The Extinction of Chiloguembelina cubensis in the Pacific Ocean: Implications for Defining the Base of the Chattian (upper Oligocene)

We conducted quantitative biostratigraphic and morphometric studies at two ocean drilling sites in the Pacific Ocean to investigate the extinction of the planktonic foraminifera genus Chiloguembelina, a distinctive biserial genus ranging in the Eocene and Oligocene. The extinction of the last species of the genus, C. cubensis, has historically been used as a correlation event for the base of the Chattian (upper Oligocene; ∼ 28 Ma). However, the bioevent has been controversial, as some authors have found a well-defined bio - horizon, while others have found a decline in abundance with a continuation of C. cubensis into the upper Oligocene. This has been reflected in the preference of using the Top Common occurrence (>5% of the foraminiferal assemblage) of the species as a correlation event for the boundary. We assessed the utility of C. cubensis as a reliable biohorizon at Ocean Drilling Program Leg 202 Site 1237 (south-east Pacific Ocean) and Integrated Ocean Drilling Program Expedition 320/321 Site U1334 (eastern equatorial Pacific Ocean). At both sites C. cubensis is a common and consistent component of early Oligocene planktonic foraminiferal assemblages. An abrupt termination of C. cubensis occurs at Site 1237 in magnetic polarity Subchron C10n.1n (27.89 Ma), while at Site U1334 peak abundances of C. cubensis are recorded in the upper Oligocene within Chron 9n with a younger datum for the extinction at ∼ 27.15 Ma. Therefore, the biostratigraphic utility of the species as a boundary marker for the base of the Chattian remains unclear. We propose that the phrase “C. cubensis crisis” is the most suitable for describing the extinction or decline in abundance of the species in the mid Oligocene, based upon the findings from these two sites and other age calibrated sites. Morphometric analysis of specimen size at the two sites shows a markedly smaller test size at Site 1237 compared with Site U1334, with specimens from the former being on average 1.37 × shorter and 1.45 × thinner. Differences in test size and extinction horizon are possibly controlled by ecological preferences, however, our biochronological compilation of ocean drilling sites does not reveal a latitudinal trend in extinction level

Giantism in Oligocene planktonic foraminifera Paragloborotalia opima: Morphometric constraints from the equatorial Pacific Ocean

The extinction of Oligocene planktonic foraminifera Paragloborotalia opima is an important biostratigraphic marker for the upper Oligocene (base Zone O6 [P22]), however the taxonomy of the morphospecies is unclear and therefore its biostratigraphic use is compromised. We conducted morphometric and scanning electron microscope analyses on the Paragloborotalia opima-nana plexus and investigated whether the two morphospecies P. opima (Bolli) and P. nana (Bolli) could be quantitatively separated or formed a continuous morphocline. These two morphospecies have previously been classified by their diameter, with P. opima defined as the larger morphospecies (0.39–0.55 mm) and P. nana confined to 0.32 mm. The problem with this classification is that many specimens fall between 0.32 and 0.39 mm. We measured the maximum size of 1215 specimens of Paragloborotalia from equatorial Pacific Ocean Integrated Ocean Drilling Program Site U1334, corresponding to planktonic foraminiferal Biozones O6–O2 and Chrons C8r to C11r (26.3 to 30.8 Ma). We found that the number of chambers and shape outline could not be used to determine these two morphotypes of Paragloborotalia, but size is a suitable delimiting character. We therefore reassess the taxonomy of the opima-nana plexus. Our data confirm that the 'transition' forms are consistent with P. opima and that the 0.32 mm criterion is valid for the identification of P. nana. Through the studied interval the maximum size of P. opima increases from 0.44 mm to 0.68 mm, with the largest specimens in the upper Oligocene in the lower part of Chron C9n. We propose that the progressive giantism of P. opima through the mid-late Oligocene in the equatorial Pacific Ocean is in response to high productivity

Ocean drilling archives and their importance to planktonic foraminiferal taxonomy, biostratigraphy and evolution

The International Ocean Discovery Program (IODP) and its predecessors have made a major contribution to the understanding of planktonic foraminifera evolutionary history through the recovery of expanded sedimentary successions, rich in microfossils. Ocean drilling cores allows the examination of how planktonic foraminifera responded through time, document their stratigraphic range and their reaction to climatic perturbations

Muted calcareous nannoplankton response at the Middle/Late Eocene Turnover event in the western North Atlantic

