Reliable laboratory-derived kinetic parameters are essential for petroleum system modeling to evaluate both conventional and unconventional resources. The gold tube pyrolysis system simulates subsurface conditions by controlling pressure and temperature, making it widely used to analyze hydrocarbon generation kinetics. This study aims to assess the uncertainty involved in extrapolating oil generation kinetic parameters derived from gold tube pyrolysis of lacustrine source rocks to geological conditions. We conduct this evaluation using 17 sample datasets and six parallel pyrolysis experiments. Results reveal a rapid increase in cumulative transformation ratio (TR) at immature stages (<0.5% Ro), indicating premature oil generation, producing a characteristic ‘dogleg’ pattern that overestimates the potential of immature oil and shale oil, and suggesting a two-peak oil generation model that is not observed in open-system kinetics. Parallel experiments identify several potential contributing factors: incomplete removal of adsorbed hydrocarbons (rock powder loading) may be released during low-temperature pyrolysis, and these compounds accumulate at the first temperature setpoint, distorting the authentic oil generation yield curve. Insufficient temperature resolution during early pyrolysis may force the kinetic program to assume a linear increase in oil yield. Both experimental artifacts produce artificially low activation energies. Limitations of the single frequency factor (SFF) model create a compensation effect that pairs low activation energies with high frequency factors, exaggerating the TR at immature stages during geological extrapolation. Practical recommendations include biomarker-based thermal maturity assessment, rigorous pretreatment to eliminate adsorbed hydrocarbons, and improved temperature resolution during early pyrolysis. Although this study focuses on identifying artifacts in early oil generation signals derived from gold tube pyrolysis, it should be noted that false compensation effects and laboratory–geologic disparities may also influence kinetic extrapolation.
African paleoecologists often describe ecosystems along a continuum from closed, woody environments to open, grassy landscapes, given the distinct implications of these end members for climate, ecology, and evolutionary habitats. n-Alkane chain length distributions are one potential proxy for how woody or grassy an ecosystem was in the past. However, these distributions are generally reported as ensemble means without rigorous evaluation of how consistent such patterns are on the individual plant level, and their multidimensional data are often collapsed into a simplified chain length ratio for proxy applications. This study applies a suite of variably complex machine learning algorithms to distinguish woody and grassy African plants using n-alkane distributions. A dataset of 625 samples (496 from literature, 129 newly generated) was used to train and validate eight supervised machine learning classifiers, yielding validation classification accuracies between 81 and 89%. Such consistently high classification accuracies indicate that a persistent and differentiable signal is present in the n-alkane distributions of individual woody and grassy plants and marks a significant improvement over previously published n-alkane classification ratio performance, which achieved ~70% classification accuracy on the same dataset. A series of next steps and best-practice recommendations are developed and presented, including: 1) increased sampling of grassy plants, 2) consistently reporting C35 n-alkane abundance due to its diagnostic power for grasses, and 3) developing and adopting standardized methodologies for sample preparation, analysis, and post-processing. We demonstrate that pairing n-alkane chain length data with machine learning offers a powerful framework for developing paleoecological proxies – one that will be best realized through methodological consistency across the organic geochemistry community.
