Daniel G. Poire¹

(1) Centro de Investigaciones Geologicas, La Plata, Argentina

ABSTRACT: Gyrochorte as Trace Fossil Indicator of Storm Events in the Neuquén Basin, Argentina

The Neuquén Basin in west-central Argentina is one of the most important oil sedimentary basins of southern South America. It is characterised by a Mesozoic and Cainozoic record (2,600 m thick), which exhibits a wide range of facies variations and a high diversity of trace fossils. The Mesozoic evolution of the Neuquén Basin includes a continental syn-rift stage (Norian/Early Sinemurian) and an post-rift thermal subsidence stage. From the Late Sinemurian to the Albian, the Neuquén Basin went through a sag evolutionary stage and behaved as a marginal marine basin. The basin infill comprises cyclically stacked siliciclastic, carbonate and evaporitic rocks. Two major cycles in the Jurassic-Cretaceous fill of the Neuquén Basin have been recognised: the "Jurásico" (Cuyo Group, Pliensbachian/ Kimmeridgian) and the "Ándico" (Mendoza and Rayoso groups, Tithonian/Albian). Cuyo and Mendoza units provide some excellent examples to recognised the sedimentological significance of Gyrochorte. In this sense, Cuyo Group normally are bearing Arenicolites, Chondrites, Cylindrichnus, Dactyloidites, Helicodromites, Monocraterion, Ophiomorpha, Phycodes, Planolites, Rhizocorallium, Skolithos, Teichichnus and Thalassinoides. But, when storm deposits are developed, Gyrochorte is the most characteristic and common ichnogenus in this sedimentary facies. If there are not storm features, Gyrochorte is not present at all. In the same way, Agrio Formation shows Arenicolites, Chondrites, Gordia, Helminthopsis, Lockeia, Palaeophycus, Phycodes, Planolites, Scolicia, Taenidium, Teichichnus and Thalassinoides for fair weather conditions and plus Gyrochorte when storm events are recognised. So, it is clear that Gyrochorte is just developed in relation with storm episodes in the Mesozoic sedimentary sequence of Neuquén Basin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado