Oxygen and carbon isotope stratigraphy of ODP Holes 107-653A and 107-654A

Stable isotope analysis of two species (or groups of species) of planktonic foraminifers: Globigerinoides ruber (or G. obliquus and G. obliquus extremus) and Globigerina bulloides (or G. falconensis and G. obesa) from ODP Hole 653A and Site 654 in the Tyrrhenian basin, records the Pliocene-Pleistocene glacial history of the Northern Hemisphere. The overall increase in mean d18O values through the interval 4.6-0.08 Ma is 1.7 per mil for G. bulloides and 1.5 per mil for G. ruber. The time interval 3.1-2.5 Ma corresponds to an important phase of 18O enrichment for planktonic foraminifers. In this interval, glacial d18O values of both species G. bulloides and G. ruber increase by about l per mil, this increase being more progressive for G. ruber than for G. bulloides. The increase of interglacial d18O values is higher for G. bulloides (1.5 per mil) than for the Gruber group (1 per mil). These data suggest a more pronounced seasonal stratification of the water masses during interglacial phases. Large positive d18O fluctuations of increasing magnitude are also recorded at 2.25 and 2.15 Ma by G bulloides and appear to be diachronous with those of Site 606 in the Atlantic Ocean. Other events of increasing d18O values are recorded between 1.55 and 1.3 Ma, at 0.9 Ma, 0.8 Ma, and near 0.34 Ma. In the early Pliocene the d18O variability recorded by the planktonic species G. bulloides was higher in the Mediterranean than in the Atlantic at the same latitude. This suggests that important cyclic variations in the water budget of the Mediterranean occurred since that time. Step increases in the d18O variability are synchronous with those of the open ocean at 0.9 and 0.34 Ma. The higher variability as well as the higher amplitude of the peaks of 18O enrichment may be partly accounted for by increase of dryness over the Mediterranean area. In particular the high amplitude d18O fluctuations recorded between 3.1 and 2.1 Ma are correlated with the onset of a marked seasonal contrast and a summer dryness, revealed by pollen analyses. Strong fluctuations towards d13C values higher than modern ones are recorded by the G. ruber group species before 1.7 Ma and suggest a high production of phytoplankton. When such episodes of high primary production are correlated with episodes of decreasing 13C content of G. bulloides, they are interpreted as the consequence of a higher stratification of the upper water masses resulting itself from a marked seasonality. Such episodes occur between 4.6 and 4.05 Ma, 3.9 and 3.6 Ma, and 3.25 and 2.66 Ma. The interval 2.66-1.65 Ma corresponds to a weakening of the stratification of the upper water layers. This may be related to episodes of cooling and increasing dryness induced by the Northern Hemisphere Glaciations. The Pleistocene may have been a less productive period. The transition from highly productive to less productive surface waters also coincides with a new step increase in dryness and cooling, between 1.5 and 1.3 Ma. The comparison of the 13C records of G ruber and G. bulloides in fact suggests that a high vertical convection became a dominant feature after 2.6 Ma. Increases in the nutrient input and the stratification of the upper water masses may be suspected, however, during short episodes near 0.86 Ma (isotopic stage 25), 0.57-0.59 Ma (isotopic stage 16), 0.49 Ma (isotopic stage 13), 0.4-0.43 Ma (isotopic stage 11), and 0.22 and 0.26 Ma (part of isotopic stage 7 and transition 7/8). In fact, changes in the C02 balance within the different water masses of the Tyrrhenian basin as well as in the local primary production did not follow the general patterns of the open ocean.

