Carbon Isotope Profiles Research Articles

Multiple controls on the preservation of organic matter in the lower Mississippian Luzhai Formation black shale in southern China

The early Carboniferous experienced profound climate cooling that drove the Earth's climate from a mid-Paleozoic greenhouse into the Late Paleozoic Ice Age. Several climate cooling events have been reported, including the Tournaisian and Visean (early to mid-Early Carboniferous). In this study, we perform multi-proxy analyses (organic carbon isotopes, nitrogen isotopes, major and trace elements and organic petrology/geochemistry) of samples from an early Carboniferous section in Nandan region (Guangxi, China). Our goal is to investigate the global carbon‑nitrogen cycle, and associated oceanic productivity and redox perturbations, during a key climatic transition interval, as well as the controls on organic matter enrichment in the sediments. The carbon and nitrogen isotope profiles of the Nandan section record major perturbations during the mid-Tournaisian and early Visean. The mid-Tournaisian carbon isotope excursion (TICE) is marked by a positive δ13Corg shift of 1.8 ‰ (from −27.7 ‰ to −25.9 ‰), correlating with a positive δ15N shift. The early Visean carbon isotope excursion (VICE) is characterized by a positive shift in δ13Corg (from −28.2 to −25.5 ‰, with an excursion magnitude of 2.7 ‰), but associated with a negative shift in δ15N (from +5 ‰ to +4 ‰). The positive δ13Corg excursions during these events most likely reflect enhanced organic matter burial with expansion of anoxic seafloor in the global ocean. The drop in nitrogen isotope values in the early Visean is interpreted to be linked with less denitrification under more oxic conditions. The decrease of organic matter contents up section is consistent with the shift to more oxic conditions and increased sedimentary dilution caused by sea-level fall, which is ultimately controlled by orogenic events and climate cooling.

Fisheries shocks provide an opportunity to reveal multiple recruitment sources of sardine in the Sea of Japan

The abrupt decline in sardine catches in the Sea of Japan and the East China Sea (SJ-ECS) in 2014 and 2019 and the recovery in the following years call into question the current assumption that sardines in the SJ-ECS form a self-recruiting subpopulation. To test this hypothesis, we analysed otolith stable oxygen and carbon isotope profiles (δ18O, δ13C) of age-0 and age-1 sardines from 2010 and 2013–2015 year-classes captured in the SJ-ECS, as geographic markers for nursery areas. Age-0 sardines generally showed a significant ontogenetic decrease in otolith δ18O from larval to juvenile stages. However, the majority of age-1 captured in spring 2011, 2015 and 2016 showed non-decreasing otolith δ18O profiles, suggesting that the age-0 off the Japanese coast were not the main source of recruitment. Different migration groups were thus indicated: the “locals” growing up off the Japanese coast and the migrating “nonlocals”. The isotope profiles of the “nonlocals” overlapped with those of age-0 captured in the subarctic North Pacific, suggesting that they may be migrants from the Pacific, or perhaps an unobserved northward migration group in the SJ-ECS. Our results highlight the considerable uncertainty in the population structure assumed in current stock assessment models for Japanese sardine.

Characterizing water solubility of fresh and aged secondary organic aerosol in PM2.5 with the stable carbon isotope technique

Abstract. The investigation of the water-soluble characteristics of secondary organic carbon (SOC) is essential for a more comprehensive understanding of its climate effects. However, due to the limitations of the existing source apportionment methods, the water solubility of different types of SOC remains uncertain. This study analyzed stable carbon isotope and mass spectral signatures of total carbon (TC) and water-soluble organic carbon (WSOC) in ambient PM2.5 samples for 1 year and established stable carbon isotope profiles of fresh and aged SOC. Furthermore, a Bayesian stable isotope mixing (BSIM) model was employed to reveal the water solubility characteristics of fresh and aged SOC in a coastal megacity of China. WSOC was dominated by secondary sources, with fresh and aged SOC contributing 28.1 % and 45.2 %, respectively. Water-insoluble organic carbon (WIOC) was dominated by primary sources, to which fresh and aged SOC contributed 23.2 % and 13.4 %. We also found that the aging degree of SOC has considerable impacts on its water solubility due to the much higher water-soluble fraction of aged SOC (76.5 %) compared to fresh SOC (54.2 %). Findings of this study may provide a new perspective for further investigation of the hygroscopicity effects of SOC with different aging degrees on light extinction and climate change.

