Trace Fossils of the Glacial to Postglacial Transition in the El Imperial Formation (Upper Carboniferous), San Rafael Basin, Argentina
Published:January 01, 2007
Pablo J. Pazos, Mercedes Di Pasquo, Cecilia R. Amenabar, 2007. "Trace Fossils of the Glacial to Postglacial Transition in the El Imperial Formation (Upper Carboniferous), San Rafael Basin, Argentina", Sediment–Organism Interactions: A Multifaceted Ichnology, Richard G. Bromley, Luis A. Buatois, Gabriela Mángano, Jorge F. Genise, Ricardo N. Melchor
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This paper reports the first ichnologic investigation in the San Rafael Basin, carried out in the glacial to postglacial transition, recorded in the El Imperial Formation at the Rio Atuel canyon. Following previous published stratigraphic schemes, three units were recognized in the field, but the upper one is ichnologically sterile and not studied in this paper. The lower unit shows evidence of glacial influence but lacks marine indicators and was deposited in a shallow paleovalley. Almost exclusively, the ichnofossils include locomotion traces produced by arthropods (Diplichnites and Diplopodichnus) or molluscs (Archaeonassa). Palynomorphs are terrestrial and show evidence of intense transport and deterioration. The middle unit contains a more varied range of ethologic categories: pascichnia (e.g., Mermia, Gordia, Cochlichnus), repichnia (e.g., Paganzichnus, Diplopodichnus, Didymaulichnus, Diplichnites, Undichna), and fodinichnia (e.g., Treptichnus) documented in transgressive deposits that record the glacial retreat and early postglacial interval. Many previous detailed studies carried out in contemporary successions of the basins of western Argentina have been the object of intense debate about the marine or nonmarine nature of these successions. In the middle unit, ichnofossils occur together with palynomorphs that show degradation and pyritization and contain scarce acritarchs suggesting brackish-water rather than fresh-water conditions in a fjord depositional system.
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Sediment–Organism Interactions: A Multifaceted Ichnology
The field of Ichnology bridges the gap between the areas of paleontology and sedimentology, but has connections to many subdisciplines within these areas. Biogenic structures record the behavior of their tracemakers and provide valuable information in paleoecologic and paleoenvironmental analysis. As in situ ethologic structures, trace fossils or ichnofossils yield valuable insights into the paleoecology of ancient benthic communities and the environmental dynamics of depositional systems. Ichnology is truly a multifaceted field, and a broad selection of its facets is represented in the 28 papers of this volume. The papers are the product of Ichnia 2004, the First International Congress on Ichnology, convened by Jorge F. Genise and held from 19 to 23 April 2004 at the Museo Paleontológico Egidio Feruglio in Trelew, Patagonia, Argentina. Seven papers connected with the congress, containing ichnotaxonomy, were published separately, in Ichnos, volume 13, issue 4. Several symposium volumes, books, and short-course notes have been published in recent years and ichnology can be considered a particularly active research area in steady growth. The 28 papers herein are arranged in five groups that reveal the broad scope of ichnology.