The differences between the free and kerogen-bound pristane (Pr) and phytane (Ph) were investigated in six Oligocene–Miocene source rocks from the western Qaidam Basin (Qaidam source rocks) and ten Jurassic coals from the Junggar Basin (Junggar coals) that were deposited under anoxic blackish-saline lacustrine and oxic swamp depositional environments, respectively. The free isoprenoid precursors in the initial bitumen are more sensitive to redox conditions compared with the bound counterparts to kerogen. Similarly, the bound isoprenoid precursors in kerogen with labile bonds (e.g., oxygen‑carbon and sulfur‑carbon bonds) are more influenced by redox conditions than those with stable carbon‑carbon bonds. This leads to different diagenetic reaction routes giving rise to different Pr/Ph between the free isoprenoids in the initial bitumen and bound isoprenoids released from kerogen and between the bound isoprenoids released from kerogen at lower and higher temperature and maturity. For the six Qaidam source rocks, the free isoprenoid precursors (e.g., phytol) in the initial bitumen are more prone to be converted to Ph than the counterparts bound to kerogen, leading to Pr/Ph that increases from substantially lower than 1 for the initial bitumens to increasingly close to 1 for the released oils with increasing temperature and maturity. In contrast, for the ten Junggar coals, the free isoprenoid precursors in the initial bitumen are more prone to be converted to Pr than the counterparts bound to kerogen, leading to Pr/Ph that decreases from greatly higher than 1 for the initial bitumens to increasingly close to 1 for the released oils with increasing temperature and maturity. The Qaidam and Junggar oils that were derived from the Qaidam source rocks and Junggar coals, respectively are substantially different from the initial bitumens but similar to pyrolysates at the bulk oil generation stage of these source rocks and coals on the basis of Pr/n-C17, Ph/n-C18, Pr/Ph and (Pr + Ph)/(n-C17 + n-C18), demonstrating that these oils were mainly generated and expelled from the Qaidam source rocks and Junggar coals, respectively at the bulk oil generation stage.
The Smoking Hills and Mason River formations in Arctic Canada were investigated to evaluate changes in high latitude terrestrial ecosystems during the middle Coniacian-early Paleocene (?). Deposition of the Smoking Hills Formation occurred during Oceanic Anoxic Event 3, reflected by a marine transgression in the Anderson Basin and surrounding areas. The Anderson Basin was characterized by highly oxygenated and productive marine surface waters, anoxic to suboxic conditions at the sediment–water interface and low input of terrigenous organic matter. Despite the low concentration of terrestrially derived organic matter, the relatively high concentration of aromatic sesqui- and diterpenoids in samples from the Smoking Hills Formation indicates that gymnosperm vegetation dominated local terrestrial ecosystems. Aromatic biomarkers in samples from the overlying lower Mason River Formation show an increase in terrigenous organic matter with a slight increase in pentacyclic triterpenoids with oleanane, ursane and lupane carbon skeletons, which are common in all angiosperm families. These aromatic compounds increase considerably in the upper part of the lower Mason River Formation, suggesting diversification of angiosperms during the latest Campanian-early Maastrichtian. This increase in abundance and diversity of angiosperm indicators is associated with a broadly contemporaneous increase in wildfires as evidenced by the high total concentrations of pyrogenic polycyclic aromatic hydrocarbons in this stratigraphic interval. Wildfires may have increased erosion in the hinterland, increasing the flux of soil-derived organic matter into the marine basin. The findings reported here align with palynological and geochemical evidence shown in previous studies that indicate a global increase in angiosperm diversity in the Late Cretaceous. Wildfires likely played a crucial role in the diversification of angiosperms and the increase in soil erosion and river runoff in the Cretaceous Arctic.
The molecular inheritance of ancient tropical rainforest-derived biomolecules preserved within the Cenozoic petroleum systems of Southeast Asia provides key insights into the nature of organic matter inputs to the source rocks of the sedimentary basins. However, a direct understanding of how rainforest-derived biomolecules, particularly sesquiterpenoids and triterpenoids, are preserved and transformed during burial and thermal maturation remains poorly explored. Here, we demonstrate the role of Dipterocarpaceae-derived resinous biomass as a potential source of molecular precursors to the hydrocarbons preserved within Cenozoic petroleum systems of Southeast Asia by experimentally simulating the thermal transformation of modern dammar resin using hydrous pyrolysis. The resulting bio-oils exhibit biomarker signatures characteristic of crude oils from the Assam, Cambay, and other Cenozoic Southeast Asian sedimentary basins. Laboratory-based hydrous pyrolysis experiments reveal that cadinene-based C15 sesquiterpenoids, abundant in the aromatic fraction of these crude oils, are also the dominant products observed in hydrous pyrolysis-derived bio-oil. Notably, C30-bicadinane, a diagnostic biomarker of Dipterocarpaceae that is ubiquitous in crude oils from Cenozoic Southeast Asian sedimentary basins, is also produced under simulated thermal maturity conditions. Further, the n-alkane distribution of the bio-oil shows partial similarities to those observed in naturally occurring crude oils. In addition, aromatic triterpenoids generally present in the aromatic fraction of natural crude oils were also observed in the diagenetically altered fossilized dammar resin. These results provide experimental insights supporting molecular similarities and a plausible precursor-product relationship between thermally altered Dipterocarpaceae-derived resin and selected biomarker assemblages identified in bio-oil and Cenozoic petroleum systems of Southeast Asia.
