A benthic foraminiferal record of middle to late Pliocene (3.15-2.85 Ma) deep water change in the North Atlantic

Records of benthic foraminifera from North Atlantic DSDP Site 607 and Hole 610A indicate changes in deep water conditions through the middle to late Pliocene (3.15 to 2.85 Ma). Quantitative analyses of modern associations in the North Atlantic indicate that seven species, Fontbotia wuellerstorfi, Cibicidoides kullenbergi, Uvigerina peregrina, Nuttallides umboniferus, Melonis pompilioides, Globocassidulina subglobosa and Epistominella exigua are useful for paleoenvironmental interpretation. The western North Atlantic basin (Site 607) was occupied by North Atlantic Deep Water (NADW) until ~2.88 Ma. At that time, N. umboniferus increased, indicating an influx of Southern Ocean Water (SOW). The eastern North Atlantic basin (Hole 610A) was occupied by a relatively warm water mass, possibly Northeastern Atlantic Deep Water (NEADW), through ~2.94 Ma when SOW more strongly influenced the site. These interpretations are consistent with benthic δ¹⁸O and δ¹³C records from 607 and 610A (Raymo et al., 1992). The results presented in this paper suggest that the North Atlantic was strongly influenced by northern component deep water circulation until 2.90–2.95 Ma. After that there was a transition toward a glacially driven North Atlantic circulation more strongly influenced by SOW associated with the onset of Northern Hemisphere glaciation. The circulation change follows the last significant SST and atmospheric warming prior to ~2.6 Ma.     

Benthic foraminiferal response to the emergence of the Isthmus of Panama and coincident paleoceanographic changes

Late Cenozoic benthic foraminiferal faunas from the Caribbean Deep Sea Drilling Project (DSDP) Site 502 (3052 m) and East Pacific DSDP Site 503 (3572 m) were analyzed to interpret bottom-water masses and paleoceanographic changes occurring as the Isthmus of Panama emerged. Major changes during the past 7 Myr occur at 6.7–6.2, 3.4, 2.0, and 1.1 Ma in the Caribbean and 6.7–6.4, 4.0–3.2, 2.1, 1.4, and 0.7 Ma in the Pacific. Prior to 6.7 Ma, benthic foraminiferal faunas at both sites indicate the presence of Antarctic Bottom Water (AABW). After 6.7 Ma benthic foraminiferal faunas indicate a shift to warmer water masses: North Atlantic Deep Water (NADW) in the Caribbean and Pacific Deep Water (PDW) in the Pacific. Flow of NADW may have continued across the rising sill between the Caribbean and Pacific until 5.6 Ma when the Pacific benthic foraminiferal faunas suggest a decrease in bottom-water temperatures. After 5.6 Ma deep-water to intermediate-water flow across the sill appears to have stopped as the bottom-water masses on either side of the sill diverge.The second change recorded by benthic foraminiferal faunas occurs at 3.4 Ma in the Caribbean and 4.0-3.2 Ma in the Pacific. At this time the Caribbean is flooded with cold AABW, which is either gradually warmed or is replaced by Glacial Bottom Water (GBW) at 2.0 Ma and by NADW at 1.1 Ma. These changes are related to global climatic events and to the depth of the sill between the Caribbean and Atlantic rather than the rising Isthmus of Panama. Benthic foraminiferal faunas at East Pacific Site 503 indicate a gradual change from cold PDW to warmer PDW between 4.0 and 3.2 Ma. The PDW is replaced by the warmer, poorly oxygenated PIW at 2.1 Ma. Although the PDW affects the faunas during colder intervals between 1.4 and 0.7 Ma, the PIW remains the principal bottom-water mass in the Guatemala Basin of the East Pacific.     

Biochronology and paleoclimatic implications of Middle Eocene to Oligocene planktic foraminiferal faunas

