Palaeogeography Palaeoclimatology Palaeoecology

Published by Elsevier
Online ISSN: 0031-0182
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Article
The Frasnian-Famennian boundary is recognized as the culmination of a global mass extinction in the Late Devonian. In western New York State the boundary is a distinct horizon within a pyritic black shale bed of the upper Hanover Shale defined by the first occurrence of Palmatolepis triangularis in the absence of Frasnian conodonts. The boundary is characterized by a minor disconformity marked by a lag concentration of conodonts. Iridium at the boundary is 0.11-0.24 ng/g, two to five times background levels of <0.05 ng/g; other Ir enrichments of 0.38 ng/g and 0.49 ng/g occur within 50 cm of the conodont-constrained boundary. Numerous Ir enrichments in the boundary interval suggest extraterrestrial accretion and platinum group element (PGE) concentration at disconformities, or mobilization and concentration in organic-rich/pyritic-rich laminations from cosmic or terrestrial sources. PGE ratios of Pt/Pd and Ku/Ir at the boundary horizon approximate chondritic ratios and are suggestive of an unaltered extraterrestrial source. These values do not conclusively establish a single extraterrestrial impact as the ultimate cause of the Frasnian-Famennian mass extinction, especially given the presence of similar Ir enrichments elsewhere in the section and the absence at the boundary of microtektites and shocked mineral grains.
 
Article
Life-death (LD) studies of shelly macrofauna are important to evaluate how well a fossil assemblage can reflect the original living community, but can also serve as a proxy for recent ecological shifts in marine habitats and in practice this has to be distinguished using taphonomic preservation pattern and estimates of time-averaging. It remains to be rigorously evaluated, however, how to distinguish between sources of LD disagreement. In addition, death assemblages (DAs) also preserve important information on regional diversity which is not available from single censuses of the life assemblages (LAs). The northern Adriatic Sea is an ecosystem under anthropogenic pressure, and we studied the distribution and abundance of living and dead bivalve and gastropod species in the physically stressful environments (tidal flat and shallow sublittoral soft bottoms) associated with the delta of the Isonzo River (Gulf of Trieste). Specifically we evaluated the fidelity of richness, evenness, abundance, habitat discrimination and beta diversity. A total of 10,740 molluscs from fifteen tidal flat and fourteen sublittoral sites were analyzed for species composition and distribution of living and dead molluscs. Of 78 recorded species, only eleven were numerically abundant. There were many more dead than living individuals and rarefied species richness in the DA was higher at all spatial scales, but the differences are lower in habitats and in the region than at individual stations. Evenness was always higher in death assemblages, and probably due to temporally more variable LAs the differences are stronger in the sublittoral habitats. Distinct assemblages characterized intertidal and sublittoral habitats, and the distribution and abundance of empty shells generally corresponded to that of the living species. Death assemblages have lower beta diversity than life assemblages, but empty shells capture compositional differences between habitats to a higher degree than living shells. More samples would be necessary to account for the diversity of living molluscs in the study area, which is, however, well recorded in the death assemblages. There is no indication of a major environmental change over the last decades in this area, but due to the long history of anthropogenic pressure here, such a potential impact might be preserved in historical layers of the deeper sedimentary record.
 
Article
A detailed ultra-high-resolution analysis of a 37-cm-long core of Upper Miocene lake sediments of the long-lived Lake Pannon has been performed. Despite a general stable climate at c. 11-9 Ma, several high-frequency oscillations of the paleoenvironments and depositional environments are revealed by the analysis over a short time span of less than 1000 years. Shifts of the lake level, associated with one major 3rd order flooding are reflected by all organisms by a cascade of environmental changes on a decadal scale. Within a few decades, the pollen record documents shifting vegetation zones due to the landward migration of the coast; the dinoflagellate assemblages switch towards "offshore-type" due to the increasing distance to the shore; the benthos is affected by low oxygen conditions due to the deepening. This general trend is interrupted by smaller scale cycles, which lack this tight interconnection. Especially, the pollen data document a clear cyclicity that is expressed by iterative low pollen concentration events. These "negative" cycles are partly reflected by dinoflagellate blooms suggesting a common trigger-mechanism and a connection between terrestrial environments and surface waters of Lake Pannon. The benthic fauna of the core, however, does not reflect these surface water cycles. This forcing mechanism is not understood yet but periodic climatic fluctuations are favoured as hypothesis instead of further lake level changes. Short phases of low precipitation, reducing pollen production and suppressing effective transport by local streams, might be a plausible mechanism. This study is the first hint towards solar activity related high-frequency climate changes during the Vallesian (Late Miocene) around Lake Pannon and should encourage further ultra-high-resolution analyses in the area.
 
Article
A high-resolution multi-proxy analysis was conducted on a 1.5-m-long core of Tortonian age (~ 10.5 Ma; Late Miocene) from Austria (Europe). The lake sediments were studied with a 1-cm resolution to detect all small-scale variations based on palynomorphs (pollen and dinoflagellate cysts), ostracod abundance, geochemistry (carbon and sulfur) and geophysics (magnetic susceptibility and natural gamma radiation). Based on an already established age model for a longer interval of the same core, this sequence can be limited to approx. two millennia of Late Miocene time with a resolution of ~ 13.7 years per sample. The previous study documented the presence of solar forcing, which was verified within various proxies on this 1.5-m core by a combination of REDFIT spectra and Gaussian filters. Significant repetitive signals ranged in two discrete intervals corresponding roughly to 55–82 and 110–123 years, fitting well within the lower and upper Gleissberg cycle ranges.
 
Article
In order to detect whether the end-Frasnian worldwide biotic crisis is related to an extraterrestrial impact, the global stratotype section of the Frasnian-Famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators: iridium. Ni-rich spinel bearing spherules and glassy microtektites. This area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off-shore deposits. Different environmental settings on oxygenated deep-water seamounts, such as the stratotype section at Coumiac, and in oxygen-depleted depressions (La Serre section) are available. The latter is investigated in more detail because it is the least condensed across the boundary, which is determined by the first occurrence of the typical morphotype of Palmatolepis triangularis, the indicator of the first Famennian conodont biozone. Samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high Ir values and no Ni-rich spinel or microtektite has been recovered. This is in contradiction with the results of earlier investigations carried out by H. Geldsetzer on the same section. In contrast, the values of Ir concentrations that we measured are always very low or not detectable. The small overabundances observed in some samples, which are about two orders of magnitude lower than what is currently observed at the Cretaceous-Tertiary boundary, are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin. At present, we have no evidence that an extraterrestrial impact occurred at the F-F transition.
 
Article
Pollen analyses have been proven to possess the possibility to decipher rapid vegetational and climate shifts in Neogene sedimentary records. Herein, a c. 21-kyr-long transgression-regression cycle from the Lower Austrian locality Stetten is analysed in detail to evaluate climatic benchmarks for the early phase of the Middle Miocene Climate Optimum and to estimate the pace of environmental change.Based on the Coexistence Approach, a very clear signal of seasonality can be reconstructed. A warm and wet summer season with c. 204-236 mm precipitation during the wettest month was opposed by a rather dry winter season with precipitation of c. 9-24 mm during the driest month. The mean annual temperature ranged between 15.7 and 20.8 °C, with about 9.6-13.3 °C during the cold season and 24.7-27.9 °C during the warmest month. In contrast, today's climate of this area, with an annual temperature of 9.8 °C and 660 mm rainfall, is characterized by the winter season (mean temperature: -1.4 °C, mean precipitation: 39 mm) and a summer mean temperature of 19.9 °C (mean precipitation: 84 mm).Different modes of environmental shifts shaped the composition of the vegetation. Within few millennia, marshes and salt marshes with abundant Cyperaceae rapidly graded into Taxodiaceae swamps. This quick but gradual process was interrupted by swift marine ingressions which took place on a decadal to centennial scale. The transgression is accompanied by blooms of dinoflagellates and of the green alga Prasinophyta and an increase in Abies and Picea. Afterwards, the retreat of the sea and the progradation of estuarine and wetland settings were a gradual progress again.Despite a clear sedimentological cyclicity, which is related to the 21-kyr precessional forcing, the climate data show little variation. This missing pattern might be due to the buffering of the precessional-related climate signal by the subtropical vegetation. Another explanation could be the method-inherent broad range of climate-parameter estimates that could cover small scale climatic changes.
 
Article
An aperiodic collision of the Earth with extra-terrestria] ice/volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. Due to the volatile nature of these bodies, evidence for their impacts, particularly in the ocean might be subtle and best seen as 'spikes' in the geochemical or fossil record against normal background. Differing effects would result depending on the site of the major break-up of the object: in the atmosphere, on land, or in the ocean. This paper focuses on the effects of adding material to the seas, oceans, and atmosphere. The treatment is largely qualitative, however mass balance calculations were used to estimate the relative mass needed to affect changes in a variety of reservoirs. Although actual impactors probably have a variable composition, the effects of water-, C-, N-, and S-containing objects are discussed. In the atmosphere, effects could include increased rain acidity, increased levels of nutrients, and enhanced greenhouse warming/cooling. Oceanic effects might include increased oceanic productivity (nitrogen-containing objects). As a result of increased chemical weathering and/or greenhouse effects, increased temperatures coupled with enhanced productivity could result in wider-spread oceanic anoxia or altered calcite/aragonite stability. Possible examples of such impacts from the geologic record and potential biotic effects are given.
 
Article
Growth increment analysis coupled with stable isotopic data (δ18O/δ13C) from Early Pliocene (ca 4.7 Ma) Austrochlamys anderssoni from shallow marine sediments of the Cockburn Island Formation, northern Antarctic Peninsula, suggest these bivalves grew through much of the year, even during the coldest parts of winter recorded in the shells. The high frequency fluctuation in growth increment width of A. anderssoni appears to reflect periodic, but year-round, agitation of the water column enhancing benthic food supply from organic detritus. This suggests that Austrochlamys favoured waters that were largely sea ice free. Our data support interpretation of the Cockburn Island Formation as an interglacial marine deposit and the previous hypothesis that Austrochlamys retreated from the Antarctic as sea ice extent expanded, this transition occurring during climate cooling in the Late Pliocene
 
Article
The Early–Middle Pleistocene lacustrine sediments at Gesher Benot Ya'aqov (GBY) in the Upper Jordan Valley span ca. 100 Ka across the Matuyama–Brunhes Boundary (MBB) at 780 Ka and oxygen isotope stages (OISs) 20 to 18, provide a continuous record of their sedimentary history and prevailing climate. The lacustrine environment is investigated using ecological and stable isotope characteristics of gastropods belonging to the family Viviparidae supplemented by other molluscan and floral indicators. The sedimentary framework of the 34 m thick sequence is bounded by channel conglomerates at its base and top, and consists of six sedimentary cycles. Each one starts with shore sediments (coquina and sand) and ends with deeper water sediments (black mud or gray mud).
 
Article
The stratigraphic distribution of warm-water molluscs, planktonic foraminifers and diatoms in Plio-Pleistocene strata (3.5–0.8 Ma) of the Sea of Japan coast of Japan is the basis for reconstructing the history of the Tsushima Current. The results indicate: (1) the Tsushima Current flowed at 3.5, 3.2, 2.9, 2.4 and 1.9 Ma, in the 3.5–1.7 Ma interval; (2) the current flowed at every interglacial highstand, except for MIS 25, 23 and 21.3, in the 1.71–0.8 Ma interval; (3) the salinity and volume of the Tsushima Current during the earlier interval may have been significantly lower and smaller, respectively, than in the latter interval; (4) the Late Pliocene altitude of the southern part of the Sea of Japan was up to 50 m above present-day sea level.
 
Article
Tropical climate is variable on astronomical time scale, driving changes in surface and deep-sea fauna during the Pliocene–Pleistocene. To understand these changes in the tropical Indian Ocean over the past 2.36 Myr, we quantitatively analyzed deep-sea benthic foraminifera and selected planktic foraminifera from > 125 μm size fraction from Deep Sea Drilling Project Site 219. The data from Site 219 was combined with published foraminiferal and isotope data from Site 214, eastern Indian Ocean to determine the nature of changes. Factor and cluster analyses of the 28 highest-ranked species distinguished four biofacies, characterizing distinct deep-sea environmental settings. These biofacies have been named after their most dominant species such as Stilostomella lepidula–Pleurostomella alternans (Sl–Pa), Nuttallides umbonifer–Globocassidulina subglobosa (Nu–Gs), Oridorsalis umbonatus–Gavelinopsis lobatulus (Ou–Gl) and Epistominella exigua–Uvigerina hispido-costata (Ee–Uh) biofacies. Biofacies Sl–Pa ranges from ~ 2.36 to 0.55 Myr, biofacies Nu–Gs ranges from ~ 1.9 to 0.65 Myr, biofacies Ou–Gl ranges from ~ 1 to 0.35 Myr and biofacies Ee–Uh ranges from 1.1 to 0.25 Myr. The proxy record indicates fluctuating tropical environmental conditions such as oxygenation, surface productivity and organic food supply. These changes appear to have been driven by changes in monsoonal wind intensity related to glacial–interglacial cycles. A shift at ~ 1.2–0.9 Myr is observed in both the faunal and isotope records at Site 219, indicating a major increase in monsoon-induced productivity. This coincides with increased amplitude of glacial cycles, which appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the tropical Indian Ocean.
 
Article
Detailed records of the carbon and oxygen isotopic ratios of Neogloboquadrina pachyderma are compared between nine high-latitude sediment cores, from the Northern and Southern Hemispheres, covering the last 140 000 yrs. The strong analogies between the δ 13C records permit to define a δ 13C stratigraphic scale, with three clear cut transitions simultaneous with the oxygen isotopic transitions (125 kyrs.), (65 kyrs.), and (13 kyrs.). The δ 13C records of N. pachyderma in the high-latitude cores, which follow the changes in δ 13C of the surface water TCO2 near areas of deep water formation present trends similar to the benthic foraminifera δ 13C records in cores V19–30 and M12–392, although amplitudes of the isotopic shifts are different. This implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean.The ratios of N. pachyderma in the North Atlantic cores display larger regional variations at 18 kyrs. B.P. than at present. To explain these differences, we have plotted the 18 kyrs. B.P. δ 13C values of N. pachyderma from 17 cores distributed N of 40°N. Comparison with published surface water temperature distribution at 18 kyrs. B.P. indicates that a strong divergent cyclonic cell, centered approximatively 55°N and 15°W, was active during most of the last ice-age maximum. This hydrology, analogous to the present Weddell Sea, explains the published evidences of bottom water formation, if located on the northern flank of the gyre, and the strong polar front on the southern flank, probable location of intermediate water formation.
 
Article
Biogenic records of the marine palaeoproductivity (carbonates, organic carbon, and C37 alkenones) and the molecular stratigraphy of past sea surface temperatures (SSTs; U37K′) were studied at high resolution in two cores of the Iberian Margin. The comparison of these records indicates that the oceanographic conditions switched abruptly during the past 160 kyr between three kinds of regimes. A first regime with high (17–22°C) SST and low productivity typifies the interglacial periods, marine isotopic stages (MIS) 5 and 1. Several periods during MIS 6, 2, and the terminations II and I are characterised by about 4–5°C colder SST and a higher organic matter accumulation, both of which define the second regime. This anticorrelation between SST and marine productivity suggests that these variations are related to the intensity of the coastal upwelling. By contrast with this upwelling behaviour, extremely low biological productivity and very cold SST (6–12°C) occurred during short phases of glacial MIS 6, 4, and 2, and as abrupt events (≈1 kyr or less) during MIS 3. The three oceanographic regimes are consistent with micropalaeontological changes in the same cores based on foraminifera and diatoms.The general trend of these hydrologic changes follows the long-term glacial/interglacial cycle, but the millennium scale variability is clearly related to Heinrich events and Dansgaard–Oeschger cycles. Strengthening of the upwelling corresponds probably to an intensification of the subtropical atmospheric circulation over the North Atlantic which was influenced by the presence of continental ice sheets. However, extreme glacial conditions due to massive discharges of icebergs interrupted the upwelling. Interestingly, both terminations II and I coincided with strong but transient intensification of the upwelling.
 
Article
Analyses of sedimentological, geochemical and micropaleontological parameters from radiocarbon-dated sediment cores retrieved from the Antarctic Peninsula’s western continental shelf reveal a detailed paleoclimatic and/or paleoceanographic history over the last 15 000 radiocarbon years. Deglaciation of the outer shelf off Anvers Island commenced prior to at least 15 000 yr BP, marked by the deposition of distal glaciomarine diamicton (facies 2) beneath a floating ice shelf, and lasted for 3800 years with increasing diatom abundance and total organic carbon (TOC) over time. A return to colder conditions occurred between 12 800 and 11 600 yr BP with a drop in TOC content and diatom abundance, which is coincident with the Younger Dryas event in the North Atlantic region. At this time, an abrupt increase in percentage sea-ice taxa as well as in the ratio of (Fragilariopsis curta+Fragilariopsis cylindrus)/Thalassiosira antarctica suggests renewed ice-shelf advance. In contrast, the inner shelf was deglaciated somewhat later about 11 000 yr BP, that is, 3000 years after the outer shelf. Prior to 11 000 yr BP, deposition of proximal glaciomarine diamicton (facies 1) close to the grounding line under a floating ice shelf and/or persistent sea ice may have occurred on the inner shelf. After this date, deposition of distal glaciomarine diamicton (facies 2) followed. A climatic optimum is recognized between 6000 and 2500 yr BP, coinciding with a ‘mid-Holocene climatic optimum’ from several other Antarctic sites, e.g. the Palmer Deep. During this time, as the glacial system receded from the shelf, greatly enhanced primary productivity occurred in open marine conditions, resulting in the deposition of diatomaceous mud (facies 3) and causing post-depositional dissolution of calcareous benthic and planktonic foraminifers in sediment. Around 2500 yr BP (the onset of the Neoglacial), diatomaceous sandy mud (facies 4), characterized by a decrease in TOC and diatom abundance, reflects the formation of more extensive and seasonally persistent sea ice, as evidenced by an increase in percentage of sea-ice taxa and in the ratio of (F. curta+F. cylindrus)/T. antarctica. Our results provide evidence of climatic change on the Antarctic Peninsula’s western shelf that helps to refine the existence and timing of late Pleistocene and Holocene millennial-scale climatic events in the Southern Hemisphere.
 
