Terrigenous Plant Research Articles

Source rock and climate model for the Cretaceous Jiufotang Formation, Kazuo Basin, China: Geochemistry and petrography

The Lower Cretaceous Jiufotang Formation, situated in western Liaoning Province, China, has attracted attention for abundant Jehol Biota fossils and the potential to improve understanding of the relationships among climate change, evolution of terrigenous organisms, and organic matter (OM) enrichment in lake systems during the Early Cretaceous. Based on organic petrology and biomarker analyses, this study investigated the depositional environment, OM sources, and enrichment mechanism of Jiufotang mudstone in the Kazuo Basin. Maceral composition shows that the OM source of Jiufotang mudstone shifted from mainly aquatic to terrigenous, and biomarkers such as abundant diterpenoids and retene indicate that terrigenous higher plants were mainly conifers during deposition of the Jiufotang Formation. Pr/Ph ratios (0.07–0.65) show that the studied section was deposited in anoxic bottom water that may be necessary for OM enrichment in lake systems. Gravity flows were accompanied by input of many clastic minerals and oxygenation of bottom waters, which is unfavorable for OM enrichment. Therefore, the best OM enrichment model for lake systems includes anoxic bottom water, stable water column stratification, low sedimentation rates, and high phytoplankton contributions. The climate changed from relatively dry to humid, which drove changes in the OM enrichment model in the lake. More importantly, the climate and terrigenous plant information obtained by biomarkers is useful to reconstruct the ecological environment of the Jehol Biota.

The source and preservation of lacustrine shale organic matter: Insights from the Qingshankou Formation in the Changling Sag, Southern Songliao Basin, China

Organic-rich shale in the Cretaceous succession of the large non-marine Songliao Basin in northeastern China, especially the Qingshankou Formation of the Turonian and Coniacian stages, provides a unique record for studying the role of global climate control on organic matter accumulation. Organic enrichment in the Qingshankou Formation along the Southeastern Uplift of the basin has been widely reported and is implicated in the formation of algal blooming and a saline anoxic water environment. However, studies on the Qingshankou Formation in the Changling Sag are relatively few, which leaves a significant gap to understand the controlling factors of organic enrichment at a basin scale. In this study, the sedimentary environment of the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) is reconstructed from petrological and geochemical data to discuss the sources and preservation mechanisms of lacustrine shale organic matter in the Changling Sag (southern Songliao Basin). The K2qn1 is subdivided into three stratigraphic units: Sq1 phase, Sq2 phase, and Sq3 phase. Biomarker (abundance of tricyclic terpane and regular steranes) and petrographical (maceral composition) data indicate that the organic matter in K2qn1 was mainly from terrigenous plants, with some algal input. Inorganic minerals (major and trace elements) and petrological (framboidal pyrite size) data suggest a humid climate and saline anoxic water environment at the Changling Sag during the most organic-rich Sq1 phase. During the Sq2 and Sq3 phases, a relative low lake level and semi-arid climatic conditions likely prevailed. Moreover, these results imply that apart from a saline anoxic water environment, the persistence of continentally derived organic matter in lacustrine shale is mainly controlled by clay minerals. Accordingly, this study proposed a new enrichment model for lacustrine shale organic matter. The new model complements existing lacustrine shale sedimentary models for sources of organic matter and emphasizes the role of clay minerals in preserving organic matter.

Paleoenvironmental reconstruction and organic matter accumulation of the paleogene shahejie oil shale in the Zhanhua Sag, Bohai Bay Basin, Eastern China

