Planktic Foraminiferal Fauna Research Articles

Planktic foraminifers and hydrography of the eastern and northern Caribbean Sea

The distribution of living planktic foraminifers and their relation to the hydrography of the Caribbean Sea was investigated in plankton net tows and surface sediment samples taken along the Antilles island arc during April/May 1996. The planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of Orinoco River water into the southeastern Caribbean Sea and inflowing Sargasso Sea water in the north. Along the Antilles island arc, Globigerinoides ruber was the dominant species in the surface waters throughout. In the southeastern Caribbean Sea, where Orinoco River outflow influences the planktic community, standing stocks of planktic foraminifers (>100 μm) between 4 and 50 specimens m −3 were medium to low. The southeastern faunas between Tobago and Guadeloupe were characterized by increased proportions of Neogloboquadrina dutertrei. Highest standing stocks of 159 specimens m −3 in the upper 20 m of the water column were recorded in the northeastern Caribbean Sea and the assemblages were characterized by high proportions of Globigerinita glutinata, associated with cyclonic eddies. In the Anegada Passage, where Sargasso Sea water flows into the Caribbean Sea, low standing stocks of 18 specimens m −3 indicate oligotrophic conditions. Together with the oligotrophic surface waters, the Subtropical Underwater enters the Caribbean Sea through the Anegada Passage in water depths between 100 and 300 m. These waters are characterized by higher concentrations of Globorotalia truncatulinoides relative to the adjacent water masses. Comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species. In the vicinity of islands Globigerinoides ruber reaches higher relative frequencies than in the open ocean, pointing towards a higher tolerance of this species towards neritic conditions than in other species.

The Cretaceous–Tertiary (K–T) mass extinction in planktic foraminifera at Elles I and El Melah, Tunisia

Planktic foraminiferal faunas across the K–T transition at Elles and El Melah in northwestern and northeastern Tunisia, respectively, reveal patterns of species extinctions and species survivorship similar to those found at the El Kef stratotype and the Ain Settara sections. Slightly more than 2/3 of the species disappeared at or before the K–T boundary event and slightly less than 1/3 survived into the Danian where most disappeared sequentially within zone P1a ( Parvularugoglobigerina eugubina). Relative species abundance patterns reveal that the 13–16 K–T survivors dominated (80%) the assemblages in the latest Maastrichtian, whereas the K–T extinct species were rare and totaled less than 20% of the total assemblages. The K–T survivors are generally small with little surface ornamentation and geographically widespread from low to high latitudes. In contrast, K–T extinct species are large, highly ornamented and geographically restricted to low latitudes. This indicates that the K–T mass extinction was selective, rather than random, and predominantly affected the less robust tropical species. With the exception of the opportunistic Guembelitria species which dominate the early Danian, most K–T survivor species suffered severely as is evident by the decreased species populations after the K–T event. Their eventual demise appears to have been related to post-K–T environmental changes and competition from evolving Tertiary species. These results reveal a complex mass extinction pattern that in addition to the K–T impact event is keyed to long-term environmental changes preceding and following this event.

The Paleocene-Eocene transition in the marginal northeastern Tethys (Kazakhstan and Uzbekistan)

We studied two sections that accumulated during the Paleocene–Eocene transition in shelf waters in the northeastern Tethys. Stable carbon isotopic compositions of marine and terrestrial biomarkers are consistent with a 13C depletion in the oceanic and atmospheric carbon dioxide pools during the Late Paleocene Thermal Maximum (LPTM; Subzone P5b). The 2–3‰ negative δ 13C excursion in planktic foraminifera coincides with minimum δ 18O values, an incursion of transient subtropical planktic foraminiferal fauna, and the occurrence of an organic-rich sapropelite unit in Uzbekistan, which accumulated at the onset of a transgressive event. Biomarker distributions and hydrogen indices indicate that marine algae and bacteria were the major organic matter sources. During the Late Paleocene (Subzones P4 and P5a), the marginal northeastern Tethys experienced a temperate to warm climate with wet and arid seasons. Most likely, warm and humid climate initiated during the LPTM (Subzone P5b) and subsequently extended during the Eocene (Zone P6) onto adjacent land areas of the marginal northeastern Tethys.

