Two low-latitude glacial events (i.e. the Sturtian and Marinoan glaciations) occurred in the Cryogenian, both of which were known as the “Snowball Earth”. The sedimentary environment and continental chemical weathering recorded in the syn-glacial, inter-glacial, and post-glacial strata are of great significance to investigate the global glaciations and to establish the Earth’s environment evolution in the Neoproterozoic. Well-preserved middle-late Neoproterozoic sedimentary sequences (including the Yalaguzi, Bolong, Kelixi, Yutang, Kuerkake, and Kezisuhumu Formations from bottom to top) have been identified at the southwestern margin of the Tarim Craton. Nevertheless, there was ongoing debate regarding the evolution of sedimentary environments and their comparison to global glaciers. Furthermore, the sedimentary processes of glacial strata and continental chemical weathering remained obscure. This study conducted detailed field investigation, detrital zircon geochronology, and whole-rock major-element composition analysis. The sedimentary environment evolved from a continental to marine environment. The purplish red conglomerate of the Yalaguzi Formation represents alluvial fan facies, and the combination of diamictites and ice-raft debris depositions in the Bolong and Yutang Formations indicates glacial facies. After the deglaciation of the Bolong glaciation, the Kelixi Formation experienced the transition from neritic-littoral to fan delta-littoral. Afterwards, the sedimentary environment changed to the glacial facies of the Yutang Formation and evolved from a littoral-neritic to shore environment of the Kuerkake Formation. By using the mean age of the youngest two or more grains that overlap in age at 1σ (YC1σ (2+)), the maximum deposition age of the Kelixi Formation has been determined to be 662 Ma, which means that the Bolong and Yutang glaciations correspond to the Sturtian and Marinoan glaciations, respectively. The presence of relatively high corrected chemical index of alteration (CIA_corr) values in otherwise low CIA values documented in the Bolong Formation implies the existence of warm-humid intervals during the overall cold climate. The low CIA_corr values recorded in the Yutang Formation are consistent with a cold event in the Marinoan glaciation. The large variety of the CIA_corr values within the Kelixi Formation suggests that continental weathering during the interglacial period exhibited a tendency of (weakly)-strong-moderately-weakly-strong evolution. Notably, the dramatic fluctuation (from weak to strong continental weathering) recorded in the upper member of the Kelixi Formation implies the arrival of the Marinoan glaciation. A sharp CIA_corr increase is observed during the transition periods between the Bolong and Kelixi Formations, as well as the Yutang and Kuerkake Formations, indicating a huge increase in the chemical weathering intensity in the aftermath of the Sturtian and Marinoan glaciations. This suggests that the Sturtian and Marinoan deglaciation might have been associated with intense continental chemical weathering. This work was financially supported by the National Natural Science Foundation of China (grants 42272249 and 41972237) and the Hong Kong Research Grants Council General Research Fund (17307918).

How to cite: Hu, H., Liu, Q., Zhao, G., Lu, L., Shao, D., Cao, X., Jing, J., and Liu, J.: Stratigraphic framework and continental weathering evolution of syn-glaciation, inter-glaciation, and post-glaciation during middle-late Neoproterozoic time in the southwestern Tarim Craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10012, https://doi.org/10.5194/egusphere-egu24-10012, 2024.

Rapid eustatic rise during deglaciations should cause sedimentary condensation and depositional hiatuses on marine shelves. Determining the duration of these hiatuses is challenging, especially in sequences that cannot be reliably dated. Recently, it was suggested that a global prolonged hiatus could have ensued following the Neoproterozoic Snowball Earth events. However, the duration and stratigraphic characteristics of these events are uncertain. Here, we utilize 3D stratigraphic forward modelling software DionisosFlow to 1) estimate its duration following a Snowball Earth when considering 800 m glacioeustatic rise over 40 kyr, and 2) explain the stratigraphic fingerprint of such an event. We tested several margin configurations and different sediment flux scenarios; our findings indicate that the duration of the hiatus, as predicted, will increase with accommodation, and decrease with sediment supply. Simulating an average (modern) glaciated margin with an average sediment flux results in prolonged sediment starvation on the outer shelf, lasting over 6 Myr. More complex models show how topography, sediment type, and sediment volume during and after the deglaciation affect the stratigraphic record. We compare the predicted model outputs with observed Snowball Earth stratigraphy from the Kimbereley region of NW Australia to reconstruct the paleoenvironmental conditions. This work demonstrates how 3D stratigraphic modeling can help clarify deglacial stratigraphy.

How to cite: Nordsvan, A., Mitchell, R., Bauer, K., Colleps, C., and McKenzie, R.: Predicting deglacial stratigraphy following Snowball Earth with 3D forward modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12967, https://doi.org/10.5194/egusphere-egu24-12967, 2024.

