Pleistocene Calcareous Nannofossil Research Articles

High‐resolution Pliocene–Pleistocene calcareous nannofossil distribution and palaeoenvironmental changes in the northwest Nile Delta, Egypt

The Pliocene–Pleistocene sequences in the Nile Delta are of immense economic significance due to their hydrocarbon potential. Hence, a better understanding of the time-calibrated basinal palaeoenvironmental changes is essential to improve the hydrocarbon recovery. A total of 182 sub-surface samples from the Sapphire-DC well in the offshore north-western part of the Nile Delta were analysed to reveal changes in calcareous nannofossil assemblage composition and palaeoenvironments during the late Miocene–Pleistocene (5.44–0.43 Ma). Sixteen marker bioevents and nine biozones are identified for the first time. The absence of Ceratolithus acutus suggests a hiatus at the Messinian–Zanclean (Miocene–Pliocene) boundary. The studied interval is marked by the dominance of five species; Pseudoemiliania lacunosa (24%), small Gephyrocapsa sp. (20%), Helicosphaera kamptneri (11%), Reticulofenestra minutula (10%) and Calcidiscus leptoporus (6%). Based on their distribution patterns, six intervals (Intervals 0 to 5) are identified. Throughout the study interval, cooler waters (except during Interval 0; Messinian Salinity Crisis, MSC, 5.44–5.26 Ma) and eutrophic conditions persisted within a shallow hemipelagic and near-continental setting, marked by moderate-to-high terrigenous input (more for Intervals 4 and 5; ˜2.73–0.42). Additionally, low species diversity and high species dominance are identified, suggesting a stressed environment. Species diversity shows a gradually declining trend, up section, whereas species dominance correspondingly increases. Interval 0 (MSC) is dominated by warm water species of Sphenolithus abies and Helicosphaera kamptneri. The cool water species, Reticulofenestra pseudoumbilica, and small Gephyrocapsa dominate in Interval 1; small Gephyrocapsa dominates in Interval 2. Interval 3 is marked by the deepening of the basin with a brief introduction of warm, somewhat oligotrophic and open-ocean waters. In the middle of this interval (at 3.73 Ma; the Early–Late Pliocene boundary), an abrupt decrease in species diversity with a corresponding increase in species dominance suggests deteriorating conditions. Interval 3 also encompasses the mid–late Pliocene warming period, which in the Nile Delta is marked by cooler waters. Intervals 3–5 are dominated by P. lacunosa, suggesting a continuation of cool waters and eutrophic conditions. Hence, throughout the study interval, cooler waters (except during the MSC) and eutrophic conditions within in a shallow hemipelagic and near-continental setting are inferred with moderate-to-high terrigenous input and low species diversity and higher species dominance, suggestive of stressed environmental conditions.

Pleistocene Calcareous Nannofossil Biostratigraphy and Gephyrocapsid Occurrence in Site U1431D, IODP 349, South China Sea

We reinvestigated the Pleistocene calcareous nannofossil biostratigraphy of Site U1431D (International Ocean Discovery Program (IODP) Expedition 349) in the South China Sea (SCS). Twelve calcareous nannofossil Pleistocene datums are identified in the site. The analysis confirms that the last occurrence (LO) of Calcidiscus macintyrei is below the first occurrence (FO) of large Gephyrocapsa spp. (>5.5 μm). The FO of medium Gephyrocapsa spp. (4–5.5 μm) is also identified in the samples through morphometric measurements, which was unreported in shipboard results. Magnetobiochronologic calibrations of the numerical ages of LO of Pseudoemiliania lacunosa and FO of Emiliania huxleyi are underestimated and need reassessment. Other potential markers such as a morphological turnover of circular to elliptical variants of Pseudoemiliania lacunosa and a small Gephyrocapsa acme almost synchronous with the FO of Emiliania huxleyi may offer biostratigraphic significance in the SCS. The morphologic changes in Gephyrocapsa coccoliths are also examined for the first time in Site U1431D. Placolith length and bridge angle changes are comparable with other ocean basins, suggesting that morphologic changes are most likely evolutionary novelties rather than being caused by local climate anomalies.

Spearlithus, a new Pleistocene calcareous nannofossil genus from shallow marine settings of the Dominican Republic

Routine examination of calcareous nannofossil of Pleistocene sediments from the uplifted fringing reef margin of the southern Dominican Republic revealed a new group of incertae sedis. This article describes a new genus and twelve new species. The new taxa allow for enhanced straigraphic subdivisions: They are Spearlithus dekaenelii, Spearlithus lusitanicus, Spearlithus acutus, Spearlithus longus, Spearlithus hartiii, Spearlithus mcneillii, Spearlithus pospichalii, Spearlithus campbellii, Spearlithus klausii, Spearlithus cachaoi, Spearlithus covingtonii, and Spearlithus quasiovatus. Arange chart showing the stratigraphic distribution of these taxa is presented.