Late Quaternary carbonate and isotope stratigraphy of DSDP Site 90-594 east of South Island, New Zealand

The late Quaternary sequence off eastern South Island, New Zealand, consists of ~100 m of alternating bluish gray pelagic oozes and greenish gray hemipelagic oozes that extend uninterruptedly back to the Brunhes/Matuyama boundary (0.73 m.y.). A very high resolution (~2400 yr.) record of sediment texture, calcium carbonate content, and planktonic and benthic foraminiferal oxygen and carbon isotope composition demonstrates an in-phase cyclical fluctuation between the sedimentary parameters that closely correspond to the pelagic-hemipelagic sedimentation cycles and the isotope composition. Pelagic oozes, formed during interglacial periods of high eustatic sea level, are characterized by calcareous microfossils, relative enrichment in sand and clay sizes, high carbonate contents, reduced delta18O values, and increased delta13C values. Hemipelagic oozes, associated with glacial episodes and lowered eustatic sea level, include common terrigenous material and siliceous microfossils, are enriched in silt sizes, have low carbonate contents, high delta18O values, and low delta13C values. The history of alpine glaciations and associated erosion of the South Island of New Zealand, as expressed by the appearance of hemipelagic oozes, can be correlated directly with the major fluctuations of Northern Hemisphere ice sheets as expressed by the influence of eustatic sea-level changes on the oxygen isotope composition of both planktonic and benthic foraminifers. This high-accumulation-rate record contains conspicuous intervals of highfrequency, high-amplitude isotope variability including the presence of multiple glacial/interglacial intervals within single isotope stages, and offers one of the best sections cored to date for detailed study of the evolution and history of climate change over the last 0.75 m.y.

An integrated biostratigraphy (conodonts and foraminifers) and chronostratigraphy (paleomagnetic reversals, magnetic susceptibility, elemental chemistry, carbon isotopes and geochronology) for the Permian-Triassic strata of Guandao section

The chronostratigraphy of Guandao section has served as the foundation for numerous studies of the end-Permian extinction and biotic recovery in south China. Guandao section is continuous from the Permian-Triassic boundary to the Upper Triassic.Conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows. Changhsingian- Griesbachian: first Hindeodus parvus, and first appearance of foraminifers Postcladella kalhori and Earlandia sp. Griesbachian-Dienerian: first Neospathodus dieneri, and last appearance of foraminifer P. grandis. Dienerian-Smithian: first Novispathodus waageni and late Dienerian first appearance of foraminifer Hoyenella ex gr. sinensis. Smithian-Spathian: first Nv? crassatus and last appearance of foraminifers Arenovidalina n. sp. and Glomospirella cf. vulgaris. Spathian-Aegean: first Chiosella timorensis and first appearance of foraminifer Meandrospira dinarica. Aegean-Bithynian: first Nicoraella germanica and first appearance of foraminifer Pilammina densa. Bithynian-Pelsonian: after last Neogondolella regalis, prior to first Paragondolella bulgarica and first appearance of foraminifer Aulotortus eotriasicus. Pelsonian-Illyrian: first Pg. excelsa and last appearance of foraminifers Meandrospira ? deformata and Pilamminella grandis. Illyrian-Fassanian: first Budurovignathus truempyi, and first appearance of foraminifers Abriolina mediterranea and Paleolituonella meridionalis. Fassanian-Longobardian: first Bv. mungoensis and last appearance of foraminifer A. mediterranea. Longobardian-Cordevolian: first Quadralella polygnathiformis and last appearance of foraminifers Turriglomina mesotriasica and Endotriadella wirzi. The section contains primary magnetic signature with frequent reversals occurring around the Permian-Triassic, Olenekian-Anisian, and Anisian-Ladinian boundaries. Predominantly normal polarity occurs in the lower Smithian, Bithynian, and Longobardian-Cordevolian. Predominantly reversed polarity occurs in the upper Griesbachian, Induan-Olenekian, Pelsonian and lower Illyrian. Reversals match well with the GPTS. Large amplitude carbon isotope excursions, attaining values as low as -2.9 per mil d13C and high as +5.7 per mil d13C, characterize the Lower Triassic and basal Anisian. Values stabilize around +2 per mil d13C through the Anisian to Carnian. Similar signatures have been reported globally. Magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the Lower Triassic and an overall decline in magnitude of fluctuation through the Middle and Upper Triassic. The largest spikes in magnetic susceptibility and gamma ray, indicating greater terrestrial lithogenic flux, correspond to positive d13C excursions. Several volcanic ash horizons occur in the Lower Triassic and Olenekian-Anisian boundary. High resolution U-Pb analysis of zircons provide a robust age of 247.2 Ma for the Olenekian-Anisian boundary.