Interannual variability of planktic foraminiferal populations and test flux in the eastern North Atlantic Ocean (JGOFS)

Planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties, between water masses, and after periodical changes and episodic events (e.g. reproduction, storms). Distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data. In this paper we discuss the short-term impacts on interannual flux rates based on data from opening–closing net hauls obtained between the ocean surface and 500 m water depth. Data were recorded during April, May, June, and August at around 47° N, 20° W (BIOTRANS) in 1988, 1989, 1990, 1992, 1993, and during May 1989 and 1992 at 57°N, 20–22°W. Species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column. In addition, species assemblages >100 μm are almost indistinguishable from assemblages that are >125 μm in test size. The standing stock of planktic foraminifers at BIOTRANS can vary by more than one order of magnitude over different years; however, species assemblages may be similar when comparing corresponding seasons. Early summer assemblages (June) are distinctly different from late summer assemblages (August). Significant variations in the species composition during spring (April/May) are independent of the mixed layer depth. Spring assemblages are characterized by high numbers of Globigerinita glutinata. In particular, day-to-day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations. This appears to be independent of the reproduction cycle. Species assemblages at 47°N and 57°N are similar during spring, although surface water temperatures and salinities differ by up to 10°C and 0.7 (PSU). We suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer. Planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations, a quasi-annual periodicity in flux levels, and substantial differences in timing and magnitude of peak fluxes. At the BIOTRANS station, the average annual planktic foraminiferal CaCO 3 fluxes at 100 and 500 m depth are estimated to be 22.4 and 10.0 g m −2 yr −1 , respectively.

A size analysis of planktic foraminifera from the Arabian Sea

Planktic foraminiferal faunas from different environments in the Arabian Sea were size fractionated using 14 sieves with meshes between 100 and 710 μm, to assess the effect of the sieve mesh size cut off level on the faunal composition and to determine the size frequency distribution of individual species. Nine samples from a plankton pump and a towed net, a sediment trap, a box-core and a piston core were selected, to cover living and settling flux faunas as well as fossil faunas from the sediment. In living faunas, most species show an exponential size frequency distribution, with highest numbers in the finest interval of the size spectrum. In sediment trap and core samples, individual species size frequency distributions may consist of: (1) an exponential distribution of relatively small pre-adult specimens; (2) a Gaussian-shaped distribution of larger specimens, which may be classified as adult or terminal; or (3) a combination of both. The distributions are separated using a best fit technique. The composition of the total planktic foraminiferal fauna strongly changes along the size spectrum. Dominant taxa in >355 μm fractions are Orbulina universa, Globorotalia menardii, Globorotalia tumida, Globigerinella siphonifera and Globigerinoides sacculifer, in 125–355 μm fractions Globigerina bulloides, Globigerinoides ruber, Neogloboquadrina dutertrei and Globigerinita glutinata, and in <125 μm fractions Dentigloborotalia anfracta, Tenuitella compressa, Tenuitella iota, Turborotalita quinqueloba and the immature specimens of larger species. Consequently, the choice of the sieve mesh size strongly determines the percent composition of the assemblage and in turn the paleoceanographic interpretations based on these counts. Species richness and the Shannon diversity increase with decreasing sieve mesh size, while equitability generally decreases with decreasing size. In the water column approximately 60% of the fauna (>100 μm) is present in the 100–125 μm fraction and 1–6% is larger than 250 μm. In samples representing a settling flux (sediment trap and sediment samples) 29–57% of the fauna is present in the 100–125 μm fraction, while 6–23% is larger than 250 μm. Size frequency distributions of the dextral Neogloboquadrina complex (= Neogloboquadrina dutertrei and Neogloboquadrina pachyderma + P–D intergrades) show a bimodal pattern; a smaller peak reflecting dextral Neogloboquadrina pachyderma, and a larger peak of adult Neogloboquadrina dutertrei. By applying a best fit technique to the data, the two species may be separated from each other. In size fractions larger than 150 μm most species have reached the adult stage of ontogeny and we recommend this mesh size for standard faunal analysis. In addition, sieve mesh sizes of 125 and 250 μm have to be used to obtain a reliable estimate of the abundance of small and large species, respectively.

