Chronostratigraphic framework at sites GeoB14403 and GeoB14414 from the Gela Basin, Sicily Channel

A multi-proxy chronological framework along with sequence-stratigraphic interpretations unveils composite Milankovitch cyclicity in the sedimentary records of the Last GlacialeInterglacial cycle at NE Gela Basin on the Sicilian continental margin. Chronostratigraphic data (including foraminifera-based eco-biostratigraphy and d18O records, tephrochronological markers and 14C AMS radiometric datings) was derived from the shallow-shelf drill sites GeoB14403 (54.6 m recovery) and GeoB14414 (27.5 m), collected with both gravity and drilled MeBo cores in 193 m and 146 m water depth, respectively. The recovered intervals record Marine Isotope Stages and Substages (MIS) from MIS 5 to MIS 1, thus comprising major stratigraphic parts of the progradational deposits that form the last 100-ka depositional sequence. Calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher-frequency (20-ka) sea level cycles punctuating this 100-ka cycle. This becomes most evident in the alternation of thick interstadial highstand (HST) wedges and thinner glacial forced-regression (FSST) units mirroring seaward shifts in coastal progradation. Albeit their relatively short-lived depositional phase, these subordinate HST units form the bulk of the 100-ka depositional sequence. Two mechanisms are proposed that likely account for enhanced sediment accumulation ratios (SAR) of up to 200 cm/ka during these intervals: (1) intensified activity of deep and intermediate Levantine Intermediate Water (LIW) associated to the drowning of Mediterranean shelves, and (2) amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions. Equally, the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of MIS 5 Interstadials, which bear a striking resemblance to modern equivalents forming on late-Holocene prodeltas of other Mediterranean shallow-shelf settings.

Bulk sedimentology from Sites M0002 and M0004 of the ACEX (Exp302) expedition to the Arctic Ocean

Except for a few discontinuous fragments of the Late Cretaceous/Early Cenozoic climate history and depositional environment, the paleoenvironmental evolution of the pre-Neogene central Arctic Ocean was virtually unknown prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition - ACEX) drilling campaign on Lomonosov Ridge in 2004. Here we present detailed organic carbon (OC) records from the entire ca. 200 m thick Paleogene OC-rich section of the ACEX drill sites. These records indicate euxinic "Black Sea-type" conditions favorable for the preservation of labile aquatic (marine algae-type) OC occur throughout the upper part of the early Eocene and the middle Eocene, explained by salinity stratification due to freshwater discharge. The superimposed short-term ("Milankovitch-type") variability in amount and composition of OC is related to changes in primary production and terrigenous input. Prominent early Eocene events of algae-type OC preservation coincide with global d13C events such as the PETM and Elmo events. The Elmo d13C Event has been identified in the Arctic Ocean for the first time.

Auxiliary material and basic geochemical and benthic foraminiferal stable isotope data for the interval bracketing Eocene Thermal Maximum 2 (ETM2) at DSDP Sites 401 and 550 in the northeastern Atlantic Ocean

Ever since its discovery, Eocene Thermal Maximum 2 (ETM2; ~53.7 Ma) has been considered as one of the "little brothers" of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) as it displays similar characteristics including abrupt warming, ocean acidification, and biotic shifts. One of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and, ultimately, biotic disruptions. Here we characterize ETM2 sections of the NE Atlantic (Deep Sea Drilling Project Sites 401 and 550) using multispecies benthic foraminiferal stable isotopes, grain size analysis, XRF core scanning, and carbonate content. The magnitude of the carbon isotope excursion (0.85-1.10 per mil) and bottom water warming (2-2.5°C) during ETM2 seems slightly smaller than in South Atlantic records. The comparison of the lateral d13C gradient between the North and South Atlantic reveals that a transient circulation switch took place during ETM2, a similar pattern as observed for the PETM. New grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity. Following ETM2, we record a distinct intensification of bottom water currents influencing Atlantic carbonate accumulation and biotic communities, while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle. Our findings highlight the similarities and differences between the PETM and ETM2. Moreover, the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early Paleogene.

