Foraminifer, coarse fraction and carbonate characteristics of sediments from ODP Leg 198 sites on Shatsky Rise

Holes 1209A and 1211A on Southern High, Shatsky Rise contain expanded, nearly continuous records of carbonate-rich sediment deposited in deep water of the equatorial Pacific Ocean during the Paleocene and Eocene. In this study, we document intervals of carbonate dissolution in these records by examining temporal changes in four parameters: carbonate content, coarse size fraction (>38 µm), benthic foraminiferal abundance, and planktonic foraminiferal fragmentation ratio. Carbonate content is not a sensitive indicator of carbonate dissolution in the studied sections, although rare intervals of low carbonate may reflect times of relatively high dissolution. The proportion of coarse size fraction does not accurately record carbonate dissolution either because the relative abundance of nannofossils largely determines the grain-size distribution. Benthic abundance and fragmentation covary (r**2 = 0.77) and are probably the best indicators for carbonate dissolution. For both holes, records of these parameters indicate two episodes of prominent dissolution. The first of these occurs in the upper Paleocene (~59-58 Ma) and the second in the middle to upper Eocene (~45-33.7 Ma). Other intervals of enhanced carbonate dissolution are located in the upper Paleocene (~56 Ma) and in the upper lower Eocene (~51 Ma). Enhanced preservation of planktonic foraminiferal assemblages marks the start of both the Paleocene and Eocene epochs.

Calcium carbonate and organic carbon at DSDP Leg 62 Holes

Percent CaCO3 was determined in selected samples aboard the ship by the carbonate-bomb technique (Müller and Gastner, 1971). Results of these analyses are listed in Table 1 and plotted in Figures 1, 3, 4, and 5 as plus signs (+). Samples collected specifically for analyses of CaCO3 and organic carbon were analyzed at three shore-based laboratories. Concentrations of total carbon, organic carbon, and CaCO3 were determined in some samples at the DSDP sediment laboratory, using a Leco carbon analyzer, by personnel of the U.S. Geological Survey, under the supervision of T. L. Valuer. Most of these samples were collected from lithologic units containing relatively high concentrations of organic carbon. Sample procedures are outlined in Boyce and Bode (1972). Precision and accuracy are both ±0.3% absolute for total carbon, ±0.06% absolute for organic carbon, and ±3% absolute for CaCO3.

Foraminiferal assemblages and stable isotopes across the early Paleogene carbonate facies of Perth Abyssal Plain off Western Australia

Bulk carbonate content, planktic and benthic foraminiferal assemblages, stable isotope compositions of bulk carbonate and Nuttallides truempyi (benthic foraminifera), and non-carbonate mineralogy were examined across ~30 m of carbonate-rich Paleogene sediment at Deep Sea Drilling Project (DSDP) Site 259, on Perth Abyssal Plain off Western Australia. Carbonate content, mostly reflecting nannofossil abundance, ranges from 3 to 80% and generally exceeds 50% between 35 and 57 mbsf. A clay-rich horizon with a carbonate content of about 37% occurs between 55.17 and 55.37 mbsf. The carbonate-rich interval spans planktic foraminiferal zones P4c to P6b (~57-52 Ma), with the clay-rich horizon near the base of our Zone P5 (upper)-P6b. Throughout the studied interval, benthic species dominate foraminiferal assemblages, with scarce planktic foraminifera usually of poor preservation and limited species diversity. A prominent Benthic Foraminiferal Extinction Event (BFEE) occurs across the clay-rich horizon, with an influx of large Acarinina immediately above. The delta13C records of bulk carbonate and N. truempyi exhibit trends similar to those observed in upper Paleocene-lower Eocene (~57-52 Ma) sediment from other locations. Two successive decreases in bulk carbonate and N. truempyi delta13C of 0.5 and 1.0? characterize the interval at and immediately above the BFEE. Despite major changes in carbonate content, foraminiferal assemblages and carbon isotopes, the mineralogy of the non-carbonate fraction consistently comprises expanding clay, heulandite (zeolite), quartz, feldspar (sodic or calcic), minor mica, and pyrolusite (MnO2). The uniformity of this mineral assemblage suggests that Site 259 received similar non-carbonate sediment before, during and after pelagic carbonate deposition. The carbonate plug at Site 259 probably represents a drop in the CCD from ~57 to 52-51 Ma, as also recognized at other locations.

