Characterization of the Ophiomorpha rudis 3D boxwork in a turbiditic succession (Oligocene of the Alicante Province, southeastern Spain)

Abstract

Slope-associated ichnoassemblages show great variability according to the physiography of the platform-slope system, sedimentary taxa and nutrient input. Ophiomorpha rudis uses to be common in turbiditic successions, therefore its detailed characterization is essential for the understanding of this kind of deposits. Ichnological, stratigraphic and sedimentological analyses were carried out in Oligocene slope deposits in the Cala Piteres section (southeastern Spain), where exceptionally preserved Ophiomorpha rudis 3D-boxworks are present. Four different sedimentary facies were recognized: (i) marls, (ii) tightly packed conglomerates, (iii) coarse-grained debrites with scattered clasts and olistoliths, (iv) gravity-flow induced calcarenites. The first facies was related to background sedimentation, while the other ones were considered to represent different gravity-flow deposits in slope channels. The ichnological analysis revealed the presence of two ichnoassemblages, dominated by Zoophycos isp. and Ophiomorpha rudis, respectively. The first ichnoassemblage developed in marls and presents Zoophycos together with Chondrites targionii and rare Rhizocorallium. The second one developed in the calcarenitic gravity-flow deposits, where Ophiomorpha exhibits complex mazes with horizontal burrows and vertical shafts. The horizontal development of Ophiomorpha on the upper surface of the beds would appear to follow organic matter distribution. On some bed surfaces, the cones representing the burrows entrance are preserved, this allowing for the estimation of the burrows penetration depth and for a detailed characterization of the colonization surface and of the whole burrow architecture. The study of the previously described ichnoassemblages let us consider the studied section as an expression of the Ophiomorpha rudis ichnosubfacies in an upper slope.