Key extinctions in two major planktonic foraminiferal groups and high taxic turnover in radiolarians have led to the identification of the Middle/Late Eocene Turnover (MLET) and point towards significant palaeoclimatic and/or palaeoceanographic changes at around 38 million years ago. Here we present quantitative calcareous nannofossil data from Ocean Drilling Program Site 1052 (Blake Nose, western North Atlantic) in order to investigate the response of phytoplankton during the MLET. Our data show only minor shifts in taxon abundance, with no strong trends identified through the interval and no nannofossil origination or extinction events associated with the MLET. The assemblages are characterised by the dominance of neritic braarudosphaerids and eurytopic reticulofenestrids. The increased abundance of warm to temperate and mesotrophic nannofossils (Reticulofenestra reticulata, Reticulofenestra bisecta and Coccolithus pelagicus) in and around the MLET occur against a backdrop of cooling, as indicated by oxygen isotopes, suggesting that changing nutrient conditions was the principle driver of these shifts in the nannoplankton assemblage. This is further supported by an increase in radiolarian accumulation rates at this time. The lack of response in the calcareous nannoplankton relative to the zooplanktonic planktonic foraminifera and radiolaria demonstrates the contrasting sensitivity to environmental change in these different plankton groups, with radiolarians showing the highest degree of change at the MLET and the nannoplankton showing little or none

Planktic foraminiferal response to early Eocene carbon cycle perturbations in the southeast Atlantic Ocean (ODP Site 1263)

At low latitude locations in the northern hemisphere, striking changes in the relative abundances and diversity of the two dominant planktic foraminifera genera, Morozovella and Acarinina, are known to have occurred close to the Early Eocene Climatic Optimum (EECO; ~ 49–53 Ma). Lower Eocene carbonate-rich sediments at Ocean Drilling Program (ODP) Site 1263 were deposited on a bathymetric high (Walvis Ridge) at ~ 40° S, and afford an opportunity to examine such planktic foraminiferal assemblage changes in a temperate southern hemisphere setting. We present here quantified counts of early Eocene planktic foraminiferal assemblages from Hole 1263B, along with bulk sediment stable isotope analyses and proxy measurements for carbonate dissolution. The bulk sediment δ13C record at Site 1263 resembles similar records generated elsewhere, such that known and inferred hyperthermal events can be readily identified. Although some carbonate dissolution has occurred, the well-preserved planktic foraminiferal assemblages mostly represent primary changes in environmental conditions. Our results document the permanent decrease in Morozovella abundance and increase in Acarinina abundance at the beginning of the EECO, although this switch occurred ~ 165 kyr after that at low-latitude northern hemisphere locations. This suggests that unfavourable environmental conditions for morozovellids at the start of the EECO, such as sustained passage of a temperature threshold or other changes in surface waters, occurred at lower latitudes first. The remarkable turnover from Morozovella to Acarinina was widely geographically widespread, although the causal mechanism remains elusive. In addition, at Site 1263, we document the virtual disappearance within the EECO of the biserial chiloguembelinids, commonly considered as inhabiting intermediate water depths, and a reduction in abundance of the thermocline-dwelling subbotinids. We interpret these changes as signals of subsurface water properties, perhaps warming, and the associated contraction of ecological niches

Taxonomy, Biostratigraphy and Phylogeny of Eocene Acarinina

The taxonomy, phylogeny and biostratigraphic ranges of 28 Eocene species of Acarinina are discussed together with detailed synonymies. The early Eocene is characterized by the radiation of two different groups - one characterized by rounded/inflated chambers and the other by anguloconical chambers - which are derived, in turn, from two late Paleocene lineages: the soldadoensis lineage (itself derived from Acarinina mckannai) and the esnaensis-wilcoxensis lineage (itself derived from Acarinina nitida). We interpret the genus Truncorotaloides as a synonym of Acarinina. Acarinina is regarded as paraphyletic, in that it gave rise to Morozovelloides Pearson and Berggren n. gen. in the upper part of the lower Eocene (see Pearson and Berggren Chapter 10, this volume). The following species are recognized in this chapter: Acarinina africana (El Naggar), Acarinina alticonica Fleisher, Acarinina angulosa (Bolli), Acarinina aspensis (Colom), Acarinina boudreauxi Fleisher, Acarinina bullbrooki (Bolli), Acarinina coalingensis (Cushman and Hanna), Acarinina collactea (Finlay), Acarinina cuneicamerata (Blow), Acarinina echinata (Bolli), Acarinina esnaensis (LeRoy), Acarinina esnehensis (Nakkady), Acarinina interposita Subbotina, Acarinina mcgowrani Wade and Pearson n. sp., Acarinina medizzai (Toumarkine and Bolli), Acarinina pentacamerata (Subbotina), Acarinina praetopilensis (Blow), Acarinina primitiva (Finlay), Acarinina pseudosubsphaerica Pearson and Berggren n. sp., Acarinina pseudotopilensis Subbotina, Acarinina punctocarinata Fleisher, Acarinina quetra (Bolli), Acarinina rohri (Brönnimann and Bermúdez), Acarinina sibaiyaensis (El Naggar), Acarinina soldadoensis (Brönnimann), Acarinina subsphaerica (Subbotina), Acarinina topilensis (Cushman), and Acarinina wilcoxensis (Cushman and Ponton)

Dextral to sinistral coiling switch in planktic foraminifer Morozovella during the Early Eocene Climatic Optimum