Plankton biochronology for the last 772,000 years from the western South Atlantic Ocean

Abstract Calcareous microfossils have potential in the biostratigraphy of Pleistocene sediments and a clear relationship with paleoceanographic studies. Conversely, there are few quantitative biostratigraphic studies of chronologically-tuned events or sections in the western South Atlantic. In order to improve the stratigraphical framework for South Atlantic paleoceanographic studies, the present work attempts to review the last 772,000 years by carrying out a quantitative analysis of the calcareous nannofossil and planktonic foraminiferal assemblages by comparing them with a high resolution marine isotopic record (δ 18 O). This work is based on the analysis of two piston cores obtained from the continental slope of the Santos Basin in the Santos Drift, southeastern Brazilian Continental Margin. Twelve Pleistocene calcareous nannofossil events and twenty planktonic foraminifera events calibrated with oxygen isotopes and correlated with literature stratigraphies are discussed. This is the first calcareous plankton biochronology study for the last 772 kyr in the western South Atlantic Ocean. More studies in this region will help to establish a more precise biochronology for these calcareous microfossils. This study also presents six new biostratigraphic events of isotopically-caibrated planktonic foraminifera which can be used as markers in the western South Atlantic.

Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes

Calcareous nannofossils are widely used in Cenozoic marine biostratigraphy. At present, the two most widely used calcareous nannofossil biozonations were established approximately 40 years ago. These were derived from marine land sections and Deep Sea Drilling Project rotary cored sediments. Over nearly three decades, we have generated Miocene through Pleistocene calcareous nannofossil data from deep sea sediments in low and middle latitude regions. The sediments used here have been mostly recovered using the advanced piston coring technique, generating less core disturbance and complete recovery via multiple penetration of the sediment column at single sites. A consistent trait in our work on calcareous nannofossil biostratigraphy has been to use semi-quantiative methods in combination with short sample distances, close enough to capture the details of the abundance behaviour of individual calcareous nannofossil taxa. Such data represent the foundation of the new biozonation presented here, which still partly relies on the pioneering work presented by Er lend Martini and David Bukry about 40 years ago. A key aim here has been to employ a limited set of selected biohorizons for the purpose of establishing a relatively coarsely resolved and stable biozonation. We present 31 biozones using a new code system: CNM1-CNM20; Calcareous Nannofossil Miocene biozones 1 through 20. CNPL1-CNPL11; Calcareous Nannofossil Plio-Pleistocene biozones 1 through 11. As the new biozonation encompasses 23 million years, the average biozone resolution becomes 0.74 million years, ranging from 0.15 to 2.20 million years. A single biohorizon is used for the definition of each biozone boundary. Auxiliary markers are avoided, as well as subzones, in order to maintain stability to the new biozonation. Virtually every biozone holds one or several additional biohorizons. These, together with all biozone boundary markers, are assigned age estimates derived chiefly from astronomically tuned cyclostratigraphies.

Gephyrocapsa occurrence during the Middle Pleistocene transition in the Northern Pacific Ocean (Shatsky Rise)

The gephyrocapsids, main component of the Pleistocene calcareous nannofossil assemblages, are here discussed as biostratigraphical and paleoclimate tools. The occurrence of the genus Gephyrocapsa is quantitatively analysed in the core ODP 198-1209B, collected in the NW Pacific Ocean. The studied stratigraphic succession covers a time interval including the Middle Pleistocene Transition (MPT), a highly investigated period characterized by important global climate changes. During the Pleistocene, Gephyrocapsa is extremely abundant and provides several bioevents used in biostratigraphy. In addition to the known standard events, we observe the occurrence of particular Gephyrocapsa morphogroups and significant changes in the relative abundance of G. caribbeanica. In the Early-Middle Pleistocene we identify four intervals based on the Gephyrocapsa content. Moreover, during the MPT, the stratigraphic distribution of Gephyrocapsa underlines a dominance of both the small morphogroup and the medium-sized G. caribbeanica that could be dependent on their paleoecology. Small Gephyrocapsa and G. caribbeanica seem to be more competitive than other coccolithophores during the global oceanographic variations and the re-organisation of the glacial-interglacial periodicity during the MPT.