Map showing the position of the IMAGES core MD972142. 
Relative abundances of six dominant species of planktic foraminifera for core MD972142, plotted against age and compared to downcore N 18 O stratigraphy. Shaded intervals indicate glacial periods.
Measured TOC concentrations, calculated TOC concentrations at constant productivity (147 g C/m 2 /yr; San DiegoMcGlone et al., 1999) and variable sedimentation rates (TOC expected, thin line), di¡erence between measured and calculated TOC concentrations (TOC residual = measured minus calculated TOC, dotted line), and SSTs for cold-and warm-season estimates by planktic foraminifer transfer functions from core MD972142, plotted against age and compared to downcore N 18 O stratigraphy. Shaded intervals indicate glacial stages.
Comparisons of MD972142 TOC, ODP 723 TOC (summer monsoon proxy) (Emeis et al., 1995) from the Arabian Sea, and Gulf of Aden benthic productivity and G. bulloides% (winter monsoon indicators) (Almogi-Labin et al., 2000) records.
Article
High-resolution records of planktic foraminifer sea-surface temperature (SST) and biogenic sediment components of carbonate and total organic carbon (TOC) concentrations were determined in an IMAGES giant piston core spanning ∼the last 500 000 years, taken near the western slope of Palawan Island in the southeastern South China Sea (SCS). The records provide information of paleoceanographic and paleoclimatological variations linked to East Asian monsoon systems in the SCS, the largest marginal sea of the western Pacific. Constrained by planktic foraminifer (Globigerinoides ruber) oxygen isotope stratigraphies, the records show a lowering of faunal SST by ∼3°C during glacial stages, indicating significant cooling in the glacial western Pacific climate. In general, they show low-frequency patterns with high SSTs, high carbonate content, and low TOC content during interglacial periods, and exhibit low SSTs, low carbonate content, and high TOC content during glacial periods. The carbonate content variations indicate that the sediment composition is mostly controlled by terrigenous inputs, which are associated with sea-level fluctuations in the SCS during past glacial–interglacial stages. The low SST and high TOC content indicate cooling and high productivity conditions in the surface oceans of the SCS, which also reflect a condition of intensified winter monsoon winds associated with glacial boundary conditions. Some rapid, high-frequency oscillations of the SST and TOC found in the records are coincident with intervals of intensified winter or summer monsoons from the Arabian Sea, implying that the Asian monsoon systems had wider regional effects than previously assumed. Time-series analyses reveal that variations in the SST, carbonate and TOC contents of this record contain statistically significant concentrations of variance at orbital frequency bands, namely 100 kyr−1, 41 kyr−1, and 23 kyr−1, suggesting that both ice volume and orbital solar insolation changes are potential mechanisms for the SCS monsoon variations.
 
Article
Variations in primary productivity (PP) have been reconstructed in eutrophic, mesotrophic and oligotrophic parts of the Arabian Sea over the past 135 000 years applying principal component analysis and transfer function to planktic foraminiferal assemblages. Temporal variation in paleoproductivity is most pronounced in the mesotrophic northern (NAST site) and oligotrophic eastern (EAST site) Arabian Sea, and comparatively weak in the western eutrophic GeoB 3011-1 site in the upwelling area off Oman. Higher PP during interglacials (250–320 g C m−2 year−1) than during cold stages (210–270 g C m−2 year−1) at GeoB 3011-1 could have been caused by a strengthened upwelling during intensified summer monsoons and increased wind velocities. At NAST, during interglacials, PP is estimated to exceed 250 g C m−2 year−1, and during glacials to be as low as 140–180 g C m−2 year−1. These fluctuations may result from a (1) varying impact of filaments that are associated to the Oman coastal upwelling, and (2) from open-ocean upwelling associated to the Findlater Jet. At EAST, highest productivity of about 380 g C m−2 year−1 is documented for the transition from isotope stage 5 to 4. We suggest that during isotope stages 2, 4, 5.2, the transition 5/4, and the end of stage 6, deep mixing of surface waters was caused by moderate to strong winter monsoons, and induced an injection of nutrients into the euphotic layer leading to enhanced primary production. The deepening of the mixed layer during these intervals is confirmed by an increased concentration of deep-dwelling planktic foraminiferal species. A high-productivity event in stage 3, displayed by estimated PP values, and by planktic foraminifera and radiolaria flux and accumulation rate, likely resulted from a combination of intensified SW monsoons with moderate to strong NE monsoons. Differential response of Globigerina bulloides, Globigerinita glutinata and mixed layer species to the availability of food is suited to subdivide productivity regimes on a temporal and spatial scale.
 
Article
Three Mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200–60 kyr BP. The isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water (δw) in the Tyrrhenian Sea and Levantine basin. Our results show a strong δw/salinity decrease in both basins associated with each sapropel. These δw decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel (S1) centred at ca. 8 kyr BP. A strong precipitation increase transformed the whole Mediterranean Sea into a non-concentration basin. The low surface salinity was responsible for the water column stratification, while nutrients brought in by the runoff enhanced productivity. It resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin. In addition, the Mediterranean Sea δ18O record is very similar to that of the Bay of Bengal. As the latter is very sensitive to the summer monsoon rain, this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon-like precipitation due to an increase in summer insolation driven by precession variations.
 
Article
A high-resolution age–depth profile is presented for a 16-m deep-sea piston core (EW9709-PC07) using three different methods: magnetostratigraphy, fish-teeth strontium isotope stratigraphy, and radiolarian biostratigraphy. Fish teeth are abundant throughout the core, allowing for precise age determinations by Sr isotope stratigraphy. Magnetostratigraphic ages, though not available for this core, were determined by correlation with the drill core record from adjacent ODP Site 1218. Biostratigraphic ages were independently assigned to the lower 12 m of the core, which contains abundant radiolaria. All three methods define an early Miocene age (∼20 Ma) for the core base. A linear sedimentation rate of ∼2.0 mm/ky was calculated for the lower 10 m of the core, which is dominated by siliceous clays and calcareous ooze. All three methods yield concordant ages over this interval (∼20 to 15 Ma). Tectonic migration of the PC-07 site away from the equatorial high productivity zone produced a significant decrease in sedimentation rates after 15 Ma, diminishing to just ∼0.30 mm/ky in the uppermost 3 m of the core. Correlated magnetic reversal and fish teeth ages are concordant within this upper red clay interval (∼10 to 0.0 Ma), which is dominated by eolian dust accumulation; however, within the 15 to 10 Ma interval, fish teeth ages appear to show more scatter, departing from the magnetic ages by as much as 2–3 million years. Age discrepancies in this dominantly siliceous clay interval are most likely due to uncertainties in magnetostratigraphic age correlations. We conclude from this that the eolian dust component in red clay cores can be reliably dated by the fish teeth strontium technique. For otherwise undatable red clay cores from the vast northern Pacific pelagic clay province, this may prove to be the only available method for developing a regional Cenozoic chrono-stratigraphy.
 
Article
We present measurements of the maximum diameter of the planktonic foraminifer Neogloboquadrina pachyderma sin. from six sediment cores (Ocean Drilling Program sites 643, 644, 907, 909, 985 and 987) from the Norwegian–Greenland Sea. Our data show a distinct net increase in mean shell size of N. pachyderma sin. at all sites during the last 1.3 Ma, with largest shell sizes reached after 0.4 Ma. External factors such as glacial–interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of N. pachyderma sin. We consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of N. pachyderma sin. to the cold water environment after 1.1–1.0 Ma. Probably, the Mid Pleistocene climate shift and the associated change of amplitude and frequency of glacial–interglacial fluctuations have triggered the evolution of this planktonic foraminifer. Oxygen and carbon stable isotope analyses of different shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis. For paleoceanographic reconstructions, the evolutionary adaptation of Neogloboquadrina pachyderma sin. to the cold water habitat has significant implications. Carbonate sedimentation in highest latitudes is highly dependent on the presence of this species. In the Norwegian–Greenland Sea, carbonate-poor intervals before 1.1 Ma are, therefore, not necessarily related to severe glacial conditions. They are probably attributed to the absence of this not yet polar-adapted species. Further, transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could, therefore, contain a large range of errors if they were applied to samples older than 1.1–1.0 Myrs.
 
Article
An interdisciplinary study of the geologic and archaeological records of a 50 ky year period at the Plio-Pleistocene boundary in Olduvai Basin (Tanzania) revealed that a small groundwater-fed wetland was a consistent focus of hominin activity during periods of climate change (wet/dry cycles). Paleoenvironmental analysis of sedimentary records from 33 excavations in Lowermost Bed II (LMB II), Olduvai Gorge (3° S) revealed evidence of significant climate fluctuations that produced two and one half lake cycles between ~ 1.79 and 1.74 Ma. The region experienced wet-dry cycles in response to combined astronomical forcing effects of eccentricity (~ 100 ky cycle) and precession of the equinox (19 and 23 ky cycles). Rhythmic variability of the monsoon system produced wet periods followed by a transition into dry periods followed by a transition back into wet climate. A high-resolution study of the stratigraphy documented a groundwater-fed wetland complex (~ 1 km2) that flourished during low lake levels (dry periods) and was drowned during high lake levels (wet periods). Stratigraphic analysis (temporal changes) of 916 artifacts from 13 excavations selected from a landscape transect across alluvial fan, spring/wetland and lake margin environments showed no notable differences in artifact type frequency and raw material type when comparing wet periods (as a group) and dry periods (as a group). However, a lateral shift of hominin activity on the landscape did occur between wet and dry periods. The Oldowan tool kit did not vary at spring sites between wet and dry periods, whereas the tool kit did vary at other lake margin sites between wet and dry periods. Both analyses suggest that climate affected the location of an activity, not type of activity. These data suggest that Oldowan hominins adapted their land-use patterns to exploit spring/wetland resources available during dry periods. A switch from wet to dry conditions likely altered surface and groundwater systems affecting food and potable water availability, forcing hominins to adjust their subsistence patterns.
 
