Volcaniclastic sediments of ODP Leg 136 sites

Sediment cores recovered from three holes drilled during Ocean Drilling Program Leg 136 include volcaniclastics probably derived from the Hawaiian islands. The volcaniclastics shallower than 10 meters below seafloor are fresh and are composed of basaltic glass (sideromelane), basaltic fragments (mainly tachylite), plagioclase, olivine, pyroxene, and opaque minerals. Most of these glasses are probably products of hydrovolcanism. Visibly, some of these volcaniclastics are recognized as bedded ash layers having thicknesses that range from 5 to 10 cm. However, many volcaniclastics are disrupted by bioturbation to some degree, and are sometimes totally mixed with ambient brown clays. No visible correlative ash layer among these holes was found. It seems that many ash layers thinner than the bedded layers were disrupted by bioturbation because of the low sedimentation rate of volcaniclastics. The volcaniclastics were probably transported one of two ways: through air fall and pelagic settling or through turbidity-current transport. Other archipelagic apron volcaniclastic sediments of volcanic seamounts suggest that turbidite transport is the favored explanation of origin.

Ice-rafted debris in sites of ODP Leg 114

All holes drilled during Leg 114 contained ice-rafted debris. Analysis of samples from Hole 699A, Site 701, and Hole 704A yielded a nearly complete history of ice-rafting episodes. The first influx of ice-rafted debris at Site 699, on the northeastern slope of the Northeast Georgia Rise, occurred at a depth of 69.94 m below seafloor (mbsf) in sediments of early Miocene age (23.54 Ma). This material is of the same type as later ice-rafted debris, but represents only a small percentage of the coarse fraction. Significant ice-rafting episodes occurred during Chron 5. Minor amounts of ice-rafted debris first reached Site 701, on the western flank of the Mid-Atlantic Ridge (8.78 Ma at 200.92 mbsf), and more arrived in the late Miocene (5.88 Ma). The first significant quantity of sand and gravel appeared at a depth of 107.76 mbsf (4.42 Ma). Site 704, on the southern part of the Meteor Rise, received very little or no ice-rafted debris prior to 2.46 Ma. At this time, however, the greatest influx of ice-rafted debris occurred at this site. This time of maximum ice rafting correlates reasonably well with influxes of ice-rafted debris at Sites 701 (2.24 Ma) and 699 (2.38 Ma), in consideration of sample spacing at these two sites. These peaks of ice rafting may be Sirius till equivalents, if the proposed Pliocene age of Sirius tills can be confirmed. After about 1.67 Ma, the apparent mass-accumulation rate of the sediments at Site 704 declined, but with major fluctuations. This decline may be the result of a decrease in the rate of delivery of detritus from Antarctica due to reduced erosive power of the glaciers or a northward shift in the Polar Front Zone, a change in the path taken by the icebergs, or any combination of these factors.

Microfossils detected in a block of ancient dense clay coated with a ferromanganese crust, Clarion-Clipperton Province, East Equatorial Pacific

The area in study is characterized by a regional stratigraphic hiatus from Early Miocene to Quaternary. Deposits from Late Eocene to Early Miocene occur on the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of Oligocene age, formed on surface layers of Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. Composition of found radiolarian and diatomaceous complexes proved that the crust formed in Quaternary on an eroded surface of Late Oligocene clay. In Quaternary Neogene sediments were eroded and washed away by bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the "Glacial Pleistocene". The erosion could be initiated by loosening and resuspension of surface sediments resulting from seismic activity generated by strong earthquakes in the Central America subduction zone. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area in study a common reason and a common Quaternary interval for formation of the following features is supposed: a regional stratigraphic hiatus, formation of residual nodule fields, and position of ancient nodules on the surface of Quaternary sediments.

