ALBERT

Description: A virtually complete composite history of Cenozoic pelagic sedimentation was recovered from ODP Sites 738 (62°43' S) and 744 (61°35' S), drilled during Leg 119 on the Kerguelen Plateau. An excellent magnetobiochronologic record was obtained from upper Eocene through Holocene sediments at Site 744, and an expanded lower Paleocene through lower Oligocene sequence was cored at Hole 738. Analysis of the stratigraphic distribution of over 125 planktonic foraminifer taxa from these sites reveals changes in species composition that were strongly influenced by the climatic evolution of Antarctic water masses. Early Paleocene planktonic foraminifer assemblages are nearly identical in species composition to coeval assemblages from low and middle latitude sites, showing the same patterns of post-extinction recovery and taxonomic radiation. Biogeographic isolation, revealed by the absence of tropical keeled species, became apparent by late early Paleocene time. Diversity increased near the Paleocene/Eocene boundary when keeled morozovellids immigrated to the Kerguelen Plateau. Greatest diversity (23 species) was achieved by early Eocene time, corresponding to a Cenozoic warming maximum that has been recognized in lower Eocene deep sea and terrestrial sediments worldwide. A gradual decline in diversity from the late early through middle Eocene, primarily due to the disappearance of acarininids, parallels the record of cooling paleotemperatures in Southern Ocean surface waters. Chiloguembelina-dominated assemblages appeared in the late middle Eocene and persisted through the early Oligocene as Antarctic surface waters became thermally isolated. Late Eocene and early Oligocene assemblages exhibit considerably lower diversity than the older Eocene faunas, and were dominated by chiloguembelinids, subbotinids, and catapsydracids during a time of pronounced climatic cooling and development of continental glaciation on East Antarctica. The small foraminifer Globigerinit? juvenilis replaced chiloguembelinids as the dominant taxon during the late Oligocene. Diversity increased slightly toward the end of the late Oligocene with new appearances of several tenuitellid, globoturborotalitid, and globigerinid species. The trend toward diminishing planktonic foraminifer diversity was renewed during the late early Miocene as siliceous productivity increased in the Antarctic surface waters, culminating with the reduction to nearly monospecific assemblages of Neogloboqu?drin? p?chyderm? that occur in Pliocene-Holocene biosiliceous sediments. An Antarctic Paleogene zonal scheme previously devised for ODP Sites 689 and 690 in the Weddell Sea is used to biostratigraphically subdivide the Kerguelen Plateau sequence. The definition of one Antarctic Paleogene biozone is modified in the present study to facilitate correlation within the southern high latitudes. The ages of 13 late Eoceneearly Miocene datum events are calibrated based on a magnetobiochronologic age model developed for Site 744.

Description: A new planktic foraminiferal zonal scheme is presented for subdivision of Upper Cretaceous pelagic carbonate sequences in the circum-Antarctic region. Definition of the zones and subzones is based study of foraminifera from 13 deep-sea sections that were poleward of 50 °S paleolatitude and within the Austral Biogeographic Realm during Late Cretaceous time. The proposed biostratigraphic scheme includes seven Upper Cretaceous zones, with an average stratigraphic resolution of 4.4 m.y., and six subzones, which are all within the Maastrichtian Stage, with an average stratigraphic resolution of 1.4 m.y. The considerably higher resolution in the Maastrichtian Stage is a result of good foraminiferal preservation, availability of high quality magnetostratigraphic sections, and complete composite stratigraphic recovery in the Atlantic and Indian Ocean sectors of the Antarctic Ocean. Diminished resolution in the pre-Maastrichtian sediments of southern high latitude sections results from: (1) incomplete recovery of the middle Campanian, lower Santonian and most of the Cenomanian-lower Coniacian intervals, (2) presence of local and regional hiatuses, (3) paleobathymetric shallowing with increasing age at some sites, resulting in impoverished older planktic assemblages, and (4) poorer preservation with increasing burial depth. Cross-latitude correlation of the Campanian and older austral sequences may be improved with future drilling by recovery of sections that span existing stratigraphic gaps. Correlation of high latitude bioevents with chemostratigraphic events and their intercalibration with the magnetostratigraphy and the Geomagnetic Polarity Time Scale are needed for better chronostratigraphic resolution in existing high latitude sequences.