The controlling factors of organic-rich shale accumulation is essential for the exploration and development of shale oil and gas resources. The sedimentary environment plays a vital role in the formation of organic-rich sediments in lacustrine facies. This article unravels the mineralogy, geochemistry, and paleoenvironmental evolution during the deposition of the Paleogene Shahejie Formation (Es3L). It discusses the effects of paleoclimate, paleosalinity, paleoredox conditions, paleowater depth, and paleoproductivity on organic matter (OM) enrichment. Finally, the OM enrichment model was established. The results show that the mineralogical compositions are mainly composed of calcite (avg. 40.13%), quartz (avg. 21.64%) and clay minerals (avg. 24.07%), accompanied by dolomite (avg. 7.07%), feldspar (avg. 6.36%) and pyrite (avg. 2.95%). The Es3L shale has a high abundance of OM, with total organic carbon (TOC) ranging from 1.07% to 5.12%. The organic matter type is mainly composed of type Ⅰ-Ⅱ1 kerogen, which is generally considered a good-quality source rock. The source of OM is a mixture of lower bacteria, algae, and plants. During the early sedimentary period, the paleoclimate was dry and cold, with high salinity, intense reducibility, and relatively low productivity. During the late sedimentary period, the climate became warmer and more humid. As a result, the salinity decreased to a level that was suitable for biological reproduction, and productivity increased gradually due to the input of terrigenous plants. Paleosalinity and paleoclimate determined the environment of the sedimentary period, in addition, paleoproductivity and paleoredox condition indicated the formation and preservation conditions of OM. The warm and humid climate, brackish water, suitable reduction conditions and high productivity are the favorable conditions for the generation and preservation of organic matter. The research results may have implications for the genetic mechanisms of organic matter accumulation. They will provide theoretical and technical insights into the exploration and development of shale oil.

Determining source-specific terrigenous organic carbon contributions in sediments from the Yellow River estuary, Northeast China: A test of source apportionment models

Molecular organic geochemistry has been used effectively to determine terrigenous organic carbon (OC) contributions from different sources in modern sediments. However, mathematic modelling using source-specific parameters could be a potentially simple-effective approach to identify the terrigenous OC signals. In this study, the Yellow River estuary was chosen to probe whether source apportionment models can determine source-specific OC contributions. The end-member mixing model suggests that terrigenous OC contributed 57.0% ± 10.2% to the sedimentary OC. n-Alkane distributions were used to perform Unmix and positive matrix factorization (PMF) to separate terrigenous and autochthonous OC into more specific sources. PMF modelling delineates the contributions of high terrigenous plants, fossil OC, macrophyte-sourced OC, and bacterial and algal-sourced OC as 22.9% ± 14.3%, 26.2% ± 19.4%, 26.5% ± 19.3%, and 24.4% ± 17.1%, respectively. In assessing terrigenous contributions, PMF results (48.7% ± 13.5%) almost agrees with the end-member mixing model (57.0% ± 10.2%), consistent and comparable with previously published data (~ 50%), while Unmix (73.9% ± 18.7%) is significantly overestimated. Interestingly, macrophyte-sourced OC from coastal wetland identified by PMF was less investigated previously and should call attention in the future study. Consequently, modelling results match well with previously published data, suggesting that mathematic modelling can be an effective approach to quantitatively evaluate source-specific terrigenous OC contributions to estuary sediments and other complex aqua-land systems. However, caution must be taken in respect to the modelling uncertainty, which could be mainly induced by sample number, diversity, and robust interpretation on chemical parameters.

C20-C21-C23 tricyclic terpanes abundance patterns: Origin and application to depositional environment identification

Reconstruction of paleo-depositional environments in a sedimentary basin is often obstructed by the absence of typical environmental indicators in sedimentary rocks. Here, we propose a biomarker method using C20-C21-C23 tricyclic terpanes (TTs) as a tracer, which is simple in analysis but robust to provide reliable and detailed environmental information. Based on the analysis of 271 C20-C21-C23TT data from 32 basins in 18 countries, we observed a relationship between C20-C21-C23TT abundance patterns and depositional environments. This relationship was attributed to the control of depositional environments on the input proportions of plankton and terrigenous plants, which act as two end-member precursors for the TTs in a depositional system. The various mixing proportions between these two end-members result in different C20-C21-C23TT abundance patterns associated with different depositional environments, e.g., C20>C21>C23TT in river-lake transitional, C20<C21<C23TT in marine or saline lacustrine environments, C20<C21>C23TT in freshwater lacustrine and C20>C21<C23TT in marine-continental transitional environments. In addition, the C23/C21TT ratio increases with elevated salinity of depositional water, and the C21/C20TT ratio increases with increasing water depths. Based on these observations, a discrimination diagram using C23/C21TT vs. C21/C20TT was developed for environmental identification. The validity of this C20-C21-C23TT biomarker method is well demonstrated by the rock samples with typical environmental indicators. This method is applicable in a broad spectrum of rocks and in maturities up to 2.4%Ro. Its strength was shown by a case study of a complex depositional system in the East China Sea Basin, which has been strongly affected by eustasy.

