Cenozoic planktonic foraminifera in the Goban Spur Region

Cenozoic planktonic foraminiferal biostratigraphy at DSDP-IPOD Leg 80 sites documents the existence of regionwide stratigraphic gaps in the Paleocene and middle Miocene. Episodes of carbonate dissolution also occurred during the Paleocene at several sites, particularly at Site 549, where destruction of foraminiferal tests may obscure evidence of an unconformity. The middle Miocene hiatus is apparent at each site where Neogene sediments were continuously cored. Upper Miocene sediments at Site 550 (the only abyssal site) are characterized by moderate to extensive dissolution of planktonic foraminifers, but they contain abundant specimens of Bolboforma that mark this stratigraphic interval (von Daniels and Spiegler, 1974, doi:10.1007/BF02986990; Roegl, 1976, doi:10.2973/dsdp.proc.35.133.1976; Murray, 1979, doi:10.2973/dsdp.proc.48.116.1979; Müller et al., 1985, doi:10.2973/dsdp.proc.80.117.1985). Although foraminiferal evidence is not conclusive, nannofossils indicate a widespread Oligocene unconformity (Müller, 1985). Several oceanographic factors, not just simple sea-level change, probably interacted to produce these regional unconformities. There are also dramatic differences in the Cenozoic sedimentary record among Leg 80 sites, indicating that each has had a distinct geologic history. The thickness of the Cenozoic section varies from 100 m at Site 551 to 471 m at Site 548. The thickness of individual chronostratigraphic units also varies, as do the number and stratigraphic position of unconformities other than those mentioned. Differences in the stratigraphic record from site to site across the continental slope result from (1) location in separate half-graben structures, (2) varying location across the developing margin, and (3) difference in position relative to the seaward edge of the enclosing half-graben. Except for turbidites, deposition at Site 550 (abyssal) was largely independent of developments on the continental slope; but it was affected by oceanographic events widespread in the North Atlantic.

Pollen profiles from 8 sediment cores from the Degersee, Southern Germany

The discovery of a neolithic pile field in the shallow water near the eastern shore of the Degersee confirmed earlier palynological and sedimentological studies stating that early man was active in the region since more than 6000 years. The already available off-site data were freshly assessed, completed by additional data from old and new cores and the interpretations revised. A common time scale for the off-site data and the on-site data was obtained by AMS dating of terrestrial macro remains of the neolithic section of off-site core De_I+De_H. The ages can thus be parallelled with AMS ages of construction timber on-site. Pollen analyses from all cores provide a further time scale. The continuously and densely sampled pollen profile of the profundal zone embracing the entire Late glacial and Holocene serves as a reference. From the Boreal onwards the relative ages are transformed by AMS ages and varve counts into calibrated and absolute. A transect cored close to the neolithic pile field across the lake marl-platform demonstrates its geological architecture in the shallow water since the Lateglacial. Studies of the microfabric of thin sections of drilled cores and of box cores from the excavations demonstrate that neolithic settlements now at 2-3,5 m water depth had been erected on lake marl freshly fallen dry, thus indicating earlier lake levels dropped by 1.5-2 m. The neolithic section of the highly resolved off-site profile in the lake=s profundal zone has laminated and calcareous zones alternating with massive ones. Assemblages of diatoms and concentrations of trace elements changing simultaneously characterise the calcareous sections as deposits of low lake levels that lasted between some 40 and more than 300 years. The ages of discovered lake shore dwellings fall into calcareous segments with low lake levels. From the end of the Upper Atlantic period (F VII) appear Secondary Forest Cycles in the beech forest, a man-made sequence of repeated vegetational development with an identical pattern: With a decrease of beech pollen appear pollen of grasses, herbs and cultural indicators. These are suppressed by the light demanding hazel and birch, those again by ash, and finally by the shade demanding beech forming a new pollen peak. Seven main Forest Cycles are identified In the upper Neolithic period each comprising some 250, 450 or 800 years. They are subdivided into subcycles that can be broken down by very dense sampling in even shorter cycles of decadal length. Farming settlers have caused minor patchy clearances of the beech-mixed-forest with the use of fire. The phases of clearance coincide with peaks of charcoal and low stands of the lake levels. The Secondary Forest Cycles and the continuous occurrence of charcoal prove a continued occupation of the region. Together with the repeated restoration of the beech climax forest they point to pulsating occupation probably associated with dynamic demography. The synchronism of the many palynological, sedimentological and archaeological data point to an external forcing as the climate that affects comprehensively all these proxies. The fluctuations of the activity of the sun as manifested in the residual d14C go largely along with the proxies. The initial clearances at the begin of the forest cycles are linked to low lake levels and negative values of d14C that point to dry and warm phases of a more continental climate type. The subcycles exist independent from climatic changes, indicating that early man acted largely independent from external forces.