The sedimentary successions provide direct evidence of climate and environment, which offer clues to the cause of the great transition from marine to terrestrial in the Early Carboniferous-Late Permian in the Ordos Basin. The eastern Ordos Basin's early Carboniferous-late Permian strata are sequentially stratified in ascending order as the Benxi Formation of the early Carboniferous, the Taiyuan Formation of the late Permian, and the Shanxi Formation of the late Permian. The Benxi Formation is composed of mudstone with a large number of siderite concretions, carbonaceous mudstone, rhythmic layers of siltstone and mudstone, and coal. The rhythmic layers indicate depositional products of lagoon and tidal flat. The Taiyuan Formation comprises carbonate and clastic sedimentary record, which lithology is mainly biological detrital limestone, limestone with chert nodules, mudstone, coal, and locally sandstone, indicating a shallow-sea shelf depositional environment. The lower part of the Shanxi Formation is a lithological combination of black mudstone, and purple-red sandy mudstone rhythmic layers interbedded with sandstone and coal seams. The black shale contains both marine biological detrital and terrestrial plant fragments. The sandy mudstone rhythmic layers have developed a large number of tidal beddings (such as flaser bedding, wave bedding, and lenticular bedding). The upper part of the Shanxi Formation is mainly depositional in the delta front-plain system. The lithology is mainly fine-coarse grained sandstone, sandy mudstone interbedded with carbonaceous mudstone containing plant fossils and coal seams. Overall, the palaeoenviroment changes from humid-semihumid to arid-semiarid are recorded by the transition from shallow-sea shelf to tidal flat-lagoon to delta deposition records. This study has established the sedimentary facies sequence of the late Carboniferous-early Permian by investigating five typical outcrops on the eastern margin of the Ordos Basin, and analyzed the paleoenvironmental characteristics of the Benxi Formation-Shanxi Formation based on geochemical methods. In addition, we believes that the Shanxi Formation has not completely transformed into terrestrial deposits in the southeastern part of the basin, and it is still in a transitional marine-terrestrial depositional environment.

How to cite: Peng, S. and Feng, C.: The transition from marine to terrestrial in the Early Permian : Evidence from the Early Carboniferous-Late Permian sedimentary records of the eastern margin of the Ordos Basin, North China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4221, https://doi.org/10.5194/egusphere-egu24-4221, 2024.

We investigate the origin of an exceptionally well-preserved Late Palaeozoic soft-sediment glacial pavement at Oorlogskloof, South Africa and make a palaeoenvironmental reconstruction of deglaciation at this time. Elongate bedforms exposed at the base of the Dwyka Group have previously been interpreted as subglacial flutes and used as evidence of a fast-flowing soft-bedded ice stream. However, analysis of near-identical bedforms of a similar age in Brazil have revealed formation through iceberg ploughing in a shallow glaciomarine environment, warranting re-examination at Oorlogskloof. Fine-resolution orthomosaics and digital terrain models generated from aerial and ground-based structure-from-motion, coupled with field observations, were used to undertake detailed geomorphological mapping of landforms at the site. Elongate bedforms (oriented ESE-WNW) include V-shaped grooves and striations, tapered flutes, and sharp crested asymmetrical ridges with centimetre-scale sediment gravity flow lobes on their slopes. These are accompanied by arcuate push ridges with elongate limbs which parallel the adjacent bedforms. We propose the elongate features were streamlined by a grounded iceberg keel in a shallow marine environment, where the convex core of the arcuate push ridges indicates scouring towards the WNW. Asymmetrical ridges are interpreted as lateral berms since the preservation of sediment gravity flow lobes on their gently dipping slopes necessitates an unconfined substrate at the margins of the grounded iceberg keels. These features further testify to the soft sediment condition of the pavement at the time of bedform formation. Our analysis reveals a pavement formed by iceberg ploughing near a dynamic, retreating ice sheet margin and contests the evidence for an LPIA ice stream positioned over this site, with key implications for locating the position of the palaeo-ice margin over this region of Gondwana. We contend that the site also serves as a valuable sedimentary analogue for contemporary and Pleistocene deglacial landsystems that remain largely inaccessible on today's seafloor.

How to cite: Jones, S., Busfield, M., Le Heron, D., Holt, T., and Glasser, N.: Grooves in the heart of glacial reconstructions: how to distinguish ice stream beds and iceberg keel ploughmarks in Earth's ancient glacial record, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-637, https://doi.org/10.5194/egusphere-egu24-637, 2024.

