(Table 1) Position and astronomical ages of sedimentary cycles in the eastern Mediterranean Sea

An astronomically calibrated timescale has recently been established [Hilgen, 1991, doi:10.1016/0012-821X(91)90082-S; doi:10.1016/0012-821X(91)90206-W] for the Pliocene and earliest Pleistocene based on the correlation of dominantly precession controlled sedimentary cycles (sapropels and carbonate cycles) in Mediterranean marine sequences to the precession time series of the astronomical solution of Berger and Loutre [1991, doi:10.1016/0277-3791(91)90033-Q ] (hereinafter referred to as Ber90). Here we evaluate the accuracy of this timescale by (1) comparing the sedimentary cycle patterns with 65°N summer insolation time series of different astronomical solutions and (2) a cross-spectral comparison between the obliquity-related components in the 65°N summer insolation curves and high-resolution paleoclimatic records derived from the same sections used to construct the timescale. Our results show that the carbonate cycles older than 3.5 m.y. should be calibrated to one precession cycle older than previously proposed. Application of the astronomical solution of Laskar [1990, doi:10.1016/0019-1035(90)90084-M], (hereinafter referred to as La90) with present-day values for the dynamical ellipticity of the Earth and tidal dissipation by the Sun and Moon results in the best fit with the geological record, indicating that this solution is the most accurate from a geological point of view. Application of Ber90, or La90 solutions with dynamical ellipticity values smaller or larger than the present-day value, results in a less obvious fit with the geological record. This implies that the change in the planetary shape of the Earth associated with ice loading and unloading near the poles during the last 5.3 million years was too small to drive the precession into resonance with the perturbation term, s6-g6+g5, of Jupiter and Saturn. Our new timescale results in a slight but significant modification of all ages of the sedimentary cycles, bioevents, reversal boundaries, chronostratigraphic boundaries, and glacial cycles. Moreover, a comparison of this timescale with the astronomical timescales of ODP site 846 [Shackleton et al., 1995, doi:10.2973/odp.proc.sr.138.106.1995; doi:10.2973/odp.proc.sr.138.117.1995] and ODP site 659 [Tiedemann et al., 1994, doi:10.1029/94PA00208] indicates that all obliquity-related glacial cycles prior to ~4.7 Ma in ODP sites 659 and 846 should be correlated with one obliquity cycle older than previously proposed.

Sedimentary cycles on the Exmouth Plateau

Sedimentary cycles are observed in the nearly complete Lower Cretaceous to Eocene pelagic carbonates at Site 762 on the Exmouth Plateau off northwest Australia. The high-frequency cycles of variable clay and foraminifers in nannofossil chalk appear as color cycles repeating on a scale of centimeters to meters in thickness. Measured cycle thickness indicate that the dominant cycles appear to be related to the precession and obliquity periods. To evaluate the high-frequency variance observed on the gamma-ray curve, spectral analysis of the log was performed on two intervals: 260 to 365 mbsf in the Cenozoic, and 555 to 685 mbsf in the Mesozoic. Average Cenozoic sedimentation rates of 10.5 m/m.y. are high enough to show that variance is present in the full suite of eccentricity bands (413-123-95 k.y.). Spectral analysis of the Mesozoic section failed to produce dominant peaks that could be correlated to predicted orbital periods. The bioturbation observed in the cores in this interval may be responsible for diluting the signal and producing high-frequency noise, which is manifested in the spectra as low, broad amplitude peaks. Orbital forcing may be affecting sedimentation on the Exmouth Plateau by influencing cycles of increased carbonate production or dissolution. Alternatively, clay abundance cycles may be related to eolian deposition during cycles of increased aridity in western Australia. Four low-frequency events were also identified at Site 762 from the core and log data. The duration of these events is approximately 13 m.y., and the conformable boundaries of these sedimentary cycles correlate with observed nondepositional surfaces in other wells in western Australia. The causal mechanism for the onset of these events may be eustatic, but alternatively may be regional tectonism with associated circulation pattern changes.