Article
Six lake sediment vibracores from the foothills and mountain valleys of southwestern Alberta were analysed on the basis of AMS radiocarbon dates, tephrochronology and sediment geochemistry. From these results, the magnitude, timing and duration of the early Holocene warm period are presented. At about 10,000 BP, immediately following the Younger Dryas cold period, climate warmed dramatically, precipitation decreased and surface evaporation increased. Previous research has identified this warm interval, but new results have improved resolution of regional scale effects, specific timing and severity. Sedimentation changed from extra-basinal clastic to intra-basinal organic between 10,000 and 9400 BP. Changes in subalpine lakes from sand/silt deposition to biogenic carbonate precipitation suggest decreases in suspended sediment load caused by complete ablation of glacial sediment sources. Peat which formed in lakes of less than 4 m (present depth) indicates climate-induced lake level lowering in the foothills. Water depth and stratigraphic position of the peat suggest that regional water table levels decreased by up to 6.5 m. At Cartwright Lake, an erosional unconformity 6.5 m below the modern lake surface indicates the lake had completely dried out either during or immediately after Mazama tephra time (6800 BP).
 
Article
A suite of piston cores recovered from Lake Malawi (9–14°S, 34–35°E), east Africa in 1986 has been analyzed for major and minor elements, organic C and N, calcium carbonate and diatoms. An internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera, Stephanodiscus and Melosira, with age control obtained primarily from 14C dating of the carbonate. Differences with time in Fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth. The depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr B.P., indicating less seasonality. Carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column. The carbonate, which precipitates from surface waters, is most abundant during the interval from about 10,000 to 6000 yr B.P. This micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced. Sedimentary evidence suggests that lake levels were 100–150 m lower than present during this period. This record is different from climatic trends in northern intertropical Africa, but appears to also be related to changes in insolation and monsoon circulation. This is the northernmost basin in Africa reported to exhibit a “southern hemisphere” response to the early Holocene northern hemisphere summer insolation maximum. The climatic hingeline north of Lake Malawi (∼ 9°S) implied by our results is significantly south of that indicated by general-circulation model simulations, however. The cores show evidence for periods of abrupt climate change during the interval of generally arid climate.
 
Article
A high-resolution, continuous 10,500 cal. yrs-long macroscopic charcoal record from a peat and lake sediment deposit at Storasjö, in the hemiboreal vegetation zone of southern Sweden, is presented. This record was compared with the microscopic charcoal record from the same core, and tentatively correlated with the macroscopic and microscopic charcoal records from another site (Stavsåkra), situated 30 km West of Storasjö. The charcoal records are also compared with regional climate proxy records with the aim to separate climate — from human-induced fire activity. The results suggest that the major signal of both microscopic and macroscopic charcoal records represents local fire history. The best record of local fire history was obtained from the continuous macroscopic charcoal analysis. A tentative correlation of the charcoal records between the sites indicates that most fire episodes of the early and middle Holocene are probably of regional character. Both sites exhibit three major phases of high fire activity 1) 8700–8300 BC, 2) 7250 BC to ca. 4000 BC, and 3) 750 BC to the 19th century. These three phases are separated by periods with lower or very low fire activity. This general trend is in good agreement with the pattern emerging for Europe from the analysis of the recently developed global charcoal database. Fire appears to have been controlled by climate during the early and middle Holocene and by humans during the late Holocene. Warmer and drier climate during the early and middle Holocene caused frequent and intensive fires, which suggests that natural fire activity might increase under predicted future climate scenarios. The results also suggest that fire was an important disturbance factor in the hemiboreal vegetation zone of Sweden and played an important role in the forest dynamics and characteristics of the flora and fauna of the region.
 
Article
Glaciolacustrine rhythmites within sediment cores from Lake Superior record the regional recession of the Laurentide Ice Sheet (LIS) from 10,700 to 8900 cal ybp [ca. 9.5–8.0 14C ka]. LIS retreat from Superior opened eastern Lake Agassiz outlets so that the rhythmites reflect the combined impacts of sediment-laden meltwater and Lake Agassiz discharge. Multiple rhythmite stratigraphies, a time series analysis of the thickness measurements, and high-resolution inorganic carbonate data demonstrate that this is an annual record (varved). The varve thickness records primarily document regional ice margin dynamics; correlative thick varve sequences at 9100 cal ybp [∼ 8.1 14C ka] and 10,400–10,200 cal ybp [∼ 9.2–9.0 14C ka] record two periods of enhanced glaciofluvial discharge, most likely moraine formation (the Nakina and Nipigon). General varve cessation is associated with the circumvention of Lake Agassiz and glacial meltwater into Lake Ojibway at 9040 cal ybp [∼ 8.1 14C ka], although adjacent to the inlets from Lake Nipigon, rhythmic sedimentation persisted for 200 years.Positively identifying Lake Agassiz catastrophic discharge events remains speculative but seems feasible. Following retreat of Marquette ice that had re-advanced to fill the basin, the initial influx of Lake Agassiz water is expected at around 10,600 cal ybp [∼ 9.4 14C ka], but at this time, most of northeastern Lake Superior was covered by ice. Three sets of thick–thin varves in western Lake Superior perhaps record influxes of Lake Agassiz at around 10,630, 10,600, and 10,570 cal ybp [∼ 9.4 14C ka]. Varve formation in Superior coincides with high lake levels in Lake Huron, suggesting that high lake levels in Huron correspond to periods of high Agassiz and/or meltwater flow into Lake Superior.
 
Article
Tectonic influences on long-term climate change are of considerable current interest and debate. This paper reviews the relationship between multi-million year periods of glaciation (glacio-epochs) over the last 3 Ga of Earth history and phases of supercontinent breakup and assembly. A preferred but not exclusive relationship is evident between glacio-epochs and their mostly glacially influenced marine record, with rifting. The earliest known glaciation (mid Archean ∼ 2.9 Ga) is recorded in the marine Mozaan Group of South Africa deposited along the passive margin of the Kapvaal Craton then part of the early continent Ur. The Paleoproterozoic glacio-epoch, exemplified by the Huronian Supergroup of Ontario, Canada (∼ 2.4 Ga) and strata in northern Europe and the U.S., is associated with rifting of Kenorland. A long Paleo-Mesoproterozoic non-glacial interval (c. 2.3 Ga to 750 Ma?) coincides with continental collisions and high standing Himalayan-scale orogenic belts marking the suturing of supercontinents Nena-Columbia and Rodinia. A near absence of glacial deposits other than at 1.8 Ga, may reflect lack of preservation. The extensive and prolonged Neoproterozoic glacio-epoch records either diachronous glaciations or discrete pulses of cooling between ∼ 750 and ∼ 580 Ma, and is overwhelmingly recorded by substantial thicknesses (1 km+) of glacially influenced marine strata stored in rift basins. These formed on the mid to low latitude (< 30°) oceanic margins of western (Panthalassa: Australia, China, Western North America) and eastern (Iapetus: Northwest Europe) margins of a disintegrating Rodinia. The youngest glacially influenced deposits formed about 580 Ma along the compressional Cadomian Belt exterior to Rodinia (Gaskiers Formation) possibly correlative with the classic passive margin Marinoan deposits of South Australia.
 
Article
This paper presents an updated, extensive review of glacier fluctuations during the past 1000 years in the extratropical Andes of South America between ca. 17° and 55°S. Given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range, regional accounts are given for the Desert Andes (∼ 17°–31°S), the Andes of central Chile and Argentina (31°–36°S), and the North (36°–45°S) and South (45°–55°S) Patagonian Andes. The techniques, dating limitations, and interpretations of the glacier records along this transect are also discussed. Information on glacier fluctuations in the Desert Andes is limited to the 20th century. Documentation on past glacier variations is more abundant in the Central Chilean-Argentinean Andes, but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited. Most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. The number and extent of glaciers increase significantly in the Patagonian region, where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area. For some Patagonian glaciers, maximum Little Ice Age (LIA) or post-LIA advances have been precisely dated by dendro-geomorphological determinations or in situ measurements. However, for most sites, the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum LIA expansion identified in most areas between the 16th and 19th centuries. Evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium. These events were generally less extensive than the LIA maximum pulses. Despite the occurrence of several post-LIA readvances over the past 100–110 years, most areas in the Andes of extratropical South America have experienced a general pattern of glacier recession and significant ice mass losses. The differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and/or the dating techniques used in each case together with the varying dominance of precipitation, temperature and other climatic and non-climatic factors on glacier mass balance and glacier dynamics. These differences indicate that the late Holocene glacier history of southern South America is more complex than commonly assumed. The evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed, well-dated records of glacier fluctuations.
 