The geochemical record of the Early Jurassic Sinemurian–Pliensbachian transition (S–P transition; ~193 Ma) is marked by a prominent negative carbon-isotope excursion and a short-lived increase in pCO₂. The paleoenvironmental responses to this carbon-cycle disturbance within the Eastern European Seaway are limited to a widespread, but minor increase in organic matter burial when compared to, e.g., the Toarcian oceanic anoxic event. In contrast, coeval deposits from the Água de Madeiros and Vale das Fontes formations, Lusitanian Basin (Portugal), located in the north-western fringes of the Tethys, comprise highly organic-rich black shales. Here, we reconstruct the paleoenvironmental and redox changes in the Lusitanian Basin across the S–P transition (oxynotum to raricostatum Zone), which are transitioning from euxinic to anoxic to oxygenated conditions. We combine major- and trace-element concentrations, biomarker analysis, and compound-specific carbon- and nitrogen isotope data including those of geoporphyrins. We assess the impact of redox changes and associated shifts in nitrogen cycling and bioavailability (e.g. denitrification) on the abundance and species composition of the marine microflora, the compound-specific carbon-isotope record and phytane-based pCO₂ reconstructions. The exceptionally well preserved, thermally immature and highly organic-rich succession allows new insights into the characteristics and the local processes governing the development of low oxygen conditions outside the temporal realm of large-scale global warming and widespread ocean anoxia.

How to cite: Storm, M., Duarte, L. V., Kraal, P., Hennekam, R., Isaji, Y., Ogawa, N. O., Ohkouchi, N., Schouten, S., and van der Meer, M. T. J.: Assessing redox-related biotic changes during the Sinemurian–Pliensbachian transition in the Lusitanian Basin, Portugal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20350, https://doi.org/10.5194/egusphere-egu24-20350, 2024.

Biogeochemical models, such as COPSE and cGENIE, have been used to predict the carbon cycle response to emissions into the atmosphere under various forcing scenarios. However, there is still significant uncertainty over model predictions of the magnitude of organic carbon burial into ocean sediments. This limits our understanding of C cycle feedbacks during periods considered to be potentially analogous to current anthropogenic induced climate change.

Stable cadmium isotopes (ẟ¹¹⁴Cd) have potential as a palaeoproxy for organic carbon burial in marine settings, due to the fractionation of Cd during burial in association with organic carbon. Therefore, the generation and evaluation of ẟ¹¹⁴Cd records in organic-rich shale sections encompassing periods of climatic and/or environmental change in the geological past is likely to be a useful tool in tracking and quantifying organic carbon burial trends during such events.

Here we present stable cadmium isotope records from four sections of organic-rich shales covering the Palaeocene-Eocene Thermal Maximum (PETM) occurring around 55.9 Ma, which is both the most recent and most analogous interval of rapid climate fluctuations in the geological record to modern-day climate change. We evaluate these records in terms of their organic carbon burial signals (and so carbon removal from the Earth system) during the lead-up to, onset, peak and recovery of the PETM event, as an initial assessment of the ability of stable cadmium isotopes to trace this process. Better quantification of organic carbon burial will enable the responses of the Earth System to rapid climate change to be better understood. 

How to cite: Elms, H. and Dickson, A.: A stable cadmium isotope perspective on organic carbon burial trends during the Palaeocene-Eocene Thermal Maximum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3530, https://doi.org/10.5194/egusphere-egu24-3530, 2024.

At present, the geothermal resources developed and utilized in the Guanzhong Basin are mainly Cenozoic sandstone and glutenite pore -fissure geothermal resources, and the development and utilization horizons are mainly Neogene thermal reservoirs. The occurrence characteristics of geothermal resources, the amount of geothermal resources, and the distribution of favorable areas for geothermal resources development are closely related to the provenance and paleo-sedimentary environment. Identifying the characteristics of Neogene mudstone provenance and paleo-sedimentary environment is helpful to indicate the characteristics of sandstone provenance and paleo-sedimentary environment in the same sedimentary period, which is of great influence for the investigation and development and utilization of geothermal resources in the Guanzhong Basin. The geochemical characteristics of elements in sedimentary rocks record important information of provenance and sedimentary environment. Based on the characteristics of major elements, trace elements and rare earth elements of Neogene mudstone core samples in Guanzhong Basin, the provenance and sedimentary environment were comprehensively studied. The results show that the tectonic setting of the source area of the Neogene mudstone in the Guanzhong Basin is mainly the active continental margin, and the source rocks are mainly the Taibai syenogranite and the Huashan biotite monzonitic granite in the northern of the basin, which contain some intermediate-basic igneous rocks. The chemical alteration index (CIA) is between 61.34 and 76.78, with an average of 70.78, reflecting that Neogene mudstone has undergone moderate weathering, indicating that the climate of Gaoling Group and Lantian-Bahe Formation is in a warm and humid climate environment during the sedimentary period, and the climate of Zhangjiapo Formation sedimentary period is transformed from warm and humid climate to cold and dry climate. Geochemical indicators comprehensively reflect that the Neogene mudstone deposition period is mainly in the reducing environment, and the paleosalinity of the water body is generally in a freshwater and brackish water environment. Finding out the provenance and paleo-sedimentary environment features has practical guiding significance for the calculation of resource quantity, the division of geothermal resources sweet spot area and the determination of key strata for development and utilization in Guanzhong Basin.