Planktonic foraminifera at DSDP Holes 72-516 and 72-518

Quantitative analysis was performed on the Quaternary planktonic foraminiferal fauna from Site 516, near the crest of the Rio Grande Rise, and Site 518, on the lower western flank of the Rise. From Hole 516, 46 samples were taken, and from Hole 518, 80 samples were taken. The mean interval between samples is 20 to 25 cm. About 50 species of Quaternary and Pliocene planktonic foraminifers were identified. Quaternary sediments, dated by the initial evolutionary appearance of Globorotalia truncatulinoides and other criteria, have thickness, of 9.8 m in Hole 516 and 16 m in Hole 518. The Globorotalia truncatulinoides Zone is subdivided into four subzones or biostratigraphic horizons (from lower to upper): (1) Globorotalia crassaformis viola, (2) Globorotalia crassaformis hessi, (3) Globigerina calida calida, and (4) Globigerinoides ruber (pink). Thickness of these horizons in Hole 516 establishes the age of the boundaries between them as 1.47, 0.81, and 0.28 Ma, respectively. All the Quaternary planktonic foraminiferal complexes sampled are subtropical. The region of the Rio Grande Rise, therefore, has been within the southern subtropical gyre continuously for the last 2 Ma. The average annual surface water temperatures were reconstructed for the Quaternary at both sites. A micropaleontologic method for the paleotemperature analysis of the thanatocoenosis registers an average Quaternary temperature of 21.2°C at Site 516 and 21.7°C at Site 518. The temperature fluctuations increase up to 3.5°C during the accumulation of the two last horizons (since 0.81 Ma). Temperature peaks are tentatively compared with oxygen isotopic stages and with continental glaciations. Levels at which planktonic foraminiferal species disappear correspond to coldwater intervals. In the Quaternary of Site 518, some layers show signs of dissolution. Corrosive to CaCO3, the northward flow of Antarctic Bottom Water through the Vema Channel increases during the cold periods. Site 518 has two layers of redeposited foraminiferal sand with Pliocene foraminifers. The average rate of the Quaternary sedimentation in Hole 516 is 0.52 cm per thousand years, and in Hole 518 it is 0.84 cm per thousand years.

The Fohsella chronocline in middle Miocene sediments from the Ontong Java Plateau, Pacific Ocean

Micropaleontologists have traditionally recognized the mid-Miocene Fohsella lineage as a flagship for phyletic gradualism within the planktic foraminifera. However, study of a deep-sea record from the western equatorial Pacific (ODP Site 806) reveals that coiling ratios within this clade suddenly (<5 kyr) shift after a prolonged, ancestral state of near randomness (~50%) to a transient phase (13.42-13.43 Ma) of dextral dominance (~75%) immediately following the first common occurrence of keeled fohsellids. This brief period of dextral dominance was abruptly (<5 kyr) succeeded by an irreversible change to sinistral dominance (~96%). Fohsellid abundances decline markedly through the interval in which the sinistral preference is established. The shift to sinistrality (13.42 Ma) predated the deepening of fohsellid depth ecology by ~240-488 kyr, indicating that these two events were unrelated. This view is supported by a lack of delta 18O evidence for depth-habitat differences between the two chiral forms, which refutes the notion that sinistral fohsellids were "pre-adapted" for ensuing hydrographic change because they occupied a deeper depth habitat than their dextral counterparts. Planktic foraminiferal assemblages become strongly oligotrophic in character through the interval in which the fohsellid delta 18O increase is recorded, indicating that the migration to deeper depths was fostered by an expansion of the mixed layer in the western equatorial Pacific. Salient aspects of this brief, but conspicuous faunal change are a marked increase in the abundance of symbiont-bearing globigerinoidids, a concomitant collapse of local Jenkinsella mayeri/siakensis populations, and reduced fohsellid abundances. The rapid and permanent nature of the Fohsella sinistral shift provides a distinct, unequivocal datum that may prove useful for correlating mid-Miocene sections throughout the Caribbean Sea and tropical regions in the western sectors of the Pacific and Atlantic. The coiling ratio changes that occurred during the evolution of the Fohsella chronocline probably reflect changing population dynamics between cryptic genotypes with different coiling preferences.

