Revision of the trace fossil Megagrapton Książkiewicz, 1968 with focus on Megagrapton aequale Seilacher, 1977 from the lower Eocene of the Lesser Caucasus in Georgia

Authors

  • Alfred Uchman Institute of Geological Sciences, Jagiellonian University
  • Zurab Lebanidze Department of Geology, Faculty of Exact and Natural Sciences, Iv. Javakhishvili Tbilisi State University, University str. 9; Tbilisi
  • Tamar Beridze Alexander Janelidze Institute of Geology, Iv. Javakhishvili Tbilisi State University, Politkovskaia 31; 0186, Tbilisi
  • Nino Kobakhidze Alexander Janelidze Institute of Geology, Iv. Javakhishvili Tbilisi State University, Politkovskaia 31; 0186, Tbilisi
  • Koba Lobzhanidze Alexander Janelidze Institute of Geology, Iv. Javakhishvili Tbilisi State University, Politkovskaia 31; 0186, Tbilisi
  • Sophio Khutsishvili Alexander Janelidze Institute of Geology, Iv. Javakhishvili Tbilisi State University, Politkovskaia 31; 0186, Tbilisi
  • Rusudan Chagelishvili Department of Geology and Paleontology, Georgian National Museum, 1,Purtseladze str., 0103, Tbilisi, Georgia
  • Davit Makadze Alexander Tvalchrelidze Caucasian Institute of Mineral Resources, Tbilisi State University, 11, Mindeli str., 0105, Tbilisi
  • Kakha Koiava Department of Geology, Faculty of Exact and Natural Sciences, Iv. Javakhishvili Tbilisi State University, University str. 9; Tbilisi
  • Nino Khundadze Alexander Tvalchrelidze Caucasian Institute of Mineral Resources, Tbilisi State University, 11, Mindeli str., 0105, Tbilisi, Georgia

Keywords:

ichnology, flysch, ichnotaxonomy, graphoglyptids, Palaeogene

Abstract

Megagrapton Książkiewicz, 1968 is a characteristic deep-sea trace fossil belonging to the group of graphoglyptids and mostly preserved as a network of irregular meshes in hypichnial semirelief. So far, eleven ichnospecies have been distinguished under this ichnogenus, though commonly on weak evidence. The so-far poorly known ichnospecies Megagrapton aequale Seilacher, 1977 is described here on the basis of the numerous, newly discovered specimens from deep-sea siliciclastic deposits of the Bolevani Subsuite (lower Eocene) in the Lesser Caucasus of Georgia, together with other collections and published examples. A neotype of this ichnospecies is designated and the diagnosis emended. M. aequale occurs in lower Cambrian to upper Miocene deep-sea turbiditic deposits, mostly in the Paleogene. It is characterized by relatively small, variable meshes, which have mostly irregular sub-pentagonal, sub-hexagonal or sub-heptagonal shapes that are variable in size and are bordered by curved or straight semicircular ridges. It has been mistaken for Paleodictyon, which forms regular hexagonal nets. Paleodictyon imperfectum Seilacher, 1977 is included in M. aequale as the ichnosubspecies M. a. imperfectum, which is characterized by relatively thin bordering ridges. After critical analysis of all ichnospecies, only M. irregulare Książkiewicz, 1968, M. submontanum (Azpeitia Moros, 1933), and M. aequale are recommended for further use. These are distinguished on the basis of the prevailing morphology of the meshes, irrespective of large differences in morphometric parameters within the ichnospecies. Irredictyon chaos Vialov, 1972 is included in M. irregulare as the ichnosubspecies M. i. chaos, which is characterized by relatively thick bordering ridges. Megagrapton is interpreted as a cast of a subsurface open burrow network with a few connections to the sea floor. The burrows probably functioned as a trap for small organisms (ethological subcategory irretichnia).

Downloads

Published

2022-06-24

Issue

Vol. 66 No. 1 (2022)

Section

Articles

License

Authors who publish with this journal agree to the following terms:
  1. Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
  2. Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
  3. Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as this can lead to productive exchanges and earlier and more frequent citation of the published work (See The Effect of Open Access).