Planktic foraminiferal assemblages have been analyzed quantitatively in six DSDP sites in the Atlantic (Site 363), Pacific (Sites 292, 77B, 277), and Indian Ocean (Sites 219, 253) in order to determine the nature of the faunal turnover during Middle Eocene to Oligocene time. Biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the Atlantic, Pacific and Indian oceans. A high resolution biochronology, based on dominant faunal characteristics and 55 datum events, permits correlation between all three oceans with a high degree of precision. Population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during Middle Eocene to Oligocene time.Planktic foraminiferal assemblage changes indicate a general cooling trend between Middle Eocene to Oligocene time, consistent with previously published oxygen isotope data. Major faunal changes, indicating cooling episodes, occur, however, at discrete intervals: in the Middle Eocene 44-43 Ma (P13), the Middle/Late Eocene boundary 41-40 Ma ( ), the Late Eocene 39-38 Ma ( ), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma ( ). With the exception of the boundary, faunal changes occur abruptly during short stratigraphic intervals, and are characterized by major species extinctions and first appearances. The Eocene/Oligocene boundary cooling is marked primarily by increasing abundances of cool water species. This suggests that the boundary cooling, which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes. Planktic foraminiferal faunas indicate that the boundary event is part of a continued cooling trend which began during the Middle Eocene.Two hiatus intervals are recognized in low and high latitude sections at the Middle/Late Eocene boundary and in the Late Eocene ( ). These hiatuses suggest that vigorous bottom water circulation began developing in the Middle Eocene, consistent with the onset of the faunal cooling trend, and well before the development of the psychrosphere at the boundary.     

Millennial-scale climatic cycles in the Early Pliocene pollen record of Ptolemais, northern Greece

Early Pliocene lacustrine sediments from the Ptolemais Basin, northern Greece, exhibit a climatically induced cyclicity, which can be correlated with the orbital cycle of precession. Superimposed on precession-controlled cycles, palynological time-series data reveal a higher-order climatic cyclicity with periodicities of ∼10, ∼2.5, and ∼1.5 ka. These millennial-scale vegetation changes are likely to reflect changes of the soil-moisture gradient on mountain slopes, caused by fluctuations in orographic winter-precipitation. Such fluctuations corroborate the concept of a NAO-like North Atlantic climatic teleconnection during Early Pliocene times. The periodicities are similar to those of climate oscillations inferred from Quaternary records. The occurrence of millennial-scale cyclicity in a time interval when the Northern Hemisphere was essentially ice-free, implies an ultimate forcing mechanism that operated independently of changes in the thermohaline circulation in the Atlantic Ocean. The cycles are likely to be related to long-period variations in solar activity.     

Globorotalia puncticulata: Population divergence, dispersal and extinction related to Pliocene–Quaternary water masses

The isolating effect of water mass partitioning of populations on the morphology, stratigraphic distribution and extinction of planktonic foraminifera is assessed from the Pliocene–Quaternary record of Globorotalia puncticulata. Southern Hemisphere, Mediterranean and North Atlantic data on these aspects of its history are examined and appear consistent with a limited dispersal biogeographic model wherein populations are largely confined by hydrographic barriers.Earliest populations appeared during the latest Miocene in Southern Hemisphere middle latitude water masses. However, morphometric analysis shows that significant differentiation in the axial shape of shells had developed by 4 Ma between Southwest Pacific populations from ODP Site 1123 (temperate water) and ODP Site 1119 (subantarctic water). These sites are in close proximity but separated by the Subtropical Front. At Site 1123 inflation of late-formed chambers and reduction in the number included in the outer whorl created shell profiles that anticipated the globose form of Globorotalia inflata. The latter's gradual evolution from G. puncticulata s.s. took place in this temperate water mass, with the earliest morphotypes with three chambers in the outer whorl present by 4.1 Ma. In contrast, subantarctic populations at Site 1119 retained four chambers but their axial shape was modified. The development of a large, highly arched aperture and increase in the number of chambers in the outer whorl in Mediterranean–North Atlantic Globorotalia puncticulata bononiensis is an example of population differentiation later in the Pliocene.Chronostratigraphy shows that the northward expansion of central temperate water populations commenced with their occupation of Southwest Pacific subtropical water about 4.8 Ma. The rather abrupt entry of substantial populations into Mediterranean and North Atlantic water at 4.5 Ma marked a major biogeographic expansion and established G. puncticulata as a bipolar species. It was widely distributed about 3 Ma, with major populations in several water masses during a period of middle Pliocene warmth.After this acme North Atlantic and Mediterranean G. puncticulata bononiensis populations collapsed as late Pliocene Northern Hemisphere glacials intensified. They were extinguished in MIS 96 (2.4 Ma). Concurrently, G. puncticulata s.s became extinct in the warm subtropical Southwest Pacific. Subantarctic populations persisted but in turn were decimated in severe glacials during the Middle Pleistocene Transition. Most had disappeared by MIS 16 (0.66 Ma). However, at Sites 594 and 1119 there was a small Lazarus-like revival in MIS 11 (0.41 Ma). The highest known occurrence is in MIS 9 (0.33 Ma) at Site 1119. Confinement of the species to subantarctic water in the Pleistocene may have raised its vulnerability to extinction.While stable isotope data indicate that the lineage's evolution is related to depth habitat selection about the thermocline, its biogeography suggests that hydrographic barriers significantly isolated populations and probably facilitated speciation. Eddies such as the North Brazil Current rings provide conduits for inter-water mass transfer of populations but the history of G. puncticulata suggests that such mechanisms seldom operated successfully.The morphology of the lectotype of G. puncticulata s.s., from beach sand at Rimini, Italy, is consistent with a lower Pliocene source. Reports of living occurrences are poorly documented and the species is considered to be extinct.     

