Paleoenvironmental Reconstructions Research Articles

A Paleoenvironmental Reconstruction of Lake Vrana on the Island of Cres (Croatia) Based on the Geochemistry and Mineralogy of the Late Pleistocene and Holocene Sediments

A 7.4 m long sediment core has been retrieved from the central part of Lake Vrana on the island of Cres to reconstruct the paleoenvironmental conditions. Lake Vrana is the deepest freshwater lake in Croatia, located in the karst region of the eastern Adriatic coast. A dated sediment sequence in Lake Vrana of 4.4 m has spanned the past 16.4 kyr, and it featured a dynamic sediment deposition until the beginning of the Holocene, including strong sediment input and supply to the lake by runoff sediments of dolomitic origin from the catchment in the period 16.4–14.4 cal kyr BP. High organic carbon content, which originates from mixed terrestrial and aquatic origins in the periods 14.4–13.3 cal kyr BP and 12.7–11.7 cal kyr BP, indicates fluctuating lake levels in shallow water environments during the Late Glacial to Holocene transition. The Holocene sequence indicates the development of more stable conditions and continuous sediment deposition, characterized by an increasing trend of siliciclastic sediments delivered into the lake during the early Holocene (11.7–10 cal kyr BP) and dominantly from 8 to 4.4 cal kyr BP, indicating enhanced input and erosion, which coincides with the humid and pluvial period recorded in the central Mediterranean region. It is followed by sediments with high organic carbon content between 4.4 and 1.6 cal kyr BP, which points to higher lake productivity. Calcite sedimentation prevailed between 1.6 to 0.4 cal kyr BP, indicating stable deeper-lake conditions. Predominantly, siliciclastic sediments from 0.4 to 0.1 cal kyr BP pointed to erosion during the Little Ice Age (LIA), with enhanced precipitation and sediment discharge from the catchment. The re-establishment of calcite sedimentation has been observed over the last 100 years.

Paleoenvironmental reconstruction of coal deposition during the Cretaceous-Paleogene transition in the Eastern Cordillera Basin, Colombian Andes

Stratal stacking patterns and factors influencing peat accumulation in coastal and continental settings represent a significant problem in studying coal-bearing sequences. To address this issue, this work focused on the Cretaceous-Paleogene Guaduas Formation on the Checua-Lenguazaque Syncline (CLS) coalfield in the Eastern Cordillera Basin (Colombian Andes). This study relies on geological survey, facies analysis, sequence stratigraphy, organic geochemistry, and coal petrography. Through these methods, depositional systems and sequences were characterized, and their relationship with coal composition was established. Sedimentary facies were categorized into four Facies Associations (FAs): lagoon, tidal flat, delta plain, and mixed fluvial system. Five T-R sequences (S1 to S5, in ascending order) were identified. S1 consists of lagoon and tidal sandstone, mudstone, and coal. S2-S4 comprise tidal, deltaic, and fluvial deposits. S5 is composed mainly of deltaic and fluvial facies. Thick coal seams (> 0.7 m) were concentrated in the regressive system tracts of S1 and S3, while the transgressive coals were deposited in S2-S3 and are associated with tidal environments. The organic petrography showed enrichment in vitrinite (30.00–85.20 %), while liptinite (0.00–16.60 %) and inertinite (4.60–34.40 %) varied according to depth and paleoenvironments. CLS coalfield displays an environmental evolution from shallow marine and lagoon deposits to deltaic and fluvial environments. Minor sea-level fluctuations, changes in accommodation, siliciclastic influx, and plant community distinguish this sedimentary succession. The deposition of the Guaduas Formation is characterized by a prograding pattern with dominant shallowing-upward cycles in a high accommodation setting. The organic matter accumulated under limno-telmatic to telmatic conditions in mesotrophic to ombrotrophic environments with nutrients derived mainly from rainfall. The paleoclimate for the Guaduas Formation indicates wet and hot conditions for flora expansion. This investigation determined paleoenvironments of the Maastrichtian-Paleocene coastal to fluvial successions within the tropical latitudes, indicating a strong relationship between depositional systems, sequence stratigraphy, paleoclimate, and coal composition.

