Research Paper
Shallow-marine trace fossils from the Silurian-Devonian Furada Formation of Asturias, Spain
MATEO ORNIA
G+2 Consultoría Medioambiental, Plaza de Longoria Carbajal, 3, 33002, Oviedo, España. mornia@gemasdos.com.
Corresponding author
LUIS A. BUATOIS
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canadá, luis.buatois@usask.ca.
M. GABRIELA MÁNGANO
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canadá, gabriela.mangano@usask.ca.
KATHERINE THUE
2Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canadá, klt015@usask.ca.
JAVIER FERNÁNDEZ-MARTÍNEZ
Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18071 Granada, España, javierfernandezm@ugr.es.
ALBERTO MARCOS†
Departamento de Geología, Universidad de Oviedo, Calle Jesús Arias de Velasco, s/n, 33005 Oviedo, España.
EXTENDED ABSTRACT
The Silurian-Devonian Furada Formation is exposed in the cliffs located between Munielles and Bahínas beaches along the Cantabrian Sea shoreline in Asturias. The bulk of the 170 m thick succession is exposed in Munielles Beach, and only the uppermost interval is seen in Bahínas Beach. The whole succession has been divided into four intervals. The basal interval is dominated by thick-bedded, fine-grained sandstone either forming amalgamated packages or interbedded with scarce, thin-bedded shale and very fine-grained sandstone. The lower interval consists of fine to very fine-grained sandstone intercalated with shale intervals. The middle unit is dominated by thick shale intervals with rare and thin siltstone and very fine- to fine-grained sandstone intercalations. The upper interval consists mostly of fine- to very fine-grained sandstone, either with thin siltstone interbeds or amalgamated. The deposits of the Furada Formation accumulated in a shallow-marine environment affected by episodic sedimentation, partly due to storm events.
Based on previous collections and new field work, 36 ichnotaxa are identified, described, and illustrated: Arenicolites isp., Asterosoma ludwigae, Bergaueria hemispherica, Bifungites munizi, Chondrites isp., Cruziana acacencis, Cruziana quadrata, Curvolithus multiplex, Davichnia cantabrica, Dimorphichnus isp., Gordia marina, Halopoa imbricata, Heimdallia chatwini, Helicodromites mobilis, Helminthoidichnites tenuis, Helminthopsis abeli, Imponoglyphus isp.,Lockeia siliquaria, Monomorphichnus isp. A, Monomorphichnus? Isp., Nereites isp., Palaeophycus tubularis, Phycodes circinatum, Planolites montanus, Protovirgularia dichotoma, Psammichnites implexus, Psammichnites plummeri, Ptychoplasma excelsum, Rusophycus pudicus, Rusophycus isp. A and isp. B, Rosselia socialis, Skolithos isp., Teichichnus rectus, Trichophycus isp., and undeterminate trackways.Previous work in these deposits recorded the presence of Arthrophycus, Didymaulichnus, Thalassinoides, Polyisthmus?, Siphonites and Spirophycus?, but their presence could not be confirmed. The specimen originally assigned to Tasmanadia is here regarded as an undertrack of Diplichnites.
Although Asterosoma ludwigae has been recently included in the ichnogenus Lamellaecylindrica, we adopt here a more classic view of Asterosoma that highlights the presence of a bulbous morphology and longitudinal striations, produced by an extensional mechanism during burrow infill. The type specimens of the ichnotaxon Davichnia cantabrica, originally described from the Furada/San Pedro formations, have been revised and diagnoses are provided. Davichnia shows similarities with the ichnogenus Curvolithus, such as flattened section and sharp changes in curvature. However, the trilobate dorsal morphology diagnostic of Curvolithus cannot be confirmed given the absence of appropriate preservational variants. Accordingly, and also considering the distinctive ornamentation of the the outer ventral lobes, Davichnia is provisionally retained. If additional specimens allow confirmation of a trilobate dorsal morphology, then Davichnia would be a junior synomym of Curvolithus, but the ichnospecies D. cantabrica should be retained as Curvolithus cantabrica, based on the distinctive ornamentation of its outer ventral lobes.