Changes in calcareous nannofossil assemblages during the Mid-Pleistocene Revolution

The distribution of calcareous nannofossils are quantitatively analysed in high-resolution deep-sea core samples from North Atlantic DSDP Site 607 and Eastern Mediterranean ODP Site 967, between marine oxygen isotope stage (MIS) 35 and 15, in order to observe the response of calcareous nannofossils to the Mid-Pleistocene Revolution (MPR). Nannofossil abundance patterns show major variations through MIS 25–22 and distinct higher amplitude changes from MIS 21 upward, sometime clearly correlatable to glacial–interglacial cycles. High amplitude, short-term, fluctuations of small placoliths and F. profunda characterize the interval through MIS 24 to 22/21, suggesting strong instability in nutricline dynamics and surface water productivity. Principal Component Analysis and Shannon–Weaver indices (diversity and dominance) highlight significant shifts, mainly related to variations in the characteristics of surface waters. In both sites a minimum in diversity is recorded at MIS 22/21, corresponding to a maximum in the dominance of Reticulofenestra spp. at Site 607 and of Pseudoemiliania lacunosa at Site 967. Above MIS 21 the increase in abundance of various taxa (C. leptoporus, Umbilicosphaera spp., Syracosphaera spp., Rhabdosphaera spp., Oolithotus spp.) and a general increase in diversity are related to a distinct trend toward more stable and oligotrophic surface waters in contrast to the higher productivity and less stratified surface waters of the Early Pleistocene.     

Orbital signatures in a late Miocene dinoflagellate record from Crete (Greece)

A high-resolution palynological study of the cyclically bedded Faneromeni section (upper Tortonian-lower Messinian) on Crete (Greece) is presented. This study aims to recognize orbitally-driven variations in the palynological record and to validate the age model based on the astronomical calibration of the sedimentary cycles. Four palynology-based environmental proxies were utilised using interpretations of fossil dinoflagellate associations based on modern ecological characteristics. Cross-spectral analysis between the proxy records and astronomical target curve, the 65°N summer insolation, yielded in most cases significant spectral power and coherence in the precession and/or obliquity frequency bands. Precession-controlled variations in the proxy records are related to lithology and indicate that maxima in continental input and minima in sea surface salinity coincide with sapropel formation. The influence of obliquity is most clearly reflected in the index of continental versus marine palynomorphs (S-D). The absence of a distinct time lag relative to obliquity indicates that the 41-kyr component in continental input is controlled by oscillations in regional Mediterranean climate rather than by glacial cyclicity. Phase relations in the different astronomical frequency bands of the spectrum, as compared with the Mediterranean Pliocene, essentially confirm the validity of the Miocene astronomical time scale. Finally, a major non-cyclic change in the palynological assemblage at 6.68 Ma indicates enhanced salinity and decreased river discharge. This shift coincides with a significant drop in sedimentation rate informally termed the “Early Messinian Sediment starvation Event”.     