Theoretical concepts about alluvial fans and debris cones: case studies of an Alluvial Fan in São Desidério (Bahia, Brazil) and a Debris Cone at Mount Somma, near the Vesuvius Volcano (Naples, Italy)

Analyzing the last 24 years of the Brazilian Journal of Geomorphology and the National Symposiums of Geomorphology (SINAGEO), it is evident that there is a lack of studies on alluvial fans in Brazil and in Portuguese literature. The situation is even more unclear concerning debris cones. This paper aims to provide a concise and comprehensive bibliographic review of alluvial fans and debris cones in Portuguese and to the Brazilian geomorphological science. These features are crucial for understanding and studying the relationship between form and process, paleoenvironmental reconstruction, sensitivity to climate variations, risks associated with mass movements on slopes, and more effective territorial planning by human actions. Additionally, the paper seeks to clarify the main theoretical and conceptual distinctions between alluvial fans and debris cones, proposing a new classification based on two particularly illustrative case studies. Do alluvial fans and debris cones represent the same or different depositional forms in the landscape? To this end, the methodology includes a detailed theoretical and conceptual review of the topic, a survey of relevant data about the subject in the main means of the Brazilian geomorphological community dissemination, a proposal of a new classification to differentiate these forms, and the mapping, characterization, comparison and analysis of two specific study areas: an Alluvial Fan identified in São Desidério (Bahia, Brazil) and a Debris Cone identified in Mount Somma, the ancient crater of the current Vesuvius Volcano (Naples, Italy).

Thermal-induced crystallographic transformation in shells of Mytilus galloprovincialis Lamarck, 1819

Biominerals in hard parts are widely used as paleoenvironmental archives, employing proxies such as elemental and isotopic composition, microstructure, and crystallography. However, the effective selection and application of these proxies in fossil materials depends on their preservational potential. Here we evaluated the preservational potential of these proxies through controlled experiments on bivalves, one of the commonly used fossils in paleoenvironmental reconstructions. We utilized cultured Mytilus galloprovincialis specimens at five controlled temperatures to investigate the impact of elevated temperatures on various proxies extracted from both aragonitic and calcitic components of the same shell, including isotopic composition, microstructure and crystallography. Elevated temperatures first induced changes in the oxygen isotope composition (in both aragonite and calcite), followed by modification in aragonitic parts, such as changes in the aragonite phase, textures, nacre microstructure, and grain size of aragonite crystals. Despite aragonite's susceptibility to temperature, the microstructure and texture of calcite remained largely unaltered, demonstrating significantly higher resilience. Our findings emphasize the preservational potential of different shell proxies under heat exposure, ranging from oxygen isotopes to microstructure and texture. A ranking of preservation potential provides a practical guide for selecting well-preserved specimens, as textures and microstructures are not always reliable indicators. In distinguishing aragonite from calcite in fossils, our study pioneers a new avenue by proposing the analysis of high-angle boundary (HAB) content, including twin boundaries, as a reference for altered aragonite.

Sedimentary organic matter and paleoenvironmental reconstruction of the Santana Group (Lower Cretaceous), Araripe Basin, Northeast Brazil

