Definition of sequences through ichnocoenoses and taphofacies: An example from the Sácaras Formation (early Cretaceous, eastern Spain)

An integrated taphonomical, ichnological and sedimentological analysis has been carried out on the Albian deposits of the Sierra Helada section (Province of Alicante, southeastern Spain). This allowed recognition and detailed characterization of the shallowing- and coarsening-upward sequences present in these deposits. Twenty sequences were detected throughout the section. They contain the following, from bottom to top: (1) the bottom of the sequence characterized by very fine-grained marls rich in echinoid tests and echinoid trace fossils with very little evidence of physical reworking-it records a distal platform, low-energy environment; (2) marls interbedded with fine-grained calcarenites, rich in large Thalassinoides and slightly reworked echinoid tests, with common bioclast-armored tubes (Ereipichnus geladensis), recording low-energy background conditions but increasing energy of the sedimentary events, (3) coarse-grained calcarenites rich in different types of small to large Thalassinoides and E. geladensis horizons, showing the intense and frequent action of storms and directed currents on the seafloor, and (4) coarse-grained, cross-bedded calcarenites, rich in Ophiomorpha nodosa, deposited under high-energy background conditions in the shallowest part of the sequence, recording the presence of shifting dunes in the inner platform. Occasionally, also the record of a rapid transgression has been pointed out through the presence of condensed tapho- and sedimentary facies and mixed ichnocoenoses at the top of the sequence just after an erosive surface. The defined ichnoceonoses and their distribution throughout the sequence reflect the shifting from a distal expression of the Cruziana Ichnofacies to the shallower archetypal Cruziana Ichnofacies and finally to the high-energy, shallow-water Skolithos Ichnofacies. The distribution of taphofacies and ichnocoenoses and development of the sequences all through the section show a general transgression followed by a regressive phase, which fit with the third-order curves described for the area on the basis of pure sedimentological analysis in previous studies (Castro et al., 2008).