Datum events and their estimated magnetochronology at DSDP Site 72-516

Calcareous plankton biostratigraphy (foraminifers and nannoplankton) and magnetostratigraphy of the upper Oligocene to Pleistocene have been studied in hydraulic piston Cores 516-1 to 516-44, 516A-5 to 516A-11, and 516F-1 to 516F-11, Rio Grande Rise (water depth 1313 m). Some 80 biostratigraphic datum events have been correlated to the magnetic polarity stratigraphy over an interval representing the Matuyama to Chron 5, and Chrons 16 to 23. Coring disturbance and biostratigraphic evidence of a condensed section preclude unambiguous identification of polarity or biostratigraphic events over an approximately 30-m interval in the middle and upper Miocene. Sedimentation rates varied considerably during the Neogene, but an abnormally thick upper Oligocene and lower Miocene section allows a high degree of magnetobiochronologic resolution. A new planktonic foraminiferal zonation for the Miocene completes the midlatitude Neogene zonation of the South Atlantic. Important magnetobiostratigraphic correlations at Site 516 and their estimated magnetochronology include: (1) Oligocene/ Miocene boundary = first appearance datum (FAD) Globorotalia kugleri = last appearance datum (LAD) Reticulofenestra bisecta = mid-Anomaly 6C (Chron 23) = 23.7 Ma; (2) Aquitanian/Burdigalian boundary = LAD G. kugleri = between base Anomaly 6A and top of unnumbered anomaly between 6A and 6B (Chron 21) = 21.8 Ma; (3) Zone N6/N7 boundary = LAD Catapsydrax dissimilis (= FAD G. pseudomiozea and G. zealandica) = Chron 16/17 boundary = 17.6 Ma; (4) early/middle Miocene (= Burdigalian/Langhian) boundary = FAD Praeorbulina sicana = midpart of Anomaly 5C (Chron 16) = 16.6 Ma or FAD P. glomerosa = just above Anomaly 5C (inferred) = 16.3 Ma; (5) Zone N8/N9 boundary = FAD Orbulina suturalis above Anomaly 5C (later part Chron 16, inferred); (6) Miocene/ Pliocene boundary = LAD Globoquadrina dehiscens LAD Globorotalia lenguaensis = basal Gilbert Chron = 5.3 Ma.

Occurrence and stratigraphy of Coccolithus pelagicus in ODP Hole 120-747A

A record based on counts of the relative abundance of the dominant calcareous nannofossil taxa Coccolithus pelagicus and Reticulofenestra spp. in sediments recovered from Ocean Drilling Program Hole 747A (Kerguelen Plateau, Southern Indian Ocean) is established in this paper. This record (17 m.y. long) virtually spans the entire Miocene. Broad, steplike variations in the abundance of C. pelagicus range between 0% and 96%. Based on these variations, five stratigraphic units characterized by high abundance in C. pelagicus are delineated. We suggest that these variations are caused by water-mass movements (such as the north/south shifting of a front). This pronounced signal is compared with paleoceanographic events revealed by isotopic (d18O and d13C) studies. The five defined units are tentatively correlated to well-known global isotopic events. In particular, Units A and D correlate respectively with the Oligocene/Miocene boundary glaciation and the middle Miocene cooling event. Time-series analysis indicates the presence of the three main periodic components of the eccentricity of the Earth's orbit. A 200-k.y. cycle is also present. The stratigraphic and paleoceanographic significance of this record is discussed.

Benthic foraminiferal biofacies and stable isotopic record of St. Stephens Quarry, Alabama

We integrate upper Eocene-lower Oligocene lithostratigraphic, magnetostratigraphic, biostratigraphic, stable isotopic, benthic foraminiferal faunal, downhole log, and sequence stratigraphic studies from the Alabama St. Stephens Quarry (SSQ) core hole, linking global ice volume, sea level, and temperature changes through the greenhouse to icehouse transition of the Cenozoic. We show that the SSQ succession is dissected by hiatuses associated with sequence boundaries. Three previously reported sequence boundaries are well dated here: North Twistwood Creek-Cocoa (35.4-35.9 Ma), Mint Spring-Red Bluff (33.0 Ma), and Bucatunna-Chickasawhay (the mid-Oligocene fall, ca. 30.2 Ma). In addition, we document three previously undetected or controversial sequences: mid-Pachuta (33.9-35.0 Ma), Shubuta-Bumpnose (lowermost Oligocene, ca. 33.6 Ma), and Byram-Glendon (30.5-31.7 Ma). An ~0.9 per mil d18O increase in the SSQ core hole is correlated to the global earliest Oligocene (Oi1) event using magnetobiostratigraphy; this increase is associated with the Shubuta-Bumpnose contact, an erosional surface, and a biofacies shift in the core hole, providing a first-order correlation between ice growth and a sequence boundary that indicates a sea-level fall. The d18O increase is associated with a eustatic fall of ~55 m, indicating that ~0.4 per mil of the increase at Oi1 time was due to temperature. Maximum d18O values of Oi1 occur above the sequence boundary, requiring that deposition resumed during the lowest eustatic lowstand. A precursor d18O increase of 0.5 per mil (33.8 Ma, midchron C13r) at SSQ correlates with a 0.5 per mil increase in the deep Pacific Ocean; the lack of evidence for a sea-level change with the precursor suggests that this was primarily a cooling event, not an ice-volume event. Eocene-Oligocene shelf water temperatures of ~17-19 °C at SSQ are similar to modern values for 100 m water depth in this region. Our study establishes the relationships among ice volume, d18O, and sequences: a latest Eocene cooling event was followed by an earliest Oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall.

