INVESTIGADORES
PONCE Juan Jose
congresos y reuniones científicas
Título:
Trace fossils of Cenozoic turbidite systems from the Fuegian Andes, Argentina
Autor/es:
LÓPEZ CABRERA, M.I.; OLIVERO, E.B.; CARMONA, N.B.; PONCE, J.J.
Lugar:
Ushuaia, Tierra del Fuego
Reunión:
Congreso; Quinta Reunión Argentina de Icnología y Tercera Reunión de Icnología del MERCOSUR; 2007
Resumen:
The relatively
complete Paleocene-Miocene stratigraphic column of the Fuegian Andes includes
ichnoassemblages of the Cruziana (Leticia Formation, late Middle Eocene), Zoophycos, and Nereites (Early Eocene-Early Miocene turbidite systems)
ichnofacies. The components of the last two ichnoassemblages represent the only
known deep marine Cenozoic trace fossils in Argentina. Interestingly, the
records of Cenozoic graphoglyptids in the Nereites ichnofacies from the Fuegian
Andes represent a rare case of high-latitude distribution of these trace
fossils. In this contribution the composition, paleoenvironmental implications,
and diversity trends of trace fossils of Cenozoic turbidite systems are
studied.The ichnogenera
recorded in the Early Eocene-Early Miocene turbidite systems are: Scolicia, Chondrites, Gyrophyllites,
Nereites, Phycodes, Phycosiphon, Phymatoderma, Stelloglyphus, Zoophycos,
Ophiomorpha, and graphoglyptids, such
as Cosmorhaphe, Desmograpton, Helicolithus,
Helicorhaphe, Helminthorhaphe,Megagrapton,
Paleodictyon, Spirocosmorhaphe, and Urohelminthoida.
The graphoglyptids are mainly recorded in thin-bedded turbidites and mudstones
(lobe deposits) and are assigned to the Paleodictyon
ichnosubfacies (Nereites ichnofacies).Ophiomorpha rudis and O. annulata are common at the contact
between thick-bedded turbidites and mudstones rich in plant material. In
sand-rich, proximal channel-lobe deposits, they characterize the Ophiomorpha rudis ichnosubfacies (Nereites ichnofacies). Scolicia prisca and Nereites isp. are common in rippled fine-grained sandstones
interbedded with thin mudstones rich in plant fragments. Zoophycos isp. is
dominant in slope mudstones with synsedimentary slumping. Concomitant with a
marked cooling trend, the late Middle-Late Eocene of the Fuegian Andes records
the maximum ichnodiversity; the basal Oligocene displays an abrupt drop in
diversity; and the Early Miocene shows a moderate diversity recovery. These
data do not support the alleged control of increased Eocene ichnodiversity by
global warming during the Cenozoic thermal maximum at the Paleocene-Eocene
boundary. Specialized food competition particularly for the graphoglyptid
organisms and generalized oligotrophy seem to offer an alternative explanation.