How to cite: Lan, H.: Geochemical characteristics of Neogene mudstone in Guanzhong Basin,recovery of provenance and paleo-sedimentary environment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4276, https://doi.org/10.5194/egusphere-egu24-4276, 2024.

In recent decades, many scientific studies have been conducted to constrain present and past source-to-sink processes and their controlling factors. The role of typhoon and monsoon summer rainfall on chemical weathering and soils erosion in east Asia is still not well established. Clay minerals and major elements, combined with Nd and Sr isotopic compositions were analyzed on sediments from Core MD18-3569 located close to the Penghu Canyon on the Taiwan margin (northeastern South China Sea) in order to establish climatic and environmental controls on source-to-sink processes and weathering history of small river basins of southwest Taiwan since the last glacial period. The ⁸⁷Sr/⁸⁶Sr ratios and ɛNd values of the detrital and clay fractions combined with the high content of illite and chlorite suggest that the mountainous rivers of southwest Taiwan are the main sources of sediments to the Taiwan margin since the last deglaciation. Such results permit to evaluate past intensity of chemical weathering in the rivers of southwest Taiwan from major elements composition and clay mineral assemblages. The long-term changes of chemical weathering intensity in Taiwan are driven by the variations of east Asian summer monsoon rainfall. During the deglaciation, the progressive strengthening of rainfall enhanced the chemical weathering intensity which peaked in the early Holocene. The Holocene is characterized by a decrease of the chemical weathering degree of sediments derived from Taiwan. This coincides with the weakening of summer monsoon rainfall, an increase in typhoon activity, and changes in vegetation cover in southwest Taiwan. These processes caused soil destabilization and erosion, regressive pedogenesis, and weaker chemical weathering intensity. This was due to the shorter residence time of sediments in the soils of southwest Taiwan. Our multi-proxy study highlights the strong link between summer monsoon and typhoon rainfalls, environmental changes, and chemical weathering history in Taiwan.

How to cite: Colin, C., Bertaz, J., Liu, Z., Dapoigny, A., Tien-Shun Lin, A., Li, Y., and Jian, Z.: Climatic and environmental impacts on source-to-sink processes in SW Taiwan since the last deglaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20349, https://doi.org/10.5194/egusphere-egu24-20349, 2024.

Marine black shale in the Lower Cambrian Qiongzhusi (QZS) Formation in the southwestern Yangtze Plate, SW China, is the primary focus for shale gas development. The formation of organic-rich shale is significantly influenced by the paleoenvironment. Through the analysis of major, trace and rare earth elements (REE), the authors examined the element composition, paleoweathering and provenance of Qiongzhusi black shale (QZS shale). The results revealed that the main components of the Qiongzhusi Formation sample are SiO₂, Al₂O₃ and total Fe₂O₃ (TFe₂O₃), with the average values of 64.08 wt%, 15.00 wt% and 5.39 wt%, respectively. Redox-sensitive elements, such as V, Cr, Ni, Zn and U, are richer in QZS shale contrasted with the upper continental crust (UCC). The total concentration of REE (∑REE) of QZS shale is 174.58 ppm on average, which is higher than that of UCC (average 146.37 ppm) and the North American Shale Composite (NASC) (average 173.21 ppm). The ratios of w(SiO₂)/w(Al₂O₃) and w(Al₂O₃)/w(TiO₂), the Zr-TiO₂ diagram, the Th/Sc vs Zr/Sc plot, the discriminant function of F1 vs F2 and F3 vs F4, as well as the discrimination diagram of ∑REE vs La/Yb indicated that the main provenances of QZS shale are sedimentary and felsic igneous rocks. The values of a chemical weathering index, the chemical index of alteration (CIA), of the Lower QZS Formation (Stage 1) range from 51.84 to 64.33, indicating a low degree of chemical weathering and a cold and dry climate. The CIA values of the Upper QZS Formation (Stage 2) range from 66.58 to 82.42, suggesting a medium degree of chemical weathering, lilely in a humid climate.

How to cite: Fang, Z. and Guo, L.: Geochemistry of marine black shale of Cambrian Qiongzhusi formation, Yangtze plate, southwestern China: implications for provenance and paleoweathering, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1923, https://doi.org/10.5194/egusphere-egu24-1923, 2024.

The (Basal) Choteč Event, first recognised in the 1980s in Czechia, is a globally widespread anoxic pulse associated with transgression and eutrophication just above the Emsian-Eifelian (Early-Middle Devonian) boundary (cycle 1c of the Johnson et al. [1985] Devonian eustatic sea-level curve). Despite being one of several anoxia-driven faunal turnovers during the Devonian, the Choteč Event remains poorly understood. The global reach, intensity, and duration of anoxia is not constrained and nor is it clear whether eutrophication had its “roots” in contemporary floral developments on land (as suggested for younger Devonian anoxic events).