A distinct manganese deposit on a Middle Permian carbonate platform in South China

During the Middle Permian, Earth experienced a period of profound environmental changes, including the final stages of the Late Paleozoic Ice Age (LPIA), global seawater regression, the Guadalupian mass extinction event, and the eruption of the Emeishan Large Igneous Province (ELIP) in South China. These events collectively induced significant shifts in both the environment and biosphere, yielding several geochemical anomalies, including deposition of manganese (Mn) deposits. The link between Middle Permian Mn deposits and the prevailing environmental conditions, however, remains unclear. Here, four sections spanning the Middle Permian Maokou Formation to the Late Permian Longtan Formation in the Zunyi area of northern Guizhou, South China are investigated. Through sedimentological and geochemical analyses, this work aims to elucidate the evolution of sedimentary environments over the Middle to Late Permian. During this period, a transition from a shallow-water carbonate platform in the 1st Member of the Maokou Formation to a deeper, siliceous deposit in its 2nd Member was recorded. This shift results in a pronounced paleogeographic differentiation in the 3rd Member, juxtaposing the shallow-water carbonate platform against a deeper Mn-enriched basin. A number of geochemical proxies indicate a strong hydrothermal signal in the Mn deposits. Combined with positive Eu anomalies and low Sr isotopes, the data underscore the profound influence of hydrothermal input linked with early subaqueous eruptions from the ELIP on the nearby marine environment. A detailed examination of carbon isotope profiles from the Maokou Formation indicates that volcanic influences, shifts in marine ecosystems, and changes in primary production caused the fluctuations of δ13Ccarb and δ13Corg. Moreover, the formation of Mn carbonate in deeper waters effectively sequestered organic C. Collectively, our new data demonstrate that the essential conditions for the development of the carbonate-hosted Mn deposits include drowning of the carbonate platform through an increase in sea level, the availability of a sufficient Mn source, and the presence of a redox-stratified water column.

Watermass architecture of the Ordovician–Silurian Yangtze Sea (South China) and its palaeogeographical implications

The South China Craton experienced large changes in climate, eustasy and environmental conditions during the Late Ordovician Hirnantian Ice Age, but their impact on the watermass architecture of the Yangtze Sea has not yet been thoroughly evaluated. Here, we reconstruct the salinity–redox structure of the Yangtze Sea based on five Upper Ordovician–Lower Silurian shale successions representing a lateral transect from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan–Hubei Arch (Pengye, Jiaoye and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan section). Carbon isotope ( δ 13 C org ) profiles show that the Guanyinqiao Bed (recording the peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan–Hubei Arch than in deeper water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation among Interval I (pre-glaciation), Interval II (Hirnantian glaciation) and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts towards more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all the study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities, implying greater proximity to the open ocean than the other four sites, and it exhibits an especially large shift towards more reducing conditions during Interval III (i.e. the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographical model for the Ordovician–Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more open OYS, arguing instead for the SW end of the IYS to have been connected to the global ocean and the OYS to have been a restricted oceanic cul-de-sac. A review of sedimentological and facies data for the IYS region suggests that our re-interpretation of the Ordovician–Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis is needed. Supplementary material: The dataset and the full crossplot of Sr/Ba v. CaO for this study are available at https://doi.org/10.6084/m9.figshare.c.7170648 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

Heterogeneous coupling of δ13Corg and δ13Ccarb during the Shuram Excursion: Implications for a large dissolved organic carbon reservoir in the Ediacaran ocean

