The South Tibetan Detachment (STD) is parallel to the east–west-trending axis of the Himalayan range over >1500 km and represents an untapped source of information for understanding the coupling between multi-scale deformation processes, fluid flow, exhumation of high-grade rocks and topography. Here, we present hydrogen isotope ( δ 2 H) geochemistry, quartz c -axis fabric deformation thermometry and electron microprobe micro-analyser data from a strand of the STD exposed in NW India (the Zanskar Detachment). Our data document intense meteoric fluid–rock–deformation interactions within the upper part of the hot (>400°C) mylonitic footwall to the detachment, which was active at 22–20 Ma. Calculated δ 2 H water values ranging from −115 to −95‰ suggest that the Zanskar area was standing at least above 2500–3000 m mean topographic elevation during the early Miocene. When compared with previous data obtained from Mt Everest, our results suggest that high topography along the Himalayan range was diachronous, occurring at c . 20 Ma in the western Himalaya (>3000) and at c . 15 Ma in the Central Himalaya (>5000 m). This study highlights the close relationships between topography, meteoric fluid flow, high heat flux and exhumation of the Himalayan Crystalline Core.

Life on Earth has been capitalizing on the C-3 photosynthetic pathway for 2.8 billion years. However, in the world's grasslands that emerged since the Paleogene, C-4 vegetation expanded dramatically between 8 and 3 Ma in response to climatic changes. Here we present the first comprehensive Late Miocene to Holocene delta C-13 soil carbonate record from the Eastern Mediterranean region (Anatolia) to reconstruct long-term geographic distributions of C-3 and C-4 plants, a region with patchy records compared to parts of Africa and Asia. Our results show a colonization of Anatolian floodplains by C-4 biomass by 9.9 Ma, similar to regions in NW and E Africa, followed by a transition from this mixed C-3-C-4 vegetation to C-4 dominance between ca. 7.1 and 4.9 Ma. The transition to C4 in Anatolia coincides with a similar shift from C-3 to C-4 vegetation in southern Asia and is generally attributed to the Late Miocene Cooling in response to decreasing atmospheric pCO(2). However, the Anatolian paleoecosystem patterns are unique due to a rapid and permanent return to C-3 dominance in the Early Pliocene, which is not observed elsewhere and occurs simultaneously with the disappearance of the open environment-adapted large mammal Pikermian chronofauna. We propose that this return to C-3 vegetation was caused by paleoclimatic processes that regionally shifted precipitation from the warm to the cool season, resembling the modern Mediterranean climate. In conclusion, changes in rainfall seasonality under subhumid climate, rather than increased aridity, drove the demise of C-4-dominated floodplains and the open-environment adapted Pikermian chronofauna at the Eurasian-African crossroads.

The extent of continental mid-latitude hydroclimate variability during Eocene warm periods is still poorly understood due to the lack of temporal resolution, coherence of preserved records or lack of proxies capable of accurately quantifying changes in the hydrological cycle. Here, we utilize the hydrogen and carbon isotopic composition of plant waxes preserved within varved maar sediments of the UNESCO World Heritage Site 'Messel Fossil Pit' (Germany) to reconstruct a high-resolution hydroclimate record between 47.7 and 47.2 Ma. Biomarker hydrogen isotopic (delta 2H) variability of up to 45 parts per thousand is only little affected by contemporaneous temperature change and thus suggests that the hydrological cycle was partly decoupled from the mid-latitude temperature history. Instead, the delta 2H variability indicates that Central Europe received moisture from different source areas characterized by distinct isotopic signatures due the fragmented paleogeography of Europe during the Eocene. In our analysis, we reconstructed changes in relative humidity by coupling biomarker delta 2H and temperature data obtained from identical stratigraphic levels. Relative humidity varied by up to 60% during the time period investigated here. Crucially, the amplitude of relative humidity changes decreased from 47.7 to 47.2 Ma. This observation coincides with changes in plant fossil assemblages and follows the long-term transition from a high to low 400 kyr eccentricity orbital configuration. We therefore suggest, that orbitally-driven changes in Northern Hemisphere insolation drove the hydroclimatic trends at Messel.