Late-glacial and Holocene paleoceanography and sedimentary environments in the St. Anna Trough, Eurasian Arctic Ocean margin

Based on stratigraphical analysis of twelve sediment cores from the Saint Anna Trough, we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the Holocene. Detailed analysis of benthic and planktic foraminiferal fauna, stable oxygen and carbon isotope analysis, lithostratigraphy and radiocarbon dates, are used to reconstruct the following evolution: After the deglaciation of the Saint Anna Trough >13,300 yr B.P. until 9500 yr B.P., the environment was mainly characterised by low biogenic production, carbonate dissolution and deposition of proximal to distal glaciomarine sediments. Intervals with high abundance of the benthic foraminifer Cassidulina teretis, may indicate influx of Atlantic Water at bottom. The transition into the present interglacial started at 9500 yr B.P. reflected by increased production of foraminifera and bivalves. After 8000 yr B.P. there was a marked drop in planktic δ18O followed by a rise in planktic foraminifera and subsequently an increase of C. teretis. These paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in Nordic seas. The early Holocene warming of the Saint Anna Trough were delayed by ca. 2000 years relative to the northeast Nordic seas. Early Holocene sedimentation rates were relatively high (>100 cm/1000 yr), declining drastically after 8000 yr B.P. (<50 cm/1000 yr). This was presumably caused by reduction in winnowing and/or riverine input.

Maastrichtian climate, productivity and faunal turnovers in planktic foraminifera in South Atlantic DSDP sites 525A and 21

Stratigraphic, faunal and isotopic analyses of the Maastrichtian at DSDP sites 525A and 21 in the South Atlantic reveal a planktic foraminiferal fauna characterized by two major events, an early late Maastrichtian diversification and end-Maastrichtian mass extinction. Both events are accompanied by major changes in climate and productivity. The diversification event which occurred in two steps between 70.5 and 69.1 Ma increased species richness by a total of 43% and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity. The onset of the terminal decline in Maastrichtian species richness began at 67.5 Ma and the first significant decline in surface productivity occurred at 66.2 Ma, coincident maximum cooling to 13°C in surface waters and the reduction of the surface-to-deep temperature gradient to less than 5°C. Major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the Maastrichtian. Between 200 and 400 kyr before the KT boundary surface and deep waters warmed rapidly by 3–4°C and cooled again during the last 100 kyr of the Maastrichtian. Surface productivity decreased only moderately across the KT boundary. Species richness began to decline during the late Maastrichtian cooling and by KT boundary time, the mass extinction had claimed 66% of the species. Viewed within the context of Maastrichtian climate and productivity changes, the KT mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact.

The Cretaceous/Tertiary boundary event in Ecuador: reduced biotic effects due to eastern boundary current setting