Late Quaternary terrigenous plant and coaly fragments found at the Vestnesa Ridge, Fram Strait: implications for postglacial plant colonization at Svalbard

Late Quaternary terrigenous plant and coaly fragments found at the Vestnesa Ridge, Fram Strait: implications for postglacial plant colonization at Svalbard

Terrigenous leaf-utilizing life of the tube-bearing annelid Anchinothria cirrobranchiata (Annelida: Onuphidae) in the deep sea

AbstractDeep-sea ecosystems are generally oligotrophic because they lack photosynthesizing producers. On deep-sea slopes near land, however, various terrestrial plant remains flow to and are deposited on near-shore deep bottoms. From a depth of 300 m off the Pacific coast of Owase, central Japan, we collected an onuphid polychaete, Anchinothria cirrobranchiata (Annelida: Onuphidae), which lives in a dorsoventrally flattened portable tube. The polychaete tubes were made of sand, as well as leaves and twigs of terrestrial evergreen trees. The leaves glued on the portable tubes were chartaceous, blackish and tough; they belonged mainly to two genera of Fagaceae, Castanopsis and Quercus, which are dominant components of coastal evergreen oak forests. In aquaria, the polychaetes fed on the leaves on their tubes, as well as autochthonous sedimented leaves, suggesting utilization of terrigenous plant litter as food. As to the evolution of Anchinothria, a molecular phylogenetic analysis suggests that Anchinothria is monophyletic with other Hyalinoeciinae (Nothria, Leptoecia, Hyalinoecia).

Origin and environmental implications of dibenzothiophenes in the Huanghekou East Sag and the Laizhouwan Northeast Sag, Bohai Bay Basin

A suite of nine oils from Huanghekou East Sag and Laizhouwan Northeast Sag, Bohai Bay Basin, China, were analysed to investigate the effect of the depositional environment on dibenzothiophenes. Five oils were high-sulfur oils (HSOs, sulfur content >1%) from Huanghekou East Sag while other four oils were low-sulfur oils (LSOs). The major organic matter inputs of all oils were algae, and specific algae might contribute to the high molecular weight alkanes and C29 steranes of HSOs. HSOs mainly originated from carbonate-rich source rocks in more saline environments while LSOs derived from clay-rich source rocks deposited in freshwater conditions, as supported by a series of biomarkers, including phytane, gammacerane, terpanes and their abundance ratios. Maturity parameters show that the samples are all in the low mature to mature stage. The methylated dibenzothiophenes are more abundant in HSOs than those in LSOs. The major sources of methylated dibenzothiophenes are algae and bacteria while the dibenzothiophene is more derived from terrigenous plants, according to the carbon isotope values of individual compounds. Abundant bacterially generated H2S as well as reducing depositional environment result in transformation from algae-originated organic matter to relatively large amount of dibenzothiophenes, further, carbonate-rich source rocks might inhibit the demethylation, leading to the more abundance of methylated dibenzothiophenes in HSOs. Parameters derived from dibenzothiophenes, such as the ratios: methyldibenzothiophenes/methylphenanthrenes, methyldibenzothiophenes/phenanthrenes, dimethyldibenzothiophenes/dimethylphenanthrenes, and dimethyldibenzothiophenes/phenanthrenes are most useful for indicating reducing depositional environments among HSOs and LSOs.

