CADIC   02618
CENTRO AUSTRAL DE INVESTIGACIONES CIENTIFICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Patagonichnus isp. from the Maastrichtian of Antarctica: implications for the constructional mechanism of Patagonichnus thalassiformis
Autor/es:
OLIVERO, E.B.; LÓPEZ CABRERA, M.I.; PONCE, J.J.; MARTINIONI, D.R.
Lugar:
Ushuaia, Tierra del Fuego
Reunión:
Congreso; Quinta Reunión Argentina de Icnología y Tercera Reunión de Icnología del MERCOSUR; 2007
Resumen:
The early
Maastrichtian Haslum Crag Sandstone exposed in NE Snow Hill Island is
dominantly composed of large, lenticular sandstone bodies that are interpreted
as the fill of tidal channels. Many of these tidal-influenced sandstone beds
bear dense, monospecific burrows of an ichnospecies of Patagonichnus, which is
very close in morphology to the enigmatic P.
Thalassiformis Olivero and López C., previously known only for the Early
Miocene of Patagonia. The main objective of this study is to document the presence
of Patagonichnus isp. from Antarctica
and to further discuss the constructional mechanism of the burrow, based on the
excellent preservation of the Antarctic material.Patagonichnus isp. from
Antarctica is a large burrow system, consisting of connected horizontal and
vertical tubular branches and associated complex bulbs, which arise from
distinct horizontal and vertical swellings along the structure. The tubular
branches that could reach a horizontal length in excess of 2 m, are connected by a
corresponding system of inner, hollow tubes surrounded by concentrically
laminated structures. The diameter of the tubular branches ranges from 1 to 3 cm, whereas the swollen
bulbs can reach up to 20 cm
in diameter. The internal structure of the bulbs is very complex and it is
characterized by multiple, concentrically backfilled structures, surrounding an
inner tube located more or less in a central position. The system of inner,
hollow tubes exhibit multiple branching, apparently with some dead ends in the
backfilled structures that compose the bulbs. Similar burrow systems of Patagonichnus isp. were also observed in
the Eocene tidal deposits of the La Meseta Formation, Seymour Island, Antarctica, but
these were not studied in detail.Patagonichnus isp. from
Antarctica is very similar to that of P.
thalassiformis described from the Early Miocene of Patagonia. The Antarctic
burrow system, however, differs in that the tubular branches have commonly an
important vertical component; the bulbs can reach a very large size, and the
whole structure with their swollen bulbs is more irregular than in P. thalassiformis. The morphology and
internal structure of Patagonichnus
isp. clearly supports the model of helicoidal backfilling as the main
constructional mechanism of this burrow system, thus rejecting potential doubts
on the possibility that the type material of Patagonichnus thalassiformis were a composite structure, originated
by the occupation and reworking of abandoned crustacean burrows (e.g. Thalassinoides), by subsequent
organisms.