Article
Ice-volume estimates for the early Miocene (23–16 Ma ATS) were determined by applying δ¹⁸O to sea-level calibrations to high-resolution δ¹⁸O records from ODP Sites 1090 and 1218. These calibrated records indicate that ice-volume ranged between 50% and 125% of the present day East Antarctic Ice Sheet (EAIS) during most of the early Miocene (23–17 Ma). Maximum ice-volume occurred at each of the early Miocene isotopic events (i.e., Mi-events) concomitant with bottom water temperatures generally between ∼1 and 2 °C. Rapid (≪ 1 myr) and high amplitude ice-volume changes also occurred intermittently during this period, with some fluctuations ranging from a fully glaciated East Antarctic continent to a partial collapse of the ice sheet (equivalent to a 50–70% reduction in the EAIS). These large-scale ice-volume changes often occurred at < 100 kyr time scales suggesting an orbitally driven dynamic EAIS existed during the early Miocene. In contrast, the calibrated δ¹⁸O record from Site 1090 indicates significantly less ice-volume (25–70% of the present-day EAIS) was present between 17 and 16 Ma. These results are supported by numerical climate–ice sheet modeling studies that show increased orbitally driven ice-volume variability with elevated levels of atmospheric CO2.
 
Article
Uppermost Maastrichtian benthic foraminiferal assemblages (> 63 μm) are diverse, indicating mesotrophic conditions in lower bathyal DSDP Hole 465A (Hess Rise, central North Pacific), in 4 lower bathyal land sections in central-East and Northeastern Mexico, and in the upper to middle bathyal Agost section (Tethys area, Southeastern Spain). They indicate more eutrophic conditions in lower bathyal ODP Hole 1049C (Blake Nose, Northwestern Atlantic). Benthic foraminifers did not suffer significant extinction at the K/Pg boundary, but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections, with the exception of DSDP Hole 465A where the percentage of infaunal taxa increased. These faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor, as a result of the collapse of primary productivity at the K/Pg boundary. The decrease in food supply apparently affected the benthic faunas least at more eutrophic NW Atlantic ODP Site 1049 and at Pacific DSDP Site 465, which is distal from the impact site of the K/Pg bolide on the Yucatan Peninsula. At these sites the faunas recovered within the Parvulorugoglobigerina eugubina Biozone (∼ 100 ky), although diversity and heterogeneity remained low through the early Danian, possibly indicating environmental stress. This stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos, such as various bloom species of dinoflagellates. Benthic assemblages recovered more slowly (∼ 300 ky) in the Mexican and Spanish sections. Low oxygen conditions after the K/Pg boundary could be inferred from the benthic assemblages at Agost (Southeastern Spain) only. A short episode of hypoxia, however, may be obscured at Pacific DSDP Hole 465A by drilling disturbance, and in the Mexican sections and Hole 1049C by incomplete sections due to downslope transport. Benthic foraminiferal assemblages thus appear to have been affected by the collapse of primary productivity at the K/Pg boundary to a different extent in different regions, and took different lengths of time for their recovery after the boundary.
 
Detail of Leg 1049C section 8X-5, and Scanning Electron Microscope photographs of some of the most characteristic benthic foraminiferal species in each unit. The scale bars correspond to 100 Am. (1): limonitic layer; (2): dark grey burrow-mottled clays. Biostratigraphy modified after Norris et al. (1999) and Huber et al. (2002). (For color see online version).  
Article
Sediments recovered at lower bathyal ODP Site 1049 on Blake Nose (Northwestern Atlantic) offer an opportunity to study environmental changes at the Cretaceous/Paleogene (K/P) boundary relatively close to the Chicxulub impact structure on the Yucatan peninsula, Mexico. In Hole 1049C, the boundary is located at the base of a 9-cm-thick layer with abundant spherules, considered to be impact ejecta. Uppermost Maastrichtian oozes below, and lowermost Danian pelagic oozes above the spherule-bed contain well-preserved bathyal benthic foraminifera. The spherule-bed itself, in contrast, contains a mixture of shallow (neritic) and deeper (bathyal) species, and specimens vary strongly in preservation. This assemblage was probably formed by reworking and down-slope transport triggered by the K/P impact. Across the spherule-bed (i.e., the K/P boundary) only ∼7% of benthic foraminiferal species became extinct, similar to the low extinction rates of benthic foraminifera worldwide. Quantitative analysis of benthic foraminiferal assemblages and morphogroups in the >63-μm size fraction indicates a relatively eutrophic, stable environment during the latest Maastrichtian, interrupted by a sudden decrease in the food supply to the benthos at the K/P boundary and a decrease in diversity of the faunas, followed by a stepped recovery during the earliest Danian. The recovery was probably linked to the gradual recovery of surface-dwelling primary producers.
 
Article
Coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of Huon Peninsula, New Guinea. Seven coral reef units, I–VII from the coast landwards spaced at about 20-kyr interval, provide a rather complete record of sea levels, oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle. The systematic sampling of the coral reefs was restricted to the massive Tridacna gigas species (the giant clam) which are about 0.7%0 enriched in 18O relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the δ18O of their aragonitic skeleton.
 
Article
We used multiple paleoceanographic proxies to examine sediments from the Blake Outer Ridge (ODP Site 1058, 2996 m water depth) that span the MIS 13–10 time interval. Benthic foraminiferal δ13C, organic δ13C, and total δ15N values are lower in MIS 12 and 10 than in MS 11, and indicate glacial–interglacial changes in both thermohaline circulation and ocean-wide biogeochemical processes that affect deep and surface waters. Three time intervals of higher productivity, as evidenced by higher organic carbon accumulation rates (1.6–4.5 g m− 2 yr− 1), occur at the end of MIS 13 and during the early and late parts of MIS 11, in association with the transition from obliquity minima to obliquity maxima. Benthic faunas in these intervals show a distinct increase in opportunistic species that feed on phytodetritus (Epistominella exigua) or are adapted to elevated but intermittent organic carbon fluxes (Bulimina aculeata and Bulimina marginata) and that imply episodes of recurrent phytoplankton blooms at the surface and consequent export of labile organic matter to the seafloor. Late interglacial MIS 11.3 is a time of low organic carbon fluxes (< 0.5 g m− 2 yr− 1) and is characterized by higher abundances of epifaunal benthic foraminiferal taxa (Cibicidoides wuellerstorfi, Gyroidina spp., Gyroidinoides spp. and Nuttallides umbonifera) that are typical of modern oligotrophic environments. In contrast, during glacial MIS 12 and 10 higher organic carbon fluxes (> 0.5 g m− 2 yr− 1) and benthic assemblages dominated by infaunal taxa (Uvigerina spp. and Bulimina alazanensis) indicate sustained organic carbon delivery and diminished pore water oxygenation.
 
Article
A 100 m long salt core (SQM #2005) from the Salar de Atacama, northern Chile (23°S, 68°W), a dry lake bed, contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central Andes of South America. Six U-series disequilibrium dates range sequentially from 106.1±6.4 to 5.4±2.7 ka. Based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments, interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods (saline lakes and expanded mudflats) existed in the Salar de Atacama from 75.7 to 60.7 ka and from 53.4 to 15.3 ka, with the wettest perennial lake interval from 26.7 to 16.5 ka. Short relatively wet periods also occurred in the Holocene from 11.4 to 10.2 ka and from 6.2 to 3.5 ka. These wet periods at Salar de Atacama correspond well with other late Pleistocene climate records from the central Andes that are a function of the net hydrologic budget. The Minchin–Tauca lake sequence from Salar de Uyuni, Bolivia, is synchronous with the 53.4–15.3 ka saline lake wet period at Salar de Atacama. The Tauca phase coincided with the wettest perennial lake interval at Salar de Atacama from 26.7 to 16.5 ka. The Coipasa lake phase from Uyuni was probably contemporaneous with the early Holocene wet period at Salar de Atacama from 11.4 to 10.2 ka. The early Holocene wet interval at Salar de Atacama was also synchronous with the maximum Holocene lake levels of the Chilean Altiplano lakes to the east and with grass-rich rodent middens between 11.8 and 10.5 ka in age from the Atacama basin.
 
Article
Late Quaternary fluctuations in the intensity of Congo River freshwater load were reconstructed using three different proxies (marine and freshwater diatoms, and the δ18O record of Globigerinoides ruber) preserved in the sediments of Ocean Drilling Program (ODP) Site 1077, located at the northern rim of the Congo River fan (5°10′S, 10°26′E). An abrupt change in the diatom assemblage is evident at Termination II: a two- to four-fold increase in (a) the relative abundance of a marine planktonic diatom tolerant of low salinity conditions (Cyclotella litoralis), and (b) in the concentration of freshwater diatoms. The microfossil data suggest a change in the environmental conditions surrounding Site 1077 from predominantly marine to mixed marine/brackish/fresh. The δ18O record of the planktic foraminifera G. ruber (pink) revealed negative deviations from the global oxygen isotope signal since Termination II which occurred during warm stage 1 and substages 3.2, 5.1, 5.3, and 5.5. Comparison of the isotopic signal of ODP Site 1077 with the record from a pelagic location (core GeoB1041 at 3°48′S, 7°05′W) confirms these results. The construction of an artificial δ18O curve using alkenone-derived sea surface temperature (SST) data from a nearby core (GeoB1008 at 6°S, 10°E) allowed us to estimate salinity and temperature effects on the ODP Site 1077 isotopic signal. Although increased SSTs may account for lighter δ18O values during warmer periods, they do not explain the extremely light values documented in the sediments of Site 1077. We used the oxygen isotope difference (Δδ18O) between our site and GeoB1041 as a proxy for freshwater input. A general trend in the Δδ18O was observed, with more negative values since Termination II. In addition, conspicuous Δδ18O negative pulses coincided with periods of northern hemisphere summer insolation maxima over the African continent, suggesting an increase in the freshwater discharge from the Congo River due to enhanced precipitation on the hinterland. Here we propose that the abrupt change in environmental conditions at Site 1077 since Termination II is a consequence of a major reorganization in the depositional environment of the Congo River delta. This reorganization involved sustained equatorward displacement of the Angola–Benguela Front causing a northward deflection of the Congo River plume thus moving plume waters further north than normal and over Site 1077.
 
