Biostratigraphic utility of coiling direction in Miocene planktonic foraminiferal genus Paragloborotalia

Trochospiral planktonic foraminifera will coil either sinistral (left) or dextral (right). The prevalence of sinistral or dextral coiling can change through the stratigraphic range of morphospecies with a preference in coiling direction. A number of coiling shifts have been applied as secondary marker events through the Recent to late Miocene (~0–7 Ma) biochronology. However, no such events have been applied beyond this age despite a number of species being known to adopt preferential coiling directions. Here we investigate selected Miocene species within the genus Paragloborotalia. Previous work in the tropical to subtropical realm has shown that the mayeri–siakensis group undergoes a shift from random to sinistrally dominated coiling in the mid Miocene (~15 Ma). We extend the investigation to other Miocene paragloborotaliids in the low (IODP Sites U1337, U1338, ODP Sites 871 and 925), mid (JOIDES-3 hole) and high latitudes (ODP Site 747) in order to assess whether there is global synchronicity and if the change is unique to the mayeri-siakensis group. In addition, a number of outcrop samples from the Cipero and Lengua formations in southern Trinidad are quantitatively compared to previously published trends. Our results show that in the low-mid latitudes the coiling shift is at ~15.37 Ma within planktonic foraminiferal Zone M5 within both Paragloborotalia siakensis and Paragloborotalia continuosa. In the high latitudes the absence of paragloborotaliids through a portion of the mid Miocene interval prevents accurate dating of a shift from early forms showing random coiling to later paragloborotaliids adopting a sinistral preference. We also find two coiling changes in the genus Globorotalia at high latitude Site 747, from random to sinistral in the mid Miocene (15.14 Ma) and sinistral to dextral (10.02 Ma) in the late Miocene. We propose the recognition of a coiling change in Paragloborotalia as a secondary bioevent in the mid Miocene at 15.37 Ma, and a useful means for the recognition of the base of the Langhian. The coiling shift as a biostratigraphic marker is likely to be particularly useful in regions where the currently applied bioevents, namely the Praeorbulina–Orbulina lineage, is rare or poorly represented

The impact of orbitally forced upwelling on Oligocene planktic foraminifera δ13C and abundances

Abstrac

Revisiting carbonate chemistry controls on planktic foraminifera Mg / Ca:implications for sea surface temperature and hydrology shifts over the Paleocene-Eocene Thermal Maximum and Eocene-Oligocene transition

Much of our knowledge of past ocean temperatures comes from the foraminifera Mg / Ca palaeothermometer. Several nonthermal controls on foraminifera Mg incorporation have been identified, of which vital effects, salinity, and secular variation in seawater Mg / Ca are the most commonly considered. Ocean carbonate chemistry is also known to influence Mg / Ca, yet this is rarely examined as a source of uncertainty, either because (1) precise pH and [CO32−] reconstructions are sparse or (2) it is not clear from existing culture studies how a correction should be applied. We present new culture data of the relationship between carbonate chemistry and Mg / Ca for the surface-dwelling planktic species Globigerinoides ruber and compare our results to data compiled from existing studies. We find a coherent relationship between Mg / Ca and the carbonate system and argue that pH rather than [CO32−] is likely to be the dominant control. Applying these new calibrations to data sets for the Paleocene–Eocene Thermal Maximum (PETM) and Eocene–Oligocene transition (EOT) enables us to produce a more accurate picture of surface hydrology change for the former and a reassessment of the amount of subtropical precursor cooling for the latter. We show that pH-adjusted Mg / Ca and δ18O data sets for the PETM are within error of no salinity change and that the amount of precursor cooling over the EOT has been previously underestimated by  ∼ 2 °C based on Mg / Ca. Finally, we present new laser-ablation data of EOT-age Turborotalia ampliapertura from St. Stephens Quarry (Alabama), for which a solution inductively coupled plasma mass spectrometry (ICPMS) Mg / Ca record is available (Wade et al., 2012). We show that the two data sets are in excellent agreement, demonstrating that fossil solution and laser-ablation data may be directly comparable. Together with an advancing understanding of the effect of Mg / Casw, the coherent picture of the relationship between Mg / Ca and pH that we outline here represents a step towards producing accurate and quantitative palaeotemperatures using this proxy

Foraminiferal turnover at the Eocene-Oligocene boundary in Tanzania and Java

Abstrac

Globigerinoides rublobatus – a new species of Pleistocene planktonic foraminifera

We describe Globigerinoides rublobatus n. sp., a new morphospecies of fossil planktonic foraminifera, from the Pleistocene sediments (∼810 ka) of the Indian Ocean and Pacific Ocean. We use image analysis and morphometry of 860 specimens from International Ocean Discovery Program Site U1483 in the tropical Indian Ocean to document morphological variability in the new morphospecies and related taxa, and we also report it from Pacific Ocean Site U1486 for the first time. The new morphospecies combines characteristics typical of Globigerinoides conglobatus (Brady, 1879) and Globigerinoides ruber (d'Orbigny, 1839), with which it co-occurs, but is distinct from both. Morphometric data indicate that G. rublobatus n. sp. is closer to G. conglobatus, potentially signalling an evolutionary affinity. We find that Globigerinoides rublobatus n. sp. occurs as two variants, a pigmented (pink) form and a non-pigmented (white) form. The non-pigmented forms are on average ∼50 % larger than the pigmented forms. This is so far only the third instance of fossil planktonic foraminifera known to exhibit this pink pigmentation. We regard the pink and white forms as variants of a single morphospecies and suggest the pink form may represent a later evolutionary adaptation

Data report: High-resolution stable isotope stratigraphy of the late Middle Eocene at Site 1051, Blake Nose

The primary aim of the this investigation was to examine the stability of subtropical sea-surface temperatures and reconstruct the surfaceto- benthos thermal gradient. High-resolution stable isotopic analyses (δ18O and δ13C) were conducted on late middle Eocene planktonic and benthic foraminifers recovered from Hole 1051B, Blake Nose, western North Atlantic. The sequence comprises a siliceous nannofossil and foraminifer ooze, with well-preserved calcareous microfossils. Isotopic examination was conducted on the mixed-layer dweller Morozovella spinulosa and the benthic foraminifer Nuttalides truempyi at this subtropical site

Bridging the extant and fossil record of planktonic foraminifera: implications for the Globigerina lineage

We conducted a morphometric study and wall texture analysis on extant and fossil specimens of the planktonic foraminifera Globigerina falconensis plexus. Our global data reveal morphological inconsistencies between fossil and extant populations. Our results are significant as G. falconensis is widely used in palaeoceanographic studies in conjunction with its sister taxon G. bulloides. Morphologically these two species are similar, with the main difference being the distinctive apertural lip present in G. falconensis. We selected cores covering the entire stratigraphic range of G. falconensis, from the early Miocene to current day, spanning sites from high latitudes in the North Atlantic Ocean and the southern Indian Ocean to sites in equatorial regions. The morphology found in the modern ocean is not consistent with the Miocene holotype of Globigerina falconensis Blow described from lower Miocene sediments in Venezuela. A more lobate morphology evolved in the late Miocene, thus, a new name is required for this morphotype, coexisting in the modern oceans with G. falconensis s.s. We thus describe the new morphospecies, G. neofalconensis for the more lobate forms which evolved in the late Miocene and inhabit the modern oceans. Additionally, we report a pseudocancellate wall texture present in the G. falconensis plexus. We use the molecular sequences from the PR2 database to explore the generic attribution of the G. falconensis lineage, confirming its close relationship with G. bulloides and its retention in the genus Globigerina

Impact of the East African Rift System on the routing of the deep‐water drainage network offshore Tanzania, western Indian Ocean

Peer reviewedPostprin

Oligocene chronostratigraphy and planktonic foraminiferal biostratigraphy: historical review and current state-of-the art

We review past and recent advances in Oligocene chronostratigraphy (and its internal subdivisions) and geochronology, the so-called “missing” Oligocene debate of the 1960s, and planktonic foraminiferal biostratigraphies of (sub)tropical and austral biogeographies. The Oligocene spans the interval from Chron C13r.0.14 to Subchron C6Cn.2n(o), corresponding to astronomical cycles 84Ol-C13n to 58OlC6Cn. It is currently subdivided into two (Rupelian and Chattian) ages/stages. The planktonic foraminiferal biostratigraphy is characterized by a 7-fold (sub) tropical and 4-fold austral zonation, respectively