Foraminiferal species and dissolution index at DSDP Hole 78-541

The calcite compensation depth (CCD) fluctuates as a result of changes in the water-mass system, thereby producing a distinct dissolution pattern. Differential dissolution changes the composition of the foraminiferal assemblages, reflecting the depositional environment in respect to the fluctuating CCD. The dissolution pattern for the comparatively shallow Site 541 on the Barbados Ridge indicates a depositional environment mostly above the CCD, but below the foraminiferal lysocline during the late Miocene to early Pleistocene. In contrast, sediments of the deeper-water Site 543 indicate a depositional environment above the CCD during the late Pliocene to early Pleistocene only. Furthermore, similarities in the dissolution pattern of corresponding time intervals of Site 541 (represented by superimposed faulted intervals termed Tectonic Units A and B) are recognizable. Sediments deposited clearly above the foraminiferal lysocline are rare

Miozene larger foraminifera in ODP Leg 133 holes

The Marion Plateau is a large carbonate platform off northeastern Queensland. Three sites (815, 816, and 826) were drilled on this platform and form the basis for this study. Larger benthic foraminifers, together with rare planktonic forms from the shallow-water carbonates that form the main part of the platform sequence, were studied to establish a biostratigraphy. The presence of Lepidocyclina (Nephrolepidiná) howchini sensu lato and Ladoronia vermicularis, together with Globorotalia (Globorotalia) praemenardii and Orbulina, indicate an early middle Miocene (N9-N12) age (i.e., lower Tf stage) for these carbonates. Dolomitization has destroyed much of the original fabric of these carbonates, making study of the larger foraminifers difficult. Sites 815 (forereef location) and 826 (backreef, lagoonal setting) provide the best faunas. However, at all sites nodular coralline algae and Halimeda are the major bioclasts; coral fragments form a major component at Sites 816 and 826. The middle Miocene neritic sequence is separated from the overlying hemipelagic sequence by an unconformity that spans much of the middle and late Miocene. At Site 815, which is in a forereef situation, the overlying hemipelagic sequence contains a Zone N17A fauna, but at Site 816, higher on the platform, a similar sequence contains a Zone N19 fauna. The faunas indicate that the platform was built up during the early middle Miocene and remained at fairly constant water depths and temperatures during this period. It was then exposed prior to subsiding rapidly during the late Miocene and Pliocene to depths similar to those of the present day.

Planktonic foraminifera abundance in sediments of ODP Leg 170 sites

From October to December in 1996, Sites 1039 through 1043 were drilled on the lower continental slope and the bottom of the Middle American Trench. Planktonic foraminifers were obtained from 377 samples of the total 487 examined. The Pliocene- to Pleistocene-age sediments of Sites 1039 and 1043 are continuous from Zones N19 through N23. At Sites 1039 and 1040, middle Miocene sediments are also continuous, encompassing Zones N8 through N12. The sequences of the upper part of Sites 1040, 1041, 1042, and 1043 are décollements, tentatively assignable to Zone N19 for Sites 1040, 1041, and 1042 and to Zone N22 for Site 1043. The oldest sediments of these sites are assigned to Zone N7 (latest early Miocene), ~17 Ma in age.

Late Miocene to Holocene planktonic foraminifers from ODP Leg 108 holes

Planktonic foraminifers were examined from 27 holes situated at 12 separate sites in the tropical Atlantic. The sites are located in various environments, including areas of upwelling, areas affected by cool currents, areas of strong dissolution, and areas that show little dissolution in warm-water settings. Paleomagnetic results were variable at these sites, but accumulation rate curves have been produced by combining the existing paleomagnetic data with the available microfaunal data. Determinations of the ages of the planktonic foraminifer datums from these accumulation rate curves show some species to be strongly diachronous, while others provide good stratigraphic markers. The warmest water sites with the least dissolution show the most complete ranges of species.

