Globorotalia Truncatulinoides Research Articles

Application of the Graphic Correlation method to Pliocene marine sequences

Biostratigraphy — the use of paleontological evidence to establish relative chronologies, forms the cornerstone of many sedimentary geological investigations. Several different approaches to biochronology are available. Traditional interval zones, defined on lowest and/or highest occurrences of selected taxa, are used to place bodies of rock in a relative chronological framework. Fossil datum levels, which are more numerous than zones, are often used as chronohorizons for correlation purposs. The Graphic Correlation method, like interval zonations, synthesizes information from a number of different taxa but does not assume synchrony of any one taxon. A magnetobiostratigraphic model for deep-sea Pliocene sequences has been constructed by graphic correlation of Deep Sea Drilling project cores from the North Atlantic (606), Caribbean Sea (502), South Atlantic (516), Tasman Sea (590), Equatorial Pacific (573) and North Pacific (577). All cores are hydraulic piston cores which contain abundant planktonic foraminifers, calcareous nannofossils and which record many of the magnetic reversals expected in the Pliocene. The model is based on internally consistent paleontologic data gathered by the author. This study demonstrates the advantages of graphic correlation over conventional biostratigraphic procedures. Accurate inter-regional correlations can be made between core sites without resorting to multiple microfossil zonations and without invoking synchrony of fossil events. Important results of this study are: (1) many Pliocene planktonic foraminifer and calcareous nannofossil events are diachronous by more than 0.20 m.y., (2) Globorotalia truncatulinoides first occurs in the Southwest Pacific Ocean, approximately 0.50 m.y. earlier than previously reported, (3) a previously undetected hiatus of short duration (0.38 m.y.) exists just above the Cochiti subchron at DSDP 577A.

Plio-Pleistocene calcareous plankton biochronology

A reliability assessment of 20 commonly employed Late Pliocene and Pleistocene calcareous plankton biostratigraphic datums published for 30 DSDP holes has revealed a subset of ten which appear to be reasonably isochronous and consistently recognizable by a large number of biostratigraphers. The assessment is based on an analysis of datum rank order reliability, and is supplemented by an examination of the absolute age estimates for the same 20 datums which were derived using the paleomagnetic stratigraphy presented for 19 of the 30 holes. The results indicate only four of the initial eleven datums based on planktonic foraminifers can be considered reliable, compared to seven reliable calcareous nannofossil datums of an initial nine. Compared to calcareous nannofossils, planktonic foraminifera thus show greater provincialism and more fluid ecophenotypic and evolutionary changes, implying that they are more interesting subjects for evolutionary studies but relatively less suitable tools for biostratigraphy. An important datum rejected by this assessment is the first appearance datum (FAD) of the planktonic foraminifer Globorotalia truncatulinoides, once considered a reliable indicator of the Plio-Pleistocene boundary. While the FAD for this species occurs at its commonly accepted level of approximately 1.9 Ma in the equatorial Pacific and throughout the temperate and tropical Atlantic, its age in the Indo-Pacific between about 15°S and 40°S is strongly diachronous. The earliest FAD is dated at a maximum of 2.6–2.7 Ma between about 20°S and 35°S in the Indo-Pacific. A global extremum in the average size of Holocene populations has been previously recognized within this same latitudinal zone.

Improved Dating of the Pliocene of the Eastern South Atlantic Using Graphic Correlation: Implications for Paleobiogeography and Paleoceanography

Graphic correlation of foraminifer and nannofossil events establishes a high resolution chronology for the Pliocene at Deep Sea Drilling Project Site 532. Coarsely sampled magnetic inclination data are reinterpreted to indicate a complete Pliocene section. The age model suggests mean accumulation rates of 9.5 cm 10-3 yr for the first half of the early Pliocene and 5.8 cm 10-3 yr throughout the later part of the early Pliocene early Pleistocene. Major upwelling began at the location of Site 532 at 3.2 Ma. Time series analysis indicated a 41 ky cyclicity to the CaCO3 record between 2 and 4.5 Ma. Data support ages of 1.9 Ma for the first appearance of Globorotalia truncatulinoides and approximately isochronous southern hemisphere first appearances for Globorotalia crassaformis (4.70 Ma), Globorotalia puncticulata (4.77 Ma), and Globorotalia inflata (3.68 Ma).