Global climate change has been linked to faunal turnover throughout geological history, but the effects of regional environmental change remain comparatively less understood. Central Asian environments changed repeatedly throughout the Paleogene (ca. 66 to 23 Ma) due to topographic reshaping and global climate change. Additionally, recently published geological records indicate that intense, regional aridification occurred during the mid-Eocene. We test the signatures of regional versus global climate change events in the fossil record, reconstructing Paleogene sampling-corrected taxonomic richness, faunal turnover, and body size change for all Central Asian mammals. We find three macroevolutionary transitions in mammal assemblages. One associated with regional Asian mid-Eocene aridification and two with global events - the Paleocene-Eocene Thermal Maximum (short-lived extreme warming 56 Ma) and the Eocene-Oligocene Transition (prolonged cooling 34 Ma). Our results indicate that both global and regional climate were associated with mammal evolution in the Paleogene of Asia. We also find that a previously described Eocene/Oligocene transition from Perissodactyla-dominated to Glires-dominated faunas - thought to be associated with cooling at the Eocene-Oligocene Transition - may be a sampling bias artifact.

The timing and mechanisms of surface uplift in western central Tibet remain debated due to inconsistent Eocene paleoelevation estimates. To address this issue, we integrate zircon U-Pb geochronology, stable and clumped isotope analyses, and compound-specific carbon isotope analyses from the Eocene Kangtuo Formation in the Gerze basin. Zircon U-Pb dating of interbedded andesite constrains the depositional age of the Kangtuo Formation between 48 and 37 Ma. Leaf wax n-alkane carbon isotopes indicate a relatively humid environment, comparable to other contemporaneous basins in central Tibet. The absence of a Gangdese-induced rain shadow implies that the central valley maintained an independent westerly-derived moisture supply. Furthermore, clumped isotope thermometry yields carbonate formation temperatures of 36-43 degrees C, which we interpret as reflecting a mean annual air temperature of similar to 25 degrees C after accounting for reasonable seasonal biases. Comparison with coeval low-elevation sea surface temperature records, applying a lapse rate of -4.0 to -6.0 degrees C/km, yields a paleoelevation of 1.2 +/- 0.4 km. This is independently supported by delta O-18-based paleoaltimetry, which suggests an elevation of 1.3 (+0.2/-0.1) km. Collectively, these multi-proxy results indicate that the Gerze basin stood at a modest elevation of 1.3 +/- 0.1 km during the middle-late Eocene. These findings imply that the >3 km of subsequent surface uplift after 37 Ma was primarily driven by lithospheric mantle delamination or convective removal rather than by additional crustal thickening. This study provides new constraints on the paleotopography and hydrological regime of central Tibet and offers insights into the geodynamic mechanisms of plateau uplift.

Asia’s exceptional biodiversity is reflected in the Hengduan Mountains fossil record in eastern Tibet, yet the timing and drivers of mammalian diversification remain enigmatic. Here we combine U–Pb dating of mammalian bone-cavity calcite and palaeosol nodules from the Relu Basin with stable-isotope palaeoaltimetry of fossil tooth enamel. We show that the Relu mammal assemblage was buried at 39.2–38.1 Ma, making it the oldest directly dated Cenozoic mammal fauna reported from the Tibetan Plateau, and that herbivores inhabited near-modern habitat elevations of 3463 m (+819/−869). This directly dated Eocene mammalian assemblage coincided with diversification of high-elevation forests, implying that a montane biodiversity hotspot had emerged by ~39 Ma. Mediterranean-type false-ring signals in 41.5-Ma fossil wood and climate-model simulations are consistent with Eocene surface uplift contributing to a strongly seasonal, bimodal-rainfall regime that predated the modern Asian monsoon and provided environmental conditions favourable for early high-elevation biotic diversification. These results refine Tibetan mammalian chronology and provide a benchmark linking mountain-building, rainfall seasonality and biodiversity. Eocene herbivorous mammals on the Tibetan Plateau inhabited elevations of 3463 m by ~39 Ma under a bimodal-rainfall regime predating the modern Asian monsoon, coinciding with the diversification of high-elevation forests, according to direct dating and palaeoaltimetry from bone-cavity calcite, palaeosols and fossil tooth enamel, together with fossil tree-ring evidence.

