Geochemistry at DSDP Hole 84-567A

Dismembered ophiolitic rocks including abundant sheared, serpentinized peridotite (mostly harzburgite) and minor basalts, dolerites, gabbros, and altered metabasites (mainly altered amphibolite) were drilled at most of the sites on the upper to lower Middle America Trench landward slope off Guatemala during Leg 84 of the Deep Sea Drilling Project. These rocks show characteristic Cataclastic deformation with zeolite facies metamorphism and alteration after amphibolite and greenschist facies metamorphism. These features indicate that the rocks originated in mid-oceanic ridge, offridge, and possibly other areas including island arc areas and were metamorphosed under a high geothermal gradient at low pressure. They were then structurally deformed and mixed within a serpentinite melange. Such ophiolite melanges may have been emplaced onto the Trench landward slope area during the initiation of subduction of the Cocos Plate. The emplacement seems to be connected to that of the Nicoya Complex in Costa Rica. The slope cover from early Eocene to Recent shows no history of these metamorphic and deformational events, therefore the emplacement of the dismembered ophiolitic rocks occurred at least before the early Eocene. The dismembered ophiolite-based Trench landward slope off Guatemala is a newly documented style of subduction, which has also recently been found at the easternmost edge of the Philippine Sea Plate along the Izu-Mariana-Yap Trench landward slope.

Bio- and magnetostratigraphic events of ODP holes of the central Kerguelen Plateau

Neogene biostratigraphic and magnetostratigraphic data are compiled from Holes 747A, 748B, and 751A drilled on the Southern Kerguelen Plateau during Ocean Drilling Program Leg 120. Neogene sections have excellent to good magnetostratigraphic signatures in many intervals. This, in addition to minimal coring gaps and the occurrence of mixed assemblages of both calcareous and siliceous microfossil assemblages, makes these valuable biostratigraphic reference sections for intra- and extraregional correlations. This paper combines the sequence of biostratigraphic events reported from diatom, radiolarian, planktonic foraminifer, calcareous nannofossil, and silicoflagellate studies of Leg 120 sediments. It correlates microfossil datums with the geomagnetic polarity time scale to test existing age estimates and to refine biostratigraphic age controls for the southern high latitudes. Significant biostratigraphic datums are presented in a series of age-depth plots. Numerous hiatuses are clearly identified through this approach, and the positions of lesser disconformities are suggested. Most Neogene intervals are represented in at least one site, although "regional" unconformities occur in the upper Pliocene, uppermost Miocene/lowermost Pliocene, middle upper Miocene, middle middle Miocene, and at the lower/middle Miocene boundaries. The longest hiatus spanned 6 m.y., with most other hiatuses representing 1 m.y. or less. This paper compiles Leg 120 biostratigraphic and magnetostratigraphic data for use in future syntheses of southern high latitude biostratigraphy and presents an age model for Leg 120 Neogene sediments.

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.

