Gypsum has been shown to serve both as a protective shield against intense solar irradiation and as a microhabitat for microbial life, particularly under extreme environmental conditions. This study presents the first report of endolithic photosynthetic microbial communities and their associated protective pigments in gypsum deposits from Los Santos (Santander, 400–800 m a.s.l.), Sáchica (Boyacá, 2200 m a.s.l.), and Chaparral (Tolima, 400–700 m a.s.l.). We investigated phototrophic biodiversity within gypsum with a focus on the photoprotective adaptation mechanisms mediated by carotenoid pigments, employing a multi-analytical approach. Raman and FT-MIR spectroscopy revealed distinct spectral signatures corresponding to β-carotene, lycopene, astaxanthin as well as potential signals of canthaxanthin, and lutein in red, yellow, black, and green pigmented zones. These results were complemented by microbiological culturing and scanning electron microscopy (SEM), which confirmed the presence of Cladophora sp., Coccomyxa sp., and Chlorella sp. (green algae), as well as Phormidium sp. (cyanobacteria), arranged as long filaments or isolated cells embedded within the gypsum matrix. These findings expand our understanding of microbial biodiversity in equatorial evaporitic environments and highlight the role of gypsum as an optical refuge that filters harmful UV radiation while transmitting photosynthetically active wavelengths. Furthermore, this study provides valuable astrobiological insights and proposes a complementary methodological framework for future missions targeting Martian gypsum deposits, which may represent protective niches for potential microbial life or preserved biosignatures from past or present life.
The Niemcza Shear Zone (NSZ) is a major structural feature in the Sudetic segment of the Variscan Belt, yet its tectonic significance remains debated, particularly with regard to its role as an intra-orogenic terrane boundary, a reworked segment of a subduction-accretion system, or the exposed core of an oceanic suture. This study provides new constraints on the metamorphic evolution of the central NSZ based on an integrated investigation of two lithologies: the strongly sheared Strach mylonite and unsheared Buk graphitic quartzite. We combine multiple geothermobarometric approaches (muscovite, garnet–biotite and Zr-in-rutile), Raman spectroscopy of carbonaceous material, and detailed major- and trace-element zoning of tourmaline. Both lithologies record comparable medium-pressure–high-temperature metamorphism within the greenschist- to amphibolite-facies range. Peak conditions of approximately 6–10 kbar and 630–710 °C were attained within the sillimanite stability field. Neither lithology preserves mineral assemblages or pressure–temperature paths indicative of subduction-related metamorphism, such as high- or very high-pressure assemblages, or rapid decompression trajectories. Tourmaline zoning documents two stages of prograde growth under largely internally buffered conditions. Muscovite breakdown reactions near peak metamorphism, accompanied by an increase in fluid pH, likely triggered partial tourmaline resorption. Subsequent retrograde overgrowths record variable degrees of system isolation controlled by deformation: shear-enhanced fluid flow promoted open-system behavior in the mylonite, whereas the quartzite retained predominantly closed-system characteristics. The absence of preserved HP metamorphic signatures in the investigated central NSZ rocks, contrasting with high-pressure metamorphism in adjacent tectonic units, indicates pronounced tectonothermal partitioning during Variscan convergence. These observations do not support interpretation of the exposed central NSZ as the primary metamorphic core of an oceanic suture. Instead, they are consistent with the NSZ representing a long-lived, lithospheric-scale and composite terrane boundary that may include strongly reworked components of a broader subduction-accretion system, subsequently overprinted by deformation, magmatism and metamorphic re-equilibration during Variscan terrane assembly.