Grain size analysis of sediment core CRP-3 from the Ross Sea, Antarctica

Grain-size analyses by sieve and Sedigraph are presented for 115 samples of core from CRP-3, 12 km off the coast of south Victoria Land. The data provide a useful check on visual core descriptions. The geographic setting for the strata sampled, some 790 m of early Oligocene nearshore marine sediments with a persistent glacial influence, is reviewed, and sediment textures interpreted in that context. Sand textures from the CRP-3 samples in the lower part of the core suggest that deposition was initially primarily wave-dominated, but that at times the influence of the waves was over-ridden by episodes of rapid sedimentation. Sedimentary cycles, recognised in the visual description of the core above 485 mbsf, show an increasing proportion of mudstone in the middle of each cycle above 330 mbsf that is interpreted to record periodic sedimentation in deeper water. Sandstone textures in the lower and upper parts of each cycle are interpreted to record departure from and return to shoreface deposition with changes in sea level. Mudstone textures above 176 mbsf indicate sedimentation below wave base. Many of the textures in both sand and mud samples show the coarse 'tail' characteristic of ice-rafted debris, but others do not, indicating ice-free periods. Many sandstones below c. 200 mbsf have virtually no silt, but significant amounts of clay (6 to 17%) that is thought to be of post-depositional origin.

The sapropel record of the eastern Mediterranean Sea

Research on sediments recovered during Ocean Drilling Leg 160 has concentrated on two issues: the first concerned the stratigraphy of sapropel formation, the second was oriented to clarify specific processes that explain sapropel origin. Progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites. On the composites, initial work has resulted in the establishment of high-resolution and intermediate-resolution stratigraphies for three sites (963, 964, 967); correlation of sedimentary cycles to astronomical (insolation) cycles extends the stratigraphies to Sites 969 and 966. The sapropel occurrences in the marine and land sequences over the entire Eastern Mediterranean are correlated; with the resolution that can be obtained from isotope studies, groups of sapropels occurred simultaneously over the entire basin. In detail, however, the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins. The differences may be related to effects of water depth, diagenesis, and post-depositional tectonic attenuation of sequences. Studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels, caused the enrichment of trace metals associated with sapropels, and helped to preserve primary sedimentary structures. Besides, all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events.

Magnetic susceptibility dataset from the early Givetian to early Frasnian in the La Thure section

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35±0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10**5 year-scale cyclicity is the result of climatic and environmental change.

Strontium isotopic ratios of evaporites of the Tyrrhenian Sea

Strontium isotopic ratios of gypsums recovered from upper Miocene (Messinian) evaporites at ODP Leg 107 Holes 652A, 653B, and 654A (Tyrrhenian Sea) are lower than expected. The values for the Messinian balatino-like gypsum, single gypsum crystals, and anhydrites range from 0.70861 to 0.70886 and are approximately 25 * 10**-5 less than would be expected for evaporites precipitated from Messinian seawater (0.70891-0.70902). Pre-evaporitic planktonic foraminifers from Hole 654A show variable degrees of dolomitization and 87Sr/86Sr values that irregularly decrease upward from normal marine values approximately 81m below the lowest evaporite occurrence. This suggests diagenetic alteration by advecting interstitial water with a low 87Sr/86Sr ratio or that the lower Sr isotopic ratios for the Messinian evaporites could have resulted from a greater influence of fresh water on the Sr isotopic composition of the desiccating Tyrrhenian Sea. Fluctuations of the 87Sr/86Sr-ratio for evaporites in the sedimentary cycles recognized for Holes 653B and 654A, the generally low Sr isotopic ratio of river water entering the Mediterranean Sea, and the presence of dwarf marine microfossils suggest that the 87Sr/86Sr ratio of the evaporites responded to hydrologic variations in a very restricted basin with variable rates of marine and fresh water input. The strontium isotopic ratios of the Messinian anhydrites from the proposed lacustrine sequence at Hole 652A fall in the same range as the marine evaporites from Holes 654A and 653B. This suggests a common or similar origin of the brines at the three locations. The complex depositional and hydrologic conditions in the Mediterranean during the Messinian salinity crisis preclude the use of Sr isotopic values from the evaporites for stratigraphic correlation and dating. They are, however, very useful in the interpretation of the depositional history of the basin. General calculations assuming a closed system suggest that the 87Sr/86Sr ratio of Messinian seawater (-0.7090) could be reduced to that of the evaporites (-0.7087) by mixing with fresh water (e.g., Nile River) in times of 10**4 to 10**5 yr.

