Witnesses of early Pliocene sea-level rise in Manilva Basin (Málaga, S Spain)

Abstract

The Sierra de la Utrera, a relief in the Manilva Basin (Málaga, SW Spain), shows bored surfaces at different heights above present-day sea level, from 96 m to 287 m. Borings occur in the eastern, central, and western parts of the Canuto de la Utrera, a prominent gorge in the central-southern part of the relief excavated in Mesozoic limestones, as well as on the western end of the Canuto Chico, a smaller canyon in the northern part. Pliocene marine deposits fossilized the bored surfaces. Bored boulders of the substrate are embedded in the Pliocene sediments. The traces Gastrochaenolites ispp., Entobia ispp., Caulostrepsis ispp., Circolites kotoucensis, and Ericichnus asgaardi have been identifi ed. Among these, Caulostrepsis is found only in the reworked blocks. This ichnoassemblage, attributed to the archetypical Entobia Ichnofacies of rocky shores, represents boring activity in high-energy, very-shallow-water settings, close to the sea level, and with a virtually null sedimentation rate. The vertical distribution of bored surfaces attests to a progressive sea-level rise. The onlap of the Pliocene deposits on the substrate is consistent with the deepening trend. Planktonic foraminiferal assemblages collected from the sediment adjacent to the Sierra de la Utrera demonstrate that boring activity spanned, at most, 1 Ma during the early Pliocene, Zanclean (biozones MPl 1 and MPl 2), ranging from 5.33 to 4.36 Ma. Benthic foraminiferal assemblages indicate oligotrophic, well-oxygenated, deepwater conditions bordering the substrate. The presence of nearly vertical, deep submarine cliffs surrounding the relief accounts for these conditions very close to the substrate.