The Ediacaran ocean recorded the largest negative carbonate carbon isotope (δ13Ccarb) excursion in Earth's history, the Shuram Excursion (SE). The relatively invariant character of organic carbon isotope (δ13Corg) profiles during the SE has been attributed to buffering by a large dissolved organic carbon (DOC) reservoir in the ocean. However, recent studies suggest that the DOC buffering may have been highly heterogeneous, a hypothesis that can be tested by assessing variability in the spatial and temporal ranges of δ13Corg buffering during the SE. In this study, we evaluated δ13Corg and δ13Ccarb records from multiple regions globally to test the heterogeneous buffering hypothesis. Making use of a high-precision astrochronological framework, we found that the buffering effect of DOC persisted for ∼2.7 Myr in Oman, ∼4.9 Myr in South China, and ∼5.9 Myr in Australia, demonstrating its temporal heterogeneity. Heterogeneous buffering is also demonstrated at a small spatial scale for South China sections based on a correlation framework subdividing the SE into three intervals: EN3a (δ13Ccarb decline from baseline to nadir), EN3b (δ13Ccarb stabilized at nadir), and EN3c (δ13Ccarb recovery from nadir value). The duration of δ13Corg buffering increased with water depth from shallow neritic to deep pelagic areas. The buffering effect terminated within EN3a in inner-shelf areas, within EN3b in an intra-shelf basin, and within EN3c in slope areas. Spatial variation in the offset between δ13Ccarb and δ13Corg values (Δ13C(carb-org)) is consistent with multiple sources of sedimentary organic matter. An average of ∼26 ‰ in inner-shelf areas implies mainly fresh phytoplankton debris, whereas an average of ∼18 ‰ in slope areas is consistent with dominance of DOC, which is thought to have been present in abundance in deeper anoxic watermasses. Thus, our study supports a large DOC reservoir in the late Ediacaran ocean that led to heterogeneous buffering during the SE at both basinal and global scales. Large shallow-to-deep oceanic δ13Ccarb and δ13Corg gradients of similar magnitude existed both before and during the SE, indicating that the circulation and productivity dynamics of the Ediacaran ocean were not significantly changed by the SE. The downward expansion of oxidant-rich surface watermasses during the SE improved the ventilation of shelf oceans while leaving the deep ocean anoxic, setting the stage for rapid biological evolution on continental shelves during the Cambrian Explosion.

Amino acid carbon isotope profiles provide insight into lability and origins of particulate organic matter

AbstractIdentifying the phytoplankton origin of particulate organic matter (POM) in the deep ocean is challenging due to the changing phytoplankton composition and varied extent of decomposition by heterotrophic bacteria and zooplankton. Here, we report vertical distributions of amino acid stable carbon isotope values (δ13C) measured in particles in the South China Sea. Carbon‐weighted amino acid δ13C values generally parallel bulk POM δ13C profiles with a positive offset from 2.4‰ in the surface water to 6.0‰ in deep. Accordingly, a lability model is introduced to describe the relative distribution and isotopic linkage of labile and refractory particulate organic carbon. Temporal changes of amino acid δ13C were observed during the microbial decomposition of two phytoplankton strains, the prokaryote cyanobacterium Synechococcus and the eukaryote diatom Thalassiosira weissflogii. Principal component analysis of individual amino acid δ13C values from the decomposing cells separate samples into two components, reflecting the influence of microbial decomposition and taxonomic differences, respectively. These two components were further applied to particles. A major contribution from decomposing phytoplankton to particles below the euphotic zone was observed, with more prokaryote organic matter in the basin and a larger contribution from eukaryotes at stations near the productive northern shelf. Our findings show the applicability of amino acid δ13C values in tracing the lability and phytoplankton origins of POM in samples with varied extents of decomposition in marine environments.

Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan

The Tajik-Afghan Basin is a large basin in Central Asia, whose sediments document the area's long tectonic and climatic history from the Paleozoic to the present. However, the sedimentary characteristics and stratigraphy of these successions remain poorly understood. The study of this basin is critical for understanding the depositional conditions that prevailed during the transformation of this area from a part of the Western Oceanic Tethys to a more restricted Para-Tethys. In the southwestern corner of the Tajik Depression, a well-exposed sedimentary sequence associated with a large anticlinal limb was sampled. The authors proposed a new age model based on a combination of biostratigraphic data from planktic foraminifera, calcareous nannofossils, and strontium chemostratigraphy (87Sr/86Sr). The lower part of the studied section is of the upper Cenomanian age (95.5 Ma), while the upper part is assigned to the early Oligocene age (34.05 Ma). The carbon isotope profile shows several excursions linked to major paleoenvironmental events including the Oceanic Anoxic Event 2 (OAE2) and the Paleocene-Eocene Thermal Maximum (PETM). The latter is revealed in the study area for the first time. New sedimentological observations and interpretations of the depositional environments and sea-level cycles are provided. The deposition in the Aktash area occurred between upper coastal lagoonal and transitional environments before fully transitioning to continental environments in the Neogene. The stratigraphic record in Aktash is divided into large-scale progradation/ retrogradation cycles that can be tentatively linked to global sea-level signals.