High-Resolution Biostratigraphy and Aminostratigraphy of ODP Hole 625B: Northeastern Gulf of Mexico: ABSTRACT

Quantitative census data of planktonic foraminifera from the Quaternary section of Ocean Drilling Program Hole 625B (Leg 100, northeastern Gulf of Mexico) have been analyzed. A high-resolution biostratigraphy that subdivides the Pleistocene into 21 stratigraphic units is established by the extension of the work of Ericson and Wollin, and Neff. This stratigraphy may be applied by generating the faunal percentage curves of only four species of planktonic foraminifera: the Globorotalia menardii complex, Globorotalia inflata, and the two coiling varieties of Globorotalia truncatulinoides. The zonation may be supplemented and calibrated by the utilization of standard industry biohorizons, or paleotops. Foraminiferal aminostratigraphy is useful chemical tool for correlation of Pliocene-Pleistocene sections. Prior studies generally demonstrate that (1) amino acid D/L values increase with increasing depth, (2) spinose foraminifera have lower apparent racemization rates than non-spinose foraminifera, and (3) racemic equilibrium is found in early Pliocene or late Miocene samples, depending on the taxa analyzed. Long, high sedimentation-rate sections such as 625B are potentially useful for establishing a detailed Pliocene-Pleistocene aminostratigraphic record. D-alloisoleucine/L-isoleucine trends in Globigerinoides ruber, orbulina universa, Neogloboquadrina dutertrei, Globorotalia menardiitumida complex, and mixed foraminifera species have been determined for the Pleistocene section of Hole 625% at 5 to 10-m samplingmore » intervals. This preliminary study demonstrates that with dense sampling and proper sample preparation, it should be possible to use multiple taxa, each an independent clock, for intercore correlation and for evaluation of hiatuses or reworking effects.« less

Shape and isotopic differences between conspecific foraminiferal morphotypes and resolution of paleoceanographic events

The principal axiom of isotope paleoceanography is that the isotopic behavior of the foraminiferal species being used to provide proxy paleoenvironmental information is consistent throughout the geographic and stratigraphic range of the taxon. We present evidence that populations of Uvigerina peregrina, Globorotalia truncatulinoides, Neogloboquadrina pachyderma, and species of the Sphaeroidinellopsis lineage are composed of complex mixtures of morphological types (morphotypes). Many of the conspecific morphotypes exhibit a different response with respect to their δ 18O and δ 13C compositions. Morphotypes are defined by a combination of image analysis, extended cabfac/extended qmodel vector analysis and isotopic analysis. In many cases, morphotypes of specimens of the same size and from the same sample exhibit significant oxygen and/or carbon isotopic differences. This “morphotype effect” may be an important contributor to intraspecific isotope variability among foraminiferal species and to the observed magnitude of isotopic changes associated with paleocenographic events. Such morphotypic-isotopic differences may have significant consequences for the interpretation of isotope paleoceanographic records.

Diachrony of Late Neogene microfossils in the southwest Pacific Ocean: Application of the graphic correlation method

The assumption of synchrony of first and last occurrences of fossil taxa can be tested using graphic correlation procedures which, by allowing measured stratigraphic sections to be compared on a common depth scale, make it possible to develop a correlation model which integrates information from a number of cores. The strategy of the test presented here is to use a graphic correlation model that is based on data from the Atlantic (Deep Sea Drilling Project (DSDP) sites 502, 516A) and north Pacific (DSDP site 577A) as a basis for determining to what extent fossil datums in the southwest Pacific are synchronous.First and last occurrences of Pliocene calcareous nannofossils and planktonic foraminifers have been compared in five DSDP cores from the southwest Pacific ocean (sites 586, 587, 588, 590A, and 592). All cores were recovered using hydraulic piston coring technology, which assures the best recovery and minimal disturbance. Most of these cores contain abundant, well‐preserved foraminifers and nannofossils, as well as a partial record of many of the expected magnetic polarity reversals in this part of the section. To assure taxonomic consistency, all taxonomic identifications were made by the author.Graphic correlation of this data set suggests that several important biostratigraphic markers are highly diachronous. For example, this study confirms that Globorotalia truncatulinoides first occurs at approximately 2.4 Ma between 20° and 35° south latitude in the southwest Pacific, approximately 0.5 m.y. earlier than it is found elsewhere in the Atlantic and Pacific. Other datums, such as the last occurrence of Discoaster brouweri, are essentially synchronous. These findings suggest that biostratigraphic models based on the assumption of synchrony of first and last occurrences of fossil taxa may be incorrect. Biostratigraphic models created with the Graphic Correlation method offer an opportunity to examine the biogeographic dimensions of origination, migration, and extinction of planktonic taxa.