Description: Oxygen and carbon isotopic ratios were measured from Maestrichtian benthic and planktonic foraminifer species and bulk carbonate samples from ODP Sites 689 and 690, drilled on the Maud Rise during Leg 113. Careful scanning electron microscope observations reveal that test calcite in some intervals was diagenetically altered, although Sr/Ca and isotopic ratios of these tests do not appear to have been modified significantly. Foraminifer d18O values at both sites document a cooling trend during early Maestrichtian time, a rapid drop in water temperatures at the time of the first appearance of Abathomphalus mayaroensis in the high southern latitude regions (about 69.9 Ma), and lower water temperatures during late Maestrichtian time. d13C values record a depletion in 13C in the latest early Maestrichtian time beginning at about 72.2 Ma, just prior to the sharp late Maestrichtian increase in d18O values. These trends are similar to those previously reported for well-preserved benthic foraminifer species from Seymour Island, in the Antarctic Peninsula. Paleotemperature estimates are also comparable to those at Seymour Island and suggest temperate climatic conditions in Antarctica and that bottom waters in the southern South Atlantic region were of Antarctic origin. Benthic and planktonic foraminifer 613C values fluctuate sympathetically and are higher in upper Maestrichtian sediments than in the lower Maestrichtian sequence.

Description: This contribution summarizes the biostratigraphy of planktonic foraminifers, calcareous nannofossils, and benthic foraminifers, in combination with the magnetostratigraphy, carbon and oxygen isotope stratigraphy of benthic foraminifers, and CaCO3 stratigraphy for the Maestrichtian through Paleogene calcareous sequences recovered at Sites 689 and 690 on Maud Rise (at about 65°S, eastern Weddell Sea, Antarctica). These data represent the southernmost calciumcarbonate record available for that interval, and thus extend the biostratigraphic and isotopic database to higher latitudes. Sites 689 and 690 form the southernmost anchor of a north-south transect through the Atlantic Ocean for Paleogene biostratigraphy and chemostratigraphy.

Description: Campanian-Maestrichtian planktonic foraminifers were examined from Sites 698 (2128 m water depth) and 700 (3611 m water depth) on the Northeast Georgia Rise (southern South Atlantic, 51°S). Site 698 penetrated 72.5 m of Campanian-Maestrichtian chalk and limestone with only 18.2% recovery, whereas Site 700 recovered 66.8% of a 152.7-m section of Coniacian-Maestrichtian limestone. Preservation of planktonic foraminifers from both sites is moderate in Maestrichtian samples, but worsens with increasing depth in the Campanian. The Northeast Georgia Rise planktonic foraminifers are typical of Late Cretaceous Austral Province faunas described from other southern high-latitude sites; species diversity is low and the assemblages are dominated by species of Heterohelix, Globigerinelloides, Hedbergella, and Archaeoglobigerina. Five species, including Globigerinelloides impensus Sliter, Archaeoglobigerina australis Huber, Archaeoglobigerina mateola Huber, Hedbergella sliteri Huber, and Rugotruncana circumnodifer (Finlay), are considered to be endemic to the Austral Province. Formation of a cool temperate water mass in the circum-Antarctic region, resulting from the final breakup of the Gondwana continents, may have led to increased provincialism of the Austral Province planktonic foraminifers during Campanian-Maestrichtian time. Magnetobiostratigraphic correlation of eight planktonic foraminifer datum events at Hole 700B with ages determined for datums at ODP Leg 113 Holes 689B and 690C (Maud Rise, 65°S) demonstrates regional synchroneity of first and last occurrences within the Austral Province. As was observed at the Maud Rise, several keeled and nonkeeled species previously thought to have been restricted to warmer low-latitude regions first occur later at the Northeast Georgia Rise than at the low-latitude sites. The causes for high-latitude diachroneity among these immigrant species are not clear; neither oxygen and carbon isotope data from the Maud Rise sites nor calcareous nannoplankton distributions for the southern South Atlantic region show conspicuous changes that correlate to the delayed first occurrences.