栲属(壳斗科)植物的现代和地史分布

根据文献资料和标本馆及化石记录,讨论了壳斗科栲属植物的现代分布和地史分布。现代栲属植物有110～134种,主要分布在东亚及东南亚,其中印度支那地区有82种栲属植物,是世界栲属植物分布最集中的地区,马来西亚地区是栲属特有种最丰富的事实是支持马来西亚地区与其它地区的区系交流十分有限的论据。中国栲属植物最丰富的地区是滇黔桂地区（29种）。栲属植物现代多样化中心在马来西亚和中南半岛。排除Chrysolepis后,栲属的分布类型应属热带亚洲分布。栲属在地质历史上有着比现在广泛的分布,最早、最可靠的栲属化石记录发现于北美始新世地层,欧洲和日本始新世也有栲属的化石记录,化石记录表明栲属起源的时间不晚于古新世,所有的壳斗科及栲属的化石都发现于北半球,现代分布也主要在北半球,壳斗科及栲属起源于北半球可以确认,由于化石证据与现代植物学的研究结果有较大差异以及关键地区化石证据的不足,具体的起源地尚不能肯定。     

A late Quaternary marine palynological record (oxygen isotope stages 1 to 7) for the humid tropics of northeastern Australia based on ODP Site 820

A late Quaternary marine palynological record from the Ocean Drilling Program (ODP) site 820, adjacent to the humid tropics region of northeastern Australia, has demonstrated marked variation in orbital scale cyclicity, and also trends associated with both climate and human impact. However, some uncertainties in interpretation have resulted from concerns about the records chronology and continuity. Here we present, for the first time, the complete palynological data from detailed analysis of the top 67 m of sediment and examine it in relation to the marine isotope sequence from the core. It is proposed that the record is relatively continuous through the last 250,000 years although the latter part of oxygen isotope stage (OIS) 5, as well OIS 4 may be missing. Despite the variation on orbital scales, most palynological changes are not in phase with those from the marine isotope record suggesting a lack of direct Milankovitch forcing on vegetation. This lack of correspondence combined with major trends towards more open and sclerophyllous vegetation in association with increased burning supports a previous proposal that major control is being exercised by El Niño-Southern Oscillation variability whose influence may have been initiated by changes in oceanic circulation in the region within the mid Pleistocene. The lack of impact on the distribution of complex rainforest suggests that increased climate variability did not involve an overall decrease in total precipitation.     

Integrated stratigraphy and paleoceanography of the Messinian (latest Miocene) across the North Atlantic Ocean

The Messinian was a time of major climatic and paleoceanographic change during the late Cenozoic. It is well known around the Mediterranean region because of the giant anhydrite/gypsum sequence and the suggested desiccation of the Mediterranean Sea. However, this interval is less constrained outside the Mediterranean region, where several paleoceanographic changes could have taken place because of the desiccation. Hence, we present an integrated stratigraphic framework for future Messinian paleoceanographic studies, determination of the effect of the Mediterranean desiccation on deep-water paleoceanography, and comparison of intra-Mediterranean paleoceanographic changes with those in the open oceans during the Messinian Stage.Four DSDP/ODP Holes (552A, 646B, 608, and 547A) from the North Atlantic Ocean and one land borehole from Morocco have been studied to integrate bio-, magneto-, and stable isotope Messinian stratigraphy with high resolution sampling. Our results produce the best assessment of the Tortonian/Messinian boundaries in all holes because they do not rely on any one signal.In paleomagnetic Subchronozone CSAn.lr in the Salé borehole and DSDP Site 609, a S/D coiling direction change of Neogloboquadrina pachyderma/acostaensis appears to indicate PMOW entering the northeastern Atlantic Ocean, at least reaching 50°N. Diachrony and synchrony of some important Messinian planktic foraminifera from these Atlantic DSDP/ODP holes and the Salé borehole, such as the LO of Gq. dehiscens, the LO of Gt. lenguaensis, the FO and LO of Gt. conomiozea, the FO of Gt. margaritae s.s., the FO of Gt. puncticulata, and the FO of Gt. crassaformis are discussed for understanding some of the paleoceanographic changes. This integrated stratigraphie framework presented here allows much better North Atlantic correlations at this critical point in Messinian geologic history.     

Cyst formation,sedimentation, and preservation: Factors affecting dinoflagellate assemblages in recent sediments from trondheimsfjord,Norway