Reconstructing the birth of the Bangong–Nujiang Tethyan Ocean remains controversial relative to Gondwana breakup and Cimmerian drift in the eastern Tethys. Specifically, the geochronological framework of the transition from continental rifting to oceanic spreading of the Bangong–Nujiang Tethyan Ocean lacks robust constraints. Here, we present new data from newly identified Early Permian meta-mafic rock blocks (Dequ meta-gabbros and Kangsha metabasites) within the Kaqiong terrane, eastern Bangong–Nujiang suture zone. Zircon U–Pb dating of the Dequ meta-gabbros yields consistent Early Permian crystallization ages of 273 ± 1 Ma and 274 ± 1 Ma. Geochemically, these meta-mafic rocks are tholeiitic, display light rare earth element depletion, and lack significant Nb–Ta anomalies, which are signatures characteristic of normal mid-ocean ridge basalts. Their whole-rock Nd–Hf and zircon Hf–O isotopic compositions collectively indicate a depleted mantle source. Integrating our new data with Late Paleozoic magmatic records from central Tibet, we interpret the late Early Permian meta-mafic rocks were formed in an intercontinental rift environment on the northern margin of Gondwana, marking the incipient detachment of the Southern Qiangtang terrane from Gondwana. This integrated interpretation, supported by multidisciplinary data, allows us to construct a refined temporal sequence for the ocean’s birth: from intracontinental rifting (300–279 Ma), via intercontinental rifting during the rift-to-drift transition ( 278–273 Ma), to the mature oceanic spreading after 273 Ma. Our study thereby provides critical constraints on the birth of the Bangong–Nujiang Tethyan Ocean and the coeval paleogeographic reorganization of the northern Gondwana margin.
The factors controlling element mobility during hydrothermal alteration at the surface of active fumarolic geothermal fields remain poorly understood, especially in andesite-hosted geothermal fields where few studies have been conducted. To address this, this study investigated the geochemical characteristics of hydrothermal alteration at the Unzen-Jigoku Geothermal Area (UJGA), an andesite-hosted active fumarolic field in the Unzen Volcano, Southwest Japan, using whole-rock compositions and mass-balance calculations. The whole-rock composition data reveal two types of alteration. Residual silicification forms under highly acidic conditions and involves extensive leaching of elements, leaving a Si-rich residue. In contrast, advanced argillic alteration is marked by alunite and kaolinite precipitation, leading to enrichment of Al, K, and light rare earth elements. Consideration of water–rock interaction (stability calculation using chemical composition of hot spring water) indicates that pH approximately 2.3 represents the threshold separating residual silicification and advanced argillic alteration. These results indicate that element mobility in the UJGA is primarily governed by fluid pH associated with the stability of secondary minerals. Comparison with rhyolite- and basalt-hosted surface fumarolic systems reveals that Al behavior follows a broadly consistent pH-controlled pattern: Al is leached at pH below approximately 2 and retained at pH above approximately 2, regardless of host rock type. However, the Al-bearing mineral assemblage differs between systems; alunite and kaolinite both precipitate in rhyolite- and andesite-hosted systems, whereas kaolinite forms predominantly without alunite in basalt-hosted systems.
Understanding long-term landscape evolution in regions experiencing low rates of surface uplift can be challenging, as geomorphic markers are generally difficult to preserve for long timescales. But on a regional scale, a geomorphic unit like a drainage divide with high geomorphic inertia can help us assess the interaction between tectonic, climatic and geomorphic processes. A stable drainage divide would mean that these processes are in equilibrium, whereas its migration would suggest imbalance. In this study, we investigate the drainage divide between two major river catchments (Ganga and Narmada) across the Central Indian Forebulge (CIF), a region characterized by low rates of surface uplift, developed due to the collision of the Indian and Eurasian plates. In order to assess the stability and regions of drainage divide migration, we performed first-order flexural modeling to constrain the geometry of the CIF and define a Forebulge Axis Zone (FAZ), and analyzed topographic metrics, such as chi (χ), Gilbert metrics, and the normalized channel steepness index (ksn) on both sides of the drainage divide. The results of the χ and ksn analyses indicate that the drainage divide between the north-flowing Ganga and the south-flowing Narmada River tributaries is not entirely in equilibrium; the western and central segments show a shift toward the north, whereas the eastern segment is stable. This finding was further corroborated by the geomorphic and field evidence. However, Gilbert metrics suggests that the drainage divide is currently in equilibrium, highlighting the different time frames captured by these analyses. This study shows that the spatial relationship between the FAZ and the drainage divide, together with progressive forebulge uplift and pre-existing topography, controls drainage divide migration across the CIF. This demonstrates that, although the drainage divide is presently stable, geomorphic evidence records past migration and indicates continued northward migration of the western and central sectors under ongoing forebulge evolution.