Article
The intensification of the Northern Hemisphere Glaciation (INHG) was a major event in the development of the current climate state, and as one of the most productive regions in the world's oceans, the behaviour of the Benguela Upwelling System (BUS) following the INHG is of wide interest. To investigate post-INHG changes in productivity and organic matter accumulation, total organic carbon and biomarker accumulation rates were determined for sediments from ODP Site 1083 and compared to alkenone-derived sea surface temperatures and nitrogen isotopic compositions. These data indicate that the interval between 2.6 and 2.4 Ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern BUS. The upwelling is reflected by significant changes in alkenone-derived SST estimates between glacial and interglacial intervals, with a total variability of 16 °C. The studied interval is also characterized by large changes in organic matter export as reflected by changes in TOC and biomarker accumulation rates, which show maxima during OIS 98 and during the transition from OIS 97 to 96. Intervals of elevated TOC are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower %CaCO3, suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released CO2 being consumed by CaCO3 dissolution. However, in apparent contrast to recent Pleistocene sediments at the same site, organic matter export after the INHG was not solely driven by upwelling intensity. Of the three Pliocene glacial–interglacial cycles examined (OIS 101 to 96), each is unique with respect to the timing and magnitude of changes in organic matter accumulation. Each is also characterized by different algal assemblages as inferred from biomarker distributions, with OIS 97 and 96 particularly dominated by diatoms. We suggest that these differences reflect the important but evolving role of Southern Ocean waters in the Pliocene BUS: nutrient depletion of SO waters occurred during parts of Pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates.
 
Article
The middle Miocene δ18O increase represents a fundamental change in earth's climate system due to a major expansion and permanent establishment of the East Antarctic Ice Sheet accompanied by some effect of deepwater cooling. The long-term cooling trend in the middle to late Miocene was superimposed by several punctuated periods of glaciations (Mi-Events) characterized by oxygen isotopic shifts that have been related to the waxing and waning of the Antarctic ice-sheet and bottom water cooling.Here, we present a high-resolution benthic stable oxygen isotope record from ODP Site 1085 located at the southwestern African continental margin that provides a detailed chronology for the middle to late Miocene (13.9–7.3 Ma) climate transition in the eastern South Atlantic. A composite Fe intensity record obtained by XRF core scanning ODP Sites 1085 and 1087 was used to construct an astronomically calibrated chronology based on orbital tuning. The oxygen isotope data exhibit four distinct δ18O excursions, which have astronomical ages of 13.8, 13.2, 11.7, and 10.4 Ma and correspond to the Mi3, Mi4, Mi5, and Mi6 events. A global climate record was extracted from the oxygen isotopic composition. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The oxygen isotope data support a causal link between sequence boundaries traced from the shelf and glacioeustatic changes due to ice-sheet growth.Spectral analysis of the benthic δ18O record shows strong power in the 400-kyr and 100-kyr bands documenting a paleoceanographic response to eccentricity-modulated variations in precession. A spectral peak around 180-kyr might be related to the asymmetry of the obliquity cycle indicating that the response of the dominantly unipolar Antarctic ice-sheet to obliquity-induced variations probably controlled the middle to late Miocene climate system. Maxima in the δ18O record, interpreted as glacial periods, correspond to minima in 100-kyr eccentricity cycle and minima in the 174-kyr obliquity modulation. Strong middle to late Miocene glacial events are associated with 400-kyr eccentricity minima and obliquity modulation minima. Thus, fluctuations in the amplitude of obliquity and eccentricity seem to be the driving force for the middle to late Miocene climate variability.
 
Article
Middle to late Miocene calcareous nannofossil data of ODP Site 1085 from the eastern South Atlantic off Namibia were analysed to document spatial and temporal changes in surface-ocean circulation, upwelling initiation, and associated productivity.Our data show that calcareous nannofossils constitute a significant part of the carbonate fraction throughout the investigated interval from 12.5 to 7.7 million years (Ma). Highest numbers of calcareous nannofossils (up to 38,000 × 106 nannofossils g− 1 sediment) were observed during the intervals 9.9 to 9.7 and 8.7 to 8.0 Ma. These elevated numbers of calcareous nannofossils may generally be linked to the initiation of upwelling at about 10 Ma in the studied region. In contrast, diminished numbers of calcareous nannoplankton, as in the interval 9.6 to 9.0 Ma, probably characterise time intervals of weaker productivity resulting in a decrease of nannofossil carbonate contents in the sediments of Site 1085. This decrease in nannofossil production could be one possible explanation for the major CaCO3 depression in between 9.6 and 9.0 Ma. Coccoliths of the genus Reticulofenestra are the most abundant taxa. Their occurrences are characterised by changes in the investigated time interval. In addition, Coccolithus pelagicus, Calcidiscus leptoporus and Umbilicosphaera spp. contribute a common part of the assemblage. Calcareous nannofossils account for more than half of the carbonate, with peak contribution up to 80% at 8.8 Ma.
 
Article
Coccolithophore assemblages at ODP Site 1089 in the southern Cape Basin (∼41°S) were used to reconstruct surface-water conditions for the late Quaternary (Marine Isotope Stages (MIS) 1–15) in a region of strong hydrographic gradients in the southeast Atlantic. Stratigraphic control was provided by oxygen isotope stratigraphy and calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. The greatest coccolith abundances occurred at glacial terminations and, to a lesser degree, during glacial stages. Conversely, coccolithophores were the least abundant during the transition between interglacial to glacial stages, when calcium carbonate dissolution was strong. With the exception of these intervals, coccolith preservation is moderate to good, allowing study of the assemblages. The total abundance of coccolithophores and calcium carbonate variations at Site 1089 result both from variations in dissolution and carbonate production. During terminations, for example, the greatest calcium carbonate concentrations occurred at the same time as a moderate-to-poor preservation of coccoliths and foraminifers. Carbonate production was relatively high during these intervals. However, during terminations IV and V, maxima in carbonate production in the ocean were linked to high-dissolution processes at Site 1089. This trend is not observed for terminations I, II and III [Hodell et al., Earth Planet. Sci. Lett. 192 (2001) 109–124]. The interval from MIS 9 to 13 is coincident with high abundances of highly calcified species such as Gephyrocapsa caribbeanica. Here we discuss the contribution of this ubiquitous species to the production of calcium carbonate and their paleoecological significance. Except for occasional coccolith-barren intervals during interglacial periods, subtropical coccolith species were present continuously at ODP Site 1089 during the late Pleistocene. This suggests that the Polar Front has been south of Site 1089 for the last 600 kyr.
 
Article
Two cores, Site 1089 (ODP Leg 177) and PS2821-1, recovered from the same location (40°56′S; 9°54′E) at the Subtropical Front (STF) in the Atlantic Sector of the Southern Ocean, provide a high-resolution climatic record, with an average temporal resolution of less than 600 yr. A multi-proxy approach was used to produce an age model for Core PS2821-1, and to correlate the two cores. Both cores document the last climatic cycle, from Marine Isotopic Stage 6 (MIS 6, ca. 160 kyr BP, ka) to present. Summer sea-surface temperatures (SSSTs) have been estimated, with a standard error of ca. ±1.16°C, for the down core record by using Q-mode factor analysis (Imbrie and Kipp method). The paleotemperatures show a 7°C warming at Termination II (last interglacial, transition from MIS 6 to MIS 5). This transition from glacial to interglacial paleotemperatures (with maximum temperatures ca. 3°C warmer than present at the core location) occurs earlier than the corresponding shift in δ18O values for benthic foraminifera from the same core; this suggests a lead of Southern Ocean paleotemperature changes compared to the global ice-volume changes, as indicated by the benthic isotopic record. The climatic evolution of the record continues with a progressive temperature deterioration towards MIS 2. High-frequency, millennial-scale climatic instability has been documented for MIS 3 and part of MIS 4, with sudden temperature variations of almost the same magnitude as those observed at the transitions between glacial and interglacial times. These changes occur during the same time interval as the Dansgaard–Oeschger cycles recognized in the δ18Oice record of the GRIP and GISP ice cores from Greenland, and seem to be connected to rapid changes in the STF position in relation to the core location. Sudden cooling episodes (‘Younger Dryas (YD)-type’ and ‘Antarctic Cold Reversal (ACR)-type’ of events) have been recognized for both Termination I (ACR-I and YD-I events) and II (ACR-II and YD-II events), and imply that our core is located in an optimal position in order to record events triggered by phenomena occurring in both hemispheres. Spectral analysis of our SSST record displays strong analogies, particularly for high, sub-orbital frequencies, to equivalent records from Vostok (Antarctica) and from the Subtropical North Atlantic ocean. This implies that the climatic variability of widely separated areas (the Antarctic continent, the Subtropical North Atlantic, and the Subantarctic South Atlantic) can be strongly coupled and co-varying at millennial time scales (a few to 10-ka periods), and eventually induced by the same triggering mechanisms. Climatic variability has also been documented for supposedly warm and stable interglacial intervals (MIS 1 and 5), with several cold events which can be correlated to other Southern Ocean and North Atlantic sediment records.
 
