INVESTIGADORES
MELCHOR Ricardo Nestor
congresos y reuniones científicas
Título:
Communal therapsid burrows from interdune facies of the Lower Jurassic Navajo Sandstone, southern Utah, USA
Autor/es:
RICARDO NESTOR MELCHOR; DAVID LOOPE
Lugar:
Indanha-a-Nova
Reunión:
Congreso; Ichnia 2016, Fourth International Congress on Ichnology; 2014
Institución organizadora:
International Association of Ichnologists
Resumen:
Tetrapod burrows with a bilobed bottom are reported from outcrops of the lower part of the Navajo Sandstone in southern Utah. The structures were identified in two close localities (38° 1.433? N, 110° 32.759?W), southeast of Hanksville. The Navajo Sandstone contains thin lacustrine carbonate lenses embedded in eolian dune cross-strata. The carbonate lenses are composed of dark micritic limestone with mudcracks, rhizoliths and invertebrate burrows. The burrow casts with bilobed bottoms occur in a set of wind-ripple cross strata overlying a bleached zone composed of calcite cemented sandstone (Fig. 1), which is laterally correlative to a carbonate lens. The burrows are shallowly penetrating (average 17°), lack enlargements and display a curved path in plan view. The burrow casts correspond to two size classes: 33-72 mm (the most common) and 128-159 mm. Burrow widths roughly match Brasilichnium trackway widths from correlative deposits. Burrow cross sections are roughly kidney-shaped, with a convex roof and bilobed bottom (Fig. 2), and vertically flattened (average burrow width/burrow height ratio= 2.1). The bottom is divided by a central depression that accounts for 1/3 of the burrow width (Fig. 3). Burrow fill is massive and mostly smooth with faint chevron-like ridges. The cross-sections suggest open burrows with a protracted occupation by scratch-digging tetrapods (probably trytilodonts). Compaction produced by the repeated passage of the occupant produced bilobed bottom, which was preferentially cemented because of excrements. Estimated body mass of the producer is 12-40 g (smaller burrows) and 324-780 g (larger burrows).