We present a geochemical (carbon isotopes; trace metals as proxies for redox and productivity; and major elements for the Chemical Index of Alteration [CIA] as a weathering proxy) and palynological study of the Cabonera section (León, Spain). This succession is part of an extensive Devonian sequence developed around isolated islands in the Armorican Terrane Assemblage that was located between the supercontinents Laurussia and Gondwana. Here, limestones of the Emsian-Eifelian Santa Lucia Formation are abruptly overlain by siltstones and shales belonging to the Eifelian Huergas Formation. This conodont- and brachiopod-constrained manifestation of the Choteč Event sees the onset of a gradual 4‰ negative δ¹³C_carb excursion (CIE) consistent with records in other regions. The lower part of the Huergas Formation (Cabornera Bed) records a brief interval of anoxia (low Th/U, elevated V/Al and U/Al) at the same level that sees the onset of the negative CIE. This appears to have been accompanied by, or was perhaps driven by, greatly enhanced primary productivity, with enrichment factors (EFs) of Ba, and particularly Ni, Zn and P, all >>1. This brief burst of productivity and anoxia soon ended, with EFs falling <<1 through the remainder of the Huergas Formation (which are also well below the values recorded in the Santa Lucia Formation). The CIA values are high throughout the succession, suggesting the prevalence of strong weathering under a warm, humid climate during the Eifelian. The highest CIA values are seen immediately above the level of high productivity and oxygen restriction, suggesting that weathering enhanced further still at that time. A less commonly employed weathering proxy, Rb/Sr, also suggests the onset of enhanced weathering in the Choteč Event beds, where the ratio increases by two orders of magnitude although we cannot rule out the role of facies changes in this.

Acritarch, chitinozoan and spore assemblages are somewhat impoverished and have a moderate-high degree of endemism, which is unsurprising considering their isolated location. More broadly, the Eifelian saw significant diversification in several plant groups. It is possible that these changes on land drove the Choteč Event through enhanced pedogenesis and runoff, but there is a mismatch between the temporal scale of land plant evolution and the brevity of the eutrophic anoxic pulse recorded at Cabornera. Instead, we suggest that the Choteč Event in the Armorican Terrane saw a brief phase of extreme productivity – driven by rapidly enhanced weathering of unknown origins – that resulted in anoxia and the shutdown of the carbonate factory.

How to cite: Bond, D., Blanco-Ferrera, S., Grasby, S., Greene, S., Hilton, J., Lopes, G., Lu, J., Marshall, J., Sanz-López, J., Wellman, C., and Yin, L.: The early Middle Devonian Choteč Event in northern Spain: a brief anoxic pulse driven by enhanced weathering and eutrophication, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21645, https://doi.org/10.5194/egusphere-egu24-21645, 2024.

Carbon cycle-climate dynamics were nonlinear through Earth’s history, driven by changes in internal and external forcing processes acting on various geological timescales. This study focuses on determining the relationship between volcanism, orbital parameters, and organic carbon burial during the Aalenian (Middle Jurassic) - a pivotal time at the dawn of the Mesozoic Marine Revolution, marked by a disruption of the carbon cycle and major climate shifts. Here, new high-resolution magnetic susceptibility and trace elements data are combined with previously published organic carbon isotopes and total organic carbon data from two sites in France and Chile. Our dataset shows for the first time a temporal coincidence between the major carbon cycle perturbation during the middle–late Aalenian and the onset of enhanced volcanic activity, suggesting a causality link. We propose that volcanic activity triggered a transient warming episode within the long-term Middle Jurassic coldhouse and played a key role in shifting organic carbon burial from the ocean to terrestrial settings. This period therefore contrasts with other Mesozoic carbon cycle perturbations, which generally record enhanced marine organic matter burial in oxygen-depleted environments during volcanism-triggered warming events.

How to cite: Fantasia, A., Thibault, N., Adatte, T., Mattioli, E., Spangenberg, J. E., Regelous, M., and Bodin, S.: Change of the locus of organic carbon burial in the aftermath of the Toarcian hyperthermal event: Patterns and drivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7408, https://doi.org/10.5194/egusphere-egu24-7408, 2024.