As the largest elevated plateau on Earth, the Tibetan Plateau has played a pivotal role in shaping both global and regional climate as well as mammalian dispersal. Yet how paleoclimate and biome shift in and around the Plateau responded to Plio–Pleistocene cooling, marked by a ~3–4 °C global temperature drop at ~2.7 million years ago (Ma) and the intensification of Northern Hemisphere glaciation, remains to be further investigated. Here we integrate novel climate and biome simulations with new carbonate stable and dual clumped isotope analyses to reconstruct past climate and ecosystems across the Tibetan Plateau and its surroundings. Our clumped-isotope temperatures indicate warmer mean annual air temperatures prior to 2.7 Ma, supporting a permafrost-free northern Plateau under climates warmer than today. Combined with climate modeling and global permafrost distribution, these results suggest that under conditions similar to the mid-Pliocene Warm Period (3.3–3.0 Ma), ~60% of alpine permafrost, containing ~85 petagrams of carbon—may have been vulnerable to thaw, compared to only ~20% of circumarctic permafrost. This implies that up to ~25% of global permafrost carbon, and associated permafrost–climate feedbacks, could originate in alpine regions. In addition, our results show the emergence of cold steppe–tundra habitats suitable for woolly rhinoceroses during Plio–Pleistocene cooling, forming plateau–circumarctic dispersal corridors. The ~3–4 °C cooling around 3.0–2.7 Ma along these corridors coincided with ~8 °C cooling on the Plateau. A >30% decline in plateau habitat suitability, alongside a ~23-fold corridor expansion, points to temperature decline as the primary driver of poleward megafaunal dispersal. Taken together, our findings highlight the amplified temperature sensitivity of high-elevation regions and underscore the central role of global temperature change in shaping the past, present, and future dynamics of cold-adapted mammals across the cryosphere.

Abstract The reconstructed stable oxygen isotopic composition of meteoric water (δ 18 O w ) is widely used for paleoclimate reconstructions. Understanding past environmental factors that drove changes in δ 18 O w is essential for interpreting past climate conditions. Here, we investigate the spatial and temporal variations of δ 18 O w in the Miocene Alpine foreland basin from multiple proxy materials with isotope‐enabled climate model simulations. Based on δ 18 O values and clumped isotope‐based temperatures of pedogenic carbonate nodules, we compare Middle Miocene δ 18 O w records from the Northern Alpine Foreland Basin (NAFB) in Switzerland and its counterpart in the Mediterranean Alpine foreland (Digne‐Valensole Basin, SE France). Additionally, we analyze isotope‐tracking atmospheric general circulation model outputs of δ 18 O in precipitation for the Middle Miocene and present‐day to assess changes in distributions. Our results highlight a latitudinal δ 18 O w gradient in the Middle Miocene that is similar to the present‐day. The occurrence of distinct N‐S differences in δ 18 O w values during the Miocene are likely the result of a similar‐to‐present climate divide (North‐Atlantic vs. Mediterranean climates). Concurrently, we suggest that shifts in atmospheric circulation over the Alpine region during certain time intervals of the Middle Miocene led to rapid high‐amplitude variations in δ 18 O w . We note significant differences in δ 18 O w values between proxy‐based reconstructions and climate model simulations that we attribute to (a) proxy biases toward higher δ 18 O w values and (b) inappropriate model resolution and topography for the Miocene Alpine region. Our study advances the use of multiproxy data‐model comparison for paleoclimate and paleoaltimetry reconstructions and points out the importance of integrating proxy and modeling approaches.