The study of this ichnofauna provides a spatial and temporal window to better understand the characteristics and composition of middle Paleozoic shallow-marine trace-fossil assemblages, which are poorly known in comparison with counterparts of other ages. The studied ichnofauna displays all the characteristics of the Cruziana Ichnofacies, namely: (1) dominance of horizontal trace fossils and subordinate presence of vertical to inclined burrows; (2) wide variety of ethologic categories, such as locomotion, feeding, resting, dwelling and grazing traces; (3) dominance of burrows and trails of deposit and detritus feeders, albeit with trace fossils produced by suspension feeders and predators also present; (4) dominance of trace fossils produced by a mobile benthos with subordinate presence of permanent dwelling burrows; (5) high ichnodiversity; and (6) high abundance. This ichnofauna documents a wide variety of ethologic categories corresponding to diverse trophic types, albeit with a marked dominance of deposit and detritus feeders. The ichnofauna from the Furada Formation is made of feeding traces of deposit feeders (Asterosoma ludwigae, Chondrites isp., Halopoa imbricata, Heimdallia chatwini, Helicodromites mobilis, Imponoglyphus isp., Phycodes circinatum, Planolites montanus, Teichichnus rectus, Trichophycus isp.), grazing traces of deposit feeders (Davichnia cantabrica, Nereites isp., Protovirgularia dichotoma, Ptychoplasma excelsum, Psammichnites implexus, Psammichnites plummeri)and detritus feeders(Dimorphichnus isp., Gordia marina, Helminthoidichnites tenuis, Helminthopsis abeli, Monomorphichnus isp. A, Monomorphichnus? isp.), locomotion traces of deposit feeders (Cruziana acacencis, Cruziana quadrata) and predators (Curvolithus multiplex), resting traces of deposit feeders (Lockeia siliquaria, Rusophycus bilobatus, Rusophycus isp. A and isp. B),and predators (Bergaueria hemispherica), and dwelling traces of suspension feeders (Arenicolites isp., Bifungites munizi, Palaeophycus tubularis, Skolithos isp.) and detritus feeders (Rosselia socialis).
As a whole, this ichnofauna records the activity of diverse benthic communities. However, there are marked fluctuations in ichnodiversity and trace-fossil abundance through the succession as a result of the influence of fairweather processes and episodic sedimentation, which controlled changes in environmental parameters, mostly hydrodynamic energy, sedimentation rate, and degree of substrate consolidation. The highest abundance and ichnodiversity correspond to packages in which thin layers of very fine- to fine-grained sandstone alternate with siltstone and shale, which is typical of the lower and upper intervals. Asterosoma ludwigae is one of the most abundant ichnotaxa in these deposits, particularly in the lower interval, which records accumulation in the intermediate portion of the depositional profile, characterized by rapid fluctuations in hydrodynamic energy and sedimentation rate. The basal and upper intervals also contain amalgamated fine-grained sandstone that typically lacks trace fossils or is host to low-diversity suites. These deposits correspond to the proximal areas of the depositional profile, which show evidence of persitent high energy levels due to dune migration. The shale-dominated middle interval contains well-preserved arthropod trace fossils, such as Dimorphichnus, Cruziana and Rusophycus, which reveal cohesive substrates in the distal portion of the depositional profile.
Key words: Trace fossils, Silurian, Devonian, Furada/San Pedro Formation, Cantabrian Zone.
How to cite: Ornia, M., Buatois, L. A., Mángano, M G., Thue, K., Fernández-Martínez, J. & Marcos, A. (2024). Trazas fósiles marinas someras de la Formación Furada, Silúrico-Devónico de Asturias, España. [Shallow-marine trace fossils from the Silurian-Devonian Furada Formation of Asturias, Spain]. Spanish Journal of Palaeontology, 39.
Received 26 Februart 2023, Accepted 6 July 2024, Published online 2 August 2024
https://doi.org/10.7203/sjp.29180
(In Spanish only)