Stratigraphy of the western Mediterranean and southern Calabrian ridges,eastern Mediterranean

The present paper illustrates the stratigraphic results of a transponder-navigated coring program carried out in 1978 on the southern Calabrian Ridge (Cobblestone Area 4) and western Mediterranean Ridge (Cobblestone Area 3).Semi-quantitative investigations of over 600 foraminiferal samples and 450 nannofossil slides from forty cores, with a total recovery of 333 m, comprise the data base of the study.Most of the sediments recovered are Late Pleistocene or Holocene in age. The high-resolution nannofossil biostratigraphic scheme recently proposed for the Quaternary, coupled with sapropel stratigraphy and with tephrachronology resulted in precise correlation of the cores.Mid-Pleistocene sediments were recovered in a single core from Area 4, and in one core from Area 3, both located on basin walls. Four cores from basin walls in Area 4 yielded Pliocene sediments. No sediments older than approximately 3 m.y. (foraminiferal Zone M Pl 4, Reticulofenestra pseudoumbilica nannofossil Zone) are exposed on the explored walls from the southern Calabrian Ridge. Early and Late Pliocene sediments were recovered from the walls of the deepest crater-like basin explored in Area 3, but only in dredges. In this latter area also two peculiar lithologies were cored, basically unfossiliferous, but thought to be pre-Pliocene in age: a mud breccia whose clasts yield a sparse assemblage of mid-Cretaceous planktonic foraminifera, and a dolomitic mudstone, which is attributed to the Late Messinian on the basis of correlation with a similar lithology cored at DSDP Site 374, and substantiated by analogy in X-ray controlled mineralogical composition.The fairly complete record of Late Pleistocene and Holocene sapropels recovered in the southern Calabrian Ridge discards the hypothesis that the southern part of the Ionian Sea did not undergo stagnant cycles during the ice ages.Another hypothesis relating the origin of Cobblestone topography to olistostromes is also considered untenable on the basis of the new data. The large number of cores, precisely located on a previously mapped, highly irregular bottom physiography, disproves that large-scale chaotic sedimentation occurred: debris flows recorded in base-of-slope cores document local slope failures.