Plankton records and 25 samples of Recent sediment from Trondheimsfjord and the adjoining shelf were studied to investigate production, sedimentation, and preservation of cysts, as factors which influence the eventual composition of dinoflagellate cyst assembleges. All sediment samples were examined for dinoflagellate cysts using routine semiquantitative palynological procedures. In addition, fjord sediments were subjected to a limited sediment analysis, and, for three samples, results from preparations both with and without acid treatments were compared. For the first time, cyst assembleges from Recent sediments were directly compared with extensive plankton records from overlying waters. Results indicate that approximately 20% of the 55 locally recorded dinoflagellate species contribute cysts to bottom sediments. Once formed, cysts behave as fine silt particles in the sedimentary regime, increasing in abundance as the percentage abundance of finer sediment increases, usually with increased water depth. Cyst-forming species are almost entirely restricted to a few genera, particularly Gonyaulax and Peridinium, within the order Peridiniales. For some groups, reasonably good correspondence was found between percentage abundances of dinoflagellates in plankton and their cysts in sediment, though plankton records covering at least five years were required to establish this. Gonyaulax grindleyi Reinecke (Von Stosch 1969) appeared to be consistently overrepresented by cysts in sediment relative to available plankton evidence; possible explanations are suggested. At least 30% of the cyst species present, including most Peridinium species, were eliminated, or rendered unreliable for semiquantitative palynology, by application of routine palynological preparation treatments. Such cysts may provide useful, non-quantitative, palynological information from Recent and possibly Quaternary sediments, but their persistence would seem unlikely. Thus, factors of preservation probably further restrict the dinoflagellate fossil record. Cyst assemblages from Trondheimsfjord are comparable with those previously recorded from the northeastern coast of U.S.A., and from Scotland and northeastern England. Fjord assemblages are dominated by small, simple, spinose cysts which would be regarded as acritarchs if culture experiments had not proved that they are dinoflagellate cysts. Much potential biogeographic and palaeoenvironmental information was included within the less abundant species.Attention is drawn to the role which future culture experiments may be expected to play in helping to resolve taxonomic difficulties currently affecting dinoflagellate studies. Palynological significance of results from the present study is discussed especially with reference to recent work by Von Stosch which strongly suggests that cysts may be hypnozygotes formed routinely in sexual cycles of dinoflagellates.     

Climate and sea‐level changes across a shallow marine Cretaceous–Palaeogene boundary succession in Patagonia,Argentina

Upper Maastrichtian to lower Paleocene, coarse‐grained deposits of the Lefipán Formation in Chubut Province, (Patagonia, Argentina) provide an opportunity to study environmental changes across the Cretaceous–Palaeogene (K–Pg) boundary in a shallow marine depositional environment. Marine palynological and organic geochemical analyses were performed on the K–Pg boundary interval of the Lefipán Formation at the San Ramón section. The palynological and organic geochemical records from the San Ramón K–Pg boundary section are characteristic of a highly dynamic, nearshore setting. High abundances of terrestrial palynomorphs, high BIT‐index values and the occasional presence of plant fossils are indicative of a large input of terrestrial organic material. The organic‐walled dinoflagellate cyst (dinocyst) assemblage is generally dominated by Senegalinium and other peridinioid dinocyst taxa, indicative of high‐nutrient conditions and decreased salinities, probably associated with a large fluvial input. The reconstructed sea surface temperatures range from 25°C to 27°C, in accordance with the tropical climate inferred by palynological and megafloral studies. As in the Bajada del Jagüel section, ~500 km north‐north‐east of San Ramón, peaks of Senegalinium spp. were recorded below and above the K–Pg boundary, possibly related to enhanced runoff resulting from more humid climatic conditions. The lithological, palynological and organic geochemical records suggest the occurrence of a sea‐level regression across the K–Pg boundary, resulting in a hiatus directly at the boundary in both sections, followed by a transgression in the Danian.     

Late Quaternary Protoperidinium cysts as indicators of paleoproductivity in the northern Arabian Sea

The reliability of organic-walled cysts of the heterotrophic dinoflagellate Protoperidinium as paleoproductivity indicators and the influence of bottom water oxygenation on cyst preservation is assessed by using Arabian Sea records of the past 125 kyr as a natural laboratory. Multidisciplinary geochemical, micropaleontological and palynological datasets are integrated to analyze the relationship between Protoperidinium cyst concentrations and other paleoproductivity proxies. Differential preservation potential is quantified in order to establish threshold oxidative degradation values for a possible application of quantitative Protoperidinium cyst records in paleoenvironmental reconstructions. Results indicate that variations in Protoperidinium cyst concentration closely correspond to other marine productivity and/or upwelling proxies. Although oxygenation will lead to significant cyst degradation, and thus decreased concentrations, down-core patterns in Protoperidinium cyst concentration still primarily reflect changes in sea surface productivity. In view of differential preservation among dinoflagellate cysts, down-core variations in relative abundance of Protoperidinium should be treated with caution.     