Granulometry, biogenic silica content, magnetic susceptibility and bulk densities of ODP Site 188-1165

The Prydz Bay area is a key region for studying and understanding the history of the eastern Antarctic Continental Ice Sheet (O'Brien, Cooper, Richter, et al., 2001, doi:10.2973/odp.proc.ir.188.2001). Ocean Drilling Program (ODP) Site 1165 is situated in a water depth of 3357 m on the continental rise offshore from Prydz Bay and lies in front of the outlet for the Lambert Glacier-Amery Ice Shelf system that today drains 22% of East Antarctica. The site was drilled into mixed pelagic and hemipelagic sediments from the southwestern side of the Wild Drift. The drift is an elongate sediment body formed by the interaction of sediment supplied from continental shelf and slope with westward-flowing bottom currents. The sedimentary sequence is characterized by alternations between a generally gray to dark gray facies and a green to greenish gray facies. The greenish facies are structureless diatom-bearing clays with common bioturbation and larger amounts (>15%-20%) of biogenic silica, dispersed clasts, and lonestones than the dark gray facies, which are mostly less bioturbated clay with some silt laminations (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.188.103.2001). High-quality advanced piston corer and extended core barrel cores containing nearly complete sections of middle Miocene to early Pliocene age allow a detailed characterization of sedimentary cycles and can provide indications for ice advances of the Lambert Glacier system into Prydz Bay, for the extent of sea ice, and for changes in oceanic circulation. The purpose of this work is to provide a data set of coarse-fraction mass percentage (>63, >125, and >250 µm) and biogenic silica content measured on sediments of late Miocene to early Pliocene age drilled at Site 1165. Additionally, high-resolution records of magnetic susceptibility (MS) and gamma ray attenuation (GRA) bulk density are presented. These shipboard data sets were edited postcruise. Furthermore, I provide a high-resolution dry bulk density record that is derived from GRA bulk density and can be used for the calculation of mass accumulation rates. These sedimentological and physical parameters will be used in future work to understand the depositional pattern of alternating biogenic and terrigenous sediments that was observed at Site 1165 (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.188.103.2001).

Sedimentology of ODP Leg 104 holes

The long-term record of glacial/interglacial cycles indicates three major paleoceanographic regimes in the Norwegian Sea. The period since the first major glaciation over Scandinavia at 2.56 Ma is characterized by high-frequency, low-amplitude oscillations of ice-rafted debris inputs, a lowered salinity, and decreased carbonate shell production in surface waters as well as overall strong carbonate dissolution at the sea floor. These conditions indicate a more zonal circulation pattern in the Northern Hemisphere and a relative isolation of surface and bottom waters in the Norwegian Sea. The generally temperate glacial climate was only interrupted by episodic weak intrusions of warm Atlantic waters. These intrusions have been detected in considerable magnitude only at Site 644, and thus are restricted to areas much closer to the Norwegian shelf than during earlier periods. The interval from 1.2 to 0.6 Ma is characterized by an increase in carbonate shell production and a better preservation, as well as a change in frequency patterns of ice-rafted debris inputs. This pattern reflects increasing meridionality in circulation-strengthening contrasts in the Norwegian Sea between strong glaciations and warm interglacials. The past 0.6 Ma reveal high-amplitude oscillations in carbonate records that are dominated by the 100-k.y. frequency pattern. Glacial/interglacial sedimentary cycles in the ODP Leg 104 drill sites reveal a variety of specific dark lithofacies. These dark diamictons reflect intense iceberg rafting in surface waters fed by surges along the front of marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea and are associated with resuspension of reworked fossil organic carbon and strong dissolution at the sea floor. Piling up of huge iceberg barriers along the Iceland-Faeroe-Scotland Ridge might have partially blocked off surface water connections with the North Atlantic during these periods

Stable isotope record and age model for sapropel stratigraphy of ODP Site 160-967