Between 5.97-5.33 Ma, kilometre-thick evaporite units were deposited in the Mediterranean Basin during an event known as the Messinian Salinity Crisis (MSC). The MSC was characterised by a strongly negative hydrological budget, with a net evaporative loss of Mediterranean basin water exceeding precipitation and riverine runoff inputs. Despite evident proves of environmental crisis at the end of the Messinian, the Mediterranean domain still lacks quantitative estimates of temperature change across the transition from the (brackish) Lago Mare, marking the end of the Miocene, to the fully marine Pliocene. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (brGDGT) biomarkers for the time period corresponding to the MSC Stage 3 (5.55-5.33 Ma) and compare them with continental temperature values obtained from Δ47 clumped isotope geochemistry measured on paleosol carbonate nodules found at few locations in the Mediterranean basin. The well-preserved organic biomarkers were extracted from outcrops onshore and offshore covering a vast portion of the Mediterranean Basin; onshore (Malaga, Sicily, Cyprus) and offshore (DSDP core holes 124 and 134 from the Balearic abyssal plane, hole 374 from the Ionian Basin and hole 376 drilled west of Cyprus). Calculated MATs for the 5.55 to 5.33 Ma time interval show values around 16 to 19 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A holes 374 and 376 are lower, around 13 to 16 ºC. Comparing the brGDGT-MAT values with Δ47-MAT values from carbonate nodules, shows high congruence between both approaches. For the northern Mediterranean Δ47-MAT is 24.6 ± 1.6 °C and brGDGT-MAT is 19 ± 4.8 ºC. For Cyprus Δ47-MAT is 20.3 ± 1.7 °C and brGDGT-MAT is 18 ºC ± 4.8 ºC. Given the very different nature of the used paleoproxies, the similarity of the obtained MAT values provides a strong indication of their (cross)validity in sampled sections. Additionally, the measured δ18O values for the carbonate nodules used for the Δ47-MAT show high δ18O of the soil water (in the range of -5 ±0.7‰) indicate highly evaporative conditions for the two onland sites where these were collected (Northern Apennines and Cyprus). We conclude that between 5.55 to 5.33 Ma the temperatures in the Mediterranean region were similar to present-day conditions, yet the region has suffered from excess evaporation as indicated by combined high δ18O values from (inorganic) carbonate nodules and δ2H values from (organic) biomarkers.

>The snow-capped peaks and majestic heights of the world’s highest places have impressed and inspired humankind throughout its history. Equally important, the Himalaya and Tibetan Plateau(TP) play a crucial role in a multitude of interactions that control the functioning and habitability of our planet:the southeastern plateau margin harbors hotspots of biodiversity [1], erosion and weathering affect Earth’s climate through feedbacks with the global carbon cycle [2],and the TP reroutes atmospheric moisture and hence provides water for billions of people [3].

High‐resolution continental temperature records from geological archives are crucial in order to evaluate temperature dynamics under fundamentally different climate conditions than today. Particularly the warm early to middle Eocene (∼56–40 million years ago) has become the focus of paleoclimate studies with the intention of quantifying temperatures under high atmospheric carbon dioxide ( p CO 2 ) levels. However, detailed proxy reconstructions of land temperature variability during the Eocene “greenhouse” are currently lacking for large parts of the continents. Here we present a ∼430 thousand‐year high‐resolution continental temperature record, reconstructed from terrestrial biomarkers preserved in the maar sediments of the UNESCO World Heritage Site “Messel Fossil Pit,” Germany during the earliest middle Eocene of Central Europe (∼47.7–47.2 million years ago). We found that continental temperatures ranged between ∼21 and 28°C, but shifted from a highly variable (fluctuations up to ∼5°C) temperature pattern (∼155 thousand years) toward a more constant temperature state (∼145 thousand years) through the time period covered here. The shift in temperature history was possibly associated with varying orbital configurations or the concurrent initiation of North Atlantic seaway changes. Moreover, we identified a pronounced warming at ∼47.5 million years, that coincides with negative benthic oxygen and carbon isotopic excursions in the time‐equivalent marine stacks, indicating that the maar lake recorded a previously unknown “hyperthermal‐like” global warming event.