Occurrence and origin of perylene in Paleogene sediments from the Tasmanian Gateway, Australia

Eocene to Lower Oligocene sediments were collected by Ocean Drilling Program Leg 189 at four sites in the Tasmanian Gateway, Australia, and geochemically characterised to investigate the occurrence and controlling factors of perylene. Perylene is enriched in samples from Site 1168, which is located closest to Tasmania, accounting for up to 53.4% of the total quantified aromatic hydrocarbons, with concentrations ranging from 15 ng/g dry weight sediment (dws) to 1700 ng/g dws. However, only trace amounts of perylene (<5 ng/g dws) are present in samples from the other three sites, except for two deep samples from Site 1171, which is furthest from Tasmania, with perylene concentrations of 15 ng/g dws and 95 ng/g dws. The concentrations of perylene increase with burial depth, suggesting its formation from diagenetic processes. Other molecular compositions, including land-plant-derived aromatic hydrocarbons, pyrogenic-related aromatic hydrocarbons and n-alkanes, indicate that the origin of perylene can be attributed to allochthonous organic material associated with terrigenous plants. Contributions from autochthonous organic matter and combustion cannot be validated. Detailed examination of the relationship between the concentrations of perylene and organic matter input and depositional conditions illustrate that both factors are important but not essential. The concentrations of perylene are positively correlated to pristane/phytane ratios, implying that perylene is probably formed under dysoxic rather than highly reducing conditions. Terrigenous-sourced organic matter was detected at all four sites, but perylene is only concentrated at the site closest to Tasmania. It is proposed that the preservation of the precursors of perylene is critical, as these are sensitive to destruction by oxidation. If the precursors of perylene are destroyed during transportation and early sedimentation, no perylene will be formed during diagenesis, no matter how strong the reducing conditions are.

Source of organic matter and paleoenvironment of deposition of crude oils from the Niger Delta Basin

The study employed thirteen (13) crude oil samples from thirteen (13) producing wells, with the aim of examining the source of organic matter and the paleoenvironment of deposition. The crude oils were deasphaltened and the maltene fraction fractionated to obtain the saturates. The saturates were subjected to gas chromatography mass spectrometer (GCMS) analysis for the steranes, Isoprenoids and n-alkanes, and triterpanes and hopanes biomarker chromatograms. The biomarker composition of the studied oils indicates weakly oxic and reducing environmental conditions for the studied samples, consistent with marine deltaic environment of deposition. The study shows that the oils are associated with a mix of terrestrial and marine organic matter with a comparatively higher terrestrial and lower marine algae organic matter input. The oleanane index of 1.8 and the presence of oleanane in the studied samples denote higher terrigenous plant input into the source rock the generated the crude oils.

Analyses of depositional environments of the Marcellus formation in New York using biomarker and trace metal proxies

The purpose of this study was to observe how the composition of organic matter (OM) and the extent of anoxia during deposition within the Marcellus Formation in New York varied by distance from the sediment source in eastern New York. Lipid biomarkers (n-alkanes and fatty acids) in the extractable organic component (bitumen) of the shale samples were analyzed, and proxies such as the average chain length (ACL), aquatic to terrestrial ratio (ATR) and carbon preference index (CPI) of n-alkanes were calculated. Fatty acids were relatively non-abundant due to the age of the shale bed, but n-alkane distributions revealed that the primary component of the OM was terrigenous plants. The presence of shorter n-alkane chain lengths in the samples indicated that there was also a minor component of phytoplankton and algal (marine) sourced OM. Whole rock analyses were also conducted, and cerium anomalies were calculated as a proxy for anoxia. All samples had a negative anomaly value, indicating anoxic conditions during deposition. Two samples, however, contained values close to zero and thus were determined to have suboxic conditions. Anoxia and total organic matter (TOM) did not show any spatial trends across the basin, which may be caused by varying depths within the basin during deposition. A correlation between nickel concentrations and TOM was observed and indicates that algae was the primary source of the marine OM, which supports the lipid biomarker analysis. It was determined that the kerogen type of the Marcellus Formation in New York State is type III, consistent with a methane-forming shale bed.

Discerning natural and anthropogenic organic matter inputs to salt marsh sediments of Ria Formosa lagoon (South Portugal).