Mesozoic Oceanic Anoxic Events (OAEs) were linked to the accumulation of organic-rich sediments in response to global climatic and environmental changes, resulting in transient episodes of oceanic deoxygenation. To better understand the evolution of seawater oxygenation in the Boreal Realm during the Early Cretaceous (late Hauterivian – early Aptian), this study presents high-resolution datasets of Rare Earth Element plus Yttrium (REE + Y; REY) patterns and redox-sensitive trace elemental (RSTE) concentrations in the Danish Central Graben (DCG). Oxygenation in the seawater column can be derived from the Cerium (Ce) anomaly (Ce/Ce*), which is based on the premise that Ce acts differently in well-oxygenated environments compared to the other REYs. At the seafloor, anoxia is indicated by the enrichment of RSTEs Vanadium (V) and Uranium (U). A decline in Ce anomaly values and low RSTE concentrations from the late Hauterivian to late Barremian indicates a shift from an oxygen-depleted to a more oxygenated seawater column and seafloor conditions in the Boreal Realm. A similar trend is observed in the Tethyan Realm, suggesting the existence of a global long-term driver of seawater oxygenation level. In the DCG, this long-term trend is interrupted by a brief drop in relative sea level, leading to partial isolation of the basin, reduced ventilation, stratification of the water column and consequently short-term anoxic conditions at the sediment–water interface. This resulted in the deposition and preservation of an organic-rich layer (Munk Marl Bed) during the early Barremian. During the early Aptian, an organic-rich layer (Fischschiefer Member) of regional extent, linked to the global OAE-1a, was deposited. Significantly elevated Ce anomaly values along with increased concentrations of U and V signify anoxic conditions within this Boreal basin, whereas the seawater column in the Tethyan Realm exhibited dysoxic conditions. Variations in anoxia and the fact that some OAEs are only observed locally, leads to the conclusion that short-term regional or local factors can overprint global changes.

How to cite: Blok, C. N., Andreasen, R., Sheldon, E., Jelby, M. E., Ineson, J., Anderskouv, K., and Bodin, S.: Taking your breath away with Early Cretaceous Boreal seawater oxygenation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17805, https://doi.org/10.5194/egusphere-egu24-17805, 2024.

The late Early Cretaceous interval (121.4 to 100.5 Ma) was characterized by a gradual warming trend superimposed on an already warm greenhouse climate. Whereas the evolution of ocean temperatures during this time interval is relatively well constrained, information on the response of continental interiors to such climatic extremes is limited. Here we report new data from two continental sections (Shivee Ovoo (SVO) and Tevshin Gobi (TSG); Choir-Nyalga Basin) from central Mongolia, which contain thick, lignite-rich successions (Khukhteeg Fm.) bearing an exceptionally well-preserved fossil flora of various pine and redwood species as well as representatives of extinct seed plant lineages. In order to reconstruct the palaeoenvironmental conditions, a combined approach including brGDGT-based palaeothermometry, coal petrology and palynology is applied, complemented by geochemical measurements (TOC, TS, δ¹³C_org). The investigated lignites show significant differences in maceral compositions with the TSG samples being rich in mineral detritus and mainly composed of huminite. In contrast, samples from SVO show higher fusinite and liptinite content with generally low mineral detrital contribution. The paleotemperature estimates represent the oldest brGDGT analyses obtained from continental strata so far. The new data indicate that the climatic conditions in mid-latitudes of paleo-Asia during the late Early Cretaceous were characterised by mean annual air temperatures of about 12 ± 5°C. Our brGDGT data show lower continental temperatures for mid-latitude paleo-Asia than previously suggested based on modelling. 

How to cite: Stoepke, F.-L., Littke, R., Burnaz, L., Zieger, L., Hasegawa, H., Ichinnorov, N., and Heimhofer, U.: Early Cretaceous lignites as archive for continental climates of paleo-Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7567, https://doi.org/10.5194/egusphere-egu24-7567, 2024.

The Cretaceous-Paleogene (K-Pg) mass extinction was a pivotal event in Earth's history and is attributed to the interplay of two major events—the Deccan Traps volcanism and the Chicxulub asteroid impact. We contribute to refine of our understanding of the volcanic stressor for this extinction by investigating the sulfur and fluorine budgets of Deccan lavas from the Western Ghats (India), spanning the K-Pg boundary [1].

Sulfur and fluorine concentrations were analyzed in clinopyroxene phenocrysts from Deccan Traps lavas, by Synchrotron-light X-ray fluorescence (beamline I18, Diamond Light Source, U.K.), and ion probe (CAMECA IMS 1280 at Nordsim Laboratory, Swedish Museum of Natural History, Stockholm, SE), respectively. The results were divided by experimentally determined partition coefficients to calculate melt concentrations.

Our analyses reveal variable magmatic volcanic fluorine concentrations ranging from 400 to 3000 parts per million, suggesting the potential for regional environmental impact. The highest sulfur concentrations, reaching up to 1800 parts per million, are observed in Deccan lavas emplaced just prior to the extinction interval, within a timeframe of 0.1 million years. In contrast, later basalts generally exhibit lower sulfur concentrations, only up to 750 parts per million.

Independent evidence [2] supports that eruption of the Deccan flood basalts occurred in multiple voluminous eruptive pulses each lasting on the order of centuries, as typical of continental flood basalts. Our findings propose that the volcanic sulfur degassing associated with such activity may have led to repeated, short-lived global temperature drops, too short to be recorded by global paleotemperature record, albeit coupled with a global cooling trend. Sulfur-induced cold snaps likely imposed stress on ecosystems long before the decisive impact of the Chicxulub bolide at the end of the Cretaceous.