Magnetic polarity stratigraphy of the Pleistocene section at Portland (Victoria), Australia

Three to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along with Globorotalia truncatulinoides within the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre- 14C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.

Evolutionary changes in some Late Neogene planktonic foraminiferal lineages and their relationships to paleoceanographic changes

The timing of evolutionary changes in some late Neogene lineages of planktonic foraminifers and major paleoceanographic events are evaluated to assess possible correspondences between paleoclimatic change (in a broad sense) and evolutionary innovations. Previously published data on evolutionary changes in the Globorotalia inflata lineage, the Globorotalia tumida lineage, and the Globorotalia truncatulinoides lineage, and new data on the Sphaeroidinella dehiscens lineage, are used in the study. Most evolutionary rate changes in these lineages are shown to occur near times of major paleoceanographic events. For example, rapid increase in conicality and weakening of the keel in the G. inflata lineage in the latest Miocene coincided with the 6.2‐Ma event (global cooling, sea level regression, and shift in carbon isotope ratios in foraminiferal tests). Disappearance of keeled morphotypes (Globorotalia conomiozea) in the same lineage, and appearance of nonkeeled forms with rounded periphery (Globorotalia puncticulata) coincided with the return of warmer, more stable climatic conditions, and transgressions at the Miocene/Pliocene boundary (5.3 Ma). Phyletic transformation from Globorotalia plesiotumida into G. tumida also took place across this boundary, and supplementary apertures first developed in the S. dehiscens lineage. Supplementary apertures in the S. dehiscens lineage were rare through the early Pliocene but became rapidly dominant in the populations in the interval between 3.4 and 3.3 Ma, where major paleoceanographic changes occurred (the 3.4‐to 3.2‐Ma event marked by cooling of surface waters and increased production of bottom waters at high latitudes, resulting in strengthening of ocean vertical and horizontal gradients). Forms without a supplementary aperture became extinct only 0.3–0.4 m.y. later (3.0 Ma), and at about the same time, G. inflata appeared in the fossil record. Although evolutionary change exhibits striking temporal correlation with climatic change, some evolutionary time series do not show any obvious relationship to paleoclimate: chamber number in the final whorl in the G. inflata lineage and conicality in G. truncatulinoides.

Paleoenvironmental changes from stable isotopes in planktonic foraminifera from Eastern Mediterranean sapropels

Parallel stable oxygen isotope analyses of six planktonic foraminiferal species from an Eastern Mediterranean deep-sea core present clear evidence for abnormal hydrographic regimes during deposition of sapropels S6 and S7. Samples from S7 are characterized by a strong depletion of 18O in epipelagic species, while meso- and bathypelagic forms are much less depleted. This indicates a shallow pycnocline. During deposition of S6 all species show a tendency towards lower values, pointing to a far more extended pycnocline. Density stratification of the watercolumn is suggested by the isotopic differences between the species Neogloboquadrina dutertrei, Globigerina bulloides and Globorotalia scitula. The latter represents the deepest element and shows the highest δ 18O values. Carbon isotopes show two species groups, each containing an epi-, meso-, and bathypelagic species. Under normal marine conditions group I ( Globigerinoides ruber, Neogloboquadrina dutertrei and Globorotalia truncatulinoides) has relatively high δ 13C values while species of group II ( Globigerina bulloides, Globorotalia scitula, and Globigerina quinqueloba) show relatively low δ 13C values, indicating a stronger “vital effect”. During sapropel deposition 12C isotopes are enriched, which we interpreted as the result of increased biological activity due to “low-oxygen” (stress) conditions. G. scitula shows different eco-phenotypes during times of sapropel deposition and the same may be true for the other members of group II. Failure to adapt to adverse environmental conditions may be the cause for the absence of the two group I members ( Globigerinoides ruber and Globorotalia truncatulinoides) in sapropel S6.