The tuffaceous mudstones of the Lower Permian Zhanjin Formation in the central part of the Qiangtang Basin (Tibet) were deposited during a phase of continental margin rifting and large-scale volcanism, resulting in anomalously high bulk Fe concentrations (averaging 8.13
Chaotic units of Palaeozoic metasedimentary rocks in the Harz Mountains have been attributed to Early Carboniferous submarine mass-flow processes or to Variscan block-in-matrix deformation. This paper aims to explain block-in-matrix deformation in terms of the remobilisation of overpressured, undercompacted muds early during Variscan deformation. Burial of the Devonian and Carboniferous sediments trapped fluids within the clay-rich muds, causing overpressure and hindering mechanical compaction. The resulting centroid effect generated extremely high fluid pressures and mobilised the muds, leading to mud injectites and brecciation of lithified carbonates and greywackes. Remobilisation may have been influenced by clay mineralogy, particularly high smectite content. Fracturing enabled the fluids to escape, reduced pore pressure and allowed the muds to compact and lithify, before Variscan contraction and metamorphism occurred. The paper describes possible analogues that are not overprinted by later deformation, including mud breccias.
The Zawar Zn-Pb deposit, located within the Proterozoic Aravalli-Delhi Fold Belt, comprises a polymetallic sulfide ore assemblage, of which sphalerite is a major component. The deposit is hosted within a siliciclastic–carbonate turbidite succession of the Aravalli Supergroup, emplaced in a rift-related basin along the Aravalli continental margin. Mineralization is predominantly hosted within siliceous dolomite as stratabound, irregular, tabular, and steeply dipping lenses of varying thickness and lateral extent, with minor occurrences of carbonaceous phyllite-hosted banded ore. Integrating field observations with petrographic, electron microprobe, and Raman microspectrometric investigations enables classification of the ores into vein, massive, fracture-controlled, disseminated, breccia-filling, banded, and foliation-controlled types. The results indicate significant post-depositional modification through deformation, metamorphism, remobilization, and replacement. Additionally, low sphalerite–galena–sphalerite interfacial angles ranging from 23° to 110° suggest possible melt-assisted remobilization. Chemical characterization of sphalerite reveals systematic variation in Fe and Cd concentration across ore types, which corresponds to the sphalerite color, and is linked to the evolving sulfur fugacity and fluid chemistry, as well as metamorphic redistribution. These compositional variations are also recorded from Raman spectra, which are in close agreement with the electron microprobe data. Sphalerite geobarometric estimates based on a buffered pyrite–pyrrhotite–sphalerite assemblage yield pressures of 5.9–8.8 kbar, which, coupled with previously published fluid inclusion temperatures, are consistent with upper greenschist-facies conditions and show a progressive decrease in confining pressure through paragenesis. Comparison with other sediment-hosted deposits indicates that, although Zawar exhibits features characteristic of SEDEX, MVT, and Irish-type deposits, it is more akin to the MVT-style mineralization.