Neogene planktonic foraminifera of DSDP Leg 41 holes

During Leg 41 Neogene sediments were recovered from five sites off northwest Africa. On the Sierra Leone Rise (Site 366), Neogene sediments consist of nanno oozes, nanno chalk, and calcareous clays 230 meters thick, resting conformably on the late Oligocene sediments. The common succession of zones occurs with two hiatuses. The lower gap corresponds to an interval around the lower/middle Miocene boundary (the Praeorbulina glomerosa and Orbulina suturalis-Globorotalia peri-pheroronda zones are absent) and the upper gap coincides with an interval around the middle/upper Miocene boundary (the Sphaeroidinellopsis sub-dehiscens-GIobigerina druryi, Globigerina nepenthes-Globorotalia siakensis and Globorotalia conlinuosa zones are missing). In the Cape Verde Basin (Site 367) deep-water Neogene turbidites (about 200-250 m thick) contain poor fauna of redeposited and sorted Cretaceous, Eocene, Oligocene, and Neogene species. On the Cape Verde Rise (Site 368) the Neogene section starts with slightly calcareous and non-calcareous clays with poor planktonic foraminifers of the lower Miocene. Later on this area was uplifted and clayey sediments have been replaced upsection in order by more shallow-water clayey nanno and nanno-foraminifer oozes and marls and pure calcareous oozes. In the middle Miocene, planktonic foraminifers are still not diverse, but since the level of the Globigerina nepenthes-Globorotalia siakensis Zone, almost all Neogene zones have been traced. The minimum thickness of the Neogene sediments is about 230 meters. On the continental slope off Spanish Sahara (Site 369) monotonous calcareous pelagic sediments of Neogene age (164 m thick) overlie the late Oligocene comformably, or with a small time gap. A set of zones beginning from the Globigerinoides primordis-Globorotaiia kugleri Zone up to the Globorotalia fohsi fohsi Zone has been revealed with a gap corresponding to the Globigerinita stainforthi and the Globigerinatella insueta-Globigerinoides irilobus zones. Above that follow sediments with heterogeneous microfauna which result from redeposition or mixing of sediments during drilling. The section ends with sediments of the late Miocene and lower Pliocene with abundant planktonic foraminifers. The latter are unconformably overlain by the Quaternary ooze. In the Morocco basin (Site 370) deep-water marls and calcareous clays of the lower Miocene contain poor assemblages of planktonic foraminifers. The middle and upper Miocene are represented by turbidites (alternation of nanno oozes, clays, siltstones, and sands) with heterogeneous microfauna. Total thickness of Neogene is up to 200 meters. In general the Neogene foraminifer microfauna of the area studied includes the majority of species which developed within the tropical-subtropical belt. The entire succession of the Miocene and Pliocene foraminifer zones occurs. The only exclusion is the Sphaeroidinellopsis subdehiscens-Globigerina druryi Zone of the middle Miocene. The distribution of species is shown on three tables. Comments are given for 47 species and subspecies of foraminifers (stratigraphic ranges, peculiarities of morphology, and ultrastructure of the shell wall).

Palynology, source vegetation, environment and age of ODP Site 188-1166 sediments

Twenty-three core catcher samples from Site 1166 (Hole 1166A) in Prydz Bay were analyzed for their palynomorph content, with the aims of determining the ages of the sequence penetrated, providing information on the vegetation of the Antarctic continent at this time, and determining the environments under which deposition occurred. Dinocysts, pollen and spores, and foraminiferal test linings were recovered from most samples in the interval from 142.5 to 362.03 meters below seafloor (mbsf). The interval from 142.5 to 258.72 mbsf yielded palynomorphs indicative of a middle-late Eocene age, equivalent to the lower-middle Nothofagidites asperus Zone of the Gippsland Basin of southeastern Australia. The Prydz Bay sequence represents the first well-dated section of this age from East Antarctica. Dinocysts belonging to the widespread "Transantarctic Flora" give a more confident late Eocene age for the interval 142.5-220.5 mbsf. The uppermost two cores within this interval, namely, those from 142.5 and 148.36 mbsf, show significantly higher frequencies of dinocysts than the cores below and suggest that an open marine environment prevailed at the time of deposition. The spore and pollen component may reflect a vegetation akin to the modern rainforest scrubs of Tasmania and New Zealand. Below 267 mbsf, sparse microfloras, mainly of spores and pollen, are equated with the Phyllocladidites mawsonii Zone of southeastern Australia, which is of Turonian to possibly Santonian age. Fluvial to marginal marine environments of deposition are suggested. The parent vegetation from this interval is here described as "Austral Conifer Woodland." The same Late Cretaceous microflora occurs in two of the cores above the postulated unconformity at 267 mbsf. In the core at 249.42 mbsf, the Late Cretaceous spores and pollen are uncontaminated by any Tertiary forms, suggesting that a clast of this older material has been sampled; such a clast may reflect transport by ice during the Eocene. At 258.72 mbsf, Late Cretaceous spores and pollen appear to have been recycled into the Eocene sediments.