The quantitative reconstruction of paleoclimatic and paleoenvironmental conditions in regions and in time periods characterized by recurrent and significant fluctuations is challenging. An example of strong paleoenvironmental change occurred in the Mediterranean Basin across the Miocene – Pliocene boundary (5.33 Ma), marked by the restoration of normal marine conditions after the 'Lago-Mare' terminal phase of the Messinian salinity crisis. Environmental conditions during the Lago-Mare phase are still uncertain due to the controversial body fossil record, consisting of freshwater to brackish assemblages (ostracods, dinocysts, mollusks, and foraminifera), as well as marine microfossils (otoliths of marine fishes, calcareous plankton).However, two scenarios were suggested to describe this transition: 1) a catastrophic and sudden sea level rise causing the drastic change from freshwater to marine deep environments; 2) a gradual sea level rise, characterized by a fast to gradual transition from brackish to marine environments.To quantify the changing conditions during the Miocene–Pliocene transition, we used a multivariate statistical approach to interpret a large array of terrestrial and aquatic molecular-based indices, in a sedimentary succession of the Northern Mediterranean (Maccarone section, Central Italy). The statistical procedure was specifically developed to address the complexities emerging from the heterogeneous dataset.An illustrative example suggests that using the TEX86, UK37’, and MBT´5ME paleothermometers, we obtained different values and trends in the changing Mediterranean during the study interval. While the study acknowledges the validity of UK37’ as a paleothermometer in variable environments, it highlights that TEX86and MBT´5ME are sometimes compromised by other sources, such as reworked sediment or other organisms that produce the same lipid inventory. In these cases, these proxies provide information about environmental processes rather different than temperatures.Cluster analysis supports a stepwise evolution during the Miocene-Pliocene transition, besides redundancy analysis (RDA) indicates that the water column structure changed from stratified (Tetrahymanol) during the Messinian to mixed during the Zanclean. A second gradual change is instead related to terrestrial vegetation modifications, indicating a gradual coastal environment reconfiguration after a marine transgression with the distancing of the costal line and a reduction of wetland aquatic plants signal. Finally, molecular fossils are also influenced by cyclical changes, not related to the Messinian salinity crisis demise but linked to astronomical-driven climatic cycles.

The evolution of restricted marine basins offers unique insights into the interplay between climatic variability and tectonic processes. This study focuses on the western Mediterranean Sea, which underwent progressive isolation beginning in the late Tortonian (similar to 8 Ma) and culminating with the Messinian Salinity Crisis (5.97-5.33 Ma), when the basin experienced quasi-disconnection from the Atlantic Ocean. Here, we present reconstructions of sea surface temperature and salinity derived from coupled analysis of organic biomarkers and oxygen isotopes on planktic foraminifera from the West Alboran Sea (ODP site 976B) for the 7.505 to 7.063 Ma time interval. The combined results show four phases with distinct paleoenvironmental conditions prevailing in this westernmost Mediterranean. During Phase 1 (7.505-7.369 Ma), the sea surface temperatures showed low-frequency, large-amplitude fluctuations (25.7 to 29.7 degrees C) accompanied by large sea surface salinity variations (37.1 to 43.3). In Phase 2 (7.369-7.241 Ma), the marine conditions shifted to low variability, high sea surface temperatures (27.9 to 29.6 degrees C) accompanied by stable and high salinities (42.7 to 43.7). In Phase 3 (7.241-7.177 Ma), stable hypersaline conditions (43.0 to 44.3) persisted alongside an even lower variability in sea surface temperatures (28.3 to 29.1 degrees C). Phase 4 (7.177-7.063 Ma) is marked by a pronounced cooling and unexpected freshening. During Phase 4, the large-amplitude, high-frequency sea surface temperature (25.3 to 29.8 degrees C) and sea surface salinity changes (35.9 to 44.0) were likely driven by the progressive closure of the Betic and Rifian gateways around 7.1 Ma, with a superimposed precession modulation. This study highlights the sensitivity of the Western Mediterranean Basin to gateway restrictions and provides a framework for understanding the broader climatic and oceanographic impacts of tectonically triggered restriction events. The system was highly sensitive to global climate variations, especially during the latest Tortonian, when the Alboran basin had a fully functional connection to the Atlantic. Starting with the earliest Messinian, changes in connectivity through the Atlantic-Mediterranean gateway likely played a pivotal role in regulating temperature and salinity of the western Mediterranean with consequences propagating further to the east, in the entire basin.

