Warm Phase Research Articles

Hydro-climatological variability in Lagunas de Vilama System, Argentinean Altiplano-Puna Plateau, Southern Tropical Andes (22° S), and its response to large-scale climate forcings

The Altiplano-Puna Plateau holds several shallow lakes, which are very sensitive to climate changes. This work is focused on a high-altitude lake system called Lagunas de Vilama (LVS), located in a complex climatic transition area with scarcity of continuous and homogeneous instrumental records. The objective of this study is to determine the regional spatial–temporal variability of precipitation and evaluate the seasonal and interannual lake responses. We use a lake-surfaces record derived from Landsat images to investigate links with regional precipitations and different climatic forcings. The results reveal that austral summer and autumn precipitations control the variability of the annual lake-surfaces. Also, we found intra-annual and interannual lags in the lake responses to precipitations, and identified several wet and dry stages. Our results show negative trends in precipitations and lake-surfaces, whose were strengthened by a shift to a warm phase of the Atlantic Multidecadal Oscillation in the 1990s. The El Niño Southern Oscillation, Pacific Decadal Oscillation, and Southern Annular Mode also exert a strong influence in the region. This study demonstrates that the variability of LVS lakes is strongly related to the South American Monsoon System dynamics and large-scale climate forcings from the Pacific and Atlantic Oceans. This work provides novel indices which demonstrated to be good indicators of regional hydro-climatological variability for this region of South America.

Drivers of river reactivation in North Africa during the last glacial cycle

North African greening phases, during which large rivers ran through the Sahara Desert, occurred repeatedly during the Quaternary and are regarded as key periods for the development of past human populations. However, the timing and mechanisms responsible for the reactivation of the presently dormant fluvial systems remain highly uncertain. Here we present hydroclimate changes over the past 160,000 years, reconstructed from analyses of the provenance of terrestrial sediments in a marine sediment record from the Gulf of Sirte (offshore Libya). By combining high-resolution proxy data with transient Earth system model simulations, we are able to identify the various drivers that led to the observed shifts in hydroclimate and landscapes. We show that river runoff occurred during warm interglacial phases of Marine Isotope Stages 1 and 5 due to precession-forced enhancements in the summer and autumn rainfall over the entire watershed, which fed presently dry river systems and intermittent coastal streams. In contrast, shorter-lasting and less-intense humid events during glacial Marine Isotope Stages 3 and 4 were related to autumn and winter precipitation over the Libyan coastal regions driven by Mediterranean storms. Our results reveal large shifts in hydroclimate environments during the last glacial cycle, which probably exerted a strong evolutionary and structural control on past human populations, potentially pacing their dispersal across northern Africa. The presence of large rivers in North Africa critical for Quaternary human migrations were controlled by a combination of orbital forcing and Mediterranean storminess, according to terrestrial proxy records from a marine core off Libya integrated with paleoclimate modelling.

Exploring a link between the Middle Eocene Climatic Optimum and Neotethys continental arc flare-up

Abstract. The Middle Eocene Climatic Optimum (MECO), a ∼500 kyr episode of global warming that initiated at ∼ 40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming.

First record of soft-winged flower beetles (Coleoptera, Malachiidae) in a late Pleistocene deposit from West Siberia with a review of known Quaternary data

Soft-winged flower beetles (Coleoptera, Malachiidae), Apalochrus femoralis pallipes Motschulsky, 1860 and Ebaeus Erichson, 1840 species, are recorded for the first time from Quaternary fossils in the deposit Ustyanka-1 near Ustyanka river, the right tributary of Alei river in Altaiskii Krai, West Siberia, Russia. The strata containing malachiid fragments belong to the warm phase of the late glacial succession. It is shown that soft-winged flower beetles are typical of Holocene deposits and practically unknown from cold phases of the Pleistocene, except in the case of Protapalochrus Evers, 1987 which has been recorded from the Pleistocene. Illustrations of the external appearance of both male and female of the beetles, and sub-fossil remains of Apalochrus femoralis pallipes Motschulsky, 1860 and three species from the Ebaeus rufipes-group distributed in the region are given, together with details of their position within the Ustyanka-1 deposit. Data on the Malachiidae in Quaternary deposits of the Northern Hemisphere are briefly reviewed.

Interactions of a shock with a molecular cloud at various stages of its evolution due to thermal instability and gravity

ABSTRACT Using the adaptive mesh refinement code mg, we perform hydrodynamic simulations of the interaction of a shock with a molecular cloud evolving due to thermal instability (TI) and gravity. To explore the relative importance of these processes, three case studies are presented. The first follows the formation of a molecular cloud out of an initially quiescent atomic medium due to the effects of TI and gravity. The second case introduces a shock whilst the cloud is still in the warm atomic phase, and the third scenario introduces a shock once the molecular cloud has formed. The shocks accelerate the global collapse of the clouds with both experiencing local gravitational collapse prior to this. When the cloud is still atomic, the evolution is shock dominated and structures form due to dynamical instabilities within a radiatively cooled shell. While the transmitted shock can potentially trigger the TI, this is prevented as material is shocked multiple times on the order of a cloud-crushing time-scale. When the cloud is molecular, the post-shock flow is directed via the pre-existing structure through low-density regions in the inter-clump medium. The clumps are accelerated and deformed as the flow induces clump–clump collisions and mergers that collapse under gravity. For a limited period, both shocked cases show a mixture of Kolmogorov and Burgers turbulence-like velocity and logarithmic density power spectra, and strongly varying density spectra. The clouds presented in this work provide realistic conditions that will be used in future feedback studies.

Seabird reproductive responses to changing climate and prey communities are mediated by prey packaging

Climatic factors drive changes in forage fish communities and may influence the productivity of piscivorous predators, but specific mechanisms of response remain poorly known. Between 1984 and 2020, we studied the rhinoceros auklet Cerorhinca monocerata, a seabird breeding in the western North Pacific at Teuri Island, Japan. We tested the hypothesis that climate-mediated prey-switching affects ‘food packaging’ (i.e. the way energy is brought to dependent offspring) and breeding success by quantifying relationships between climate, prey energy density, amount of food delivered, and the growth and survival of chicks. Prey composition switched 4 times: 1988-1992, 1997-1998, 2013-2014, and 2017-2018. All but the last of these switches were associated with (lagged) shifts in seawater temperature/Pacific Decadal Oscillation. Rhinoceros auklets brought multiple fish in each meal-load to chicks, and numbers were inversely correlated with the size of the fish. These relationships varied between fish species. The heaviest meal-loads were achieved when diets were dominated by anchovy Engraulis japonicas, which occurred during warm phases (1992-2013). Chick production, growth rates, and mass at fledgling were also highest during the warm phases. This study shows that climate affects seabird reproduction by shifting the manner in which food is selected relative to changes in forage fish community structure and abundance.

Anomalous changes of temperature and ozone QBOs in 2015−2017 from radiosonde observation and MERRA-2 reanalysis

Anomalous changes of zonal wind quasi-biennial oscillation (QBO) in winter 2015−2016 have received close attention. Combining radiosonde and satellite observations and reanalysis data, we investigate anomalous changes in temperature and ozone QBOs from the lower to middle stratosphere. As wind shear direction is reversed due to unexpected changes of zonal wind QBO at about 24−30 km, the shortest cold phase at 21−27 km appears in temperature QBO. This is different from the completely interrupted westward phase in zonal wind QBO, while the longest cold phase above almost 27 km lasts for 2−3 years from 2015 to 2017, owing to the absence of corresponding warm phase. Meridional scale reduction of temperature QBO causes a small temperature anomaly, thus the thermal wind relationship looks seemingly different from that in the other regular QBO cycles. QBO in the ozone mixing ratio anomaly shows a double-peak with inverse phase, and its phase below (above) 30 km is in agreement with (opposite to) the phase of temperature QBO because of different control mechanisms of ozone. Following temperature QBO variation, QBO in the ozone mixing ratio anomaly exhibits a less positive phase at 20−30 km in 2016−2017, and a very long positive phase above 30 km from 2015 to 2017. QBO in total column ozone shows a small peak in winter 2016−2017 since ozone is mainly concentrated at 20 to 30 km. Anomalous changes of temperature and ozone QBOs due to unexpected QBO zonal wind variation can be well-explained according to thermal wind balance and thermodynamic balance.

Water evaporation model of a catalyst converter in the context of hybrid electric vehicles energy and pollutants management

The energy and pollutants management of Hybrid Electric Vehicles (HEV) consists in determining at each instant the optimal torque split between the Internal Combustion Engine (ICE) and the Electric Motor (EM). This torque choice aims to minimize both fuel consumption and pollutants emissions. A critical piece of information in this context is the value of the Three-Way Catalyst Converter (3WCC) conversion efficiency. This value is highly dependent on the 3WCC temperature; it is hence of major importance to have an accurate estimation of it. Although the literature is abundant about simple 0D thermal models of 3WCC, it is tempting to implement a more accurate and consequently complex model. In particular, both moisture from the exhaust gases during engine start and from ambient air during cooling phases lead to the formation of a liquid water film on the monolith’s exchange surface, causing a strong temperature plateau during the warm-up phase. The water evaporation causing a delay in the 3WCC temperature increase, it could lead to a serious degradation of the pollutants emissions if not taken into account. This paper proposes hence a 1D thermal model including water phase changing that allows a 72% decrease in the 3WCC temperature estimation error during the warm up phase. This accuracy gain, occurring in a phase where the converter temperature has not reached its full efficiency, provides a 1-2% reduction in CO, HC and NO x emissions.

Comparison of seasonal climate in China during the cold and warm phases of ENSO

El Niño-Southern Oscillation (ENSO) events have serious impacts on weather patterns, agriculture and ecosystems, and play an important role in predicting regional and global climate. A 2-tailed Student’s t-test was used to analyze the differences of seasonal air temperature and rainfall between ENSO years (El Niño/La Niña years) and non-ENSO years in China, and the results indicate that summer temperature was lower, and winter, spring and autumn rainfall was higher in El Niño years, while in La Niña years, winter temperature was lower and summer rainfall was higher in China as a whole. There were significant regional differences in seasonal temperature and rainfall between ENSO and non-ENSO years. In El Niño years, summer temperatures in most regions of China were lower than those in non-ENSO years. Summer and autumn rainfall was higher in the mid-lower reaches of the Yangtze River but lower in North China, and winter rainfall was lower in southern China. In La Niña years, winter temperatures were lower in the mid-lower reaches of the Yangtze River and South China, and summer rainfall was higher in Northeast China, North China, the mid-lower reaches of the Yangtze River and Southwest China than those in non-ENSO years. We conclude that the impacts of ENSO on rainfall are more obvious than those on temperature, and the responses of seasonal temperature and rainfall to El Niño are more obvious than those to La Niña events in China.

Rainfall Variability over Tanzania during October to December and Its Association with Sea Surface Temperature (SST)

The current study examines the interannual rainfall variability and its associated atmospheric circulation in Tanzania during October-December (OND) rainfall season based on 1974 to 2010 climatology. The Empirical Orthogonal Function (EOF), composite and correlation analysis were used in this study. Years with enhanced precipitation are found to be associated with the low level moist and unstable wind from Congo basin which organizes and forms a confluent zone, an inter tropical convergence zone (ITCZ) extending from Congo to northern sector of the country. It however, characterizes low-level westerly moisture flux transport sourced from Congo basin, ascending limb of the local Indian Ocean Walker circulation over East Africa which enhances convection for wetness condition. Wet years are also coupled with the positive Indian Ocean Dipole (IOD) and the warm phase of the El Nino Southern Oscillation (ENSO) condition. On the spatial scale, both the IOD and ENSO indices are well correlated with OND rains over the bimodal areas (Lake Victoria basin, North Eastern Highlands (NEH), and northern coast) with strong correlation being to the NEH. Strong temporal correlation is revealed between the OND rains and IOD (r = 0.6304) compared to ENSO (r = 0.5538) indicating that anomalous warming over the western Indian Ocean has a faster response to OND rains in Tanzania than the remote influence induced by anomalous warming from the central Pacific Ocean. The patterns associated with dry years are found to be linked with the low-level divergence accompanied by convergence in the upper level. This condition enhances continuous descending motion accompanied with suppression in rainfall activities. Dry years are also associated with negative IOD, cold phase of ENSO condition, descending limb of the Walker Circulation and significant reduction in the westerly moisture flux transport sourced from Congo basin towards the western sector and Lake Victoria basin.

Impact of a northern-hemispherical cryosphere on late Pliensbachian–early Toarcian climate and environment evolution

AbstractThe historical view of an equable Jurassic greenhouse world has been challenged by recent studies documenting recurrent alternation between contrasting climate modes. Cooling of high-latitudinal areas may have been caused by orogenic processes at the northern margin of the Tethys Ocean that reduced heat transport towards the polar regions. Warm phases correlate to periods of intensified volcanism. The Jenkyns Event occurred during the transition from a late Pliensbachian icehouse into an early Toarcian greenhouse. Parallel evolution of different environmental processes, including sea level, climate and carbon cycle, indicate a causal mechanism tied to astronomical forcing. Insolation-controlled variations in the extent of the cryosphere (ice caps and permafrost) facilitated orbitally paced sea-level cycles via waxing and waning of the polar ice caps, and negative carbon isotope excursions via the release of cryosphere-bound12C-enriched carbon. This review and synthesis of sedimentological, geochemical and palaeontological palaeoenvironment indicators, and of simulations from climate models, aims to reconstruction, in particular, the high-latitudinal environmental conditions of late Pliensbachian–early Toarcian times. Focus is laid on the extent of the regions that were potentially suitable for hosting a cryosphere. An environmental response to cryosphere dynamics is considered to have been a key component of the Jenkyns Event.

La relación entre la precipitación en Ecuador y la temperatura superficial del mar en el Océano Pacífico

In this study we analyze the temporal and spatial relationship of precipitation in Ecuador and the sea surface temperature (SST) in the Pacific Ocean adjacent to the coast of Ecuador. This relation is most evident during the warm phase of El Niño – Southern Oscillation (ENSO) when warming in the eastern tropical Pacific is associated with increased rainfall in the Pacific coastal regions of South America. This region incorporates the entire coastal region of Ecuador and the northern coastal region of Peru. Although all warm events are associated with increased precipitation in the region, the magnitude of this increase varies greatly. The decreased precipitation associated with the cold events is also variable. In both cases this variability cannot be easily explainedusing the indices typically used to measure the strength of ENSO. We make a detailed analysis of SST in a global ocean model incorporating data assimilation and precipitation observations for the periods from 1950-2010 and1981-2010. This study helps to  determine the spatial regions in the Pacific where warming has the greatest impact on precipitation and the coastalregions of Ecuador that are most affected by this variability in precipitation

Atlantic Multidecadal Variability and North Atlantic Jet: A Multimodel View from the Decadal Climate Prediction Project

AbstractThe influence of the Atlantic multidecadal variability (AMV) on the North Atlantic storm track and eddy-driven jet in the winter season is assessed via a coordinated analysis of idealized simulations with state-of-the-art coupled models. Data used are obtained from a multimodel ensemble of AMV± experiments conducted in the framework of the Decadal Climate Prediction Project component C. These experiments are performed by nudging the surface of the Atlantic Ocean to states defined by the superimposition of observed AMV± anomalies onto the model climatology. A robust extratropical response is found in the form of a wave train extending from the Pacific to the Nordic seas. In the warm phase of the AMV compared to the cold phase, the Atlantic storm track is typically contracted and less extended poleward and the low-level jet is shifted toward the equator in the eastern Atlantic. Despite some robust features, the picture of an uncertain and model-dependent response of the Atlantic jet emerges and we demonstrate a link between model bias and the character of the jet response.

Drivers to dust emissions over dust belt from 1980 to 2018 and their variation in two global warming phases

Dust storms are one of the major disasters in arid and semi-arid regions. Understanding the impact factors is crucial for early warning and disaster mitigation. Many factors have been affecting the spatiotemporal patterns of dust storms. However, the relative importance of those factors to dust emissions in recent 40 years over the whole dust belt has not been well documented. This study explored the relative importance of those factors to the interannual variation in dust emissions over the whole dust belt. The difference in the primary contributors over two global warming phases was compared to investigate the association of dust emission trend with global warming. The results indicated that the wind regimes, such as the nocturnal low-level jet, were key factors to the wintertime dust emissions over the Sahel. The springtime dust storms related to cold air and cyclones primarily occurred in the southern coast of the Mediterranean and northwestern China. The cold high and heat low were typical mechanisms for the summertime dust emissions, which frequently formed in western North Africa, the Middle East, and northwestern Indian subcontinent. Whereas the land cover and drought conditions play significant roles in the relatively wetter regions, i.e., the southern coast of the Mediterranean, the Ustyurt Plateau, the northwest coast of Indian Ocean, the Thar desert and the Taklimakan desert. The wintertime global warming coincided well with the decreasing trend of dust emissions over the dust sources inland with a more significant effect seen in Asia. The positive anomalies of summertime dust emissions were primarily found over the dust sources in the low-lying coastal areas on the foot of high mountains. Understanding the relative importance of those drivers to dust emission trends and their variation under different warming periods can improve the prediction of dust storm evolutions and mitigate their impacts under future climate change.

LANDSCAPES OF THE BELARUSIAN POLESIE EASTERN AREA DURING THE CLIMATIC OPTIMUM OF THE MURAVIAN INTERGLACIAL

The paleolandscapes existed in the eastern area of the Belarusian Polesie region during the climatic optimum of the Muravian Interglacial were reconstructed.
 This work was based on the paleogeomorphological chart compiled with the core data of boreholes located in the investigation area, the composition of sediments, an approximate depth to the groundwater table, as well as on the evidences of the flora and vegetation in the warmest phase of the Muravian Interglacial obtained as a result of the palynological studies of the relevant sediments.
 The data available suggest that the flat landscapes of the temperate continental broad-leaved forest type existed in the investigation area at that time. This type landscapes are divided into 6 groups including 14 kinds and 10 varieties.
 The represented chart of the paleolandscapes reflects an absolute predominance of the broad-leaved forests, but in contrast to the western part of the Belarusian Polesie with a lesser participation of the West European species peculiar to the areas with the warmer oceanic climate.
 The completed reconstructions can be used to forecast the possible future landscape changes on the Belarusian
 Polesie region under the global warming conditions, which can exceed the parameters of the Holocene climatic optimum and reach the climax of the Muravian interglacial.

On the relationship of lake-effect snowfall and teleconnections in the Lower Peninsula of Michigan, USA

It is well known that lake-effect snowfall (LES) attributed to Lake Michigan has a significant impact on transportation in the Lower Peninsula of Michigan (LPM). Better understanding of the inter-annual variability and factors contributing to LES will provide a sound basis for local and regional community safety management and improve weather forecasting. This study attempts to examine the trend in LES and its influencing factors in the LPM using station snowfall measurements and statistical analysis. LES generally increased for the period of 1933–2015 with a higher increase before 1969 and less change since 1970. The warm phase (El Niño) of the ENSO has stronger impacts on LES than the cold phase, as demonstrated by stronger negative correlations between LES and sea surface temperatures in the Niño 3.4 region (SST34) during El Niño years. Both regionally averaged air temperatures and NAO have negative correlations with LES. Further, a larger amount of LES is produced during the years with negative phases of NAO than the years with positive phases. During the years with higher maximum ice coverage on Lake Michigan, LES increases in December and January and decreases in February as the ice coverage peaks in February/March. Findings from this study can provide insight to the impact of both regional environmental variables and teleconnections on LES in the LPM.

Effects of Weak and Strong Winter Currents on the Thermal State of the South China Sea

AbstractThe thermal state of the South China Sea (SCS) modulates the regional climate variability over Southeast Asia. Currents in the SCS are an important factor impacting the thermal state of the SCS, but their relationship is not clearly understood. There is an asymmetry in the thermal effect of weak and strong SCS winter currents. Weak SCS winter currents favor stable warm advection of mean temperature by the anomalous horizontal velocity (i.e., Advha), which drives the SCS into a warm phase. However, the cooling effect of strong SCS winter currents on the SCS is weak, due to small and variable negative Advha. The basin-integrated Advha is primarily set by meridional heat flux in the southern SCS, which is mainly determined by the western boundary current (WBC) anomaly. The eastern boundary current (EBC) anomaly with opposite direction of WBC anomaly acts to weaken the Advha. In weak (strong) SCS winter current years, the wind stress anomaly over the southern SCS is localized around the western (eastern) boundary, which induces a weak (strong) EBC anomaly. Therefore, warm Advha in weak SCS winter current years is large enough to drive the SCS into a warm phase. However, the negative Advha in strong SCS winter current years is variable, which can be occasionally offset by positive advection of anomalous temperature by the mean horizontal velocity and then the SCS presents a warm phase, as in 1998. Thus, the strong SCS winter current exerts a weak cooling effect on the SCS.

The multiphase and magnetized neutral hydrogen seen by LOFAR

Faraday tomography of polarimetric observations at low frequency in the radio is a unique tool for studying the structure of the magneto-ionic diffuse interstellar medium (ISM) based on Faraday depth. LOFAR data below 200 MHz have revealed a plethora of features in polarization, whose origin remains unknown. Previous studies have highlighted the remarkable association of such features with tracers of the magnetized-neutral ISM, such as interstellar dust and atomic hydrogen (HI). However, the physical conditions responsible for the correlation between magneto-ionic and neutral media have not been clarified yet. In this Letter we further investigate the correlation between LOFAR data and the HI spectroscopic observations at 21 cm from the Effelsberg-Bonn HI Survey (EBHIS). We focus on the multiphase properties of the HI gas. We present the first statistical study on the morphological correlation between LOFAR tomographic data and the cold (CNM), lukewarm (LNM), and warm (WNM) neutral medium HI phases. We use the Regularized Optimization for Hyper-Spectral Analysis approach to decompose the HI phases based on a Gaussian decomposition of the HI spectra. We study four fields of view – Fields 3C196, A, B, and C – and find, in at least the first two, a significant correlation between the LOFAR and EBHIS data using the histograms of oriented gradients (HOG) feature. The absence of a correlation in Fields B and C is caused by a low signal-to-noise ratio in polarization. The observed HOG correlation in Fields 3C196 and A is associated with all HI phases and it is surprisingly dominant in the CNM and LNM phases. We discuss possible mechanisms that would explain the correlation between CNM, LNM, and WNM with polarized emission at Faraday depths up to 10 rad m−2. Our results show how the complex structure of the ionic medium seen by the LOFAR tomographic data is tightly related to phase transition in the diffuse and magnetized neutral ISM traced by HI spectroscopic data.

Fire–vegetation relationships during the last glacial cycle in a low mountain range (Eifel, Germany)

Lake sediments can provide useful archives to reconstruct past vegetation changes or fire history. To comprehend how vegetation and fire history have correlated during the last 130,000 years, we used two lake sediment records with known patterns of pollen and botanical macro remains and supplemented this data by analyses of lignin-derived phenols as markers for local vegetation inputs and by benzene polycarboxylic acids (BPCAs) as markers for total fire residue inputs (black carbon, BC). The two sediment archives originated from two maar lakes in the Eifel, which is part of the low mountain ranges in central Germany. A lignin-derived phenol index showed woody angiosperms and gymnosperms as fire fuel in the periods with the highest BC amounts. We recorded 3 g BC per kg sediment for phases covered by forest, while BC contents during colder and drier climates were much smaller (≤0.2 g BC per kg sediment), confirming the hypothesis that fires mostly occurred during humid periods in which forest were established. Both records pointed to forested phases with strong fire activity from 48,000–60,000 years before the year 2000 (b2k). Furthermore, the record reaching back to 130,000 years showed a strong fire activity at about 28,000–30,000 yr b2k, and was free of vegetation macro remains and fire markers from 60,000–118,000 yr b2k. All paleobotanical and chemical biomarker results documented the next oldest forested and fire interval, from 118,000 to 130,000 yr b2k, which includes the Eemian of the last interglacial. Thus, nearly all forested phases were accompanied by fire peaks. Overall, biomarker analyses confirmed that analyses of pollen and botanical macro remains. Fire events were highest during warm and humid forested phases.

Glauconite within Albian-Cenomanian Aitamir Formation, Kopet-Dagh Basin, northeastern Iran: origin and implications of cretaceous seawater

An integrated petrographical, geochemical, and mineralogical investigation reveals the wide variation in the mineral chemical composition of glauconites within the Albian-Cenomanian Aitamir Formation. Bounded between a black shale (Sanganeh Formation) below and chalky limestone (Abderaz Formation) above the Aitamir Formation represents an inner shelf deposit. Glauconite may occur either as pellets or as altered zones within feldspar and mica. Poor sorting and deeply penetrative crack indicate the authigenic nature of glauconite pellets. The contents of Fe2O3, MgO, Al2O3, and SiO2 of glauconites vary widely while the K2O exhibits a limited spread indicating the evolved nature of the glauconite. The glauconite matures at a fixed and high value of K2O with variable Fe2O3 (total) supporting the replacement origin. The X-ray diffraction study reveals a negligible interstratification within glauconites. The micro-textural study attests to the highly evolved nature of the glauconite. The shallow marine glauconite within the Albian-Cenomanian Aitamir Formation formed under sub-oxic, shallow depositional setting during the middle Cretaceous global warming phase within the Tethyan domain.