Sedimentary organic matter (OM) origin and molecular composition provide useful information to understand carbon cycling in coastal wetlands. Core sediments from threors' Contributionse transects along Ria Formosa lagoon intertidal zone were analysed using analytical pyrolysis (Py-GC/MS) to determine composition, distribution and origin of sedimentary OM. The distribution of alkyl compounds (alkanes, alkanoic acids and alkan-2-ones), polycyclic aromatic hydrocarbons (PAHs), lignin-derived methoxyphenols, linear alkylbenzenes (LABs), steranes and hopanes indicated OM inputs to the intertidal environment from natural-autochthonous and allochthonous-as well as anthropogenic. Several n-alkane geochemical indices used to assess the distribution of main OM sources (terrestrial and marine) in the sediments indicate that algal and aquatic macrophyte derived OM inputs dominated over terrigenous plant sources. The lignin-derived methoxyphenol assemblage, dominated by vinylguaiacol and vinylsyringol derivatives in all sediments, points to large OM contribution from higher plants. The spatial distributions of PAHs (polyaromatic hydrocarbons) showed that most pollution sources were mixed sources including both pyrogenic and petrogenic. Low carbon preference indexes (CPI > 1) for n-alkanes, the presence of UCM (unresolved complex mixture) and the distribution of hopanes (C29-C36) and steranes (C27-C29) suggested localized petroleum-derived hydrocarbon inputs to the core sediments. Series of LABs were found in most sediment samples also pointing to domestic sewage anthropogenic contributions to the sediment OM.

Palaeoenvironment and organic matter of the Triassic Chang 9 lacustrine shales, Ordos Basin, China

The Ordos Basin, a large mainly non‐marine basin, is an important petroliferous basin in northern China. The Triassic Chang 9 shales, including the delta plain shale (DPS), delta front shale (DFS), and deep lake shale (DLS), are proven to be the main source rocks in the lower Yanchang Formation (LYF). This study investigates the source rock potential, palaeoenvironment, and organic matter (OM) source. According to the OM thermal maturity, abundance, and type, the shales have excellent source rock potential. The DLS has the highest quality with average TOC of 7.08%, S1 + S2 of 14.41 mg HC/g rock, and Type II1–II2. According to correlations of Rb/Sr versus Sr/Cu, the shales were mainly deposited in arid conditions. Based on the major element (S), trace elements (V, Ni, Co, Cr, U, and Th), rare earth element (Ce) concentrations, and biomarkers (Pr, Ph, dibenzofuran, fluorene, and dibenzothiophene), redox conditions for the DPS, DFS, and DLS were oxidizing, sub‐oxidizing to sub‐reducing, and reducing, respectively. The palaeosalinity was fresh‐ to brackish‐water, ascertained by the trace elements (Sr and Ba) and biomarkers (gammacerane). The water stratification was controlled by the temperature changes and the palaeosalinity differences, and the maximum water depth was ~100 m during the Chang 9 deposition. Aquatic microorganisms (e.g., algae, bacteria, and phytoplankton) were the main organic matter sources for the shales, mixed together with terrigenous plants in DPS and DFS. The DLS has the most aquatic microorganisms and has the least higher plant fragments, supported by the higher TOC (up to 14%), lowest vitrinite contents (Avg. = 14.1%), and highest liptinite contents (Avg. = 59.5%). Laterally, the DPS, DFS, and DLS were distributed successively from the lake margin to the depocentre. Vertically, the DLS, DFS, and DPS were developed successively from the bottom lake to the upper lake. The DLS was mainly formed in an environment of high‐level sapropelinite and favourable preservation conditions, and the DPS was mainly formed in an environment of high‐level terrigenous inputs and poor preservation conditions, while the DFS was mainly formed in an environment of medium‐level of sapropelinite productivity and terrigenous inputs and fair preservation conditions. The DPS and DFS were formed during both the early stage (shallow lake) and the late stage (deep lake) of the Chang 9 deposition, while the DLS was only developed in the deep lake during the late Chang 9 deposition. The high‐level sapropelinite production and favourable preservation controlled the formation of the organic‐rich shales, especially for the organic‐rich DLS.