Although microbial processing has been identified as a key mechanism for terrigenous organic carbon loss in marine systems, the underlying reasons for its extensive consumption remain poorly understood. To address this knowledge gap, we conducted experiments under controlled salinity conditions, tracking the behavior of plant-derived n-alkanes and microbial-derived glycerol dialkyl glycerol tetraethers (GDGTs) during the transition from terrestrial to marine environments. Our results demonstrate distinct preservation patterns between these biomarker classes. While the distributions of n-alkanes and GDGTs showed no significant changes, the concentration of n-alkanes in terrigenous sediments remained essentially unchanged after 12 months in seawater incubation, whereas GDGT concentrations decreased substantially upon marine exposure. Soil aggregate analysis revealed that small macroaggregates (2–0.25 mm) broke down into microaggregates (0.25–0.053 mm) under saline conditions. The substantial total organic carbon loss observed during this process suggests that aggregate destruction serves as the primary driver of carbon mineralization. These findings support a conceptual model in which both plant and microbially derived terrigenous carbon are initially preserved within soil aggregates and undergo differential degradation during fluvial transport. When these aggregates enter marine systems, cations disrupt their structural integrity, releasing protected microbial-derived organic carbon that is rapidly consumed by marine microorganisms. This mechanism is corroborated by the proliferation of Proteobacteria and Bacteroidetes, which are known as major degraders of terrestrial organic matter and respond directly to the released microbial-derived organic carbon liberated from disrupted soil aggregates. Our study provides new mechanistic insights into the fate of terrigenous organic carbon in marine environments, highlighting the critical role of soil aggregates stability in regulating carbon persistence across the land-ocean interface.
Understanding how atmospheric carbon dioxide concentrations (pCO2) changed through time is vital for assessing how carbon cycle perturbations will impact our near future. A widely used pCO2 proxy is based on the photosynthetic carbon isotopic fractionation recorded by phytoplankton biomarkers, such as derivatives of chlorophyll-a (phytol/phytane) or more typically haptophyte-derived alkenones. However, the phytol-based proxy has limited Pleistocene data available, hindering validation against ice core pCO2 records. The alkenone-based proxy has demonstrated mixed success in reconstructing Pleistocene ice core pCO2 variations, presumably due to how the carbon demand parameter b has been constrained, using either empirical phosphate-growth rate relationships or cell size considerations. Here, we test the ability of both biomarker approaches to reconstruct pCO2 across the last ~350,000 years. Employing a bulk organic matter-derived b for phytol and a phosphate-derived b for alkenones yields pCO2 estimates which consistently exceed ice core values by ~50–300 ppm. By applying a modern ocean phytol-derived calibration for our phytol-based reconstruction and incorporating published coccolith size corrections into our alkenone-based reconstruction, we obtain lower pCO2 estimates, with phytol-based pCO2 values being more consistent with values from the ice core records. However, both lack the full amplitude of glacial-interglacial variations. We suggest this dampened variability is associated with two main issues: proxy insensitivity to small pCO2 changes and the upregulation of carbon concentrating mechanisms. Our findings highlight the need for further research on understanding the mechanistic limitations of the phytoplankton biomarker-based pCO2 proxies during low pCO2 periods of Earth's history.