Early Eocene benthic foraminifera of DSDP Hole 48-401

Within the last decade, several early Eocene hyperthermals have been detected globally. These transient warming events have mainly been characterized geochemically - using stable isotopes, carbonate content measurements or XRF core scanning - yet detailed micropaleontological records are sparse, limiting our understanding of the driving forces behind hyperthermals and of the contemporaneous paleoceanography. Here, detailed geochemical and quantitative benthic foraminiferal records are presented from lower Eocene pelagic sediments of Deep Sea Drilling Project Site 401 (Bay of Biscay, northeast Atlantic). In calcareous nannofossil zone NP11, several clay-enriched levels correspond to negative d13C and d18O bulk-rock excursions with amplitudes of up to ~0.75 per mil, suggesting that significant injections of 12C-enriched greenhouse gasses and small temperature rises took place. Coeval with several of these hyperthermal events, the benthic foraminiferal record reveals increased relative abundances of oligotrophic taxa (e.g. Nuttallides umbonifera) and a reduction in the abundance of buliminid species followed by an increase of opportunistic taxa (e.g. Globocassidulina subglobosa and Gyroidinoides spp.). These short-lived faunal perturbations are thought to be caused by reduced seasonality of productivity resulting in a decreased Corg flux to the seafloor. Moreover, the sedimentological record suggests that an enhanced influx of terrigenous material occurred during these events. Additionally, the most intense d13C decline (here called level d) gives rise to a small, yet pronounced long-term shift in the benthic foraminiferal composition at this site, possibly due to the reappraisal of upwelling and the intensification of bottom water currents. These observations imply that environmental changes during (smaller) hyperthermal events are also reflected in the composition of deep-sea benthic communities on both short (<100 kyr) and longer time scales. We conclude that the faunal patterns of the hyperthermals observed at Site 401 strongly resemble those observed in other deep-sea early Paleogene hyperthermal deposits, suggesting that similar processes have driven them.

Supplementary material: XRF core scanning data, CaCO3 values, foraminiferal carbon and oxygen isotope data, Mg/Ca data, clay mineralogy and helium isotope results

The Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) is associated with abrupt climate change, carbon cycle perturbation, ocean acidification, as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned. We report a clear exception to the behavior of the PETM as a reversing climatic transient in the eastern North Atlantic (Deep-Sea Drilling Project Site 401, Bay of Biscay) where the PETM initiates a greatly prolonged environmental change compared to other places on Earth where records exist. The observed environmental perturbation extended well past the d13C recovery phase and up to 650 kyr after the PETM onset according to our extraterrestrial 3He-based age-model. We observe a strong decoupling of planktic foraminiferal d18O and Mg/Ca values during the PETM d13C recovery phase, which in combination with results from helium isotopes and clay mineralogy, suggests that the PETM triggered a hydrologic change in western Europe that increased freshwater flux and the delivery of weathering products to the eastern North Atlantic. This state change persisted long after the carbon-cycle perturbation had stopped. We hypothesize that either long-lived continental drainage patterns were altered by enhanced hydrological cycling induced by the PETM, or alternatively that the climate system in the hinterland area of Site 401 was forced into a new climate state that was not easily reversed in the aftermath of the PETM.

Late Miocene to Pleistocene paleoceanographic records from the Feni and Gardar Drifts: Pliocene reduction in abyssal flow

Magnetic fabric analyses from two North Atlantic drift deposits provide proxies for determining relative variations in the strength of abyssal flow over the last 10 my. The data show a cessation of current-controlled sedimentation at the shallower Feni Drift (2417 m) at the time of onset of Northern Hemisphere glaciation (2.6 Ma). Drift formation ended nearly 2 my earlier (4.2 Ma) at the deeper Gardar Drift (3220 m), implying stepwise reduction in deep-water flow. Relatively light delta18O values at the deeper Gardar Drift indicate a warmer, thus also more salty, water mass site prior to 6 Ma. We interpret this as representing Mediterranean Sea water, which flowed north at depths greater than that of the Feni Drift Site. The supply of Mediterranean Water to the North Atlantic was shut off as the Gibraltar Straits closed, causing the Messinian salinity crisis, and never returned to that position in the water column after the Mediterranean opened again.

TOC, carbonate, opal composition and trace element concentration from ODP Holes 175-1082A and 175-1084A

Distinctive light-dark color cycles in sediment beneath the Benguela Current Upwelling System indicate repetitive alternations in sediment delivery and deposition. Geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid-Pleistocene intervals from ODP Sites 1082 and 1084. Concentrations of total organic carbon (TOC) vary between 3.5 and 17.1%. Concentrations of CaCO3 vary inversely to TOC and Al, which suggests that both carbonate dissolution and terrigenous dilution contribute to the light-dark cycles. Opal concentrations are independent of both TOC and CaCO3, therefore eliminating diatom production and lateral transport of shelf material as causes of the light-dark cycles. d13Corg and d15Ntot values do not vary across light-dark sediment intervals, implying that the extent of relative nutrient utilization did not change. The stable d15Ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the TOC-rich layers. Parallel changes in concentrations of indicator trace elements and TOC imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen. Cu, Ni, and Zn are enriched in the darker sediment as a consequence of greater organic matter delivery. Redox-sensitive metals vary due to loss (Mn and Ba) or enrichment (Mo) under reducing conditions created by TOC oxidation. Organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution, sulfate reduction and the concentration of metals. Thus, export production is considered ultimately responsible for the generation of the color cycles.

Organic geochemistry of Lower Cretaceous sediments from the northwetsern Pacific guyits

Organic geochemical data of Lower Cretaceous shallow water sediments from two sites (865 and 866) drilled during ODP leg 143 are presented. The organic matter is mainly terrestrial at the bottom of the sedimentary column at site 865, whereas algal and/or bacterial organic matter is dominant at site 866. This is the first evidence of shallow water deposition of organic matter during the Early Cretaceous in the Northwestern Pacific. The lower Aptian organic carbon-rich layers from the shallow water sediments of site 866 are geochemically similar to coeval mid-water sediments of site 463.