Article
During Leg 177 of the Ocean Drilling Program, an expanded sequence of Pliocene to Holocene calcareous muds was recovered at Site 1089 on a drift deposit in the southern Cape Basin (SE South Atlantic). The reconstruction of detrital sources and modes of sediment transport gives insight into the operational modes of regional current systems in response to climate variability over the last 590 kyr, as inferred from sedimentological and mineralogical parameters of the terrigenous sediment fraction. Terrigenous sediments mainly originate from African sources with minor contributions from distant southern sources (South America and Antarctica) and are supplied by circumpolar water masses, North Atlantic Deep Water (NADW), and surface currents of the Agulhas Current. Changes in clay mineralogy as tracers of deep and shallow ocean circulation, best displayed by variations in quartz/feldspar ratios and kaolinite/chlorite ratios of clay, reflect both the northward displacement of NADW injection into the Antarctic Circumpolar Current and a weakening of Agulhas Current leakage from the Indian Ocean around South Africa to the South Atlantic during glacial stages, sub-stages, and stadials. Modifications of these regional current patterns are consistent with perturbations in global conveyor circulation and climate variability on Milankovitch and sub-Milankovitch time scales. Elevated mass-accumulation rates of terrigenous matter generally document high particle fluxes and focusing effects by bottom-current action throughout the late Quaternary. Current sorting and coarsening of terrigenous mud, independently of its source signals, prevails during interglacial periods and is linked to a stronger flow of Antarctic Bottom Water and the invigoration of deep contour currents in response to long-term changes (100-kyr cyclicity) in Antarctic ice-sheet dynamics, high-amplitude fluctuations in global sea level, and increased bottom-water formation.
 
Article
A detailed palynological analysis of two cores recovered from a swamp in the Southern Batéké Plateaux (Congo), provides information on the botanical history of this region during the last 24,000 yr B.P. Rich and well-diversified pollen counts exhibit changes in the vegetational communities related to hydrological and climatic fluctuations. Around 24,000 yr B.P., the occurrence of hydromorphous forest elements gives evidence of a humid phase. Between 24,000 and around 13,000 yr B.P., swampy herbaceous communities expanded, indicating slightly drier climatic conditions. From approximately 13,000 yr B.P. onward, the beginning of a humid episode is reflected by the development of mesophilous forests. The decrease of these forests is documented since 3000 yr B.P. Grasslands are found to extend locally whereas Elaies guineensis (oil palm) spreads out, indicating both climatic change but also anthropogenic activities.
 
Article
Changes in ocean circulation and climate during the Cenozoic led to the development of the Antarctic Circum-polar Current (ACC) and permanent Antarctic ice sheets. However, the timing of the opening of the Drake Passage and the establishment of the ACC is poorly constrained. We present geochemical proxies of terrigenous inputs and export production at a single site in the southeastern Atlantic Ocean that suggest the Drake Passage had opened to intermediate and deep water by 32.8 Ma. Two separate styles of sedimentation and geochemical composition of terrigenous material are observed, with the change in sediment geochemical characteristics occurring at 32.8 Ma. Middle to late Eocene records are highly variable, while latest Eocene to early Miocene records exhibit cyclic variations in elemental records and terrigenous material. Based on Al/Ti ratios, metal sources change from continental crust to oceanic crust sources at the Eocene/Oligocene transition, which we suggest reflects a change in deep-water circulation. Phosphorus/metal ratios indicate that there are two distinct intervals of enhanced export production, one in the middle Eocene and one throughout the Eocene/Oligocene transition. Elevated Al/Ti ratios, greater than any lithic source, in the middle Eocene provide evidence of particulate scavenging and thus increased export production. Barium ratios further support changes in productivity in the middle Eocene and at the Eocene/Oligocene transition. Permanent changes in the Ba concentration record in the early Oligocene further support a change in deep-water circulation due to the opening and deepening of the Drake Passage at 32.8 Ma.
 
Article
Quantitative study on calcareous nannofossil assemblages has been performed in high time resolution (2–3 kyr) at the Ocean Drilling Program Site 1090. The location of this site in the Southern Ocean is crucial for the comprehension of thermohaline circulation and frontal boundary dynamics, and for testing the employ of nannoflora as paleoceanographical tool. The chronologically well constrained investigated record spans between Marine Isotope Stage (MIS) 35 and 15, through an interval of global paleoclimate and paleoceanographical modification also known as mid-Pleistocene revolution (MPR). Measures of ecological (Shannon–Weaver diversity and paleoproductivity) and dissolution indices together with spectral and wavelet analyses carried out on the acquired time series provide valuable information for interpretation of data in terms of paleoecology and paleoceanography. Assemblages are mainly represented by dominant small Gephyrocapsa, common Calcidiscus leptoporus s.l., Coccolithus pelagicus s.l., Gephyrocapsa (4-5.5 μm), the extinct Pseudoemiliania lacunosa and Reticulofenestra spp. (R. asanoi and Reticulofenestra sp.). Morphotypes discriminated within Calcidiscus leptoporus s.l. and Coccolithus pelagicus s.l., reveal that they may have had different ecological preferences during Pleistocene with respect to the present. The composition and fluctuation in nannofossil assemblage and their comparison with the available Sea Surface Temperature (SST) and C-org curves suggest a primary ecological response to paleoenvironmental changes; relationships to different surface water features and boundary dynamics, as well as to different efficiencies and motions of the intermediate and deep water masses have been inferred. A more northward position of Subantarctic Front (SAF) during most of the Early Pleistocene record has been highlighted based on assemblage composition characterised by common Calcidiscus leptoporus s.l., Coccolithus pelagicus s.l., medium Gephyrocapsa (4–5.5 μm), and by the rarity or absence of Umbilicosphaera spp., Rhabdosphaera spp., Pontosphaera spp., Oolithotus fragilis. Exceptions are the more intense interglacials MIS 31, 17, and probably MIS 15, when a southward displacement of frontal system occurred, coincident with peaks in abundance of Helicosphaera spp. and Syracosphaera spp. Higher nutrient content and more dynamic conditions occurred between MIS 32 and MIS 25, in relation to shallower location of nutrient-rich Antarctic Intermediate Water (AAIW) core and to reduction of glacial–interglacial variability. A nannofossil barren interval is coincident with the known stagnation of South Atlantic deep water circulation during MIS 24, when North Atlantic Deep Water (NADW) was reduced or suppressed and an enhanced northward deep penetration of the more corrosive Circumpolar Deep Water (CPDW) took place. An event of strong instability in nutricline dynamics characterised the transition MIS 23–22 as suggested by sharp fluctuations in paleoproductivity proxies, linked to major changes in oceanographic circulation and to the first distinct increase of larger ice volumes at this time. From MIS 21 upward the nannofossil variations seem to be primarily controlled by glacial–interglacial cyclicity and temperature fluctuations. The cyclic fluctuation recognised in nannofossil abundance seems to be linked to orbitally-forced climatic variation, primarily to the obliquity periodicity recorded in the patterns of C. leptoporus intermediate (5–8 μm) and C. pelagicus pelagicus (6–10 μm); however no obvious and linear relations may be always observed between nannoflora fluctuation and Milankovitch parameters, suggesting more complex and unclear relationships between nannofossils and environmental change.
 
Article
One important goal of Leg 177 of the Ocean Drilling Program (ODP) was to explore the nature of the mid-Pleistocene climate transition (MPT) on the southern hemisphere. A suitable MPT record was encountered at Site 1090 in the southeastern South Atlantic, where a 44-m-thick sequence of Quaternary diatom-bearing foraminiferal muds and oozes was recovered on the Agulhas Ridge. Environmental responses to the MPT comprised changes in terrestrial climate, biological productivity, and regional ocean circulation, as inferred from compositional sediment data and clay mineralogy. A shift towards more arid conditions occurred between 900 and 800 ka in southern Africa. Changes in palaeoceanography already started earlier. Since 1150 ka, northward displacements of the Polar Front appeared during glacial periods and shifted the area of dominant diatom deposition towards Site 1090. Likewise, glacial–interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka. However, while changes in regional conveyor circulation likely responded in tune with global ice-volume changes and show the onset of 100-kyr cycles after 1200 ka, an unusual 130-kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka, probably in response to imperfect adaptation of regional climate to the global 100-kyr climate cycles.
 
Article
Pleistocene summer sea-surface temperatures (SSST) have been reconstructed on a composite core section recovered in the Subantarctic Zone of the Southern Ocean from planktonic foraminifers applying the Modern Analog Technique. The composite consists of Core PS2489-2 and the sections recovered at ODP Site 1090, and documents the last 1.83 Ma. Three distinct climatic periods can be identified that mirror the Pleistocene development of the Southern Ocean hydrography. Cold climatic conditions prevailed at 43°S during glacial as well as during interglacial periods during the early Pleistocene (1.83–0.87 Ma), indicating a northward shift of isotherms that characterize the present-day Polar Front Zone by about 7° of latitude. Evidence shows a strong linkage between Southern Ocean and low latitude climate during that interval time. Between the Mid-Pleistocene Revolution (ca. 0.9 Ma) and the Mid-Brunhes Event (ca. 0.4 Ma), we observe higher amplitude fluctuations in the SSST between glacial and interglacial periods, corresponding to the temperature range between the present Polar Front and Subantarctic Front. These climatic variations have been related to changes in the northern hemisphere ice sheets. The past 0.4 Ma are characterized by strong SSST variations, of up to 8°C, between glacials and interglacials. Only during the climatic optima (stages 11.3, 9.3, 7.5, 7.1, 5.5, and the early Holocene), SSST exceeded present SSST at the core locality (10.2°C). Although the carbonate dissolution record exhibits high variability during the Pleistocene, it can be shown that SSST estimates were not significantly biased. The Mid-Brunhes dissolution cycle as well as the Mid-Pleistocene enhanced carbonate preservation appear to belong to a global long-term variability in carbonate preservation.
 
