ASGP (2023), vol. 93: 353–361
AMMONITE ASSEMBLAGE AND AGE OF The HYDROCARBON SEEP LA ELINA, NEUQUÉN BASIN, ARGENTINA
Horacio PARENT (1*), Andrzej KAIM (2) & Alberto C. GARRIDO (3)
1) Laboratorio de Paleontología, IFG, FCEIA, Universidad Nacional de Rosario, Pellegrini 250, 2000 Rosario, Argentina; e-mail: parent@fceia.unr.edu.ar
2) Institute of Paleobiology, Polish Academy of Science, Twarda 51/55, PL-00-818 Warszawa, Poland; e-mail: kaim@twarda.pan.pl
3) Museo Provincial de Ciencias Naturales “Prof. Dr. Juan A. Olsacher”, Dirección Provincial de Minería, Etcheluz y Ejército Argentino, 8340 Zapala, Argentina & Centro de Investigación en Geociencias de la Patagonia, Departamento Geología y Petróleo, Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén, Argentina; e-mail: albertocarlosgarrido@gmail.com
*) Corresponding author
Parent, H., Kaim, A. & Garrido, A. C., 2023. Ammonite assemblage and age of the hydrocarbon seep La Elina, Neuquén Basin, Argentina. Annales Societatis Geologorum Poloniae, 93: 353–361.
Abstract: The ancient hydrocarbon seep deposits at the La Elina Ranch, Neuquén Basin, northern Patagonia, Argentina, are the only Mesozoic seep site in South America yielding metazoan fossils. Apart from benthic mollusc shells and worm tubes, they yielded a number of nektonic ammonoids. Four species of ammonoids were identified: Hildaitoides retrocostatus, Hammatoceras ex gr. insigne, Calliphylloceras cf. nilssoni, and Phylloceras sp. The occurrences of three species (H. ex gr. insigne, C. cf. nilssoni, and Phylloceras sp.) probably are fortuitous, while H. retrocostatus might have actually thrived in, or around the seep, as indicated by numerous well-preserved juveniles, in addition to some adult specimens. The bathymetric estimates indicate a depth not greater than 200 m, while the benthic molluscs, typical of hydrocarbon seeps, indicate a much greater depth. It is hypothesized that the deep-water taxa might have occurred in a shallower setting, owing to rising anoxia and/or strong input of continental waters from the eastern and/or southeastern deltaic system. The ammonite assemblage indicates that the seep at La Elina is (Andean) Middle Toarcian, probably Chilensis Zone, in age.
Manuscript received 9 February 2023, accepted 5 June 2023