Mangroves store a large amount of organic carbon (OC) within the sediment to a depth of a meter or beyond. Nevertheless, little information is available about the difference in chemical composition of sedimentary OC in young restored versus old intact forests. To understand such pattern of changes in molecular composition of OC according to mangrove development, we conducted a detailed study at two contrasting settings on the Panay Island, the Philippines, where sediment properties were examined by applying advanced measurement tools (e.g.1H nuclear magnetic resonance spectroscopy and C and N stable isotopes), in addition to biomass and water quality data. Organic carbon was preserved in greater proportion with mangrove development (6 month to 40 years old) as indicated by its higher ratio to specific surface area (OC/SSA, 61 to 143 μmol C m−2) and stock estimates (from young to old as above-ground biomass: 27 to 568 Mg dry matter ha−1, below-ground biomass: 14 to 309 Mg dry matter ha−1, sediment: 28 to 77 Mg C ha−1 between 0 cm and 50 cm depth). Chemical differences between alkali-extractable OC samples were visible in the chemical shift regions of 1H NMR, as we found a distinct separation of sediment from the old to the young sites. The relative abundances of the %olefinic H and %carbohydrate H were higher in the sediment of old mature stands than the young, restored sites, where %aliphatic H and %functionalized aliphatic H dominated. The composition of alkali-extractable OC was determined mainly by the forest age, sediment depth and decomposition of mangrove-derived OC input. Finally, this work provides important baseline information for future projection of sediment maturity level after plantation in the studied mangrove forest.
3-Hydroxy fatty acids (3-OH-FAs) are key components of bacterial membranes and hold great potential as proxies for paleoceanographic reconstruction. However, previous studies have mainly focused on the empirical relationships between sedimentary 3-OH-FAs and environmental parameters, with limited attention to the roles of bacterial membrane adaptation and shifts in bacterial community in shaping particulate 3-OH-FAs distributions prior to deposition. Here, we examine the particulate 3-OH-FAs as freshly produced biomarkers alongside multiple environmental parameters and bacterial communities in the East China Sea. Our results identified 17 bacterial classes as promising candidate producers of marine 3-OH-FAs, including abundant taxa such as Alphaproteobacteria and Cyanobacteriia, as well as less abundant taxa such as Nitrospira and Desulfobacteria. Seawater salinity and temperature were primary abiotic factors controlling the composition of particulate 3-OH-FAs. For some homologues, their influence conformed to homeoviscous adaptation framework, whereas for others deviations from this framework were observed due to microbial effects. Nonetheless, variation partitioning analysis indicates that homeoviscous adaptation remains the dominant control on 3-OH-FAs compositions over microbial effects. Furthermore, the depth-integrated RAI15 and RANs proxies exhibited significant negative correlations with seawater temperature, while BNA13 proxy showed a significant negative correlation with salinity. These findings suggest that temperature and salinity signals are imprinted into particulate 3-OH-FAs in the water column and faithfully preserved during particle settling to sediments.
The impact of eutrophication-induced phytoplankton blooms on organic carbon (OC) burial in lake systems largely depends on OC loss within the water column and surface sediment, a process that remains poorly constrained, particularly in shallow lakes. In this study, phytoplankton-related n-heptadecane (n-C17) is introduced to quantify the sinking and burial efficiencies of phytoplankton-derived OC in Lake Taihu, East China, a typical large shallow eutrophic lake. The results show that only 2.3 ± 2.2% of primary productivity can be buried in the sediments in the bloom season due to low sinking (27.2 ± 2.2%) and burial (8.5 ± 8.1%) efficiencies. Inherently high bioavailability of phytoplankton-derived OC and elevated temperatures collectively lead to low sinking efficiency in Lake Taihu, even within shallow lakes. Extended oxygen exposure in large shallow lakes accelerates microbial decomposition, resulting in the massive OC loss during transport from the water body to surface sediments and further leading to an inefficient OC burial in large shallow lakes. By synthesizing published data, we demonstrate that lake morphology predominantly regulates how eutrophication affects OC burial across global lakes. Compared to small and deep ones, large subtropical shallow lakes usually have inefficient OC burial. Our findings advance our understanding and prompt a reassessment of the contribution of lake eutrophication to the global carbon cycle, and the method developed here could be used in the field of limnology with respect to the assessment of OC burial.