Geochemistry of carbonate cements of ODP Leg 112 samples

The evolution of pore fluids migrating through the forearc basins, continental massif, and accretionary prism of the Peru margin is recorded in the sequence of carbonate cements filling intergranular and fracture porosities. Petrographic, mineralogic, and isotopic analyses were obtained from cemented clastic sediments and tectonic breccias recovered during Leg 112 drilling. Microbial decomposition of the organic-rich upwelling facies occurs during early marine diagenesis, initially by sulfate-reduction mechanisms in the shallow subsurface, succeeded by carbonate reduction at depth. Microcrystalline, authigenic cements formed in the sulfate-reduction zone are 13C-depleted (to -20.1 per mil PDB), and those formed in the carbonate-reduction zone are 13C-enriched (to +19.0 per mil PDB). Calcium-rich dolomites and near-stoichiometric dolomites having uniformly heavy d18O values (+2.7 to +6.6 per mil PDB) are typical organic decomposition products. Quaternary marine dolomites from continental-shelf environments exhibit the strongest sulfate-reduction signatures, suggesting that Pleistocene sea-level fluctuations created a more oxygenated water column, caused periodic winnowing of the sediment floor, and expanded the subsurface penetration of marine sulfate. We have tentatively identified four exotic cement types precipitated from advected fluids and derived from the following diagenetic environments: (1) meteoric recharge, (2) basalt alteration, (3) seafloor venting and (4) hypersaline concentration. Coarsely crystalline, low-magnesium (Lo-Mg) calcite cements having pendant and blocky-spar morphologies, extremely negative d18O values (to -7.5 per mil PDB), and intermediate d13C values (-0.4 per mil to +4.6 per mil PDB) are found in shallow-marine Eocene strata. These cements are evidently products of meteoric diagenesis following subaerial emergence during late Eocene orogenic movements, although the strata have since subsided to greater than 4,000 m below sea level. Lo-Mg calcite cements filling scaly fabrics in the late Miocene accretionary prism sediments are apparently derived from fluids having lowered magnesium/calcium (Mg/Ca) and 18O/16O ratios; such fluids may have reacted with the subducting oceanic crust and ascended through the forearc along shallow-dipping thrust faults. Micritic, high-magnesium (Hi-Mg) calcite cements having extremely depleted d13C values (to -37.3%c PDB), and a benthic fauna of giant clams (Calyptogena sp.) supported by a symbiotic, chemoautotrophic metabolism, provide evidence for venting of methane-charged waters at the seafloor. Enriched d18O values (to +6.6%c PDB) in micritic dolomites from the continental shelf may be derived from hypersaline fluids that were concentrated in restricted lagoons behind an outer-shelf basement ridge, reactivated during late Miocene orogenesis.

Chemical and isotopic composition of interstitial waters and hydrocarbon composition at ODP Site 184-1146

Bottom-simulating reflectors were observed beneath the southeastern slope of the Dongsha Islands in the South China Sea, raising the potential for the presence of gas hydrate in the area. We have analyzed the chemical and isotopic compositions of interstitial water, headspace gas, and authigenic siderite concretions from Site 1146. Geochemical anomalies, including a slight decrease of chlorine concentration in interstitial water, substantial increase of methane concentration in headspace gas, and 18O enrichment in the authigenic siderite concretion below 400 meters below seafloor are probably caused by the decomposition of gas hydrate. The low-chlorine pore fluids contain higher molecular-weight hydrocarbons and probably migrate to Site 1146 along faults or bedded planes.

Selected age-diagnostic datums of ODP Site 184-1148

The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of ~20-30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene-Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (~33-28.5 Ma), changing spreading southward (28.5-23 Ma), stable spreading to end of spreading (23-15 Ma), post-spreading balance (15-9 Ma), further modification and monsoon influence (9-5 Ma), and glacial prevalence (5-0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma.

