Campanian-Maastrichtian coprolites from northern patagonia: paleoenvironmental and paleobiological significance

PARRAS, A.; MANERA DE BIANCO, T.; MONTALVO, C.

Trelew

Congreso; First International Congress on Ichnology, Ichnia 2004; 2004

Museo Edgidio Feruglio

Coprolites collected in the Loncoche and Allen Formations (Campanian-Maastrichtian, northern Patagonia) are described and their paleoenvironmental and paleobiological significance is analysed. The available material consists of 101 specimens collected at three different localities: El Matuasto and Yaminué in Río Negro Province and Arroyo Calmu-Co in Mendoza Province. The coprolite-bearing beds are medium-grained sandstones with freshwater and brackish molluscs and vertebrate fragments. These beds are interpreted as channelled sandy bodies where the coprolites have been hydrodynamically accumulated. At Yaminué coprolites also occur in massive and laminated siltstones, suggesting that the coprolites were buried in situ, in a lower-energy environment,probably floodplains or lakes. Morphological features and type of inclusions present in each specimen were studied. Thin sections and X-ray spectrometry were also performed. The most common shape is cylindrical with rounded ends and a central constriction. However, a few rounded and heteropolar and amphipolar spiral specimens were observed. The mean length is 32 millimetres (12.8-67.4 millimetres) and the mean diameter is 14 millimetres (7.7-21 millimetres). They have a phosphatic fine-grained matrix, a smooth surface and lack any obvious striations or ribs. Fifty nine percent show inclusions of fish vertebrae, spines and scales; seven percent of them also carry ostracods. The morphological features and type and characteristics of the inclusions, together with an analysis of the associated faunal assemblage, suggest that the possible producers were carnivorous vertebrates, such as fish, amphibians and/or reptiles