Stable oxygen isotope data from four holes drilled at the Ocean Drilling Program Site 967, which is located on the lower northern slope of the Eratosthenes Seamount, provide a continuous record of Eastern Mediterranean surface-water conditions during the last 3.2 Ma. A high-resolution stratigraphy for the Pliocene-Pleistocene sequence was established by using a combination of astronomical calibration of sedimentary cycles, nannofossil stratigraphy, and stable oxygen isotope fluctuations. Sapropels and color cycles are present throughout the last 3.2 Ma at Site 967, and their ages, as determined by calibration against the precessional component of the astronomical record, are consistent with those estimated for the sapropels of the classical land-based marine sequences of the Punta Piccola, San Nicola, Singa, and Vrica sections (southern Italy). The Site 967 oxygen isotope record shows large amplitude fluctuations mainly caused by variations in surface water salinity throughout the entire period. Spectral analysis shows that fluctuations in the d18O record were predominantly influenced by orbital obliquity and precessional forcing from 3.2 to 1 Ma, and all main orbital frequencies characterize the d18O record for the last million years. The start of sapropel formation at 3.2 Ma indicates a possible link between sapropel formation and the build up of northern hemisphere ice sheets. The dominance of the obliquity cycle in the interval from 3.2-1 Ma further points to the sensitivity of Eastern Mediterranean climate to the fluctuations in the volume of Arctic ice sheets. An intensification of negative isotope anomalies at Site 967, relative to the open ocean, supports a link between high run-off (during warm periods) and sapropel formation. freshwater input would have inhibited deep-water formation, which led to stagnation of deeper waters. Comparison with the land sections also confirms that differential preservation and diagenesis play a key role in sapropel occurrence.

Pleistocene rhyolithic tephra of ODP Leg 181 sites

Taupo Volcanic Zone (TVZ), in the North Island, New Zealand, is arguably the most active Quaternary rhyolitic system in the world. Numerous and widespread rhyolitic tephra layers, sourced from the TVZ, form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences. In deep-sea cores from Ocean Drilling Program (ODP) Leg 181 Sites 1125, 1124, 1123 and 1122, located east of New Zealand, ca 100 tephra beds are recognised post-dating the Plio-Pleistocene boundary at 1.81 Ma. These tephras have been dated by a combination of magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. The widespread occurrence of ash offshore to the east of New Zealand is favoured by the small size of New Zealand, the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field. Although some tephras can be directly attributed to known TVZ eruptions, there are many more tephras represented within ODP-cores that have yet to be recognised in near-source on-land sequences. This is due to proximal source area erosion and/or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near-source welded ignimbrites. Despite these difficulties, a number of key deep-sea tephras can be reliably correlated to equivalent-aged tephra exposed in uplifted marine back-arc successions of Wanganui Basin where an excellent chronology has been developed based on magnetostratigraphy, orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra. Significant Pleistocene tephra markers include: the Kawakawa, Omataroa, Rangitawa/Onepuhi, Kaukatea, Kidnappers-B, Potaka, Unit D/Ahuroa, Ongatiti, Rewa, Sub-Rewa, Pakihikura, Ototoka and Table Flat Tephras. Six other tephra layers are correlated between ODP-core sites but have yet to be recognised within onshore records. The identification of Pleistocene TVZ-sourced tephras within the ODP record, and their correlation to Wanganui Basin and other onshore sites is a significant advance as it provides: (1) an even more detailed history of the TVZ than can be currently achieved from the near-source record, (2) a high-resolution tephrochronologic framework for future onshore-offshore paleoenvironmental reconstructions, and (3) well-dated tephra beds correlated from the offshore ODP sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore Plio-Pleistocene sedimentary sequences (e.g. Wanganui Basin, cf. Naish et al. (1998, doi:10.1016/S0277-3791(97)00075-9).