Calcareous nannofossil evidence for Marine Isotope Stage 31 (1 Ma) in Core AND-1B, ANDRILL McMurdo Ice Shelf Project (Antarctica)

ANDRILL Core AND-1B, recovered in the Western Ross Sea of Antarctica, has been examined in search of calcareous nannofossils. Exhaustive and detailed analyses of the interval from 86.61 to 98.99mbsf revealed for the first time at an extreme southern high latitude (77.88° S) the presence of lower Pleistocene calcareous nannofossils, together with Tertiary and Upper Cretaceous reworked species. Other calcareous microfossils in the assemblage include, spicules of calciosponges and small foraminifers.The short normal magnetozone between 84.97 and 91.13mbsf is correlated with the Jaramillo Subchron (C1r.1n) (Wilson et al., 2007). The presence of nannofossils in the biogenic interglacial sediments is consistent with an episode of warm surface waters and open-marine conditions during the Jaramillo subchron, at ~1Ma, which corresponds with Marine Isotope Stage (MIS)-31 (Scherer et al., 2007; Naish et al., 2007). Climate proxies such as oxygen isotope stratigraphy and calcareous nannofossils at ODP Site 1165 (Pospichal, 2003; Villa et al., 2008) and the diatom assemblage in a shelly carbonate sequence at Cape Roberts 1 (Bohaty et al., 1998) also support a warming event during this time and suggest it extended around the Antarctic Continent. This in turn implies a total or partial collapse of the McMurdo Ice Shelf and a concurrent shift or temporary dissipation of the Polar Front (Antarctic Convergence) and Antarctic Divergence that currently serve as barriers to the influx of calcareous nannofossils to the margins of Antarctica.

Pleistocene calcareous nannofossil stratigraphy for ODP Leg 177 (Atlantic sector of the Southern Ocean)

Seven Ocean Drilling Program (ODP) sites recovered during ODP Leg 177 in the Atlantic sector of the Southern Ocean were analyzed to study the Pleistocene calcareous nannofossil record. Calcareous nannofossil events previously described from intermediate and low latitudes were identified and calibrated with available geomagnetic and stable isotope stratigraphic data. In general, Pleistocene southern high latitude calcareous nannofossil events show synchronicity with those observed from warm and temperate latitudes. The first occurrence (FO) of Emiliania huxleyi and the last occurrence (LO) of Pseudoemiliania lacunosa are observed in marine isotope stages (MIS) 8 and 12, respectively. A reversal in abundance between Gephyrocapsa muellerae and E. huxleyi is observed at MIS 5. MIS 6 is characterized by an increase in G. muellerae and MIS 7 features a dramatic decrease in the proportion of Gephyrocapsa caribbeanica. This latter species began to increase its proportions from MIS 14 to 13. The LO of Reticulofenestra asanoi is observed within subchron C1r.1r and the FO of R. asanoi occurs at the top of C1r.2r. A re-entry of medium-sized Gephyrocapsa can be identified in some cores during subchron C1r.1n. The LO of large morphotypes of Gephyrocapsa is well correlated through the studied area, and occurs during the middle-low part of subchron C1r.2r, synchronous with other oceanic regions. The FO of Calcidiscus macintyrei and FO of medium-sized Gephyrocapsa occur in the studied area close to 1.6 Ma.

Southern Ocean Pleistocene calcareous nannofossil events: calibration with isotope and geomagnetic stratigraphies

Several cores recovered from the northern belt of the Southern Ocean were analysed to study the Pleistocene calcareous nannofossil records. Calcareous nannofossil events previously described in medium and low latitudes were identified and calibrated with the oxygen isotope and geomagnetic time scales. Although sedimentation rates, hiatuses and degree of calcareous nannofossil preservation sometimes prevent the identification and/or accurate calibration of some of these events, a useful stratigraphic framework was obtained. The possibility of using these calibrated events from high to low latitudes facilitates correlations and should facilitate isotope event identification in a region with low temperature, where calcareous plankton stratigraphies are in general restricted. In general, Pleistocene southern high latitude calcareous nannofossil events show synchronism with those observed in warm and temperate surficial waters. Small discrepancies in the assigned ages are sometimes related to low sampling resolution due to low sedimentation rates. The first occurrence (FO) of Emiliania huxleyi and the last occurrence (LO) of Pseudoemiliania lacunosa are observed in Marine Isotope Stages (MIS) 8 and 12, respectively. A reversal in abundance between Gephyrocapsa muellerae and E. huxleyi is observed close to the MIS 4/5 boundary. MIS 6 is characterised by an increase in G. muellerae and MIS 7 features a dramatic decrease in the proportion of Gephyrocapsa caribbeanica. This latter species began to increase its proportions from the MIS 13/14 boundary to MIS13, showing diachronism between the different sites. The LO of Reticulofenestra asanoi is observed at MIS 22, confirming this event as a global synchronous reference datum. By contrast, the FO of R. asanoi occurs at MIS 35 and is diachronous with the existing data from other oceanic regions. A re-entry of medium sized Gephyrocapsa (3–5 μm maximum diameters) can be identified in some cores close to MIS 25; although the low abundance of this taxon prevents an accurate calibration, it may be concluded that this event is diachronous as compared with the existing low-latitude data. The LO of large morphotypes of Gephyrocapsa is well correlated with MIS 37, showing synchronism with other oceanic regions, whereas the FO of this species is not well calibrated due to the absence of age-control points.