Mid-Pliocene deep-sea bottom-water temperatures based on ostracode Mg/Ca ratios

We studied magnesium:calcium (Mg/Ca) ratios in shells of the deep-sea ostracode genus Krithe from a short interval in the middle Pliocene between 3.29 and 2.97 Ma using deep-sea drilling sites in the North and South Atlantic in order to estimate bottom water temperatures (BWT) during a period of climatic warmth. Results from DSDP and ODP Sites 552A, 610A, 607, 658A, 659A, 661A and 704 for the period Ma reveal both depth and latitudinal gradients of mean Mg/Ca values. Shallower sites (552A, 610A and 607) have higher mean Mg/Ca ratios (10.3, 9.7, 10.1 mmol/mol) than deeper sites (661A, 6.3 mmol/mol), and high latitude North Atlantic sites (552A, 610A, 607) have higher Mg/Ca ratios than low latitude (658A: 9.8 mmol/mol, 659A: 7.7 mmol/mol, 661A: 6.3 mmol/mol) and Southern Ocean (704: 8.0 mmol/mol) sites. Converting Mg/Ca ratios into estimated temperatures using the calibration of Dwyer et al. (1995) [Dwyer, G.S., Cronin, T.M., Baker, P.A., Raymo, M.E., Buzas, J.S., Corrège, T., 1995. North Atlantic deepwater temperature change during late Pliocene and late Quaternary climatic cycles. Science 270, 1347–1351] suggests that mean middle Pliocene bottom water temperatures at the study sites in the deep Atlantic were about the same as modern temperatures. However, brief pulses of elevated BWT occurred several times between 3.29 and 2.97 Ma in both the North and South Atlantic Ocean suggesting short-term changes in deep ocean circulation.     

ISLANDINIUM BREVISPINOSUM SP. NOV. (DINOFLAGELLATA), A NEW ORGANIC‐WALLED DINOFLAGELLATE CYST FROM MODERN ESTUARINE SEDIMENTS OF NEW ENGLAND (USA)1

Modern estuarine environments remain underexplored for dinoflagellate cysts, despite a rapidly increasing knowledge of cyst distributions in open marine sediments. A study of modern estuarine sediments in New England has revealed the presence of Islandinium brevispinosum sp. nov., a new organic‐walled dinoflagellate cyst that is locally common and probably of heterotrophic affinity. Resistance of this cyst to standard palynological processing indicates its geological preservability, although fossils are not yet known. Previously assigned species of the genus Islandinium are characteristic of polar and subpolar environments today and cold paleoenvironments in the Quaternary. The present record of I. brevispinosum extends the ecological and geographical range of this genus into the warm temperate zone, where I. brevispinosum occupies specific environments with reduced salinities and elevated nutrient levels.     

Calcareous nannofossil biostratigraphy and turnover dynamics in the late Campanian–Maastrichtian of the tropical South Atlantic

The complete late Campanian–Maastrichtian succession of the South Atlantic reference DSDP Site 525A has been investigated to establish a detailed record of calcareous nannofossil biohorizons. A complete holostratigraphy of the core is presented for this interval and allows for global correlations to other Tethyan and Boreal reference sections for that interval. The new study allows for proposing a new time scale with a tie of Tethyan and Boreal nannofossil zonations. A new subzonation is proposed for the late Campanian UC16 Zone in the Tethyan Realm and the last occurrences of Uniplanarius trifidus and Zeugrhabdotus praesigmoides are demonstrated as markers of the Campanian–Maastrichtian boundary. The difference between cumulative first and last occurrences reflects the turnover dynamics of calcareous nanoplankton in the South Atlantic and highlights 6 major events. Five of them appear well related to major changes in sea-surface temperatures whereas the sixth event is likely the expression of a global decrease in primary productivity in the late Maastrichtian. Surprisingly, the turnover dynamics in calcareous nannoplankton appears completely unrelated to that observed in planktic foraminifera which shows only 4 major events with different timings. The two groups thus seem to have responded either very differently to similar environmental constraints or to different direct environmental constraints in the photic zone, although caused by the same global changes in climate.     