Depositional controls of the Santana Group in the Araripe Basin are still being debated. The main controversial subject is their marine influence and paleoenvironmental evolution. In this study, palynofacies analysis was performed on 59 samples from one core drilled at Sítio Romualdo in the Araripe Basin to investigate sedimentary organic matter. Three palynofacies associations (structureless, continental particles, and aquatic + opaque) were identified. The Santana Group consist of Barbalha, Crato, Ipubi and Romualdo formations. Based on palynofacies associations we conclude that the depositional setting of the Barbalha Formation reflects a fluvially-fed lacustrine system under oxic conditions. The Crato Formation, associated with tidal flats, coastal lakes, and lagoons within an open bay environment, represents a bayhead delta system. The Ipubi Formation corresponds to a coastal plain typical of sabkha paleoenvironments, characterized by low energy under reducing conditions, during drier climate conditions. The Romualdo Formation records mainly an estuarine paleoenvironment characterized by dysoxic to anoxic conditions. The presence of palynomorph groups typifies a late Aptian age for the Santana Group, which is based on the range of guide species marked mainly by the presence of Sergipea variverrucata biozone (P-270), as well as the occurrence of Complicatisaccus cearensis and Equisetosporites maculosus. The identification of marine palynomorphs (dinoflagellate cysts Subtilisphaera and foraminiferal test linings) are indicative of several, local marine incursions.

Paleoenvironmental reconstruction of Lake Van and Lake Erçek over the last millennium using varved sediments (Eastern Türkiye)

Detailed lithological and geochemical studies of the bottom sediments were conducted based on the original sampling of brackish adjacent lakes: Lake Van and Lake Erçek in Eastern Anatolia, Türkiye. Seasonal variations in the accumulation of weather-driven element content were determined using high-resolution Synchrotron Radiation X-Ray Fluorescence (SR-XRF) analysis of the annual layers in the solid prepare. The results were utilized to approximate the regional paleo-temperature of both lakes and the water level of Lake Van. Visual counting of the varve as well as annual oscillation of measured geochemical series was employed to create a time scale. The element content series were synchronized with recent changes in external climatic environments and lake water level fluctuations. Subsequently, the geochemical series were transformed into climate units, using calibration on synchronous meteorological data. Finally, the original quantitative reconstruction of the regional climate variations was performed over the last millennium period with annual time resolution; for Lake Erçek (840 years ago) and Lake Van (1300 years ago). It was revealed that the sediments of these adjacent lakes (Lake Van and Lake Erçek), located 30 km apart from each other, provided synchronous responses to regional environmental changes, which confirmed the reliability of the reconstructions.

Late Jurassic paleoenvironmental reconstruction based on stable oxygen isotopes in bulk carbonates from the Qiangtang Basin, eastern Tethys

A composite eastern Tethyan oxygen and carbon isotope curve reveals major climate changes through the Late Jurassic. Despite significantly lower values and different amplitudes in scale, the δ18O data from whole-rock carbonates present fluctuant temperature results similar with well-studied composite δ18O curves of diagenetically-screened biogenic calcites, and are possibly acceptable as a paleotemperature proxy. The paleoclimate trends imply a cool global Callovian-Oxfordian transition, a mid-Oxfordian warming, a late Oxfordian cooling, a turbulent Kimmeridgian climate, a warm earliest Tithonian and rapid early Tithonian cooling event. The climate shift from the earliest Tithonian warmth to the middle early Tithonian cool climate was up to 8 °C decrease in some regions. These paleoclimate changes are greatly consistent with the eustatic sea-level changes, biological evolutions and paleoatmospheric CO2 reconstructions, and are recorded by coeval carbon isotope perturbations relating to the organic carbon accumulations in marine sediments. Coupled δ18O and δ13C chemostratigraphy evidence that higher temperatures lead to more rapid continental weathering, increased nutrient-rich runoff into the oceans, and intensified marine productivity, resulting in increased organic‑carbon burial and more positive δ13C values in limestones. The decrease in primary productivity and burial rates during cooling periods is, in turn, commonly accompanied by low δ13C values.