Shape changes in Globorotalia truncatulinoides as a function of ontogeny and paleobiogeography in the Southern Ocean

Morphological evolution of the planktonic foraminifer Globorotalia truncatulinoides in the southern Indian Ocean accompanied changes in the species' paleobiogeographic range during the late Quaternary. The first sustained migrational appearance of G. truncatulinoides in subantarctic waters during oxygen isotopic stage 13 (∼500,000 years ago) involved peripheral populations dominated by juvenile-sized kummerform types. The stage 13 colonization of subantarctic waters coincided with a southward migration of the Subtropical Convergence (STC). The first sustained appearance of the species in northern Antarctic waters during isotopic stage 7 (∼200,000 years ago) is followed by fluctuations in the species' paleobiogeographic range due to glacial-interglacial water mass changes and increasing tolerance to the colder waters of the subantarctic and Antarctic regions. Examination of allometric shape changes during the ontogenetic development of G. truncatulinoides reveals a statistically significant shape change from elongate, axially compressed juveniles to conical, axially extended adults in samples from isotopic stages 1 and 2 in core E48-28. The results provide evidence that the morphotype of a species which originally invades a new biogeographic area may rapidly take on shape characteristics which differ significantly from the original colonizing population.

Les Foraminifères des carottages holocènes de la plate-forme continentale sarde

The object of this work is to present the foraminifera associations found in seven cores of holocoenic period from the continental shelf of southern Sardinia. The percentage of benthos is always definitely greater than 82,5 % . The benthic species are very numerous. There are no extinct species or species which present a paleoclimatic interest. The top-core samples collected from the infralittoral zone present two different associations based on its granulometry (sand and silt). The species most commonly found in sand are : Cibicides lobatulus, Ammonia beccarii, Rosalina globularis, Asterigerinata mamilla, Gavelinopsis praegeri, Buccella frigida granulata, Eponides répandus, Quinqueloculina aspera, etc. The species most commoly found in silt are Rosalina globularis, R. obtusa, Cibicides lobatulus. The presence of Posidonia oceanica may lead to a greater peercentage of some species (i.e. Nubecularia lucifuga, Rosalina bradyï). They may be referred respectively to the biocenose of well calibrated fine sands ("SFBC" of Peres & Picard, 1964) and to the biocenose of the "herbier" of Posidonie ("HP" of Peres & Picard, 1964). The species most commoly found in the top-core samples of the circalittoral zone are Asterigerinata mamilla, Cibicides pseudoungerianus, C. lobatulus, Neoconorbina terquemi, Ammonia beccarii, Spiroplectammina wrighti, etc. The planktonic foraminifera are mostly represented by Globorotalia truncatulinoides, Globigerina bulloides, Globorotalia inflata, Neogloboquadrina pachyderma, Globigerinoides trilobus. The association may be attributed, with great probability, to the biocenose of the coastal detritus ("DC" of Peres & Picard, 1964). Along the cores, the associations present characteristics similar to those of the surface samples.

Morphometric and stable isotopic evidence for subpopulations of Globorotalia truncatulinoides

Morphometric and stable isotopic evidence for subpopulations of Globorotalia truncatulinoides

Globorotalia truncatulinoides (d'Orbigny) in the Mediterranean Upper Pliocene Geologic Record

Globorotalia truncatulinoides (d'Orbigny) in the Mediterranean Upper Pliocene Geologic Record

Eigenshape analysis of microfossils: A general morphometric procedure for describing changes in shape

A general morphometric procedure is described that organizes collections of microfossil outlines according to their shape. It involves representing the greatest proportion of variation observed among a collection of shapes by the least number of different shapes. Since these are determined as empirical orthogonal shape functions—eigenfunctions—of the observed shapes, the procedure is termed eigenshape analysis. Observed shapes are arranged and their shape differences systemized by reference to these determined eigenshape functions. The well-known ecophenotypic shape variation with latitude exhibited by the Pleistocene planktonic foraminifer Globorotalia truncatulinoides (d'Orbigny)serves as an example.

