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| 2. |
- Landing, Ed, et al.
(författare)
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Cambrian Evolutionary Radiation : Context, correlation, and chronostratigraphy-Overcoming deficiencies of the first appearance datum (FAD) concept
- 2013
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 123, s. 133-172
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Tidskriftsartikel (refereegranskat)abstract
- Use of the first appearance datum (FAD) of a fossil to define a global chronostratigraphic unit's base can lead to intractable correlation and stability problems. FADs are diachronous-they reflect species' evolutionary history, dispersal, biofacies, preservation, collection, and taxonomy. The Cambrian Evolutionary Radiation is characterised by diachronous FADs, biofacies controls, and provincialism of taxa and ecological communities that confound a stable Lower Cambrian chronostratigraphy. Cambrian series and stage definitions require greater attention to assemblage zone successions and non-biostratigraphic, particularly carbon isotope, correlation techniques such as those that define the Ediacaran System base. A redefined, basal Cambrian Trichophycus pedum Assemblage Zone lies above the highest Ediacaran-type biotas (vendobionts, putative metazoans, and calcareous problematica such as Cloudina) and the basal Asteridium tornatumComasphaeridium velvetum Zone (acritarchs). This definition and the likely close correspondence of evolutionary origin and local FAD of T. pedum preserves the Fortune Head, Newfoundland, GSSP of the Cambrian base and allows the presence of sub-Cambrian, branched ichnofossils. The sub-Tommotian-equivalent base of Stage 2 (a suggested "Laolinian Stage") should be defined by the l'/L4/ZHUCE delta C-13 positive peak, bracketed by the lower ranges of Watsonella crosbyi and Aldanella attleborensis (molluscs) and the Skiagia omata-Fimbrioglomerella membranacea Zone (acritarchs). The W. crosbyi and A. attleborensis FADs cannot define a Stage 2 base as they are diachronous even in the Newfoundland "type" W. crosbyi Zone. The Series 2 base cannot be based on a species' FAD owing to the provincialism of skeletalised metazoans in the Terreneuvian-Series 2 boundary interval and global heterochrony of the oldest trilobites. A Series 2 and Stage 3 (a suggested "Lenaldanian Series" and "Zhurinslcyan Stage," new) GSSP base is proposed at the Siberian lower Atdabanian delta C-13 IV peak-which correlates into South China, Avalonia, and Morocco and assigns the oldest trilobites to the terminal Terreneuvian Series.
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| 3. |
- Landing, Ed, et al.
(författare)
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Geochronology of the Cambrian : a precise Middle Cambrian U-Pb zircon date from the German margin of West Gondwana
- 2015
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Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 152:1, s. 28-40
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Tidskriftsartikel (refereegranskat)abstract
- A volcanic tuff 1.0 m above the base of the Triebenreuth Formation in the Franconian Forest provides the first precise and biostratigraphically bracketed date within the traditional Middle Cambrian. The first illustration of fossils from the Triebenreuth Formation in this report and their discussion allow a more highly refined correlation within the Middle Cambrian. A weighted mean Pb-206-U-238 date of 503.14 +/- 0.13/0.25/0.59 Ma on zircons from this subaerial pyroclastic tuff was determined by U-Pb chemical abrasion isotope dilution mass spectrometry (CA-TIMS) techniques. At c. 6.0-7.0 Ma younger than the base of the traditional Middle Cambrian in Avalonia, the new West Gondwanan date from east-central Germany suggests that estimates of 500 Ma for the base of the traditional Upper Cambrian and 497 Ma on the base of the Furongian Series may prove to be too old'. Biostratigraphically well-bracketed dates through most of the Middle Cambrian/Series 3 and below the upper Upper Cambrian/upper Furongian Series do not exist. An earlier determined 494.4 +/- 3.8 Ma date from the Southwell Group of Tasmania may actually prove to be a reasonable estimate for the age of the base of the traditional Upper Cambrian. Until high precision dates are determined on the base of the traditional Upper Cambrian and base of the Furongian Series, the rates of biotic replacements and geological developments and the durations of biotic zones in the Middle/Series 3 and Upper Cambrian/Furongian Series remain as best guesses'.
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| 4. |
- Landing, Ed, et al.
(författare)
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Global standard names for the Lowermost Cambrian Series and Stage
- 2007
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Ingår i: Episodes. - 0705-3797. ; 30:4, s. 287-289
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Tidskriftsartikel (refereegranskat)abstract
- The GSSP marking the base of the Cambrian System was ratified by the IUGS in 1992. Ratification of the GSSP point at the base of the Trichophycus pedum Ichnozone in the Fortune Head section, eastern Newfoundland, Canada, automatically defined the conterminant base of the lowermost series and stage of the Cambrian although names for those subdivisions were not proposed at the time of the decision. In 2007, the IUGS ratified the names Terreneuvian Series and Fortunian Stage for these previously unnamed chronostratigraphic subdivisions. The Terreneuvian Series replaces the provisional name "Series 1," and the Fortunian Stage replaces the provisional name "Stage 1," of the Cambrian System.
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| 5. |
- Streng, Michael, et al.
(författare)
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Linguliform brachiopods from the terminal Cambrian and lowest Ordovician of the Oaxaquia microcontinent (Southern Mexico)
- 2011
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Ingår i: Journal of Paleontology. - : Cambridge University Press (CUP). - 0022-3360 .- 1937-2337. ; 85:1, s. 122-155
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Tidskriftsartikel (refereegranskat)abstract
- Eighteen taxa of linguliform brachiopods, mainly represented by acrotretoids, are reported from the Upper Cambrian (Furongian, Stage 10) and Lower Ordovician (Tremadocian) Tinu Formation of Oaxaca State, Mexico. At the time of deposition, this area was part of Oaxaquia, which was either a microcontinent or an integral part of the Gondwanan margin. Whereas certain trilobites seem to indicate a Gondwanan affinity, the Tinu brachiopod faunas show a less definite paleogeographic relationship. Some taxa have previously only been reported from Laurentia (Eurytreta cf. fillmorensis, Eurytreta cf. campaniformis), and one taxon is best known from the Avalon microcontinent (Eurytreta cf. sabrinae). However, the relatively high percentage of new and potentially endemic taxa (Oaxaquiatreta labrifera n. gen. n. sp., Tapuritreta reclinata n. sp., Oaxaquiatreta sp., Eurytreta? n. sp., Acrotretidae n. gen. n. sp., Obolinae gen. and sp. indet.) and the lack of other typical Laurentian, Gondwanan, or Avalonian taxa suggest either a certain degree of insularity of Oaxaquia or reflects a more temperate, unrestricted marine environment during the Early Paleozoic. Other taxa reported from the Tinu Formation include Semitreta sp., Lingulella? spp., Obolinae gen. and sp. indet., Eoscaphelasma? sp., Ottenbyella? sp. A and sp. B, and Acrotretidae gen. and sp. indet. A, B, and C. Eurytreta and Semitreta are critically reviewed and several taxa previously assigned to them have been excluded. An emended diagnosis for the genus Eurytreta is presented. The presence of delthyrium and notothyrium-like structures in the siphonotretid Oaxaquiatreta n. gen. further strengthens the previously proposed relationship between the Siphonotretida and Paterinida.
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