J. E. Caracuel

Paleoenvironmental changes during the late Miocene (Messinian)–Pliocene transition (Bajo Segura Basin, southeastern Spain): Sedimentological and ichnological evidence

ABSTRACT A detailed sedimentological and paleontological analysis of the uppermost Miocene (Messinian)–Pliocene boundary at the northern border of the Bajo Segura Basin, southeastern Spain, was carried out in order to describe the evolution of the regional paleocoastline during the Pliocene reflooding of the Mediterranean immediately after the sea-level fall related to the Messinian Salinity Crisis. Multiple trace fossils typical of firm- and hardgrounds were recognized, allowing identification of Glossifungites (two different types), Entobia, and Gnathichnus ichnofacies. Trace-fossil analysis showed that lithology and media consistency exerted considerable control on the development of the different ichnocoenoses and that there was a clear decrease in hydrodynamic energy from a coastal to a shallow-water shelf environment related to progressive sea-level rise. Ichnological and sedimentological data provide evidence that the definitive flooding of the Mediterranean was rapid and synchronous throughout the northern margin of the Bajo Segura Basin. The following model for the Pliocene transgression in the study area is therefore proposed: (1) the marine ingression penetrated along the incised paleovalleys carved as a consequence of the fall in sea level, where the first two Pliocene systems were deposited (P0–P1); (2) during the maximum flooding surface of the transgression, the sea overflowed the margins of the paleovalleys and extended throughout the entire northern margin of the basin; and (3) the third Pliocene system was deposited, forming the lower part of a highstand systems tract (P2).

Taphonomic tools to evaluate sedimentation rates and stratigraphic completeness in Rosso Ammonitico Facies (epioceanic Tethyan Jurassic).

A combined multidisciplinary approach has been applied to calculate minimum values of the stratigraphic completeness and, secondarily, sedimentation rates in 9.2 m thick Rosso Ammonitico facies from central Apennines (Italy) and 11 m thick deposits of the same facies in Southern Spain. Middle - Upper Toarcian expanded sedimentation in Valdorbia section (Umbria-Marche Apennines) and extremely condensed Oxfordian-Tithonian sedimentation at Puerto Escano section (External Subbetic) have been investigated using combined taphonomic, ichnologic and sedimentologic data and analyses. At Valdorbia, infaunal tiering is largely preserved and 27 horizons of infaunal-tiering truncation and casting reveal strong erosional activity forced by tempestite/turbidite events. Therefore, microstratigraphic gaps could be evaluated without biostratigraphic control. In this expanded section, 13 horizons of firm- and hardgrounds have been recorded showing simple or gradational tiering. Conversely, in the condensed Puerto Escano section, taphonomic analysis reveals 25 horizons of bioclasts truncation (mainly in ammonites), and 56 horizons of firm-hardgrounds intensively bioturbated. In Valdorbia rather than in Puerto Escano section, the evaluation of flattening in burrows and spherical bioclasts reveal a measurable mechanical compaction and dissolution. In addition, Rosso Ammonitico at Valdorbia section favoured the calculation of decompaction coefficients (nd) for each lithology easier than in Puerto Escano section. In condensed and essentially hiatal Rosso Ammonitico, mottled deposits due to intense bioturbation dominate and tiering cannot be recognizable. This fact is accentuated by usual overprinting of elementary depositional events, which in turn hampered the accurate calculation of missing deposits. Therefore, in condensed Rosso Ammonitico the latter was only available in terms of minimal missing-record trough the analysis of truncated bioclasts.

Lower Cretaceous (Albian) shell-armoured and associated echinoid trace fossils from the Sácaras Formation, Serra Gelada area, southeast Spain

This work was financially supported by the Biosedimentary Laboratory of Perugia University, Italy and the research Project GV04B-629 (Generalitat Valenciana, Spain).