Stable carbon and oxygen isotopes of foraminifera fand carbon content of ODP Leg 107 holes

High-resolution bio- and chemostratigraphy of an earliest Pliocene section from ODP Site 652 indicates that postflood paleoceanographic conditions in the Tyrrhenian Sea can be sub-divided into two discrete intervals. The first is manifested by an acme of Sphaeroidinellopsis spp., increasing carbonate contents, and a progressive decrease upsection in both the d13C and dl8O values of the planktonic foraminifera. The lower part of the acme interval contains unusual surface-to-bottom water isotope gradients suggesting a stratification of two water masses. Normal gradients in the upper part of the acme interval suggest a well-mixed water body. Between the end of the acme interval and the MP11/MP12 boundary, denoted by the first occurrence (F.O.) of Globorotalia margaritae, a migrational first appearance, there was a catastrophic collapse of the gradient marking an onset of the second post-flood interval. The disintegration of habitable conditions is suggested by a sharp decrease in carbonate content and the disappearance of the benthonic assemblage, which is subsequently replaced predominantly by Uvigerinapygmea, indicative of cold, low-oxygenated bottom waters. The introduction of benthonic species denoting well-oxygenated bottom conditions occurs within the lower MP12 zone. Superimposed on these overall trends are shorter term, warm-cold cycles, which are interpreted as orbitally induced, climatic fluctuations. Correlative studies of the less complete earliest Pliocene sections from ODP Holes 653B and 654A confirm these interpretations. A scenario derived from an integration of all the stratigraphic data indicates that normal paleoceanographic conditions were operating in the Tyrrhenian Sea only approximately 250,000 yr after the cessation of Messinian evaporative conditions at the Miocene/Pliocene boundary. The post-flood interval is marked by an initial period of gradual infilling, the Sphaeroidinellopsis spp. acme interval, followed by a disintegration of oceanographic conditions and a second recovery period. A sudden influx of cold, deep Atlantic waters into the Tyrrhenian Sea, resulting from a major tectonic break in the Gibraltar sill, may have caused this catastrophic reversal in the orderly recovery of normal paleoceanographic conditions in the post-flood period.

Planktonic foraminifera of ODP Site 117-722

Quantitative analysis of the late Cenozoic planktonic foraminiferal record from western Arabian Sea Site 722 revealed long term trends in the history of oceanography and climate. The modern western Arabian Sea surface waters are highly influenced by the monsoonal wind system. Summer upwelling, a result of southwestern winds, occurs along the coast of Somalia which produces distinct foraminiferal assemblages which are dominated by G. bulloides d'Orbigny. Consequently, variations in the distribution record of G. bulloides through time monitor the upwelling history associated with monsoonal activities. G. bulloides was a minor constituent of the foraminiferal fauna from the bottom of the hole (~14.5 Ma) until about 8.6 Ma ago. Then a rapid shift occurred toward higher values, up to 53% at 7.4 Ma. We interpret this rapid increase as a major step in the evolution of the monsoonal history. It is either the establishment of the system or at least a strong intensification of the monsoonal winds. At 5.5 Ma a significant drop of the G. bulloides relative abundance occurred which may indicate less upwelling, or alternatively other biota may have been favored in this period. From 5.0 Ma to Recent the G. bulloides record indicates that upwelling has occurred with minor fluctuations.

Calcareous nannofossils and planktonic foraminifera of ODP Hole 132-810C

The 136 m of calcareous oozes recovered in Hole 810C span the interval from upper Maastrichtian to middle Pleistocene. Three major hiatuses interrupt the sequence, with the topmost part of the Maastrichtian through the entire lower Paleocene, most of the lower Eocene, and the entire middle Eocene through most of the middle Miocene missing. Severe reworking and displacement affected the lower part of the succession from the Maastrichtian through the middle Miocene. Reworking and displacement gradually decreased in the upper portion. Calcareous nannofossil biostratigraphy enabled us to calibrate precisely the nearly complete magnetic reversal sequence of the Pliocene to the late Pleistocene. Two minor hiatuses detected by calcareous nannofossils across the Pliocene/Pleistocene boundary and in the upper lower Pleistocene, respectively, resulted in shortening of the Olduvai and Jaramillo Events within the Matuyama Chron of the magnetic reversal sequence.