Terminal Eocene Event Research Articles

Nouveaux enjeux pour la réhabilitation respiratoire dans la bronchopathie chronique obstructive

The Eocene/Oligocene boundary in Europe is marked by major discontinuities in all environments: the “Grande Coupure” in continental mammals; the elimination of semitropical elements from high-latitude floras; the virtually complete replacement of the shallow-marine malacofauna; and an extraordinary downslope excursion of carbonate deposition in deep-ocean basins (drop in the CCD). These phenomena collectively represent the “Terminal Eocene Event” (TEE). In the Carpathian Mountains, the TEE is manifested in the thin but regionally persistent Globigerina Marl, a calcareous unit containing abundant cool-water microplankton that occurs within very thick, siliceous, bathyal flysch sequences. In southern Poland, the marl is of very latest Eocene age, within planktonic foraminifera zone P17, calcareous nannoplankton zone NP19/20, and the zone of the dinoflagellate Rhomdodinium perforatum. Zircons from bentonites bracketing the marl are dated by fission-track analysis; at Polany, two underlying bentonites are 41.7 and 39.8 Ma, and at Znamirowice two overlying bentonites are 34.6 and 28.9 Ma, in sequence. This accords with glauconite K/Ar ages in Western Europe by which the Eo/Oligocene boundary age is estimated at 37–38 Ma. Global correlations indicate that the TEE corresponds to a major glacio-eustatic regression with a duration of about 0.5 Ma, in which a large Antarctic ice cap was formed, the ocean circulation was permanently changed to the psychrospheric condition, and world climate shifted irreversibly towards the modern state.

Age and palaeoenvironmental constraints on the genesis of the Yandi channel iron deposits, Marillana Formation, Pilbara, northwestern Australia

Fossil pollen and spores preserved in organic‐rich claystones near the base of the palaeochannel hosting the Tertiary Yandi channel iron deposits (CID) provide an in situ constraint on the age of this world‐class orebody. This assemblage also aids understanding of the palaeoenvironment leading to the deposition and preservation of the host Marillana Formation. The provisional Early Oligocene age of claystones links the genesis of the Yandi CID to the profound disruption of global climates and oceanography at the Eocene‐Oligocene transition (Terminal Eocene Event) and provides circumstantial evidence that ore formation was linked to the development of a warm south‐flowing proto‐Leeuwin Current along the Pilbara coast. It is likely that rainfall increased but remained strongly seasonal (monsoonal?) as global climates warmed during the Late Oligocene — Early Miocene. The same fossil evidence indicates that wood fragments, the iron‐oxide‐replaced remains of which are a significant component of cemented goethitic gravel making up CID, came from Casuarinaceae‐ and Myrtaceae‐dominated sclerophyll communities lining the channel banks. Increasingly dry conditions since the late Early Miocene Climatic Optimum are likely to have contributed to the preservation of CID at Yandi.

Eocene-Oligocene extinction and paleoclimatic change near Eugene, Oregon

Thick ash-fl ow tuffs provide marker beds through fossiliferous Eocene and Oligocene marine and non-marine sedimentary rocks near Eugene, Oregon. New mapping, radiometric dating, and paleomagnetic stratigraphy of these tuffs and rocks now allow dating of local fossil fl oras. The Comstock, Goshen, Rujada, and Willamette fl oras have been widely used as evidence for Eocene-Oligocene climatic cooling and drying. Eocene leaves from Comstock and Hobart Butte included such thermophilic taxa as Liquidambar. The early Oligocene Goshen fl ora lacked Liquidambar but retained many thermophilic species with large leaves that have entire margins and acuminate apices (drip tips). In contrast, fossil leaves from later Oligocene Rujada and Willamette fl oras are small and serrate, and most lack drip tips. Marine faunas also indicate climatic cooling and local disappearance of thermophilic molluscs such as Anadara, Ficus, and Conus. Our dating and compilation of plant and molluscan fossil occurrences indicate a steady rise in species diversity from 46 Ma to maximal diversity of thermophilic taxa at 35‐34 Ma, then extinctions of 60% of plant species after 33.4 Ma and 32% of marine invertebrates after 33.2 Ma, both signifi cantly postdating the Eocene-Oligocene boundary at 33.7 Ma. Plant diversity rebounds during the early Oligocene, but marine invertebrates continue to decline into the Oligocene in part due to the retreat of fully marine environments from the Eugene area. Neither these data, nor evidence from coeval fossil plants and soils in central Oregon, support the notion of a “Terminal Eocene Event,” nor any other single, abrupt paleoclimatic shift or extinction. The Eocene-Oligocene biotic and climatic transition was drawn out over some 6 m.y. Abrupt forcings such as meteorite impacts or volcanic eruptions are less likely explanations for cooling and diversity decline than long-term processes such as mountain building, changing ocean currents, or reorganization of the carbon cycle by coevolution of grasses and grazers.