Fourier shape analysis of Globorotalia truncatulinoides from late Quaternary sediments in the southern Indian Ocean

Fourier shape analysis has been used to determine the morphological variation within the planktonic foraminifera, Globorotalia truncatulinoides from the southern Indian Ocean. Measured specimens are from 20 Recent core top samples distributed from 22°S (central gyre water mass) to 47°S (subantarctic water mass). Fourier analysis determined that the two most significant components of shape within this species are elongateness and conicalness which are characterized by harmonics 2 and 3, respectively. Mean harmonic 2 values are significantly correlated with the percentage of sinistral coiled individuals in each sample ( r = +0.91). Mean values for harmonic 3 have a correlation coefficient with water temperature and salinity at 200 m of r = +0.85 and +0.88. Specimens become less elongate and more conical in a traverse from south to north. Fourier shape analysis of planktonic foraminifera was then shown to be useful in investigations of late Quaternary paleoceanographic problems. Four piston cores were examined from the southern Indian Ocean. Total faunal and oxygen isotope analyses provided the stratigraphic framework. The results indicated that the central gyre water mass remained relatively stable during glacial stages. The region of the Subtropical Convergence was strongly affected, however, by the northward migration of the Polar Front.

Late Pleistocene Eucampia antarctica Abundance Stratigraphy in the Atlantic Sector of the Southern Ocean

A stratigraphy based upon abundance changes in the marine diatom Eucampia antarctica (Castr.) Mangin is presented for Late Pleistocene sediments of the Atlantic sector of the Southern Ocean south of the Polar Front. This stratigraphy is directly tied to lithology and concentrations of ice-rafted detritus. We find a positive correlation between E. antarctica abundance, increased ice-rafted detritus, and silty diatomaceous sediment. Low E. antarctica counts are associated with little or no ice-rafted detritus and diatomaceous ooze. Tentative correlation with the oxygen isotope record indicates that low E. antarctica abundances are associated with Oxygen Isotope Stages 1, 5a, 5c, and 5e. Late Pleistocene Eucampia antarctica abundance stratigraphy in the Atlantic sector of the Southern Ocean INTRODUCTION The Antarctic region plays a significant role in the world climate system (Fletcher, 1969). Fletcher pointed out that ice cover in the Southern Ocean influences ocean/atmosphere heat exchange and that yearly variations in ice cover may be important in enhancing the climatic effects of minor changes in global heating. It is therefore important to be able to identify both shortand long-term climatic fluctuations in the Southern Ocean recorded in deep-sea sediments. Central to this theme is the development of high resolution stratigraphic schemes. Since foraminifera and coccoliths are largely absent from high southern latitude sediments, the responsibility for a suitable stratigraphic scheme rests with the radiolarians and diatoms. Regional stratigraphies in the deep-sea sediments based upon abundance changes of individual species (Ericson, 1961; Ericson et al., 1961; Hays et al., 1976; Morley and Hays, 1979) or morphologic changes of selected species [e.g. coiling direction in Globorotalia truncatulinoides (d'Orbigny) (Ericson and Wollin, 1956), size change in Coscinodiscus nodulifer A. Schmidt (Arrhenius, 1952; Burckle and McLaughlin, 1977)] have been used to resolve time intervals of less than 50,000 years. Within the past few years it has been possible to further refine the resolution of some of these stratigraphies by correlating them with the globally synchronous oxygen isotope record (Shackleton and Opdyke, 1973, 1976). Using such an approach, Hays et al. (1976) and Morley and Hays (1979) have resolved time intervals of less than 10,000 years with a stratigraphy based upon changes in abundance of the radiolarian Cycladophora davisiana Ehrenberg. In the Southern Ocean, and particularly south of the Polar Front, a number of diatom species show abundance variations during the Late Pleistocene (unpublished data L.H.B.). These include such well-known forms as Coscinodiscus lentiginosus Janisch, Nitzschia kerguelensis (O'Meara), and Eucampia antarctica (Castr.) Mangin. This paper describes variations in abundance of this latter species which is found in the Antarctic and sub-Antarctic regions of the Southern Ocean and is also a constituent of the displaced diatom flora entrained in the Antarctic Bottom Water (Burckle and Stanton, 1975). Five cores in the South Atlantic were selected for this study (see table 1). Four were located south of the Polar Front and one (V29-105) north of it. Although we have studied E. antarctica abundances in other sectors of the Southern Ocean, we have not yet assured ourselves that the fine details of each abundance curve are indeed correlative around the Antarctic. micropaleontology, vol. 29, no. 1, pp. 6-10, 1983 6 This content downloaded from 157.55.39.45 on Tue, 19 Jul 2016 05:50:29 UTC All use subject to http://about.jstor.org/terms

Equatorward migration of Globorotalia truncatulinoides ecophenotypes through the Late Pleistocene: Gradual evolution or ocean change?

