CADIC   02618
CENTRO AUSTRAL DE INVESTIGACIONES CIENTIFICAS
Unidad Ejecutora - UE
capítulos de libros
Título:
TRACE FOSSILS OF CENOZOIC TURBIDITE SYSTEMS FROM
Autor/es:
LÓPEZ CABRERA, M.I.; OLIVERO, E.B.; CARMONA, N.B.; PONCE, J.J.
Libro:
Fifth Argentinean Ichnologic Meeting and Third Ichnologic Meeting of the MERCOSUR - Field Trip Guidebook
Referencias:
Año: 2007; p. 21 - 26
Resumen:
The relatively complete Paleocene-Miocene stratigraphic column (Fig. 4) of the Fuegian Andes includes ichnoassemblages of the Cruziana (Leticia Formation, late Middle Eocene), Zoophycos, and Nereites (Early Eocene-Early Miocene turbidite systems) ichnofacies (Figs. 5, 6, 7 y 8). 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 (Fig. 5). 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. Cruziana (Leticia Formation, late Middle Eocene), Zoophycos, and Nereites (Early Eocene-Early Miocene turbidite systems) ichnofacies (Figs. 5, 6, 7 y 8). 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 (Fig. 5). 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.