PERSONAL DE APOYO
MARTINIONI daniel Roberto
congresos y reuniones científicas
Título:
Patagonichnus isp. from the Maastrichtian of Antarctica: Implications for the constructional mechanism of Patagonichnus thalassiformis.
Autor/es:
E. B. OLIVERO; M. I. LÓPEZ CABRERA; J. J. PONCE; D. R. MARTINIONI
Lugar:
Ushuaia
Reunión:
Congreso; Quinta Reunión Argentina de Icnología y Tercera Reunión de Icnología del MERCOSUR; 2007
Institución organizadora:
Laboratorio de Geología Andina (CADIC-CONICET)
Resumen:
ABSTRACT:   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.