The Permian-Lower Triassic Choiyoi Magmatic Province comprises intermediate to silicic igneous rocks that cover nearly 900,000 km2 in central-western Argentina and central Chile. Their geodynamic origin remains debated, with long-lived subduction and slab break-off representing the principal competing models. Here we present zircon U–Pb geochronology, whole-rock geochemistry, Sr–Nd isotopic data, and mineral chemistry for the Huingancó Granitoids (Northern Neuquén Precordillera, Argentina; 37°S) and the Cajón Troncoso Granodiorites (Cordillera Principal, Chile; 36°S), a key transitional region between the Andean and North Patagonian sectors of the province. New U–Pb ages redefine the timing and duration of Permian magmatism in the study area. The Cajón Troncoso Granodiorites, previously assigned to the Miocene, yields a Middle Permian age ( 273 Ma), whereas the Huingancó Granitoids record a prolonged magmatic history from the Early Permian ( 286–281 Ma) to the Late Permian ( 258 Ma). Both units display predominantly high-K calc-alkaline, subalkaline, I-type signatures, with subordinate S-type affinities reflecting moderate crustal contributions. Mineral chemistry and thermobarometric estimates indicate crystallization from hydrous, oxidised magmas at shallow crustal levels ( 5–9 km) and temperatures of 700–900 °C. Initial isotopic compositions (⁸⁷Sr/⁸⁶Srᵢ = 0.70631; εNdᵢ = -2.31) suggest mantle-derived magmas variably modified by crustal assimilation. Integration of these data with regional plutonic records indicates an evolution from syn-orogenic arc magmatism during the San Rafael Orogenic Phase to post-orogenic magmatism related to slab rollback and lithospheric thinning. The overall geochemical evidence supports sustained subduction throughout the Permian along the southwestern Gondwana margin.
The Münchberg Massif, located in northern Bavaria, is a series of nappes. The lowermost nappe, referred to as the Prasinit-Phyllit-Serie, contains numerous serpentinite bodies. Previous studies of these serpentinites have been focused primarily on their mineralogy and crystallography, while comprehensive whole-rock geochemical data have remained limited. However, detailed mineral analysis and whole-rock major and trace element analyses provide insights into the formation history of serpentinites with respect to protolithic mantle material and temperature conditions during serpentinization. In this study, we present new petrological and chemical data for serpentinites from two localities in the Münchberg Massif, namely Peterleinstein in the west and Zell in the southeast of the massif, whose locations are approximately 20 km apart. The serpentinites from the two localities display distinct geochemical signatures. The major and rare earth element compositions indicate that the Peterleinstein serpentinites are derived from a depleted harzburgitic protolith. In contrast, the serpentinites from Zell exhibit a less depleted harzburgitic to dunitic protolith composition. Additionally, the major and trace element compositions indicate that the protoliths of both locations are derived from a related but not unequivocally identical geological environment within the Rheic Ocean framework. Petrographic analysis of the rocks reveals that those at Peterleinstein are almost entirely serpentinized, which differs from the relatively high proportion of unserpentinized minerals, such as olivine or pyroxene, present at Zell. While several serpentine minerals occur at both localities, their relative proportions significantly vary. X-ray diffraction analysis reveals the presence of different dominant serpentine minerals, namely antigorite at Zell and lizardite at Peterleinstein. Microscopic observations combined with confocal Raman analysis corroborate at least two stages of serpentinization and concomitant metasomatism. The presence of abundant unserpentinized minerals at Zell suggests that this location had lower fluid availability than the western part of the massif. These findings suggest that the serpentinites of Peterleinstein and Zell were close to or within a subduction zone. However, the differences in petrology and geochemistry reflect formation at different positions within a subduction setting. The presence of serpentinite with varying compositions in different locations has been documented within the sutures of the Variscan Orogen by previous studies. In contrast, serpentinites that formed distant from a suture tend to exhibit homogeneous petrology and geochemistry.