During the Middle Miocene, the Earth shifted from a warm state, the Miocene Climatic Optimum (MCO; 16.9–14.7 Ma), to a colder state associated with the formation of extensive and permanent ice sheets on Antarctica. This climatic shift, the Middle Miocene Climatic Transition (MMCT; 14.7–13.8 Ma) strongly affected the composition and structure of major biomes, ocean circulation, and precipitation patterns. Although Middle Miocene climate dynamics are well documented in marine records, our knowledge of terrestrial climate change is not well constrained. Here we present a long-term (23–13 Ma) stable (δ13C, δ18O) and clumped (Δ47) isotope record of soil carbonates from a northern Mediterranean Alpine foreland basin: the Digne–Valensole basin (DVB), France. Δ47-derived soil carbonate formation temperatures indicate a highly dynamic dry season temperature pattern that is consistent with multiple periods of reorganization of atmospheric circulation during the MCO. We propose that changes in atmospheric circulation patterns modified the seasonality of precipitation and, ultimately, the timing of pedogenic carbonate formation. Consequently, Δ47 soil carbonate temperature data record the combined effects of long-term regional temperature and carbonate formation seasonality change. The data are consistent with the existence of a proto-Mediterranean climate already during certain MCO time intervals. Following the MMCT, the stable and clumped isotope record displays pronounced cooling after 13.8 Ma accompanied by a rather large (−5.0 %) decrease in soil water δ18O values. Our northern Mediterranean foreland basin climate record shares strong similarities with time-equivalent records from the terrestrial European mid-latitudes and the global oceans and enhances our understanding of the circum-Alpine Middle Miocene terrestrial climate dynamics.

Global ice losses will likely continue with ongoing climate warming, culminating in an almost ice-free planet analogous to that which persisted throughout much of the Cretaceous. Despite extensive research, Early Cretaceous cryosphere responses to temperature and atmospheric P CO 2 fluctuations over short, human, timescales remain uncertain. Here, we show rapid late Valanginian (~133 million years ago) seasonal fluctuations in sea surface temperature (SST) and δ 18 O mainly driven by atmospheric P CO 2 . Two distinctive features emerge: large seasonal variability of up to 15.9° ± 4.9°C in Southern Hemisphere mid-latitudes, comparable to that found today, a positive sea surface δ 18 O value related to evaporation (expressed as salinity increases), and the existence of polar ice. Model-predicted patterns of SST change match with high statistical confidence those derived from clumped isotopes in well-preserved oyster fossils from Madagascar and display consistent warm/cold seasonality. Given its relative coolness in a Cretaceous context, the late Valanginian is a valuable analog for Earth’s future climate.

The European Alps, one of the most studied mountain ranges worldwide, are hypothesized to have experienced diachronous surface uplift resulting from slab-breakoff (Schlunegger and Kissling, 2018; Handy et al., 2015). However their surface elevation history is yet not well constrained (Campani et al., 2012; Krsnik et al., 2021; Botsyun et al., 2020). Quantifying surface elevation of an orogen through geological time is essential for our understanding of the geodynamic drivers, as well as the paleoenvironmental impacts of surface uplift.Here, we present Early to Middle Miocene stable isotope-based paleoelevation reconstructions of the Western, Central, and Eastern Alps. Stable isotope paleoaltimetry (the 𝛿-𝛿 approach) is based on the systematic decrease of oxygen (𝛿18O) and hydrogen (𝛿D) isotopic composition of precipitation with increasing elevation and strongly benefits from contrasting high and low elevation records of past rainfall.Accordingly, contrasting temperature-corrected near sea level pedogenic carbonate 𝛿18O values with time-equivalent 𝛿D values of K-Ar dated clay minerals from fault gouges allows for the calculation of the differential elevation between a foreland basin and an orogen’s interior through time. Recent paleoaltimetry research with focus on the Middle Miocene Central Alps indicates elevations exceeding 4 km (Krsnik et al., 2021).With a spatiotemporally enhanced coverage of the European Alps, we present estimates of paleoelevation covering the time interval between ca. 23 and 12 Ma. In addition, paleoclimate simulations for a number of topographic scenarios allow for the isolation of contribution of local elevation complex climate change, and regional topographic configuration signals (Boateng et al., 2023).Our quantitative stable isotope paleoaltimetry estimates indicate peak elevations of >4km in the Central Alps already during the earliest Miocene (ca. 23 Ma). 𝛿D values from fault gouge-derived illites are up to 25 ‰ higher in the Eastern Alps than in the Central Alps for the time interval between 21-16 Ma and suggest that the Eastern Alps were significantly lower during that time interval. Our results from the Mont Blanc massif are in line with isotopic measurements from fluid inclusions in quartz veins, which highlight the Mont Blanc massif in the Western Alps, did not exceed an average elevation of ca. 1 km until the end of the Miocene (Melis, 2023). Collectively, these results confirm a scenario of west-to-east surface uplift as suggested on the basis of slab-breakoff and tearing.