Sedimentology and hydrocarbon habitat of the submarine-fan deposits of the Central Carpathian Paleogene Basin (NE Slovakia)

The Central Carpathian Paleogene Basin accommodates a subsiding area of the destructive plate-margin. The basin history comprises marginal faulting and alluvial fan accumulation (E 2); transgressive onlap by shoreface sediments and carbonate platform deposits (E 2); glacio-eustatic regression induced by cooling (Terminal Eocene Event); forced regression, tectonic subsidence and growth-fault accumulation of basin-floor and slope fans (E 3); decelerating subsidence, aggradation and sea-level rising during the mud-rich deposition (O 1); high-magnitude drop in sea-level (Mid-Oligocene Event), retroarc backstep of depocenters and lowstand accumulation of sand-rich fans and suprafans (O 2–M 1); subduction-related shortening and basin inversion along the northern margins affected by backthrusting and transpressional deformation (O 2–M 1). The basin-fill sequence has poor (TOC≤0.5%) to fair (TOC<1.0%) quality of source rocks. Maturity of OM ranges from initial to relic stage of HC generation. Paleogene rock-extracts display a good correlation with scarce trapped oils. The presence of solid bitumens and HC-rich fluid inclusions indicates overpressure conditions during HC generation and migration. Potential HC reservoirs can be expected in porous lithologies (scarp breccias), in basement highs and traps related to backthrusting, fault-propagation folding and strike–slip tectonics.

Roadblocks on the Kill Curve: Testing the Raup Hypothesis

The documented presence of two large (-100-km diameter), possibly coeval impact craters of late Eocene age, requires modification of the impact-kill curve proposed by David M. Raup. Though the estimated meteorite size for each crater alone is large enough to have produced considerable global environmental stress, no horizons of mass mortality or pulsed extinction are known to be associated with either crater or their ejecta deposits. Thus, either there is no fixed relationship between extinction magnitude and crater diameter, or a meteorite that would produce a crater of >100-km diameter is required to raise extinction rates significantly above a -5% background level. Both impacts took place -1-2 m.y. before the Terminal Eocene Event(=early Oligocene pulsed extinction). Their collective long-term environmental effects, however, may have either delayed that extinction pulse or produced threshold conditions necessary for it to take place.

Early Palaeocene &amp;lt;i&amp;gt;Parvularugoglobigerina&amp;lt;/i&amp;gt; and late Eocene &amp;lt;i&amp;gt;Praetenuitella&amp;lt;/i&amp;gt;: does evolutionary convergence imply similar habitat?

Abstract. The species of the earliest Palaeocene planktonic foraminiferal genus Parvularugoglobigerina are characterized by a small test with a smooth, microperforate wall and an elongate aperture. Pore-mound structures may occur on some specimens, while the coiling mode varies from high- to low-trochospiral. Four morphotypes are distinct enough to be recognized as species: P. eugubina (Luterbacher &amp;amp; Premoli Silva) is low spiral and multichambered and P. perexigua n. sp. is four-chambered; P. fodina (Blow) has a Globigerina bulloides-type morphology and P. alticonusa n. sp. has a high trochospire. With the exception of the high spire, this general morphology is repeated in late Eocene forms classified as Praetenuitella: P. insolita (Jenkins), P. patefacta Li, and other associated forms.The two groups acquired their strong similarities – highly distinctive, peculiarly elongated aperture and microperforate walls – through evolutionary convergence, not by being directly related. Stratigraphically they each have a brief occurrence in a geologically significant slice of Palaeogene time: the one during the recovery of ecosystems in the earliest Palaeocene; the other immediately prior to the great cooling and in the time of rapid change known as the Terminal Eocene Event. This study shows that Praetenuitella flourished in eutrophic conditions and that their evolution might have been nutrient-driven. We suggest by morphological pattern analogy that forms of Praetenuitella and Parvulorugoglobigerina reflect similar habitat in their similar form and especially in their aperture.