Article
Diatom assemblages from ODP Leg 177 sites 1093, 1094 and core PS2089-2, from the present Antarctic sea ice free zone and close to the Polar Front, were analyzed in order to reconstruct the climate development around the Mid-Brunhes Event 400 000 yr ago, as reflected by summer sea surface temperature (SSST) and sea ice distribution. Dense sample spacing allows a mean temporal resolution during Marine Isotope Stage (MIS) 11 (423–362 ka) of 300–400 yr. SSST values were estimated from diatom assemblages using a transfer function technique. The distribution pattern of sea ice diatoms indicates that the present-day ice free Antarctic Zone was seasonally covered by sea ice during the cold MIS 12 and MIS 10. These glacial periods are characterized by sea ice fluctuations with a periodicity of 3 and 1.85 kyr, suggesting the occurrence of Dansgaard–Oeschger-style millennial-scale oscillations in the Atlantic sector of the Southern Ocean during the glacial stages MIS 12 and MIS 10. Termination V (MIS 12/11) is characterized by a distinct temperature increase of 4–6°C, intersected especially at the southern site 1094 and core PS2089-2 by two distinct cooling events reminiscent of the Younger Dryas, which are associated with a northward shift of the winter sea ice edge in the Antarctic Zone. The SSST record is characterized by distinct temperature intervals bounded by stepwise, rapid changes. Maximum temperatures were reached during Termination V and the early MIS 11, exceeding modern values by 2°C over a period of 8 kyr. This pattern indicates a very early response of the Southern Ocean to global climate on Milankovitch-driven climate variability. The SSST optimum is marked by millennial-scale temperature oscillations with an amplitude of ca. 1°C and periodicities of ca. 1.85 and 1.47 kyr, probably reflecting changes in the ocean circulation system. The SSSTs during the MIS 11 temperature optimum do not exceed values obtained from other interglacial optima such as the early periods of MIS 5 or MIS 1 from the Antarctic Zone. However, the total duration of the warmest period was distinctly longer than observed from other interglacials. The comparison of the South Atlantic climate record with a high-resolution record from ODP Leg 162, site 980 from the North Atlantic shows a strong conformity in the climate development during the studied time interval.
 
Article
We present 35 10Be surface exposure ages from quartzite moraine boulders at Tres Lagunas in the Sierra de Santa Victoria, NW Argentina. Additionally, an ~ 8 m sediment core from a glacial lake was investigated to provide independent radiocarbon age control. The oldest and most extensive glaciation occurred ≥ 116.3 ka and likely coincides with the lake transgression phase Ouki on the Altiplano. Maximum glaciation in phase with the global Last Glacial Maximum (LGM) is dated to 22–25 ka and documents a glacial mass-balance response to substantially lower temperatures and minor precipitation increase in phase with the Sajsi lake transgression phase. After initial deglaciation and formation of a small paleolake at Tres Lagunas, a glacial readvance is documented by an outwash diamict in the sediment core and radiocarbon dated to 19–17 ka, as well as by a moraine surface exposure dated to ~ 17 ka. The most prominent moraine was deposited at ≥ 14.5 ka coinciding with the lake transgression phase Tauca on the Altiplano. This Late Glacial advance reflects the massive intensification of the South American Summer Monsoon (SASM) in response to northern hemispheric cooling during Heinrich I and the resultant southward shift of the intertropical convergence zone (ITCZ) and La Niña like conditions in the eastern equatorial Pacific. Rapid deglaciation started after ~ 14.5 ka, interrupted only by minor glacial still stands at ~ 13.8 ± 1.5 ka and 12.0 ± 1.5 ka, the latter one correlating with the Coipasa transgression phase on the Altiplano and the Younger Dryas.
 
Article
A key area for the understanding of the southeastern Iran geodynamics, the Hormoz Strait area, was investigated. Tectonically active, it provides useful sequences of Quaternary deposits whose deposition may have ended either when the climate dried or when the tectonic activity uplifted the riverbed. In-situ produced cosmogenic 10Be provides surface abandonment ages at 5.6 ± 0.6, 8.4 ± 1.0, 12.8 ± 1.0, 20.1 ± 1.5, and 44.0 ± 3.4 10Be kyr.Located at the transition between the Mediterranean Winter Rain and the Indian Monsoon domains, and south of the northernmost position of the ITCZ (InterTropical Convergence Zone), the studied area is very sensitive to climate changes. Some of the calculated 10Be abandonment ages are within the entire investigated area coincidental with large-scale climate shifts: the offset of the mid-Holocene humid period (5.6 ± 0.6 10Be kyr), the onset of the dry Younger Dryas cold and dry episode (12.8 ± 1.010Be kyr), and the end of the Last Glacial Maximum (LGM; 21 ± 2 kyr) at 20.1 ± 1.5 10Be kyr. These events correspond to large-scale changes in atmospheric circulation linked to global climate changes, and/or to sea-level fluctuations in the Persian Gulf, which was totally dry during the LGM.Locally observed abandonment ages at 8.4 ± 1.0 and 44.0 ± 3.4 10Be kyr may likely be related to enhanced tectonic activity without regional impact.
 
Vernon, new malacological investigations. List of different species recognized in the samples and individuals counted. 
Article
Tufa deposits in the Seine and the Avelasse Valleys have yielded numerous molluscsassemblages belonging to the Lyrodiscus Biome. These malacofaunas, primilarily indicative of forest which developed under a warm climate, have no present-day counterpart. The biostratigraphical study of several localities based on new investigations at Vernon (Seine Valley) and Arrest (Avelasse Valley) and a reexamination of the faunas from St Pierre-lès-Elbeuf suggests the allocation of a holsteinian age. This is supported by U/Th dates for Vernon and the stratigraphy of the loess sequence of St Pierre-lès-Elbeuf. Similar assemblages yielded by tufas of the same age in England and Germany indicate that the Lyrodiscus Biome was widespread. The warm climate recorded by the molluscs of the tufa deposits is aggreement with pollen and marine analyses for the isotopic stage 11 (362–423 kyr B.P.). In this way, the Lyrodiscus Biome appears as an interesting marker for the continental Quaternary in Western Europe. If the occurrence of these particular molluscan assemblages is due to climate, refuges from the declined Tertiary biota, from which i.e. R. (Lyrodiscus) could have emigrated, also needed to exist.
 
Article
Shipboard analysis of the 1183-m sedimentary section recovered at Site 918 in the Irminger Basin during Ocean Drilling Program Leg 152 revealed material of glacial origin (diamictons, ice-rafted debris (IRD) and dropstones) as deep as 543 m below sea floor (bsf). The sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 Ma, pushing back the date for the onset of glaciation on southern Greenland by 5 Ma. Thin layers of fine sand were found as much as 60 m deeper in the core, raising the possibility of an even earlier date for glaciation. To determine the sedimentary history of these deeper sand layers, the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope. The results suggest that the grains in the 60-m interval below the deepest dropstone have a glacial history. At that level, an 11-Ma Sr-isotope date was obtained from planktonic foraminifers. This late Miocene timing is supported biostratigraphically by both nannofossil and foraminifer assemblages, indicating a new minimum age for the onset of glaciation on southern Greenland and in the North Atlantic.
 
Article
Mio-Pliocene fluvial rocks containing buried paleosols are common in Greece and Turkey. We used the carbon and oxygen isotopic composition of pedogenic carbonates associated with these paleosols to estimate the proportion of C3 (trees, shrubs, and cool growing season grasses) and C4 (warm growing season grasses) plants once present on the landscape. Evidence from the paleosols in well-known fossil-bearing formations in the lower Axios Valley in Macedonia, and from Samos, Pikermi near Athens, and Rhodes all show that Mio-Pliocene vegetation was dominated by C3 plants, as the entire region is today. In addition, nearly all paleosols contained carbonate, indicating that mean annual pitation has remained under about 1 m/yr during the last 11 Ma. The carbon isotopic evidence thus precludes the presence of Serengeti-type C4 grasslands favored by summer precipitation, but permits C3 forest or grasses fed by winter rains, or forest with mixed seasonal precipitation. However, there is no evidence in the published palynological records from the region for abundant grasses. Given these lines of evidence, we suggest that dry forest and woodland (largely C3) dominated the vegetation of the region. C3 grasslands, if present, were probably of very restricted extent. This reconstruction is supported by carbon isotopic evidence from fossil teeth from Samos and from Paşalar in NW Turkey, and by published evidence on masticatory morphology of Turolian-age ruminants from Samos and Pikermi. Our findings imply that the classic fossil-bearing localities on Samos and at Pikermi, and from the lower Axios Valley in Macedonia were not open savannas, as has been previously suggested, but rather, woodlands or forests.
 
Top-cited authors
Volker Mosbrugger
  • Senckenberg Research Institute
Torsten Utescher
  • Senckenberg Research Institute
Michael M. Joachimski
  • Friedrich-Alexander-University of Erlangen-Nürnberg
Françoise Gasse
  • Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement
Thure E Cerling
  • University of Utah