Abstract. The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse world to an icehouse climate, involving the first major glaciation of Antarctica and global cooling occurring ∼34 million years ago (Ma) and lasting ∼790 kyr. The change is marked by a global shift in deep-sea δ18O representing a combination of deep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxies for ocean temperature indicate sea surface cooling, and major changes in global fauna and flora record a shift toward more cold-climate-adapted species. The two principal suggested explanations of this transition are a decline in atmospheric CO2 and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. Here we review and synthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of climate model simulations of temperature change across the EOT. The simulations compare three forcing mechanisms across the EOT: CO2 decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstrate the need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographic changes. We find that CO2 forcing involving a large decrease in CO2 of ca. 40 % (∼325 ppm drop) provides the best fit to the available proxy evidence, with ice sheet and palaeogeographic changes playing a secondary role. While this large decrease is consistent with some CO2 proxy records (the extreme endmember of decrease), the positive feedback mechanisms on ice growth are so strong that a modest CO2 decrease beyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheet growth. Thus, the amplitude of CO2 decrease signalled by our data–model comparison should be considered an upper estimate and perhaps artificially large, not least because the current generation of climate models do not include dynamic ice sheets and in some cases may be under-sensitive to CO2 forcing. The model ensemble also cannot exclude the possibility that palaeogeographic changes could have triggered a reduction in CO2.

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A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO 2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO 2 , we show that pCO 2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO 2 in parts of the Oligocene was similar to latest Eocene values. These results suggest that a decrease in pCO 2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene-Oligocene transition and that when a certain threshold of pCO 2 change was crossed, the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.Published by Copernicus Publications on behalf of the European Geosciences Union.

Yunnan, in southwestern China, straddles two of the world's most important biodiversity hot spots (i.e., a biogeographic region that is both a reservoir of biodiversity and threatened with destruction) and hosts more than 200 fossiliferous sedimentary basins documenting the evolutionary history of that biodiversity, monsoon development, and regional elevation changes. The fossil biotas appear modern and have been assumed to be mostly Miocene in age. Dating has been by cross-correlation using palynology, magnetostratigraphy, and lithostratigraphy because numerical radiometric ages are lacking. Here we report the first unequivocal early Oligocene age (33-32 Ma) of a section in the Lühe Basin (25.141627°N, 101.373840°E, 1890 m above mean sea level), central Yunnan, based on U-Pb zircon dates of unreworked volcanic ash layers in a predominantly lacustrine succession hosting abundant plant and animal fossils. This section, located in Lühe town, is correlated with an adjacent section in the Lühe coal mine previously assigned to the upper Miocene based on regional lithostratigraphic comparison. Our substantially older age for the Lühe town section calls into question previous estimates for the surface uplift and climate history of the area, and the age of all other correlative basins. The modernization of the biota ~20 m.y. earlier than previously thought overturns existing concepts of vegetation history in southwestern China, and points to Paleogene modernization of the biota in Yunnan and associated Asian biodiversity hot spots.

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Fossil conifers from the Early Cretaceous, most likely late Aptian, Crato Formation were studied. The excellent preservation of several of those fossils allowed detailed investigations of the leaf epidermis by light microscope (LM) and by scanning electron microscope (SEM). Members of two conifer taxa were recognized: The Araucariaceae are represented by a female cone of cf. Aruucuriu spec. A juvenile cone (Araucuriostrobus spec.) and sterile foliage shoots of Brachyphyllum obesuni might be attributed to the Araucariaceae as well. The morpho-genus Lindleycludus (incertae sedis) is represented by foliage shoots. The occurrence of Lzndleycludus is the first record of this extinct morpho-genus in the Southern Hemisphere. Anatomical features of these conifers are interpreted as adaptations to a warm seasonally dry climate. Taphonomic problems concerning these conifer remains are discussed. ZusammenfassungFossile Koniferen aus der unterkretazischen, hochstwahrscheinlich oberaptischen Crato Formation wurden untersucht. Die ausgezeichnete Erhaltung einiger Exemplare gestattete die Analyse von Blattepidermen mittels Licht-und Rasterelektronenmikroskop. Vertreter zweier Koniferentaxa wurden nachgewiesen: Araucariaceae kommen mit einem weiblichen Zapfen von cf. Araucuriu spec. vor. Ein juveniler Zapfen (Araucuriostrobus spec.) und sterile Zweige mit der Beblatterung der Morpho-Species Brachyphyllum obesum werden unter Vorbehalt ebenfalls zu den Araucariaceae gestellt. Vegetative Organe der Morpho-Gattung Lindleycludus (incertae sedis) sind ebenfalls erhalten. Das Vorkommen von Lindleycludus ist ein erster Nachweis dieser fossilen Morpho-Gattung in der Sudhemisphare. Anatomische Merkmale dieser Koniferen werden als Anpassungen an ein warmes, saisonal trockenes Klima gedeutet. Im Zusammenhang mit den Koniferenresten werden taphonomische Probleme diskutiert.

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Araucarioxylon Kraus is a widely known fossil-genus generally applied to woods similar to that of the extant Araucariaceae. However, since 1905, several researchers have pointed out that this name is an illegitimate junior nomenclatural synonym. At least four generic names are in current use for fossil wood of this type: Agathoxylon Hartig, Araucarioxylon, Dadoxylon Endl. and Dammaroxylon J.Schultze-Motel. This problem of inconsistent nomenclatural application is compounded by the fact that woods of this type represent a wide range of plants including basal pteridosperms, cordaitaleans, glossopterids, primitive conifers, and araucarian conifers, with a fossil record that extends from the Devonian to Holocene. Conservation of Araucarioxylon has been repeatedly suggested but never officially proposed. Since general use is a strong argument for conservation, a poll was conducted amongst fossil wood anatomists in order to canvass current and preferred usage. It was found that the community is divided, with about one-fifth recommending retention of the well-known Araucarioxylon, whereas the majority of others advocated use of the legitimate Agathoxylon. The arguments of the various colleagues who answered the poll are synthesized and discussed. There is clearly little support for conservation of Araucarioxylon. A secondary aspect of the poll tackled the issue as to whether Araucaria-like fossil woods should be either gathered into a unique fossil-genus, or whether two fossil-genera should be recognized, based on the respective presence or absence of axial parenchyma. A majority of colleagues favoured having one fossil-genus only. Agathoxylon can be used legitimately and appears to be the most appropriate name for such woods. However, its original diagnosis must be expanded if those woods lacking axial parenchyma are to be included.