Cooling during the Eocene-Oligocene Transition (EOT; 34 Ma) and a shift towards open habitats during the end of the Oligocene (similar to 26 Ma) are key characteristics of the paleoclimatic history of western North America. Yet, the paleo-temperature evolution during the rest of the Oligocene remains poorly constrained. Here, we present a new temperature record from the high-elevation North American Cordillera (Sage Creek Basin; SW Montana, USA) covering 34 to 27 Ma as revealed by zircon U-Pb geochronology of four volcanic tuffs. High-precision dual clumped isotope thermometry (Delta(47) and Delta(48)) is used to identify calcretes unbiased by NO2 contaminants and kinetic effects. The Delta(47) values of these calcretes show no major temperature change across the EOT, but instead gradual cooling of 10 +/- 1 degrees C during the early Oligocene (32 +/- 1 to 29 +/- 2 Ma). Protracted cooling after, rather than abrupt temperature changes during the EOT, may explain the lack of mammalian turnover in North American fossil assemblages compared with other continents. Reconstructed water oxygen isotope compositions remain unchanged during the early Oligocene cooling, indicating no major surface uplift at this location. Furthermore, global climate reconstructions show only a minor decrease in atmospheric CO2 concentrations at this time. The mechanisms driving this Oligocene cooling thus remain elusive, but may be related to land surface feedbacks operating in the high-elevation North American Cordillera. Given the large magnitude of the cooling that we observe in SW Montana, these mechanisms should be considered in climate model simulations and proxy reconstructions of high-elevation regions.

Between 5.97 and 5.33 Ma, the Mediterranean area was fundamentally impacted by the Messinian Salinity Crisis (MSC), a pivotal event that led to the transformation of the Mediterranean Sea into an extensive evaporitic basin, caused by rapidly changing environmental conditions. The MSC was caused by a combination of tectonic and climatic factors, resulting in severe connectivity restriction between the Mediterranean-Paratethys system and the Atlantic Ocean. The Sorbas Basin, thanks to its proximity to the Atlantic gateway and astronomically dated sedimentary succession, represents a key element in understanding the nature of palaeoceanographic transformations affecting the Western Mediterranean, preceding and announcing the MSC. Here, we present the first sea surface temperature (SST) and sea surface salinity (SSS) estimates recorded in Sorbas (i.e., Western Mediterranean) for the time interval between 7.3 to 6.0 Ma. The studied section includes the lower Abad Member (cyclic alternations of homogenous marls and indurated layers) and the upper Abad Member (cyclic alternations of sapropels, diatomites and marls). SSTs were estimated using TEX86 and UK´37 biomarker-based proxies, with cross validation at distinct levels. To further constrain the SSS changes, we combined the TEX86 and UK´37 based SST estimates with δ18O values measured at the same stratigraphic levels on the planktonic foraminifera Orbulina universa. The temperature estimates vary between 17 and 27 °C, with a pronounced cold (17 °C) peak at 7.1 Ma, following the restriction of the Betic and Rifian corridors. This cooling is followed by a generally warmer period lasting until 6.27 Ma, when a colder trend emerges and lasts until 6.18 Ma. A marked and sharp cooling from 27 to 18 °C is observed at 6 Ma, preceding the onset of the MSC. The SST-δ18O- calculated salinity ranges between 34 and 44 for most of the levels. However, several levels around 7.0, 6.74, 6.52 and 6.06 Ma, generated SSS values as low as 20, provoked by exceptionally low, yet not fully understood , δ18OO. universa component in our SSS calculation. The low values might be associated with a significant local influx of fresh water, considering the basin's restricted nature. When comparing our results to coeval records existing for the Eastern and Central Mediterranean (Agios Myron, Kalamaki and Monte dei Corvi), we notice a correlation of warmer and colder peaks across the Mediterranean, albeit with minor leads and lags. Importantly, the Sorbas SST values are well within the range of SSTs in the Eastern and Central Mediterranean. The SSS values of Sorbas are also within the range reported in the Eastern Mediterranean with the exception of those levels presumably affected by fresh water input. In the absence of a full explanation for the associated low-δ18OO. universa values, we observe the dominance of the C37:4 alkenone component, exclusively associated with fresh to brackish water environments, at some of these levels, strongly suggesting the occurrence of repeated fresh water influx into the basin.