A multidisciplinary study of a new Cretaceous-Tertiary (K/T) boundary section near Guayaquil, Ecuador, reveals an unusually cool water, low diversity planktic foraminiferal fauna and a high diversity radiolarian fauna similar to those found in southern high-latitude K/T sequences despite the fact that this section was deposited near the Cretaceous equator. The K/T boundary is located by planktic foraminifera within a narrow interval bounded by last appearances of tropical Cretaceous species and first appearances of Tertiary species including Parvularugoglobigerina eugubina. As in southern high latitudes, there is no major mass extinction of either planktic foraminifera or radiolarians at this level. A major radiolarian faunal discontinuity occurs some 6 m higher in the section within foraminiferal Zone Plc, some 300–500 kyr after the K/T event. δ 13C values from bulk carbonates show both high- and low-latitude characteristics. Similarly to low latitudes, there is a 3%. negative δ 13C excursion at the K/T boundary which is generally interpreted as a major decrease in primary productivity. But unlike the low latitudes, recovery occurs within a few thousand years, as compared with 300–500 kyr, and suggests rapid nutrient influx from the Antarctic region via a current similar to the Humboldt current today. Similarly to high-latitude K/T sequences, a negative δ 13C shift occurs in the early Danian Zone Plb about 300 kyr after the K/T boundary. Sedimentologic and mineralogic data indicate a late Maastrichtian with relatively low biogenic quartz and high carbonate followed by increasing biogenic quartz (>50%) and decreasing carbonate (<5%) during the early Danian. This suggests intensified atmospheric and oceanic circulation and upwelling off Ecuador during the early Danian. The K/T transition is marked by increased volcanic activity, continental erosion and terrigenous influx, but this also occurs in the early Danian Zone at the P1a P1b zonal transition and is thus not unique to the K/T boundary. We suggest that the catastrophic biotic effects normally observed at the K/T boundary in low latitudes are greatly reduced or absent in the eastern equatorial Pacific because this region was dominated, then as now, by upwelling and current transport of nutrient-rich waters from the Antarctic Ocean. As a result, the biotic patterns are characteristic of southern high latitudes, whereas the δ 13C pattern combines ameliorated low-latitude effects with predominantly high-latitude trends.

Biogeography of cretaceous/tertiary (k/t) planktic foraminifera

As a result of the process‐level connections between biogeography, systematics, and ecology, analyses of the spatial distribution of organisms across major extinction events can be used to probe the paleobiological structure of those events and constrain the range of plausible explanatory models. Investigation of the biogeography of planktic foraminiferal faunas across the Cretaceous/Tertiary (K/T) boundary using a high‐resolution, taxonomically‐consistent, global database of more that 22 different boundary sections and deep‐sea cores reveals that this group did not undergo a stratigraphically instantaneous ‘mass extinction’ at the K/T boundary that is co‐incident with unambiguous independent evidence for a bolide impact. Rather, this event is better described as an extended or prolonged faunal turnover that was spread over a stratigraphic interval that, in some sections, spans several meters which, in turn, are estimated (using radiometric calibration) to represent as much 2–3 m.y. Beginning in the upper...

Planktonic foraminiferal faunas across the Cretaceous-Tertiary succession of Mexico: Implications for the Cretaceous-Tertiary boundary problem

Four consecutive planktic foraminiferal faunas characterize the planktic transformation recorded from continuous Cretaceous-Tertiary boundary successions of Mexico; from older to younger, these are mayaroensis , aegyptiaca , relict, and cancellate. The mayaroensis fauna, containing the nominal taxon and lacking gansseri , is followed by the aegyptiaca fauna, characterized by the absence of mayaroensis , indicating that this taxon disappeared before the major extinction of Cretaceous Hedbergellacea. The relict (“small globigerinas”) fauna contains taxa whose wall structure and umbilical apparatuses are directly linked to Cretaceous Hedbergellacea rather than Tertiary Globigerinacea. The cancellate fauna represents the first appearance of true Tertiary forms. The mayaroensis and aegyptiaca faunas are found immediately below the spherulite and clastic units attributed to the asteroid impact in Yucatan. The relict fauna is found immediately above the clastic unit, whereas the cancellate fauna is usually found ∼30 cm above this unit. The stratigraphic positions of the four consecutive faunas indicate that (1) the faunal changes observed started before the physical features attributed to the impact, and (2) the major evolutionary planktic event, i.e., the appearance of the cancellate wall, is the only unequivocal feature that defines the entry of the Tertiary planktic foraminiferal fauna.