Geochemical characteristics and sources of the crude oil of Yan’an formation Yan 9 in Zhao’an area, Ordos Basin, China

A certain scale of Yan 9 reservoir was found in Zhao’an area, but the oil source is not clear. The geochemical characteristics of Yan 9 crude oil and potential source rocks were analyzed by using gas chromatograph-mass method. Analysis results showed that the parent materials of Yan 9 crude oil were sourced from lower aquatic organism and higher terrigenous plants and formed in freshwater- brackish water lacustrine facies. Oil-source correlation results showed that Yan 9 crude oil was derived from the source rocks of Chang 7.

Characterizing DOC sources in China’s Haihe River basin using spectroscopy and stable carbon isotopes

The Haihe River Basin is a polluted area affected by the developing industry and intensive agricultural activities in China. Dissolved organic matter (DOC) and light-absorbing characteristics of chromophoric dissolved organic matter (CDOM) were monitored in different tributaries of China within the Haihe River basin during spring and autumn. The concentration of DOC during spring was higher than during autumn (p < 0.01), and the evaporation was an important factor affecting the concentration of DOC in the basin. By contrast, the proportion of inputs due to terrigenous plants during autumn was higher than during spring. Carbon stable isotope analysis δ13C and C: N ratio of DOC, evidenced the inputs of DOC in the Haihe River basin from different sources including sewage, terrestrial plants, soil, and plankton. Isotopic analysis of δ13C and excitation-emission matrix (EEM) with fluorescence regional integration (FRI) analysis supported the hypothesis that allochthonous inputs contributed substantially to the inputs of DOC in the Haihe River basin, coming largely from sewage (9.8%–81.2%) and terrestrial plants (13.3%–65.8%). Depending on the source of DOC and contribution, four types with different EEM spectra were set. Type I, river water from sewage (81.2%); Type II, river water with input from terrestrial plants (65.8%); Type III, river water with plankton (36.4%), and Type IV, river water with soil-derived DOC (33.9%). The results demonstrated that the combined methodology using 13C stable isotope and EEM-FRI can be used to characterize the components of DOC in river waters. This approach was important for tracking the concentration and composition of DOC in river waters from different input sources and for better understanding concerning the local regulation of the terrestrial carbon cycle.

Geochemical characteristics and origins of the crude oil of carboniferous formation in Dajing area, Junggar basin, China

Dajing area is one of the key exploration areas in Junggar basin. In this paper, based on scientific exploration and exploitation, the geochemical characteristics of the carboniferous crude oil and potential source rocks were analyzed using gas chromatograph-mass method. The correlation of biomarkers showed that the parent materials of the carboniferous crude oil formed in freshwater-mildly brackish water environment and were sourced from low grade aquatic organisms and terrigenous higher plants. Oil-source correlation results showed that the carboniferous crude oil in Dajing area was derived from the source rocks of Songkaersu.

Bio-markers based oil to source rock correlation and paleo-environmental interpretation: A case study from Talang Akar Formation, South Sumatra Basin, Indonesia

Talang Akar Formation is a proven hydrocarbon source rock in South Sumatra basin. This study used 3 crude oil sample and 6 well-cutting obtained from Talang Akar Formation. Biomarkers analysis has been used to determine the depositional environment of Talang Akar Formation. The techniques utilized include gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis of normal alkanes, isoprenoids, triterpene, and steranes. The most commonly used, pristine (Pr) to phytane (Ph) ratio is a good indicator of the depositional environment. The results in this research show that Pr/Ph ratios range from 5.90-10.08. Pr/Ph indicating abundant terrigenous plant input deposited under oxic to suboxic conditions. The oil/source rock correlation analysis using biomarker data shows that the oils field is correlated with the oils in source rock of Talang Akar Formation. This study concludes that the source rock in Talang Akar Formation was deposited in a transitional (Fluvio-deltaic) to marginal marine environment under oxic conditions.