Magnetic susceptibility stratigraphy for Pleistocene and Pliocene sediments of ODP Leg 110 samples

Whole-core magnetic susceptibility measurements define a detailed stratigraphy that enables correlation between the various Pleistocene, Pliocene, and upper Miocene sections cored on ODP Leg 110, near the Tiburon Rise. The magnetic susceptibility in these sections is primarily related to the content of volcanic ash, rich in titanomagnetite, and also inversely related to calcium carbonate content. The high resolution of the susceptibility record enables correlations with a resolution of about 0.3 m of sediment thickness, and the identification of minor faults not definable by biostratigraphic means. Reverse and normal faults identified in Hole 672A are probably a result of normal oceanic sediment dewatering and compaction processes. This work indicates some of the problems of using visible ash layers as time-stratigraphic markers.

Tab. 1: Meerfelder Maar Drilling B4, stratigraphy and sequence of the lake sediments (pdf 215 kB)

A core from Meerfelder Maar, with a basal age of 29,000 years, provides a continuous sedimentary sequence from Late-Glacial times to the present. It includes the stratigraphical marker of the Laach Pumice Tuff. Sedimentological, geochemical, palynological, palaeobiological, palaeomagnetic and palaeontological analyses permit reconstructions of the history of the lake and its catchment area, and hence of the climate of the region, to be made. The discovery of Middle Oligocene marine, detrital fossils in the maar sediments provides insights into the palaeogeography of the Eifel region during Tertiary times.

Strontium-isotope stratigraphy and oxygen- and carbon-isotope record of Middle Jurassic to Early Cretaceous belemnites in the South Atlantic

87Sr/86Sr data of belemnites are presented from a Middle Jurassic-Early Cretaceous succession from the Falkland Plateau (Deep Sea Drilling Project Sites 511 and 330) that was deposited in a periodically anoxic, semi-enclosed shallow water basin. Diagenetically screened strontium-isotope values of 0.706789 rise to 0.707044 before increasing sharply to 0.707428 in the uppermost part of the sampled succession. Comparison with published strontium calibration curves suggests that the oldest samples were Callovian to Oxfordian in age, whilst the remainder of the Jurassic part of the succession consisted of Kimmeridgian and Early Tithonian age sediments. The nannofossil, dinoflagellate and molluscan assemblages provide comparable age determinations. The strontium-isotope analysis of the youngest belemnites points to a Hauterivian-Barremian age, whilst age interpretations based upon the fauna provide a wide age range from the Barremian to early Albian. Strontium-isotope stratigraphy of this succession hence offers increased age resolution providing data regarding the timing of episodes of bottom water anoxia which have been recorded throughout the South Atlantic Basin. Well-preserved belemnite specimens display an oxygen-isotope range between +0.08 and -2.22? (PDB, Peedee belemnite international standard) and a carbon-isotope range from +2.35 to -1.33? (PDB). Delta13C values become increasingly negative through the Late Jurassic-Early Cretaceous and in concert with the 87Sr/86Sr data reveal a trend that could be accounted for by increasing levels of weathering and erosion. The oxygen-isotope data if interpreted in terms of palaeotemperature are consistent with warm palaeotemperatures in the Kimmeridgian and slightly cooler temperatures for the Tithonian and Early Cretaceous parts of the succession. The proposed relative Kimmeridgian warmth (based upon strontium-isotope age assignments) is thus in good agreement with other published palaeotemperature records.