Coiling direction is a basic characteristic of trochospiral planktic foraminifera. Modifications in the coiling direction within ancient planktic foraminiferal populations may reflect important changes in evolution or environment, yet they remain scarcely discussed. Here we investigate fluctuations in the coiling direction within Morozovella assemblages from sections that span the interval of peak Cenozoic warmth, the Early Eocene Climatic Optimum (EECO; ~53-49 million years ago, Ma), at Atlantic Ocean Drilling Program (ODP) sites 1051, 1258 and 1263. The surface-dwelling genus Morozovella is of particular interest because it dominated tropical-subtropical early Paleogene assemblages then suffered an abrupt and permanent decline in abundance and taxonomic diversity at the start of the EECO. At all ODP sites, morozovellids display a dominant dextral coiling preference during the interval preceding the EECO. However, all the Morozovella species at all sites modify their coiling from preferentially dextral to sinistral coiling within the EECO < 200 kyr after the K/X event (~52.8 Ma), providing a new biostratigraphic tool for correlation. We also document that before the major shift in morozovellid coiling, transient excursions to higher abundances of sinistral tests occurred in conjunction with negative carbon isotope excursions. Significantly, carbon isotope data reveal that sinistral morphotypes belonging to the same morphospecies typically have lower 13C values. The dominance of sinistral morphotypes, at the expense of dextral forms within the EECO, coupled with the lower 13C signatures of the former, suggests that the sinistral forms were less dependent on their photosymbiotic partnerships and thus able to adapt more readily to paleoceanographic change at the EECO. The observed sinistral and dextral coiling of morozovellids can be a genetically heritable characteristic that lies within cryptic speciation across multiple morphologically defined species. Alternatively the coiling changes were exclusively ecophenotypic responses whereby different species were able to preferentially adopt sinistral coiling in reaction to the changed conditions in the mixed-layer during the EECO. Previous interpretations of coiling flips in planktic foraminifera in the early Eocene, especially including morozovellids, have favoured a genetic explanation rather than an ecological response. Our present data cannot validate or disprove this idea, but should stimulate renewed thought on the matter

Problematica

The taxonomy of Oligocene planktonic foraminifera of uncertain affinity are discussed and reviewed in this chapter. The following taxa are considered Problematica: Acarinina inaequiconica Subbotina, Globigerina brevis Jenkins, Globigerina? grata Todd, Globigerina khadumica Bykova, Globigerina postcretacea Myatliuk, Globigerina pseudoedita Subbotina, Globigerina spirata Bornemann, Globigerina stainforthi Hofker, Globigerinella evoluta Subbotina, Globigerinella liverovskae Bykova, Globigerinella praemicra Subbotina, Globigerinella subangulata Ivanova, Globigerinoides inusitatus Jenkins, Globorotalia denseconnexa Subbotina, Globorotalia hexacamerata Subbotina, Globorotalia tetracamerata Subbotina, Guembelina plana Ivanova, Guembelina pseudostriata Ivanova, Subbotina droogeri Myatliuk, Subbotina vialovi Myatliuk, Turborotalia bannerblowi Blaicher, and Turborotalia czeczvaensis Myatliuk. Our understanding of each of these taxa, along with many new SEMs of the holotypes, are presented

Taxonomy, biostratigraphy, and phylogeny of Oligocene Acarinina

The taxonomy, phylogeny and biostratigraphic ranges of three Oligocene species of Acarinina are discussed together with their synonymies. Acarinina diversified in the Paleocene and Eocene and only a few species remain in the Oligocene. The following taxa are recognized as valid species: Acarinina collactea (Finlay), Acarinina echinata (Bolli), and Acarinina medizzai (Toumarkine and Bolli)

Evolution of deep-sea sediments across the Paleocene-Eocene and Eocene-Oligocene boundaries

The composition and distribution of deep-sea sediments is the result of a multitude of climatic, biotic and oceanic conditions relating to biogeochemical cycles and environmental change. Here we utilize the extensive sediment archives of the International Ocean Discovery Program (IODP) and its predecessors to construct maps of deep-sea sediment type across two critical but contrasting boundaries in the Paleogene, one characterised by an interval of extreme warmth (Paleocene/Eocene) and the other by global cooling (Eocene/Oligocene). Ocean sediment distribution shows significant divergence both between the latest Paleocene and Paleocene Eocene Thermal Maximum (PETM), across the Eocene-Oligocene Transition (EOT), and in comparison to modern sediment distributions. Carbonate sedimentation in the latest Paleocene extends to high southern latitudes. Disappearance of carbonate sediments at the PETM is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon-cycle perturbation. Biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early Paleogene ocean. In the Southern Ocean, we attribute the low in biosiliceous burial, to the warm deep water temperatures which would have impacted biogenic silica preservation. In the late Eocene, our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial Pacific. Enhanced biosiliceous deposits in the late Eocene equatorial Pacific and South Atlantic are due to increased productivity and the spin-up of the oceans. Our compilation documents the enhanced global carbonate sedimentation in the early Oligocene, confirming that the drop in the carbonate compensation depth was global