INVESTIGADORES
BELLOSI Eduardo Sergio
congresos y reuniones científicas
Título:
Evolution of Mesozoic-Cenozoic terrestrial ichnofaunas from Southern South America
Autor/es:
GENISE J., R. MELCHOR, E. BELLOSI, M. V. SÁNCHEZ, J. M. KRAUSE, L. SARZETTI, M. VERDE & E. BEDATOU
Lugar:
Praga
Reunión:
Congreso; 2nd International Congress on Ichnology; 2008
Resumen:
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Southern
South America, and particularly Patagonia, contains a protracted record of
continental deposits bearing diverse invertebrate ichnofossils. The study of
these deposits, mostly composed by primary and recycled volcaniclastic
materials, and ranging in age from Jurassic to Miocene, allows to trace the
evolution of Mesozoic-Cenozoic terrestrial ichnofaunas. The Late Jurassic to
Early Cretaceous Bajo Grande Formation and Baqueró Group contain similar
ichnofabrics dominated by large vertical, lined Y burrows (Loloichnus) and meniscate burrows of
similar diameter attributed to crayfish producers. This ichnofabric may be
overprinted by a boxwork of unlined, small burrows (sometimes meniscated), and
rare chambers, which is assigned to the work of earthworms. A less common
ichnofabric from these deposits are the first known crayfish nesting or
recruitment trace fossils (Dagnichnus and
Cellicalichnus). During the Late
Cretaceous, as exemplified from the Bajo Barreal and Laguna Palacios Formation,
the crayfish and earthworm ichnofabrics
continue to be important and well developed. In addition, the first insect
trace fossils appear, including pupal chambers (Rebuffoichnus, Pallichnus) and bee nests (Cellicalichnus). The K-T event produced a change from
crayfish/earthworm dominated ichnofaunas to insect dominated ones. The late
Paleocene-middle Eocene Río Chico Group shows few trace fossils, probably due
to taphonomic causes: Eatonichnus (brood
structure of coprophagous beetles), Feoichnus
(cicada feeding chambers), and rare occurrences of the earthworm
ichnofabric. In contrast with the paucity of trace fossils in paleosols,
contemporaneous early to middle Eocene floras from Laguna del Hunco and Río
Pichileufú display a large variety of insect traces in leaves. These include
leaf-cutting, mining, galls, bite marks and oviposition traces, suggesting a large insect diversity
which parallels the enormous diversity of plants. The probably
coetaneous paleosols of the Asencio Formation from Uruguay (early Eocene) also
display a large diversity of insect ichnofossils, essentially dominated by bee
and coleopteran trace fossils (Coprinisphaera,
Celliforma, Corimbatichnus, Ellipsoideichnus,
Palmiraichnus, Teisseirei, Uruguay, Rebuffoichnus and Monesichnus). The producers of this ichnofauna, ocurring at a lower
latitude, probably reached Patagonia later, resulting in the burst of insect
trace fossils from the middle
Eocene-Lower Miocene Sarmiento Formation and the early Miocene Pinturas
Formation. Paleosols of these units contain a highly diversified ichnofauna
with abundant insect trace fossils, especially brooding balls of dung beetles (Coprinisphaera). Other recorded trace
fossils include Teisseirei, Celliforma,
Pallichnus, Feoichnus, Lazaichnus and rare Loloichnus and earthworm traces. The dominance of Coprinisphaera in the Sarmiento
Formation ichnofauna, along with other sedimentologic, paleopedologic and
paleontologic evidence, records the appearance and evolution of one of the
oldest (middle Eocene) open grasslands ecosystems worldwide