The biogeography of differences in average shape of the modern planktonic foraminifer Globorotalia truncatulinoides (d'Orbigny) exhibits systematic relationships to changes in the ocean's surface environment. Comparison of these shape changes, as they exist today in the Southern Hemisphere, with fossil shapes preserved in a Late Pleistocene record from the South Atlantic Ocean, shows that the biogeography of G. truncatulinoides ecophenotypes has changed markedly through time. Beginning at least 700,000 yr ago and continuing up to the present, there has been a gradual but clear migration of certain morphotypes of G. truncatulinoides toward lower latitudes. The history of this migration bears no simple relationship to the cyclic climatic changes that characterize the Late Pleistocene. We conclude that either (1) phenotypic variants of Gr. truncatulinoides reflect some previously unmeasured, gradually changing aspect of Late Pleistocene oceans, or (2) we are witnessing a gradual evolution of the environment preferences of G. truncatulinoides.

Late glacial to recent cores from the eastern Mediterranean

Variations in the planktonic foraminiferal population in sediment cores from the eastern Mediterranean indicate a slow warming from about 24,000 y BP to the climatic optimum at 4700 y BP; there is evidence of an earlier warm phase in two cores. Globorotalia truncatulinoides and G. pachyderma are not found in sediments younger than 10,400 y BP. Dates are confirmed by 14C dating at 10,438 and 4722 y BP. G. sacculifer becomes more abundant than G. ruber for a short interval at 1200 y BP. A dark olive green microburrowed horizon in the cores coincident with a reduction in the benthonic foraminferal population between 9300 and 6700 y BP represents the sapropel found in the deeper basins. Planktonic foraminiferal productivity was highest at 9000 and 4700 y BP; benthonic productivity was highest in the late Glacial between 12,000 and 10,000 y BP. 18O composition of the foraminifera shows a rapid depletion of 18O from 13,000 to 10,000 y BP, caused by melting ice and temperature increase, indicating the end of glacial conditions. The magnetic fabric of three cores is similar to that of British lake cores and in conjunction with the 14C dates and foraminiferal changes can be used to date eastern Mediterranean sediments. The overall mineralogy and sedimentation rates in the area are controlled by proximity to Cyprus; part of the fine clay fraction (<2 μm) are believed to be derived from the Turkish mainland. A decrease in the relative amount of montmorillonite, which commenced at 12,000 y BP in the deep-water cores, coincides with the introduction of ice melt-water from the Black Sea into the eastern Mediterranean; at 6700 y BP (the end of the sapropel) the amount of montmorillonite increases to that of glacial times.

Neogene planktonic foraminiferal biostratigraphy and evolution: Equatorial to subantarctic, South Pacific