Bedform measurements from the San Francisco Bay Coastal System

The morphology of ~45,000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the San Francisco Bay estuary and adjacent outer coast. The spatially-averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport. Additionally, the region-wide, ebb-oriented asymmetry of 5% suggests net seaward-directed transport within the estuarine-coastal system, with significant seaward asymmetry at the mouth of San Francisco Bay (11%), through the northern reaches of the Bay (7-8%), and among the largest bedforms (21% for lambda > 50 m). This general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary, particularly along clearly defined seaward transport pathways, will limit the supply of sand to chronically eroding, open-coast beaches. The bedform asymmetry measurements significantly agree (up to ~ 76%) with modeled annual residual transport directions derived from a hydrodynamically-calibrated numerical model, and the orientation of adjacent, flow-sculpted seafloor features such as mega-flute structures, providing a comprehensive validation of the technique. The methods described in this paper to determine well-defined, cross-validated sediment transport pathways can be applied to estuarine-coastal systems globally where bedforms are present. The results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply-related impacts.

Grain size distribution and clay mineralogy of upper Miocene sediments of ODP Hole 107-652A

The upper Miocene sedimentary sequence of Site 652, located on the lower continental margin of eastern Sardinia, was cored and logged during Ocean Drilling Program (ODP) Leg 107. Geophysical and geochemical logs from the interval 170-365 m below seafloor (mbsf), as well as various core measurements (CaCO3, grain size, X-ray diffraction), provide a mineralogical-geochemical picture that is interpreted in the framework of the climatic and tectonic evolution of the western Tyrrhenian. The results indicate the presence of short- and long-term mineralogical variations. Short-term variations are represented by calcium-carbonate fluctuations in which the amount of CaCO3 is correlated to the grain size of the sediments; coarser sediments are associated with high carbonate content and abundant detrital material. Long-term variation corresponds to a gross grain-size change in the upper part of the sequence, where predominantly fine-grained sediments may indicate a gradual deepening of the lacustrine basin towards the Pliocene. Regional climatic changes and rift-related tectonism are possible causes of this variability in the sedimentation patterns. The clay association is characterized by chlorite, illite, and smectite as dominant minerals, as well as mixed-layers clays, kaolinite, and palygorskite. Chlorite, mixed-layers clays, and illite increase at the expense of smectite below the pebble zone (335 mbsf). This is indicative of diagenetic processes related to the high geothermal gradient and to the chemistry of the evaporative pore waters, rather than to changes in the depositional environment.

Helium isotope ratios and sedimentation rate models of ODP holes

A continuous age model for the brief climate excursion at the Paleocene-Eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3He (3He[ET]) to the seafloor. 3He[ET] measurements from ODP Site 690 provide quantitative evidence for the rapid onset (seafloor methane hydrate, as the proximal cause of the event. However, the 3He[ET] technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre-event values. The 3He[ET]-based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle, and so may indicate additional or accelerated mechanisms of carbon removal from the ocean-atmosphere system during this period. 3He[ET] was also measured at ODP Site 1051 to test the validity of the Site 690 chronology. Comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at Site 1051, an observation consistent with sediment structures and previous age modeling efforts. The Site 1051 age model shows a ~30 kyr period in which climate proxies return toward pre-event values, after which they remain invariant for ~80 kyr. If this rise represents the recovery interval identified at Site 690, then the 3HeET-based age models of the two sites are in good agreement. However, alternative interpretations are possible, and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion. Regardless of these details, this work shows that the 3HeET technique can provide useful independent evidence for the development and testing of astronomically calibrated age models.

(Table 5) Quaternary paleoproductivity of organic carbon in oceans based on DSDP cores

By analogy with the present-day ocean, primary productivity of paleoceans can be reconstructed using calculations based on content of organic carbon in sediments and their accumulation rates. Results of calculations based on published data show that primary productivity of organic carbon, mass of phosphorus involved in the process, and content of phosphorus in ocean waters were relatively stable during Cenozoic and Late Mesozoic. Prior to precipitation on the seafloor together with biogenic detritus, dissolved phosphorus could repeatedly be involved in the biogeochemical cycle. Therefore, only less than 0.1% of phosphorus is retained in bottom sediments. Bulk phosphorus accumulation rate in ocean sediments is partly consistent with calculated primary productivity. Some epochs of phosphate accumulation also coincide with maxima of primary productivity and minima of the fossilization coefficient of organic carbon. The latter fact can testify to episodes of acceleration of organic matter mineralization and release of phosphorus from sediments leading to increase in the phosphorus reserve in paleoceans and phosphate accumulation in some places.

