Graptolites from near the Ordovician-Silurian boundary in Illinois and Iowa

Loydell, David K.; Mallett, Andrew; Mikulic, Donald G.; Kluessendorf, Joanne; Norby, Rodney D.

doi:10.1017/s0022336000017418

Cited by 8 publications

(3 citation statements)

References 5 publications

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“…These are problematic when we are considering the timing of events during the history of biogeographical divisions. For example, there has been biostratigraphical uncertainty as to whether some units in the Edgewood Province are latest Ordovician (Gamachian) or earliest Silurian (earliest Llandovery, early Rhuddanian), or span the Ordovician -Silurian boundary (Elias & Young 1992;Loydell et al 2002;Butcher et al 2010). The Hirnantian isotopic carbon excursion, indicating a latest Ordovician age, has recently been recognized in some of these units (Kleffner et al 2005;Bergström et al 2006).…”

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Chapter 9 Coral biogeography in the Late Ordovician (Cincinnatian) of Laurentia

Elias

Young²,

Lee

et al. 2013

Memoirs

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During the Late Ordovician, Cincinnatian, the epicontinental seas and continental margin of Laurentia provided habitats that were suitable for corals. Biogeographical differentiation occurred within this equatorially placed continent, when corals were introduced to areas that had fundamentally different environments. There were four biogeographical divisions, characterized by distinctive faunas that included some endemic taxa: the Red River–Stony Mountain Province, Richmond Province, Edgewood Province and the less well understood, informal ‘Continental Margin’ Area. In each division, the potential for diversification and the capacity for diversity were determined by factors such as the duration and size of the division, the amount of immigration, the extent of evolution and biogeographical differentiation, faunal responses to changes in sea-level and climate, and the complexity of the ecological structure. The development of multiple biogeographical divisions, each contributing to overall diversity, enhanced the ‘Great Ordovician Biodiversification Event’. During the latest Ordovician mass extinction, there was a reduction of diversity and loss of biogeographical divisions within Laurentia. The divisions were terminated when their characteristic taxa disappeared, in response to major environmental changes associated with glaciation in Gondwana and subsequent global warming.

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confidence: 99%

Chapter 9 Coral biogeography in the Late Ordovician (Cincinnatian) of Laurentia

Elias

Young²,

Lee

et al. 2013

Memoirs

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“…However, Loydell et al (2002) collected new material and re-examined existing collections, and were able to assign specimens from the lower Wilhelmi Fm in northern Illinois to either the uppermost Ordovician persculptus or the lowermost Silurian ascensus-acuminatus graptolite biozones. The possibility is therefore introduced that the Ordovician-Silurian boundary lies within the Wilhelmi Fm, rather than the commonly held view that the boundary occurs at the unconformity with the underlying Maquoketa Group strata.…”

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Melanosclerites from the Wilhelmi Formation (Lower Silurian, north-eastern Illinois, USA)

Trampisch

Butcher

2009

Paläontol. Z.

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“…omega (DAVIES, 1929) which was first described by Williams in 1983 as Glyptograptus cf. persculptus but later considered synonymous to N. parvulus (H. LAPWORTH) by Zalasiewicz and Tunnicliff [1994], who refigured the lectotype and by Loydell et al [2002], Chen et al, [2005] and again Loydell [2007]. N. parvulus has not been revised and its variability remains an unknown quantity, making all comparisons difficult.…”

Section: Systematic Palaeontologymentioning

confidence: 99%

Faunal specificity, endemism and paleobiogeography: the post-glacial (Hirnantian-early Rhuddanian) graptolite fauna of the North-African border of Gondwana: a case study

Legrand¹

2009

Bulletin De La Société Géologique De France

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Several types of stratigraphic successions are found at the top of the glacial to periglacial "Complexe terminal" forming the uppermost Ordovician of the North-African border of Gondwana. Locally, there may be a progressive transition from microconglomeratic clays (diamictites) with dropstones to more normal marine clays accompanied by the almost immediate reappearance of graptolites. Study of the graptolites has revealed a distinctive composition at the specific level, differing from contemporaneous faunal associations in adjacent regions, which consist of such classical species as "Glyptograptus" persculptus, Akidograptus ascensus, Parakidograptus acuminatus, etc.The faunal composition has long posed a chronostratigraphic problem, which has now been largely resolved, the fauna being interpreted as Hirnantian to early Rhuddanian in age. On the other hand, the clear evidence of faunal specificity poses a number of problems in the post-glacial context, namely: a) the disappearance of graptolites in the mid-Caradoc from these regions poses a problem as to the origin of the new specific fauna. Three hypotheses are considered, none of which is satisfactory. Most available data point to an eastern communication, although it is possible that the rejuvenation of the Mauritanides to the west "erased" all prior evidence, giving a wrong idea as to the communications which existed in the area under consideration; b) what mechanisms caused and maintained this isolation? The hypothesis of a wide, east-west trending depression produced by the overloading of the frontal ice sheet and its progressive disappearance concomitant with the glacial rebound is being considered; c) what were the effects of isolation on the morphology of graptolites and their population? The virgella and the virgula in several species are remarkably long and this could be attributed to a reduction in water density. The size of monospecific populations also attests to an adaptation to a restricted regime with sandy deposition; d) how can one explain why some species like N. pseudovenustus, N. inazzaouae, N. normalis brenansi and Ps. kiliani, occur also in other parts of the world? If these species occur where the classical species are absent, the opposite is even more difficult to explain, leading one to postulate the presence of a selective "filter"; e) how did this faunal specificity disappear progressively? The extent of the sea with Nd. africanus and Nd. fezzanensis put an end to isolation, although it respected the east-west trend. However, there was an opening to the adjacent regions corresponding to present-day Libya.To conclude, if pelagic faunas are considered to be poor paleogeographic tools, faunal specificity rather than endemism should be regarded as the starting point for further reflection. However, all faunal specificity must be fully documented and the results integrated in a framework that includes all aspects of sedimentology, tectonics and climatology.Seven new species are briefly described: Normalograptus nseirati sp. nov., Normalogra...

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Graptolites from near the Ordovician-Silurian boundary in Illinois and Iowa

Cited by 8 publications

References 5 publications

Chapter 9 Coral biogeography in the Late Ordovician (Cincinnatian) of Laurentia

Chapter 9 Coral biogeography in the Late Ordovician (Cincinnatian) of Laurentia

Melanosclerites from the Wilhelmi Formation (Lower Silurian, north-eastern Illinois, USA)

Faunal specificity, endemism and paleobiogeography: the post-glacial (Hirnantian-early Rhuddanian) graptolite fauna of the North-African border of Gondwana: a case study

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