Late Pleistocene sea level change and tectonism control on the formation of the Old Red Sand along the southeastern coast of China

The Zhe-Min Uplift (ZMU) has undergone tectonic subsidence, which has been associated with a notable transgression in the northern marginal seas of China since the middle Pleistocene. However, its uplift history during the late Quaternary is still inadequate. The Old Red Sand (ORS) is a late Pleistocene deposit that is widely distributed along the southeastern coast of China. The ORS consists of partially-cemented fine- to medium-grained sand. In this paper, we focus on mud-rich ORS deposits of the Liushui area, Pingtan Island, Fujian Province, and report optically stimulated luminescence (OSL) ages, and new datasets of grain size, mineralogy (detrital zircon, clay and detrital minerals) and organic carbon and nitrogen isotope profiles to improve understanding of chronology, provenance, palaeoenvironmental evolution and tectonic infuence. Based on the OSL data, we hypothesize that the development of the ORS was associated with lower sea levels, with most deposition occurring within MIS4. Based on comparison of detrital zircon UPb ages, the coarse fraction of the Liushui ORS was mainly derived from the Minjiang River, with modest input from weathering of coastal granites. The East Asian Winter Monsoon contributed some materials from the East China Sea shelf during the last glacial period, as indicated by the fine-grained nature of the Liushui ORS, low K-feldspar/plagioclase ratios, high dolomite content and the frequency of Neoproterozoic and Palaeoproterozoic detrital zircons. The deposition of the ORS was influenced by both the East Asian Winter Monsoon and sea level changes. The clay minerals in the mud layers of the Liushui ORS were dominated by kaolinite and illite, with little chlorite and no smectite, indicating that they originated from the Minjiang River. The TOC/TN ratios of the mud layers, as well as their isotope characteristics, indicate the organic matter was derived from marine sources, presumably during the transgression event in MIS5. The average uplift rate of the ORS was about 0.03 mm/yr. The uplift of the ORS provided new insights into the geological records of the ZMU, which differed from the subsidence observed in the northern region of the Minjiang River during the late Pleistocene.

Factors Controlling Organic Matter Enrichment in Alkaline Lacustrine Source Rocks: A Case Study of the Late Paleozoic Fengcheng Formation in the Junggar Basin, NW China

AbstractThe late Paleozoic Fengcheng Formation shale (LPF shale) in the Junggar Basin, NW China, is the oldest alkaline source rock discovered in the world, providing a unique perspective with which to explore organic matter (OM) enrichment in alkaline lake environments. Combined with the organic carbon isotope profile and paleoenvironmental proxies, this study reveals that the LPF shale was deposited in an arid climate with high salinity and a strong reducing environment, accompanied by frequent volcanic activity. High TOC values are concentrated in two intervals with frequent fluctuations in OM types. A negative excursion due to changes in sedimentary OM source is found in the δ13Corg profile. The excursion corresponds to the OM enrichment interval and is accompanied by abnormally high values of Sr/Ba and Sr/Cu. This implies that the extreme arid climate has led to high salinity, resulting in strong reducibility and changes in paleontological assemblages, which in turn controlled the differential enrichment of OM. The Fengcheng Fm. high‐quality source rocks are the result of the combined action of climatic events, volcanism, high‐salinity water environment and superior hydrocarbon‐generating organisms. The results provide new insights into the formation conditions of terrestrial alkaline high‐quality source rocks and the factors controlling alkaline OM enrichment.

Diagenetic constraints in carbon-isotope stratigraphy of the Upper Jurassic-Lower Cretaceous Vaca Muerta-Quintuco system, Neuquén Basin, Argentina: Implications for a global correlation