Helium concentrations of late Miocene sediments

Throughout the history of the Solar System, Earth has been bombarded by interplanetary dust particles (IDPs), which are asteroid and comet fragments of diameter 1-1,000 µm. The IDP flux is believed to be in quasi-steady state: particles created by episodic main belt collisions or cometary fragmentation replace those removed by comminution, dynamical ejection, and planetary or solar impact. Because IDPs are rich in 3He, seafloor sediment 3He concentrations provide a unique means of probing the major events that have affected the IDP flux and its source bodies over geological timescales (Farley et al., 1998, doi:10.1126/science.280.5367.1250; Takayanagi and Ozima, 1987, doi:10.1029/JB092iB12p12531; Farley, 1995, doi:10.1038/376153a0; Kortenkamp and Dermott, 1998, doi:10.1126/science.280.5365.874). Here we report that collisional disruption of the >150-km-diameter asteroid that created the Veritas family 8.3 +/- 0.5 Myr ago (Nesvorny et al., 2003, doi:10.1086/374807) also produced a transient increase in the flux of interplanetary dust-derived 3He. The increase began at 8.2 +/- 0.1 Myr ago, reached a maximum of 4 times pre-event levels, and dissipated over 1.5 Myr. The terrestrial IDP accretion rate was overwhelmingly dominated by Veritas family fragments during the late Miocene. No other event of this magnitude over the past 10**8 yr has been deduced from main belt asteroid orbits. One remarkably similar event is present in the 3He record 35 Myr ago, but its origin by comet shower (Farley et al., 1998, doi:10.1126/science.280.5367.1250) or asteroid collision (Tagle and Claeys, 2004, doi:10.1126/science.1098481) remains uncertain.

Benthic foraminifera across the Cretaceous/Paleogene boundary in the Southern Ocean

The impact of an asteroid at the Cretaceous/Paleogene (K/Pg) boundary triggered dramatic biotic, biogeochemical and sedimentological changes in the oceans that have been intensively studied. Paleo-biogeographical differences in the biotic response to the impact and its environmental consequences, however, have been less well documented. We present a high-resolution analysis of benthic foraminiferal assemblages at Southern Ocean ODP Site 690 (Maud Rise, Weddell Sea, Antarctica). At this high latitude site, late Maastrichtian environmental variability was high, but benthic foraminiferal assemblages were not less diverse than at lower latitudes, in contrast to those of planktic calcifiers. Also in contrast to planktic calcifiers, benthic foraminifera did not suffer significant extinction at the K/Pg boundary, but show transient assemblage changes and decreased diversity. At Site 690, the extinction rate was even lower (~3%) than at other sites. The benthic foraminiferal accumulation rate varied little across the K/Pg boundary, indicating that food supply to the sea floor was affected to a lesser extent than at lower latitude sites. Compared to Maastrichtian assemblages, Danian assemblages have a lower diversity and greater relative abundance of heavily calcified taxa such as Stensioeina beccariiformis and Paralabamina lunata. This change in benthic foraminiferal assemblages could reflect post-extinction proliferation of different photosynthesizers (thus food for the benthos) than those dominant during the Late Cretaceous, therefore changes in the nature rather than in the amount of the organic matter supplied to the seafloor. However, severe extinction of pelagic calcifiers caused carbonate supersaturation in the oceans, thus might have given competitive advantage to species with large, heavily calcified tests. This indirect effect of the K/Pg impact thus may have influenced the deep-sea dwellers, documenting the complexity of the effects of major environmental disturbance.

