Middle Miocene Climatic Optimum Research Articles

Simulating surface warming in Earth's three polar regions during the Middle Miocene Climatic Optimum using isotopic and non-isotopic versions of the Community Earth System Model

The Earth's North and South Poles and the Tibetan Plateau — collectively referred to as the ‘three poles’ — are regions that are very sensitive to climate changes and are known to amplify shifts in global temperature. In the case of the polar regions this effect is well known as polar amplification. The climate patterns during the Middle Miocene Climatic Optimum (MMCO) are considered a past analog to future climate, which could develop patterns and characteristics bearing similarity to MMCO by the end of the century. Therefore, analyzing MMCO environmental conditions in these regions in comparison to a pre-Industrial reference state provides valuable insights into possible future surface temperature changes at the Earth's three poles. We conducted simulations of the MMCO, focusing on surface temperature anomalies at the Earth's three poles. As a modelling tool we employed two versions of the Community Earth System Model (CESM), one of them equipped with model dynamics to simulate stable water isotopes. During the MMCO, we show 1) temperature anomalies at the three poles exceeded global averages, with Antarctica warming most, followed by the Tibetan Plateau and the Arctic, highlighting the role of the Tibetan Plateau as a key factor in global climate change often overlooked; 2) temperature anomalies at the Tibetan Plateau are higher in boreal winter (DJF), while in the Arctic and Antarctic temperature anomalies are larger in boreal summer (JJA), highlighting a seasonal shift between the maximum of climate change signals at the third pole; 3) Changes in clear-sky surface downwelling longwave radiation fluxes (∆Trlds_clearsky) and changes in surface albedo forcing (∆TSAF) constitute the primary and secondary mechanisms driving the annual surface temperature anomaly at the Earth's three poles. In contrast, the leading physical processes governing the seasonal cycle are subject to regional variation.

Geochemical and Mineralogical Approaches in Unraveling Paleoweathering, Provenance, and Tectonic Setting of the Clastic Sedimentary Succession (Western Central Paratethys)

Pronounced tectonic and paleogeographic changes were detected in the Alpine–Pannonian region during the Miocene at the interface between the Alps, the Dinarides, and the Pannonian Basin. To understand the major tectonic, paleogeographic, and paleoclimatic changes during this period, geochemical and mineralogical investigations were carried out on the fine-grained clastic sedimentary rocks in the Tunjice Hills. The paleoweathering indicates a cold and/or arid to a warm and humid period. The paleoclimate and the regional climatic conditions correspond well with the Middle Miocene Climatic Optimum. The mineral composition shows an abundance of quartz and calcite. Quartz is associated with detrital origin from volcanic and metamorphic rocks of the Eastern and Southern Alps and with authigenic processes in sediments. Calcite is related to authigenic origin formed in shallow marine environments and to detrital provenance from the Southern Alps. Not all discriminant functions based on major oxides provided adequate results in determining the tectonic setting. The source rocks were subjected to oceanic island arc and collision. Moreover, sedimentation was influenced by both active and passive margin settings. The former is related to the Alpine collision, which continued from the Cenozoic onward, and the latter is connected to the processes associated with the formation of the Pannonian Basin System, which began in the late Early Miocene.

Geochemistry of Miocene sediments of the Middle and South Caspian basins (within Azerbaijan): climate, chemical maturity and provenance