The δ13Ccarb profiles of the Vaca Muerta Formation (Neuquén Basin, Argentina), span the Tithonian to lower Valanginian (Jurassic-Cretaceous transition). The investigated interval was sampled from two sections: the Pampa de Tril (PDT, ∼120 m-thick covering the lower Vaca Muerta Formation) and Puerta Curaco (PC, ∼670 m-thick covering the entire Vaca Muerta and Quintuco formations). The succession consists of organic-rich marine carbonates alternating with mudrock beds. A multitechnique screening protocol, including petrography and geochemistry, has been applied to evaluate the degree of preservation of the studied carbonates. The Pampa de Tril and Puerta Curaco sections have δ13Ccarb values that vary from −12.2 ‰VPDB (at the bottom) to 2.9 ‰ VPDB (at the top) and δ18Ocarb values from −13.2 ‰VPDB to −5.3 ‰VPDB. The δ13Ccarb values of the analysed samples, exhibit insignificant correlations with their Mn/Sr (rs = −0.13) and ∑REE (rs = −0.19) counterparts. This supports the preservation of at least near-primary δ13Ccarb compositions that can be implemented to construct a reliable high-resolution carbon-isotope profile for global correlations. The δ13Ccarb profiles of the Vaca Muerta Formation display a negative excursion of ∼8–10 ‰ at the bottom of the formation (Tithonian) which can be correlated with the VOICE (Volgian Isotope Carbon Excursion) event.

N-Alkane 13C/12C indicates differential metabolic controls of fatty lipid chain extension in C3 and C4 grasses.

Fundamental differences in metabolic control of fatty acids chain extension are reflected in the contrasting carbon isotopic composition profiles of C3 and C4 grasses.

Multiple carbon isotope excursions during the Carnian (Late Triassic) pluvial event: implications for global and regional perturbation

The Late Triassic Carnian pluvial event (CPE) was an interval marked by global climatic and environmental changes that occurred simultaneously with enhancement of the hydrological cycle. This event is characterized by multiple negative carbon isotope excursions (NCIEs). However, the driving mechanism behind these multiple NCIEs remains elusive because each of the NCIEs had different magnitudes in different geological settings. In this study, we present a high-resolution record of carbonate carbon isotope ( δ 13 C carb ) and major and trace element data from Well QZ-8 in the Qiangtang Basin, eastern Tethys. The carbon isotope profile from this well displays a similar trend to those for contemporaneous strata in the NW Tethys and South China. This trend is characterized by a distinct negative excursion during the CPE, supporting a global event. Interestingly, our results reveal five NCIEs for the first time in the marine sedimentary succession. Furthermore, each of these NCIEs corresponds well to changes in Ti/Al, Sr/Al and Sr/Ba, suggesting a regional effect of the hydrological cycle on carbon isotope excursions. This study emphasizes that each of the NCIEs was influenced by regional hydrological cycles although the long carbon isotope excursion during the CPE was driven by the global carbon cycle. Supplementary material: Tables showing major element, isotope and trace element data and element ratios, and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6805266

A GC/C/IRMS-based method for position-specific carbon isotopic analysis of saturated long chain fatty acids

Intramolecular carbon isotope profiles (13C/12C) of mid- and long-chain saturated fatty acids represent a potentially rich source of pathway and flux information on fatty lipid biosynthesis. Accessing the PSIC-13C (position-specific carbon isotope composition) of saturated long chain fatty acids, however, proves a challenge as neither 13C NMR, nor online pyrolysis, can measure all carbons successfully. We have developed a wet chemistry procedure (α-bromination, α-hydrolysis and decarboxylation) to stepwise shorten the targeted saturated fatty acid, followed by GC/C/IRMS (gas chromatography/combustion/isotope ratio mass spectrometry) measurement of the 13C/12C ratios of fatty acids, with minimal purification. Isotope mass balance was then applied to calculate the 13C/12C ratios of individual carbons. The triplicated PSIA precision varies from position to position in the range 3.95–5.25 mUr (averaging 4.44 mUr, equivalent to ‰).Applying this method to a commercial C16:0 fatty acid of C3 botanical origin revealed an intramolecular odd-over-even 13C enrichment pattern, consistent with that obtained with 13C NMR. Although PSIA-13C was attempted only on a single fatty acid, the method can potentially be applied to obtain PISC-13C for all fatty acids in a mixture simultaneously, and to long chain saturated alkanes after proper functionalization. The method should prove useful in studies of lipid metabolism and biogeochemistry as both saturated long chain fatty acids and alkanes are the dominant organic archives of climate in petroleum deposits, sediments and soils.