Detailed planktonic foraminiferal zonations have been established for the Neogene (Latest Oligocene through present) in six DSDP sites in the South Pacific ranging from equatorial to subantarctic latitudes (48°S). Two basic zonal schemes are readily recognized: tropical and temperate. The tropical zonation is best developed in DSDP Site 289 and the temperate zonation in Sites 206, 207A and 284. Tropical and temperate zonations can be linked by a warm subtropical scheme in Site 208, because this sequence includes a mixture of tropical and temperate elements. A site located close to the Subantarctic Convergence (Site 281) contains a zonation largely of temperate character, but the present of cooler elements and some differences in biostratigraphic ranges have required a slightly different biostratigraphic scheme. Although two broad schemes are recognized, none of the biostratigraphic sequences are identical between any of the sites. This reflects differences in biogeography, evolution and diachronous extinction at various latitudes during the entire Neogene. Diachronism in biostratigraphic ranges continue to create difficulties in correlation across such wide latitudes. Our detailed work has required the establishment of new biostratigraphic zonations in certain parts of the Neogene sequence and modifications in some other parts. Otherwise, previously established schemes are followed as closely as possible. In the temperate region, a new zonation has been established for the Early Miocene to early Middle Miocene. For the remainder of the Neogene the zonation of Kennett (1973) has been largely used. The tropical zonation of Blow (1969) is employed in the equatorial Site 289, but with further subdivisions for Zones N4 and N17. For areas intermediate between tropical and temperate latitudes (Site 208), a modified Early Miocene zonation is established based on changes in tropical and temperate elements. The zonal schemes are established on taxa that exhibit both diachronous and isochronous ranges across the latitudes. Zones that are at least partly diachronous include the Globigerinoides trilobus and Globorotalia miozea Zones of Early Miocene age; perhaps the Globorotalia mayeri Zone (its base) of the Middle Miocene; the Globorotalia conomiozea Zone of the Late Miocene; and the Globorotalia crassaformis Zone of the Early Pliocene. A large number of datum levels are recognized based on first evolutionary appearances or extinctions. The most widely applicable datums are as follows: latest Oligocene — Globigerinoides F.A.; Early Miocene — Globoquadrina dehiscens, F.A., Globorotalia kugleri L.A., Catapsydrax dissimilis L.A. and Praeorbulina glomerosa F.A.; Middle Miocene — Orbulina suturalis F.A., Globorotalia peripheroacuta F.A., Fohsella lineage L.A., Globorotalia mayeri L.A.; Late Miocene — “ Neogloboquadrina” continuosa L.A., Globoquadrina dehiscens L.A., Globorotalia cibaoensis F.A.; Early Pliocene — Globorotalia puncticulata F.A., Globorotalia margaritae F.A.; Early Pleistocene — Globorotalia truncatulinoides F.A. A number of other datums are identified which assist with correlation over more restricted latitudinal ranges. The evolution of most Neogene planktonic foraminifera is now well established for a wide range of water masses. Evolutionary lineages are primarily centered in the temperate and tropical regions. Tropical lineages have recently been reviewed by Srinivasan and Kennett (1981) and are not discussed in detail here. However, Sphaeroidinellopsis seminulina is now considered to have evolved directly into S. paenedehiscens during the Late Miocene and S. subdehiscens Blow is considered to be junior synonym of S. seminulina. A new evolutionary lineage is recognized in the warm subtropics (Site 208) whereby Globigerina woodi woodi gave rise to Globigerinoides subquadratus via Globigerina brazieri. The discovery of this lineage clearly demonstrates that Globigerinoides is a polyphyletic “genus”. Another major phylogenetic lineage is recognized within the temperate globorotaliids of Early Miocene age as follows: “ N.” continuosa → Globorotalia zealandica incognita → G. zealandica zelandica → G. praescitula → G. miozea. Although parts of this lineage have been recognized earlier, the entire phylogeny has previously been underscribed. A new Early to Middle Miocene lineage is recognized in the subantarctic to temperate areas which involve a transition from Globorotalia praescitula to G. challengeri n. sp. via intermediate forms. Two major Neogene globorotaliid lineages — the Menardella of the tropics and Middle Miocene to Recent forms of Globoconella of the temperate areas — are both considered to have evolved from Globorotalia praescitula beginning in the Early Miocene. This evolution initially was restricted to temperate areas but has since separated into distinctly tropical and temperate phylogenetic elements.

Late neogene biostratigraphy and stable isotope stratigraphy of a drilled core from the Gulf of Mexico

Late Neogene stable isotope stratigraphy and planktonic foraminiferal biostratigraphy have been examined in a high sedimentation rate core (E67-135, Shell Oil Co.) drilled at 725 m water depth in the De Soto Canyon, Gulf of Mexico. The 305 m core contains sections that are Late Miocene, Early Pliocene, Late Pliocene, and Quaternary in age, and is rich in well-preserved assemblages of planktonic foraminifera. A biostratigraphy has been established based on the ranges of 34 selected species of foraminifera. The core 3orrelates with sections from the Gulf of Mexico, the Caribbean Sea, and the subtropical North and South Atlantic Oceans using, as datums, the evolutionary appearances of Globorotalia miocenica Palmer and Globorotalia margaritae evoluta Cita, the extinction of Globorotalia miocenica and the first appearance of Globorotalia truncatulinoides (d'Orbigny). Oxygen and carbon isotope stratigraphy is based on analysis of the benthonic foraminifer, Uvigerina d'Orbigny. Isotopic trends are similar to those observed in the Pacific and Atlantic Oceans. From Early Pliocene to Late Pleistocene time, average δ 18O values increase (2.42‰ to 3.36‰) and exhibit a wider range of values (0.71‰ in Early Pliocene compared to 1.65‰ in Late Pleistocene sediments), probably reflecting Late Neogene climatic deterioration. The ratio 13 C 12 C decreases significantly by −0.21‰ from the Late Miocene to the Early Pliocene. A decrease in δ 13C is observed in other cores and is probably related to changing oceanic circulation patterns in Late Miocene time.