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Palaeosols of the Koluel‐Kaike Formation, a red colour‐banded, pyroclastic succession from southern Argentina, constitute a proxy for Eocene climate changes. Reticulated and vertically elongated ferric mottles, along with iron and manganese nodules are the most significant climate indicators, which originated by alternating cycles of waterlogging and drying conditions causing Fe‐Mn mobilization and fixation. Clay minerals vary from a kaolinite > smectite suite in the lower and middle sections, to a smectite > kaolinite one in the upper part. High concentrations of iron oxides/hydroxides and kaolinite, lack of exchangeable bases, absence of carbonate cement, presence of ironstone and redness of hue in most of the palaeosols suggest intense chemical weathering related to leaching and lateritization processes. Five pedotypes, ordered in a stratigraphic sense, were identified. Strongly developed, red to orange Chornk (Fragiaquult) and Kápenk (Plinthaquult) pedotypes display argillic horizons, abundant ferric nodules and slickensides; they are dominant in the lower and middle sections, and formed in seasonal humid and megathermic (tropical) conditions with a mean annual precipitation of 1200 to 1300 mm and a mean annual temperature of 15 °C. Weakly developed, less structured Ornek (Vitrand) and Pólnek (Placaquand) pedotypes occur in the middle and upper sections, and originated in sub‐humid and mesic‐megathermic conditions with a mean annual precipitation around 1000 mm and a mean annual temperature around 12 °C. The brownish Soorsh (Argialboll) pedotype exhibits a granular structure and is present at the uppermost part of the unit. It developed in sub‐humid/semi‐arid and mesic conditions, with a mean annual precipitation of 600 to 700 mm and a mean annual temperature around 10 °C. This pedotype succession and clay mineral distribution indicates a decrease in chemical weathering and degree of soil development with time. Koluel‐Kaike palaeosols from Central Patagonia are some of the first continental non‐palaeobiological data linked to the Early Palaeogene global warming in South America; they show an especially close relationship with the Early Eocene Climatic Optimum and the following long‐term cooling and drying initiated by Middle to Late Eocene time.

The Río Chico Group in the San Jorge Basin of central Patagonia (Argentina) preserves some of South America's most significant Paleogene records of biotic and climatic change. Three of its constituent formations, the Peñas Coloradas, Las Flores, and Koluel-Kaike, host vertebrate faunas referred to the "Carodnia faunal zone," the Itaboraian South American Land Mammal Age (SALMA), and the Riochican SALMA. However, the precise absolute ages of these units, and thus their asso ciated faunas and paleoclimate records, are poorly resolved. Herein, we report new paleomagnetic and geochronologic results from these formations in south-central Chubut Province, Argentina. U-Pb dating of four volcanic ashes, using both laser abla tionmulticollector-inductively coupled plasmamass spectrometry and high-resolution chemical abrasion-isotope dilution-thermal ionization mass spectrometry, indicates ages of igneous crystallization of 51.403 ± 0.037 (0.045) [0.071] Ma for a level within the middle Las Flores Formation and 46.714 ± 0.012 (0.026) [0.057] Ma, 44.579 ± 0.013 (0.026) [0.054] Ma, and 42.856 ± 0.017 (0.027) [0.054] Ma for levels in the lower, middle, and upper Koluel-Kaike Formation, respectively. Combining these with previous isotopic ages in our new magnetostratigraphic framework, we correlate the Peñas Coloradas Formation to chrons C27n-26r (ca. 62.5 to ca. 61.6 Ma; late Danian) and the section from the middle Las Flores to the uppermost Koluel-Kaike to chrons C23n to C19r (ca. 51.4-42.2 Ma; mid Ypresian-late Lutetian). We combine these data with other recently published chronostratigraphic results from Paleogene units in Patagonia to better constrain the ages of noteworthy Paleogene plant and mammal fossil sites in Patagonia and to develop a revised temporal calibration of the Las Flores, Vacan, and "Sapoan" faunas.

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Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.

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Hemispherical pan or dish-shaped trace fossils from the Cenozoic of the Central Patagonia are attributed to the burrowing action of cicadas. A new ichnotaxon, Feoichnus challa igen. et isp. nov. is characterized by its hemispherical shape, mostly subvertical orientation, smoothed internal lining showing knobbly surface texture, and rough and irregular external surface devoid of ornamentation. The wall is composed of a lining plus a layer of soil material consolidated passively by cicada excretions. In other specimens the wall shows a repetition of linings and soil layers reflecting changes in the position of the chambers. Grooves, which represent traces of roots originally related to the feeding activities of cicada nymphs, are located in the wall of many specimens of F. challa. These grooves are subvertical to subhorizontal and show smooth surfaces with longitudinal striations. The cicadan origin of these traces is supported by comparison of the fossils to modern cicada nymph chambers and by laboratory experiments. The most significant characters that emerged from the comparison are the differential preservation of the basal part of the chambers, the interior lining with similar surface texture, and the presence of root traces in the wall and in the interior of the chamber. Additional records of F. challa from the Cretaceous-Pliocene of the USA, the Oligocene of Ethiopia, and the Miocene of the United Arab Emirates and Kenya complete the current information yielded by the known body fossil record to help understand the evolutionary history of cicadas.