Endemic bioturbation: distinctive Neogene eolian trace fossil assemblages dominated by large meniscate burrows from Patagonia, Argentina

RICARDO NESTOR MELCHOR; ALDO MARTÍN UMAZANO; MARIANO PEREZ; JAVIER MARCELO KRAUSE

Indanha-a-Nova

Congreso; Ichnia 2016, Fourth International Congress on Ichnology; 2016

International Association of Ichnologists

Eolian trace fossil assemblages dominated by large meniscate burrows (ichnogenus Nagtuichnus) have been reported from late Miocene-early Pliocene damp and dry interdune deposits of coastal dunes and Holocene dry interdune sediments of a marginal lacustrine eolian system (Melchor et al. 2012). Nagtuichnus producer are fossil relatives of the extant pink fairy armadillo (Dasypodidae, Chlamyphorinae), which developed subterranean habits between 32 and 17 Ma. Here we present a further example from the eolian section of the middle Miocene (Langhian) Santa Cruz Formation near Comodoro Rivadavia, Chubut province. Logged sections are Pico Salamanca (45° 34.432′S, 67° 20.328′W) and Cañadón Ferrais (45° 38.994′ S, 67°39.296′ W). Both sections are interpreted as a dune field composed of transverse dunes with dry (sandflat) and wet (lacustrine and fluvial) interdune areas. The dominant trace fossil in dune and dry interdune deposits are Nagtuichnus isp. (Fig. 1), which occurs preferentially above and below the lower bounding surface of crossbeds (Fig. 2), with variable orientation. These are unbranched, cylindrical burrows with a uniform meniscate filling (average meniscus thickness= 13 mm, n= 23) that range in width from 44 to 82 mm. Diagnostic features of Nagtuichnus found in these burrows are a filling composed of a discontinuous, outer massive layer (Fig. 3) and a central meniscate core. Occurrence at the lower bounding surface of cross-strata suggests colonization of toesets of migrating dunes and underlying moister sediments. As chlamyphorines are restricted to southern South America, these examples can represent a case of Neogene endemism for the ichnogenus Nagtuichnus.