Description: Neutron activation analyses of iridium and other chemical elements were performed across a 1-m-thick, partly nonbioturbated, clay-rich interval at the Cretaceous/Tertiary boundary in ODP Hole 738C. The results show that the boundary interval holds one of the highest Ir enrichments (320 ng Ir/cm2) of all known Cretaceous/Tertiary boundary layers. Iridium concentrations are highest (18 ppb Ir, whole-rock samples) a few centimeters above the base of the clayrich interval and gradually tail off upsection. Compared with background levels the most Ir-rich interval also shows strongly enhanced concentrations of Cr (215 ppm) and slightly elevated Co concentrations (13 ppm). The Ir-rich interval shows low As (〈 15 ppm) and Sb (〈0.8 ppm) concentrations, a fact that is congruent with absence of abundant authigenic sulfides in the sediment. Irregularly distributed Fe enrichments and a greenish gray color of the Fe-rich intervals may indicate the presence of glauconitic clay minerals and suboxic, slightly reducing conditions during deposition. Rare earth element (REE) abundance patterns change considerably across the Cretaceous/Tertiary boundary interval, reflecting either a change in Cretaceous/Tertiary boundary seawater REE composition or the occurrence of different REE fractionation processes due to changing depositional environment. Element-vs.-element ratios of Hf, Ta, Th, U, Cs, and Sc are similar between the most Ir-rich layers of the boundary section and other levels with lower Ir concentrations. This may imply that the clay fraction of the Ir-rich layers of the Cretaceous/Tertiary boundary interval is made up predominantly of locally derived material. Calculated calcite-free abundances of Hf, Ta, Th, U, Cs, and Sc, on the other hand, are reconcilable with an extraneous origin of the bulk of the clay in the most Ir-rich layers. The Ir in the Cretaceous/Tertiary boundary clay-rich zone in Hole 738C is most likely derived from an earth-impacting asteroid; however, the origin of the clay-rich zone remains enigmatic.

Description: A biostratigraphically complete upper Maestrichtian-Danian sequence was recovered at ODP Leg 119 Site 738 on the southern Kerguelen Plateau (62°S). Planktonic foraminifers are abundant and well to moderately preserved in all upper Maestrichtian samples to within 6 cm of the Cretaceous/Tertiary boundary, where foraminifers are rare and poorly preserved due to increased sediment lithification. Lowermost Danian samples are also poorly preserved, but specimen abundance is sufficient for preliminary quantitative biostratigraphic analysis. Despite the poor foraminifer preservation, evidence is presented for paleoenvironmental change immediately below a thin, iridium-rich calcareous clay horizon that is recognized as the Cretaceous/Tertiary boundary. The most significant indicators for preboundary change include; (1) loss of sediment bioturbation; (2) loss of keeled planktonic foraminifers; and (3) diminished size and diversity of benthic foraminifers. Planktonic foraminifers showing transitional morphologies between Cretaceous and Tertiary planktonic biserial heterohelicids first appear 4 cm below the boundary clay. Although some Cretaceous planktonic foraminifers consistently occur with early Danian marker species in initially high abundance above the boundary clay, they are not considered as survival species, but are considered as reworked because of their co-occurrence with Campanian and Maestrichtian species whose extinctions took place well before the end of the Maestrichtian. The recovered Maestrichtian planktonic foraminifers are identical to Austral Realm assemblages found in the southern South Atlantic region. All five species previously recognized as being endemic to this realm were recovered from Hole 738C. Lower Danian assemblages strongly resemble coeval low-latitude foraminifer faunas, whereas upper Danian assemblages differ only in the absence of indicator species, particularly the morozovellids. The stratigraphy of this sequence is correlated using existing zonal schemes for the southern high-latitudes, with modification of one Antarctic Paleogene zone and subzone. Only broad subdivisions of tropical zonal schemes were recognized, as most of the nominate taxa are absent from the southern high-latitudes.

Description: High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertiary boundary interval in Section 119-738C-20R-5 from the southern Kerguelen Plateau is summarized and interpreted. The change of the calcareous nannoflora and of the planktonic foraminifers is spread over a laminated interval of about 15 cm thickness. The base of this laminated interval lies in uppermost Maestrichtian chalks, 2 cm below a distinct 2-mm-thick "gray clay" layer, which shows the highest iridium enrichment (18 ppb) measured in this section. No shocked quartz or microspherules, characteristic of an impact, were found. No change in the clay mineralogy, which could be expected for a large volcanic or impact event, could be identified. Elevated metal and iridium concentrations (〉 1.6 ppb) occur already in the bioturbated uppermost Maestrichtian chalks several centimeters below the "gray clay" and decrease above the iridium peak gradually over a laminated 12-cm-thick interval to background values of 0.1-0.3 ppb Ir. Application of bio- and magnetochronology shows that the accumulation rates of carbonates and clays, but not of the metals, decreased dramatically at the Cretaceous/Tertiary boundary and thus, the lack of dilution may have led to the observed metal concentrations.