Age, Deposition and Biotic Effects of the Cretaceous/Tertiary Boundary Event at Mimbral, NE Mexico

The Mimbral outcrop in northeastern Mexico represents nearly continuous sedimentation across the Cretaceous/ Tertiary (K/T) transition. The K/T boundary is present in a 4 cm clay layer and 3 mm red layer above the top of a channel-fill deposit. The 60 m wide and 3 m high channel-fill deposit is of latest Maastrichtian age (A. mayaroensis Zone). It consists of faunally, lithologically and mineralogically distinct units that appear to represent a series of gravity flows related to the latest Maastrichtian sealevel lowstand. The biotic effects of the K/T boundary event were not catastrophic for planktic foraminiferal faunas at Mimbral, NE Mexico. Although 2/3 of the species disappeared at or below the K/T boundary, the effect on the overall foraminiferal population was small (< 17%) because only rare, already endangered taxa disappeared

Comparative biogeographic analysis of planktic foraminiferal survivorship across the Cretaceous/Tertiary (K/T) boundary

It is now widely recognized that a large number of Cretaceous planktic foraminiferal species are commonly found associated with fully Danian faunas in many K/T boundary sections and deep-sea cores. This “Cretaceous” fauna has traditionally been regarded as representing the reworking of older Cretaceous sediments into younger strata, though recent isotopic data from some species indicates that, at least in these instances, the reworking hypothesis is false. To further test this reworking hypothesis the biogeography of this “Cretaceous” fauna is compared to the underlying uppermost Maastrichtian biogeography and to the biogeography of lowermost Danian planktic foraminiferal faunas. Results show that there is no regular decline in species richness, extinction, or faunal co-occurrence values for this “Cretaceous” fauna at progressively higher (=younger) Danian stratigraphic horizons. Moreover, there is no compelling association between the stratigraphic persistence of this “Cretaceous” fauna and shallow depositional settings. Instead, this fauna is characterized by: (1) a close (and predictive) association between “Cretaceous” and indigenous Danian species richness values throughout the lower Danian, (2) a close numerical and geographic correspondence between Danian speciation and the disappearance of “Cretaceous” species from the Danian fossil record, and (3) a pronounced similarity between changes in the general biogeographic structures of the “Cretaceous” and associated Danian faunas throughout the study interval. These data suggest that the K/T planktic foraminiferal extinction event exhibited a marked geographic structure with low and middle latitude faunas experiencing differentially high extinction rates in the lowermost Danian zones P0 and P1a and high latitude survivor faunas persisting more or less unchanged into the overlying zone, P1b and P1c. Taken together, these results challenge the traditional concept of an instantaneous uppermost Cretaceous planktic foraminiferal mass extinction and its proposed causal connection to bolide impact.

Temporary repopulation by low-oxygen tolerant benthic foraminifera within an Upper Pliocene sapropel: Evidence for the role of oxygen depletion in the formation of sapropels

Foraminiferal study of a continuous set of samples across the Upper Pliocene C2 sapropel (Singa section, southern Italy) revealed an interval containing substantial numbers of benthic foraminifera, bound by sediments in which benthic foraminifera are absent. The absence of benthic foraminifera is indicative of anoxic conditions. The interval with benthic foraminifera contains an association that is strongly dominated by the species Bulimina marginata, which is tolerant to low oxygen concentrations. The bottom water oxygenation did not improve sufficiently to allow development of a more diverse benthic foraminiferal fauna, or the return of intensively burrowing organisms. Variations in the planktic foraminiferal fauna and in the stable isotope records suggest that a surface water cooling preceded the benthic repopulation. A warming seems to have coincided with the return to bottom anoxia. The planktic productivity markers Globigerina bulloides and Neogloboquadrina show minor variations across the repopulated interval. The benthic repopulation, which reflects improved bottom water oxygenation, was probably favored by enhanced dense water formation in response to general cooling of the surface waters.