[1] Sara Callegaro, et al., (2023) Recurring volcanic winters during the latest Cretaceous: Sulfur and fluorine budgets of Deccan Traps lavas. Sci. Adv. 9, eadg8284 doi:10.1126/sciadv.adg8284.

[2] I. M. Fendley, et al., 2019. Constraints on the volume and rate of Deccan Traps flood basalt eruptions using a combination of high-resolution terrestrial mercury records and geochemical box models. Earth Planet Sci Lett. (524) 115721. 

How to cite: Callegaro, S., Baker, D. R., Renne, P. R., Melluso, L., Geraki, K., Whitehouse, M. J., De Min, A., and Marzoli, A.: Sulfur and fluorine degassing from Deccan Traps lavas inferred from pyroxene chemistry: potential for end-Cretaceous volcanic winters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21751, https://doi.org/10.5194/egusphere-egu24-21751, 2024.

Alongside the mass extinction, the Cretaceous–Paleogene (K–Pg) boundary interval experienced major climate perturbations due to the Chicxulub meteorite impact and Deccan Trap volcanism. The volcanism and release of climate modifying gases likely had a drastic effect on global climate, though hypotheses of this change remain largely untested.

Recent work applied the lipid biomarker palaeotemperature proxy MBT'5me to two highly chronologically constrained lignites from the Western Interior, USA (palaeolatitudes 45–51°N). This reconstruction showed that mean annual air temperatures increased by 3°C during the last ~100 ka of the Cretaceous, likely driven by Deccan volcanism and long-term release of organic carbon into the atmosphere. A transient cooling event of up to 5°C is superimposed on to the longer-term warming trend, beginning ~35 ka before the K–Pg boundary. This cooling coincided with the second (Poladpur) eruptive phase of Deccan volcanism, which correlates with the modelled climatic cooling predicted by the release of associated aerosolised SO₂ emissions.

To gain a more holistic understanding of the end-Cretaceous climate system, here we use the hydrogen-isotope composition of plant-wax from the same lignites to reconstruct palaeohydrology. Determining the link between volcanism-induced temperature change and hydrology prior to the Chicxulub impact will provide a framework for understanding post-impact hydrological changes.

This work presents the first opportunity to evaluate palaeohydrology at a millennial scale in the Cretaceous, alongside temperature and carbon-cycling. Further, the excellent chronological constraints allow a unique insight into the relative timing of different climatic processes and major climate perturbations in the lead-up to and across the K–Pg boundary.

How to cite: O'Connor, L., Jerrett, R., Sluijs, A., Price, G., van Dongen, B., Lengger, S., and Peterse, F.: A plant-wax δD record of palaeohydrology over the Cretaceous–Paleogene boundary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21347, https://doi.org/10.5194/egusphere-egu24-21347, 2024.

The Eastern Mediterranean sapropels were deposited during periods of increased monsoonal runoff, enhanced export productivity, salinity stratification and deep-sea anoxia since the Miocene. The most pronounced sapropels, with total organic carbon (TOC) contents up to 30%, formed during the late Pliocene (3.16-2.94 Ma). It remains enigmatic which environmental conditions caused the deposition of these high-TOC sapropels.

Here, we aim to record spatiotemporal changes in sea surface salinity (SSS) and sea surface temperature (SST) associated with sapropel formation. We use compound-specific hydrogen isotope analysis of C_37:2 alkenones (δ²H_alkenone) as a proxy for SSS. This proxy is, in contrast to δ¹⁸O_foram, independent of temperature and can be applied to organic-rich samples that lack foraminifera. In addition, we use alkenone-based Uk'37 to estimate SSTs. We compare the δ²H_alkenone signatures across the strongest late Pliocene sapropels from ODP sites 967 and 969 to that of a slightly younger, lower-TOC sapropel.

The δ²H_alkenone value in marls is comparable to modern-day Mediterranean δ²H_alkenone values and across the strongest sapropels, the δ²H_alkenone shift of 15-35‰ is comparable to that recorded in sapropel S5. This suggests that freshwater forcing was not exceptionally strong during the deposition of the late Pliocene sapropels. However, in the marls prior to the high-TOC sapropel at 2.95 Ma, δ²H_alkenone is ~20‰ more depleted and reconstructed SSTs are higher.

We discuss the salinity forcing on sapropel development and investigate if and how initial warmer and fresher surface waters could have affected the formation of this particularly high-TOC sapropel.

How to cite: van der Hoeven, I., Hättig, K., Mol, E., van der Meer, M., Hennekam, R., and Reichart, G.-J.: Alkenone-based sea surface salinity and temperature reconstructions across late Pliocene sapropels from the Eastern Mediterranean Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9118, https://doi.org/10.5194/egusphere-egu24-9118, 2024.