Stable isotope stratigraphy of ODP Site 167-1014

Late Quaternary oxygen (d18O) and carbon (d13C) isotopic records for the benthic foraminifer Uvigerina and the planktonic foraminifer Globigerina bulloides are presented for the upper 20 meters composite depth sediment sequence of Ocean Drilling Program Site 1014, Tanner Basin, in the outer California Borderland province. The benthic oxygen isotopic record documents a continuous >160-k.y. sequence from marine isotope Stage (MIS) 6 to the present day. The record closely resembles other late Quaternary North Pacific benthic isotope records, as well as the well-dated deep-sea sequence (SPECMAP), and thus provides a detailed chronologic framework. Site 1014 provides a useful record of the California response to climate change as it enters the southern California Border-land. Sedimentation rates are relatively constant and high (~11.5 cm/k.y. ). The planktonic foraminiferal record is well pre-served except during marine isotope Substages 5b and 5d, when normally high G. bulloides abundance is strongly diminished as a result of dissolution. The planktonic oxygen isotopic shift of ~3 per mil between the last glacial maximum and the Holocene suggests a surface water temperature shift of <7°C, similar to estimates from Hole 893A (Leg 146) to the north. Unlike Santa Barbara Basin, G. bulloides d18O values during the last interglacial (MIS 5) at Site 1014 were significantly higher than during the Holocene. In particular, marine isotope Substage 5e (Eemian) was ~0.8 per mil higher. This is unlikely to reflect a cooler Eemian but is instead the result of preferential dissolution of thin-shelled (low d18O) specimens during this interval. In this mid-depth basin, a large benthic d18O shift during Termination I suggests dramatic temperature and salinity changes in response to switches in the source of North Pacific Intermediate Water. Although d13C values of the planktonic foraminifer G. bulloides are in disequilibria with seawater and hence interpretations are limited, the G. bulloides record exhibits several negative d13C excursions found at other sites in the region (Sites 1017 and 893). This indicates a response of G. bulloides d13C to regional surface water processes along the southern California margin. A general increase in benthic carbon isotopic values (-1.75 per mil to -0.75 per mil) in Tanner Basin during the last 200 k.y. is overprinted with smaller fluctuations correlated with climate change. The coolest intervals during the last glacial maximum (MISs 2 and 4) exhibit lower benthic d13C values, which correlate with global 13C shifts. The opposite relationship is exhibited during the last interglacial before 85 ka, when lower benthic d13C values are associated with warmer intervals (marine isotope Substages 5c and 5e) of the last interglacial. These time intervals were also marked by decreased intermediate water ventilation. Increased dissolution and organic accumulation during Substages 5b and 5d are anticorrelated with the benthic d13C record. These results suggest that a delicate balance in intermediate water d13C has existed between the relative influences of global 13C and regional ventilation changes at the 1165-m water depth of Site 1014.

Pleistocene calcareous nannofossil stratigraphy for ODP Leg 177, Atlantic sector of the Southern Ocean

Seven Ocean Drilling Program (ODP) sites recovered during ODP Leg 177 in the Atlantic sector of the Southern Ocean were analyzed to study the Pleistocene calcareous nannofossil record. Calcareous nannofossil events previously described from intermediate and low latitudes were identified and calibrated with available geomagnetic and stable isotope stratigraphic data. In general, Pleistocene southern high latitude calcareous nannofossil events show synchronicity with those observed from warm and temperate latitudes. The first occurrence (FO) of Emiliania huxleyi and the last occurrence (LO) of Pseudoemiliania lacunosa are observed in marine isotope stages (MIS) 8 and 12, respectively. A reversal in abundance between Gephyrocapsa muellerae and E. huxleyi is observed at MIS 5. MIS 6 is characterized by an increase in G. muellerae and MIS 7 features a dramatic decrease in the proportion of Gephyrocapsa caribbeanica. This latter species began to increase its proportions from MIS 14 to 13. The LO of Reticulofenestra asanoi is observed within subchron C1r.1r and the FO of R. asanoi occurs at the top of C1r.2r. A reentry of medium-sized Gephyrocapsa can be identified in some cores during subchron C1r.1n. The LO of large morphotypes of Gephyrocapsa is well correlated through the studied area, and occurs during the middle-low part of subchron C1r.2r,synchronous with other oceanic regions. The FO of Calcidiscus macintyrei and FO of medium-sized Gephyrocapsa occur in the studied area close to 1.6 Ma.