Methane concentration profiles and isotopic composition of sediment cores from the Black Sea

We present high resolution profiles for the methane concentration and the carbon isotope composition of methane from surface sediments and from the sediment-water transition in the Black Sea. At shallow water sites methane migrates from the sediment into the water column, and the magnitude of this upward migrating flux depends on the depth of the sulfate-methane transition (SMT) in the sediment. The isotope data reveal that the sediments at shallow water sites are a source for methane depleted in 13C relative to the isotope composition of methane in the water column. At deep water sites the methane concentration first decreases with depth in the sediment to reach lowest values at the Unit I to Unit II transition. Below this transition the concentration increases again. Numerical modeling of methane concentration and isotope data shows that high methane oxidation rates occur in the surface sediment layer, indicating that the removal of methane in the surface sediments is not related to the anaerobic oxidation of methane coupled to sulfate reduction that occurs a few meters deep in the sediment, at the SMT. Instead, near-surface methane consumption in the euxinic Black Sea sediments appears to be related to lithological stratification. Furthermore, a map of the diffusive methane fluxes in the Black Sea surface sediments indicates that approximately half of the Black Sea seafloor acts as a sink for methane and thus limits the flux of methane to the atmosphere.

Lower Cretaceous radiolarians from the northwestern Australian margin

During Leg 123, abundant and well-preserved Neocomian radiolarians were recovered at Site 765 (Argo Abyssal Plain) and Site 766 (lower Exmouth Plateau). The assemblages are characterized by a scarcity or absence of Tethyan taxa. The Berriasian-early Aptian radiolarian record recovered at Site 765 is unique in its density of well-preserved samples and in its faunal contents. Remarkable contrasts exist between radiolarian assemblages extracted from claystones of Site 765 and reexamined DSDP Site 261, and faunas recovered from radiolarian sand layers of Site 765. Clay faunas are unusual in their low diversity of apparently ecologically tolerant species, whereas sand faunas are dominated by non-Tethyan species that have never been reported before. Comparisons with Sites 766 and 261, as well as sedimentological observations, lead to the conclusion that this faunal contrast results from a difference in provenance, rather than from hydraulic sorting. Biostratigraphic dating proved difficult principally because of the paucity or even absence of (Tethyan) species used in published zonations. In addition, published zonations are contradictory and do not reflect total ranges of species. Radiolarian assemblages recovered from claystones at Sites 765 and 261 in the Argo Basin reflect restricted oceanic conditions for the latest Jurassic to Barremian time period. Neither the sedimentary facies nor the faunal associations bear any resemblance to sediment and radiolarian facies observed in typical Tethyan sequences. I conclude that the Argo Basin was paleoceanographically separated from Tethys during the Late Jurassic and part of the Early Cretaceous by its position at a higher paleolatitude and by enclosing landmasses, i.e., northeastern India and the Shillong Block, which were adjacent to the northwestern Australian margin before the opening. Assemblages recovered from radiolarian sand layers are dominated by non-Tethyan species that are interpreted as circumantarctic. Their sudden appearance in the late Berriasian/early Valanginian pre-dates the oceanization of the Indo-Australian break-up (Ml 1, late Valanginian) by about 5 m.y., but coincides with a sharp increase in margin-derived pelagic turbidites. The Indo-Australian rift zone and its adjacent margins probably were submerged deeply enough to allow an intermittent "spillover" of circumantarctic cold water into the Argo Basin, creating increased bottom current activity. Circumantarctic cold-water radiolarians transported into the Argo Basin upwelled along the margin and died en masse. Concomitant winnowing by bottom currents led to their accumulation in distinct radiolarite layers. High rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with the two pronounced late Berriasian-early Valanginian lowstands in sea level. Hypothetically, both phenomena might have been caused by a glaciation on the Antarctic-Australian continent, which was for the first time isolated from the rest of Gondwana by oceanic seaways as a result of Jurassic and Early Cretaceous seafloor spreading. The absence of typical Tethyan radiolarian species during the late Valanginian to late Hauterivian period is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization (Mil) and rapid spreading between southeast India and western Australia. The reappearance and gradual increase in abundance and diversity of Tethyan forms along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the Barremian and early Aptian and may have resulted from the establishment of an oceanic connection with the Tethys Ocean during the early Aptian.