Miocene to Pliocene calcareous nannofossil biostratigraphy at ODP Leg 117 Sites 1088 and 1090, Southern Ocean

The calcareous nannofossil biostratigraphy of ODP Leg 177 Sites 1088 and 1090 (Subantarctic sector from the Atlantic Ocean) is discussed. Most nannofossil zonal boundaries of Martini (1971) and Okada and Bukry (1980) were recognized for the studied mid-high-latitude sediments. Conventional low-latitude marker species such as Amaurolithus spp., Discoaster spp., Triquetrorhabdulus spp., Ceratolithus spp. were recorded as rare and scattered, which impeded the development of a detailed nannofossil biostratigraphic zonation of some Miocene and Pliocene intervals. Because of the absence of some primary biostratigraphic marker species, additional second-order bioevents, such as the first occurrence of Calcidiscus macintyrei and the last occurrence of Coccolithus miopelagicus, have been used to approximate the base of zones NN7 and NN8, respectively. Several disconformities disturbing the Pliocene and Miocene intervals of Site 1090 could be determined based on nannofossil distribution although the occurrence of intervals with dissolved nannofloras and low species diversity prevented a reliable age assignment. An acme of small Gephyrocapsa was recognized near the lower/middle Pliocene boundary, close to the NN15-NN16 zonal boundary, presenting an event for further improvement of the calcareous nannofossil biostratigraphy of this interval time. The first occurrence of Pseudoemiliania lacunosa (>4 µm) occurs close to this interval, representing a fairly reliable event to approximate the base of NN15 zone when other biozonal events are absent. A paracme of R. pseudoumbilicus (>7 µm) was detected in the lower Pliocene NN12 and in the upper Miocene NN11. These temporary absences of the species seem to be isochronous between high-latitude and low-middle-latitude areas.

Composition of palygorskite-rich and montmorillonite-rich zeolite-containing sediments from DSDP Sites 164 and 196

Cretaceous, Tertiary, and Quaternary sediments from Deep Sea Drilling Project Sites 164 and 196 (13°12' N, 161°31' W and 30°07' N, 148°34' E, respectively) were analyzed for major chemical elements and mineralogy. Sediments from these sites contain large proportions of authigenic minerals: mainly palygorskite, clinoptilolite and chert in the Cretaceous, and montmorillonite, phillipsite and chert in the Tertiary. The montmorillonite-phillipsite assemblage is thought to be derived from volcanic ash or glass, and the palygorskite-clinoptilolite assemblage is thought to be derived by reaction of biogenic silica with volcanic ash or glass or with montmorillonite and phillipsite. Both assemblages have generally moderate Ti/Al ratios, ranging from 0.026 to 0.047, so most of the palygorskite, clinoptilolite, montmorillonite and phillipsite could not be derived in situ from alteration of basaltic material. Plagioclase compositions suggest that the volcanic precursors were silicic or intermediate, but it is also possible that the sediments have been extensively fractionated by redistribution from nearby seamounts. Available data on other Late Cretaceous sediments in the Pacific were analyzed. Clinoptilolite and chert are present nearly everywhere where palygorskite is abundant; phillipsite is rare where palygorskite is abundant. It is suggested that increased water temperatures during the Cretaceous increased reaction rates and determined the alteration products.

40Ar-39Ar investigation of volcanic clasts in glaciogenic sediments at ODP Sites 1097 and 1103

Three selected diamictite samples recovered within sequence group S3 at Sites 1097 (Sample 178-1097A-27R-1, 35-58 cm) and 1103 (Samples 178-1103A-31R-2, 0-4 cm, and 36R-3, 4-8 cm) of Ocean Drilling Program Leg 178 have been investigated by scanning electron microscope, electron microprobe, and 40Ar-39Ar laser-heating techniques. They contain variable proportions of fragments of volcanic rock groundmass (mostly in the range of 100-150 µm) with textures ranging from microcrystalline to ipocrystalline. Their rounded shapes indicate mechanical reworking. Fresh groundmass glasses, recognized only in grains from samples of Site 1103, show mainly a subalkaline affinity on the basis of total alkali-silica variations. However, they are characterized by relatively high TiO2 and P2O5 contents (1.4-2.8 and 0.1-0.9 wt%, respectively). Because of the small size of homogeneous grains (100-150 µm), they were not suitable for single-grain total fusion 40Ar-39Ar analyses. The incremental laser-heating technique was applied to milligram-sized samples (only for Samples 178-1097A-27R-1, 35-58 cm, and 178-1103A-36R-3, 4-8 cm) and to various small fractions (each consisting of 10 grains for the sample from Site 1097 and 30 grains for samples from Site 1103). The latter approach resulted in more effective resolution of sample heterogeneity. Argon ages from the small fractions show significantly different ranges in the three samples: 75-173 Ma for Sample 178-1097A-27R-1, 35-58 cm, 18-57 Ma for Sample 178-1103A-31R-2, 0-4 cm, and 7.6-50 Ma for Sample 178-1103A-36R-3, 4-8 cm. Ca/K ratios derived from argon isotopes at Site 1103 suggest that the data mainly refer to outgassing of groundmass glass. At Site 1103, we observe an overall apparent age increase with decreasing sample depth. This is compatible with glacial erosion that affected with time deeper levels of a volcanic sequence previously deposited on the continent. The youngest apparent age of 7.6 ± 0.7 Ma detected close to the bottom of Hole 1103A (340 meters below seafloor [mbsf]) is compatible with the age range of the diatom Actinocyclus ingens v. ovalis Zone (6.3-8.0 Ma) determined for the interval 320-355 mbsf and with the maximum ages derived from strontium isotope composition of barnacle fragments obtained at 262-263 mbsf at the same site. Nevertheless, this age cannot be taken as the maximum youngest age of the volcanic sequence sampled by glacial erosion or as the maximum age for the deposition of the Sequence S3 at 340 mbsf unless validated by further research.