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.

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.

Stable carbon isotope record of benthic foraminifera across the Paleocene-Eocene thermal maximum in the New Jersey Coastal Plain

In the New Jersey Coastal Plain, a silty to clayey sedimentary unit (the Marlboro Formation) represents deposition during the Paleocene-Eocene thermal maximum (PETM). This interval is remarkably different from the glauconitic sands and silts of the underlying Paleocene Vincentown and overlying Eocene Manasquan Formation. We integrate new and published stable isotope, biostratigraphic, lithostratigraphic and ecostratigraphic records, constructing a detailed time frame for the PETM along a depth gradient at core sites Clayton, Wilson Lake, Ancora and Bass River (updip to downdip). The onset of the PETM, marked by the base of the carbon isotope excursion (CIE), is within the gradual transition from glauconitic silty sands to silty clay, and represented fully at the updip sites (Wilson Lake and Clayton). The CIE "core" interval is expanded at the updip sites, but truncated. The CIE "core" is complete at the Bass River and Ancora sites, where the early part of the recovery is present (most complete at Ancora). The extent to which the PETM is expressed in the sediments is highly variable between sites, with a significant unconformity at the base of the overlying lower Eocene sediments. Our regional correlation framework provides an improved age model, allowing better understanding of the progression of environmental changes during the PETM. High-resolution benthic foraminiferal data document the change from a sediment-starved shelf setting to a tropical, river-dominated mud-belt system during the PETM, probably due to intensification of the hydrologic cycle. The excellent preservation of foraminifera during the PETM and the lack of severe benthic extinction suggest there was no extreme ocean acidification in shelf settings.

Osmium, and stable carbon and oxygen isotope record accross the PETM

In the latest Paleocene an abrupt shift to more negative d13C values has been documented at numerous marine and terrestrial sites (Bralower et al., 1997, doi:10.1130/0091-7613(1997)025<0963:HRROTL>2.3.CO;2; Cramer et al., 1999; Kaiho et al., 1996, doi:10.1029/96PA01021; Kennett and Stott, 1991, doi:10.1038/353225a0; Koch et al., 1992, doi:10.1038/358319a0; Stott et al., 1996; Thomas and Shackleton, 1996, doi:10.1144/GSL.SP.1996.101.01.20; Zachos et al., 1993). This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°-6°C (Kennett and Stott, 1991, doi:10.1038/353225a0) and more moderate warming in the subtropics (Thomas et al., 1999, doi:10.1029/1999PA900031). Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a >10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate (Walker et al., 1981). Estimates of the duration of late Paleocene CIE (Bains et al., 1999, doi:10.1126/science.285.5428.724; Bralower et al., 1997, doi:10.1130/0091-7613(1997)025<0963:HRROTL>2.3.CO;2; Norris and Röhl, 1999, doi:10.1038/44545; Röhl et al., 2000, doi:10.1130/0091-7613(2000)28<927:NCFTLP>2.0.CO;2) in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104-105 years. This interpretation requires that the late Paleocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.

Integrated Paleocene calcareous plankton magnetobiochronology of DSDP Hole 43-384 in the Northwest Atlantic Ocean