Long-chain alkenones (LCAs) produced by haptophyte algae are widely used for paleotemperature reconstructions in marine environments, whereas their application in freshwater lakes is still being refined, as the ecology and environmental controls of LCA producers (Group 1 Isochrysidales) are not yet fully understood. In this study, we investigated the occurrence, genetic diversity, and environmental conditions associated with Group 1 Isochrysidales in three freshwater lakes in northern Japan: Lake Ichinomegata, Lake Onuma, and Lake Toyoni. Sedimentary DNA analyses targeting the 18S rRNA gene revealed that both Group 1a and Group 1b (subclades) occur in all three lakes, whereas no sequences belonging to Groups 2 or 3 were detected. Surface sediments from the three lakes contained LCAs characterized by the tri-unsaturated isomers diagnostic of Group 1. LCA compositional parameters fall within the range previously reported for LCAs from northern high-latitude freshwater lakes. Major-ion compositions of the three lakes differ considerably, indicating that Group 1 haptophytes are not restricted to a specific water chemistry type. Temperatures reconstructed from U37K in surface sediments correspond well to observed early spring surface water temperatures, despite differences in seasonal stratification patterns and ice-cover conditions among the three lakes. These results provide new evidence for the genetic diversity and environmental distribution of Group 1 haptophytes in Japanese lakes and support the interpretation that U37K primarily records winter-to-spring thermal conditions in cold-region freshwater lakes.
Hydrogen isotopes of leaf wax lipids (δ2Hwax) have been applied in various ways to reconstruct hydrological change. As such, considerable research has been dedicated to elucidating the mechanisms that impart changes in the δ2H signal as it is transformed from water to wax. In this study, we compare the results of multiple models to assess the environmental and biological processes that significantly influence δ2Hwax in surface sediments from 76 lakes across Mexico and Central America. δ2Hwax exhibits a weak, albeit significant relationship to δ2H values of June precipitation (R2 = 0.16, p = 0.03), suggesting that the leaf wax values record the isotopic signature of source water from the period of most intense leaf flush. Using a Craig-Gordon model, we demonstrate that soil water evaporation and transpiration do not significantly improve the predictive power of δ2Hwax based on the application of fractionation factors (⍺precip/wax) generated from a training set of our lake sites. When our sites are grouped into one of seven established forest vegetation types found within Mexico and Central America, we find a significant effect of vegetation type on δ2Hwax values. Furthermore, by combining biosynthetic fractionation values (εbio) of the two most common taxa within each forest type with the δ2H values of June precipitation, we can accurately model δ2Hwax (R2 = 0.76, p = 0.00001) from a subset of our study lakes (n = 31). These results demonstrate that δ2Hwax in this region is mainly controlled by biosynthetic fractionation rather than changes in aridity or source water values, which will impact paleo-reconstructions from Mexico and Central America that rely upon sedimentary leaf waxes to address questions about paleohydrology.
Hydrocarbon biomarkers, the geologically stable remnants of cellular lipids, maintain the isotopic fingerprints of the metabolisms employed in their biosynthesis. The lipid biomarkers of cyanobacteria, photosynthetic prokaryotes, are prevalent in both modern and ancient sediments. Despite this, few studies have systematically examined the carbon isotope compositions of individual lipids in cultured cyanobacteria. Eight batch cultures comprising Synechococcus, Synechocystis, Nostoc, and Fischerella taxa were grown using isotopically characterized CO2 (g) and their biomass and lipids were examined for their carbon isotope compositions. The isotopic difference between biomass and source CO2 across species varied between −5.2‰ and − 19.4‰, with filamentous, branching cyanobacteria demonstrating significantly smaller offsets compared to unicellular forms. A smaller range of carbon isotope differences between biomass and individual lipids was observed, among which acetogenic lipids were depleted in 13C compared to isoprenoid lipids, yielding the following individual δ13C ordering: alkanes/alkenes < fatty acids < monoacylglycerols < phytol < carotenoids and hopanoids. Within this ordering, a consistent, approximately 8.1‰ offset between cyanobacterial biomass and phytol was recovered. This exceeds the magnitude of the same isotopic difference previously observed for algae and is consistent with the general isotopic ordering trend largely observed in Phanerozoic sedimentary hydrocarbons and kerogens. The expanded inventory of cyanobacterial lipid carbon isotope compositions and isotopic offsets will complement continuing efforts in biomarker source assignment, paleoenvironmental reconstruction, and carbon flux and metabolic modeling.