Geochemical and petrographic characteristics of the Miocene rocks of the Shamakhi-Gobustan trough (South Caspian basin) and the North Absheron uplift zone (Middle Caspian basin) indicate that these sediments contain products of erosion of the magmatic rocks of the Eurasian continent’s active margin - the volcanic arc of the Lesser Caucasus, as well as granitic basement of the Garabogaz High and Mesozoic-Eocene sedimentary strata of the Middle Caspian basin and the Greater Caucasus. The uplift of the Greater Caucasus, which began in the Middle Eocene as a result of the collision of the Afro-Arabian and Eurasian plates, brought to the exposure of the Mesozoic-Eocene sedimentary rocks of the Tethys Ocean that were deposited from the detrital material of the disintegrated igneous rocks of the Lesser Caucasus and the granitic basement of the Russian platform. The clastic material of these eroded Cretaceous-Eocene sedimentary rocks was accumulated in the Miocene basin that caused the geochemical characteristics of the Miocene sediments demonstrating the occurrence of igneous rocks of active margins or products of their erosion in the sources area. The accumulation of thick quartz-containing sand beds in the Chokrakian time (analogous to the Langhian stage) in a number of fields of the Shamakhi-Gobustan trough was the result of the exposure removal to the surface of quartz-rich Cretaceous rocks of the Greater Caucasus because of collisional processes, and their intensive erosion due to humidization of the climate during the Middle Miocene climatic optimum. Judging by the geochemical characteristics, during deposition of shale mudrocks the arid conditions prevailed. Keywords: Miocene; South Caspian and Middle Caspian basins; geochemistry; provenance; climate; geodynamic setting.

Environmental and taphonomic controls on the shell beds and fauna of the middle Miocene Chipola Formation of Florida, USA

Thick (2–10's m) and laterally extensive shell beds are common in the stratigraphic record, however, relatively little is known about their genesis since no single cause can explain the formation of these shell deposits. The goal of this study is to use lithologic, faunal, and taphonomic analyses to elucidate how the thick and laterally extensive shell beds of the middle Miocene Chipola Formation of Florida formed and became one of the most species-rich Cenozoic faunas in the western Atlantic Province. This study examined Chipola Formation outcrops at Alum Bluff, Cooter Bluff, and Farley Creek. Lithologic and trace fossil analyses indicate that the Alum Bluff shell bed represents an upper to middle shoreface setting, whereas the Farley Creek and Cooter Bluff shell beds represent lower shoreface and/or proximal offshore-transitional environments. Faunal data further support that Farley Creek and Cooter Bluff were deeper environments relative to Alum Bluff. Environmental preferences of most of the fauna indicate that all localities had normal, open-marine salinities with seagrass and unvegetated substrates. Samples are classified as within-habitat time-averaged assemblages, which were spatially averaged by various physical and ecological factors. Spatial averaging mixed the mosaic of communities that are represented by different types of substrate-controlled habitats within, but not across, significant variation in water depth. Finally, shell beds were accumulated by winnowing and/or high-energy events, such as storms, which produced the relatively thick, laterally extensive shell beds at each locality. Understanding the high diversity of the Chipola Formation is complicated and is likely best explained by multiple controls. Variation in alpha diversity among the localities is linked with differences in water depth as well as time and/or spatial averaging. The elevated diversity at each site was likely influenced by spatial averaging of habitats within a single depth zone, within-habitat time averaging, and poleward expansion of tropical taxa into the northern Gulf of Mexico due to environmental conditions associated with the middle Miocene Climatic Optimum. Similar poleward shifts of tropical taxa as those recorded in the Chipola Formation could hypothetically occur in the future as global temperatures and sea level rise. Future studies need to examine the biological changes associated with the middle Miocene Climatic Optimum to better understand the future impacts of ocean-climate change on marine communities.

U–Pb zircon ages, mapping, and biostratigraphy of the Payette Formation and Idaho Group north of the western Snake River Plain, Idaho: Implications for hydrocarbon system correlation