Reconstruction of land and freshwater palaeoenvironments near the Eocene-Oligocene boundary, southern England

Mammalian assemblages in the Bembridge Limestone Formation of late Eocene age, Headon Hill, Isle of Wight, England, indicate habitats ranging from open woodland to closed forest. Distinctive 'lower' and 'upper' mammalian faunas reflect different fauna1 provinces, probably in response to climatic fluctuations that foreshadowed the terminal Eocene event. In order to improve our understanding of these patterns, we have examined a variety of other palaeoenvironmental indicators from this section. These include palynological organic matter (POM), plant macrofossils, non-mammalian faunas, organic geochemistry and stable isotopes. The evidence shows that the depositional setting was a tranquil, shallow, freshwater lake, with a brief lagoonal interval. However, evidence for habitats surrounding the lake is contradictory, emphasizing the necessity for multidisciplinary approaches to palaeoenvironmental reconstruction. The mammal faunas give unequivocal evidence for woodland or forest, yet, apart from some of the land snails, there is no other indication of the presence of trees. Furthermore, according to the mammalian evidence the lake was bordered by distinctive vegetation at different times, with closed forest/woodland during mar1 deposition and open woodland during black mud deposition, but there are no parallel fluctuations in other biotic elements.

Local Extinction Patterns and the Decline of the Jamaican Paleogene Echinoid Fauna

An analysis of the Jamaican Upper Oligocene echinoids, based on new collections made from the Brown's Town Formation, has identified 12 species, a diversity comparable with other Caribbean faunas of the same age and also with later Eocene faunas of Jamaica. While the main extinction of Caribbean echinoid taxa was apparently at (or before) the Terminal Eocene Event, Jamaica's fauna underwent a reduction in species diversity in the mid middle Eocene, coincident with the change in sedimentation from the impure Yellow Limestone Group to the pure White Limestone Supergroup. Although certain Yellow Limestone species persisted into the late Eocene, the Upper Oligocene fauna shows considerable taxonomic turn-

Late eocene—early oligocene integrated isotope stratigraphy and biostratigraphy for paleoshelf sequences in southern Australia: paleoceanographic implications

A late Eocene—early Oligocene planktonic foraminiferal oxygen-isotope stratigraphy derived for two overlapping sections (Browns Creek and Castle Cove) through paleoshelf sequences in southern Victoria, Australia, contains a pronounced late Eocene depletion (warm) peak (∼1.2%PDB) centred at about 41 Ma, followed by a two-stage enrichment (cooling) pattern, the later one coinciding with the well known Terminal Eocene Event (∼37 Ma), exhibiting ∼1.0%PDB) erinchment. The early Oligocene isotope stratigraphy shows fluctuations of about 1.0%PDB, with prominent depletion peak immediately following the terminal Eocene δ 18O enrichment. The start of the terminal Eocene δ 18O enrichment coincides with the LAD of the nannofossil indicator of the Eo-Oligocene boundary, Discoaster saipanensis (early NP21 Zone). On this basis the traditional southern Australia planktonic foraminiferal Eocene-Oligocene boudary markers (LAD Globigerapsis index, LAD Subbotina linaperta Subbotina linaperta) locally survived into Zone NP22, well into the early Oligocene. Sea-surface paleotemperature estimates derived from the δ 18O data assuming a δW value of −1.2%PDB, show that the late Eocene ingression of the tropical planktonic foraminiferal genus Hankenina coincided with peak surface-water tempertures of ∼24°C. The temperature decline in the southern Australia shelf waters associated with the Terminal Eocene Event may have been as much as 7°C, reaching a minimum value of ∼13°C. The later survival of G. index and S. linaperta coincides with a rapid recovery of water temperatures over the south Australian shelf following the Terminal Eocene Event. This is attributed to the local warming of waters in shallow broad embayments where circulation patterns were decoupled from the developing Circum-Antartic Current to the south.

Comment and Reply on "Late Eocene diatomite from the Peruvian coastal desert, coastal upwelling in the eastern Pacific, and Pacific circulation before the terminal Eocene event"

Comment and Reply on "Late Eocene diatomite from the Peruvian coastal desert, coastal upwelling in the eastern Pacific, and Pacific circulation before the terminal Eocene event"

Late Eocene diatomite from the Peruvian coastal desert, coastal upwelling in the eastern Pacific, and Pacific circulation before the terminal Eocene event

Previously undocumented late Eocene diatomaceous sediments are present near Fundo Desbarrancado (FD) in southern Peru. These sediments are similar to Miocene diatomite from the same area but, unlike the Miocene diatomite, the FD sediments contain cherty layers, are enriched in CaCO/sub 3/, have a diverse and abundant radiolarian fauna, and possess varved-massive and millimeter- and meter-scale biogenic-terrigenous alternations. The FD sediments are part of an Eocene sequence that includes the clastic sediments of the Paracas Formation, and they are correlative to the Chira Formation of northern Peru. The Paleogene biogenic sediments of western South America show that coastal upwelling developed in the eastern Pacific before the latest Eocene, argue for the existence of a proto-Humboldt current at this time, and suggest that the terminal Eocene event was the culmination of gradual changes and not a catastrophic event at the Eocene/Oligocene boundary.