The Toarcian Oceanic Anoxic Event in a shelf environment (Eastern Tethys): Implications for weathering and redox conditions

The Toarcian Oceanic Anoxic Event (T-OAE) is characterized by significant environmental perturbation and climatic instabilities due to a substantial release of greenhouse gasses. Several investigations of the T-OAE were conducted based on reliable and well-developed integration of multi-proxy approaches, revealing the global distribution of this event in the Panthalassic, Boreal, and Western Tethyan regions. However, a few marine shelf T-OAE records are reported from the Eastern Tethys. This study presents high-resolution organic and inorganic and isotope geochemistry, mineralogical, and sedimentological analyses from the marine Suobucha section of the Qiangtang Basin to assess the role of continental weathering and paleoceanographic conditions, including paleoredox and paleoproductivity conditions, and factors that govern organic carbon accumulation during the T-OAE in the Eastern Tethys. The carbon isotope profile of Suobucha displays a long-term negative excursion characterizing the Jenkyns Event, which is recognized in geographically widespread sedimentary archives indicating its global nature. Continental weathering was intensified at the onset of the Jenkyns Event. Increased values of fluvial detrital proxies (i.e., Si/Al and Ti/Al) and the occurrence of coarser-grained sediments (i.e., silty mudstones) at Suobucha indicated enhanced terrigenous input at the onset of the Jenkyns Event, which was driven by accelerated continental weathering at this time. The lower Toarcian interval in the marine shelf environment of the Qiangtang Basin is characterized by fully oxidizing conditions intermittent with minor phases of dysoxic setting, especially during the Jenkyns Event interval. Given that a stratified water column with anoxic bottom water occurred in the proximal and more restricted lagoonal area (i.e., the Bilong Co area), redox conditions were spatially variable and controlled by basin hydrography and water depth during the Jenkyns Event in the Qiangtang Basin. Oxygen-enriched conditions and low marine bioproductivity were responsible for the low organic carbon burial within the Suobucha section.

Integrated biochemostratigraphy of the Permian-Triassic boundary interval and Lower Triassic succession in the eastern Cimmerian continent (Baoshan block, West Yunnan, southwest China)

The records of extreme biotic and environmental crises have been well documented worldwide from Permian-Triassic successions. However, the Cimmerian continent, a Gondwana-derived continental terrane/block strip, has received insufficient attention in terms of its eastern part including the Baoshan block. Here, we report an integrated conodont biostratigraphic zonation and carbon isotope profile from the Permian-Triassic boundary (PTB) beds and Lower Triassic succession of the Baoshan block. The conodont faunas obtained from the dolomitized Hewanjie Formation at the Dajianshan section are dominated by Hindeodus and Isarcicella species. Representatives of Eurygnathodus and the Ellisoniidae are also present. Five conodont zones are recognized in ascending order: the Hindeodus parvus Zone, the Isarcicella staeschei Zone, the Isarcicella isarcica Zone, the Hindeodus postparvus Zone, and the Eurygnathodus costatus Zone. The carbon isotope curve exhibits two pulses of negative excursion around the PTB. In general, both the conodont zones and the carbon isotope profile correlate well with those from other well-documented sections in the world. The Permian-Triassic boundary, extinction horizons and Induan-Olenekian boundary are calibrated in terms of conodont and carbon isotopic data. In addition, conodont biofacies analyses show that the depositional water-depth was shallow in general, as indicated by the lack of gondolellids and neospathodids and the presence of ellisonids and Eurygnathodus.

Geochemical records and environmental analysis of the Ediacaran-Cambrian boundary in Eastern Yunnan, South China

