The Eocene-Oligocene Boundary in the Umbrian Pelagic Sequences, Italy

An essentially complete Paleogene record was recovered on the Central and Southern Kerguelen plateaus (55°-59°S) in a calcareous biofacies. Recovery deteriorated in the middle Eocene and down to the upper Paleocene because of the presence of interbedded cherts and chalks. The stratigraphic distribution of about 70 taxa of planktonic foraminifers recovered at Sites 747-749 is reported in this paper. Faunas exhibited fairly high diversity (approximately 20-25 species) in the early Eocene, followed by a gradual reduction in diversity in the middle Eocene. A brief incursion of tropical keeled morozovellids occurred near the Paleocene/Eocene boundary, similar to that recorded on the Maud Rise (ODP Sites 689 and 690).The high-latitude Paleogene zonal scheme developed for ODP Leg 113 sites has been adopted (with minor modifications) for the lower Eocene-Oligocene part of the Kerguelen Plateau record. A representative Oligocene (polarity chronozones 7-13) and late Eocene-late middle Eocene (questionably polarity chronozones 16-18) magnetostratigraphic record has allowed the calibration of several biostratigraphic datum levels to the standard Global Polarity Time Scale (GPTS) and established their essential synchrony between low and high latitudes.

Section: Eocene/oligocene Boundarymentioning

confidence: 71%

Section: Eocene/oligocene Boundarymentioning

confidence: 99%

Paleogene Planktonic Foraminifer Magnetobiostratigraphy of the Southern Kerguelen Plateau (Sites 747-749)

Berggren¹

1992

“…On the basis of paleomagnetic data (Hailwood and Clement, this volume) the Eocene/Oligocene boundary is estimated to occur at about 122 mbsf via correlation to the Umbrian sequences (Nocchi et al, 1986). Above the inferred Eocene/ Oligocene boundary we recorded the F0 of small-sized specimens named Catapsydrax cf.…”

Section: Site 703mentioning

confidence: 97%

“…The identification of Chron 13N at the top of Core 114-703A-13H suggests that the Eocene/ Oligocene boundary would fall lower in the missing portion of Core 114-703A-13H (Nocchi et al, 1986). …”

Section: Zones P16-17mentioning

confidence: 98%

Planktonic Foraminiferal Biostratigraphy and Paleoenvironmental Interpretation of Paleogene Faunas from the Subantarctic Transect, Leg 114

Nocchi¹,

Amici²,

Silva³

1991

Self Cite

Paleogene planktonic foraminifers recovered during ODP Leg 114 in the subantarctic region exhibit a cosmopolitan character at the opening of the Paleocene, and then they evolve similarly to faunas from lower latitudes. They begin to differentiate from lower latitude faunas by the early late Paleocene when large morozovellids disappear from the region and cool deep-water-dwelling Globorotaloides appear much earlier than at lower latitudes. By early Eocene time large morozovellids immigrate into the subantarctic area during the warmest episode of the entire Eocene. From that time up to the end of the middle Eocene planktonic foraminiferal faunas exhibit a temperate character, as indicated by the abundance of common acarininids. At the same time dissolution at depth causes depauperated planktonic faunas at the deeper sites. A new warming episode during the late Eocene is marked by the immigration of Globigerinatheka luterbacheri into the subantarctic region. The cooling trend during the late Eocene causes a progressive decrease in species richness, which only sporadically is less than 10 species. The early Oligocene is also characterized by relatively rich planktonic faunas, but after that time the western subantarctic region is occasionally invaded by few planktonic foraminiferal species. These immigrations coincide with the warmer episodes on the climatic curve, such as Zones P21a and P22-"N4."Beginning in late early Eocene and through the Oligocene eastern subantarctic planktonic foraminiferal faunas exhibit a much warmer character than those from the western side and are more similar to warm temperate faunas. Therefore, the eastern faunas provide a more refined biostratigraphy. Oligocene time is characterized by a trend toward a warmer climate; however, this trend was reversed in the early Miocene.A dissolution event, possibly coeval with an erosional event, occurs within Zone P21b across the subantarctic region.

“…From several studies of low-latitude sections in Italy and Spain, it was observed that the extinction of disc-shaped discoasters is coeval with the extinction of Globigerinatheka index (Nocchi et al, 1986Monechi, 1986). Moreover, it slightly predates the Eocene/Oligocene boundary defined by planktonic foraminifers, the extinction level of Hantkenina and Cribrohantkenina.…”

Section: Eocene/oligocene Boundarymentioning

confidence: 99%

Late Eocene to Early Oligocene Calcareous Nannofossil Assemblages from Sites 699 and 703, Subantarctic South Atlantic Ocean

M.¹

1991

Calcareous nannofossil assemblages were studied from Sites 699 and 703, drilled during ODP Leg 114 to the west and east, respectively, of the Mid-Atlantic Ridge in the subantarctic South Atlantic Ocean. Recovery at the two sites consists of an almost continuous sequence of upper Eocene-lower Oligocene sediments. This study describes the calcareous nannofossil assemblages at the transition between the Eocene and Oligocene and correlates these assemblages with those described in lower latitude sections. Quantitative analyses were performed on several important taxa in order to improve the biostratigraphic resolution and permit some paleoenvironmental interpretations. Several discrepancies were noted between the two sites and between the Eocene and Oligocene assemblages. The Eocene assemblages show a great number of species and warmer water conditions; the early Oligocene assemblages are less diversified and are indicative of cooler conditions. The Eocene/Oligocene boundary was not defined by planktonic foraminifers because of the strong dissolution, poor recovery, and drilling disturbances. On the other hand, the calcareous nannofossil assemblage allowed recognition of the interval where the Eocene/ Oligocene boundary can possibly be placed.