Late Eocene perturbations: Foraminiferal biofacies and evolutionary overturn, southern Australia

Abundance patterns of planktonic and benthic foraminifera in profiles of neritic successions at high southern paleolatitudes show evidence that they represent systemic stratigraphic signals from the global ocean. In an interval correlated with upper Zone P15 and Zone P16, long‐distance correlations can be made on benthic Sphaeroidina and the aragonitic Robertinacea. Among the plankton, increased numbers of Globigerinatheka alternate with high abundances of Chiloguembelina and increased numbers of Pseudohastigerina, especially during an Hantkenina ingression. Those alternations indicate environmental fluctuations in the upper part of the water column, just as alternations in Cibicididae/Uvigerinidae ratios give similar signals from the benthic communities. The fluctuations are considered to be directly or indirectly linked to available oxygen. Several local neritic events can be correlated with oceanic events, and on the basis of those correlations the suggestion of a stratified ocean during Zone P16 is supported. Near the end of Zone P16 there is a major benthic species overturn and disappearance or weakening of signals of water column stratification and restricted bottom water circulation. I conclude that local events such as species overturn, biofacies spikes, and a brief regression (the Chinaman Gully regression at about the end of Zone P16) are of global significance as part of the stepwise configuration of the Terminal Eocene Event.

Neritic, southern extratropical foraminifera and the terminal eocene event

If the “Terminal Eocene Event” (TEE) records a major bolide impact or other extraterrestrial happening, then there ought to be disruption of benthonic foraminiferal communities especially in rather shallow neritic environments. We record the arrivals and departures of 180 species in a composite succession through the later Middle Eocene, Late Eocene and earliest Oligocene in southern Australia. The rate of new arrivals increases at each of several transgressions, each of which also marks a climatic amelioration. The sharpest increase in rate of departure is found at a regional regression within the latest Eocene. There is no evidence of major disruption of the fauna at the end of the Eocene. The TEE, on this data, was not extraterrestrial in origin and was hardly cataclysmic. The study suggests, instead, that the origins of late Eocene biotic change should be sought through earthly configurations of climate and sea level.

Neritic, southern extratropical Foraminifera and the terminal Eocene event: McGowran, Brian and Amanda Beecroft, 1986. Palaeogeogr. Palaeoclimatol. Palaeoecol., 55(1):23–34

Neritic, southern extratropical Foraminifera and the terminal Eocene event: McGowran, Brian and Amanda Beecroft, 1986. Palaeogeogr. Palaeoclimatol. Palaeoecol., 55(1):23–34

Mid-Oligocene Extinction Event in North American Land Mammals

Interest in extraterrestrial causes for the apparent 26-to 32-million-year periodicity of mass extinctions has focused on the terminal Eocene event and older events, although there is now evidence of a mid-Oligocene event near the early/late Oligocene boundary, or about 32.4 million years ago. An abrupt (200,000 years or less) mid-Oligocene extinction event appears in the record of North American land mammals, which results in the selective disappearance of archaic members of the fauna and later diversification of other taxa. The selective nature of the extinctions suggests climatic and ecological causes rather than an extraterrestrial catastrophe. Increased mid-Oligocene glaciation, worldwide cooling, a major regression event, and abrupt changes in the flora are probably the immediate causes, and these may have resulted from changes in global oceanic circulation.

North American mammalian diversity and Eocene–Oligocene extinctions

Diversity and faunal turnover of North American land mammals are calibrated against the magnetic polarity time scale for million-year intervals for the latest Eocene through late Oligocene. A major, gradual Late Eocene decline in diversity, caused mostly by an extended period of extinction of archaic forms, seems to be related to the worldwide crisis known as the “Terminal Eocene Event.” Along with other evidence of gradual changes in deep-sea microfossils, this evidence argues against a catastrophic explanation for late Eocene extinctions.Faunal stability characterized the rest of the Oligocene except for a wave of extinctions in the mid-Oligocene (Chadronian-Orellan boundary, about 32.4 ma). This mid-Oligocene event is sudden and severe, occurring in less than 200,000 yr, based on estimates from sedimentation rates calibrated from magnetic polarity interval boundaries. The mid-Oligocene event is found in many paleoclimatic records, but not in all of them. It may be related to the completion of the Circum-Antarctic Current and to increased mid-Oligocene glaciation.

