(Table 1) K-Ar age determinations on biotite from coarse sand within DSDP Sample 72-516F-76-4,107-115

Qualitative petrographic study of selected clastic horizons within the Eocene section of Hole 516F has revealed the presence of abundant fine-grained lithic fragments, probably volcanic, along with coarser fragments of quartz and feldspar apparently derived from a nearby plutonic terrain. In detail, poor sorting, presence of graded bedding, and an abundance of clay suggest these are turbidite horizons locally derived from a mixed volcanic/plutonic terrain, possibly with some direct contribution from contemporary volcanic ash falls. A progressive increase in plutonic versus volcanic components with time is, however, more consistent with an erosional origin for most of this material. Unusual euhedral dark biotite is abundant in several of the lower clastic horizons; it is most easily interpreted as microphenocrysts weathered in situ out of alkalic volcanic ash. Biotite separated from Sample 516F-76-4,107-115 cm, has been dated by the K-Ar method at about 46 Ma. Alkaline volcanoes active on the Rio Grande Rise in the middle Eocene would be the most probable source of this ash and would be consistent with other evidence for potassic, alkaline volcanism along the Rio Grande Rise and at the Tristan da Cunha hot spot.

Benthic foraminifera and ostracoda in ODP Hole 107-650A

Twenty-three sediment intervals from top of Site 650 down to 510 m below seafloor have been studied. Their thicknesses vary between 0.25 m and about 40 m. The studied deposits are turbidites or parts of them except one which is interpreted as an ash-fall layer. The composition of the turbidites signalizes sources from shallow water/coastal areas as well as from deep water levels. Repeated mobilization and displacement seems to have been common. Volcaniclastic material is the dominant component of the whole studied part of Site 650 sedimentary sequence. Ashfall deposits as well as normal open marine sediments are rare.

Composition of Messinian sediments from the Tyrrhenian Sea

The data base for this study is represented by essentially nonevaporitic Messinian sediments recovered at ODP Sites 654, 653, 652, and 656 along the eastern Sardinian margin, and of the overlying early Pliocene oozes. Grain-size distribution, carbonate content, and microscopic observation of the sand size fractions were investigated. Messinian paleoenvironments, documented in the western Tyrrhenian Sea (ODP Sites 654 and 653), provide additional evidence supporting the deep basin desiccation model. A sharp lithologic contrast between early Pliocene pelagic oozes and latest Messinian conformable gypsiferous silts supports this model. The "lago-mare" biofacies was only occasionally observed in the shallowest site and is limited to the topmost part of the Messinian. Sites 652 and 656, lying in the deeper part of the Tyrrhenian and located on the downthrown side of an important eastward dipping fault system known as "Faglia centrale" are characterized by terrigenous sedimentation, with partly recycled minor evaporites. Of special interest is Site 652, where the thickness of the (probable) Messinian is 530 m. Sedimentary characters indicate a permanently subaqueous but nonmarine environment, with turbidites accumulating in a rapidly subsiding basin. According to the model proposed, this basin was fed by continental waters during times of maximum evaporitic draw-down, with temporary marine incursions from the west or southwest when the water level was higher. A basement ridge separated the evaporating pond from this endoreic lake located on the opposite (eastern) margin of the Tyrrhenian Basin, which was then limited to its western part. Post-Messinian reactivation of the "Faglia centrale" is necessary to account for the inversion of the relief.

Plio-Pleistocene benthic foraminifera of the Tyrrhenian Sea

Benthic foraminifers from Site 652, Site 653 (Hole 653A), and Site 654 of Leg 107 (Tyrrhenian Sea, Western Mediterranean), which penetrated with more or less good recovery the Plio-Pleistocene stratigraphic interval, were studied in a total of 699 close-spaced samples. A total number of 269 species have been classified and their quantitative distribution in each sample is reported. The benthic foraminifers assemblage is more diversified in Site 654, less diversified in Site 652. Less than a half of the benthic foraminifers species listed from Plio-Pleistocene Italian land sections are present in the coeval deep-sea Tyrrhenian record, in which shallow water species are missing and Nodosarids are poorly represented. A very few species have comparable stratigraphic distribution in the three deep-sea sequences and in Italian land sections when compared against calcareous plankton biostratigraphy. In the same three sites, the first appearance levels of several species are younger and younger, and last appearance levels are earlier and earlier from Site 654 to Site 653 and Site 652. Five biostratigraphic events, biochronologically evaluated and occurring at the same level in the deepsea Tyrrhenian record and in several land sections, have been selected as zonal boundaries of the proposed benthic foraminifers biostratigraphic scheme. The Plio-Pleistocene interval has been subdivided into four biozones and one subzone, recognizable both in the deep-sea and land-based sequences. The Cibicidoides (?) italicus assemblage zone stretches from the base of the Pliocene to the extinction level of the zonal marker, biochronologically evaluated at 2.9 Ma. The Cibicidoides robertsonianus interval zone stretches from the Cibicidoides (?) italicus extinction level to the Pliocene Mediterranean FO of Gyroidinoides altiformis, evaluated at 2.4 Ma. The Gyroidinoides altiformis interval zone stretches from the Mediterranean Pliocene FO of the zonal marker to the appearance level of Articulina tubulosa, evaluated at 1.62 Ma. The Articulina tubulosa assemblage zone stretches from the appearance level of the zonal marker to the Recent. In the Articulina tubulosa biozone, the Hyalinea baltica subzone is proposed. The appearance level of Hyalinea baltica is evaluated at 1.35 Ma, well above the Plio-Pleistocene boundary as defined in the Vrica stratotype section.