The Ediacaran–Cambrian transition is characterized by an unprecedented change in biosphere, lithosphere, and atmosphere. However, the identification of this transition and its global correlation remains debated. East Yunnan is a region of utmost importance in the study of the Ediacaran-Cambrian transition. Although strata from this region have been well studied, recognition of the base of the Cambrian continues to be controversial. This paper presents, a carbon chemostratigraphic isotope and trace element profile through the Dengying and Zhujiaqing formations in the Sujiawa section in East Yunnan. Through carbon isotope and trace element analyses of the Dengying and Zhujiaqing formations we attempt to regionally correlate the section and discuss the paleo-marine redox environment changes during this period. The Fe content of samples is low and the Mn/Sr ratios of the majority of the Sujiawa section samples is lower than 10 and shows no correlations with δ13Ccarb and δ18Ocarb values, indicating that the samples retain near-primary δ13Ccarb characteristics. The carbon isotope profile from the Sujiawa section, shows a prominent negative δ13Ccarb in the basal Zhongyicun Member (N1’, −7.3‰) that most likely represents the prominent negative excursion recorded in Ediacaran-Cambrian strata across the world. REE patterns and Y/Ho ratios were used to screen samples, to ensure that the primary seawater REE features and Ce anomalies were preserved. The samples satisfying this screening process show seawater-like REE distribution patterns in leached carbonates and may have recorded Ce anomalies of the seawater from which the carbonates precipitated. These data show that the Baiyanshao Member has Ce/Ce* values between 0.57 and 0.88, the Daibu Member between 0.56 and 0.83, and the Zhongyicun Member between 0.60 and 0.96. The Ce anomalies through the section indicates that the region experienced suboxic-oxic-anoxic conditions throughout the Ediacaran-Cambrian period. Carbon isotope and trace element analyses indicate that the strata record a negative carbon isotope excursion event and anoxic conditions during the period of deposition. This study complements the carbon chemostratigraphic information and trace element data in the region and provides valuable clues for understanding the lithofacies changes through the Ediacaran and Cambrian in different regions of South China.

The early Ediacaran Brachina sequence, Flinders Ranges, South Australia: its age, formation and plate tectonic setting

Throughout the Flinders Ranges of South Australia, the red bed Brachina sequence comprises the lower of two regressive, coarsening-upward successions that together constitute the Ediacaran-aged Wilpena Group. Detailed examination of the Brachina sequence has identified evidence of ice-rafting, supporting the contention that frigid climatic conditions continued well after cessation of the Marinoan Glaciation, as well as features postulated to be harbingers of the macroscopic metazoans that occur in abundance higher in the local stratigraphy. Although tuffaceous and lying stratigraphically between deposits of the Marinoan Glaciation and the Acraman Impact/Gaskiers Glaciation, no absolute age dates exist for the sequence. However, through correlation to the global carbon isotope profile, the timespan of Brachina sequence deposition can be constrained to between 635 and 586 Ma, when the regression climaxed with terrestrial deposition upon a local disconformity. The tuffaceous input is timed to have begun at 620 Ma, essentially coincident with initial formation of the passive volcanic continental margin of southeastern Australia and initiation of both the Volyn Large Igneous Province and activity within the Central Iapetus Magmatic Province, all components marking the demise of Rodinia and initial amalgamation of Gondwana.

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Astrochronology and carbon-isotope stratigraphy of the Fengcheng Formation, Junggar Basin: Terrestrial evidence for the Carboniferous-Permian Boundary

The Carboniferous–Permian Boundary (CPB) is a major stratigraphic boundary and a marker for global stratigraphic correlation. However, the delimitation and global correlation of the CPB is hindered by the erosion during the Late Paleozoic Ice Age. Several carbonate platforms show a negative carbon isotope excursion (NCIE) in response to the CPB, which has great potential for the delimitation of this boundary. However, the response of terrestrial profiles to the CPB is unclear, and the global synchroneity of this NCIE is controversial. We studied a high paleolatitude section to evaluating the feasibility of the NCIE for delimitating CPB. We used astrochronological analysis of the 340 m Gamma Ray log of the Fengcheng Formation in Mahu Sag, Junggar Basin, northwest China, where the CPB may have been recorded. We constructed a high-resolution chronostratigraphic framework for the Fengcheng Formation, which precisely defines the chronostratigraphic attribution of the Fengcheng Formation as the Gzhelian–Asselian, and confirms that the CPB is recorded in the Fengcheng Formation. In addition, a global correlation of carbon isotope profiles revealed a negative excursion in terrestrial carbon isotope profiles across the CPB, which is consistent with the characteristics of NCIEs in several marine profiles. The similarity of the NCIE records supports their global synchrony and confirms that they can be used to delimit the CPB in terrestrial sections. Combining the astronomical time scale and the carbon isotope profile, we constrain the position of the CPB to the depth range of 4694.84–4703.56 m, with 4698.9 m as a preliminary estimate of the CPB. This new astronomical timescale and the stratigraphic position of the CPB enable the revision of the chronostratigraphic attribution of the terrestrial strata in the Junggar Basin. Overall, our results contribute to studies of the Carboniferous–Permian global carbon cycle, high-latitude glaciation, eustatic fluctuations, global volcanism, and their potential relationships.