Lower Δ13 Research Articles

Petrography, geochemistry and genesis of dolomites in the upper Cambrian Sanshanzi Formation of the western Ordos Basin, northern China

The Cambrian Sanshanzi Formation is an important dolomite horizon in the Ordos Basin of northern China, and is well exposed in the western part of that basin. This paper focuses on the petrography and geochemistry of dolomites in this formation with an aim to provide a better understanding of their genesis. Reflux seepage, burial, and hydrothermal dolomites are identified in the Sa nshanzi Formation. Reflux seepage dolomites include dolomitic grainstone and powder crystal dolomite, and have high Sr and low Mn contents, a high CaO/MgO ratio and low δ13 C values, and the reflux seepage dolomitization was formed by high-salinity and Mg2+-enriched fluid penetrates downward into the limestone. Burial dolomites are the main type of dolomite distributed through the Sanshanzi Formation. Burial dolomites are composed of fine- to coarse-crystal dolomite and have low Sr and high Mn contents, a low CaO/MgO ratio, and high δ13C values. The features of high salinity, strong reducibility and negative δ18O values indicate the burial dolomites formed under high-temperature and high-pressure conditions, the burial dolomitization was due to the limestone deeply buried during the later diagenetic stage. Hydrothermal dolomites are mainly characterized by saddle dolomite features, a positive δEu anomaly, and low δ18O values, and the hydrothermal dolomitization occurred during Mg2+-rich hydrothermal fluid invaded. The reflux seepage and hydrothermal dolomite developed in local areas, with the hydrothermal dolomite affected by the distribution of faults.

Seasonality and interindividual variation in mandrill feeding ecology revealed by stable isotope analyses of hair and blood.

Mandrills are large-bodiedterrestrial forest primates living in particularly large social groups of several hundred individuals. Following these groups in the wild to assess differences in diet over time as well as among individuals is demanding. We here use isotope analyses in blood and hair obtained during repeated captures of 43 identified free-ranging mandrills (Mandrillus sphinx) from Southern Gabon, to test how dietary variation relates to the season as well as an individual's age and sex. We measured the stable carbon (δ13 C‰) and nitrogen (δ15 N‰) isotope ratios in 46 blood and 214 hair section samples as well as from a small selection of mandrill foods (n = 24). We found some seasonal isotopic effects, with lower δ13 C values but higher δ15 N values observed during the highly competitive long dry season compared to the fruit-rich long rainy season. Variation in δ13 C was further predicted by individual age, with higher δ13 C values generally found in younger individuals suggesting that they may consume more high canopy fruit than older individuals, or that older individuals consume more low canopy foliage. The best predictor for δ15 N values was the interaction between age and sex, with mature and reproductively active males revealing the highest δ15 N values, despite the observation that males consume substantially less animal food items than females. We interpret high δ15 N values in these mature male mandrill blood and hair sections to be the result of nutritional stress associated with intense male-male competition, particularly during mating season. This is the first study showing isotopic evidence for nutritional stress in a free-ranging primate species and may spark further investigations into male mandrill diet and energy balance.

Mapping carbon and nitrogen isotopic composition of fingernails to demonstrate a rural-urban nutrition transition in the Center-West, Northeast, and Amazon regions of Brazil.

The main objective of this study is to investigate diet patterns among rural and urban populations of the Center-West, Northeast, and Amazon regions of Brazil through the carbon and nitrogen isotopic composition of fingernails, recognizing that the extent of market integration is a key driver of food consumption. In the Center-West, Northeast, and Amazon regions of Brazil, fingernails were sampled in clusters encompassing a major city, town, and rural village. A total of 2,133 fingernails were analyzed. Fingernails were clipped by donors using fingernail clippers. In the laboratory, samples were cleaned then weighed in small tin capsules before being isotopically analyzed for carbon and nitrogen. The overall mean δ13 C and δ15 N were -19.7 ± 2.8‰ and 10.6 ± 1.1‰, respectively. In the more remote villages, where access to food markets is more challenging, lower δ13 C prevails, suggesting that Brazilian staple foods (rice, beans, and farinha) still dominate. In areas with easier access to food markets, δ13 C values were higher, suggesting a change to a diet based on C4 plants, typical of a Brazilian supermarket diet. The variability among inhabitants in the same location expressed by a significant inverse correlation between δ13 C and δ15 N fingernail values suggested that "market integration" does not affect everyone equally in each community. The nutrition transition has not yet reached some remote villages in these regions of Brazil or that the nutrition transition has not yet reached all residents of these remote villages. On the other hand, in several villages there is a considerable adherence to the supermarket diet or that some residents of these villages are already favoring processed food.

The trophic niche of sculpins Cottus spp. in forage fish assemblages of boreal lakes.

We compared the trophic niches of freshwater sculpins Cottus spp. with those of other co-habiting forage fishes in two groups of boreal lakes with distinct habitats and fish communities. Near North Lakes (45° 00' to 47° 30' N) were deeper, stratified and contained lake trout Salvelinus namaycush as the apex piscivore, whereas Far North Lakes (51° 10' to 52° 20' N) were shallower, did not stratify and contained pike Esox lucius and walleye Sander vitreus as the apex piscivores. Trophic niches of sculpins and other forage fishes were compared based on niche metrics calculated from muscle stable carbon (δ13 C) and nitrogen (δ15 N) isotope ratios. In Near North Lakes, sculpins were found almost exclusively in deep, offshore waters and their niche positions reflected a greater reliance on pelagic production (lower δ13 C) and a higher trophic elevation (higher δ15 N) compared with most other forage fishes. Furthermore, sculpins in Near North Lakes tended to have larger trophic niches (occupied greater area in δ13 C- δ15 N space), particularly in the food chain (δ15 N) dimension, than other cohabiting forage fishes. In contrast, sculpins in Far North Lakes were commonly found in the nearshore and had trophic niche positions and sizes that were similar to those of the other cohabiting forage fishes. This study illustrates the flexibility in the realised trophic niches of sculpins in relation to habitat availability and fish community composition in boreal lakes.

Contrasting water sources and water-use efficiency in coexisting desert plants in two saline-sodic soils in northwest China.

Soil degradation resulting from various types of salinity is a major environmental problem, especially in arid and semiarid regions. Exploring the water-related physiological traits of halophytes is useful for understanding the mechanisms of salt tolerance. This knowledge could be used to rehabilitate degraded arid lands. To investigate whether different types of salinity influence the water sources and water-use efficiency of desert plants (Karelinia caspia, Tamarix hohenackeri, Nitraria sibirica, Phragmites australis, Alhagi sparsifolia, Suaeda microphylla, Kalidium foliatum) in natural environments, we measured leaf gas exchange, leaf carbon and xylem oxygen isotope composition and soil oxygen isotope composition at neutral saline-sodic site (NSS) and alkaline saline-sodic site (ASS) in northwest China. The studied plants had different xylem water oxygen isotope compositions (δ18 O) and foliar carbon isotope compositions (δ13 C), indicating that desert plants coexist through differentiation in water use patterns. Compared to that at the NSS site, the stem water in K.caspia, A.sparsifolia and S.microphylla was depleted in 18 O at the ASS site, which indicates that plants can switch to obtain water from deeper soil layers when suffering environmental stress from both salinity and alkalinisation. Alhagi sparsifolia had higher δ13 C at the ASS site than at the NSS site, while K.caspia and S.microphylla had lower δ13 C, which may have resulted from interspecific differences in plant alkali and salt tolerance ability. Our results suggest that under severe salinity and alkalinity, plants may exploit deeper soil water to avoid ion toxicity resulting from high concentrations of soluble salts in the superficial soil layer. In managed lands, it is vital to select and cultivate different salt-tolerant or alkali-tolerant plant species in light of local conditions.

Influence of dry season on Quercus suber L. leaf traits in the Iberian Peninsula.

Water deficit and drought conditions are increasing in intensity, frequency, and duration in the Iberian Peninsula. We observed natural variation in leaf traits across the range of Quercus suber L. (cork oak), an ecologically important species within this region. Stomatal traits (e.g., pore length, maximum aperture) and carbon isotope composition (δ13 C) provide an opportunity to examine the integrative effects of drought and dry-season intensity on leaf development, maximum stomatal conductance, and adaptation to precipitation regimes. Gross leaf traits (e.g., area, thickness), stomatal traits (e.g., pore length, size, aperture), and carbon isotope discrimination were measured in Q. suber leaves, and maximum stomatal conductance to water vapor (gwmax ) was calculated. Trees were sampled from nine natural populations across a climate gradient in the Iberian Peninsula, including trees from two genetic lineages. Linear mixed models compared total water deficit to leaf traits, accounting for tree and site as random effects. Quercus suber gross leaf morphology remained consistent across the climate gradient, but increasing water deficit was correlated with smaller stomata at the leaf level and low δ13 C at the tree level. No traits were significantly different between the two genetic lineages. While there were no significant differences in gross leaf morphology across the climate gradient or between the genetic lineages, stomatal traits and δ13 C responded to climate, suggesting that Q. suber can inhabit a range of environments in the Iberian Peninsula via micro-adjustments of the trait that controls water loss into the atmosphere.

The influence of diet composition and tissue type on the stable isotope incorporation patterns of a small‐bodied southern African minnow Enteromius anoplus (Cypriniformes, Cyprinidae)

In trophic ecology, the use of stable isotope data relies on the general understanding of isotope turnover rates and diet-to-tissue discrimination factors (DTDFs). Recent studies on the application of stable isotope data have shown that isotope turnover rates and DTDFs can be influenced by many factors, including diet composition and tissue type. This study investigated the influence of diet composition and tissue type on stable isotope incorporation patterns in a small-bodied African minnow, the chubbyhead barb Enteromius anoplus. The isotopic incorporation patterns of carbon (δ13 C values) and nitrogen (δ15 N values) into white muscle and caudal fin tissues of the chubbyhead barb were examined using two isotopically different diets. Controlled-diet stable isotope feeding trials using a fishmeal-based diet (diet 1) and a soya-based diet (diet 2) were conducted over a 180-day period for the chubbyhead barb. The two diets had contrasting isotopic incorporation patterns: diet 1 was associated with progressively high δ13 C and δ15 N values, whereas diet 2 was associated with progressively low δ13 C and δ15 N values over time for both muscle and fin tissues. The δ13 C turnover rates were similar for both tissues (56 and 61 days), whereas the δ15 N turnover rates differed between fin and muscle tissue in both diets (diet 1 = 4 and 130 days, and diet 2 = 72 and 300 days, respectively). The DTDFs were similar for both tissues in diet 1 (Δ13 C: -3.96 to -2.62‰, Δ15 N: 1.98 to 2.61‰) and diet 2 (Δ13 C: 4.05 to 5.24‰, Δ15 N: 8.45 to 9.69‰). These results suggest that fin tissue can potentially be used as an alternative for muscle tissue in food web studies with a reasonable level of error. The isotopic turnover rate and DTDFs estimates for E. anoplus, however, require consideration of diet composition because different diets may differ in their isotopic incorporation patterns.

The "isohydric trap": A proposed feedback between water shortage, stomatal regulation, and nutrient acquisition drives differential growth and survival of European pines under climatic dryness.

Climatic dryness imposes limitations on vascular plant growth by reducing stomatal conductance, thereby decreasing CO2 uptake and transpiration. Given that transpiration-driven water flow is required for nutrient uptake, climatic stress-induced nutrient deficit could be a key mechanism for decreased plant performance under prolonged drought. We propose the existence of an "isohydric trap," a dryness-induced detrimental feedback leading to nutrient deficit and stoichiometry imbalance in strict isohydric species. We tested this framework in a common garden experiment with 840 individuals of four ecologically contrasting European pines (Pinus halepensis, P.nigra, P.sylvestris, and P.uncinata) at a site with high temperature and low soil water availability. We measured growth, survival, photochemical efficiency, stem water potentials, leaf isotopic composition (δ13 C, δ18 O), and nutrient concentrations (C, N, P, K, Zn, Cu). After 2years, the Mediterranean species Pinus halepensis showed lower δ18 O and higher δ13 C values than the other species, indicating higher time-integrated transpiration and water-use efficiency (WUE), along with lower predawn and midday water potentials, higher photochemical efficiency, higher leaf P, and K concentrations, more balanced N:P and N:K ratios, and much greater dry-biomass (up to 63-fold) and survival (100%). Conversely, the more mesic mountain pine species showed higher leaf δ18 O and lower δ13 C, indicating lower transpiration and WUE, higher water potentials, severe P and K deficiencies and N:P and N:K imbalances, and poorer photochemical efficiency, growth, and survival. These results support our hypothesis that vascular plant species with tight stomatal regulation of transpiration can become trapped in a feedback cycle of nutrient deficit and imbalance that exacerbates the detrimental impacts of climatic dryness on performance. This overlooked feedback mechanism may hamper the ability of isohydric species to respond to ongoing global change, by aggravating the interactive impacts of stoichiometric imbalance and water stress caused by anthropogenic N deposition and hotter droughts, respectively.

Evaluation of childhood nutrition by dietary survey and stable isotope analyses of hair and breath.

The natural abundances of carbon, nitrogen, and sulfur stable isotopes in hair, and of carbon isotopes in breath serve as quantitative biomarkers of protein and carbohydrate sources, but applicability of isotopes for evaluating children's diet has not been demonstrated. In this study, we sought to describe the stable isotope patterns observed in the hair and breath of children and to assess dietary variations in relation to age and ethnicity, hypothesizing that these would reflect dietary differences across age and ethnic groups and would correlate with intake variables derived from a Food Frequency Questionnaire. Data were obtained from a cross-sectional study of non-Hispanic white (N = 115) and Hispanic (N = 97) children, aged 9-16 years, in Salt Lake City, Utah. Sampling included a hair sample, breath samples (AM and PM), and a youth/adolescent food questionnaire (YAQ). Hair was analyzed for carbon (δ13 C), nitrogen (δ15 N), and sulfur (δ34 S) isotopes, and breath samples for δ13 CAM/PM of respired CO2 . Non-Hispanic whites had lower δ13 C, δ15 N, δ13 CAM , and δ13 CPM values than Hispanics. Hair δ13 C and δ15 N values were correlated with protein sources, particularly for non-Hispanics. Breath δ13 C values were correlated with carbohydrate sources, particularly for Hispanic students. Non-Hispanic white students reported greater intake of total protein, animal protein, dairy, and grain than Hispanic students. Hispanic students reported higher intake of carbohydrates, particularly sweetened beverages. While YAQ and stable isotope data reflected strong cultural influences in diet, no significant gender-based nor age-based differences were detected. Significant covariation between YAQ and isotopes existed and demonstrate the potential of stable isotopes for characterizing children's diet.

Breastfeeding, weaning, and dietary practices during the Western Zhou Dynasty (1122-771 BC) at Boyangcheng, Anhui Province, China.

Here we investigate breastfeeding and weaning practices and adult dietary habits at the Western Zhou Dynasty (1122-771 BC) site of Boyangcheng () located in Anhui Province, China. In addition, we utilize the differences in bone collagen turnover rates between rib and long bones from the same individual to examine past life histories, such as changes in diet or residence. Bone collagen from both the rib and long bones (either femora or humeri) of 42 individuals was measured for stable isotope ratios of carbon (δ13 C) and nitrogen (δ15 N). In addition, δ13 C and δ15 N values are reported for 35 animals (dogs, cows, horses, pigs, and deer). The human δ13 C values range from -20.7‰ to -12.0‰ with a mean value of -18.8 ± 1.6‰. The human δ15 N values range from 9.1‰ to 13.4‰ with a mean value of 10.9 ± 1.0‰. The animals display a wide range of δ13 C (-21.5‰ to -8.2‰; -15.8 ± 4.5‰) and δ15 N values (4.0‰ to 9.5‰; 6.5 ± 1.8‰). The adult δ13 C and δ15 N results indicate that mixed C3 (rice) and C4 (millet) terrestrial diets with varying levels of animal protein (mostly pigs and deer) were consumed. The elevated subadult δ15 N results return to adult levels by approximately 3-4 years of age, indicating that the weaning process was completed during this period. Individuals between 2 and 10 years old, with lower δ13 C and δ15 N results than the adult mean, possibly consumed more plant-based diets, and this is consistent with Chinese medical teachings ∼1500 years later during the Tang Dynasty (AD 618-907). The isotopic offsets between the ribs and long bones revealed that five adults experienced dramatic dietary shifts in their later lives, switching from predominately C3 /C4 to C3 diets. This research provides the first isotopic information about ancient Chinese breastfeeding and weaning practices and establishes a foundation for future studies to examine diachronic trends.

Grain-scale stable carbon and oxygen isotopic variations of the international reference calcite, IAEA-603.

The new international reference material IAEA-603 (calcite) for stable carbon and oxygen isotopes (δ13 C and δ18 O values) was released in 2016 to replace the previous reference material, NBS19 (exhausted). We examined the grain-scale isotopic variations in IAEA-603 for application to microscale isotopic analysis of carbonate samples. Individual grains of IAEA-603 were analyzed with an IsoPrime100 isotope ratio mass spectrometer with a customized continuous-flow gas preparation system (MICAL3c). The individual grains of IAEA-603 were observed by optical and scanning electron microscopy, and their observational characteristics (grain color and size) were compared with their stable isotope compositions. Translucent grains (main component of IAEA-603; grain weight, 4-132μg) had homogeneous isotopic ratios, comparable with the grain-scale isotopic homogeneity of NBS 19. Their average δ13 C and δ18 O values were the same as the recommended values determined by the IAEA. Opaque (whitish) grains (1-2 per 100 grains; grain weight, 8-63μg) were significantly more depleted in 13 C and 18 O than the translucent grains. Low-abundance opaque grains (1-2 grains out of 100 grains) have lower δ13 C and δ18 O values, suggesting that these grains should be eliminated when using IAEA-603 for single-grain (microscale) isotope analysis.

Organic matter in surface sediments from the Gulf of Mexico and South China Sea: Compositions, distributions and sources

Sediments from the Gulf of Mexico (GOM) and the South China Sea (SCS) were analyzed. The low δ13 C values of pentamethylicosane (PMIs) and fatty acids (−81.3 to −85.2‰) were found in only the S-1 sample collected from the GOM, indicating that methanogenic archaea associated with gas hydrate formation contributed to the sediment organic matter. Principle component analysis of fatty acids suggested that similar microbial biomass was found in the S-1, S-9, O-3 and O-5 samples. However, a comparison of the alkanes, fatty acids, and alcohols indicated that the percentage of n-alkan-2-ols in the S-1 sample from the GOM was the highest, while n-alkanes and n-fatty acids were the highest percentages in other samples from the GOM and SCS. This finding suggests that microbial species or the oxidation/reduction environment of the sample site of S-1 were different from those of the other samples. The present study provides a basis for detecting gas hydrate sites on the seafloor of the SCS.

Post-fire environments are favourable for plant functioning of seeder and resprouter Mediterranean shrubs, even under drought.

Understanding how drought affects seeder and resprouter plants during post-fire regeneration is important for the anticipation of Mediterranean vegetation vulnerability in a context of increasing drought and fire caused by climate change. A Mediterranean shrubland was subjected to various drought treatments (including 45% rainfall reduction, 7months droughtyr-1 ), before and after experimental burning, by means of a rainout-shelter system with an irrigation facility. Predawn shoot water potential (Ψpd ), relative growth rate (RGR), specific leaf area (SLA) and bulk leaf carbon isotopic composition (δ13 C) were monitored in the main woody species during the first 3yr after fire. Cistus ladanifer seedlings showed higher Ψpd , RGR and SLA, and lower δ13 C, than unburned plants during the first two post-fire years. Seedlings under drought maintained relatively high Ψpd , but suffered a decrease in Ψpd and RGR, and an increase in δ13 C, relative to control treatments. Erica arborea, E.scoparia and Phillyrea angustifolia resprouts had higher Ψpd and RGR than unburned plants during the first post-fire year. Resprouters were largely unaffected by drought. Overall, despite marked differences between the two functional groups, post-fire environments were favourable for plant functioning of both seeder and resprouter shrubs, even under the most severe drought conditions implemented.

Fast-slow life history is correlated with individual differences in movements and prey selection in an aquatic predator in the wild.

Fast and slow life histories are proposed to covary with consistent individual differences in behaviour, but little is known whether it holds in the wild, where individuals experience natural fluctuations of the environment. We investigated whether individual differences in behaviour, such as movement traits and prey selection, are linked to variation in life-history traits in Eurasian perch (Perca fluviatilis) in the wild. Using high-resolution acoustic telemetry, we collected the positional data of fish in a whole natural lake and estimated individual movement traits by fitting a two-state correlated random walk model. Prey selection was inferred from stable isotope analysis using scale samples. Life-history traits were estimated by fitting a biphasic growth model to an individual growth trajectory back-calculated from scale samples. Life-history traits were correlated with behavioural traits such as movements and prey selection. Individuals with higher reproductive effort were found to switch more frequently between active and inactive modes and show greater reliance on prey from pelagic pathways (indicated by lower δ13 C). Further, individuals with faster juvenile growth were found to stay active for a longer time during the adult stage. Our results demonstrate the link between individual behavioural differences and fast-slow life-history traits under ecologically relevant conditions.

Activation tagging in indica rice identifies ribosomal proteins as potential targets for manipulation of water-use efficiency and abiotic stress tolerance in plants.

We have generated 3900 enhancer-based activation-tagged plants, in addition to 1030 stable Dissociator-enhancer plants in a widely cultivated indica rice variety, BPT-5204. Of them, 3000 were screened for water-use efficiency (WUE) by analysing photosynthetic quantum efficiency and yield-related attributes under water-limiting conditions that identified 200 activation-tagged mutants, which were analysed for flanking sequences at the site of enhancer integration in the genome. We have further selected five plants with low Δ13 C, high quantum efficiency and increased plant yield compared with wild type for a detailed investigation. Expression studies of 18 genes in these mutants revealed that in four plants one of the three to four tagged genes became activated, while two genes were concurrently up-regulated in the fifth plant. Two genes coding for proteins involved in 60S ribosomal assembly, RPL6 and RPL23A, were among those that became activated by enhancers. Quantitative expression analysis of these two genes also corroborated the results on activating-tagging. The high up-regulation of RPL6 and RPL23A in various stress treatments and the presence of significant cis-regulatory elements in their promoter regions along with the high up-regulation of several of RPL genes in various stress treatments indicate that they are potential targets for manipulating WUE/abiotic stress tolerance.

Facies and integrated stratigraphy of the Upper Turonian (Upper Cretaceous) Großberg Formation south of Regensburg (Bavaria, southern Germany)

ABSTRACT Niebuhr, B., Richardt, N. and Wilmsen, M. 2012. Facies and integrated stratigraphy of the Upper Turonian (Upper Cretaceous) Grosberg Formation south of Regensburg (Bavaria, southern Germany). Acta Geologica Polonica, 62 (4), 595-615. Warszawa. The Upper Turonian Grosberg Formation of the Regensburg area (Danubian Cretaceous Group, Bavaria, southern Germany) has a mean thickness of 20-25 m and consists of sandy bioclastic calcarenites and calcareous sandstones which are rich in bryozoans, serpulids and bivalves (oysters, rudists, inoceramids). Eight facies types have been recognized that characterize deposition on a southward dipping homoclinal ramp: the inner ramp sub-environment was characterized by high-energy sandwave deposits (sandy bioclastic rud- and grainstones, bioclastic sandstones) with sheltered inter-shoal areas. In mid-ramp settings, bioturbated, glauconitic, calcareous sand- and siltstones as well as bioturbated, bioclastic wacke- and packstones predominate. The carbonate grain association of the Grosberg Formation describes a temperate bryomol facies with indicators of warm-water influences. An inferred surplus of land-derived nutrients resulted in eutrophic conditions and favoured the heterozoan communities of the Grosberg Ramp. Carbon stable isotope geochemistry cannot significantly contribute to the stratigraphic calibration of the Grosberg Formation due to the depleted and trendless bulk-rock δ13 C values, probably resulting from a shallow-water aquafacies with depleted δ13 C DIC values and low δ13 C values of syndepositional and early diagenetic carbonate phases. However, strongly enriched skeletal calcite δ13 C values support a correlation of the Grosberg Formation with the mid-Late Turonian positive Hitch Wood isotope event (Hyphantoceras Event of northern Germany). This interpretation is supported by biostratigraphic data and a range from the Mytiloides striatoconcentricus Zone into the lower My. scupini Zone is indicated by inoceramid bivalves. Both the base and top of the Grosberg Formation are characterized by unconformities. Sequence boundary SB Tu 4 at the base is a major regional erosion surface (erosional truncation of the underlying Kagerhoh Formation in the Regensburg area, fluvial incision at the base of the Seugast Member of the Roding Formation in the Bodenwohr area towards the north and northeast). It is suggested that this unconformity corresponds to a major sea-level drop recognized in many other Cretaceous basins below the Hitch Wood or Hyphantoceras Event. The transgression and highstand of the Grosberg Formation is concomitant to the deposition of the fluvial Seugast Member and the onlap of the marginal-marine “Veldensteiner Sandstein” onto the Frankische Alb. The unconformity at the top of the Grosberg Formation (late Late Turonian SB Tu 5) is indicated by a ferruginous firm-/ hardground and an underlying zone of strongly depleted δ13 C values. The abrupt superposition by deeper marine marls of the lower Hellkofen Formation (uppermost Turonian-Lower Coniacian) may be connected with inversion tectonics at the southwestern margin of the Bohemian Massif.

Holocene chemical weathering and climatic oscillations in north China: evidence from lacustrine sediments

Holocene lacustrine sediments from two isolated lakes in north China are investigated. Based on palaeoclimatic significance of independent proxies in lake sediments, Holocene chemical weathering, and hence climate change, has been reconstructed for dated sediment cores from Daihai Lake and Aibi Lake. During early to mid‐Holocene, higher weathering intensity occurred in the Daihai catchment under warm and humid climate conditions, and this reached a maximum at ˜5 kyr BP. However, synchronous proxy shifts from the two widely separated, isolated lake sediments indicate that there was a cool climate event during the early to mid‐Holocene transition. This is characterized by reduced weathering in each catchment, low δ13 C and δ18O of authigenic carbonate, and by lake level fluctuations. These might correspond to a global cooling signal identified in lakes, oceans, mollusc sequences, and polar ice cores, typically centred between ˜8.0 and 8.5 kyr BP. Dry conditions were experienced in Greenland, the North Atlantic and surrounding regions, and in broad monsoonal regions including Daihai at this time. However, recent extensive evidences as well as our data from the Aibi Lake sediments show that cool but wet conditions occurred in the central Eurasian continent at this time. After ˜2.5 kyr BP, a significant shift of independent sediment proxies indicates the beginning of the Neoglaciation with a higher frequency of fluctuations, including both the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Our continental records provide new evidence of the Holocene climate variability with global significance and highlight the different spatial nature of the response to oscillations associated with different climate patterns.

Post-metamorphic low δ13 C calcite in the Cycladic complex (Greece) and their implications for modeling fluid infiltration processes using carbon isotope compositions

Calcite veins and overgrowths with δ 13 C values of -12 ‰ to -8 ‰ and δ 18 O values of 24 ‰ to 27 ‰ are shown to be characteristic features of the Cyclades metamorphic complex of Greece. Field and petrographic characteristics and the marked carbon and oxygen isotope disequilibrium that the veins and overgrowths show with host metamorphic rocks indicate that they developed during post-metamorphic evolution of the complex. The low δ 13 C values are interpreted to be either the result of the oxidation of organic carbon or solution of soil CO 2 by surface waters moving downwards along extensional fractures generated during the late stages of exhumation. Carbon and oxygen isotopic compositions reported for the carbonate fraction of many pelitic schists on Naxos overlap with the range of these late carbonates and may in part reflect a contribution of this late calcite. Uncertainties regarding the origin of low δ 13 C values in the carbonates of metamorphic rocks shows that they must be used with caution as tracers of fluid-rock exchange

Diagenetically altered sabkha‐type Pleistocene dolomite from the Arabian Gulf

ABSTRACTDiagenetically altered Pleistocene dolomite occurs in the shallow subsurface of the Arabian Gulf, offshore of Al Jubayl, Saudi Arabia. This dolomite accumulated in relatively shallow marine to sabkha depositional environments. In contrast with the thin extent of most other Quaternary sabkha and sabkha‐related dolomite deposits, these deposits comprise a thick (>56 m) accumulation. Additionally, this Pleistocene dolomite displays a high degree of ordering and has a more nearly ideal stoichiometric composition than the dolomite from the depositionally and diagenetically analogous Abu Dhabi sabkha complex. The Pleistocene dolomite also has lower δ13 and δ18O values than the modern Abu Dhabi sabkha dolomite, and higher values than those commonly reported for analogous dolomite from the ancient rock record. The low δ18O values, in conjunction with the geological setting, indicate that the diagenetic waters were meteoric or mixed meteoric and marine in composition. Thus, the degree of ordering, stoichiometric and stable isotopic values indicate that this dolomite has undergone diagenetic alteration relative to its presumed Holocene precursor.