The Southern Ocean is characterized by various ocean fronts that separate surface waters with different hydrographic properties. Ocean fronts’ position changed over glacial-interglacial cycles, which, consequently, affected surface water properties and productivity through time at any given location. The present study reconstructs changes in biogenic carbonate and opal burial at Del Caño Rise (DCR), Indian Ocean sector of the Southern Ocean, over the last three climate cycles. Based on Accelerator Mass Spectrometry radiocarbon dating of planktonic foraminifera as well as comparison of oxygen isotopes of planktonic foraminifera with LR04 stack, the studied core MD19-3575CQ, located today in the Subantarctic Zone, covers the last ~250,000 years. Biogenic carbonate content shows consistent low values during all glacial periods (average 32.4%) and high values during all interglacial periods (average 61.5%). In contrast, biogenic opal content increased during all glacial periods (average 12.8%), compared to interglacial periods (average 8.5%). TOC exhibited a similar pattern to the biogenic opal content, with higher values during glacial periods (average 0.38%) and lower values during interglacial periods (average 0.17%). The increased biogenic opal content during glacial periods is attributed to enhanced silica supply to surface waters due to northward migration of the Subantarctic Front, possibly shifting north of DCR during these periods. However, the relatively low biogenic opal content in the study area compared to other regions of the Polar Frontal Zone (average 55.6%) suggests insufficient silica supply to support high diatom production. The reduction in biogenic carbonate content during glacial periods is related to the decrease in coccolithophore productivity due to low ocean temperatures (~2ºC) and the competition for nutrients and light with diatoms. Despite the shallow water depth (~2400 m) at the core location, the weakened Atlantic Meridional Overturning Circulation and thickening of the corrosive Southern Ocean bottom waters during glacial times may have increased carbonate dissolution. Our study emphasizes that changes in surface water properties by ocean front’s migration impact on regional productivity, which may influence global biogeochemical  cycles.

How to cite: Choi, H., Civel-Mazens, M., Crosta, X., Billy, I., Irino, T., Takata, H., Ha, S., and Khim, B.: Orbital-scale competition of biogenic carbonate and opal production at the Del Caño Rise in the Indian sector of the Southern Ocean during the late Pleistocene , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7572, https://doi.org/10.5194/egusphere-egu24-7572, 2024.

Abstract

The lower Cambrian shale, a significant source rock, has been witness to substantial tectonic and environmental shifts on Earth. However, the correlation between early Cambrian tectonic history and organic matter enrichment (OME) remains elusive. The Sichuan Basin in the northwestern Yangtze Block hosts the largest Precambrian-Cambrian gas field in China. The primary source rocks contributing to this reservoir are mainly the lower Cambrian shales. The organic matter enrichment of the lower Cambrian shale is commonly ascribed to paleoproductivity, redox conditions, localized hydrothermal activity, upwelling currents, and terrigenous inputs. However, organic matter enrichment varies across the Yangtze Block due to different influencing factors. Particularly, little information has been employed to elucidate the tectonic impact on OME in the lower Cambrian shales within the Sichuan Basin. This study presents detrital zircon U-Pb ages and geochemical data obtained from late lower Cambrian shales in the Sichuan Basin, SW China. The black shales exhibited similar chondrite-normalized REE patterns. They display a slightly right-dipping trend in LREE, a gentle slope in HREE, and a significant Eu anomaly in some samples. Additionally, trace elements generally exhibited a slightly right-leaning pattern, with distinct depletions observed in Nb, Ta, Sr, and Ti. These suggest a complex provenance and origin of the Cambrian shales. The maximum deposition ages of YB-10, NHX-22, and O1H-4 samples were 541Ma, 580Ma, and 523Ma, respectively. These samples were analyzed in cumulative scale maps (crystallization and deposition ages), and it was found that the samples all fell into the collision environment. The detrital zircon U-Pb ages signify a novel magmatic activity in a continental arc setting from the Ediacaran to the early Cambrian, acting as a major sedimentary provenance. It suggests that a weakening retreating subduction-related weak extensional basin rather than a passive marginal or foreland basin of the early Cambrian Sichuan Basin, which had led to diminished extensional and broad trough-platform shales. The compiled geochemical data indicate that OME during the early Cambrian was strongly linked to high primary productivity, redox conditions, and detrital input. However, the influence of these factors on organic matter enrichment varied spatiotemporally, likely due to the unstable and variable tectonic-sedimentary environment associated with the retreating subduction event. This case study illuminates the effects of retreating subduction on the differential organic matter enrichment in the platform shales.

Keywords: Cambrian; shale; retreating subduction; organic matter enrichment; tectonic effect; Sichuan Basin

How to cite: Tang, J., Wang, J., and Wu, G.: Tectonic setting and its effect on organic matter enrichment of the lower Cambrian shales in the Sichuan Basin (SW China), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9566, https://doi.org/10.5194/egusphere-egu24-9566, 2024.