Extractable hydrocarbon and carbon isotope geochemistry of Lower Cretaceous sediments of the Exmouth Plateau

The organic geochemical character of rocks selected from Aptian, Valanginian, and Berriasian clay stone and siltstone sequences encountered in Ocean Drilling Program (ODP) Holes 762C and 763C on the Exmouth Plateau was determined by means of a variety of analytical procedures. These sequences represent distal portions of the Mesozoic Barrow delta, in which petroleum source rocks and reservoirs exist on the Australian continent. The organic matter at the ODP sites is thermally immature type III material. Biomarker hydrocarbon compositions are dominated by long-chain, waxy n-alkanes and by C29 steranes, which reflect the land-plant origin of organic matter. Organic carbon d13C values ranged from -26 per mil to -28 per mil, consistent with a C3 land-plant source. Kerogen pyrolysate compositions and hopane isomerization ratios revealed progressively larger contributions of recycled organic matter as the depth of the deltaic sedimentary layers became greater.

Calcareous dinocysts and grain size distribution along profile Stevns-Klint

The distribution patterns of calcareous dinoflagellate cysts were studied in the classic Cretaceous Tertiary (K-T) boundary section of Stevns Klint, Denmark, focusing mainly on the response of the cyst association to an abrupt environmental catastrophe. A major part of the Fish Clay, which covers the K-T boundary at its base and is exposed in the investigated section, contains fallout produced by an asteroid impact. Calcareous dinoflagenate cysts are the best preserved remains of carbonate-producing phytoplankton in this layer. The potential of this group of microfossils for the analysis of survival strategies and extinction patterns has been underestimated. The cyst species of the investigated section can be grouped into four assemblages that represent victims, survivors, opportunists, and specially adapted forms. The victims (Pithonelloideae) were an extremely successful group throughout the Upper Cretaceous, but were restricted to the narrow outer shelf. This restriction minimized their spatial distribution, which generally should be large to facilitate escape from unfavorable conditions. Spatial restriction optimized the population decrease by mass mortality, disabling a successful recovery. In contrast, the survivors that became the dominating group in the Danian had a wide spatial range from the shelf environment to the oceanic realm. A unique calcareous dinocyst assemblage in the Fish Clay shows that even under the stressed conditions immediately following the impact event, some species flourished due to special adaptation or high ecological tolerance. The ability of these dinoflagellate species to form calcareous resting cysts in combination with their generally wide spatial distribution in a variety of environments appears to be the main reason for a low extinction rate at the K-T boundary as opposed to the high extinction rate of other phytoplankton groups, such as the coccolithophorids.

Carbonate composition of Pliocene-Pleistocene sediments of the Maledives

Ocean Drilling Program (ODP) Leg 115 post-cruise research was focused on two Maldives sites, more precisely on the top 108 m of Hole 716B (water depth, 540 m), equivalent to the past 3.5 m.y., and the top 19.5 m of Hole 714A (water depth, 2195 m), equivalent to the past 0.55 m.y. These sediments consist of mostly unaltered and undisturbed, turbidite-free, periplatform ooze. Results of our research are compared with existing data on Hole 633A (water depth, 1681 m), drilled in the Bahamas during ODP Leg 101, using age/depth models built on the basis of oxygen isotope, nannofossil, and magnetic stratigraphies. Climate-induced, long-term (roughly 0.5 m.y.) aragonite cycles, superposed on short-term (roughly 0.04 and 0.1 m.y.) aragonite cycles, have been established at least during the past 2.0 m.y., in the Maldives and the Bahamas. Our most interesting result is the clear correlation among the aragonite long-term cycles in the Maldives and the Bahamas and the carbonate-preservation, long-term cycles from the open Pacific, Indian, and North Atlantic oceans. The mid-Brunhes dissolution interval, corresponding to the youngest preservation minima of the carbonate-preservation, longterm cycles, is clearly defined by fine aragonite minimum values in the deep periplatform sites, and by maximum fragmentation of pteropod tests in the shallow sites. Aragonite and planktonic d18O records, usually in phase during the late Pleistocene, display, further back in time, discreet intervals where the two records do not match with one another. Major mismatches between both records occur synchronously in the Maldives and Bahamas periplatform sites and seem to correspond to extreme events of either carbonate-preservation or dissolution in the deep pelagic carbonate sites of the equatorial Pacific Ocean. Based on our findings, short- and long-term aragonite cycles can no longer be explained only by variations of aragonite input from the nearby shallow carbonate banks, in response to their alternate flooding and exposure through cyclic sea-level fluctuations. The aragonite long-term cycles in the periplatform environments are interpreted as carbonatepreservation cycles at intermediate-water depths. Their occurrence shows, therefore, that the carbonate chemistry of the entire water column has been influenced by long-term (0.5 m.y.) cyclic variations during the past 2.0 m.y. These major changes of the water-column carbonate chemistry are linked to the climate-induced carbon cycling among the different atmospheric, oceanic, and sedimentary carbon reservoirs.