The Cretaceous-Tertiary boundary transition in the Antarctic Ocean and its global implications

Three Antarctic Ocean K/T boundary sequences from ODP Site 738C on the Kerguelen Plateau, ODP Site, 752B on Broken Ridge and ODP Site 690C on Maud Rise, Weddell Sea, have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies. Results show that Site 738C, which has a laminated clay layer spanning the K/T boundary, is biostratigraphically complete with the earliest Tertiary Zones P0 and P1a present, but with short intrazonal hiatuses. Site 752B may be biostratigraphically complete and Site 690C has a hiatus at the K/T boundary with Zones P0 and P1a missing. Latest Cretaceous to earliest Tertiary planktic foraminiferal faunas from the Antarctic Ocean are cosmopolitan and similar to coeval faunas dominating in low, middle and northern high latitudes, although a few endemic species are present. This allows application of the current low and middle latitude zonation to Antarctic K/T boundary sequences. The most abundant endemic species is Chiloguembelina waiparaensis, which was believed to have evolved in the early Tertiary, but which apparently evolved as early as Chron 30N at Site 738C. Since this species is only rare in sediments of Site 690C in the Weddell Sea, this suggests that a watermass oceanographic barrier may have existed between the Indian and Atlantic Antarctic Oceans. The cosmopolitan nature of the dominant fauna began during the last 200,000 to 300,000 years of the Cretaceous and continued at least 300,000 years into the Tertiary. This indicates a long-term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature, oxygen, salinity and nutrient conditions. A few thousand years before the K/T boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress. There is no evidence of a sudden mass killing of the Cretaceous fauna associated with a bolide impact at the K/T boundary. Instead, the already declining Cretaceous taxa gradually disappear in the early Danian and the opportunistic survivor taxa ( Ch. waiparaensis and Guembelitria cretacea) increase in relative abundance coincident with the evolution of the first new Tertiary species.

High resolution late Pliocene sea-surface temperature record from the northeast Atlantic Ocean

Application of quantitative micropaleontologic methods of sea-surface temperature (SST) estimation to the planktic foraminiferal faunas at Hole 548 in the northeast Atlantic between 3.5 and 2.0 Ma provide a detailed record of Pliocene surface temperature changes during the onset of major Northern Hemisphere glaciation. SST estimates indicate a relatively warm interval of “enhanced interglacials (warm peaks)” between 3.2 and 2.8 Ma followed by steady cooling with a significant step-like change toward colder temperatures occurring about 2.4 Ma. This record compares well with faunal and SST records from other North Atlantic sites.

Planktic foraminiferal diversity as indicator of ocean environments

The combination of the number of species (simple diversity), an information function (Shannon diversity) and a measure of equitability is used to characterize modern ocean environments based on planktic foraminiferal faunas. Regional environmental conditions can be recognized as deviations from the global latitudinal trend. Simple diversity (number of species) offers relatively little resolution itself, because it is sensitive to the addition of rare species. Variable conditions, such as the highly productive spring bloom and upwelling, are characterized by relatively low diversity and equitability values. Relatively high diversity and a lesser increase in equitability are found in mixing zones of adjacent water masses. In extreme conditions diversity is low, whereas equitability is intermediate to high. Modern patterns can be applied to fossil sections, to reconstruct regional paleoceanographic conditions. Thus relatively low Shannon diversity with low equitability in Maastrichtian heterohelicid faunas from El Kef, Tunisia, is interpreted as indicating variable conditions. An increase in simple diversity mostly traces evolution of the heterohelicids as a group, which diversified during the Maastrichtian. The number of species through time is a function of available niches and as such related to oceanic circulation on a global scale. Therefore, when applying modern patterns to fossil sections, a distinction has to be made between global diversity trends and regional environmental change. The correlation between Cenozoic stable isotope record and number of planktic foraminiferal species suggest indeed that simple diversity registers changes in global circulation. Maximum number of species occurred in the Maastrichtian, the Middle Eocene and the early Middle Miocene. In these three instances the maxima are found after the start of a cooling trend and are interpreted as transition periods between two modes of ocean circulation, causing the temporary coexistence of old and new species.

