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Earliest Ordovician (Early to Middle Tremadocian) radiolarian faunas of the Cow Head Group, western Newfoundland
- Mun-Zu Won, William J. Iams, Katherine Reed
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- Journal:
- Journal of Paleontology / Volume 79 / Issue 3 / May 2005
- Published online by Cambridge University Press:
- 20 May 2016, pp. 433-459
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Well-preserved earliest Ordovician (early to middle Tremadocian) radiolarian faunas were recovered from carbonate rocks of the Cow Head Group of the Great Northern Peninsula of the island of Newfoundland, Canada. The earliest Ordovician faunal assemblages are from Green Point, Martin Point, Broom Point North and South, and St. Paul's Inlet in Gros Morne National Park. Latest Cambrian faunas were also recovered from Green Point and St. Paul's Inlet, but are extremely low in both abundance and diversity. The radiolarian faunas include five families, 10 genera, and 24 species. Of these, one family Aspiculumidae, one genus, and 19 species are new. The new family and new genus are Aspiculumidae and Aspiculum, respectively. The new species are Pararcheoentactinia? cowheadensis, Aspiculum eccentricum, Aspiculum? angulatum, Parechidnina delicata, P. variospina, Curvechidnina multiramosa, Echidnina conexa, E. laxa, E. semiconexa, E. severedeformis, Echidnina? immanis, Palaeospiculum curvum, P. multifurcatum, P. neofurcatum, P. tetractium, Protoentactinia deformis, P. kozuriana, P. primigena, and P. transformis. The Aspiculumidae is established on the basis of the new genus Aspiculum and on Parechidnina, whose family-level assignments were previously indeterminate. The new family Aspiculumidae is distinguished from the other four families by the absence of the spicule system.
All genera of the earliest Ordovician radiolarian faunas can be placed in the families Aspiculumidae, Archeoentactiniidae, Echidninidae, Palaeospiculumidae, and Protoentactiniidae, as can the genera of the Cambrian radiolarian faunas. However, echidninids from Cambrian faunas are generally characterized by interlocked or fused spicules whose original structure is recognizable, while those from the earliest Ordovician are commonly characterized by fused and/or modified spicules. Also, the very rare protoentactinids of the Late Cambrian are extremely abundant and diverse in the earliest Ordovician faunas described herein. Specimens of the families Palaeospiculumidae and Archaeoentactinidae are less diverse and/or less plentiful in the earliest Ordovician compared to those in Cambrian. The genus Parechidnina, which now belongs to Aspiculumidae, is more plentiful and very diverse in the earliest Ordovician, and, at the same time, lineages of the new genus Aspiculum and a related not-yet-named genus began to evolve.
The detailed biostratigraphic ages of the earliest Ordovician radiolarian faunas were determined mainly by the co-occurring conodonts. The age range of the earliest Ordovician faunas represented extends from the Cordylodus lindstromi Zone through the C. angulatus Zone to the Rossodus manitouensis Zone.
Earliest Arenig radiolarians from the Cow Head Group, Western Newfoundland
- Mun-Zu Won, William J. Iams
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- Journal:
- Journal of Paleontology / Volume 85 / Issue 1 / January 2011
- Published online by Cambridge University Press:
- 14 July 2015, pp. 156-177
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Radiolarians have been recovered from lowermost Arenigian rocks of the Cow Head Group in Gros Morne National Park, Newfoundland. Two new faunal assemblages include eight families, 13 genera, and 25 species. Among these, the family Neoaspiculumidae, the genus Neoaspiculum, and 11 species, Beothuka aitchisoni, B. grosmornensis, B. stougei, B.? stellata, Neoaspiculum cancellium, N. headense, N. transformum, N. laxum, N.? amplum, Proventocitum cylindricum, and P. piriforme, are new.
This study elucidates the reason for the significant difference in species composition between pre-Arenigian and Arenigian radiolarian faunas. This difference does not appear to be due to mass extinction, but rather to phylogenetic evolution: most radiolarian families that flourished during pre-Arenig time were gradually but significantly reduced by the earliest Arenig. Characteristic features of the earliest Arenig assemblages that distinguish them from their Tremadocian predecessors are 1) the development of a distinctive skeletal constructional element referred to as “bandage” structure that evolved through modification of a mesh of thin bars and 2) the appearance of multiple concentric shells including a proloculus (or a microsphere), which developed from a primitive three-dimensionally interwoven meshwork or spongy shell wall. These forms, represented by beothukids, antygoporids, and inaniguttids, are rare but they appear to originate in the earliest Arenig. Transitional characteristics among those forms are developed in the Neoaspiculumidae, which flourished during the earliest Arenig.
The precise biostratigraphic age of one of the assemblages was determined with the recovery of the index condont Prioniodus adami Stouge and Bagnoli, 1988 from strata belonging to the Tetragraptus approximatus Graptolite Zone, which is at the base of the Arenigian.
Late Cambrian radiolarian faunas and biostratigraphy of the Cow Head Group, western Newfoundland
- Mun-Zu Won, William J. Iams
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- Journal:
- Journal of Paleontology / Volume 76 / Issue 1 / January 2002
- Published online by Cambridge University Press:
- 14 July 2015, pp. 1-33
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Well-preserved Late Cambrian radiolarian faunas were recovered from carbonate rocks of the Cow Head Group of the Great Northern Peninsula of the island of Newfoundland, Canada. Several different faunal assemblages were recognized from three strata at Green Point, one from a stratum at Martin Point, and three from strata at Broom Point South in Gros Morne National Park. The faunas contain nine genera, five of which are new, and 33 species, all but two of which are new. The five new genera are Curvechidnina, Grosmorneus, Pararcheoentactinia, Ramuspiculum, and Subechidnina. Most of the genera belong to the families Archeoentactinidae, Echidninidae, Palaeospiculumidae, and Protoentactiniidae; a few taxa have an uncertain taxonomic position. Echidnina, whose taxonomic identity was uncertain, is shown to be a radiolarian.
The diversity of each of these faunas is similar, but the difference in faunal compositions among the faunas examined is distinct. From this analysis, the Late Cambrian strata between Martin Point and Green Point can be more precisely correlated, and the previous correlation has been revised. With the recovery of the conodonts in this study, the provisionally placed boundary between the Franconian and Trempealeauan at Martin Point by earlier researchers is revised and positioned between unit 30 and unit 31.
The biostratigraphic range of the co-occurring conodonts indicates that the youngest fauna described in this paper belongs to the Eoconodontus notchpeakensis Zone of late Trempealeauan age and that the other faunas (from Martin Point and Green Point) are of Franconian age.