Calibration of Upper Pliocene‐Lower Pleistocene Nannofossil Events with Oxygen Isotope Stratigraphy

Twelve upper Pliocene‐lower Pleistocene calcareous nannofossil events are calibrated with oxygen isotope stratigraphy at eight DSDP/ODP sites ranging from 53°N to 41°S latitudes in different oceans in order to determine their ages and to reveal their synchrony or diachrony within a significantly higher‐resolution time scale than the geomagnetic polarity time scale allows. Six nannofossil events appear to be synchronous from low to middle latitudes (the last occurrences of Reticulofenestra asanoi (oxygen isotope stage 22), Gephyrocapsa spp. A‐B (stage 37), Discoaster brouweri (stage 71), Discoaster surculus (stage 99), Discoaster tamalis (stage 111), and the first occurrence of Gephyrocapsa spp. A‐B (stage 59)), five appear to be diachronous (the first occurrences of Gephyrocapsa spp. C‐D, Reticulofenestra asanoi, and Gephyrocapsa spp. A‐B larger than 5.5 µm, and the last occurrences of Helicosphaera sellii and Discoaster pentaradiatus), and one is synchronous at low latitudes (the last occurrence of Calcidiscus macintyrei).

Quantitative biochronology of Pliocene and early Pleistocene calcareous nannofossils from the Atlantic, Indian and Pacific oceans

Semi-quantitative methods have been used to refine the precision with which Pliocene and early Pleistocene nannofossil datums may be applied for biostratigraphic purposes. Using these methods, the datums may be applied with a precision of between 0.01 m.y. (e.g. Calcidiscus macintyrei and Discoaster brouweri) and 0.2 m.y. (e.g. Discoaster asymmetricus). The age of each datum is estimated by interpolation between magnetic reversals, so that the uncertainty in each age estimate is a function of proximity to the nearest reversal as well as of uncertainties in the reversal chronology but is probably better than 0.1 m.y. for all the datums studied here. The following ages are estimated for biostratigraphically useful datums: LAD Helicosphaera sellii, 1.37 Ma (diachronous; earlier outside the equatorial zone); LAD Calcidiscus macintyrei, 1.45 Ma; LAD Discoaster brouweri, 1.88 Ma; LAD Discoaster asymmetricus, 2.2 Ma; LAD DisDiscoaster pentaradiatus, 2.35 Ma; LAD Discoaster surculus, 2.41 Ma; LAD Discoaster tamalis, 2.65 Ma; LAD Discoaster variabilis, 2.90 Ma; LAD Sphenolithus spp., 3.45 Ma; LAD Reticulofenestra pseudoumbilica, 3.56 Ma; LAD Amaurolithus delicatus, 3.66 Ma; FAD Ceratolithus rugosus, 4.62 Ma. The final 0.15 m.y. of the range of Discoaster brouweri is characterised by a high (about 20%) proportion of the triradiate form, which is a useful pointer for the extinction of this species even in the presence of considerable reworking.

Late Pleistocene calcareous nannofossils in the caribbean and their interoceanic correlation

Pleistocene climatic fluctuations as determined by means of oxygen isotope ratios from the pelagic sedimentary record of the Caribbean can be recognized also by changes included in the calcareous nannoplankton. Of 23 species tabulated from the Pleistocene fossil record two species, Ceratolithus cristatus and Umbellosphaera tenuis, are more abundant during temperature maxima. Seven species, Coccolithus pelagicus, Disoaster perplexus, Discolithina japonica, Discosphaera tubifera, Gephyrocapsa caribbeanica, Oolithotus antillarum and Umbellosphaera irregularis, occur more abundantly during temperature minima in the Caribbean. Pseudoemiliania lacunosa, a species which becomes extinct during Pleistocene, is more abundant at times of temperature maxima during the last two temperature cycles of its existence, but prior to that appears to have been more common during temperature minima in tropical latitudes. Gephyrocapsa oceanica is the most abundant species in the Pleistocene record. It is represented by two distinct morphotypes, one more common during temperature minima and the other more common during temperature maxima. The interval examined in detail represents less than one-half million years, but contains two distinct biostratigraphic data; the Pseudoemiliania lacunosa extinction and the earliest occurrence of Emiliania huxleyi.