At Deep Sea Drilling Site 384 (J-Anomaly Ridge, Grand Banks Continental Rise, NW Atlantic Ocean) Paleocene nannofossil chalks and oozes (~70 m thick) are unconformably/disconformably underlain (~168 m; upper Maastrichtian) and overlain (~98.7 m; upper lower Eocene) by sediments of comparable lithologies. The chalks are more indurated in stratigraphically higher levels of the Paleocene reflecting increasing amounts of biosiliceous (radiolarians and diatoms) components. This site serves as an excellent location for an integrated calcareous and siliceous microfossil zonal stratigraphy and stable isotope stratigraphy. We report the results of a magnetostratigraphic study which, when incorporated with published magnetostratigraphic results, reveals an essentially complete magnetostratigraphic record spanning the interval from Magnetochron C31n (late Maastrichtian) to C25n (partim) (late Paleocene, Thanetian). Integrated magnetobiochronology and stable isotope stratigraphy support the interpretation of, and constrain the estimated duration of, a short hiatus (~0.9 my) within the younger part of Chron C29r (including the K/P boundary) and an ~6 my hiatus separating upper Paleocene (Magnetozone C25n) and upper lower Eocene (Magnetozone C22r) sediments. Some 30 planktonic foraminiferal datum levels [including the criteria used to denote the Paleocene planktonic foraminiferal (sub)tropical zonal scheme of Berggren and Miller, Micropaleontology 34 (4) (1988) 362-380 and Berggren et al., SEPM Spec. Publ. 54 (1995) 129-212, Geol. Soc. Am. Bull. 107 (11) (1995) 1272-1287], and nearly two dozen calcareous nannoplankton datum levels have been recognized and calibrated to the magnetochronology. Planktonic foraminiferal Subzones P4a and P4b of (upper Paleocene) Zone P4 are emended/redefined based on the discovery of a longer stratigraphic extension of Acarinina subsphaerica (into at last Magnetozone C25n). Stable isotope stratigraphies from benthic foraminifera and fine fraction (<38 µm) carbonate have been calibrated to the biochronology and magnetostratigraphy. A minimum in benthic foraminifer delta13C was reached near the Danian/Selandian boundary (within Chron C26r, planktonic foraminiferal Zone P3a and calcareous nannoplankton Zone NP4) and is followed by the rise to maximum delta13C values in the late Thanetian (near the base of C25n, in Zone P4c and NP9a, respectively) that can be used for global correlation in the Paleocene.

Magnetobiostratigraphy and stable isotope record of Paleocene sediments from ODP Hole 122-761B in the subtropical Indian Ocean

Surface and deep water circulation patterns in the eastern Indian Ocean during the Paleocene Epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of Ocean Drilling Program Hole 761B, drilled on the Wombat Plateau. A combination of magnetostratigraphy, biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous, or nearly continuous sedimentation through the Paleocene are punctuated by a series of hiatuses, some of which exceeding a duration of 1 Myr. Therefore, our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions. We compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from Hole 761B with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern Indian Ocean. Although Site 761 was situated at low latitudes during the Paleocene, its surface waters were predominantly influenced by circulation originating from the Southern Ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients. We suggest that deep waters in the eastern Indian Ocean were not directly fed by the Southern or Tethys Oceans. Rather, the more negative delta13C composition of the bottom waters recorded by benthic foraminifera implies the presence and/or active contribution of aged deep waters from the Pacific during this time, at least prior to ~60.2 Ma and subsequent to ~59.0 Ma. The Indian continent, Ninetyeast Ridge, Kerguelen Plateau and Broken Ridge may have played a significant role as submarine barriers to deep water circulation during the Paleocene.

Stable isotope record and trace element ratios of Eocene and Oligocene foraminifers from ODP Site 120-748

Stable carbon and oxygen isotope analyses were conducted on well-preserved planktonic and benthic foraminifers from a continuous middle Eocene to Oligocene sequence at Ocean Drilling Program (ODP) Site 748 on the Kerguelen Plateau. Benthic foraminifer d18O values show a 1.0 per mil increase through the middle and upper Eocene, followed by a rapid 1.2 per mil increase in the lowermost Oligocene (35.5 Ma). Surface-dwelling planktonic foraminifer d18O values increase in the lowermost Oligocene, but only by 0.6 per mil whereas intermediate-depth planktonic foraminifers show an increase of about l.0 per mil. Benthic foraminifer d13C values increase by 0.9 per mil in the lowermost Oligocene at precisely the same time as the large d18O increase, whereas planktonic foraminifer d13C values show little or no change. Site 748 oxygen isotope and paleontological records suggest that southern Indian Ocean surface and intermediate waters underwent significant cooling from the early to late Eocene. The rapid 1.2 per mil oxygen isotope increase recorded by benthic foraminifers just above the Eocene/Oligocene boundary represents the ubiquitous early Oligocene d18O event. The shift here is unique, however, as it coincided with the sudden appearance of ice-rafted debris (IRD), providing the first direct link between Antarctic glacial activity and the earliest Oligocene d18O increase. The d18O increase caused by the ice-volume change in the early Oligocene is constrained by (1) related changes in the planktonic to benthic foraminifer d18O gradient at Site 748 and (2) comparisons of late Eocene and early Oligocene planktonic foraminifer d18Ovalues from various latitudes. Both of these records indicate that 0.3 per mil to 0.4 per mil of the early Oligocene d18O increase was ice-volume related.

Stable carbon and oxygen isotope record of planktonic foraminifera across the Paleocene-Eocene boundary

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic 'events' near the Paleocene-Eocene boundary provide strati-graphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera bio-stratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean's carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO2. As a consequence of this exchange of 12C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.