Mid-Miocene Climatic Optimum Research Articles

Palaeoenvironmental reconstruction of the Konin Basin (central Poland) during lignite accumulation linked to the mid-Miocene climate optimum

We reconstruct palaeoenvironmental conditions during the formation of the first Mid-Polish Lignite Seam (MPLS-1) of the Konin Basin of central Poland, which is of mid-Miocene age. In terms of macropetrography, the MPLS-1 comprises different lithotype associations, predominantly xylodetritic lignite, and represents the peat deposits of mires most likely inhabited by Myricaceae-Cyrillaceae shrubs. Palynological assemblages obtained from the MPLS-1 at the Adamów Lignite Opencast Mine indicate the existence of wetland/palustrine and mesophytic vegetation during the accumulation of the peat. Applying the Coexistence Approach to the palynological assemblages, climate is inferred to have been warm temperate and humid with a mean annual temperature (MAT) of 15.7–18.0 °C with plant communities similar to modern pocosins developed on coastal plains in southeastern USA. The palynological assemblages from the MPLS-1 at Jóźwin IIB Lignite Opencast Mine show palaeofloristic cyclicality. In the studied section, five cycles were identified, dominated by swamp forests (Taxodium/Glyptostrobus–Nyssa) similar to modern forests in southeastern USA and China. The climate at that time was warm temperate and humid (MAT = 15.7–20.5 °C) based on CA application. This is consistent with the significant contribution of warm temperate plants, typical of mixed mesophilous forests, which grew in the vicinity of the swamp forests. The results of geochemical analyses are generally in agreement with palaeobotanical studies, indicating angiosperm dominated the peat-forming vegetation. However, the geochemically-derived average temperature ranges of ca. 24.2–25.0 °C, based on the carbon preference index (CPI), is significantly higher. These differences between palynologically- and geochemically-derived MATs can be explained by the influence of changes in vegetation on the CPI values. The periodic contribution of algae and microorganisms to the biomass while the water table was raised is indicated by elevated abundances of short-chain n-FAs. In contrast, under acidic conditions, bacterial activity was limited, as indicated by ββ/(ββ + αβ) hopane ratios and low sulfur content. Based on sedimentological data, the MPLS-1 was mainly formed either proximal (Jóźwin IIB, Tomisławice) or more distal (Adamów) to the river channels as evidenced by the presence or absence of siliciclastic partings within the MPLS-1. In summary, the MPLS-1 accumulated mostly as low-lying mires under freshwater conditions, corresponding to the last peak of the Mid-Miocene Climatic Optimum and to the period thereafter when the climate showed a cooling trend. Our findings are placed in the context of palaeotectonics and palaeoclimates at regional and global scales.

Iguanian lizards from the Split Rock Formation, Wyoming: exploring the modernization of the North American lizard fauna

Terrestrial ecosystems in North America changed substantially during the Neogene. Previous authors have documented changes in plants and mammals but squamates have received comparatively little attention. Several Miocene lizard fossils were described previously from the Split Rock Formation (Wyoming), which was deposited just before or during the mid-Miocene Climatic Optimum (c. 18–14 Ma). I re-evaluate the identifications of some of the previously published fossil lizards from the Split Rock Formation and describe several new fossil lizards. I focus on the iguanians and revise the biogeographical and temporal context for the evolution of several clades. I establish a minimum age for crown Phrynosomatidae and describe the oldest known occurrence of Crotaphytidae. The fossils provide evidence of a relatively modern lizard fauna in central North America by ∼17.5 Ma and support a substantial turnover from the Eocene to the middle Miocene. I also describe a new taxon, Caeruleodentatus lovei, with a distinctive dentary morphology. The revised iguanian lizard fauna is more diverse than previously described. I discuss difficulties and considerations with using apomorphies to identify fossils, biogeographical biases that affect fossil identifications, and the previous and future use of fossils from the Split Rock Formation in divergence time analyses. I recommend that comparative samples used for identifying fossils should not be intentionally limited by biogeography or stratigraphy, and underscore the importance of topology selection when constructing an apomorphy-based diagnosis. While apomorphy-based diagnoses may decrease taxonomic resolution of fossil identifications, they do not necessarily decrease our capacity to interpret the phylogenetic, biogeographical or ecological significance of fossils. http://zoobank.org/urn:lsid:zoobank.org:pub:F15984C6-144C-4110-A317-6714C6EEE295

New constraints on the palaeo-environmental conditions of the Eastern Paratethys: Implications from the Miocene Diatom Suite (Azerbaijan)

The Miocene Diatom Suite sediments of the Eastern Paratethys Sea, Azerbaijan, provide significant information to establish how Middle Miocene climate influenced erosion, sedimentation and deposition in the marine environments and continental source areas of Western Asia. Discriminant function analyses, ratios of Ti/Al, Si/Ca and Sr/Ca as well as mineralogical composition data indicate the Karaganian-Konkian sediments from the Pereküşkül-Diatom section were derived largely from the Greater Caucasus with a recognizable input from the Russian Platform during earliest Konkian. The chemical index of alteration and detrital clay mineral content document a change in climatic conditions from humid to relatively arid conditions occurred in the Greater Caucasus and Russian Platform area during the Karaganian-Konkian. The distribution of redox-sensitive elements across the Miocene Diatom Suite indicates oxic conditions prevailed in the Eastern Paratethys Sea Basin during the deposition of the Karaganian-Konkian sediments. Geochemical proxies suggest that, despite the Cenozoic been a period of global cooling, eastern Azerbaijan mainly characterised by a moderately humid to arid climate during this time. This indicates that warm climatic conditions, as seen during the mid-Miocene Climatic Optimum, were notably prolonged in the region of the Eastern Paratethys Sea basins and adjacent source areas, possibly reflecting palaeo-geographic changes in ocean and wind circulation patterns and/or local climate forcing associated with regional volcanic methane emissions.

An Early Neogene—Early Quaternary Contourite Drift System on the SW Barents Sea Continental Margin, Norwegian Arctic

AbstractThe onset and evolution of the middle to late Cenozoic “icehouse” world was influenced by the development of the global ocean circulation linking the Norwegian–Greenland Sea‐Arctic Ocean to the Atlantic Ocean. The evolution of the early Neogene to early Quaternary Bjørnøyrenna Drift, located at the SW Barents Sea continental margin, shed new light on this important hydrological event. By analyzing seismic data and exploration wellbores, it is found that the drift likely started to form in the early/middle Miocene, probably as a result of an ocean circulation reorganization following the opening of the Fram Strait gateway (c. 17 Ma) and subsidence of the Greenland–Scotland Ridge (c. 12 Ma). Thus, the onset of drift growth is considered to have happened close in time to the Mid Miocene Climatic Optimum at 16–14 Ma, and was part of a regional onset of large‐scale ocean circulation in the Norwegian–Greenland Sea that influenced the subsequent climate cooling. The drift continued to grow under the influence of early Quaternary glacimarine sedimentation, and later overtopping of the drift mound by downslope transfer of glacigenic sediments during full‐glacial conditions resulted in a submarine failure. For the first time, minimum average sedimentation rates of a Neogene to Quaternary drift in this area is calculated, giving rates of 0.020–0.031 m/Kyr. These values are comparable to average deep‐sea sedimentation rates from modern low‐latitude river systems such as the Amazon and Mississippi, but lower than the Quaternary glacial sedimentation rates from the Barents Sea and Fennoscandian continental margins.

Neogene climate evolution of the Tarim Basin, NW China: Evidence from environmental magnetism of the southern Tian Shan foreland

The Tarim Basin, located in the rain shadow of the Tibetan Plateau and other central Asian active orogens, is one of the most arid areas in the mid-latitude of the Northern Hemisphere. Its aridification history is important for understanding climate changes in the context of global cooling and regional tectonics. In this study, we present an environmental magnetism study of the early Miocene-early Pliocene (~20–4 Ma) terrestrial sediments in the Southern Tian Shan foreland. Magnetic parameters representing the relative/absolute concentrations of hematite in the sediments, together with color parameters, are used to reconstruct the Neogene climate evolution of the Tarim Basin. Our results reveal that the Tarim Basin was dominated by relative warm and wet climate between ~17 Ma and ~14 Ma, corresponding to the Mid-Miocene Climatic Optimum (MMCO), followed by three stepwise cooling/drying events at ~14 Ma, ~7 Ma and ~5.3 Ma, respectively. The dramatic cooling event at ~14 Ma is attributed to the expansion of East Antarctic Ice Sheet. The stepwise aridification at ~7 Ma and ~5.3 Ma in the Tarim Basin was controlled first-order by global cooling but superimposed by regional tectonics. The late Miocene aridification at ~7 Ma is partly due to the reduced moisture transport to the Tarim Basin related to the Mediterranean Salinity. Basin-wide extreme aridification since ~5.3 Ma is dominated by the final collision between Pamir and Tian Shan, which blocked the water-vapor brought by the westerlies from the Paratethys Sea to the downwind Tarim Basin.

The Oligo\u2013Miocene closure of the Tethys Ocean and evolution of the proto-Mediterranean Sea

The tectonically driven Cenozoic closure of the Tethys Ocean invoked a significant reorganization of oceanic circulation and climate patterns on a global scale. This process culminated between the Mid Oligocene and Late Miocene, although its exact timing has remained so far elusive, as does the subsequent evolution of the proto-Mediterranean, primarily due to a lack of reliable, continuous deep-sea records. Here, we present for the first time the framework of the Oligo–Miocene evolution of the deep Levant Basin, based on the chrono-, chemo- and bio- stratigraphy of two deep boreholes from the Eastern Mediterranean. The results reveal a major pulse in terrigeneous mass accumulation rates (MARs) during 24–21 Ma, reflecting the erosional products of the Red Sea rifting and subsequent uplift that drove the collision between the Arabian and Eurasian plates and the effective closure of the Indian Ocean-Mediterranean Seaway. Subsequently, the proto-Mediterranean experienced an increase in primary productivity that peaked during the Mid-Miocene Climate Optimum. A region-wide hiatus across the Serravallian (13.8–11.6 Ma) and a crash in carbonate MARs during the lower Tortonian reflect a dissolution episode that potentially marks the earliest onset of the global middle to late Miocene carbonate crash.

The Dawn of Desmatophocidae: A New Species of Basal Desmatophocid Seal (Mammalia, Carnivora) from the Miocene of Oregon, U.S.A.

ABSTRACT Desmatophocidae (Mammalia, Carnivora) represents the first of the four major pinniped clades to appear in the fossil record. However, the majority of its known diversity consists of derived species and little is known about the nascence of this early pinniped lineage. Here we report the discovery of Eodesmus condoni, gen. et sp. nov., represented by a nearly complete cranium from the Burdigalian Iron Mountain Bed of the Astoria Formation from the central coast of Oregon, U.S.A. Notably, this specimen possesses nasolabialis fossae, a plesiomorphic trait shared with stem pinnipedimorphs and the basal phocid Devinophoca sp., but not with any other desmatophocid. Phylogenetic analysis (98 characters, 27 taxa) resolved Eodesmus condoni as the most basal desmatophocid yet described. Poor support for the monophyly of Otarioidea, Odobenidae, and Phocoidea demonstrate that high-level relationships within Pinnipedia have yet to be conclusively resolved. The identification of another desmatophocid species at the already pinniped-rich Iron Mountain Bed suggests that the approximately synchronous mid-Miocene Climatic Optimum played a role in this increase in pinnipedimorph species diversity. http://zoobank.org/urn:lsid:zoobank.org:pub:C9335617-3A0D-414A-937A-72C859C0075F

Evaluating weathering of palaeosols in Cameroon (Central Africa) as a tool for paleoenvironmental reconstruction

Palaeosols formed from different igneous rocks have been identified and characterized in the humid savannas (1400 mm mean annual rainfall, 22 °C mean annual temperature) of the Adamaoua region in north-central Cameroon by means of macro- and micromorphology, geochemical analyses and bulk mineralogy. The studied sequence at Mangoli is about 11 m deep and is divided into three sections, in terms of weathering products: (1) Precambrian granite, located in the base; (2) vesicular porphyritic basalt, in the middle section; (3) aphanitic basalt in the uppermost layer. The products of weathering from the Precambrian granite consist of the following horizons, from bottom to top: a saprolite with granite structure, a yellowish to whitish fine saprolite, and Btg and Bt horizons. The saprolite horizon is dominated by quartz, feldspars (plagioclases and microcline), and muscovite. Primary minerals, except quartz, show weathering, while clay fills the pores and fractures and kaolinite dominates the clay mineralogy. The granite weathering products are slightly acidic (pH ranging from 5.9 to 6.3) and display low values of Fe extracted with dithionite-soluble Fe (Fed) and high Chemical Index of Alteration (CIA) and Mineral Index of Alteration (MIA) values. The middle section of the sequence consists of different areas of the basalt’s spheroidal weathering zone, from the more advanced to the less weathered phase. The clay mineralogy is dominated by kaolinite. The zones with the most alteration are the fractures, where thick, reddish clay coatings are observable. In these areas, the minerals are well crystallized. The kaolinite crystals share areas with Fe oxides. The upper section of the sequence constitutes the modern soil from the aphanitic basalt and consists of a spheroidal weathering zone divided into three horizons. The lowest is a C horizon, overlaid by Bt horizons. The C horizon shows a high degree of weathering in some areas, but it is still possible to identify the primary minerals. Their products of weathering are slightly acidic (pH = 6) and have high Fed, CIA and MIA values, which are indicative of intense weathering. The results suggest warm and humid climates during the formation of all of the palaeosols, similar to modern environmental conditions. We conclude that Palaeosol 1, formed from the granite, represents a soil formed during the Mid-Miocene Climatic Optimum, when the temperatures are assumed to have been 3–6 °C warmer than today. Features discovered during field investigations reveal that the former valley at the surface of the landscape has been filled by lava flows and today occupies the top of the plateau. Meanwhile, the former top of the plateau is located on the slopes and lower altitudes; the burial of soils by volcanic materials at Mangoli increased the altitudes of the former plateau and resulted in landscape inversion (slopes). These palaeosols and their top layers that induced the slope inversion have not yet been described and appear as a unique example worldwide.

Isotope sclerochronology indicates enhanced seasonal precipitation in northern South America (Colombia) during the Mid-Miocene Climatic Optimum

Abstract During the Mid-Miocene Climatic Optimum (MMCO, 14.7–17.3 Ma), global temperatures were warmer than present, and similar to predicted temperatures for the coming century. Limited paleoclimate data exist from the tropics during this period, despite its potential as an analog for future climate conditions. This study presents new subannual stable isotope data (δ18O and δ13C) from a large population of Miocene Turritella gastropods from the Jimol and Castilletes Formations of the Guajira Peninsula, Colombia. Turritellids are aragonitic marine mollusks that live in shallow coastal waters, and their rapid growth rates allow for high-resolution subannual records. We compare these fossils to modern Turritella gastropods from multiple tropical localities to reconstruct subannual climate conditions. The seasonal range in δ18O in the modern shells correlates with the seasonal variance of local precipitation, once temperature seasonality is accounted for. The Miocene fossils show larger (in some cases >2‰) seasonal variation in δ18O than modern Turritella from the same location, suggesting increased seasonality of precipitation in Miocene northern Colombia relative to today. We propose that this increased seasonality of precipitation was due to a more northerly position of the Intertropical Convergence Zone during the mid-Miocene. The resulting wet Miocene paleoenvironment is in stark contrast to semiarid conditions on the Guajira Peninsula today, indicating that this area of tropical South America has undergone a drastic environmental change since the Miocene.

The complete mitogenome of Arion vulgaris Moquin-Tandon, 1855 (Gastropoda: Stylommatophora): mitochondrial genome architecture, evolution and phylogenetic considerations within Stylommatophora.

Stylommatophora is one of the most speciose orders of Gastropoda, including terrestrial snails and slugs, some of which are economically important as human food, agricultural pests, vectors of parasites or due to invasiveness. Despite their great diversity and relevance, the internal phylogeny of Stylommatophora has been debated. To date, only 34 stylommatophoran mitogenomes were sequenced. Here, the complete mitogenome of an invasive pest slug, Arion vulgaris Moquin-Tandon, 1855 (Stylommatophora: Arionidae), was sequenced using next generation sequencing, analysed and compared with other stylommatophorans. The mitogenome of A. vulgaris measures 14,547 bp and contains 13 protein-coding, two rRNA, 22 tRNA genes, and one control region, with an A + T content of 70.20%. All protein coding genes (PCGs) are initiated with ATN codons except for COX1, ND5 and ATP8 and all are ended with TAR or T-stop codons. All tRNAs were folded into a clover-leaf secondary structure except for trnC and trnS1 (AGN). Phylogenetic analyses confirmed the position of A. vulgaris within the superfamily Arionoidea, recovered a sister group relationship between Arionoidea and Orthalicoidea, and supported monophyly of all currently recognized superfamilies within Stylommatophora except for the superfamily Helicoidea. Initial diversification time of the Stylommatophora was estimated as 138.55 million years ago corresponding to Early Cretaceous. The divergence time of A. vulgaris and Arion rufus (Linnaeus, 1758) was estimated as 15.24 million years ago corresponding to one of Earth’s most recent, global warming events, the Mid-Miocene Climatic Optimum. Furthermore, selection analyses were performed to investigate the role of different selective forces shaping stylommatophoran mitogenomes. Although purifying selection is the predominant selective force shaping stylommatophoran mitogenomes, six genes (ATP8, COX1, COX3, ND3, ND4 and ND6) detected by the branch-specific aBSREL approach and three genes (ATP8, CYTB and ND4L) detected by codon-based BEB, FUBAR and MEME approaches were exposed to diversifying selection. The positively selected substitutions at the mitochondrial PCGs of stylommatophoran species seems to be adaptive to environmental conditions and affecting mitochondrial ATP production or protection from reactive oxygen species effects. Comparative analysis of stylommatophoran mitogenome rearrangements using MLGO revealed conservatism in Stylommatophora; exceptions refer to potential apomorphies for several clades including rearranged orders of trnW-trnY and of trnE-trnQ-rrnS-trnM-trnL2-ATP8-trnN-ATP6-trnR clusters for the genus Arion. Generally, tRNA genes tend to be rearranged and tandem duplication random loss, transitions and inversions are the most basic mechanisms shaping stylommatophoran mitogenomes.

Magnetochronology of Mid-Miocene mammalian fauna in the Lanzhou Basin, northeastern Tibetan Plateau: Implications for Asian mammal migration

The Quantougou (QTG) Fauna in central Lanzhou Basin is an important late Mid-Miocene fauna on the northeastern Tibetan Plateau margin, but its numerical age remains a matter of debate. Here, we present a new magnetostratigraphic record for a fluvio-lacustrine section to further constrain the age of the QTG Fauna. Results suggest that the studied section spans from polarity chrons C5Cn.2n to C5n.2n or C5An.1n, with ages of ca. 16.5 Ma to 10 ​Ma or 16.5 Ma to 12 ​Ma. The QTG Fauna is located at the top of polarity chron C5r.3r or C5Ar.2r, which corresponds to an age of 11.7 Ma or 12.8 ​Ma for the fauna. Accordingly, the associated Myocricetodontinae (a subfamily of Gerbillidae, Rodentia) is suggested to have appeared in the Lanzhou Basin at 11.7 ​Ma or 12.8 ​Ma, which is the oldest Myocricetodontinae in East Asia but is still much younger than the ~20 ​Ma appearance of this subfamily in West and South Asia. Our age data support the interpretation that East Asian Myocricetodontinae originated from South Asia. The QTG fauna further suggest a dry and open grassland environment, which is consistent with global cooling after the Mid-Miocene Climatic Optimum.

Stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid-Miocene Climatic Optimum, in Idaho, U.S.A

The effects of global climate change are manifested at the regional level; consequently, evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional-scale climate data. Here we test whether climate change influenced faunal and floral patterns leading up to, and during, the mid-Miocene Climatic Optimum (MMCO) based on datasets collected in the Railroad Canyon section (RCS), central-eastern Idaho, U.S.A. Specifically, we use isotope compositions of herbivore tooth enamel to investigate how Mean Annual Precipitation (MAP), Mean Annual Temperature (MAT), Cold Month Mean Temperature (CMMT), and temperature seasonality varied through the RCS and how this local record compares to global climate reconstructions. Isotope compositions of teeth from the fossil equid Merychippus and rhinocerotid Diceratherium were compared across five time bins from c. 23 to c. 15 Ma. Bulk δ18O values of both taxa indicate that meteoric water compositions were unchanged through the study interval (consistently c. −15.6‰) but were c. 1.9‰ higher than current regional meteoric water. This difference points to warmer climates in central-eastern Idaho during the Miocene, post-middle Miocene topographic uplift in western North America, and/or shifts to air mass trajectories. Serial sampling of enamel shows seasonal fluctuations in water compositions and temperature. Bulk δ13C values indicate an average MAP of 190 (range: 10–510 mm·yr−1), with no significant change through the study interval, comparable to today's MAP (236 mm·yr−1). The reconstructed semi-arid, seasonal, warm climate for the RCS agrees with phytolith assemblage data from the same strata indicating dominantly open, grassy habitats. However, it is inconsistent with previously held ideas of warm-wet mid-Miocene climates in the northern Rocky Mountains (NRM) based on paleosol analyses. Our inferred, stable climate conditions for the MMCO of the NRM contrast with coeval records from Europe and Asia indicating sustained or enhanced warm and wet climates. These differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change.

A Cenozoic Great Barrier Reef on Australia's North West shelf

Abstract The Great Barrier Reef of Australia is the largest modern coral reef system on Earth. However, a similar-sized barrier reef (~2000 km long) existed on Australia's north-western margin in the middle Miocene and to some extent, still exists today. Seismic profiles reveal that this reef system was first initiated in the late Paleogene (~34–28 Ma) and reached its zenith as a prograding barrier reef during the middle Miocene (16–15 Ma). This giant reef system backstepped in the late Miocene (~10 Ma), forming a series of isolated atolls and pinnacle reefs. These remaining reefs were gradually extinguished, leaving only a few surviving isolated atolls today (Rowley Shoals, Scott Reef, Seringapatam Reef and Ashmore Reef). The distribution of these extant reefs therefore outlines the former presence of the mid-Miocene Great Barrier Reef of the Australian North West Shelf. This middle Miocene shallow-water rimmed-reefal shelf grew contemporaneously on a deeper-water heterozoan ramp, producing an unusual mixed heterozoan/photozoan carbonate system for most of its length. The initiation of reef growth appears related to Australia's northward drift into lower latitudes, combined with warm mid-Miocene climatic optimum conditions. However, the sudden and simultaneous initiation of reef growth in the mid-Miocene across the North West Shelf was probably also related to changes in paleoceanography (increased aragonite saturation and/or nutrient-depletion) perhaps influenced by changing climatic conditions (increased aridity). From the late Miocene (~10 Ma) to Holocene, high rates of subsidence across the North West Shelf probably set the scene for ultimate demise of this giant barrier reef system and led to widespread backstepping with the development of a series of isolated atolls and pinnacle reefs. It is likely that other paleoceanographic and climatic events (like nutrient supply, carbonate saturation, eustasy etc) combined with continued high subsidence rates acted to gradually extinguish the reef system in a series of steps over a period of 10 million years. The onset (~1 Ma) of a strong Leeuwin Current (with the delivery of warm and nutrient depleted water from the north) and its effect on the Quaternary reefs of the Western Australian coast is a good example of a paleoceanographic process that would be difficult to recognize in an ancient setting. It is likely that similar paleoceanographic events have controlled the rich and complex history of reef growth and drowning since the mid-Miocene on the North West Shelf.

Composition of lipids from the First Lusatian lignite seam of the Konin Basin (Poland): Relationships with vegetation, climate and carbon cycling during the mid-Miocene Climatic Optimum

Samples of detrital lignite have been collected for detailed organic geochemical and carbon isotope analyses from the First Lusatian lignite seam at the Adamów, Jóźwin IIB and Tomisławice opencast mines, deposited after the last peak of the Mid-Miocene Climatic Optimum. Carbon isotopic compositions of biomarkers from Polish lignite are reported for the first time. The aim of the study is to improve the chemotaxonomic value of biomarkers by relating the results to existing paleobotanical data, and to gain information about the influencing factors on δ13C of lignite and lipids. Furthermore, biomarker and isotopic proxies are tested for their applicability in paleoclimate studies.The molecular composition of the extracted lipids is highly variable, including leaf-wax n-alkanes in the C23 to C31 range, diterpenoids, hopanoids, and angiosperm-derived triterpenoids, as well as saturated fatty acids, long-chain n-alkanols and n-alkan-2-ones. The relative abundances of mid-chain (C23, C25) n-alkanes and their 1–2‰ higher δ13C values compared to long-chain n-alkanes (C29, C31) argue for a minor contribution of macrophytes (graminoids, etc.) to peat formation, enhanced during periods of raised water level. The presence of ferruginol and dehydroferruginol testifies the contribution of Taxodiaceae. The abundances of pimarane-type diterpenoids and the presence of non-aromatic abietane-derivatives argue for the contribution of Pinaceae. Based on the presence of lupeol and lupane-type triterpenoids, an input of Betulaceae can be concluded. The contribution of further angiosperms cannot be specified based on the composition of pentacyclic triterpenoids. However, the results indicate mixed vegetation, and are in agreement with paleobotanical data highlighting abundant conifers of the Taxodiaceae/Cupressaceae and Pinaceae families, as well as angiosperms of various families (e.g., Nyssa, Quercus, Fagus), including Betulaceae (e.g., Alnus, Betula, Corylus). Based on the relationship between the carbon preference index of n-alkanes and mean annual air temperatures, obtained from a global database of peatlands, an average temperature of 24.5 °C is obtained. This value is significantly higher as estimated from paleobotanical data (15.7–19.7 °C), probably due to the influence of changes in vegetation on carbon preference index.The relative abundances of diterpenoids versus di- plus angiosperm-derived triterpenoids in detrital lignite samples revealed variable contributions of gymnosperms and angiosperms during the middle Miocene. Consistent with these results, a positive relationship exists between the di-/(di- + tri-) terpenoid biomarker ratios and δ13C of lignite samples, indicating the dominating role of varying gymnosperm/angiosperm contributions on the carbon isotopic composition of lignite. The C-isotope data of long-chain n-alkanes, diterpenoids, and angiosperm-derived triterpenoids co-vary within the profiles, arguing for an overall control of changes in δ13C of atmospheric CO2 on δ13C of plant lipids. Fluctuations in δ13C of individual compounds may also be related to changes in carbon cycling within the peat, humidity and air temperature. The influence of local variations in ambient CO2 (e.g., the canopy effect) cannot be excluded.

Temporal patterns of diversification in Brassicaceae demonstrate decoupling of rate shifts and mesopolyploidization events.

Whole-genome duplication (WGD) events are considered important driving forces of diversification. At least 11 out of 52 Brassicaceae tribes had independent mesopolyploid WGDs followed by diploidization processes. However, the association between mesopolyploidy and subsequent diversification is equivocal. Herein we show the results from a family-wide diversification analysis on Brassicaceae, and elaborate on the hypothesis that polyploidization per se is a fundamental driver in Brassicaceae evolution. We established a time-calibrated chronogram based on whole plastid genomes comprising representative Brassicaceae taxa and published data spanning the entire Rosidae clade. This allowed us to set multiple calibration points and anchored various Brassicaceae taxa for subsequent downstream analyses. All major splits among Brassicaceae lineages were used in BEAST analyses of 48 individually analysed tribes comprising 2101 taxa in total using the internal transcribed spacers of nuclear ribosomal DNA. Diversification patterns were investigated on these tribe-wide chronograms using BAMM and were compared with family-wide data on genome size variation and species richness. Brassicaceae diverged 29.9 million years ago (Mya) during the Oligocene, and the majority of tribes started diversification in the Miocene with an average crown group age of about 12.5 Mya. This matches the cooling phase right after the Mid Miocene climatic optimum. Significant rate shifts were detected in 12 out of 52 tribes during the Mio- and Pliocene, decoupled from preceding mesopolyploid WGDs. Among the various factors analysed, the combined effect of tribal crown group age and net diversification rate (speciation minus extinction) is likely to explain sufficiently species richness across Brassicaceae tribes. The onset of the evolutionary splits among tribes took place under cooler and drier conditions. Pleistocene glacial cycles may have contributed to the maintenance of high diversification rates. Rate shifts are not consistently associated with mesopolyploid WGD. We propose, therefore, that WGDs in general serve as a constant 'pump' for continuous and high species diversification.

Rock magnetic constraints for the Mid-Miocene Climatic Optimum from a high-resolution sedimentary sequence of the northwestern Qaidam Basin, NE Tibetan Plateau

The thick sequence of Cenozoic deposits in the Qaidam Basin of the NE Tibetan Plateau has great potential for understanding the tectonic and climatic evolution of the region. In this study, we performed detailed rock magnetic analyses of a well-dated (~20.7–11.2 Ma) Upper Cenozoic sedimentary sequence from the Huatugou (HTG) section in the NW Qaidam Basin. The magnetic susceptibility of the sequence is relatively low before 17.4 Ma, high during 17.4–14.5 Ma, and lower after 14.5 Ma again. This pattern is consistent with the occurrence of the Mid-Miocene Climatic Optimum (MMCO) during 17.4–14.5 Ma, with global climatic cooling thereafter. Measurements of multiple rock magnetic parameters indicate a peak in the concentration of fine-grained magnetic minerals during 17.4–14.5 Ma. This feature demonstrates that the enhancement of the magnetic susceptibility is due to the pedogenic production of superparamagnetic (SP) and single domain (SD) magnetite, suggesting the occurrence of relatively high effective precipitation and high temperature in the Qaidam Basin at this time. Comparing with regional and global climatic records, the warm and humid climatic conditions coincide with the MMCO, implying that global climate changes were responsible for the climatic evolution in the Qaidam Basin throughout the MMCO. However, after 14.5 Ma, the rapid uplift of the northern Tibetan Plateau caused it to reach a critical elevation which blocked the moisture supply to the Qaidam Basin and may also have contributed to the observed climatic changes.

Early Miocene climate and biomes of Turkey: Evidence from leaf fossils, dispersed pollen, and petrified wood

The early Miocene was a period of major palaeogeographic reorganization in the eastern Mediterranean region, during which time the Anatolian Plateau became subaerial and several intracontinental basins intermittently became connected to the Paratethys and Mediterranean seas. In this paper, we analyse early Miocene vegetation and climate using leaf records, palynological assemblages, and fossil wood at 36 localities from western and central Turkey, most of which have precise age control based on radiometric dating and mammal faunal ages. Using the leaf flora of Güvem (Beş Konak, Keseköy), Climate Leaf-Analysis Multivariate Program (CLAMP) analyses and Köppen signatures were employed to infer a palaeoclimate typical of modern laurel forest regions. Based on the palynological records, abundance of various pollen-taxa was used as a measure of openness of vegetation and regional presence of major tree taxa. Most pollen floras are dominated by tree pollen (ranging from 85 to 98%) and indicated widespread afforestation. In the pollen diagrams, shifts in dominance from swamp forest elements (Taxodioideae) to well-drained forests (Pinaceae) indicate changes in lake levels or phases of basin development. Such shifts may have been associated with the development of more xeric forest vegetation. Wood anatomical features such as false tree rings further may indicate seasonal climate. Pollen diagrams and macrofossils reflect zonal and azonal broadleaf and needleleaf forest and extrazonal open vegetation. The latter occurred in areas with shallow soils on volcanic rocks or limestone (e.g. cycads, Dracaena), or coastal areas (herb dominance). Taxonomic composition and biogeographic affinities suggest laurel forest as a major forest biome on well-drained soils and ecotones between laurel forest and broadleaf deciduous forest biomes. A comparison with younger floras shows that these are neither more diverse nor more warmth-loving despite an increase in global temperature (Mid-Miocene Climatic Optimum) suggesting bottlenecks during previous (Oligocene) cooler times for warmth-loving taxa.

Rates of niche and phenotype evolution lag behind diversification in a temperate radiation

Environmental change can create opportunities for increased rates of lineage diversification, but continued species accumulation has been hypothesized to lead to slowdowns via competitive exclusion and niche partitioning. Such density-dependent models imply tight linkages between diversification and trait evolution, but there are plausible alternative models. Little is known about the association between diversification and key ecological and phenotypic traits at broad phylogenetic and spatial scales. Do trait evolutionary rates coincide with rates of diversification, are there lags among these rates, or is diversification niche-neutral? To address these questions, we combine a deeply sampled phylogeny for a major flowering plant clade-Saxifragales-with phenotype and niche data to examine temporal patterns of evolutionary rates. The considerable phenotypic and habitat diversity of Saxifragales is greatest in temperate biomes. Global expansion of these habitats since the mid-Miocene provided ecological opportunities that, with density-dependent adaptive radiation, should result in simultaneous rate increases for diversification, niche, and phenotype, followed by decreases with habitat saturation. Instead, we find that these rates have significantly different timings, with increases in diversification occurring at the mid-Miocene Climatic Optimum (∼15 Mya), followed by increases in niche and phenotypic evolutionary rates by ∼5 Mya; all rates increase exponentially to the present. We attribute this surprising lack of temporal coincidence to initial niche-neutral diversification followed by ecological and phenotypic divergence coincident with more extreme cold and dry habitats that proliferated into the Pleistocene. A lack of density-dependence contrasts with investigations of other cosmopolitan lineages, suggesting alternative patterns may be common in the diversification of temperate lineages.

Origin and evolution of halite based on stable isotopes (δ37Cl, δ81Br, δ11B and δ7Li) and trace elements in Tuz Gölü Basin, Turkey

The Tuz Gölü basin located in Central Anatolia contains ancient (Miocene) and recent evaporite deposits. The aim of this study is to determine the origin and evolution of the ancient halite deposits in the basin, particularly whether there is a marine origin. For this purpose, the mineralogical, geochemical and isotopic properties of halite samples taken from three different drillings at the southern part of the Tuz Gölü basin were determined. Halite samples in the Tuz Gölü basin are characterized by Cl (60.20–61.00%), Na (39.00–39.40%) and Br (5-637 ppm) contents. The Cl−, Br−, Ca, Mg2+, SO42−, and K+ values and Cl/Br (948-86428) ratios indicated that during the formation of the ancient halites in the Tuz Gölü basin, the mixture of solutions had different compositions/origins and that the dissolution, recrystallization and dedolomitization mechanisms were effective.The δ81Br, δ37Cl, δ7Li, and δ11B isotopic compositions of the pure halites range from −0.06 to 0.82, −0.80 to 1.28, −0.70 to 30.60 and −14.70 to 11.60, respectively. The low δ37Cl (from −0.06 to 0.06‰), low δ81Br (from 0.03 to 0.95‰), high δ 11B (from −6.40–11.60‰) and high δ7Li (from 26.00 to 30.60‰) values clearly indicate that the brine involved in the formation of the halites of the Tuz Gölü basin was largely derived from seawater during the Mid-Miocene Climatic Optimum (MMCO) period. Additionally, the Cl−, Br−, Ca2+, Mg2+, and SO42− contents, as well as the intermediate δ81Br (0.34–0.95‰) values of the Tuz Gölü samples, indicated that the origin of the ancient halites in the basin is not only a marine composition but also a mixture of solutions having different compositions, ratios or origins (e.g., seawater or saline water and groundwater/fresh water).

The Mid Miocene Climatic Optimum (MMCO) Indication at Low Latitude Sediment Case Study: The Miocene Cibulakan Formation, Bogor Basin, Indonesia

Middle Miocene Climatic Optimum (MMCO) is widely distributed and associated with increasing temperature and CO2 content in the atmosphere. The effects of MMCO are identified in the mid-latitude region, with lack of examples from the low latitude areas. In this study, we aim to determine the effect of MMCO at Cibulakan Formation of Bogor Basin, Indonesia, which is situated in lower latitude. We took 58 samples from the Cibulakan Formation, which is exposed along Cileungsi River, for quantitative nannoplankton (the abundance of Helicosphaera carteri) analysis to mark increasing and decreasing salinity event, as they are sensitive to temperature. Temperature relates to the salinity of the seawater due to evaporation. From our analysis, we identified sea surface temperature change in Early Miocene which was presumably due to small scale Early Miocene glaciation and active tectonic during the period. The warmer temperature took place on Middle Miocene as the effect of a warm and open sea environment during Mid Miocene Climatic Optimum. Afterward, the temperature continued to rise until the late Miocene, as it had been triggered by the increasing global temperature at the Pacific Ocean and widely distributed clean water at North West Java Basin during the depositional period.