Continental margins are efficient sinks for organic carbon, integrating marine production with terrigenous organic matter (OM) supplied by riverine systems. Identifying and distinguishing terrestrial OM sources is therefore essential for understanding land-ocean carbon transfer. Here, molecular distributions and compound-specific δ13C values of long-chain n-alkanes were analyzed in surface sediments along the Southwestern Atlantic Margin (SAM; 23°–37°S) to characterize terrigenous OM inputs under modern environmental conditions. The combined use of n-alkane indices (ACL25–33, Norm31) and homolog-specific δ13C values reveals three main continental contributions: (i) grassland-dominated OM exported by the Río de la Plata (RdlP), (ii) tropical rainforest-derived OM from rivers draining the São Paulo Bight, and (iii) arid vegetation-derived OM from the Paraíba do Sul River basin. OM associated with the RdlP and Paraíba do Sul rivers shows higher ACL25–33 and Norm31 values and relatively enriched δ13C signatures, whereas rainforest-derived OM is characterized by lower molecular indices and more depleted δ13C values. Spatial patterns indicate that RdlP-derived OM extends farther northeastward and toward the continental slope than previously recognized, while local riverine inputs and shelf circulation promote strong mixing within the São Paulo Bight. Systematic offsets between δ13C values of n-C29 and n-C31 further suggest that homolog-specific isotopic signatures reflect hydroclimatic controls and grass inputs rather than simple C3-C4 mixing alone. By defining representative molecular and isotopic end-members for major terrigenous OM sources to the SAM, this study provides a robust geochemical framework for tracing continental inputs in marine sediments and establishes a reference for paleoenvironmental reconstructions of vegetation, hydroclimate, and land-ocean carbon exchange.
Compound-specific hydrogen isotope (δD) analysis is frequently limited by low analyte abundance, which can lead to disproportionately elevated analytical uncertainty and incomplete environmental records. Here, we evaluate an isotope dilution approach designed to improve the measurability of low-abundance compounds through controlled mixing with an isotopically characterized spike. Using n-alkane isotope reference mixtures, we systematically assess the influence of spike-sample mixing ratios and injection strategies on recovered δD values. Comparison of inlet introduction methods shows that pre-mixed injections outperform autosampler co-injections, reducing RMSE by approximately a factor of two. Uncertainty analyses indicate that variability in the measured isotope ratios is the dominant contributor to propagated uncertainty, whereas mixing-ratio variability contributes a smaller but non-negligible component. Our results define a practical operating window in which the injected spike concentration may reach up to 2.8 times that of the sample, increasing total injected analyte abundance nearly fourfold while maintaining reliable isotope recovery. Under these conditions, long-chain homologs (C27 and C29) achieve RMSE values of approximately 5–6 ‰, within ~1.5‰ of those obtained from independent high-abundance measurements. These results demonstrate that isotope dilution provides a practical means of extending compound-specific δD measurements to substantially lower analyte abundance, expanding analytical access to low-concentration biomarkers in paleoclimate and environmental archives.
