Microbioerosión en substratos esqueléticos del Neógeno y el Cuaternario marinos del Mediterráneo Occidenta

Endolithic microorganisms (bacteria, algae, fungi, etc.) produce perforations that have been used in the fossil record for paleoenvironmental interpretation of marine deposits. The particular characteristics of these organisms and their traces allow identifying the photic zone, which in turn can be related to the relative palaeobathymetry. Moreover, microboring assemblages are used as indicators of paleotemperature variation. In the present thesis these structures have been studied through electron microscope techniques. Microboring assemblages occur in mollusk and brachiopod shells from many localities of Pliocene and Pleistocene deposits in northeastern Iberian Peninsula (Mediterranean coast). The epibenthic bivalves and brachiopods were firstly collected from various marine basins in the Spanish Mediterranean coast (Alt Emporda, Baix Llobregat, Baix Ebre, Cope and Aguillas). Later, endo and epibenthic bivalves were recovered in offshore in Würm deposits from the Catalan coast (Cabo Cope, Blanes, Delta de l’Ebre and Palamós). Thirty different ichnospecies were identified, described and figured. Twenty-six of them occur in Pliocene deposits (9 autotrophic and 17 heterotrophic) and twenty-two were identified in the Pleistocene (5 and 17). The 60% of the identified ichnotaxa share both periods (Pliocene and Pleistocene). A new icnoapecies belonging to genus Saccomorpha has been defined. Moreover, four other forms have been proposed as new ichnotaxa. However, the poor preservation status of these microborings hasn’t allows providing a formal nomination. Six boring structures have been described for the first time in Pliocene deposits (Planobola macrogota, Rhopalia clavigera, Planobola radicatus, Polyactina araneola, Entobia nana, Aurimorpha varia). The high number of microboring from Pleistocene deposits has allowed us to use ecological index for the first in the fossil record (diversity, affinity). Ecological indexes have been used for measurement and comparison between different locations and / or skeletal substrates. Many authors proposed a bathymetric zonation for each period (Pliocene and Pleistocene) many taking into consideration distribution of microboring assemblages on shells. This thesis has taken into account taphonomic processes which allow to precise palaeoenvironmental interpretations. As a main conclusion ichnoassemblages from Pliocene deposits indicate illuminated waters. In contrast, ichnoassemblages from Pleistocene deposits suggest less illuminated waters.