Stable isotope ratios of benthic foraminifera in mid-Pleitsocene sediments of ODP Site 108-664 in the equatorial Atlantic

Five delta13C records from the deep ocean, extending back to 1.3 Ma, were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41- to 100-ka climate transition. These data show that significant perturbations in mean ocean carbon chemistry were associated with the mid-Pleistocene climate transition. Notable features of the last 1.3 Myr are (1) a pronounced ~0.3? decrease in mean ocean delta13C between 0.9 and 1.0 Myr, followed by a return to pre-1.0 Ma values by 400 ka B.P., which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean, possibly associated with an increase in global aridity (and decrease in the size of the biosphere) across the 41- to 100-ka transition; (2) no change in the Atlantic-Pacific (A-P) delta13C gradient over the last 1.3 Myr, suggesting no change in mean ocean nutrient content accompanied the addition of light carbon; and (3) stronger vertical nutrient fractionation in the North Atlantic in the middle Pleistocene between sites 607 and 552, suggesting weaker North Atlantic Deep Water formation at this time relative to the early and late Pleistocene. We also find evidence for a more pronounced deep recirculation gyre in the western North Atlantic basin in the early Brunhes, as evidenced by "aging" of deep northern basin water (site 607) relative to deep water in the equatorial Atlantic (site 664).

Stable carbon and oxygen isotope record of planktonic and benthic foraminifera at ODP Site 111-677 in the Panama Basin

Oxygen and carbon isotope ratio measurements are presented for Globigerinoides ruber and for benthic species (mainly Uvigerina spp.) in the Pleistocene and uppermost Pliocene section of ODP Hole 677A in the Panama Basin. This provides the best available continuous Pleistocene stable isotope records from any location, fully justifying the recoring of DSDP Site 504. Oxygen isotope stage 22 (age about 0.85 Ma) was of similar magnitude to the most extensive glacials of the Brunhes and constitutes a logical base for the middle Pleistocene. Oxygen isotope stages as defined by Ruddiman et al. (1986, doi:10.1016/0012-821X(86)90024-5) and by Raymo et al. (1989, doi:10.1029/PA004i004p00413) back to stage 104 are recognized. Although the internationally agreed base of the Quaternary at or near stage 62 (about 1.6 Ma) is not marked by a major isotopic event, it does approximate the base of a regime characterized by highly regular 41,000-yr climate cycles. The records at Site 677 are ideal for time-series analyses and will permit a new attempt to develop a chronology for the early Pleistocene based on tuning to the orbital frequencies. The carbon isotope records also appear to contain considerable variance at orbital frequencies throughout the sequence analyzed.