This study investigates Zirconium (Zr) content variations and their genetic implications in Early Cretaceous A-type granites from the Gan-Hang Belt, southeastern China, and aims to elucidate how Zr traces continental crustal evolution. Through systematic analyses of geochronological, geochemical, and isotopic data, these rocks can be classified into low-Zr and high-Zr magma systems; the high-Zr magma system includs the Caiyuan monzoporphyry, Honggong quartz syenite, and Dazhou rhyolite. High-Zr magma system shows coherent major-element trends: TiO2, Al2O3, FeOT, MgO + Fe2O3, CaO, and P2O5 decrease as increasing SiO2. Trace elements reveal declining Ba, Sr, Eu/Eu*, La/Yb, and Sr/Y with rising Rb/Sr. The samples are characterized by LREE enrichment, HREE depletion, and negative Eu anomalies, along with enrichments in Rb, Th, U, Nb, Ta, Zr, but Hf and depletions in Ba, Sr, Eu, and Ti. Isotopically, Isotopic data (εNd(t) = −8.3 to −5.5 and zircon εHf(t) = −15.1 to +7.2) and two-stage Nd-Hf model ages overlap with regional A-type granites, which suggests a common source involving ancient crust mixed with mantle-derived mafic magmas. The key control on Zr enrichment is the thermal state of the magma system: high-temperature, high-flux mantle inputs induced Zr undersaturation, dissolution of early zircons, and Zr release into melts. Subsequent melt segregation transported Zr-enriched liquids to shallow crustal levels, providing key insights into Zr behavior during crustal differentiation and crust-mantle interaction.
The transition from collisional to post-collisional stages in Neoproterozoic orogens is commonly associated with shoshonitic magmatism; however, whether this magmatism reflects localized processes or regionally coherent lithospheric conditions remains debated. In particular, the pressure–temperature conditions under which these magmas crystallize are still poorly constrained, limiting our understanding of crustal stabilization during the final stages of orogenic evolution. This study investigates Ediacaran shoshonitic plutonism in the Borborema Province (NE Brazil) to constrain the physicochemical conditions of magma crystallization and to evaluate the extent to which these processes are regionally consistent. Mineral–chemical data from monzodioritic to granitic plutons distributed across the Rio Piranhas–Seridó and São José do Campestre domains were used to estimate crystallization conditions. The results indicate high crystallization temperatures (910–1020 °C) and emplacement pressures of 4.1–5.5 kbar, corresponding to mid-crustal depths ( 15–20 km), under oxygen fugacity conditions near the Ni–NiO buffer. Despite their occurrence in distinct tectonic domains, the studied plutons display consistent mineral compositions and similar crystallization conditions. These findings demonstrate that shoshonitic magmatism in the Borborema Province records a regionally coherent mid-crustal thermal regime, rather than isolated magmatic events, providing new constraints on lithospheric reorganization during the transition from active orogenesis to tectonic stabilization in the final stages of West Gondwana assembly.
The distribution of detrital sediments across continental shelves can provide important information on mineral concentrations, geological processes, and ecosystem substrates. On the southwestern Portuguese continental shelf, this distribution is governed by a complex interplay of hydrodynamic energy gradients, seafloor morphology, and eustatic sea-level changes. In particular, the strong energy gradient from the coastline to the shelf break, combined with open-ocean-wave dynamics, tidal regimes, and active continental uplift, determines the specific nature and grain size of submarine deposits. To better understand these dynamics, this study employed continuously recording geophysical methods, including multibeam echosounder bathymetry and backscatter, complemented by ultra-high-resolution seismic profiling and sediment sampling. Our results reveal four distinct depositional environments: homogeneous fine-grained sediments near the shelf break, sorted bedforms on the flat outer shelf, isolated sorted bedforms on the mid-shelf, and a homogeneous sand sheet near the coast. Notably, the presence of isolated bedforms at depths exceeding 80 meters suggests they are generated by wave action, reflecting the long-term impact of the Holocene sea-level rise over the last 8,000 years and possibly active mobilization under modern hydrodynamic conditions. Consequently, these findings highlight how high-resolution mapping can reveal sediment patterns and environmental histories that remain hidden through traditional discrete sampling.