Tertiary geology across an allochthon—autochthon contact, Whangaroa County, Northland, New Zealand

Abstract Near Whangaroa, New Zealand, Waipapa Group cherts and metasediments are unconformably overlain by an autochthonous, north-dipping sequence of Bortonian-Kaiatan (Ab-Ak; Mid-Late Eocene) age, correlated with Ruatangata Sandstone. The sequence comprises (base to top): 0–40 m+ of massive, sparsely fossiliferous greensand (Waiare lithofacies) containing low-diversity agglutinated foraminiferal faunas suggesting a shallow, brackish environment; 50 m of massive, grey to red, variably siliceous siltstone (Ketetawa lithofacies); and 120 m+ of massive, bluish grey, brown-weathering finegrained calcareous muddy sandstone (Inumia lithofacies) containing moderately rich benthic and planktic foraminiferal faunas that indicate deposition at mid-shelf depths. This autochthonous sequence is discordantly overlain by allochthonous, sheared and deformed, multicoloured claystone of Teurian (Paleocene) age, containing low-diversity siliceous and agglutinated benthic foraminiferal faunas indicative of deposition at lower bathyal or deeper depths; and containing, near the base, a raft of underlying strata incorporated during emplacement. Both the allochthon and the underlying autochthon were differentially offset by high-angle faults active before, after, and probably during, emplacement of the allochthon. These faults do not offset overlying Miocene volcanogenic andesitic breccia (Wairakau Andesite) or argillaceous and tuffaceous lacustrine sediments associated with it Erosion of the breccia was followed by eruption of basalt, prior to incision of the present drainage system, along the channels of which minor soda water and gas seepages are found.

The Neogene larger foraminiferal sequence in the Australian and New Zealand regions, and its relevance to the East Indies Letter Stage Classification

In northern Australia, Neogene larger foraminifera range from the Late Oligocene into the earliest Middle Miocene, and are restricted to the late Early Miocene in southern Australia. In contrast, these forms range over a longer interval in New Zealand, from Late Oligocene to mid-Middle Miocene. Even though correlation with the Letter Stages lower T e to lower T f can be achieved, the usefulness of these stages to southeastern Australia and New Zealand is reduced because of the lower diversity of faunas in this area, compared with areas nearer the equator. The association of good planktic foraminiferal faunas with the larger foraminifera further reduces the usefulness of the Letter Stage correlations because finer correlations can be achieved using planktic forms. The presence of larger foraminifera gives considerable environmental and palaeogeographic information.

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 ( P14 P15 ), the Late Eocene 39-38 Ma ( P15 P16 ), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma ( P20 P21 ). With the exception of the E 0 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 E 0 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 E 0 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 ( P15 P16 ). 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 E 0 boundary.

Rb-Sr glauconite isochron of the Eocene Castle Hayne Limestone, North Carolina

The 11-m-thick lectostratotype of the Castle Hayne Limestone in New Hanover County, North Carolina, consists of lower phosphate pebble biomicrudite; middle bryozoan biosparrudite; and upper bryozoan-sponge biomicrudite. The relative age of the Castle Hayne Limestone is equivocal. The planktic foraminiferal fauna and part of the molluscan fauna suggest that the entire formation should be correlated with the Gulf Coast Claibornian Stage (middle Eocene), whereas calcareous nannofossils, bryozoans, barnacles, and some molluscs indicate that the upper bryozoan-sponge biomicrudite is a Gulf Coast Jacksonian Stage (upper Eocene) equivalent. Because of problems correlating the Castle Hayne Limestone to equivalent Gulf Coast stages, the lectostratotype was dated by application of the Rb-Sr glauconite isochron. Five hand-picked glauconite concentrates analyzed for Rb, Sr, and Sr-isotopic composition yielded an isochron age of 34.8 ± 1 m.y. (λ Rb 87 = 1.42 × 10−11 yr−1) with an initial (Sr87/Sr86) ratio of 0.7083 ± 0.0004. The determined initial (Sr87/Sr86) ratio is in good agreement with previous estimates of the Sr-isotopic composition of sea water during the Eocene. Although the age is younger than the value of 37 m.y. earlier proposed for the Eocene/Oligocene boundary, it agrees with fission-track and K-Ar ages of tektites and microtektites, and K-Ar ages of bentonites and glauconites in upper Eocene marine and nonmarine units throughout the world.