ABSTRACT Sedimentary deposits north of the western Snake River Plain host Idaho’s first and only producing oil and gas field. They consist of the lower to middle Miocene Payette Formation, the middle to upper Miocene Poison Creek and Chalk Hills Formations, and the Pliocene to lower Pleistocene Glenns Ferry Formation. Using new geochronology, palynomorph biostratigraphy, and geologic mapping, we connect updip surface features to subsurface petroleum play elements. The Payette Formation is a likely main source of the hydrocarbons, and acts as one of the reservoirs in the unnamed basin. Here, we redefine the Payette Formation as 0 to ~3,500 ft (0 to ~1,000 m) of mudstone, with lesser amounts of sandstone overlying and interbedded with the Columbia River Basalt Group and Weiser volcanic field. Index palynomorphs, including Liquidambar and Pterocarya, present in Idaho during and immediately after the middle Miocene climatic optimum, and new U–Pb ages of 16.39 and 15.88 Ma, help establish the thickness and extent of the formation. For the first time, these biostratigraphic markers have been defined for the oil and gas wells. The Poison Creek Formation is sandstone interbedded with mudstone that is ~800–1,800 ft (250–550 m) thick. The Chalk Hills Formation is a tuffaceous siltstone, claystone, and sandstone that is as much as ~4,200 ft (1,280 m) thick. New U–Pb ages are 10.1, 9.04, and 9.00 for the Poison Creek Formation, along with maximum depositional ages of 10.7 to 9.9 Ma for four samples from the Poison Creek Formation. A single U–Pb age of 7.78 Ma was determined from pumice low in the Chalk Hills Formation. Like the Payette Formation, the Poison Creek Formation can be a reservoir, whereas the Chalk Hills Formation acts as a sealing mudstone facies. The overlying sandstone, siltstone, and conglomerate of the Glenns Ferry Formation act as the overburden to the petroleum system in the subsurface, and were important for burial and hydrocarbon maturation. The Glenns Ferry Formation is up to 500 ft (150 m) thick in the study area, as much has been eroded. Whereas the Payette and Poison Creek Formations were deposited during the mid-Miocene climatic optimum amongst and above volcanic flows, the Chalk Hills and Glenns Ferry Formations were deposited within ancient Lake Idaho during an overall increase in aridity and cooling after the mid-Miocene climatic optimum.

Historical biogeography and evolutionary diversification of Lilium (Liliaceae): New insights from plastome phylogenomics

Here, we infer the historical biogeography and evolutionary diversification of the genus Lilium. For this purpose, we used the complete plastomes of 64 currently accepted species in the genus Lilium (14 plastomes were newly sequenced) to recover the phylogenetic backbone of the genus and a time-calibrated phylogenetic framework to estimate biogeographical history scenarios and evolutionary diversification rates of Lilium. Our results suggest that ancient climatic changes and geological tectonic activities jointly shaped the distribution range and drove evolutionary radiation of Lilium, including the Middle Miocene Climate Optimum (MMCO), the late Miocene global cooling, as well as the successive uplift of the Qinghai-Tibet Plateau (QTP) and the strengthening of the monsoon climate in East Asia during the late Miocene and the Pliocene. This case study suggests that the unique geological and climatic events in the Neogene of East Asia, in particular the uplift of QTP and the enhancement of monsoonal climate, may have played an essential role in formation of uneven distribution of plant diversity in the Northern Hemisphere.

Global warming drove the Mid-Miocene climate humidification in the northern Tibetan Plateau

The Miocene is a key transitional period for the Asian monsoon evolution and establishment of modern-like geomorphic landscapes in the northern Tibetan Plateau. Elucidating the Miocene paleoenvironmental changes and their relationships with climate and tectonics are significant in understanding future hydrological changes in the northern Tibet under a warming climate. In this study, detailed lithological and rock magnetic investigations were conducted on a Miocene fluvial-lacustrine sediment sequence from the Linxia Basin in Northeast Tibet, to understand the paleoenvironmental and palaeohydrological response to the tectonics and global climatic change, especially to the effects of the Middle Miocene Climatic optimum (MMCO). The results demonstrated that strong waterlogged reducing environments during MMCO precluded the occurrences of pedogenesis in the Linxia Basin owing to highly humid climates. As the precipitation decreased significantly before and after MMCO, pedogenesis occurred increasingly owing to temperate and well-drained conditions. A synthesis of the lithological and magnetic variations in Miocene fluvial-lacustrine sediments further indicated that climate humidification prevailed in most areas of the northern Tibetan Plateau during MMCO. These observations demonstrate that global climate change, rather than the tectonic uplift, significantly influenced the Mid-Miocene paleoenvironmental evolution in northern Tibet.

Simulation of the climate and ocean circulations in the Middle Miocene Climate Optimum by a coupled model FGOALS-g3

Simulation of the climate and ocean circulations in the Middle Miocene Climate Optimum by a coupled model FGOALS-g3

Neoisoptera repeatedly colonised Madagascar after the Middle Miocene climatic optimum

Madagascar is home to many endemic plant and animal species owing to its ancient isolation from other landmasses. This unique fauna includes several lineages of termites, a group of insects known for their key role in organic matter decomposition in many terrestrial ecosystems. How and when termites colonised Madagascar remains unknown. In this study, we used 601 mitochondrial genomes, 93 of which were generated from Malagasy samples, to infer the global historical biogeography of Neoisoptera, a lineage containing more than 80% of described termite species. Our results indicate that Neoisoptera colonised Madagascar between 7 and 10 times independently during the Miocene, between 8.4 and 16.6 Ma (95% HPD: 6.1–19.9 Ma). This timing matches that of the colonization of Australia by Neoisoptera. Furthermore, the taxonomic composition of the Neoisopteran fauna of Madagascar and Australia are strikingly similar, with Madagascar harbouring an additional two lineages absent from Australia. Therefore, akin to Australia, Neoisoptera colonised Madagascar during the global expansion of grasslands, possibly helped by the ecological opportunities arising from the spread of this new biome.

Latest Oligocene to middle Miocene low-latitude calcareous nannofossil biostratigraphy and paleoenvironmental interpretations of stratigraphic well 4, Sinú-San Jacinto onshore basin, northwest Colombia

Calcareous nannofossils are one of the main fossil groups used in the petroleum industry to determine the relative age and correlation of lithofacies identified in gas and oil wells. A limited number of biostratigraphic zonation schemes based on nanoplankton and paleoceanographic reconstructions have been suggested to onshore Colombian Caribbean. Most of them are compiled in several publications for the northern Colombian units (Mejía-Molina et al., 2008, 2010). In this study, a medium to high-resolution biostratigraphy study was carried out on one of the best-known Neogene sedimentary successions in the Sinú-San Jacinto onshore Basin, where the Stratigraphic Well 4 (SW4) was drilled by Ecopetrol, the Colombian state-run oil company. The nannoplankton biostratigraphic zonation proposed here constitutes the first calcareous nanoplankton research to construct a biochronologic scheme for the Neogene of northern Colombia, which has direct applications for oil exploration, global energy matrix and the transition to clean energy in the onshore areas of the Sinú-San Jacinto domain. The section studied has a thickness of ∼269 m and comprises mainly a very thick succession of claystone and mudstone with occasional intercalations of silty sandstones corresponding to the El Carmen Formation. The studied interval is assigned to the nannofossils Zones NP25 (CP19) to NN4 (CN3) of Martini (1971) and Okada and Bukry (1980), spanning from the latest Oligocene (latest Chattian) to middle Miocene (early Langhian), approximately 24 Ma to 15 Ma. Intervals without fossil content were identified in the record and could constitute hiatuses, but the nannofloral events, which define the limits of the biozones, can be identified. Global and regional climatic changes which occurred in the Caribbean region at those times are reflected in important changes in the fossil assemblages and abundance pattern of nanoplankton. These could indicate variability in environmental conditions linked to temperature and increased nutrients within the nannofossil communities in this part of the San Jacinto folded belt (SJFB), northwest Colombia. Middle Miocene Climate Optimum (MMCO) episodes of “blooming” intervals of Sphenolithus were identified, accompanied with a drastic reduction in total nannofossil abundance and CaCO3 content. Since the Caribbean geology is framed in a very complex scenario, the data acquired and presented in this research has a potential application to improve the current stratigraphy in the area, targeted to hydrocarbon exploration and studies related to the global energy matrix and the transition to clean energy. It also strengthens the paleoceanographic reconstructions based on these organisms at low latitudes.

A new Early–Middle Miocene phalangerid (Marsupialia: Phalangeridae) from the Riversleigh World Heritage Area, Boodjamulla (Lawn Hill) National Park, northwestern Queensland

Archerus johntoniae represents a new genus and species of phalangerid possum from the Early to Middle Miocene of the Riversleigh World Heritage Area, northwestern Queensland. The new taxon is the tenth extinct phalangerid species to be described and is the seventh species recognized from the diverse Riversleigh fossil assemblages. A. johntoniae has its closest morphometric affinities (such as relatively short molars, narrow premolars, an anteriorly narrow upper first molar, and posteriorly narrow fourth molars) with trichosurine and stem phalangerids. Morphologically, A. johntoniae has similarities to phalangerines and trichosurines, but is most dissimilar to other fossil phalangerids. The new species is one of the smallest (ca 1.3 kg) phalangerids known and may have occupied Early and Middle Miocene frugivorous/insectivorous niches demarcated from other phalangerids by body size and diet. A. johntoniae is one of a minority of Riversleigh species to have survived a significant decline in marsupial diversity associated with a rapid spike in global temperature at the Middle Miocene Climatic Optimum.Troy Myers [t.myers@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth & Environmental Sciences, UNSW Sydney, NSW 2052, Australia; Kirsten Crosby [Kirsten.crosby@gmail.com], GHD Group Pty Ltd, Level 15, 133 Castlereagh St, Sydney, NSW, 2000 (currently), School of Biological, Earth & Environmental Sciences, UNSW Sydney, NSW 2052, Australia.

Increased primary mineral dissolution control on a terrestrial silicate lithium isotope record during the middle Miocene Climate Optimum

Lithium isotopes have great potential to fractionate at subaerial environment, so they are promising proxies for tracing chemical weathering history. However, it remains uncertain how to relate lithium isotopic compositions (δ7Li) in sediments to silicate weathering and past climate in terrestrial setting. To tackle this question, we choose the warm and wet middle Miocene climate optimum (MMCO, 17–14 Ma) with large climate variation amplitude and the following cold and dry middle Miocene climate cooling period (MMCC, 14–11 Ma) with damped climatic variation amplitude, as two climate contrasting intervals to study lithium isotopes and content ([Li]) variations of terrestrial mudrocks. Our study site is located at the eastern Qaidam Basin of the northeastern Tibetan Plateau and the precipitation pattern of this part of the basin is similar to the Chinese Loess Plateau over the two studied intervals. The study site is suitable for clarifying link between climate and δ7Li variations because previous studies have demonstrated no provenance shift over the studied interval and short transport distance from source to the study site suggests little chemical weathering over the transportation process. Both δ7Li and [Li] values show larger amplitude over the MMCO (spanning from −1.2 to 3.2 ‰ and from 32.8 to 93.9 ug/g, respectively) than the MMCC interval (−1.8 to 1.2 ‰ and 41.7–80.8 ug/g, respectively), consistent with general feature of global and Chinese Loess Plateau climate. However, δ7Li data are higher over the MMCO in comparison with the MMCC, contrary to expectation of more lithium isotope fractionation at warm interval. We interpret the more positive δ7Li values over the MMCO using increased ratio of primary mineral dissolution over secondary mineral precipitation. Qaidam mudrock and benthic Li records show complementary changes, suggesting their possible link. Furthermore, past research reveals lack of focused uplift of the northeastern Tibetan Plateau over the studied 18–11 Ma. So we conclude that global climate, rather than Tibetan uplift, played an important role in modulating inland Qaidam Basin climate variations over the middle Miocene and that increased chemical weathering over warm climate can lead to a small magnitude of lithium isotope fractionation. Therefore, interpreting chemical weathering history, and hence climate, using lithium isotope data in terrestrial setting requires considering relative importance of primary mineral dissolution versus secondary mineral precipitation.

First fossil record of Pelekium (Thuidiaceae) from the middle Miocene Zhangpu amber in Asia

ABSTRACT Zhangpu amber is an important source of Miocene bryophytes in China. Zhangpu amber originates from the Middle Miocene Climatic Optimum (MMCO), which is well known for the appearance of Dipterocarpaceae-dominated megathermal forests in East Asia. The humid and warm climate of these forests might have triggered the development of diverse epiphytic bryophytes; however, the Middle Miocene fossils of bryophytes are rare in Asia. Here, we present evidence for Pelekium (Thuidiaceae) in Zhangpu amber. The fossil is characterised by: (i) regularly pinnate ramifications; (ii) deltoid leaves with a single and percurrent Costa; (ⅲ) abundant unbranched and uniseriate paraphyllia covering the stems and branches; (ⅳ) differentiated stem and branch leaves. It represents the first fossil record of Pelekium, showing that the genus already existed in Fujian, South China during the Middle Miocene. Our fossil enriches the Neogene fossil record of bryophytes in East Asia. Extant Pelekium species comprises stenoecious plants that are mainly distributed in tropical areas, often grow on bark in humid forests. The occurrence of fossil Pelekium from Zhangpu amber is in good accordance with the palaeoclimatic reconstruction based on the Climate Leaf Analysis Multivariate Program.

Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years

AbstractGlobal ice volume (sea level) and deep‐sea temperature are key measures of Earth's climatic state. We synthesize evidence for multi‐centennial to millennial ice‐volume and deep‐sea temperature variations over the past 40 million years, which encompass the early glaciation of Antarctica at ∼34 million years ago (Ma), the end of the Middle Miocene Climate Optimum, and the descent into bipolar glaciation from ∼3.4 Ma. We compare different sea‐level and deep‐water temperature reconstructions to build a resource for validating long‐term numerical model‐based approaches. We present: (a) a new template synthesis of ice‐volume and deep‐sea temperature variations for the past 5.3 million years; (b) an extended template for the interval between 5.3 and 40 Ma; and (c) a discussion of uncertainties and limitations. We highlight key issues associated with glacial state changes in the geological record from 40 Ma to present that require attention in further research. These include offsets between calibration‐sensitive versus thermodynamically guided deep‐sea paleothermometry proxy measurements; a conundrum related to the magnitudes of sea‐level and deep‐sea temperature change at the Eocene‐Oligocene transition at 34 Ma; a discrepancy in deep‐sea temperature levels during the Middle Miocene; and a hitherto unquantified non‐linear reduction of glacial deep‐sea temperatures through the past 3.4 million years toward a near‐freezing deep‐sea temperature asymptote, while sea level stepped down in a more uniform manner. Uncertainties in proxy‐based reconstructions hinder further distinction of “reality” among reconstructions. It seems more promising to further narrow this using three‐dimensional ice‐sheet models with realistic ice‐climate‐ocean‐topography‐lithosphere coupling, as computational capacities improve.

Enhanced ocean oxygenation during Cenozoic warm periods

Dissolved oxygen (O2) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming1,2. However, models provide an unclear picture of future ODZ change in both the near term and the long term3–6. The paleoclimate record can help explore the possible range of ODZ changes in warmer-than-modern periods. Here we use foraminifera-bound nitrogen (N) isotopes to show that water-column denitrification in the eastern tropical North Pacific was greatly reduced during the Middle Miocene Climatic Optimum (MMCO) and the Early Eocene Climatic Optimum (EECO). Because denitrification is restricted to oxygen-poor waters, our results indicate that, in these two Cenozoic periods of sustained warmth, ODZs were contracted, not expanded. ODZ contraction may have arisen from a decrease in upwelling-fuelled biological productivity in the tropical Pacific, which would have reduced oxygen demand in the subsurface. Alternatively, invigoration of deep-water ventilation by the Southern Ocean may have weakened the ocean’s ‘biological carbon pump’, which would have increased deep-ocean oxygen. The mechanism at play would have determined whether the ODZ contractions occurred in step with the warming or took centuries or millennia to develop. Thus, although our results from the Cenozoic do not necessarily apply to the near-term future, they might imply that global warming may eventually cause ODZ contraction.

Middle Miocene (Serravallian) wetland development on the northwest edge of Europe based on palynological analysis of the uppermost Brassington Formation of Derbyshire, United Kingdom

In this paper, we describe palynological assemblages in the Middle Miocene (Serravallian) Kenslow Member of the Brassington Formation at Bees Nest Pit, near Brassington, Derbyshire, U.K., and infer vegetation types and their palaeoclimate implications. The limited lateral extent of the 1.33 m-thick succession of clay and lignite, and its position surrounding fragments of a large tree trunk, suggests that the succession may have accumulated within a tree throw hole or possibly within a shallow stagnant pond, although aquatic lacustrine palynomorphs have not been identified to confirm this latter hypothesis. The stratigraphical distribution of palynological assemblages, based on 58 samples allows reconstruction of a wetland succession. Two pollen zones were identified using CONISS cluster analysis, and a predominantly warm-temperate and mixed mesophytic forest biome was recognised with Tsuga conifer pollen-types being dominant (<42%) in both pollen zones. Changes in the make-up of this forested wetland were in response to local environmental changes rather than major climatic shifts. Wetland development culminated in the formation of a relatively open shrub and reed-dominated mire which produced the lignite-precursor peat. Applying the Co-existence Approach, Mean Annual Temperature was 15.6–21.7 °C and Mean Annual Precipitation was 703–1682 mm indicating a warm-temperate to subtropical palaeoclimate, and both parameters show no significant change through the section. Findings suggest that, following the Middle Miocene Climatic Optimum, the Serravallian climate of the northwestern margin of Europe remained much wetter than Central Europe, where more arid climates have been reconstructed, and this difference may have been due to the influence of the proto-North Atlantic Current.

Early Miocene redwood fossils from Inner Mongolia: CO2 reconstructions and paleoclimate effects of a low Mongolian plateau

The early Miocene (~16–23 Ma) marks a critical transition in the Earth climate history from an Oligocene (~23–34 Ma) cooling trend towards the well-documented warm middle Miocene Climate Optimum at ~15 Ma. In eastern Asia, this transition links changes of key topographic features, such as the Tibetan plateau and the Mongolian plateau, and their impact on the reorganization of climate systems, such as the Eastern Asian summer monsoon. Yet the dynamics of the interplay among these factors remain poorly understood, precluding our understanding of future climate changes. Global temperatures during the early Miocene were warmer than the present day by 3–4 °C, which are seemingly incompatible with both the low (<300 ppm) and high (>800 ppm) ends of presently available reconstructions of atmospheric carbon dioxide (CO2). Here we report a rare co-occurrence of two redwoods, Metasequoia and Sequoia, from sediments of the early Miocene Hannuoba Formation in Zhuozi County in China’s Inner Mongolia at the southeastern margin of the current Mongolian plateau. The Zhuozi Metasequoia fossils possess uneven type cuticles, which dominate its living population but have rarely been reported throughout the abundant fossil record of this genus. By applying well-constrained Franks model parameters obtained from these redwood fossils using a cleared leaf epidermis method, we estimated the early Miocene CO2 level at ~400 ppm, putting it at the lower end of the model requirement for sustaining a relatively warm global temperature during this period. Our Franks model estimates are ~100 ppm higher than that obtained using stomatal index method based on Metasequoia material, further confirming a systematic underestimation of ancient CO2 using the Metasequoia stomatal index method reported in previous analyses. We recommend a re-examination of previous CO2 reconstructions solely based upon Metasequoia’s inverse relationship between stomatal index and CO2 concentrations. Ultimately, the occurrence of these redwood fossils in Inner Mongolia is consistent with a weak or muted Eastern Asian summer monsoon in the region with the absence of an elevated Mongolian plateau during the early Miocene. A shift of moisture sources for the region accompanying the change from a Westerlies-dominated climate to the present-day monsoon-dominated climate system occurred after the early Miocene time.

Phylogeography of Pholidopterini: Revising molecular clock calibration by Mid-Aegean Trench

Abstract The present study examines the phylogeography of Pholidopterini (Orthoptera, Tettigoniidae), a lineage distributed in the East Mediterranean and estimated substitution rates for the three mitochondrial and two nuclear gene segments. The last common ancestor of Pholidopterini was dated to 18 myr ago, in Early Miocene. Phylogeography of the lineage was marked with three waves of radiations, first during the Middle Miocene Climatic Optimum, the second during the Serravallian, and third during the ending of Messinian. The substitution rate estimations were 0.0187/0.018/0.0141/0.0010207 s/s/myr for COI/ND2/12S-tRNAval-6S/ITS1-5.8S rRNA-ITS2. The following main conclusions were drawn; (i) Radiation of Pholidopterini directed by the climatic shifts, (ii) signs of vicariant speciation were poor, contrary to the active tectonic history, (iii) the ultimate generic ancestors were dated to the Langhian and Serravallian, and (vi) the Tortonian transgression of Mid-Aegean Trench appears to be a reliable geographic calibration point for lineage splitting between Crete and Anatolia.

Long-lagged (∼19 Myr) response of accelerated river incision to rock uplift on the northern margin of the Tibetan Plateau

Quantifying tectonic-climatic interaction in shaping the margins of Tibetan Plateau is essential for understanding outward plateau growth. Here we investigate the histories of rock uplift and erosion along the northwestern margin of the Tibetan Plateau in the Altyn Shan, using low-relief high-elevation surfaces (LRHES) and combined bedrock and detrital apatite (U-Th)/He (AHe) analyses. Bedrock AHe dates and associated thermal modeling of samples collected from the mountain flank reveal a phase of very fast cooling starting at ∼36 Ma, followed by subsequent moderate cooling since ∼31 Ma. We argue that this pattern results from rock uplift caused by tectonic activity of the North Altyn fault (NAF), which separates the uplifted Altyn Shan from the low-lying Tarim Basin to the north. However, detrital AHe analysis and associated numerical modeling indicate that accelerated river incision in the Altyn Shan was delayed to as late as ∼17 Ma merely ∼10 km away from the NAF. Taken together, the data imply a long-lagged (∼19 Myr) response of accelerated river incision to tectonic-driven rock uplift. This delayed incision likely results from very low erosional efficiency associated with arid climate during the interval of ∼36 – 17 Ma, with increased erosional efficiency during the relatively wet climate of the middle Miocene climate optimum (∼17 – 14 Ma). These findings illustrate the interplay between tectonics and climate in developing landforms on the northern margin of the Tibetan Plateau, and bear implications for both the Cenozoic evolution of this margin, and, more broadly, thermochronometer-based study of rock uplift and erosion.

Multi-attribute geomorphological characterization of the Cenozoic deep-water strata in the Exmouth Plateau, Northern Carnarvon Basin: a contribution to the understanding of deep-water mixed carbonate–siliciclastic environments

Abstract The stratigraphic architecture and relationships to the expression of deep-water architectural elements geomorphology are explored for Cenozoic deposits in the Exmouth Plateau Sub-basin in Northern Carnarvon Basin. We used a high-quality 3D seismic survey and an integrated seismic attribute analysis to provide a guide for seismic interpretation of the mixed carbonate–siliciclastic depositional systems focused on four aspects: morphology, lithology, strata thickness and reflector distortion. Three depositional elements are classified into several categories: mass transport deposits (MTDs), channel systems (channel–levee and braided-like) and lobes, whose deposition is closely related to eustatic changes, and can be explained in a sequence stratigraphic framework. The falling stage system tract is characterized by the initial development of MTDs deposited on the basin floor and small erosive channels on the upper slope. Lobes are deposited in lowstand system tracts while highstand system tracts are characterized by the deposition of MTDs and progradational segments. This mixed carbonate–siliciclastic example proved to be sensitive to other variables such as climate (Middle Miocene Climate Optimum) and plate tectonics (northward Australian Plate drift), which affect geomorphological aspects such as the dimensions and preservation of internal characteristics.