Quaternary through early Eocene benthic foraminifera off Peru

Stratigraphic assemblages of Quaternary through early Eocene benthic foraminifers were recovered among 10 Peru margin drill sites. Various hiatuses and intervals barren in foraminifers characterize the sections, but numerous samples contain abundant, well-preserved benthic foraminifers. Bathymetry of the extant species and California-based estimates of the paleobathymetry of the extinct species permit recognition of Quaternary sea-level fluctuations between shelf and upper bathyal depths that produced vertical migrations of oxygenated and low-oxygen habitats at the six shallow sites. Assemblages from lower-slope sites at about 9° and 11°S indicate a general subsidence of the continental margin from shelf or upper bathyal depths in Eocene time to the present lower bathyal depths. Data from 11°S suggest a major part of this subsidence occurred in late Oligocene to early Miocene time. Downslope-transported shelf specimens, particularly the small biserial species, Bolivina costata and B. vaughani, are major contributors to these lower bathyal assemblages from the middle Miocene through Quaternary time.

Distribution of benthic abyssal gastropods in the Iberian Deep-Sea Basin (Table 2)

During the cruises 3 and 15 of R.V. "Meteor", representatives of 7 families of benthic abyssal gastropods were collected. The prevalent group was the Turridae; the Naticidae are represented by 2 species, the remaining families by a single species each. A survey of the frequency and distribution of the species within the study area is given. A systematic part deals with the individual species in detail, including notes on taxonomy, material and distribution. Concerning the composition of the abyssal gastropod fauna of the present material, Neogastropoda are 4 times as many as Archaeogastropoda and 6 times as many as Mesogastropoda and Opisthobranchia. 89 % of all specimens are Neogastropoda. Usually deep-sea organisms have a non-pelagic development, but many of the Iberian deep-sea Turrids have a planktotrophic protoconch, that means a long pelagic larval period. Among the 19 species, 2 are cosmopolitan, 9 show a transatlantic distribution and 8 are confined to East-Atlantic basins.

Oxygen and carbon isotopic composition in Eocene and Oligocene planktonic and benthic foraminifera from DSDP sediments

Oxygen and carbon isotope ratios in Eocene and Oligocene planktonic and benthic foraminifera have been investigated from Atlantic, Indian, and Pacific Ocean locations. The major changes in Eocene-Oligocene benthic foraminiferal oxygen isotopes were enrichment of up to 1 per mil in 18O associated with the middle/late Eocene boundary and the Eocene/Oligocene boundary at locations which range from 1- to 4-km paleodepth. Although the synchronous Eocene-Oligocene 18O enrichment began in the latest Eocene, most of the change occurred in the earliest Oligocene. The earliest Oligocene enrichment in 18O is always larger in benthic foraminifera than in surface-dwelling planktonic foraminifera, a condition that indicates a combination of deep-water cooling and increased ice volume. Planktonic foraminiferal d18O does not increase across the middle/late Eocene boundary at our one site with the most complete record (Deep Sea Drilling Project Site 363, Walvis Ridge). This pattern suggests that benthic foraminiferal d18O increased 40 m.y. ago because of increased density of deep waters, probably as a result of cooling, although glaciation cannot be ruled out without more data. Stable isotope data are averaged for late Eocene and earliest Oligocene time intervals to evaluate paleoceanographic change. Average d18O of benthic foraminifera increased by 0.64 per mil from the late Eocene to the early Oligocene d18O maximum, whereas the average increase for planktonic foraminifera was 0.52 per mil. This similarity suggests that the Eocene/Oligocene boundary d18O increase was caused primarily by increased continental glaciation, coupled with deep sea cooling by as much as 2°C at some sites. Average d18O of surface-dwelling planktonic foraminifera from 14 upper Eocene and 17 lower Oligocene locations, when plotted versus paleo-latitude, reveals no change in the latitudinal d18O gradient. The Oligocene data are offset by ~0.45 per mil, also believed to reflect increased continental glaciation. At present, there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from Eocene to Oligocene time using oxygen isotopes.

Benthic foraminiferal genera in DSDP Hole 95-612

On the basis of lithologic, foraminiferal, seismostratigraphic, and downhole logging characteristics, we identified seven distinctive erosional unconformities at the contacts of the principal depositional sequences at Site 612 on the New Jersey Continental Slope (water depth 1404 m). These unconformities are present at the Campanian/Maestrichtian, lower Eocene/middle Eocene, middle Eocene/upper Eocene, upper Eocene/lower Oligocene, lower Oligocene/upper Miocene, Tortonian/Messinian, and upper Pliocene/upper Pleistocene contacts. The presence of coarse sand or redeposited intraclasts above six of the unconformities suggests downslope transport from the adjacent shelf by means of sediment gravity flows, which contributed in part to the erosion. Changes in the benthic foraminiferal assemblages across all but the Campanian/Maestrichtian contact indicate that significant changes in the seafloor environment, such as temperature and dissolved oxygen content, took place during the hiatuses. Comparison with modern analogous assemblages and application of a paleoslope model where possible, indicate that deposition took place in bathyal depths throughout the Late Cretaceous and Cenozoic at Site 612. An analysis of two-dimensional geometry and seismic fades changes of depositional sequences along U.S.G.S. multichannel seismic Line 25 suggests that Site 612 was an outer continental shelf location from the Campanian until the middle Eocene, when the shelf edge retreated 130 km landward, and Site 612 became a continental slope site. Following this, a prograding prism of terrigenous debris moved the shelf edge to near its present position by the end of the Miocene. Each unconformity identified can be traced widely on seismic reflection profiles and most have been identified from wells and outcrops on the coastal plain and other offshore basins of the U.S. Atlantic margin. Furthermore, their stratigraphic positions and equivalence to similar unconformities on the Goban Spur, in West Africa, New Zealand, Australia, and the Western Interior of the U.S. suggest that most contacts are correlative with the global unconformities and sea-level falls of the Vail depositional model.