Biostratigraphy and paleoceanographic significance of Paleocene radiolarians from offshore eastern New Zealand

A 100-m-thick Paleocene sequence of mainly pelagic sediments at ODP Site 1121, on the eastern flanks of the Campbell Plateau, contains few to common radiolarians of relatively low diversity in the lower 40 m (Early to early Late Paleocene) and abundant, diverse radiolarian assemblages in the upper 60 m (mid-Late Paleocene). The 150 taxa recorded from the entire Paleocene interval are thought to under-represent the actual species diversity by at least one half as many morphotypes have not been differentiated below the level of genus. Assemblages in the lower 40 m are similar to those described from onland New Zealand and DSDP Site 208 (northern Lord Howe Rise); they are correlated with South Pacific radiolarian zones RP4 and RP5. Assemblages in the upper 60 m differ from other known Late Paleocene assemblages in the great abundance of plagiacanthids and cycladophorids. Similarities are noted with later Cenozoic cool-water assemblages. This upper interval is correlated with South Pacific zone RP6, as revised herein, based on comparison with faunas from Site 208 and Marlborough, New Zealand. The interval is also correlated with the upper part of North Atlantic zone RP6 (RP6b–c) based on the presence of Aspis velutochlamydosaurus, Plectodiscus circularis and Pterocodon poculum. Other species, such as Buryella tetradica and Buryella pentadica, are valuable for local correlation but exhibit considerable diachroneity between the Pacific, Indian and Atlantic Oceans. An age model for the Paleocene interval at Site 1121, based on well-constrained nannofossil and radiolarian datums, indicates that the rate of compacted sediment accumulation doubles from 15 to 30 mm/ka at the RP5/RP6 zonal boundary. In large part this is due to a sudden and pronounced increase in accumulation rates for all siliceous fossils; radiolarians and larger diatoms increase from <100 to >10 000 specimens/cm²/ka. This apparent increase in biosiliceous productivity is age-equivalent to a mid-Paleocene cooling event (57–59 Ma) identified from global stable isotope records that is associated with the heaviest δ¹³C values for the entire Cenozoic.     

Middle Miocene high-resolution calcareous plankton biostratigraphy at Site 926 (Leg 154, equatorial Atlantic Ocean): palaeoecological and palaeobiogeographical implications

High-resolution calcareous plankton (planktonic foraminifera and calcareous nannofossils) biostratigraphy is presented from the Middle to early Late Miocene interval (from 14.45 to 8.86 Ma) at Site 926 (ODP Leg 154, equatorial Atlantic Ocean). The main bioevents used in the low-latitude zonal schemes, and also auxiliary events revealing potential biostratigraphic value have been recognised. The investigated succession ranges from N.10 to N.16 Zones based on planktonic foraminifera, and from NN5 (CN4) to NN10 (CN8) Zones based on calcareous nannofossils. The evolution of the planktonic foraminiferal Globorotalia fohsi lineage appears to be environmentally controlled. The main diagnostic features of the species of this lineage are not always evident, rendering problematic the definition of the N.9/N.10, N.10/N.11 and N.11/N.12 zonal boundaries. Calcareous plankton events have been calibrated on the basis of the Astronomical Time Scale of Shackleton and Crowhurst 〚Shackleton, N.J., Crowhurst, S., 1997. Sediment fluxes based on an orbitally tuned time scale 5 Ma to 14 Ma, Site 926. In: Curry, W.B., Shackleton, N.J., Richter, C., Bralower, T.J. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program) 154, pp. 69–82〛. The astrobiochronology obtained at Site 926 has been compared with that of the Mediterranean astronomically calibrated deep marine successions, allowing the evaluation of the degree of synchroneity and diachroneity of bioevents. Some bioevents, such as the last occurrence of Globigerinoides subquadratus dated at 11.55 Ma, the last occurrence of Sphenolithus heteromorphus dated at 13.51 Ma and the last common occurrence of Cyclicargolithus floridanus calibrated at 13.32 Ma, are near-synchronous events between the equatorial Atlantic and the Mediterranean area indicating their high biostratigratigraphic value in global correlation. The diachroneity of the last occurrence of Paragloborotalia siakensis, the first occurrence of Neogloboquadrina acostaensis and the last occurrence of Globorotalia peripheroronda between equatorial Atlantic and the Mediterranean reflect a different spatial and temporal distribution of these marker species probably due to a sharp definition of surface plankton provinces related to the latitudinal thermal gradient.     