Geochemical characteristics and origins of the crude oil of Yanchang Formation Chang 2 in Ansai Area, Erdos Basin, China

Ansai Oilfield is one of the earliest discovered oilfields in the Ordos Basin. In this paper, based on the scientific exploration and exploitation, the geochemical characteristics of the Chang 2 crude oil and potential source rocks were analyzed using gas chromatography–mass spectrometry method. The correlation of biomarkers showed that the parent materials of the Chang 2 crude oil formed in freshwater-mildly brackish water environment and were sourced from low-grade aquatic organisms and terrigenous higher plants. Oil-source correlation results showed that the Chang 2 crude oil in Ansai area was derived from the source rocks of Chang 7.

Hydrocarbon-generation potential of upper Eocene Enping Formation mudstones in the Huilu area, northern Pearl River Mouth Basin, South China Sea

Upper Eocene Enping Formation mudstones in the Pearl River Mouth Basin, South China Sea, which formed during a lake-flooding event, are one of the most important sets of cap rocks in the basin. However, the generation potential (GP) of Enping Formation mudstones remains poorly understood and controversial. Despite a lack of documentation, these mudstones are presumed to have the potential to generate hydrocarbons. In this study, new organic geochemical data for these mudstones are provided based on several new wells drilled into Eocene strata in the Huilu area, northern Pearl River Mouth Basin, which illustrate their hydrocarbon GP. Total organic carbon content ranges from 0.55 to 3.3 wt. % (mean, 1.31 wt. %) with kerogens dominated by type III organic matter (OM) derived from terrigenous plant material. The Zhuqiong II movement, a rifting episode that occurred during the late Eocene (ca. 38 Ma), was associated with the introduction of a large quantity of terrigeneous higher plants by rivers that led to type III OM accumulation and preservation of Enping Formation mudstones. Rapid transverse facies changes led to the geochemical heterogeneity of the source rocks. The OM in these rocks reached an early–midmature stage in uplifted areas (vitrinite reflectance [Ro] e 0.5%–1.0%) and a late–mature stage in sags (Ro e 1.0%–1.3%), stages wherein hydrocarbons can be generated. Therefore, the Enping Formation mudstones may have had the potential to generate hydrocarbons, especially gas, and hence deserve attention in future exploration.

Late Cretaceous marine arthropods relied on terrestrial organic matter as a food source: Geochemical evidence from the Coon Creek Lagerstätte in the Mississippi Embayment.

The Upper Cretaceous Coon Creek Lagerstätte of Tennessee, USA, is known for its extremely well-preserved mollusks and decapod crustaceans. However, the depositional environment of this unit, particularly its distance to the shoreline, has long been equivocal. To better constrain the coastal proximity of the Coon Creek Formation, we carried out a multiproxy geochemical analysis of fossil decapod (crab, mud shrimp) cuticle and associated sediment from the type section. Elemental analysis and Raman spectroscopy confirmed the presence of kerogenized carbon in the crabs and mud shrimp; carbon isotope (δ13 C) analysis of bulk decapod cuticle yielded similar mean δ13 C values for both taxa (-25.1‰ and -26‰, respectively). Sedimentary biomarkers were composed of n-alkanes from C16 to C36 , with the short-chain n-alkanes dominating, as well as other biomarkers (pristane, phytane, hopanes). Raman spectra and biomarker thermal maturity indices suggest that the Coon Creek Formation sediments are immature, which supports retention of unaltered, biogenic isotopic signals in the fossil organic carbon remains. Using our isotopic results and published calcium carbonate δ13 C values, we modeled carbon isotope values of carbon sources in the Coon Creek Formation, including potential marine (phytoplankton) and terrestrial (plant) dietary sources. Coon Creek Formation decapod δ13 C values fall closer to those estimated for terrigenous plants than marine phytoplankton, indicating that these organisms were feeding primarily on terrigenous organic matter. From this model, we infer that the Coon Creek Formation experienced significant terrigenous organic matter input via a freshwater source and thus was deposited in a shallow, nearshore marine environment proximal to the shoreline. This study helps refine the paleoecology of nearshore settings in the Mississippi Embayment during the global climatic shift in the late Campanian-early Maastrichtian and demonstrates for the first time that organic δ13 C signatures in exceptionally preserved fossil marine arthropods are a viable proxy for use in paleoenvironmental reconstructions.