INVESTIGADORES
PONCE Juan Jose
congresos y reuniones científicas
Título:
Phymatoderma granulata from the Oligocene-Miocene of Tierra del Fuego: morphology and ethology. First International Congress on Ichnology
Autor/es:
OLIVERO, E.B.; PONCE, J.J.; LÓPEZ CABRERA, M.I.; MARTINIONI, D.R.
Lugar:
Trelew
Reunión:
Congreso; First International Congress on Ichnology; 2004
Resumen:
Phymatoderma
is rare in the fossil record and it is mainly known from shelf and deep-sea
deposits in Europe and Ecuador.
Deep-sea Oligocene-Miocene deposits from Tierra del Fuego
are characterized by few, but highly bioturbated horizons choked with large Phymatoderma
granulata. Associated ichnogenera include Zoophycos; Chondrites;
Tasselia; and a vertical spreite structure.
The P. granulata burrow
system consists mainly of subhorizontal, irregularly branched tunnels
completely filled with ovoid fecal pellets. Small feather-like branches, also
filled with pellets are occasionally present at the tube margins. In horizontal
view, well-preserved specimens show that the longer axis of the pellets are
arranged within the tube into sigmoidal and/or short convex bends, which most
likely represent a retrusive spreite formed by the joined lateral and proximal
migration of a J-shaped causative burrow. In vertical section the tube shows
concave-upward laminae suggesting that the causative burrow also moved upwards.
Branching frequently occurs toward the inner bend of the J-shaped spreite,
implying that new branches were formed by a sudden, distal extension of the
causative burrow. The study of thin sections shows that the finest grains -silt
grains, foraminifera and radiolaria--, and a very fine carbonate micrite were
selectively concentrated within the fecal pellets. On the contrary, the
non-bioturbated sediment consists of abundant fine-medium sand grains, a
coarser-grained carbonate micrite, and few microfossils. The evidence is
coherent with the food-mining behavior proposed for Phymatoderma even
though in our material the structure was built from deeper to shallower levels
within the sediment.