Palaeoceanographical changes recorded by Cenozoic deep-sea ostracod assemblages from the South Atlantic and the Southern Ocean (ODP Sites 1087 and 1088)

Cenozoic palaeoceanography of the SE Atlantic and Southern Oceans has been investigated using Late Eocene/Early Oligocene to Quaternary ostracod assemblages from 49 samples of ODP Sites 1087 and 1088. Although the overall abundance of ostracods is relatively low (means of 17 and 49 specimens per sample at Sites 1087 and 1088, respectively) and there is an apparently high level of endemism (ranging from 50% to 80% at Sites 1087 and 1088), three major changes in the faunal assemblages are identified at Site 1087 (denoted A, B and C) and two at Site 1088 (denoted B' and C'). The assemblage boundaries, detected on the basis of stepwise changes in the abundance, diversity, dominance, endemism, faunal turnover and relative abundance of common taxa, coincide broadly with previously identified, ostracod-based palaeoceanographical 'events' discussed by Benson and co-workers over the last two decades. The data do not extend sufficiently far back to record the initiation of Assemblage A, but the faunal change between Assemblages A and B, marked by a decline in abundance, species diversity and faunal turnover, occurs within the Middle Miocene (NN5-6). It coincides with a previously documented palaeoceanographical 'event' at 16-14 Ma which, we suggest, may be related to the initiation of North Atlantic Deep Water (NADW) production and/or an expansion of the East Antarctic ice sheet. Assemblage B' is subdivided into the two Sub-assemblages B'¹ and B'² mainly on the basis of an increase in diversity, a peak in faunal turnover and a drop in the relative abundance of the genus Krithe in early Late Miocene time (NN9, c. 10.5 Ma). The B'¹/B'² Sub-assemblage boundary cannot be related to any previously documented faunal change in deep-sea ostracods. Changes associated with the boundaries between Assemblages B and C, and B' and C', which we believe to be synchronous, both include a decrease in diversity and abundance. In addition, two strong turnover peaks occur near the B'/C' boundary at Site 1088. The B/C and B'/C' boundaries coincide with a previously documented midPliocene 'event' (3.5 Ma) (NN15-16) which may be linked to putative closure of the Straits of Panama and increased production of NADW, the latter in turn leading to increased production of Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Alternatively, fiuctuations in size of the Antarctic ice sheet during possible Pliocene warm periods could indirectly be responsible for the observed midPliocene faunal changes.     

Callovian (Middle Jurassic) marine microplankton from southwestern Germany: Biostratigraphy and paleoenvironmental interpretations

Late Middle Jurassic dinoflagellate cyst assemblages are documented from a section in Kandern and in samples from additional localities in southern Germany. The changes in the composition of the marine microfloras through the Callovian sections are related to fluctuations in sea-levels and changes in depositional environments. The Lower Callovian claystones, which represent inner shelf, soft bottom deposits, contain rich, diverse and well preserved dinoflagellate cyst assemblages. In the Kandern section a marked transition from the Lower Callovian claystone facies to the Anceps-oolite occur within the Calloviense zone. This transition was caused by a regression, and coincides with the LZA−3.1/LAZ−3.2 boundary on the cycle chart of Haq et al. (1987). Diverse dinoflagellate cyst assemblages also occur in the Anceps-oolite, but they are not so abundant as the acritarchs which dominate the overall palynofloras. The Anceps-oolite is interpreted as representing an offshore, but shallow marine environment. The transition to the overlying Upper Callovian “Renggeri Clay” is more gradual, but accompanied by marked changes in the overall composition of the marine microfloras. The “Renggeri Clay”, which represent an outer shelf, soft bottom depositional environment, shows a higher species diversity and abundance of dinoflagellate cysts than the underlying sequences. The distribution pattern of selected species through the Kandern section indicates that some species were related to specific environments, i.e. open marine forms, and that others could have been opportunistic forms, tolerating more shallow marine environments.

The distribution of the dinoflagellate cysts from southern Germany is related to the standard Northwest European ammonite zonation. The ranges of selected biostratigraphic key species are compared with ranges previously reported from the British and northwest European Jurassic. There are several discrepancies with respect to the earliest appearance and extinction datums, the only relevant Callovian palynostratigraphic “events” coinciding in southern Germany and Britain being: The extinction of Aldorfia aldorfensis at the top of the Calloviense zone, and the earliest incoming of Belodinium spp. and Liesbergia scarburghensis at the base of the Lamberti zone.