Gyrophyllites cristinae isp. nov. from Lower Ordovician Shallow-Marine Deposits of Northwest Argentina

Abstract

The lower Paleozoic marine siliciclastic succession of the Central Andean Basin, northwestern Argentina, provides a valuable record of the onset of the Great Ordovician Biodiversification Event in western Gondwana. A new ichnospecies of rosette trace fossil, Gyrophyllites cristinae, is documented from lower and upper Tremadocian (Tr1 and Tr2) deposits of this basin. It is characterized by five to six non-overlapping petaloid lobes and can be easily differentiated from the other four formally defined ichnospecies. Gyrophyllites cristinae occurs at the top of hummocky cross-stratified sandstone regularly interbedded with mudstone. These deposits are interpreted as reflecting the alternation of high-energy storm events and low-energy fair-weather conditions immediately below the fair-weather wave base, representing deposition in offshore transition environments. Gyrophyllites has been traditionally interpreted as the product of worms of uncertain taxonomic affinity that mined the sediment in search for food (fodinichnia). The occurrence of Gyrophyllites cristinae in these Ordovician deposits records post-storm colonization. Storms may have increased oxygenation and supplied fresh organic detritus that were exploited by worm-like, surface detritus- or shallow deposit-feeders exploring the uppermost silt-rich fine-grained sediments.

Keywords:

• Ichnology
• rosette trace fossils
• radial trace fossils
• tempestites
• Great Ordovician Biodiversification Event

Acknowledgments

We thank Tony Ekdale and Andreas Wetzel for comments on an early version of the manuscript, and to Alfred Uchman and an Eduardo Olivero for feedback on the manuscript. We also thank to A. Uchman for making valuable literature available; E. Sferco for help with German literature; and L. Marengo, M.J. Salas, N.E. Vaccari, A. Bignon, B. Waisfeld, F. Meroi Arcerito, R. Vaucher, C. Solano and M. Navarro for the invaluable help in different field trips. We acknowledge the Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), CONICET-Universidad Nacional de Córdoba, and the University of Saskatchewan for providing logistical facilities. Field trips and fossil collections were made under permission of the Secretaría de Cultura de la Provincia de Jujuy (Res. 01390_SC/2015) and the Secretaría de Cultura, Ministerio de Cultura y Turismo de la Provincia de Salta (Disp. int. 007/2014). This is a contribution to PUE 2016 (CICTERRA – CONICET) and to the IUGS-IGCP Project 653 “The onset of the Great Ordovician Biodiversification Event”.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support for this study was provided by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Grant PIP 112-201201-00581 and Agencia Nacional de Promocion Científica y Tecnológica (ANPCyT-FONCyT) PICT 2016-0588 in which Muñoz is a contributor and Natural Sciences and Engineering Research Council (NSERC) Discovery Grants 311727–15 and 311726–13 awarded to Mángano and Buatois, respectively.