Characterization of hydrocarbon source rocks for paleoenvironmental reconstruction is often precluded by thermal overprinting, especially in sedimentary basins affected by igneous intrusions. In the Parnaíba Basin (NE Brazil), organic-rich Devonian shales of the Pimenteiras Formation were disturbed by sill emplacement related to the Central and Equatorial Atlantic magmatic provinces (Triassic-Jurassic). We applied a multiproxy geochemical approach in three wells: two wells with multiple volcanic intrusions and one well without intrusions, used here as reference of primary signatures. Total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), δ13Corg, and δ15N were complemented with geophysical logs and multivariate geostatistical classification (Mahalanobis distance, calculated from TOC vs. TN and δ13Corgvs. δ15N), to distinguish pristine and thermally affected intervals. The reference well exhibits a strong TOC-TN correlation (r = 0.96), whereas the thermally affected wells show no correlation (r = 0.04 and −0.11) and are marked by Contact Low-Resistivity Zones (CLRsZ), reflecting modifications on geochemical and petrophysical properties. Wells with intrusions have up to ∼80% of samples plotting outside the reference geochemical values, however, an interval (1995–2109 m) preserves pristine signatures. Within this section, six chemozones record a transgressive–regressive history. Transgressive phases are marked by dominant marine organic matter (δ13Corg around −28‰; TOC/TN < 5), whereas regressive phases reflect stronger terrestrial input (TOC/TN > 20), both accumulated under anoxic conditions. Despite thermal overprinting, a multiproxy approach provides a reproducible workflow able to distinguish organic-rich rocks with depositional signals from magmatic alteration. This framework enables assessing source-rock quality and predicting maturation of organic matter in atypical petroleum systems.
The burial of sedimentary organic matter (SOM) in shelves represents a key component of the global carbon cycle yet understanding of SOM sources and reactivity across large-river-dominated shelves are insufficient by single geochemical proxy, due to natures of dynamic and complex biogeochemical processes. In this study, an East China Sea transect, ranging from Changjiang River Estuary (CJE) to the Okinawa Trough (OT), was selected to investigate the sources and reactivity of OM in surface sediments using multi-geochemical proxies, to overcome the limitations of using a mono-proxy. Carbon to nitrogen ratios, stable isotopic signatures, and organic carbon-normalized lignin phenols indicated dominance of marine production, with relatively higher terrestrial vascular-plant contributions nearshore. Lignin-derived parameters suggested relatively stronger gymnosperm associated signals in the estuary, whereas nonwoody angiosperm associated signals were more pronounced offshore. The total hydrolysable amino acids and neutral sugars indicated that the SOM reactivity exhibited a bimodal distribution pattern along the transect, probably regulated by hydrodynamic forcing associated with the Changjiang Diluted Water and the Kuroshio Current, sediment sorting, and biological‑carbon-pump-related marine organic matter supply. Interpolated sedimentation rates and estimated organic carbon burial fluxes were highest in the CJE prodeltaic sediments and lowest in the OT. Terrestrial OM proxies attenuated seaward and fit power-law models, indicating weakening terrestrial signals during cross-shelf transport, whereas marine OC dominated source-specific burial on the shelf and in the OT. This integrated proxy framework provides a more coherent interpretation of SOM source, reactivity, transport-related attenuation, and burial than can be obtained from any single proxy alone.
Wildfires are a significant ecological disturbance and a sensitive proxy for past climate changes. Here, we report the first confirmed occurrence of all three anhydrosugars—levoglucosan (L), mannosan (M), and galactosan (G) in Middle Miocene (Badenian, 13.8–13.0 Ma) marine deposits of the Central European Paratethys. These compounds co-occur with fusinites and polycyclic aromatic hydrocarbons (PAHs), indicating the preservation of pyrolytic signals in sediments over 13 million years old. Bulk geochemical and biomarker analyses demonstrate a predominance of terrigenous organic matter, including both angiosperm and gymnosperm sources. The compounds identified as typical for gymnosperms include simonellite, ferruginol, dehydroferruginol, sugiol, and dehydroabietic acid, while the biomarkers for angiosperms are des-A-ursenes, α-amyrin, β-amyrin, and amyrone. Fusinite reflectance and PAH ratios suggest wildfire temperatures of 300–500 °C, consistent with a mixture of surface, ground, and crown fires. The relative distributions of L, M, and G suggest that the burned biomass originated from a mixed source, with softwoods predominating over hardwoods. The preservation of anhydrosugars in these sediments appears to be controlled by dysoxic to anoxic depositional conditions, reduced microbial activity, and limited thermal maturity (vitrinite reflectance <0.4%). This study suggests that anhydrosugars can serve as wildfire tracers in geological records significantly older than previously documented, offering new insights into Miocene fire dynamics and vegetation composition.