North Atlantic late Miocene stable-isotope stratigraphy, biostratigraphy, and magnetostratigraphy

Upper Miocene foraminiferal nannofossil ooze and chalk from DSDP Hole 552A in the northeast Atlantic Ocean have been closely sampled for biostratigraphic, paleomagnetic, and stable-isotopic studies. Sampling at 10-cm intervals resulted in an uppermost Miocene isotope stratigraphy with a 1000- to 3000-yr. resolution. Covariance in benthic (Planulina wuellerstorfi) and planktonic (Globigerina bulloides) foraminiferal d18O records is taken as evidence for variability in continental ice volume. Our best estimate is that glacial maxima occurred at -5.0 and ~ 5.5 Ma and lasted no more than 20,000 yrs. These events probably lowered sea level by 60 m below the latest Miocene average. There is little oxygen-isotope evidence, however, for a prolonged glaciation during the last 2 m.y. of the late Miocene. High- and low-frequency variability in the d13C record of foraminifers is useful for correlation among North Atlantic DSDP Sites 408, 410, 522, 610, and 611, and for correlation with sites in other oceans. Similar d13C changes are seen in P. wuellerstorfi and G. bulloides, but the amplitude of the signal is always greater in G. bulloides. Variability in d13C common to both species probably reflects variability in the d13C of total CO2 in seawater. Major long-term features in the d13C record include a latest Miocene maximum (P. wuellerstorfi = 1.5 per mil ) in paleomagnetic Chron 7, an abrupt decrease in d13C at -6.2 Ma, and a slight increase at -5.5 Ma. The decrease in d13C at -6.2 Ma, which has been paleomagnetically dated only twice before, occurs in the upper reversed part of Chronozone 6 at Holes 552A and 611C, in excellent agreement with earlier studies. Cycles in d13C with a period of ~ 10 4 yrs. are interpreted as changes in seawater chemistry, which may have resulted from orbitally induced variability in continental biomass. Samples of P. wuellerstorfi younger than 6 Ma from throughout the North Atlantic have d13C near lo, on average ~ l per mil greater than samples of the same age in the Pacific Ocean. Thus, there is no evidence for cessation of North Atlantic Deep Water production resulting from the Messinian "salinity crisis." Biostratigraphic results indicate continuous sedimentation during the late Miocene after about -6.5 Ma at Hole 552A. Nannofossil biostratigraphy is complicated by the scarcity of low-latitude marker species, but middle and late Miocene Zones NN7 through NN11 are recognized. A hiatus is present at -6.5 Ma, on the basis of simultaneous first occurrences of Amaurolithusprimus, Amaurolithus delicatus, Amaurolithus amplificus, and Scyphosphaera globulata. The frequency and duration of older hiatuses increase downsection in Hole 552A, as suggested by calcareous nannofossil biostratigraphy and magnetostratigraphy. Paleomagnetic results at Hole 552A indicate a systematic pattern of inclination changes. Chronozone 6 was readily identified because of its characteristic nannoflora (sequential occurrences of species assigned to the genus Amaurolithus) and the d13C decrease in foraminifers, but its lower reversed interval is condensed. Only the lower normal interval of Chronozone 5 was recognized at Hole 552A; the upper normal interval and the lowest Gilbert sediment are not recognized, owing to low intensity of magnetization and to coring disturbance. Interpreting magnetic reversals below Chronozone 6 was difficult because of hiatuses, but a lower normally magnetized interval is probably Chronozone 7. Correlation between DSDP Hole 552A and other North Atlantic sites is demonstrated using coiling direction changes in the planktonic foraminifer Neogloboquadrina. At most sites this genus changed its coiling preference from dominantly right to dominantly left during the late Miocene. At Hole 552A this event probably occurred about 7 m.y. ago. At the same time, P. wuellerstorfi had maximum d13C values. A similar d13C maximum and coiling change occurred together in Chron 7 at Hole 611C, and at Hole 610E. In sediment younger than -5.5 Ma, the coiling of small Neogloboquadrina species is random, but the larger species N. atlantica retains preferential left coiling.