Natural remanent magnetization (NRM) from ODP Site 1263 covering magnetochron C20r and C21n and high-resolution bulk carbon isotope (d13C) records from Sites 702 and 1263

To explore cause and consequences of past climate change, very accurate age models such as those provided by the astronomical timescale (ATS) are needed. Beyond 40 million years the accuracy of the ATS critically depends on the correctness of orbital models and radioisotopic dating techniques. Discrepancies in the age dating of sedimentary successions and the lack of suitable records spanning the middle Eocene have prevented development of a continuous astronomically calibrated geological timescale for the entire Cenozoic Era. We now solve this problem by constructing an independent astrochronological stratigraphy based on Earth's stable 405 kyr eccentricity cycle between 41 and 48 million years ago (Ma) with new data from deep-sea sedimentary sequences in the South Atlantic Ocean. This new link completes the Paleogene astronomical timescale and confirms the intercalibration of radioisotopic and astronomical dating methods back through the Paleocene-Eocene Thermal Maximum (PETM, 55.930 Ma) and the Cretaceous-Paleogene boundary (66.022 Ma). Coupling of the Paleogene 405 kyr cyclostratigraphic frameworks across the middle Eocene further paves the way for extending the ATS into the Mesozoic.

Contents, partition, and isotopic composition of sulphur in sediments from ODP Sites 680 and 686

We have determined (1) the abundance and isotopic composition of pyrite, monosulphide, elemental sulphur, organically bound sulphur, and dissolved sulphide; (2) the partition of ferric and ferrous iron; (3) the organic carbon contents of sediments recovered at two sites drilled on the Peru Margin during Leg 112 of the Ocean Drilling Program. Sediments at both sites are characterised by high levels of organically bound sulphur (OBS). OBS comprises up to 50% of total sedimentary sulphur and up to 1% of bulk sediment. The weight ratio of S to C in organic matter varies from 0.03 to 0.15 (mean = 0.10). Such ratios are like those measured in lithologically similar, but more deeply buried petroleum source rocks of the Monterey and Sisquoc formations in California. The sulphur content of organic matter is not limited by the availability of porewater sulphide. Isotopic data suggest that sulphur is incorporated into organic matter within a metre of the sediment surface, at least partly by reaction with polysulphides. Most inorganic Sulphur occurs as pyrite. Pyrite formation occurred within surface sediments and was limited by the availability of reactive iron. But despite highly reducing sulphidic conditions, only 35-65% of the total iron was converted to sulphide; 10-30% of the total iron still occurs as Fe(III). In surface sediments, the isotopic composition of pyrite is similar to that of both iron monosulphide and dissolved sulphide. Either pyrite, like monosulphide, formed by direct reaction between dissolved sulphide and detrital iron, and/or the sulphur species responsible for converting FeS to FeS2 is isotopically similar to dissolved sulphide. Likely stoichiometries for the reaction between ferric iron and excess sulphide imply a maximum resulting FeS2:FeS ratio of 1:1. Where pyrite dominates the pool of iron sulphides, at least some pyrite must have formed by reaction between monosulphide and elemental sulphur and/or polysulphide. Elemental sulphur (S°) is most abundant in surface sediments and probably formed by oxidation of sulphide diffusing across the sediment-water interface. In surface sediments, S° is isotopically heavier than dissolved sulphide, FeS and FeS2 and is unlikely to have been involved in the conversion of FeS to FeS2. Polysulphides are thus implicated as the link between FeS and FeS2.