Gyrophyllites cristinae isp. nov. from Lower Ordovician shallow-marine deposits of northwest Argentina

MUÑOZ, DIEGO F.; MÁNGANO, M. GABRIELA; BUATOIS, LUIS A.

ICHNOS-AN INTERNATIONAL JOURNAL FOR PLANT AND ANIMAL TRACES

TAYLOR & FRANCIS INC

Lugar: Londres; Año: 2018 vol. 26 p. 243 - 255

1042-0940

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 depositfeeders exploring the uppermost silt-rich fine-grained sediment.