The terminal eocene event and the polish connection

The Eocene/Oligocene boundary in Europe is marked by major discontinuities in all environments: the “Grande Coupure” in continental mammals; the elimination of semitropical elements from high-latitude floras; the virtually complete replacement of the shallow-marine malacofauna; and an extraordinary downslope excursion of carbonate deposition in deep-ocean basins (drop in the CCD). These phenomena collectively represent the “Terminal Eocene Event” (TEE). In the Carpathian Mountains, the TEE is manifested in the thin but regionally persistent Globigerina Marl, a calcareous unit containing abundant cool-water microplankton that occurs within very thick, siliceous, bathyal flysch sequences. In southern Poland, the marl is of very latest Eocene age, within planktonic foraminifera zone P17, calcareous nannoplankton zone NP19/20, and the zone of the dinoflagellate Rhomdodinium perforatum. Zircons from bentonites bracketing the marl are dated by fission-track analysis; at Polany, two underlying bentonites are 41.7 and 39.8 Ma, and at Znamirowice two overlying bentonites are 34.6 and 28.9 Ma, in sequence. This accords with glauconite K/Ar ages in Western Europe by which the Eo/Oligocene boundary age is estimated at 37–38 Ma. Global correlations indicate that the TEE corresponds to a major glacio-eustatic regression with a duration of about 0.5 Ma, in which a large Antarctic ice cap was formed, the ocean circulation was permanently changed to the psychrospheric condition, and world climate shifted irreversibly towards the modern state.

Floristic changes indicate a cooling climate in the Eocene of southern England

A major climatic cooling at the close of the Eocene (the ‘terminal Eocene event’) is suggested by studies of leaf floras in North America1,2; and by oxygen isotope studies, of mollusc shells from the North Sea3 and of planktonic and benthic foraminifera from the North and South Pacific4. Climatic fluctuations in the French Palaeogene5–8 inferred from palynological studies, are difficult to interpret in terms of this single event. The Pacific faunal studies4 and preliminary palynological evidence from the Isle of Wight, southern England9 indicates an onset of cooling earlier in the Eocene. We have therefore examined fossil floras (fruits, seeds, pollen and spores) from the Palaeogene deposits of the London and Hampshire Basins of southern England which form a continuous sequence from the early Eocene. We find no evidence for a sudden climatic change at the end of the Eocene (taken to be near the base of the Bembridge Marls in the Hampshire Basin10). Our evidence, in the form of two major periods of floristic change, suggests a more gradual cooling, commencing in the latest early Eocene.

Late Eocene rings around the Earth?

The suggestion of O'Keefe (1980) that the terminal Eocene event was caused by rings of tektite material encircling the earth is discussed. It is argued that the assumption that the tektites are of lunar volcanic origin is unwarranted and contrary to existing data, including the lack of lunar rocks of suitable composition, the lack of lunar rocks of the correct age, the lack of evidence that the North American tektites fell throughout a sedimentary rock column of a few million years, and the nondetection of a tektite with a measurable cosmic ray exposure age. Alternatively, it is suggested that the terminal Eocene event may be associated with volcanic ash, air-fall tuff and bentonite in the late Eocene. O'Keefe replies that the hypothesis of the terrestrial origin of the tektites conflicts with the laws of physics, for example in the glass structure and shaping of the tektites. Furthermore, evidence is cited for lunar rocks of the proper major-element composition and ages, and it is noted that the proposed solar Poynting-Robertson effect would account for the particle fall distributions and cosmic ray ages.

Earth's Saturnlike ring

A ring similar to those surrounding Saturn today may have existed around Earth 34 million years ago, according to John A. O'Keefe of NASA's Goddard Space Flight Center. He calculates that the ring, composed of tektites (glass meteorites), lasted one to several million years. The shadow of the rings on Earth's surface caused dramatic climatic changes in the temperate zones.The sudden climatic change 34 million years ago has been known to geologists for many years as the terminal Eocene event. This change is considered to be the most profound climatic event to have occurred during the entire Tertiary period, between 65 million and 2 million years ago.