Benthic foraminifera in Tertiary sediments of DSDP Leg 90 holes

Eocene through Pliocene benthic foraminifers were examined from seven sites located at middle and lower bathyal depths on the Lord Howe Rise in the Tasman Sea, from another site at lower bathyal depths in the Coral Sea, and from a site in the intermediate-depth, hemipelagic province of the Chatham Rise, east of southern New Zealand. Age-related, depth-related, and bioprovincial faunal variations are documented in this chapter. One new species, Rectuvigerina tasmana, is named. The paleoecologic indications of several key groups, including the miliolids, uvigerinids, nuttallitids, and cibicidids, are combined with sedimentologic and stable isotopic tracers to interpret paleoceanographic changes in the Tasman Sea. Because the total stratigraphic ranges of many bathyal benthic foraminifers are not yet known, most endpoints in the Tasman Sea are considered ecologically controlled events. The disappearances of Uvigerina rippensis and Cibicidoidesparki and the first appearances of U. pigmaea, Sphaeroidina bulloides, and Rotaliatina sulcigera at the Eocene/Oligocene boundary can be considered evolutionary events, as also can the first appearance of Cibicides wuellerstorfi in Zone NN5. Species which are restricted to the lower bathyal zone except during discrete pulses, most of which are related to the development of glacial conditions, include Melonis pompilioides, M. sphaeroides, Pullenia quinqueloba, Nuttallides umbonifera, and U. hispido-costata. Middle bathyal indigenes include U. spinulosa, U. gemmaeformis, Ehrenbergina marwicki, R. sulcigera, and all rectuvigerinids except Rectuvigerina spinea. Although the miliolids first occurred at lower bathyal depths, they were more common in the middle bathyal zone. Although the Neogene hispido-costate uvigerinids first developed at lower bathyal depths and at higher middle latitude sites, in the later Neogene this group migrated to shallower depths and became predominant also in the middle bathyal zone. Despite the relatively similar sedimentologic settings at the six middle bathyal Tasman sites, there was extensive intrageneric and intraspecific geographic variation. Mililiolids, strongly ornamented brizalinids, bolivinitids, Bulimina aculeata, Osangularia culter, and strongly porous morphotypes were more common at higher latitudes. Osangularia bengalensis, striate brizalinids such as Brizalina subaenariensis, Gaudryina solida, osangularids in general, and finely porous morphotypes were more common in the subtropics. There was strong covariance between faunas at lower middle latitude, lower bathyal Site 591, and higher middle latitude, middle bathyal Site 593. The following oceanographic history of the Tasman Sea is proposed; using the stable isotopic record as evidence for glacials and examining the ecologic correlations between (1) miliolids and carbonate saturation, (2) nuttallitids and undersaturated, cooled, or "new" water masses, (3) uvigerinids with high organic carbon in the sediment and high rates of sediment accumulation, and (4) cibicidids and terrestrial organic carbon. The glacial located near the Eocene/Oligocene boundary is characterized by the penetration of cooler, more corrosive waters at intermediate depths in high southern latitudes. This may have caused overturn, upwelling pulses, in other Tasman areas. The development of Neogenelike conditions began in the late Oligocene (Zone NP24/NP25) with the evolution of several common Neogene species. A large number of Paleogene benthics disappeared gradually through the course of the early Miocene, which was not well preserved at any Tasman site. Corrosive conditions shallowed into the middle bathyal zone in several pulses during the early Miocene. The development of glacial conditions in the middle Miocene was accompanied by major changes throughout the Tasman Sea. Sediment accumulation rates increased and high-productivity faunas and corrosive conditions developed at all but the lowest-latitude Site 588. This increase in productivity and accumulation rate is attributed to the eutrophication of Antarctic water masses feeding Tasman current systems, as well as to invigorated circulation in general. It overlaps with the beginning of the Pacific High-productivity Episode (10-5 Ma). During the latest Miocene glacial episode, corrosive conditions developed at lower bathyal depths, while cooler water and lower nutrient levels shallowed to middle bathyal depths. Lower input of terrestrial organic carbon may be related to the lower nutrient levels of this time and to the termination of the Pacific High-productivity Episode. The moderate glacial episode during the mid-Pliocene (Zone NN15/NN16, ~3.2 Ma) corresponds to a decline in sediment accumulation rates and a reorganization of faunas unlike that of all other times. New genera proliferate and indices for cool, noncorrosive conditions and high organic carbon expand throughout the middle bathyal zone coeval with the sedimentation rate decreases. By the latest Pliocene (about 2.5 Ma), however, during another glacial episode, faunal patterns typical of this and later glacials develop throughout the Tasman Sea. Benthic foraminiferal patterns suggest increased input of terrestrial organic matter to Tasman Sea sediments during this episode and during later glacials.

Toba Tephra across India

A controversy currently exists regarding the number of Toba eruptive events represented in the tephra occurrences across peninsular India. Some claim the presence of a single bed, the 75,000-yr-old Toba tephra; others argue that dating and archaeological evidence suggest the presence of earlier Toba tephra. Resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples, allowing comparison of the Indian samples to those from the Toba caldera in northern Sumatra, Malaysia, and, importantly, the sedimentary core at ODP Site 758 in the Indian Ocean - a core that contains several of the earlier Toba tephra beds. In addition, two samples of Toba tephra from western India were dated by the fission-track method. The results unequivocally demonstrate that all the presently known Toba tephra occurrences in peninsular India belong to the 75,000 yr B.P. Toba eruption. Hence, this tephra bed can be used as an effective tool in the correlation and dating of late Quaternary sedimentary sequences across India and it can no longer be used in support of a middle Pleistocene age for associated Acheulian artifacts.

