenia, and Dalmanella), and other genera (such as Cliftonia, Draborthis, Hindella, Hirnantia, Leptaena, Mirorthis, Plectothyrella, Skenidioides, and Xenocrania) are recorded for the first time. This high diversity Hirnantia Fauna represents an ecological differentiation within the benthos of the Sibumasu Terrane during the end Ordovician global crisis. The palaeoeco-unit named herein as the Kinnella-Paromalomena Association is assigned to lower BA3. This paper includes a taxonomic revision with the following conclusions: 1) Sinomena Zeng et al. and Yichangomena Zeng et al. are treated as junior synonyms of Eostropheodonta Bancroft; 2) Hubeinomena Zeng et al. is regarded as a juvenile form of Coolinia Bancroft; 3) Paramirorthis Zeng et al. is considered an immature growth stage of Mirorthis Zeng; 4) Shanomena Cocks and Fortey is treated as a junior synonym of Paromalomena Rong; 5) Scenidium? medlicotti Reed is redesignated as the type species of Kinnella Bergström to replace Hirnantia? kielanae Temple. The distribution of the Hirnantia Fauna in Myanmar, Thailand and western Yunnan of the Sibumasu Terrane highlights the distinctive nature of the Mandalay fauna, and the analyses of the Hirnantia Fauna and others of Sibumasu shows that Sibumasu was not located far from the South China and Lhasa palaeoplates during late Middle and Late Ordovician

New fossil assemblages from the Early Ordovician Fezouata Biota

The Fezouata Biota (Morocco) is a unique Early Ordovician fossil assemblage. The discovery of this biota revolutionized our understanding of Earth’s early animal diversifications—the Cambrian Explosion and the Ordovician Radiation—by suggesting an evolutionary continuum between both events. Herein, we describe Taichoute, a new fossil locality from the Fezouata Shale. This locality extends the temporal distribution of fossil preservation from this formation into the upper Floian, while also expanding the range of depositional environments to more distal parts of the shelf. In Taichoute, most animals were transported by density flows, unlike the in-situ preservation of animals recovered in previously investigated Fezouata sites. Taichoute is dominated by three-dimensionally preserved, and heavily sclerotized fragments of large euarthropods—possibly representing nektobenthic/nektic bivalved taxa and/or hurdiid radiodonts. Resolving whether this dominance reflects a legitimate aspect of the original ecosystem or a preservational bias requires an in-depth assessment of the environmental conditions at this site. Nevertheless, Taichoute provides novel preservational and palaeontological insights during a key evolutionary transition in the history of life on Earth

A synopsis of the Ordovician System in its birthplace - Britain and Ireland

Rock successions in Britain and Ireland, and more especially those in North Wales, were instrumental in the founding and naming of the Ordovician System, and the Anglo-Welsh series established both initially and subsequently were used widely as a standard for Ordovician chronostratigraphy. Although now largely superseded in the global scheme of series and stages, they retain their local and regional importance. The Ordovician System in Britain and Ireland documents the history of a segment of the Earth's crust that incorporated opposing peri-Gondwanan and peri-Laurentian/Laurentian margins of the Iapetus Ocean during its closure, and is accordingly complex. The complexity arises from the volcanic and tectonic processes that accompanied oceanic closure coupled with the effects of eustatic sea-level changes, including the far-field effects of the Late Ordovician glaciation. For the past three decades, Ordovician successions in Britain and Ireland have been discussed in terms of terranes. Here we review Ordovician successions in each terrane, incorporating the results of recent research and correlating those successions via biostratigraphical schemes and radiometric dates to the global Ordovician series and stages