Sr stratigraphy and biostratigraphy for samples from DSDP Hole 32-305 and ODP Hole 123-766A

The strontium isotope ratios (87Sr/86Sr) of marine barite microcrystals separated from Cretaceous sedimentary deposits from Ocean Drilling Program and Deep Sea Drilling Project sites from the Pacific and Indian Oceans have been compared to the composite Sr isotope curve of McArthur et al. The barite in these cores accurately recorded the seawater 87Sr/86Sr ratio, thereby reaffirming the composite Cretaceous strontium curve. Moreover, marine barite is a more reliable recorder of 87Sr/86Sr than is carbonate in sedimentary deposits with high clay content, thereby providing an opportunity for Sr isotope stratigraphy and dating in carbonate-poor or diagenetically altered sections. We have used the barite-derived Sr isotope record to refine the biostratigraphic age models of the sites investigated.

Planktonic foraminifera stratigraphy of ODP Holes 198-1209C and 198-1211C

During Leg 198, the Cretaceous/Paleocene (K/P) boundary was recovered in a remarkable set of cores in nine separate holes at Sites 1209, 1210, 1211, and 1212 on the Southern High of Shatsky Rise. The boundary succession includes an uppermost Maastrichtian white to very pale orange, slightly indurated nannofossil ooze overlain by lowermost Paleocene grayish orange foraminiferal ooze. The boundary between the uppermost Maastrichtian and the lowermost Paleocene is clearly bioturbated. The contact surface is irregular, and pale orange burrows extend 10 cm into the white Maastrichtian ooze. Preliminary investigations conducted on board revealed that the deepest sections of these burrows yielded highly abundant, minute planktonic foraminiferal assemblages dominated by Guembelitria with rare Hedbergella holmdelensis and Hedbergella monmouthensis, possibly attributable to the lowermost Paleocene Zone P0. The substantial thickness of the uppermost Maastrichtian Micula prinsii (CC26) nannofossil Zone and the lowermost Danian Parvularugoglobigerina eugubina (Palpha) foraminiferal Zone suggested that the K/P boundary was rather expanded compared to the majority of deep-sea sites (see Bralower, Premoli Silva, Malone, et al., 2002, doi:10.2973/odp.proc.ir.198.2002). This data report concerns the planktonic foraminiferal biostratigraphy across the K/P boundary in Hole 1209C, the shallowest site (2387 m water depth), and in Hole 1211C, the deepest site (2907 m water depth), where the foraminiferal record across the boundary appeared to be best preserved.

Oligocene strontium isotope stratigraphy of Indian Ocean sediments

Strontium isotope (87Sr/86Sr) ages have been established for Oligocene samples of Leg 119 Site 744, Leg 120 Sites 747 and 748, and Leg 121 Sites 756 and 757. Ages were determined using the strontium isotope age equation of Miller et al. (1988) and preliminary correlations have been made with available nannofossil biostratigraphy. The strontium isotope ages calculated here augment biostratigraphy, which for the Oligocene is characterized by long biozones, and provide additional detail where the paleomagnetic record is not clear (Sites 756 and 757). Results from the lower latitude Ninetyeast Ridge sites where standard calcareous nannofossil datums are present are compared to those of the higher latitude Kerguelen Plateau sites in order to examine biostratigraphic events across latitude in the Indian Ocean. The 87Sr/86Sr determined ages are used here as a tool for correlation.