The North Saxon Volcanic Complex (Germany) is one of the largest exposed Permo-Carboniferous caldera systems in central Europe that includes two supervolcanoes. Contrasting age data still hinder a temporal interpretation of the volcano-sedimentary processes. We applied high-precision U-Pb chemical abrasion-isotope dilution-thermal ionization mass spectrometry to five samples covering the whole succession from the earliest volcanic members to the latest. The new ages indicate that volcanic activity lasted ca. one Myr, which is considerably shorter than previously assumed. The volcanic activity in the North Saxon Volcanic Complex belongs to the magmatic flare-up at the Permo-Carboniferous transition. Contemporaneous volcanic layers are preserved in many volcano-sedimentary basins within and north to the Bohemian Massif. A compilation of high-precision ages in these basins supports the short duration of a few Myr for the volcanic flare-up at the Carboniferous-Permian transition. The melt sources of the two studied supervolcanoes are dominated by crustal material according to new initial strontium isotope data and document an increasing mantle input towards the latest supervolcano. The Sr isotope results confirm together with published whole rock geochemical data the previously recognised north–south trend for Permo-Carboniferous volcanic rocks. Melts in the north (Oslo graben) are dominated by mantle sources, whereas towards the south approaching the Bohemian Massif crustal components contribute increasingly to magma generation.
The Galim-Legalgorou Au–Ag prospect in Northwestern Cameroon has been recently classified as epithermal based on the wall-rock alteration assemblages, ore mineralogy, and chemistry of electrum plus sphalerite. However, questions regarding the host-rock compositions and how these may have interacted with mineralizing fluids remained unanswered. This study presents the host-rock compositions as well as features of quartz-hosted fluid inclusions related to mineralization. Whole-rock major element data show a highly evolved magmatic rock series from basalt to rhyolite, with the latter being the major host to the mineralization. Rare-earth element data of the trachyte and rhyolites show a slight enrichment trend in LREE relative to HREE, with a negative europium anomaly (Eu/Eu*CN = 0.09 to 0.51), suggestive of plagioclase fractionation at the magma source. Coexisting liquid-rich and vapor-rich secondary fluid inclusions are consistent with boiling and vapor loss during the late stages of fluid evolution. LA-ICP-MS data show that Na and K are the dominant ions in fluid inclusions, suggesting that the fluid was in equilibrium with alkali-rich host rocks at the time of mineralization. Homogenization temperatures of 180–303 °C (average 273 °C), with salinities around 2.2 wt
The Dinaric fold-and-thrust belt forms the link between the Alpine and Hellenic orogenic systems, where the transition between differently rotating domains is a key problem in Mediterranean tectonics. The Shkodër–Peć fault system has been regarded as a major structure within this transition and as a possible boundary between counter-clockwise-rotated northern and clockwise-rotated southern segments. This study tests this interpretation by investigating the palaeomagnetic evolution of the southeastern External Dinarides, focussing on the rotational history of the High Karst Unit, Dalmatian and Budva Zones relative to this major transverse structure. Palaeomagnetic investigation was conducted at 62 geographically distributed localities over these 3 zones. The main target was the Budva Zone, for which we document a general 50° clockwise vertical-axis rotation of post-Cretaceous age. An important feature of this zone is the fan-like distribution of clockwise-rotated declinations, which correlates with the general trend of the thrust front and is characteristic of a salient-recess-type thin-skinned thrust. Whilst the northwestern Dalmatian Zone shows no post-Cretaceous rotation, Jurassic localities of the southeastern High Karst Unit show clockwise rotation of similar magnitude to that of the Mesozoic localities of the Budva Zone. These clockwise rotations match those documented in the northwestern parts of the Hellenides. They indicate that the Shkodër–Peć fault system is not the primary boundary between differently rotating domains; instead, the main change occurs near the northwestern terminus of the Budva Zone.
Establishing a chronostratigraphic framework for lacustrine sediments is a classic problem throughout Earth history, and pyroclastic deposits are essential for their correlation as they can provide numerical ages. Sediments of the Late Miocene–Pliocene brackish Lake Pannon in Central Europe accumulated over 8 Ma, and a well-established biochronostratigraphic scheme using endemic biota has been developed and widely applied for their subdivision. Here, we describe a recently discovered unique tephra layer in the lacustrine succession from the Pécs–Danitzpuszta outcrop in SW Hungary, which, if found in other outcrops, can be an essential marker horizon in the region. Mineralogical and geochemical data suggest the Pásztori volcano, located 200 km to the north, as the most probable source of the tephra. Dating of the layer with several radiometric methods constrains the eruption to 11.3 ± 0.4 Ma, shortly after the beginning of the Pannonian age at 11.6 Ma. This is slightly older than predicted by biostratigraphic considerations and challenges the accepted biochronostratigraphic system of Lake Pannon deposits. Here, we present an alternative calibration for the system, which should be tested by future investigations.
