uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Age constraints for the Ediacaran-Cambrian boundary in the Iberian Chains, NE Spain
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.ORCID iD: 0000-0001-7790-0478
2019 (English)In: Alvaro, J.J. & Jensen, S. (eds.), International meeting on the Ediacaran System and the Ediacaran-Cambrian transition. Estudios Geológicos 75 (2), 2019Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The Paracuellos Group is the oldest sedimentary sequence of the Iberian Chains in north-east Spain. The group is subdivided into three formation which are, in stratigraphic order, the Sestrica Formation, known only from drill cores, the Saviñan Formation and the Aluenda Formation (Álvaro & Blanc-Valleron, 2002). The sequence has traditionally been considered as Neoproterozoic in age based on its stratigraphic position (e.g., Lotze, 1961), the occurrence of the trace fossil Torrowangeaaff. roseiWebby in the middle part of the Saviñan Formation (Liñan & Tejero, 1988), and putative fossils of CloudinaGerms in the Aluenda Formation (Streng, 1996; Álvaro & Blanc-Valleron, 2002). 

The Paracuellos Group is exposed in two geographically separated areas where it forms the core of faulted anticlines, the Paracuellos antiform and the Codos antiform in the in the northwestern and central Eastern Iberian Chains, respectively (Álvaro & Blanc-Valleron, 2002). In the Paracuellos antiform, the boundary between the Paracuellos Group and the overlying Bámbola Formation is represented by an erosive contact and represents a hiatus (Liñan & Tejero, 1988; Álvaro & Blanc-Valleron, 2002). In contrast, in the Codos antiform a more gradual transition between the two formations can be observed (Streng, 1996; Álvaro et al., 2002). The Ediacaran-Cambrian boundary was traditionally placed at the boundary between the Aluenda Formation and the Bámbola Formation.

The putative Cloudinafossils have been recovered from a carbonate bed that forms the base of the Aluenda Formation in the Codos antiform, termed the Codos Bed by Álvaro & Blanc-Valleron (2002). However, already at the time of discovery, Streng (1996) pointed out that the tube-shaped fossils lack the characteristic cone-in-cone structure of Cloudina. In addition, cross-sections of a variety of other tube-like small shelly fossils had been observed within the carbonate bed, partly exhibiting internal septate structures and/or external ornamentation (Streng, 1996), and indicating an unusual diversity of shelly fossils for the Neoproterozoic. Similar observations were also made by Álvaro et al. (2016) who placed the Aluenda Formation with the Codos Bed questionably in the early Cambrian (Tommotian). Gámez Vintaned et al. (2018) re-studied the section (their ‘Codos formation’) and also observed a variety of shelly fossils within the carbonate bed. They reported the presence of at least seven genera, including taxa such as CupithecaDuan, CobboldiellaKerber, and PseudorthothecaCobbold as well as halkieriid sclerites. In addition, a new genus and species with a tube-shaped shell was introduced, Codositubulus grioensis. Despite the rich fossil content and the identification of common early Cambrian taxa, Gámez Vintaned et al. (2018) argue for a late Ediacaran or earliest Cambrian age for the association. One of their reasons for this age is the supposed absence of molluscan shelly fossils in the Codos Bed.

Re-investigation of crack-out material of the Codos Bed, however, has revealed the presence of also molluscan taxa. Poorly preserved composite(?) molds of two helcionellid taxa were recovered, which tentatively have been assigned to Anabarellacf. planaVostokova and Igorellasp. Specimens are rare though and each taxon is represented by a single specimen only. Nevertheless, they unambiguously indicate a Terreneuvian age (late Fortunian to Cambrian Age 2) of the Codos Bed and confirm the stratigraphic position proposed by Álvaro et al. (2016). In combination with the recent fossil findings by Gámez Vintaned et al. (2018), a previously suggested correlation of the Codos Bed with the Heraultia Limestone of southern France also gains additional support (Álvaro et al., 2010, 2016). The fossils initially described as Cloudina? sp. by Streng (1996) are currently under scrutiny and are considered to represent small shelly fossils characteristic for the lowermost Cambrian, potentially similar to forms such as Pseudorthothecaor TiksithecaMissarzhevsky, rather than Cloudina. Also, their affinity with the new taxon Codositubuluswill be tested.

In conclusion, the newly discovered fossils from the Codos Bed confirm that the Paracuellos Group is not in its entirety Neoproterozoic in age but that it is in part early Cambrian. The Ediacaran-Cambrian boundary is stratigraphically below the Aluenda Formation, i.e. within the 300 to 400 m thick sequence of the two underlying formations. Paleontological re-investigation of the sandstones and shales of especially the Saviñán Formation, as well as re-evaluation of the stratigraphic significance of Torrowangeaaff. rosei, are required to further constrain the position of the boundary. 

Place, publisher, year, edition, pages
2019.
Series
Estudios Geológicos, ISSN 0367-0449
Keywords [en]
Ediacaran-Cambrian boundary, Iberian Chains, Paracuellos Group, Codos Bed
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-400160OAI: oai:DiVA.org:uu-400160DiVA, id: diva2:1380332
Conference
International meeting on the Ediacaran System and the Ediacaran-Cambrian transition (IMECT)
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-18

Open Access in DiVA

No full text in DiVA

Search in DiVA

By author/editor
Streng, Michael
By organisation
Palaeobiology
Geology

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 75 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf