Organic Carbon Isotope Research Articles

Influence of a chromium reduction treatment in the analysis of organic carbon isotopes in Quaternary coastal plain incised valley sediments

This paper reports bulk organic carbon isotope data from a laboratory study designed to evaluate whether acid chromium reduction (ACR), commonly used to prepare rock/sediment samples for sulfur isotope analysis, significantly fractionates bulk organic carbon isotopes compared with the standard decarbonation (SD) method in Quaternary coastal plain incised valley sediments. In this study, 36 sediment samples obtained from a Quaternary sediment core from the Qiantang River incised valley on the East China coastal plain were tested. The results show differences in the δ13Corg values between the ACR and SD methods for Quaternary incised valley sediments ranging from – 0.97‰ to +0.34‰, with most values (86%) showing a negative bias. Approximately half of the samples yield δ13Corg values that differ by ≥ ± 0.3‰. The carbonate and total organic carbon (TOC) contents of the sediment samples have no significant effects on the bulk organic carbon isotopes derived by ACR. There is also no obvious correlation between the organic carbon loss by ACR and the difference of the δ13Corg values. We believe that ACR loses more 13C-enriched labile organic carbon and/or volatile organic compounds (VOCs) than SD, which leads to a negative bias in the δ13Corg values. The mineral composition was speculated to be related to a significant positive bias in the δ13Corg values by ACR observed in two particular samples and requires further study. Consequently, ACR should be used with caution for sediments containing primarily young labile organic carbon with medium to high TOC contents (TOC ≥ 0.5 wt %), as it may cause a large offset of the δ13Corg values compared with SD. However, ACR may be used for sediments containing organic matter primarily from terrestrial plants with relatively low TOC contents (TOC < 0.5 wt %).

Atmospheric and Oceanographic Forcing Impact Particle Flux Composition and Carbon Sequestration in the Eastern Mediterranean Sea: A Three-Year Time-Series Study in the Deep Ierapetra Basin

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the biotic composition and seasonal variability of sinking particles reaching abyssal depths. Herein, sinking particle flux data, collected in the deep Ierapetra Basin for a three-year period (June 2010 to June 2013), have been examined at the light of atmospheric and oceanographic parameters and main mass components (lithogenic, opal, carbonates, nitrogen, and organic carbon), stable isotopes of particulate organic carbon (POC) and source-specific lipid biomarkers. Our aim is to improve the current understanding of the dynamics of particle fluxes and the linkages between atmospheric dynamics and ocean biogeochemistry shaping the export of organic matter in the deep Eastern Mediterranean Sea. Overall, particle fluxes showed seasonality and interannual variability over the studied period. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Summer export was approximately fourfold higher than mean wintertime, fall and springtime (except for the episodic event of spring 2012), fueling efficient organic carbon sequestration. Lipid biomarkers indicate a high relative contribution of natural and anthropogenic, marine- and land-derived POC during both spring (April–May) and summer (June–July) reaching the deep-sea floor. Moreover, our results highlight that both seasonal and episodic pulses are crucial for POC export, while the coupling of extreme weather events and atmospheric deposition can trigger the influx of both marine labile carbon and anthropogenic compounds to the deep Levantine Sea. Finally, the comparison of time series data of sinking particulate flux with the corresponding biogeochemical parameters data previously reported for surface sediment samples from the deep-sea shed light on the benthic–pelagic coupling in the study area. Thus, this study underscores that accounting the seasonal and episodic pulses of organic carbon into the deep sea is critical in modeling the depth and intensity of natural and anthropogenic POC sequestration, and for a better understanding of the global carbon cycle.

Evidence of terrestrial organic carbon inputs on Niger Delta Sea Shelf

The objective of this research is to determine the actual source of organic matter in the Niger Delta Sea Shelf (NDSS). Organic carbon (OC) and n-alkanes were investigated in the suspended matter (SM) and surfcial sediments of the Niger and Imo Rivers and the opposite Niger Delta Sea Shelf. Organic nitrogen and carbon isotope (δ13C) values were determined as additional parameters in the sediments. OC and n-alkane concentrations were highly variable. This variability was interpreted as the result of sources of materials from the inland basins and a complex sedimentation pattern involving the discharges of these two rivers. Using the constant ratio of high molecular weight odd n-alkanes to OC in both rivers, the estimated value of more than 70% of the OC preserved in shelf sediments were terrestrially-derived. This result was substantiated by the overall dominance of land-derived n-alkanes. A second approach using δ13C values and assuming binary dilution of riverine and marine OC led to the determined source of organic matter.&#x0D; Keywords: Organic carbon; δ13C; n-Alkanes; Niger River; Imo River; Niger Delta Sea Shelf.

Carbon and sulfur isotope variations through the Upper Ordovician and Lower Silurian of South China linked to volcanism

Pronounced excursions of carbon and sulfur isotopes (δ13C and δ34S) spanning the Ordovician–Silurian (O–S) transition have been recognized globally, yet the causes of these isotope events and their causal relationships to environmental changes, especially during Early Silurian time, remain the topics of debate. In this study, we present organic carbon and pyrite sulfur isotope (δ13Corg and δ34Spyr) records and elemental concentrations from a drill core spanning from the Upper Ordovician (Katian) to Lower Silurian (Aeronian) succession of the Yangtze Platform, China. The newly presented δ13Corg profile records previously recognized positive excursions, including the Hirnantian isotopic carbon excursion (HICE), the middle Rhuddanian excursion, and the early Aeronian positive carbon isotope excursion (EACIE). In addition, two negative δ13Corg excursions are recognized during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian stages. The δ34Spyr profile exhibits a great amount of variation (−17.8‰ to +19.6‰) but mimics the δ13Corg record. Coupled positive δ13Corg and δ34Spyr excursions during the middle Hirnantian and late Rhuddanian to Aeronian are associated with decreased total organic carbon (TOC) content and less reducing water column conditions, whereas the negative δ13Corg and δ34Spyr excursions during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian are associated with enhanced TOC values and the establishment of more strongly anoxic to euxinic conditions. The δ13C and δ34S excursions during the O–S transition, then, cannot be explained by changes in redox conditions or the burial of organic carbon and pyrite. The heavier and less variable middle Hirnantian and late Rhuddanian to Aeronian δ34Spyr values probably reflect low marine sulfate concentration. In contrast, negative Katian to early Hirnantian and late Hirnantian to middle Rhuddanian δ34Spyr excursions may reflect increased sulfate concentration. The two negative δ13Corg and δ34Spyr excursions associated with the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian correspond with episodes of volcanism. We therefore propose that volcanism was the main driver of coupled negative δ13Corg and δ34Spyr excursions. As volcanism diminished during the middle Hirnantian and late Rhuddanian to Aeronian, both δ13Corg and δ34Spyr returned to more positive values. Our results indicate that volcanism played a crucial role in triggering carbon and sulfur isotope perturbations and environmental changes during the Late Ordovician and Early Silurian.

Biostratigraphic significance and geometric morphometrics of Euestheria gutta (Crustacea: Branchiopoda: Spinicaudata): An index fossil of continental Permian–Triassic transitional beds

The Permian–Triassic mass extinction was the largest biotic extinction event in the Phanerozoic and affected both marine and continental life. Marine Permian–Triassic transitional sequences can be correlated in many regions, but this has proved difficult for continental successions. A growing number of studies show that spinicaudatans are some of the most common fossils in continental strata and can be used as index fossils for continental stratigraphic division and correlation. Here we document the morphology and biostratigraphic significance of Euestheria gutta based on well‐preserved fossils from southwestern China. It shows strong intraspecific morphological variation, while the most important feature is the strongly convex larval valve and significant finely pitted to weakly reticulated ornamentation on the growth bands. Evidence from palaeobotany, charcoal, and organic carbon isotopes indicated that the continental mass extinction in southwestern China was marked by the catastrophic loss of tropical rainforest vegetation, enhanced wildfire and a negative carbon isotope excursion (CIE) during the P–Tr transition. Meanwhile, abundant E. gutta first appeared at the onset of the negative CIE and just above the horizon of the loss of macroflora. Based on the global geographic distribution of E. gutta and temporal correlation, we conclude that this species existed from the latest Permian to the earliest Triassic, and the occurrence of E. gutta could be used as an index fossil of the continental mass extinction interval or P–Tr transitional beds.

Deep‐Water Formation in the North Pacific During the Late Miocene Global Cooling

AbstractA multiproxy study including organic carbon and bulk nitrogen isotopes along with major and trace element concentrations in sediments from Integrated Ocean Drilling Program (IODP) Sites U1425 and U1430 in the Japan Sea have been conducted in order to trace deep‐water evolution in the Japan Sea and the North Pacific since the late Miocene. The high total organic carbon (TOC) flux, as well as other published geochemical and sedimentary evidence, indicates the occurrence of anoxic deep‐water in the Japan Sea before ∼7.4 Ma. The low‐nitrogen isotope values probably suggest nearly complete denitrification. In contrast, the sharply enhanced biological production but decreased burial of organic matter during ∼7.4–4 Ma, as shown by high enrichment factor of Ba (BaEF) values, together with low TOC flux, highlights enhanced deep‐water oxygenation in the Japan Sea during that time. We suggest that deep‐water formation in the North Pacific ventilated the deep Japan Sea via northern deep seaways before the sea became semi‐closed in the early Pliocene. The synchronously increased equator‐to‐pole temperature gradients driven by late Miocene global cooling may have caused southward shift of mid‐latitude storm tracks, coupled with the weakened East Asian summer monsoon and moisture transport, leading to decreased precipitation in mid‐latitude regions. The potential increases in surface salinity in the North Pacific may have broken the ocean stratification and favored deep‐water formation, and further caused deep‐water ventilation in the Japan Sea.

Water depth control on n-alkane distribution and organic carbon isotope in mid-latitude Asian lakes

The relative proportion of mid-chain to long chain n-alkane homologues and isotopic compositions of total organic carbon (Paq and δ13Corg) have been proposed as potential lake-level proxies since such features mainly come from submerged aquatic plants living within an optimum range of lake water depth. With limited dataset available, the applicability of both indices and their sensitivity to lake water depth changes across a broad geographic extent need further investigation. Here we report Paq and δ13Corg values in surface sediments collected from 55 lakes in mid-latitude Asia. We have found an arched relationship between Paq index and water depth, with high Paq values occurring at the depth of ~1–10 m, while sediments from shallower and deeper water lakes have relatively low Paq values. δ13Corg variation resembles an arched pattern with depth in freshwater and brackish lakes, with relatively high δ13Corg values also corresponding to the depth of ~1–10 m, but substantially high δ13Corg values in hypersaline environments (salinity > ~100,000 mg/L) obscure the arched δ13Corg-depth relationship. We suggest that both indices respond to the structure of aquatic plant community, especially the biomass of submerged plants. Our results confirm that Paq and δ13Corg can be used to infer lake-level changes in mid-latitude Asia, but other influencing factors have to be considered before applying the two proxies to down-core reconstructions, and combined utilization of the Paq and δ13Corg indicators could improve the reliability of paleohydrological reconstructions.

Preliminary Assessment of Carbon and Nitrogen Sequestration Potential of Wildfire-Derived Sediments Stored by Erosion Control Structures in Forest Ecosystems, Southwest USA

The role of pyrogenic carbon (PyC) in the global carbon cycle is still incompletely characterized. Much work has been done to characterize PyC on landforms and in soils where it originates or in “terminal” reservoirs such as marine sediments. Less is known about intermediate reservoirs such as streams and rivers, and few studies have characterized hillslope and in-stream erosion control structures (ECS) designed to capture soils and sediments destabilized by wildfire. In this preliminary study, organic carbon (OC), total nitrogen (N), and stable isotope parameters, δ13C and δ15N, were compared to assess opportunities for carbon and nitrogen sequestration in postwildfire sediments (fluvents) deposited upgradient of ECS in ephemeral- and intermittent-stream channels. The variability of OC, N, δ13C, and δ15N were analyzed in conjunction with fire history, age of captured sediments, topographic position, and land cover. Comparison of samples in 2 watersheds indicates higher OC and N in ECS with more recently captured sediments located downstream of areas with higher burn severity. This is likely a consequence of (1) higher burn severity causing greater runoff, erosion, and transport of OC (organic matter) to ECS and (2) greater cumulative loss of OC and N in older sediments stored behind older ECS. In addition, C/N, δ13C, and δ15N results suggest that organic matter in sediments stored at older ECS are enriched in microbially processed biomass relative to those at newer ECS. We conservatively estimated the potential mean annual capture of OC by ECS, using values from the watershed with lower levels of OC, to be 3 to 4 metric tons, with a total potential storage of 293 to 368 metric tons in a watershed of 7.7 km2 and total area of 2000 ECS estimated at 2.6 ha (203-255 metric tons/ha). We extrapolated the OC results to the regional level (southwest USA) to estimate the potential for carbon sequestration using these practices. We estimated a potential of 0.01 Pg, which is significant in terms of ecosystem services and regional efforts to promote carbon storage.

Changes in depositional environment of the Savitri (tropical) estuary, central west coast of India

Transformation of coastal regions as a result of recent climate change and localised human influences is of concern. Thus, understanding of the changes that have already occurred, the processes responsible for these changes, and their impact on coastal depositional environment is important. Large and well-developed intertidal mudflats of Savitri estuary of central west coast of India are well suited for this purpose. The distribution of sediment components, total organic carbon, total nitrogen, total phosphorous, sedimentary organic carbon isotope ratios (δ13Corg), diatoms, pH, and metals (Fe, Mn, Al, Ni, Cr, Co, Zn, Pb) of two mudflat sediment cores, S-18 from lower estuary and S-41 from middle estuary of Savitri estuary, are presented in this paper. The enrichment of δ13Corg values from bottom to surface as well as dominance of marine diatom species towards the surface of core S-18 was attributed to the decrease in freshwater inflow to the estuary as a result of decreased rainfall, and runoff, while, increase in organic nutrient load in cores S-18 and S-41, was may be due to input from anthropogenic activities in recent years and changes in depositional environment of Savitri estuary.

Middle Holocene Coastal Environmental and Climate Change on the Southern Coast of Korea

We obtained a 15 m drill core from Deukryang Bay on the southwest coast of Korea, which is now an area of reclaimed land used for agriculture. We investigated changes in the depositional environment and hydrological climate responses to sea level changes using sedimentary facies, radiocarbon ages, grain-size analysis, total organic carbon (TOC), total sulfur (TS), and stable carbon isotopes (δ13C). Sediment deposition began at 12,000 cal yr BP and was divided into four stages based on changes from fluvial to intertidal environments related to Holocene marine transgression events. Stage 1 (&gt;10,000 cal yr BP) is represented by fluvial sediments; Stage 2 (10,000–7080 cal yr BP) is represented by the deposition of mud facies in an intertidal zone in response to sea level rise; Stage 3 (7080–3300 cal yr BP) was a period of gradually descending sea level following the Holocene maximum sea level and is characterized by gradual changes in TOC, TS, and C/S ratios compared with the mud facies of Stage 2. Stage 4 (3300 to present) was deposited in a supratidal zone and contains low TS and an abundance of TOC. Based on our TS and C/S ratio results, the south coast of Korea was mainly affected by sea level rise between 7000 and 3000 cal yr BP, during the middle Holocene. At 3000 cal yr BP, sea level began to stabilize or gradually decrease. In addition, changes in δ13C values are clearly observed since ca. 5000 cal yr BP, in particular, large hydrological changes via freshwater input are confirmed in 4000–3000 cal yr BP. We consider these shifts in freshwater input indicators of an increased influence of El Niño and La Niña conditions, related to the weakening of the East Asian Summer Monsoon (EASM) and changes in sea surface temperature (SST) of the Western Pacific Ocean during the middle Holocene climatic optimum (between 7800 and 5000 cal yr BP). The cooling periods of SST in East Asia between 8400 and 6600 cal yr BP reported from the west coast of Korea are related closely to changes in vegetation (as evidenced by δ13C) from 7700 cal yrs BP to the present in the southwest coast of Korea. We interpret the freshwater input events at 4000–3000 cal yr BP to be related to changes in SST in response to the weakening of the EASM on the southwest coast of Korea. However, additional research is needed to study the southward migration effect of the westerly jet related to SST and atmospheric circulation controlling terrestrial climate in the middle Holocene.

Biogeochemical evolution and organic carbon deposition on the Northwestern European Shelf during the Toarcian Ocean Anoxic Event

The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) represents a well-known episode of organic-rich deposition, which is accompanied by a substantial negative carbon-isotope excursion (CIE). Underpinning the relationships between the carbon-cycle perturbation, ocean anoxia, primary productivity feedbacks and the enrichment of sedimentary organic carbon remains a major challenge. Here, we present high-resolution geochemical, palynological and organofacies data from three lower Toarcian successions from the NW European shelf, spanning the T-OAE. Chronostratigraphic calibration of the successions is achieved through organic carbon isotope (δ13C) records. Iron-speciation and major and trace-element data indicate that bottom-waters were euxinic and intermittently anoxic-ferruginous prior to, throughout and beyond the CIE. In terms of organofacies and palynological composition, the CIE-interval is dominated by dense clusters of amorphous organic matter containing abundant small spherical prasinophyte cysts (Halosphaeropsis liassica). The peak CIE is bracketed by a major increase in abundance of prasinophycean vegetative cysts (Tasmanites and Pleurozonaria spp.). On the basis of their modern physiology, this suggests shoaling of the chemocline into the photic zone. The combined proxy data suggest a scenario in which anoxygenic photosynthetic productivity proliferated in nutrient-rich, anoxic to seasonally euxinic surface-waters of the stratified NW-European shelf during the CIE. A return to oxic-marine conditions is recorded by the recurrence of organic-walled dinoflagellate cysts in accordance with enhanced water column mixing post CIE. This is concurrent with a gradual termination of strongly stratified conditions across the NW-European shelf.

Mineralogy and geochemistry of deeply-buried marine sediments of the Vaca Muerta-Quintuco system in the Neuquén Basin (Chacay Melehue section), Argentina: Paleoclimatic and paleoenvironmental implications for the global Tithonian-Valanginian reconstructions

The Vaca Muerta-Quintuco (VM-Q) system of Tithonian-early Valanginian age was studied in the Chacay Melehue section of the Neuquén Basin (western Argentina) by means of sedimentological, mineralogical and geochemical analyses in order to determine the main driving factors that triggered the paleoenvironmental change from a carbonate ramp (Vaca Muerta Formation, VMFm) to a mixed siliciclastic/carbonatic marine environment (Quintuco Formation, QFm). The VMFm was divided into two stratigraphic intervals: Lower VMFm (LVMFm) and Upper VMFm (UVMFm), whereas the QFm is subdivided into the Puesto Barros Member (PBMb) and the Cerro La Visera Member (CVMb), which can be correlated to other sections in the basin (e.g., Puerta Curaco). Isolated, turbiditic sandstone beds, correlated to the Huncal Member, are included in the QFm.The LVMFm (Tithonian) and the UVMFm (Berriasian) are constituted by dark, well-laminated marls, mudstones, calcite concretions and tuffs. The PBMb (earlier early Valanginian) is constituted by marls and sandstones, whereas the CVMb (later early Valanginian) is constituted by marls, mudstones, siltstones, sandstones and coquinas. The LVMFm (Total organic carbon, TOC ~ 1–4 wt%) is characterized by the enrichment of redox sensitive trace elements (RSTE), where the enrichment of Ni and Cu suggest high productivity in the water column, and the enrichment of Mo, U, V points to sea bottom anoxia, with periods of increased oxygenation as deduced from higher P concentrations in marls and mudstones. The clay mineral association is constituted by mixed-layer illite/smectite formed by the transformation of smectitic layers. The predominance of smectite in coeval sucessions, less overprinted by burial diagenesis, suggests a temperate and semi-arid climate in the adjacent continent. The UVMFm (TOC ~ >1 wt%) is characterized by a gradual decrease of the RSTE pointing to a decrease in productivity and a slight increase in the oxygenation of the sea bottom. In addition, a change towards more humid conditions in the continent is inferred by both the increase in the Chemical Index of Alteration and the Al2O3/TiO2 ratio. The PBMb (TOC ~1 wt%) has even lower content of RSTE indicating diminished sea water productivity and a gradual rise of the oxygenation of the sea bottom. In this interval, increased illite contents suggest periods of enhanced physical weathering, probably related to the tectonic uplift of the Huincul Ridge. The RSTE in the CVMb (TOC <1 wt%) documents a fully oxygenated sea bottom, where the productivity of the water column was negligible. The presence of kaolinite and the increment of the detrital sedimentation in the CVMb indicate a change towards more humid conditions in the hinterlands. The enhanced runoff caused by this paleoclimatic change towards more humid conditions that started in the early Berriasian and increased during the later early Valanginian triggered the change from carbonate ramp to mixed siliciclastic/carbonatic to siliciclastic marine paleoenvironments. The organic carbon isotope composition (δ13Corg vs. VPDB) of the VMFm ranges between −30.0 and −23.4‰, whereas in the QFm values range between −29.0 and −23.9‰. Two positive carbon isotope excursions (PCIE) are recorded in the system: PCIE-A in the lower part of the VMFm (early Tithonian) with δ13Corg values ~ −25‰, and PCIE-B in the upper part of the QFm (later early Valanginian) with δ13Corg values ~ −24.5‰. The shift in δ13Corg at PCIE-B is up to +4.2‰ and marks the onset of the Weissert Event. This is the first time that the onset of this event is recorded in the Neuquén Basin, within the Lissonia riveroi ammonite zone. The results of our study confirm that clay mineralogy, trace elements and stable isotopes are valuable proxies of past ocean-climate variability even in sediment deposits that underwent near-surface and deep burial diagenesis.

Soil carbon degradation during the Paleocene-Eocene Thermal Maximum in the Piceance Basin, USA

The Paleocene-Eocene Thermal Maximum (PETM) warming event is marked by a negative carbon isotope excursion (CIE). The magnitude and shape of the CIE differs among carbon archives, but bulk organic carbon isotopes (δ13Corg) in terrestrial sections are often particularly variable and attenuated. Multiple lines of evidence from the Bighorn Basin, Wyoming, USA have revealed that extensive organic carbon degradation and increased refractory or allochthonous carbon inputs diminished the δ13Corg excursion magnitude. To test if this was a spatially widespread phenomenon and to understand possible underlying mechanisms, we examined the abundance of total organic carbon (%TOC) and polycyclic aromatic hydrocarbons (PAHs) as metrics of soil degradation at a neighboring terrestrial basin, the Piceance Basin in Colorado. Outcrop samples reveal both diminished %TOC and PAH concentrations across the Paleocene-Eocene boundary. Using PAHs as a proxy for intermediate refractory carbon, such as found in mineral soils, evidence from the Piceance Basin supports increased organic carbon degradation and greater proportions of refractory allochthonous carbon remaining. Correlations between %TOC and elemental oxides (e.g., Al2O3 and TiO2) suggest soil organic carbon was stabilized by its association with clay minerals. We hypothesize that decreased clay content in the soils (which reduced soil capacity to stabilize fresh carbon) and increased fluctuations in soil moisture (which destabilized older, refractory carbon), in conjunction with increased temperatures (which increased microbial decomposition rates), contributed to reduced soil organic matter preservation during the PETM. These mechanisms destabilized carbon on millennial timescales and, with sustained higher temperatures across the PETM (~150,000 years), increased soil carbon degradation persisted for tens of thousands of years.

Geochemical characteristics of organic carbon and pyrite sulfur in Ordovician-Silurian transition shales in the Yangtze Platform, South China: Implications for the depositional environment

Global climate change and tectonism are principal causes of spatial and temporal differences in Ordovician-Silurian (OS) transition sedimentary environments of China's Upper Yangtze Platform. However, the relative significance of each of these drivers is not always obvious. This paper describes results of a geochemical study of a drill core section (Well X3) recovered from Xiang'e Submarine High in the central part of the Upper Yangtze Platform. This work focused on shale deposits of the Wufeng Formation and Longmaxi Formation that accumulated during the OS transition. Geochemical characteristics, including total organic carbon (TOC), pyrite S (Spy), stable carbon and sulfur isotopes, and Mo and U enrichment values, were combined with pyrite framboid size distribution data to reconstruct the OS paleoenvironmental evolution of this region of the Upper Yangtze Platform. The studied succession appears to record the transition from lower Katian-Hirnantian shale deposited under sulfate-limited conditions to Rhuddanian organic-rich shale and finally to organic-depleted Aeronian sediment. The depositional history of these deposits was controlled by changes in water depth and watermass chemistry as a result of changing sea level. The sea-level history of the studied succession was largely controlled by global climate change related to Hirnantian glaciation and Rhuddanian warming and tectonism associated with the Kwangsian Orogeny that resulted in uplift of the Xiang'e Submarine High. Similar geochemical investigation of the Pengshui and Shuanghe sections, also in the Upper Yangtze Platform, demonstrate the dominant role of global climate change and tectonism in controlling organic carbon content and thickness of potential shale gas targets. Specifically, the low concentrations of organic carbon in thin shale deposits proximal to uplifted regions of the basin pose a major risk to shale gas exploration.

LONG-TERM CHANGES IN 14C AGE DIFFERENCES BETWEEN HUMIC ACID AND PLANT FRAGMENTS AND THEIR LINKS TO PAST CLIMATE CHANGE

ABSTRACTRadiocarbon (14C) dating has been widely used to determine the age of deposits, but there have been frequent reports of inconsistencies in age among different dating materials. In this study, we performed radiocarbon dating on a total of 33 samples from 8-m-long sediment cores recovered from the wetland of the Muljangori volcanic cone on Jeju Island, South Korea. Ten pairs of humic acid (HA) and plant fragments (PF) samples, and three pairs of HA and humin samples, from the same depths were compared in terms of age. The PF were consistently younger than the HA. Interestingly, the age difference between HA and PF samples showed a long-term change during the past 8000 years. To test whether there was an association between this long-term age difference and climate change, we compared with the carbon/nitrogen (C/N) ratios and total organic carbon isotope (δ13CTOC) values of the sediments, as indicators of the relative abundance of terrestrial and aquatic plants; these parameters showed similar long-term trends. This suggests that the increasing (decreasing) trend in age difference was influenced by long-term dry (wet) climate change.

Alternative viewpoints on the nature and importance of a prominent syncline at the northeastern edge of Wyoming’s Hanna Basin

ABSTRACTThe geologic history of Wyoming’s Hanna Basin is still being written. Surprisingly, here appeared an opportunity to share insights from previously accomplished work with that conducted anew by other scholars. The area of study was in the southeastern quadrant of Wyoming, which exhibits the state’s most complex history with respect to the Laramide orogeny. Especially important for present purposes were the tectonic conditions of the late Paleocene and earliest Eocene, recorded within the Hanna Formation. Of central focus is the 2020 publication by Dechesne and her six co-authors. Geographically, the landscape they covered was a thin, synclinal slice of the northeastern margin of the Hanna Basin. Key goals for the present publication have been to illustrate positive linkages and to highlight discrepancies between Dechesne et al. (2020) and relevant prior geological work. A concern that permeates all facets of this approach is the ability to verify viability of brand-new geologic descriptions, data, and resulting conclusions. Essential graphical elements were introduced first into this present publication. Once that package of background information was available, more focused analyses were rigorously pursued on diverse issues within the Dechesne et al. (2020) publication. Dechesne’s team presented a significantly modified but adequately defended approximation of the Paleocene–Eocene boundary. Data from fossil plants (macro- and palynofloras), continental mollusks, and bulk organic-carbon isotopes all agree within one measured section (of five sections studied) with an approximated Paleocene–Eocene boundary along with a ‘carbon isotope excursion’ (CIE). Strength of available evidence seems questionable, however, in that the inordinately high variability in bulk organic carbon (characteristic of a CIE) has been demonstrated only in the Hanna Draw Section. Although fluvial, paludal, and lacustrine facies are considered in several contexts, in no sense does the publication’s organizational form provide a ‘detailed stratigraphic framework.’ One zircon-based U–Pb depositional date (54.42 ± 0.27 Ma) came from this study that matched early Wasatchian time. Participants in the Dechesne et al. (2020) project are to be commended in that their resulting paper ranged broadly across the geologic setting, stratigraphy, paleocurrents, paleobotany, continental mollusks, zircon geochronology, associated lithofacies, and paleogeography. Despite that breadth, there exists a plethora of unexpected and wholly avoidable inconsistencies, strong contradictions within what should be homogeneous datasets, and seemingly inexplicable omissions of obviously necessary and sometimes clearly existing but unutilized data, one must question the reliability of much of the information presented in their paper.

Reconstructing past variations in environmental conditions and paleoproductivity over the last ∼ 8000 years off north-central Chile (30° S)

Abstract. The aim of this project was to establish past variations in the main oceanographic and climatic features of a transitional semiarid ecosystem on the north-central Chilean coast. We analyzed recent sedimentary records retrieved from two bays, Guanaqueros and Tongoy (30∘ S), for geochemical and biological analyses, including the following: sensitive redox trace elements, biogenic opal, total organic carbon (TOC), diatoms and stable isotopes of organic carbon and nitrogen. Three remarkable periods were established with different environmental conditions and productivities: (1) &gt; 6600 cal BP, (2) 4500–1800 cal BP and (3) 140 cal BP to the present (2015 CE). The first period was characterized by a remarkably higher productivity (higher diatom abundances and opal) in which large fluxes of organic compounds were also inferred from the accumulation of elements, such as Ba, Ca, Ni, Cd and P, in the sediments. Meanwhile, significantly reduced conditions at the bottom of the bays were suggested based on the large accumulation of Mo, Re and U, showing a peak at 6600 cal BP, when sulfidic conditions could have been present. According to the pollen moisture index (PMI), this was also identified as the driest interval. These conditions should be associated with an intensification of the Southern Pacific Subtropical Anticyclone (SPSA) and stronger southerly western winds, emulating La Niña-like conditions, as has been described for the SE Pacific during the early Holocene and part of the mid-Holocene. During most of the second period, lower productivity was observed; however, a small increase was identified between 3400 and 4000 cal BP, although lower amounts of diatom (valves g−1) and nutrient-type metal accumulations were evident. Anoxic conditions at the bottom of the bays changed to an almost stable suboxic condition during this time interval. The third period was marked by intense oxygenation after 1800 cal BP, as observed by a drastic change in the accumulation of U, Mo and Re. This was followed by a return to more reduced conditions over the past 2 centuries, characterized by a small productivity rise after ∼140 cal BP, as suggested by the opal accumulations. Overall, lower primary productivity, lower reduced conditions at the bottom and higher-humidity conditions were established after 6600 cal BP to the present. We suggest that the oxygenation might be associated with a weak effect from the oxygen minimum zone over the shelf and intensified El Niño activity, introducing oxygenated waters to the coastal zones through the propagation of equatorial waves and establishment of conditions that reduced the primary productivity from the mid-Holocene toward the beginning of the modern era.

Characteristics and geological significance of germanium in Taiyuan coal formation of Huainan Coalfield, Anhui, China

HN-1# is the first fully working coring well of the Taiyuan Formation (Ty) in the Huinan Coalfield and exploration studies are currently underway on the associated resources of the coal-bearing strata. The HN-1# well is located in the Fufeng thrust nappe structural belt in the south of the Huainan Coalfield. Three coal samples from the Ty were collected from HN-1# and inductively-coupled plasma mass spectrometry and inductively-coupled plasma atomic emission spectrometry were used to determine the Ge content of each sample. Based on proximate and ultimate analyses, microscopy data, and analyses of the ash products, some important findings were made. The Ty coal samples had a relatively high total sulfur (St,d) content (4.24%), thus the coal was considered to be a lower ranked coal (high volatility bituminous coal), which also had a low coal ash composition index (k, 1.87). Collodetrinite was the main submaceral of the Ty coal. Small amounts of pyrite particles were found in the coal seams of the Ty, while the contents of pyrite and algae in the top and bottom sections of the coal seam were relatively high, which meant that the swampy peat conditions which existed during the formation of the coal seams were affected by seawater; also the degree of mineralization of the coal seam was relatively high, which is consistent with reducing conditions in a coastal environment setting. Atomic force microscopy (AFM) experiments showed that the modes of occurrence of Ge in the Ty coal were mainly those for organic-bound and adsorbed Ge species. The organic carbon isotope values for the Ty coal ranged from − 24.1‰ to − 23.8‰, with an average value of − 24.0‰, which is equivalent to the value for terrestrial plants (average value − 24.0‰). The Ge content of the Ty coal was 13.57 mg/kg. The Ge content was negatively correlated with volatile matter and the ash yield.

Early Jurassic (Toarcian) warming identified from lacustrine sediments of eastern Liaoning, China

AbstractThis study focuses on the Tianshifu Basin, eastern Liaoning, China, which is filled with Lower–Middle Jurassic fluviolacustrine sediments rich in macroplants. Our aim is to explore the continental climate features of the late Early Jurassic period. The composition of the Early–Middle Jurassic flora and the carbon isotopic ratios of organic matter, total organic carbon, total organic nitrogen and sulphur of the rock samples from the Changliangzi section (the upper part of the Lower Jurassic deposits) have been investigated. Based on the flora, eastern Liaoning was generally characterized by temperate and humid conditions during the Early–Middle Jurassic period, but with rising temperatures during late Early Jurassic time. The sediments of the Changliangzi section show a transformation from shallow-lake facies to deep-lake facies. A positive organic carbon isotope excursion correlates with the deepening of this palaeolake, considered to be caused by climate warming. The late Early Jurassic climate warming indicated by floral and isotopic evidence corresponds to the climatic events recorded elsewhere in marine and continental sequences during the Toarcian Age, the so-called Toarcian Anoxic event, and may be associated with enhanced global greenhouse warming. This study provides new continental data supporting global warming during the late Early Jurassic period.

Molecular and isotopic evidence reveals the end-Triassic carbon isotope excursion is not from massive exogenous light carbon

The negative organic carbon isotope excursion (CIE) associated with the end-Triassic mass extinction (ETE) is conventionally interpreted as the result of a massive flux of isotopically light carbon from exogenous sources into the atmosphere (e.g., thermogenic methane and/or methane clathrate dissociation linked to the Central Atlantic Magmatic Province [CAMP]). Instead, we demonstrate that at its type locality in the Bristol Channel Basin (UK), the CIE was caused by a marine to nonmarine transition resulting from an abrupt relative sea level drop. Our biomarker and compound-specific carbon isotopic data show that the emergence of microbial mats, influenced by an influx of fresh to brackish water, provided isotopically light carbon to both organic and inorganic carbon pools in centimeter-scale water depths, leading to the negative CIE. Thus, the iconic CIE and the disappearance of marine biota at the type locality are the result of local environmental change and do not mark either the global extinction event or input of exogenous light carbon into the atmosphere. Instead, the main extinction phase occurs slightly later in marine strata, where it is coeval with terrestrial extinctions and ocean acidification driven by CAMP-induced increases in Pco2; these effects should not be conflated with the CIE. An abrupt sea-level fall observed in the Central European basins reflects the tectonic consequences of the initial CAMP emplacement, with broad implications for all extinction events related to large igneous provinces.