Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Miocene to Pliocene calcareous nannofossil biostratigraphy at ODP Leg 117 Sites 1088 and 1090, Southern Ocean

The calcareous nannofossil biostratigraphy of ODP Leg 177 Sites 1088 and 1090 (Subantarctic sector from the Atlantic Ocean) is discussed. Most nannofossil zonal boundaries of Martini (1971) and Okada and Bukry (1980) were recognized for the studied mid-high-latitude sediments. Conventional low-latitude marker species such as Amaurolithus spp., Discoaster spp., Triquetrorhabdulus spp., Ceratolithus spp. were recorded as rare and scattered, which impeded the development of a detailed nannofossil biostratigraphic zonation of some Miocene and Pliocene intervals. Because of the absence of some primary biostratigraphic marker species, additional second-order bioevents, such as the first occurrence of Calcidiscus macintyrei and the last occurrence of Coccolithus miopelagicus, have been used to approximate the base of zones NN7 and NN8, respectively. Several disconformities disturbing the Pliocene and Miocene intervals of Site 1090 could be determined based on nannofossil distribution although the occurrence of intervals with dissolved nannofloras and low species diversity prevented a reliable age assignment. An acme of small Gephyrocapsa was recognized near the lower/middle Pliocene boundary, close to the NN15-NN16 zonal boundary, presenting an event for further improvement of the calcareous nannofossil biostratigraphy of this interval time. The first occurrence of Pseudoemiliania lacunosa (>4 µm) occurs close to this interval, representing a fairly reliable event to approximate the base of NN15 zone when other biozonal events are absent. A paracme of R. pseudoumbilicus (>7 µm) was detected in the lower Pliocene NN12 and in the upper Miocene NN11. These temporary absences of the species seem to be isochronous between high-latitude and low-middle-latitude areas.

Size variations of Discoaster multiradiatus across the Paleocene-Eocene thermal maximum

Size measurements of the calcareous nannofossil taxon Discoaster multiradiatus were carried out across the Paleocene-Eocene Thermal Maximum (PETM) in Ocean Drilling Program Holes 690B (Maud Rise, Weddell Sea) and 1209B (Shatsky Rise, Pacific Ocean). Morphometric investigations show that D. multiradiatus specimens are generally larger at ODP Site 1209 than at ODP Site 690. A limited increase in size of D. multiradiatus is recorded at ODP Site 1209, whereas significant enlargements characterize ODP Site 690. Preservation is comparable at both sites: nannofossils are moderately preserved with some evidence of etching/overgrowth in the PETM interval. Yet, D. multiradiatus variations do not correlate with preservation state and morphometric data most likely represent primary signals rather than diagenetic artifacts. There is a direct relationship between D. multiradiatus size and paleotemperatures: largest specimens are coeval with global warming associated with the PETM, inferred to result from excess atmospheric CO2 due to (partial) oxidation of massive quantities of methane. Size increases and largest specimens of D. multiradiatus occur at different stratigraphic levels within PETM at ODP Sites 690 and 1209. A marked shift in diameter size was observed at the onset and peak of the Carbon Isotopic Excursion (CIE) at ODP Site 690, but only at the end of CIE and initial recovery interval at ODP Site 1209. This diachroneity is puzzling, but indeed correlates well with reconstructed changes in surface and thermocline water masses temperature and salinity in the PETM interval at low and high latitudes. The presumed high concentrations of carbon dioxide seem to have not influenced the morphometry of D. multiradiatus. The major size increase of D. multiradiatus in the CIE of ODP Site 690 could represent the migration of larger-sized allochtonus specimens that moved from peri-equatorial/subtropical areas to higher latitudes during the warmest interval of the PETM, although no direct evidence of distinct populations/subpopulations has been obtained from the frequency diagrams. As a result, we infer that D. multiradiatus is a proxy of water masses stratification and might be used for deriving temperature-salinity-nutrient conditions in the mixed layer and thermocline and their dynamics.

