Jordi M. de Gibert¹, Pau Arbués², Marta Puig³, Mariano Marzo¹

(1) Universitat de Barcelona, Barcelona, Spain
(2) University of Barcelona, Barcelona, Spain
(3) University of Barcelona, Spain

ABSTRACT: Ichnological Signatures of Turbidite Channels from the Eocene Ainsa Slope Complex (Spanish Pyrenees)

The Eocene Ainsa basin fill is mostly formed by a mudstone-dominated slope complex (4000 m thick) in which seven coarse-grained lithosomes occur at different stratigraphic positions. They represent deposition in turbidite channels and related environments. The ichnology of the Gerbe-Banaston and Ainsa turbidite systems has been studied in order to analyze the correlation between ichnofacies and lithofacies. Three distinct ichnofacies have been recognized. The monoichnospecific Diplocraterion ichnofacies relates to channel fills mostly made of intraformational mudstone breccias and conglomerates which record episodes of channel erosion and bypass of finer-grained sediment, as shown by the fill of the burrows. The Ophiomorpha ichnofacies is dominated by Thalassinoides, Ophiomorpha and Scolicia. It is associated to thick-bedded sandstones which represent the passive fill of turbidite channels. The Chondrites ichnofacies is the most diverse, including Chondrites, graphoglyptids and Nereites among others. It is characteristic of a thin-bedded sandstone/mudstone facies which was deposited in channel margin, overbank and frontal splay environments. Preliminary observations in the Jaca basin, which is the basin floor correlative to the Ainsa slope complex, reveal the presence of a more diverse ichnofacies, characterised by Zoophycus, Chondrites and graphoglyptids. The general pattern of correlation described above provides with a general ichnofacies model for the studied turbidite systems. A more detailed study of aspects such as vertical and lateral variation in ichnotaxonomic composition, tiering, depth of burrowing, intensity of bioturbation, burrow size etc. is being currently developed. This ichnofabric approach will improve the stratigraphic subdivision and correlation of turbidite lithosomes.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado