Hasil untuk "Geology"

Z. Dubinsky, N. Stambler

P. Kapp, P. DeCelles

The Himalayan-Tibetan orogen culminated during the Cenozoic India – Asia collision, but its geological framework and initial growth were fundamentally the result of multiple, previous ocean closure and intercontinental suturing events. As such, the Himalayan-Tibetan orogen provides an ideal laboratory to investigate geological signatures of the suturing process in general, and how the Earth's highest and largest orogenic feature formed in specific. This paper synthesizes the Triassic through Cenozoic geology of the central Himalayan-Tibetan orogen and presents our tectonic interpretations in a time series of schematic lithosphere-scale cross-sections and paleogeographic maps. We suggest that north-dipping subducting slabs beneath Asian continental terranes associated with closure of the Paleo-, Meso-, and Neo-Tethys oceans experienced phases of southward trench retreat prior to intercontinental suturing. These trench retreat events created ophiolites in forearc extensional settings and/or a backarc oceanic basins between rifted segments of upper-plate continental margin arcs. This process may have occurred at least three times along the southern Asian margin during northward subduction of Neo-Tethys oceanic lithosphere: from ∼174 to 156 Ma; 132 to 120 Ma; and 90 to 70 Ma. At most other times, the Tibetan terranes underwent Cordilleran-style or collisional contractional deformation. Geological records indicate that most of northern and central Tibet (the Hoh-Xil and Qiangtang terranes, respectively) were uplifted above sea level by Jurassic time, and southern Tibet (the Lhasa terrane) north of its forearc region has been above sea level since ∼100 Ma. Stratigraphic evidence indicates that the northern Himalayan margin of India collided with an Asian-affinity subduction complex – forearc – arc system beginning at ∼60 Ma. Both the Himalaya (composed of Indian crust) and Tibet show continuous geological records of orogenesis since ∼60 Ma. As no evidence exists in the rock record for a younger suture, the simplest interpretation of the geology is that India – Asia collision initiated at ∼60 Ma. Plate circuit, paleomagnetic, and structural reconstructions, however, suggest that the southern margin of Asia was too far north of India to have collided with it at that time. Seismic tomographic images are also suggestive of a second, more southerly Neo-Tethyan oceanic slab in the lower mantle where the northernmost margin of India may have been located at ∼60 Ma. The geology of Tibet and the India – Asia suture zone permits an alternative collision scenario in which the continental margin arc along southern Asia (the Gangdese arc) was split by extension beginning at ∼90 Ma, and along with its forearc to the south (the Xigaze forearc), rifted southward and opened a backarc ocean basin. The rifted arc collided with India at ∼60 Ma whereas the hypothetical backarc ocean basin may not have been consumed until ∼45 Ma. A compilation of igneous age data from Tibet shows that the most recent phase of Gangdese arc magmatism in the southern Lhasa terrane initiated at ∼70 Ma, peaked at ∼51 Ma, and terminated at ∼38 Ma. Cenozoic potassic-adakitic magmatism initiated at ∼45 Ma within a ∼200-km-wide elliptical area within the northern Qiangtang terrane, after which it swept westward and southward with time across central Tibet until ∼26 Ma. At 26 to 23 Ma, potassic-adakitic magmatism swept southward across the Lhasa terrane, a narrow (∼20 km width), orogen-parallel basin developed at low elevation along the axis of the India – Asia suture zone (the Kailas basin), and Greater Himalayan Sequence rocks began extruding southward between the South Tibetan Detachment and Main Central Thrust. The Kailas basin was then uplifted to >4 km elevation by ∼20 Ma, after which parts of the India – Asia suture zone and Gangdese arc experienced >6 km of exhumation (between ∼20 and 16 Ma). Between ∼16 and 12 Ma, slip along the South Tibetan Detachment terminated and east-west extension initiated in the northern Himalaya and Tibet. Potassic-adakitic magmatism in the Lhasa terrane shows a northward younging trend in the age of its termination, beginning at 20 to 18 Ma until volcanism ended at 8 Ma. We interpret the post-45 Ma geological evolution in the context of the subduction dynamics of Indian continental lithosphere and its interplay with delamination of Asian mantle lithosphere.

K. Hodges

I. Seguro, K. Vikström, K. Vikström et al.

<p>The balance between the uptake of CO<span class="inline-formula">₂</span> by phytoplankton photosynthesis and the production of CO<span class="inline-formula">₂</span> from prokaryoplankton, zooplankton and phytoplankton respiration controls how much carbon can be stored in the ocean and hence how much remains in the atmosphere to affect climate. Yet, despite its crucial role, knowledge on the respiration of plankton groups is severely limited because traditional methods cannot differentiate the respiration of constituent groups within the plankton community. The reduction of the iodonitrotetrazolium salt (INT) to formazan, which when converted to oxygen consumption (O<span class="inline-formula">₂</span>C) using an appropriate conversion equation, provides a proxy for both total and size fractionated plankton respiration. However, the method has not been thoroughly tested with prokaryoplankton. Here we present respiration rates, as O<span class="inline-formula">₂</span>C and formazan formation (INT<span class="inline-formula">_R</span>), for a wide range of relevant marine prokaryoplankton including the gammaproteobacteria <i>Halomonas venusta</i>, the alphaproteobacteria <i>Ruegeria pomeroyi</i> and <i>Candidatus Pelagibacter ubique</i> (SAR11), the actinobacteria <i>Agrococcus lahaulensis</i>, and the cyanobacteria <i>Synechococcus marinus</i> and <i>Prochlorococcus marinus</i>. All species imported and reduced INT, but the relationship between the rate of O<span class="inline-formula">₂</span>C and INT<span class="inline-formula">_R</span> was not constant between oligotrophs and copiotrophs. The range of measured O<span class="inline-formula">₂</span>C <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="880d1b22cfae9b4167ff115d05c6894c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-6225-2025-ie00001.svg" width="8pt" height="14pt" src="bg-22-6225-2025-ie00001.png"/></svg:svg></span></span> INT<span class="inline-formula">_R</span> conversion equations equates to an up to 40-fold difference in derived O<span class="inline-formula">₂</span>C. These results suggest that when using the INT method in natural waters, a constant O<span class="inline-formula">₂</span>C <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="8550e2e9970f84100ffbfa4da4f4f543"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-6225-2025-ie00002.svg" width="8pt" height="14pt" src="bg-22-6225-2025-ie00002.png"/></svg:svg></span></span> INT<span class="inline-formula">_R</span> relationship cannot be assumed, but must be determined for each plankton community studied.</p>

Biswajit Bera

Abstract Garhwal Himalaya is one of the most landslide-prone regions in the Himalayan Belt due to its seismo-tectonic background, geological complexity, climate, geomorphological setting and large-scale human interference. A gigantic rock avalanche happened on July 10, 2024, near Patalganga-Langsi Tunnel on the Badrinath Highway (NH-7) of the Chamoli district and disconnected the Joshimath, Badrinath, and Nanda Devi National Park for a few hours. This road corridor is a significant gateway for valued pilgrimage destinations and Indo-Tibet Border security. A detailed investigation has been done on the recent reactivated rock cum debris avalanche at the Patalganga-Langsi Tunnel site. The Artificial Neural Network (ANN) model identifies this area as a high landslide susceptible zone, and the entire Patalganga-Langsi is tectonically controlled by the Main Central Thrust (MCT) and other proximity minor thrusts. Rainfall and exposed slope conditions are the primary triggering factors behind this rock avalanche, and geologically, this slope is still vulnerable as the Factor of Safety (FoS) is near the threshold value (1.019). Subsequently, the Schmidt hammer rebound test showed poor rock strength (approximately 30 or sometimes below 30), and the rocks have numerous structural signatures, which make them more vulnerable. Results of kinematic analysis for the two studied road cut slopes (Slope 1 and 2) emphasized a tendency to wedge failure. After the geo-technical study and the hazard potential of the slide site, sustainable geo-environmental management techniques should be immediately executed to maintain the socio-economic lifeline as well as Indo-Tibetan Border security management. Geo-technical parameters of the Patalganga-Langsi site reflect that there is a very high probability of wedge-type rockfall and rock-cum-debris fall.

Ben Thuy, Mats E. Eriksson, Manfred Kutscher et al.

Due to the fragility of the ophiuroid (brittle star) skeleton, the bulk of the group’s fossil record consists of dissociated ossicles preserved as microfossils. In spite of their great potential as basis for taxonomic and phylogenetic studies, however, ophiuroid ossicles from the Paleozoic have received very little attention so far. Here, we provide an exhaustive taxonomic assessment of such fossils retrieved from sieving residues from the Silurian of Gotland, Sweden. This material was used in a previous study to describe two key taxa that allowed constraining the origin of the extant ophiuroid clade. The remaining taxa belonging to that same lineage are described in the present paper. The evidence at hand suggests that the stem of the extant ophiuroid clade was formed by two genera, Ophiopetagno and Ophiolofsson gen. nov., including six and five species, respectively, and spanning at least the upper Llandovery through upper Ludlow. We conclude that Ophiopetagno and Ophiolofsson represent sister genera that coexisted through most of the Silurian in the shallow tropical seas of Gotland. They underwent repeated body size reductions in correlation with environmental perturbations, with Ophiopetagno paicei eventually giving rise to Muldaster haakei; the first member of the living Ophiuroidea. Herein, we also introduce two new clades, Ankhurida clade nov. and Ophiovalida clade nov., and the following eight new species: Ophiolofsson joelmciveri gen. et sp. nov., O. obituary gen. et sp. nov., O. immolation gen. et sp. nov., O. archspire gen. et sp. nov., O. hendersonorum gen. et sp. nov., Ophiopetagno bonzo sp. nov., O. kansas sp. nov., O. doro sp. nov.; and two probably new species in open nomenclature: Ophiopetagno sp. 1, and Ophiopetagno sp. 2.

Imad Ali, Maryam Bayati khatibi, Sadra Karimzadeh

This study aimed to delineate groundwater recharge zones using a combination of analytical hierarchy process (AHP), fuzzy-AHP, and frequency ratio (FR) models. Additionally, it aimed to compare the effectiveness of these models in groundwater recharge potential zone mapping. To achieve these objectives, nine groundwater influencing factors were considered, including geology, soil types, lineament density, elevation, slope, topographic wetness index, drainage density, land use land cover, and rainfall. Thematic maps for all these factors were generated using satellite and conventional data in the ArcGIS environment. Weight was assigned to each thematic layer based on its significance to recharge. All thematic layers were combined using AHP model-l (WLC), AHP model-ll (Weighted sum), fuzzy-AHP overlay, and FR-based model using ArcGIS. The findings revealed that 15% and 39% of the study area have high recharge potentials according to AHP-based model-l and model-ll, respectively. The FAHP model demarcated 43% of the area as high recharge zones while the FR model demarcated 42% of the area as high recharge zones. The majority of high groundwater recharge areas were found in the central part of the study area, while the southern part was demarcated as a moderate recharge zone. The eastern and western parts were demarcated as low recharge potentials zones. To validate the accuracy of these models, the study used receiver operating characteristic (ROC) validation curves. The ROC curves revealed that AHP model-ll had the highest accuracy (AUC=89%) followed by the FAHP model (AUC=88%), AHP model-l (AUC=84%), and FR (AUC=81%)...

P. Voit, M. Heistermann

<p>Counterfactuals are scenarios that describe alternative ways of how an event, in this case an extreme rainfall event, could have unfolded. In this study, we present the results of a counterfactual search for flash flood events in Germany. We used a radar-based precipitation dataset from Germany's national meteorological service (Deutscher Wetterdienst) to identify the 10 most extreme precipitation events in Germany from 2001 to 2022 and then assumed that any of these top 10 events could have happened anywhere in Germany. In other words, the events were shifted around all over Germany. For all resulting positions of the precipitation fields, we simulated the corresponding peak discharge for any affected catchment smaller than 750 km<span class="inline-formula">²</span>. From all the realizations of this simulation experiment, the maximum peak discharge was identified for each catchment.</p> <p>In a case study, we first focused on the devastating flood event in July 2021 in western Germany. We found that a moderate shifting of the event in space could change the event peak flow at the Altenahr gauge by a factor of 2. Compared to the peak flow of 1004 m<span class="inline-formula">³</span> s<span class="inline-formula">⁻¹</span> caused by the event in its original position, the worst-case counterfactual of that event led to a peak flow of 1311 m<span class="inline-formula">³</span> s<span class="inline-formula">⁻¹</span>. Shifting another event that had occurred just 1 month earlier in eastern Germany over the Ahr River valley even effectuated a simulated peak flow of 1651 m<span class="inline-formula">³</span> s<span class="inline-formula">⁻¹</span>.</p> <p>For all analysed subbasins in Germany, we found that, on average, the highest counterfactual peak exceeded the maximum original peak (between 2001 and 2022) by a factor of 5.3. For 98 % of the basins, the factor was higher than 2.</p> <p>We discuss various limitations of our analysis, which are important to be aware of, namely, the quantification and selection of candidate rainfall events, the hydrological model, and the design of the counterfactual search experiment. Still, we think that these results might help to expand the view of what could happen in the case that certain extreme events occurred elsewhere and thereby reduce the element of surprise in disaster risk management.</p>

Heng‐Ci Tian, Jialong Hao, Yangting Lin et al.

Abstract Knowledge regarding the abundance and distribution of solar wind (SW)‐sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E‐5 drill core sampled at depths of 0.45–0.8 m. High water contents of 0.13–1.3 wt.% are present on approximately half of the grain surfaces (topmost ∼100 nm), comparable to the values of Chang'E‐5 scooped soils. The extremely low δD values (as low as −995‰) and negative correlations between δD and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW‐derived water in the vertical direction, providing compelling evidence for the well‐mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water.

علی غلامعلی زاده, نسرین قربان زاده, محمد باقر فرهنگی et al.

سابقه و هدف: هدررفت فسفر از اراضی کشاورزی و ورود آن به منابع آبی سبب پدیده سرشارسازی و شکوفایی جلبکی شده و کنترل فسفر ورودی به زیست‌بوم‌های آبی را به چالشی مهم برای مدیریت این منابع تبدیل کرده است. آزمون جلبکی به عنوان قابل اعتمادترین روش برای کمی‌سازی پتانسیل زیست‌فراهمی فسفر محسوب می‌شود. این پژوهش با هدف بررسی زیست‌فراهمی فسفر در سه نمونه خاک شالیزاری و ارتباط آن با رشد ریزجلبک کلرلا انجام گرفت. مواد و روش‌ها: نمونه‌برداری خاک از عمق 10-0 سانتی‌متری اراضی شالیزاری واقع در پنج منطقه پسیخان، پیربازار، سیاه درویشان، فخب و لاکان انجام شد. این اراضی برای مدت طولانی و به صورت سالانه کود فسفری دریافت کرده بودند. ابتدا با عصاره‌گیری پی در پی به روش هدلی بخش‌های مختلف فسفر در 5 نمونه خاک تعیین شد و سپس با توجه به مقدار فسفر کل، فسفر در بخش‌های مختلف و درصد رس، سه نمونه از خاک‌ها (پسیخان، پیربازار و لاکان) به عنوان تنها منبع فسفر به محیط کشت ریزجلبک کلرلا اضافه شدند. آزمایش در قالب طرح کاملاً تصادفی به روش اندازه‌های تکرار شده در زمان با سه تکرار انجام شد. مقدار کلروفیل a، تعداد سلول‌های ریزجلبک، فسفر کل محلول و فسفر ذره‌ای در روزهای صفر، 7، 14، 21 و 28 انکوباسیون اندازه-گیری شد. یافته‌ها: دو خاک پیربازار و فخب از نظر بخش‌بندی فسفر مشابه و ترتیب بخش‌ها به صورت اکسیدی< باقی‌مانده< کربناتی< محلول-تبادلی بود. در حالی‌که در سه خاک دیگر بخش‌بندی فسفر به صورت باقی‌مانده< اکسیدی<کربناتی< محلول-تبادلی بود. مقدار کلروفیل a ریزجلبک در هر سه نمونه خاک روند افزایشی نشان داد و در روز چهاردهم به بیشترین مقدار رسید و پس از آن ثابت شد. تعداد سلول‌های ریزجلبک در تیمار خاک پیربازار تا روز چهاردهم انکوباسیون و در خاک‌های لاکان و پسیخان تا پایان دوره انکوباسیون روند افزایشی نشان داد. فسفر کل محلول در تمامی تیمارها در طول دوره انکوباسیون تا روز هفتم روند افزایشی داشت و پس از آن کاهش یافت. فسفر ذره‌ای در روز هفتم انکوباسیون به شدت کاهش و سپس در ادامه انکوباسیون افزایش نشان داد. مقدار کلروفیل a و تعداد سلول‌های ریزجلبک در دو هفته اول انکوباسیون همبستگی مثبت و معناداری با فسفر کل محلول نشان دادند و در دو هفته بعد رشد ریزجلبک تحت تاثیر فسفر ذره‌ای قرار گرفت. نتیجه‌گیری: از آن‌جا ‌که خاک می‌تواند به عنوان منبع فسفر امکان رشد ریزجلبک را فراهم نماید، بنابراین توجه به فسفر ورودی به زیست‌بوم‌های آبی از طریق اراضی کشاورزی حاشیه رودخانه‌ها برای مدیریت پدیده سرشارسازی در تالاب انزلی ضروری است.

I. Campbell

It was in 1950 just a little over 20 years ago that a group of geologists in Tulsa, Oklahoma, recognized the desirability of agreement on definitions, and for standardization of many terms commonly, but often differently, used by geologists. Not only did they recognize the need they did something about it! They outlined a plan of action and submitted it to the Research Committee of the American Association of Petroleum Geologists. The committee, favorably impressed by the proposal but having some doubt as to its appropriateness for AAPG, recommended that the project might better be undertaken by the American Geological Institute thereby providing for input from the many special fields represented by the AGI member societies. Thus was the first Glossary Project initiated. Under the dedicated guidance of J.V. Howell (whose name deservedly will be forever associated with the AGI Glossary) and with contributions from a great number of individuals, committees, and some societies, a Glossary of geology and related sciences embodying some 14,000 entries was published in 1957 under the imprimatur of the National Academy of Sciences National Research Council.

R. Reyment

Claudia L. Martín Rincón, Roberto Terraza Melo, Nadia R. Rojas Parra et al.

De tiempo atrás se conoce que los fosfatos económicamente explotables en Colombia se encuentran en sucesiones sedimentarias marinas del Cretácico Superior (Cathcart y Zambrano, 1967; Mojica, 1987; Zambrano y Mojica, 1990). En el occidente de la subcuenca de Neiva del Valle Superior del Magdalena (VSM), estos niveles están restringidos al intervalo Santoniano-Maastrichtiano, representado en las formaciones Lidita Inferior, Lidita Superior y Yaguará. Los fosfatos son lateralmente discontinuos y presentan variaciones faciales en distancias cortas. El análisis facial y las correlaciones estratigráficas permitieron inferir que las facies presentes en estas unidades representan un ambiente marino muy somero desde la zona de transición con el offshore hasta el shoreface superior, incluyendo condiciones de laggon para la Formación Aico. Posiblemente, la paleotopografía y la subsidencia diferencial han afectado la continuidad lateral y el espesor de las unidades litoestratigráficas del intervalo Santoniano-Maastrichtiano, y los eventos tectónicos posteriores han modificado la distribución espacial de los depósitos de fosfatos. La falla de La Plata (Chusma) divide la zona en cuestión en dos dominios estructurales: uno localizado en el occidente, en el bloque levantado, donde afloran las rocas más antiguas del basamento pre-Cretácico, y otro dominio localizado en el oriente, en el bloque hundido, donde aflora la secuencia sedimentaria cretácica-cuaternaria característica de la subcuenca de Neiva. En el bloque hundido se encuentran pliegues importantes, como el Sinclinal de Media Luna y el Anticlinal de San Francisco en el norte, el Anticlinal de La Guagua en la parte central, y el Anticlinal de La Hocha y el Sinclinal de El Vegón en el sur. Algunos de estos pliegues están truncados por fallas regionales inversas con componente de rumbo dextral, como las fallas de La Plata (Chusma), San Francisco y Betania.

Marakushev Sergey, Belonogova Olga

In most modern studies of lithospheric (petrogenic) carbonreservoirs in the earth’s crust, it is assumed that crude oil and natural gas (petroleum) are thermal generation products from the relics of biological organic matter accumulated in sedimentary rocks during geological time and deeply buried in a region of high pressure and temperature. In this sedimentary-migration (“biogenic”) concept of the origin of oil, the direction of the proposed evolutionary process of carbon transformation was determined: buried biological material → kerogen → oil → gas as a manifestation of progressive metamorphism (pressure and temperature increase). However, the discovery of kerogen in the meteorite’s composition does not allow us to suggest a biological source of carbon for the formation of this polymeric “organic” substance, but in turn allows us to suggest inorganic sources of kerogen, namely “oil” and “gas"non methane hydrocarbons (HCs), originated in the depths of their parent bodies (icy planetesimals). The genetic relationship of oil, natural gas and carbon matter of black shale formations (kerogen) on Earth is also beyond doubt, and therefore, in this paper, the evolution of petrogenic carbon reservoirs, including oil shale rocks in the lithosphere, is considered on the basis of a deep inorganic concept, in which the direction of the carbon transformation process is the opposite of the biogenic concept and is represented as HCs → gas → oil → kerogen. The analysis of phase diagrams and experimental data made it possible to determine two trends in the evolution of non-methane hydrocarbons in the Earth’s interior. In the upper mantle, the “metastability” of heavy (with a lower H/C ratio) HCs increases with depth. However, at temperatures and pressures corresponding to the surface mantle-crustal hydrothermal conditions, the “relative metastability” of heavy hydrocarbons increases with approach to the surface. When deep HCs fluids rise to the surface, petrogenic oil reservoirs are formed as a result of the decreases in hydrogen fugacity and a phase transition: gas HCs → liquid oil. At the physical and chemical conditions of an oil reservoir, metastable reversible phase equilibria are established between liquid oiland H2O, gas HCs and CO2, and solid (pseudocrystalline) “mature” and “immature” kerogens of “oil source” rocks. A decrease in hydrogen pressure and temperature leads to a stoichiometric phase transition (“freezing”) of liquid oil into solid kerogens. This occurs as a result of oil dehydrogenation in the processes of high-temperature CO2 fixation and low-temperature hydration of oil hydrocarbons, which are the main geochemical pathways for its transformation into kerogen. Thus, the formation of carbon matter in petrogenic reservoirs is the result of regressive (retrograde) metamorphism of deep hydrocarbon fluids, natural gas, liquid oil, and naphthide accumulations.

K. Valdiya

B. Siegal, A. Gillespie

J. Suppe

S. Drury

Frédérique Eynaud, Sébastien Zaragosi, Mélanie Wary et al.

Since its existence, paleoceanography has relied on fossilized populations of planktonic foraminifera. Except for some extreme environments, this calcareous protist group composes most of the silty-to-sandy fraction of the marine sediments, i.e., the foraminiferal oozes, and its extraction is probably the simplest among the currently existing set of marine fossil proxies. This tool has provided significant insights in the building of knowledge on past climates based on marine archives, especially with the quantification of past hydrographical variables, which have been a turning point for major comprehensive studies and a step towards the essential junction of modelling and paleodata. In this article, using the modern analog technique and a database compiling modern analogs (n = 1007), we test the reliability of this proxy in reconstructing paleohydrographical data other than the classical sea-surface temperatures, taking advantage of an update regarding a set of extractions from the World Ocean Atlas for transfer functions. Our study focuses on the last glacial period and its high climatic variability, using a set of cores distributed along the European margin, from temperate to subpolar sites. We discuss the significance of the reconstructed parameters regarding abrupt and extreme climate events, such as the well-known Heinrich events. We tested the robustness of the newly obtained paleodata by comparing them with older published reconstructions, especially those based on the complementary dinoflagellate cyst proxy. This study shows that the potential of planktonic foraminifera permits going further in reconstructions, with a good degree of confidence; however, this implies considering ecological forcings in a more holistic perspective, with the corollary to integrate the message of this fossil protist group, i.e., the obtained parameters, in light of a cohort of other data. This article constitutes a first step in this direction.

C. W. Nooitgedacht, H. J. L. van der Lubbe, M. Ziegler et al.

Abstract Biogenic and inorganic calcium carbonates contain considerable amounts of internal water, both as free and organically associated water. The oxygen isotopic compositions (δ18O) of internal water and hosting carbonate are analyzed for various carbonates before and after heating at 175°C for 90 minutes. During heating, the δ18O values of internal water significantly increased in biogenic aragonites and speleothem calcite, whereas the δ18O carbonate values were lowered. Correspondingly, an aragonitic bivalve’s clumped‐isotope distribution (Δ47) changed during heating, increasing reconstructed paleotemperatures. In contrast, an inorganic aragonite crystal, containing a comparable amount of internal water, showed no oxygen isotope exchange, and its Δ47 values remained unaltered during heating, implying that there is a link between internal oxygen isotope exchange and Δ47 resetting. This alteration process occurred without any detectable transformation from aragonite to calcite. Our results therefore reveal a mechanism that facilitates oxygen isotope exchange between biogenic aragonite and its internal water, while simultaneously resetting the Δ47 values, without affecting mineralogy. Future studies may therefore apply coupled water‐carbonate analyses to scrutinize these kinds of diagenetic alteration processes. It appears that in biogenic aragonites, more carbonate is available for exchange reactions with the internal water reservoir than in inorganic aragonites, a feature that can be attributed to the distribution of organic‐associated water and/or high surface area fluid inclusions. This water‐aragonite exchange occurs at lower temperatures than those required for solid‐state bond reordering at the same timescale, and thus likely has occurred earlier during the burial of biogenic aragonites.