Calcareous microfossil isotopes and Miocene datum events of ODP Holes 189-1170A and 189-1172A

Downcore oxygen and carbon stable isotope records of planktonic and benthic foraminifers and fine-fraction carbonate from the southern high latitudes provide critical paleohydrographic constraints on the evolution of the Southern Ocean climate. In particular, the potential effects of an intensified Antarctic Circumpolar Current on the thermal isolation and cooling of the southern high latitudes, production of cold deep waters, and, ultimately, accumulation of continental ice on Antarctica in the middle Miocene are matters of interest. Using sediment materials from Ocean Drilling Program Leg 189 Sites 1170 and 1172 off Tasmania, Ennyu and Arthur (2004, doi:10.1029/151GM13) established the surface- and deepwater stable isotope records in the Southern Ocean across the middle Miocene event of the east Antarctic ice sheet expansion and discussed the paleoclimate proxy records in terms of the thermal evolution of the southern high latitudes and its effect on deepwater circulation. This report provides data tables and other supporting information relevant to discussions presented in Ennyu and Arthur (2004, doi:10.1029/151GM13). Items included in this report are (1) the oxygen and carbon stable isotope data measured on the Miocene bulk fine-fraction (i.e., <63 µm, primarily polyspecific nannofossil assemblage) carbonate and planktonic and benthic foraminifers from Holes 1170A and 1172A and (2) the Miocene depth-age models for the two sites.

(Table 1) Compressional-wave velocities and anisotropies and wet-bulk densities of calcareous rocks and some cherts at DSDP Holes 62-463 and 62-465A

Anisotropy in compressional-wave velocities in sedimentary rocks recovered by DSDP has been recognized by several investigators (Boyce, 1976; Tucholke et al., 1976; Carlson and Christensen, 1977). The anisotropy is also observed at elevated pressures in laboratory experiments, and thus probably persists at depth in some calcareous rocks (Schreiber et al., 1972; Christensen et al., 1973; Carlson and Christensen, 1979). Carlson and Christensen (1979) suggested that the observed velocity anisotropy was produced not by the alignment of cracks but by the alignment of c axes of calcite perpendicular to bedding during compaction, diagenesis, and recrystallization. On DSDP Leg 62, calcareous rocks were recovered from the western Mid-Pacific Mountains (sub-bottom depths of 452-823 m, Site 463) and southern Hess Rise (276-412 m, Site 465). Most of the calcareous rocks are horizontally laminated and color-banded, and ages are early Cenomanian to late Barremian (Site 463 and 465 reports, this volume). The purpose of this study is to confirm the velocity anisotropy in the calcareous rocks and to identify any relationship of anistropy to bulk density, mean velocity, and burial depth.

Calcareous dinocysts and grain size distribution along profile Stevns-Klint

The distribution patterns of calcareous dinoflagellate cysts were studied in the classic Cretaceous Tertiary (K-T) boundary section of Stevns Klint, Denmark, focusing mainly on the response of the cyst association to an abrupt environmental catastrophe. A major part of the Fish Clay, which covers the K-T boundary at its base and is exposed in the investigated section, contains fallout produced by an asteroid impact. Calcareous dinoflagenate cysts are the best preserved remains of carbonate-producing phytoplankton in this layer. The potential of this group of microfossils for the analysis of survival strategies and extinction patterns has been underestimated. The cyst species of the investigated section can be grouped into four assemblages that represent victims, survivors, opportunists, and specially adapted forms. The victims (Pithonelloideae) were an extremely successful group throughout the Upper Cretaceous, but were restricted to the narrow outer shelf. This restriction minimized their spatial distribution, which generally should be large to facilitate escape from unfavorable conditions. Spatial restriction optimized the population decrease by mass mortality, disabling a successful recovery. In contrast, the survivors that became the dominating group in the Danian had a wide spatial range from the shelf environment to the oceanic realm. A unique calcareous dinocyst assemblage in the Fish Clay shows that even under the stressed conditions immediately following the impact event, some species flourished due to special adaptation or high ecological tolerance. The ability of these dinoflagellate species to form calcareous resting cysts in combination with their generally wide spatial distribution in a variety of environments appears to be the main reason for a low extinction rate at the K-T boundary as opposed to the high extinction rate of other phytoplankton groups, such as the coccolithophorids.