New findings of invertebrate trace fossils in a Late Miocene loess-paleosol succession, Cerro Azul Formation, La Pampa, Argentina

RENATA SOSTILLO; M. CRISTINA CARDONATTO; CLAUDIA I. MONTALVO; GRACIELA VISCONTI; RICARDO N.MELCHOR

Santa Rosa, La Pampa

Simposio; SLIC; 2013

Facultad de Cs. Exactas y Naturales-UNLPam

The Cerro Azul Formation is a monotonous succession of reddish-brown massive siltstones (mostly comparable with mollisols). Sedimentological and paleontological evidence suggest deposition under a semiarid temperate and seasonal climate with savanna-like vegetation. In this Pampa province are described. These localities are distributed in an area with a maximum latitudinal range of 200 km and more than 300 km in the E-W direction. The new material can be assigned to Coprinisphaera, Rebuffoichnus, Celliforma, Rosellichnus and Taenidium. The description of the trace fossil assemblages is arranged according to the dominant ichnofossils. Coprinisphaera isp. is Coprinisphaera isp. is spherical or hemispherical trace fossil with Specimens of Taenidium barretti with arcuate menisci are also recorded from SG. Previous records of ichnofossils from these localities include Attaichnus kuenzelii, Coprinisphaera isp., Celliforma isp., vertebrate burrows and invertebrate meniscate burrows. The material from the remaining localities is assigned to Rebuffoichnus, Celliforma and Rosellichnus. Specimens of Rebuffoichnus are recorded Rebuffoichnus cf. sciuttoi (LT and LM) is an ovoid structure (mean diameter 18 mm) with a slightly oval cross section, a broken R. cf. casamiquelai and Rebuffoichnus isp. (PB, C, BG) are 20-36 mm in diameter empty chambers with a thick wall showing millimetre-sized holes and an internal smooth ovoid cavity. Celliforma germanica (C) is a small cell (17 mm long, 7 mm wide) with a marked neck. Celliforma isp. is recorded from El Guanaco (EG;; cell casts (11 mm wide) with a rounded end and the other broken. Rosellichnus isp. (from EG) is a cluster containing at least 5 and probably 7 cells (about 32 mm long and 10 mm wide) arranged in a single layer and three rows with the ends of cells reaching the same level and showing a very thin and a surface texture consisting of small rounded mounds and millimetre root traces. The trace fossil association from SG and TE is compared with the Coprinisphaera ichnofacies, typical of paleosols associated with herbaceous communities. Although scarce, the dominant trace fossil in the remaining localities are Celliforma and Rebuffoichnus in calcareous paleosols. The later are compared with the Celliforma ichnofacies, which is indicative of a drier climate and lower vegetation coverage than those represented by the Coprinisphaera ichnofacies, particularly scrubs and woodlands. The occurrence of the analyzed localities.