This study establishes the provenance evolution of the Raniganj Basin and paleoclimatic conditions during Permo-Triassic sedimentation through an integrated analysis of framework mineralogy and heavy minerals. The QFL modal composition indicates transitional continent and cratonic interior provenance for the sediments. Garnet, tourmaline, and rutile are the most common heavy mineral assemblages. ZTR values decrease from the Barakar (74
Abiogenic hydrocarbons in geological settings, particularly in mid-ocean-ridge hydrothermal systems, have been proposed as potential precursors to life and as sources of primitive nutrients for surrounding biomes. Formate (HCOO−), an abundant and relatively stable organic anion in such systems, is regarded as an intermediate in abiotic reaction pathways. In this study, we performed two sets of hydrothermal simulation experiments using sodium formate as the carbon source and magnetite or olivine as catalysts. Both experiments produced methane-dominated gaseous hydrocarbons, primarily through hydrogenation of formate and methanation of its decomposition products (e.g., CO and CO2). Notably, the elevated yield of i-C4 results in total C4 abundances exceeding those of C3. In addition, the gaseous products deviate from the typical Anderson–Schulz–Flory distribution, which may reflect a possible contribution from C₂-unit coupling, although this interpretation remains speculative and is not directly supported by the present experimental data. Hydrocarbon gases are enriched in deuterium relative to the coexisting H2 and exhibit a systematic trend of δDC2 < δDC3 < δDC4. This pattern may be consistent with kinetic isotopic effects associated with deuterated surface intermediates. Based on these observations and the alkylene growth mechanism, we suggest a carbon isotopic fractionation model characterized by a monotonic increase and convergence with increasing carbon number. Our results further indicate that, in the presence of magnetite or olivine, aqueous sodium formate can generate detectable amounts of gaseous hydrocarbons under hydrothermal conditions without the addition of elemental iron. This finding suggests the potential significance of formate-driven hydrocarbon formation in alkaline hydrothermal systems.
The Middle Pleistocene Ludwigshafen Fm. (LuFm) of the Upper Rhine Graben is an ideal target to study the interplay of tectonic processes and climatic factors impacting sediment deposition. It consists of a spatially variable fining-upward sequence, whose stratigraphic placement, timespan of deposition, and environmental context are still debated. We revisit previous research drillings, and present new sedimentological, geochronological, and palynological data to reconstruct its deposition in response to overarching factors. Common stacking patterns and facies transitions allow the subdivision into a diamictic lower, a coarse-grained middle, and a fine-grained upper LuFm. The depositional architecture in the graben is tectonically controlled, and the lower LuFm is interpreted to mark the onset of a period of accelerated relative subsidence and seismic activity. In contrast, middle and upper LuFm reflect the transition from glacial toward interglacial climatic conditions. Geochronological data based on different methodical approaches consistently suggest an age of 400–500 ka for this transition, corresponding to marine isotope stages (MIS) 12–11. The dating results also attest considerable age gaps at the formation boundaries. Pollen assemblages in the upper LuFm support the inferred transition to interglacial conditions. However, the assemblages do not fit the typical (Holsteinian) vegetation development during MIS 11 and, together with other biological indicators, rather point towards a position in MIS 13 (late Cromerian). The overall facies development supports this placement, as it coincides with rapid uplift in the downstream Rhenish Massif, accounting for some of the observed relative subsidence. Our data further stress the occurrence of several small- and large-scale hiati within and at the formation boundaries, respectively, and call into question the postulated broad continuity of the graben fill.