Miocene to Pliocene planktonic foraminifers in ODP Hole 134-832B

One hundred and sixty core samples were analyzed from Hole 832B to evaluate planktonic foraminiferal datum levels, and to zone and correlate the borehole succession. A total of 32 biostratigraphic events were recognized in the interval from Core 134-832B-59R through 134-832B-73R (702.49 through 846.4 meters below seafloor [mbsf]). These include 17 first appearance datum levels (FAD), 10 last appearance datum levels (LAD), and 5 coiling-change events in trochospiral species. The studied succession has been subdivided into nine planktonic foraminiferal zones (viz. downsequence N.22, N.21, N.20, N.19, N.18, N.17B, N.17A-N.16, N.15, N.8). The zonal index species occur in the expected stratigraphic order for zonal correlation, but some of the zonal boundaries may be diachronous compared to other localities in the western Pacific region. The FAD of Globorotalia (Truncorotalia) truncatulinoides (d' Orbigny) at 714.10 mbsf defines the boundary between the Zone N.22 and N.21; the boundary between Zones N.21 and N.20 at 741.73 mbsf is marked by the FAD of Globorotalia (Truncorotalia) tosaensis Takayanagi and Saito. The lower boundary of Zone N.20 is placed at 747.65 mbsf, based on the FAD of Globorotalia (Truncorotalia) crassaformis s.s. (Galloway and Wissler); the FAD of Sphaeroidinella dehiscens (Parker and Jones) at 756.61 mbsf defines the boundary between Zones N.18 and N.19. The FAD of Globorotalia (Globorotalia) tumida tumida (Brady) at 811.15 mbsf marks the boundary between Zones N.18 and N.17B. The boundary between Zones N.17B and N.17Ais placed at 843.52 mbsf, based on the FAD of Pulleniatina primalis Banner and Blow. A change in depositional conditions occurs at 846.4 mbsf just below the Zone N.17B lower boundary and is marked by the first appearance of abundant planktonic foraminifers in the region. The interval between 849.13 and 856.1 mbsf is placed in undifferentiated Zones N.17A and N.16, based on the rare occurrence of Neogloboquadrina acostaensis (Blow). The sparsely fossiliferous volcanic sandstone unit between 934.19 and 955.67 mbsf is positioned within Zone N.15 based on the presence of Globigerina (Zeaglobigerina) nepenthes Todd and Globigerinoides (Zeaglobigerina) druryi Arkers, and absence of N. acostaensis and Globorotalia (Jenkinsella) siakensis LeRoy. An unconformity between 955.67 and 971.80 mbsf may explain the absence of Zones N.14 through N.9. Basal Zone N.8 is recognized at 971.80 to 1008.60 mbsf by the presence of Globigerinoides sicanus De Stefani and the absence of Praeorbulina and Orbulina spp. The age of the succession between 702.49 and 1008.6 mbsf extends from the latest Pliocene or earliest Pleistocene (Zone N.22) to the earliest middle Miocene (Zone N.8). Among the datum levels evaluated here, the following events are considered to be the most reliable for time correlation in the studied region: the FADs of G. (T.) truncatulinoides, G. (T.) tosaensis, G. (T.) crassaformis, S. dehiscens, G. conglobatus (Brady), G. (G.) tumida tumida, and P. primalis; and the LADs of Globorotalia (Menardella) multicamerata Cushman and Jarvis, and Dentoglobigerina altispira altispira (Cushman and Jarvis). Application of a chronometric scale to part of the succession, suggests that the interval of calcareous sediment between 702.49 and 846.4 mbsf accumulated at about 30 m/m.y.