Pore water and solid-phase measurements on sediment cores from the Black Sea

The surface sediments in the Black Sea are underlain by extensive deposits of iron (Fe) oxide-rich lake sediments that were deposited prior to the inflow of marine Mediterranean Sea waters ca. 9000 years ago. The subsequent downward diffusion of marine sulfate into the methane-bearing lake sediments has led to a multitude of diagenetic reactions in the sulfate-methane transition zone (SMTZ), including anaerobic oxidation of methane (AOM) with sulfate. While the sedimentary cycles of sulfur (S), methane and Fe in the SMTZ have been extensively studied, relatively little is known about the diagenetic alterations of the sediment record occurring below the SMTZ. Here we combine detailed geochemical analyses of the sediment and pore water with multicomponent diagenetic modeling to study the diagenetic alterations below the SMTZ at two sites in the western Black Sea. We focus on the dynamics of Fe, S and phosphorus (P) and demonstrate that diagenesis has strongly overprinted the sedimentary burial records of these elements. Our results show that sulfate-mediated AOM substantially enhances the downward diffusive flux of sulfide into the deep limnic deposits. During this downward sulfidization, Fe oxides, Fe carbonates and Fe phosphates (e.g. vivianite) are converted to sulfide phases, leading to an enrichment in solid phase S and the release of phosphate to the pore water. Below the sulfidization front, high concentrations of dissolved ferrous Fe (Fe2+) lead to sequestration of downward diffusing phosphate as authigenic vivianite, resulting in a transient accumulation of total P directly below the sulfidization front. Our model results further demonstrate that downward migrating sulfide becomes partly re-oxidized to sulfate due to reactions with oxidized Fe minerals, fueling a cryptic S cycle and thus stimulating slow rates of sulfate-driven AOM (~ 1-100 pmol/cm**3/d) in the sulfate-depleted limnic deposits. However, this process is unlikely to explain the observed release of dissolved Fe2+ below the SMTZ. Instead, we suggest that besides organoclastic Fe oxide reduction, AOM coupled to the reduction of Fe oxides may also provide a possible mechanism for the high concentrations of Fe2+ in the pore water at depth. Our results reveal that methane plays a key role in the diagenetic alterations of Fe, S and P records in Black Sea sediments. The downward sulfidization into the limnic deposits is enhanced through sulfate-driven AOM with sulfate and AOM with Fe oxides may provide a deep source of dissolved Fe2+ that drives the sequestration of P in vivianite below the sulfidization front.

Magnetic susceptibility and particle size for the Shilou red clay section on the eastern Chinese Loess Plateau

The Chinese Loess Plateau red clay sequences display a continuous alternation of sedimentary cycles that represent recurrent climatic fluctuations from 2.58 Ma to the Miocene. Deciphering such a record can provide us with vital information on global and Asian climatic variations. Lack of fossils and failure of absolute dating methods made magnetostratigraphy a leading method to build age models for the red clay sequences. Here we test the magnetostratigraphic age model against cyclostratigraphy. For this purpose we investigate the climate cyclicity recorded in magnetic susceptibility and sedimentary grain size in a red clay section previously dated 11Myr old with magnetostratigraphy alone. Magnetostratigraphy dating based on only visual correlation could potentially lead to erroneous age model. In this study the correlation is executed through the iteration procedure until it is supported by cyclostratigraphy; i.e., Milankovitch cycles are resolved in the best possible manner. Our new age model provides an age of 5.2Ma for the Shilou profile. Based on the new age model, wavelet analysis reveals the well-preserved 400 kyr and possible 100 kyr eccentricity cycles on the eastern Chinese Loess Plateau. Further, paleomonsoon evolution during 2.58-5.2Ma is reconstructed and divided into three intervals (2.58-3.6Ma, 3.6-4.5Ma, and 4.5-5.2Ma). The upper part, the youngest stage, is characterized by a relatively intensified summer monsoon, the middle stage reflects an intensification of the winter monsoon and aridification in Asia, and the earliest stage indicates that summer and winter monsoon cycles may have rapidly altered. The use of cyclostratigraphy along withmagnetostratigraphy gives us an effectivemethod of dating red clay sequences, and our results imply that many presently published age models for the red clay deposits should be perhaps re-evaluated.

Sedimentary records of ODP Site 198-1209 on Shatsky Rise

The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity conditions of the continental region supplying the dust, as well as the "gustiness" of the climate system. Detailed studies of Pleistocene glacial-interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation (Milankovitch cycles). While the orbital cycles found in sedimentary archives of the Pleistocene are intricately related to glacial growth and decay, similar global orbital signals recognized in deep-sea sediments of early Paleogene age, the last major greenhouse interval ~65-45 million years ago, could not have been linked to the waxing and waning of large ice sheets. Thus orbital signals recorded in early Paleogene sediments must reflect some other climate response to changes in solar insolation. To explore the potential connection between orbital forcing and the climate processes that control dust accumulation, we generated a high-resolution dust record for ~58 Myr old sediments from Shatsky Rise (ODP Site 1209, paleolatitude ~15°N-20°N). The dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early Paleogene, indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate. Furthermore, the relative amplitude of the dust flux response during the early Paleogene greenhouse was comparable to that during icehouse climates. Thus, subtle variations in solar insolation driven by changes in Earth's orbit about the Sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial-interglacial states.