In recent years, numerous studies focused on reconstructing the surface uplift history of the Central Anatolian Plateau (CAP) and the associated driving mechanisms such as slab breakoff, removal of lithospheric mantle, or crustal thickening (e.g. McPhee et al., 2021). The CAP forms the westward portion of the Turkish−Iranian plateau and has mostly been above sea level since ca. 41 Ma (Okay et al., 2020). Most of its present-day topography, featuring mean elevations of ca. 1.0-1.5 km, however, has been shaped since the Late Miocene (e.g. Meijers et al., 2018; Schildgen et al., 2012a,b). Perhaps the most spectacular discovery is the recognition of 2 km of surface uplift of a portion of the southern plateau margin, the Tauride Mountains, since ca. 0.5 Ma (Öğretmen et al., 2018).Here, we provide stable isotope paleoaltimetry estimates for the Late Miocene for the southern CAP margin. The method is based on the inverse relationship between the oxygen isotopic composition (δ18O) of meteoric waters and elevation. We therefore contrast the δ18O values of age−equivalent low and (potential) high elevation soil carbonates (the δ−δ method; Mulch, 2016) from central Anatolia with published Anatolian and Aegean soil carbonate δ18O values (Böhme et al., 2017; Meijers et al., 2018; Quade et al., 1994). Our results reveal a low (ca. 0.5 km) orographic barrier between the Aegean and Mediterranean coastlines and central Anatolia at ca. 10 Ma, which increased to an elevation of ca. 1 km by ca. 8−6 Ma. This trend in increasing surface elevations during the Late Miocene is in agreement with stable isotope−derived paleoelevation estimates from Anatolian lacustrine carbonate records (Meijers et al., 2018). Given proposed post−0.5 Ma surface uplift of the southernmost plateau margin (Öğretmen et al., 2018), our results imply a phase of significant local subsidence bracketed between the latest Miocene and ca. 0.5 Ma. From the Pliocene onward, we also observe long-term trends toward higher δ18O values in soil carbonate data sets from the Aegean Sea and CAP region, which indicate increased aridification and possibly seasonality of rainfall in the region since the Pliocene. Additionally, our ‘modern’ soil carbonate records from central Anatolia underestimate the elevation of the modern Tauride orographic barrier (ca. 2.2 ± 0.5 km) at the southern plateau margin by ca. 0.5 to 1.0 km (non−linear vs. linear lapse rate, respectively). We attribute this underestimation to the mixing in of higher δ18O atmospheric moisture derived from the Black Sea compared to atmospheric moisture derived from the Mediterranean Sea during spring and early summer, a signal that is likely incorporated into soil carbonates that form at the onset of the dry summer season. Although atmospheric moisture derived from the Black Sea yields lower δ18O values than Mediterranean atmospheric moisture at sea level (Schemmel et al., 2013), the former undergoes less distillation across the significantly lower northern plateau margin (the Pontide Mountains). The presently observed mixing of Black Sea and Mediterranean Sea moisture sources might have also led to an underestimation of southern orographic barrier elevations in the geologic past.