Miocene foraminiferal, bolboformid, dinoflagellate and diatom age calibrations for the northeastern North Atlantic

This study presents a new Miocene biostratigraphic synthesis for the high-latitude northeastern North Atlantic region. Via correlations to the bio-magnetostratigraphy and oxygen isotope records of Ocean Drilling Program and Deep Sea Drilling Project Sites, the ages of shallower North Sea deposits have been better constrained. The result has been an improved precision and documentation of the age designations of the existing North Sea foraminiferal zonal boundaries of King (1989) and Gradstein and Bäckström (1996). All calibrations have been updated to the Astronomically Tuned Neogene Time Scale (ATNTS) of Lourens et al. (2004). This improved Miocene biozonation has been achieved through: the updating of age calibrations for key microfossil bioevents, identification of new events, and integration of new biostratigraphic data from a foraminiferal analysis of commercial wells in the North Sea and Norwegian Sea. The new zonation has been successfully applied to two commercial wells and an onshore research borehole. At these high latitudes, where standard zonal markers are often absent, integration of microfossil groups significantly improves temporal resolution. The new zonation comprises 11 Nordic Miocene (NM) Zones with an average duration of 1 to 2 million years. This multi-group combination of a total of 92 bioevents (70 foraminifers and bolboformids; 16 dinoflagellate cysts and acritarchs; 6 marine diatoms) facilitates zonal identification throughout the Nordic Atlantic region. With the highest proportion of events being of calcareous walled microfossils, this zonation is primarily suited to micropaleontologists. A correlation of this Miocene biostratigraphy with a re-calibrated oxygen isotope record for DSDP Site 608 suggests a strong correlation between Miocene planktonic microfossil turnover rates and the inferred paleoclimatic trends. Benthic foraminifera zonal boundaries appear to often coincide with Miocene global sequence boundaries. The biostratigraphic record is punctuated by four main stratigraphic hiati which show variation in their geographic and temporal extent. These are related to the following regional unconformities: basal Neogene, Lower/Middle Miocene ("mid-Miocene unconformity"), basal Upper Miocene and basal Messinian unconformities. Further coring of Neogene sections in the North Sea and Norwegian Sea may better constrain their extent and their effect on the biostratigraphic record.

Stable carbon and oxygen isotope record of IODP Site 306-U1313, MIS 23-19

Since the seminal work by Hays et al. (1976), a plethora of studies has demonstrated a correlation between orbital variations and climatic change. However, information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial-scale climate variability is still fragmentary. The Marine Isotope Stage (MIS) 19, an interglacial centred at around 785 ka, provides an opportunity to pursue this question and test the hypothesis that the long-term processes set up the boundary conditions within which the short-term processes operate. Similarly to the current interglacial, MIS 19 is characterised by a minimum of the 400-kyr eccentricity cycle, subdued amplitude of precessional changes, and small amplitude variations in insolation. Here we examine the record of climatic conditions during MIS 19 using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess the stability and duration of this interglacial, and evaluate the climate system's response in the millennial band to known orbitally induced insolation changes. Benthic and planktonic foraminiferal d18O values indicate relatively stable conditions during the peak warmth of MIS 19, but sea-surface and deep-water reconstructions start diverging during the transition towards the glacial MIS 18, when large, cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal. The glacial inception occurred at ~779 ka, in agreement with an increased abundance of tetra-unsaturated alkenones, reflecting the influence of icebergs and associated meltwater pulses and high-latitude waters at the study site. After having combined the new results with previous data from the same site, and using a variety of time series analysis techniques, we evaluate the evolution of millennial climate variability in response to changing orbital boundary conditions during the Early-Middle Pleistocene. Suborbital variability in both surface- and deep-water records is mainly concentrated at a period of ~11 kyr and, additionally, at ~5.8 and ~3.9 kyr in the deep ocean; these periods are equal to harmonics of precession band oscillations. The fact that the response at the 11 kyr period increased over the same interval during which the amplitude of the response to the precessional cycle increased supports the notion that most of the variance in the 11 kyr band in the sedimentary record is nonlinearly transferred from precession band oscillations. Considering that these periodicities are important features in the equatorial and intertropical insolation, these observations are in line with the view that the low-latitude regions play an important role in the response of the climate system to the astronomical forcing. We conclude that the effect of the orbitally induced insolation is of fundamental importance in regulating the timing and amplitude of millennial scale climate variability.