Developing a European aquatic macrophyte transfer function for reconstructing past lake-water chemistry

Quantitative paleoecological reconstructions using biological proxies, such as diatoms, Cladocera, and chironomids, have revolutionized paleolimnology and have greatly contributed to the understanding of the past local and regional environmental changes, as well as to nature conservation. While macrophytes are good ecological indicators, they have rarely been used to reconstruct past lake-water chemistry. The present study investigates which environmental variable best explains aquatic plant community composition in Finnish, Polish, and Swedish lakes for its further use in quantitative paleoenvironmental reconstructions. The method involved the creation of a modern macrophyte-environment calibration dataset, calculation of modern calibration functions using simple averaging regression, and final reconstruction of past environmental conditions in Lake Linówek (NE Poland) from a fossil assemblage using weighted averaging calibration. The data demonstrate that conductivity and alkalinity best explained macrophyte community composition in our dataset. Species “optima” for alkalinity were influenced by the presence/absence of carbon concentrating mechanisms (CCMs), enabling the utilization of HCO3− as a carbon source. Quantitative paleoenvironmental reconstruction indicates that past water conductivity and alkalinity fluctuated depending on internal lake processes and the supply of basic ions to the lake from the catchment related to climate and soil development in the watershed during the late Glacial (∼14,500–11,700 calibrated years before the present; cal BP) and the Holocene (11,700 cal BP–recent). We conclude that macrophytes can be successfully used for past lake-water chemistry reconstruction. Furthermore, calculated modern calibration functions for conductivity and alkalinity can be used in nature conservation for determining habitat requirements of numerous endangered macrophyte species as a basis for successful (re)introductions.

Current understanding, knowledge gaps, and challenges of mountain permafrost research in the Chilean and Argentinean Andes

Mountain permafrost extends over a vast area throughout the Chilean and Argentinean Andes, making it a key component of these mountain ecosystems. To develop an overview of the current state of knowledge on southern Andean permafrost, it is essential to outline appropriate research strategies in a warmer climate context. Based on a comprehensive review of existing literature, this work identifies eight main research themes on mountain permafrost in the Chilean and Argentinean Andes: paleoenvironmental reconstructions, permafrost-derived landforms inventories, permafrost distribution models, internal structure analysis, hydrogeochemistry, permafrost dynamics, geological hazards, and transitional landscape studies. This extensive review work also highlights key debates concerning the potential of permafrost as a water resource and the factors influencing its distribution. Furthermore, we identified several challenges the scientific community must address to gain a deeper understanding of mountain permafrost dynamics. Among these challenges, we suggest tackling the need to broaden spatial focus, along with the use of emerging technologies and methodologies. Additionally, we emphasize the importance of developing interdisciplinary approaches to effectively identify the impacts of climate change on mountain permafrost. Such efforts are essential for adequately preparing scientists, institutional entities, and society to address future scenarios.

Supercritical‐Flow Deposits: A New Quantitative Tool to Characterise Deep‐Marine Depositional Environments (Oligocene Annot Sandstones, SE France)?

ABSTRACTDespite a growing interest, few studies integrate quantitative supercritical‐flow deposit (SFD) distribution into paleoenvironmental reconstructions in deep‐marine settings. We present a re‐evaluation of the Oligocene Annot Sandstones (SE France) in terms of flow criticality, by examining the spatial distribution of SFDs. Proximal settings exhibit SFD proportion varying from ~90% to 40% with a common occurrence of cyclic steps, whereas distal environments show <40% SFDs with antidunes and upper‐plane beds prevalent. Comparing SFD spatial distribution to other proxies in the Annot Sandstones and published proxies from the Eocene Ainsa‐Jaca basins (Spanish Pyrenees), SFD trends appear more consistent than those in sandstone percentages, or the distribution of the Bouma sequence divisions. Our approach achieves two goals: (1) establishing the reliability of quantitatively analysing SFDs as a proxy for paleoenvironment reconstructions, characterising the proximal‐to‐basin floor transition at ~40% SFDs and (2) providing fundamental insights into the formation processes compared to other proxies.

Lateral migration differs between phytolith morphotypes on sand dune surfaces

AbstractArid and semi‐arid lands are exceptionally sensitive to climate change. However, the application of phytolith analysis to these environments is hindered by the potential for lateral migration of phytoliths during wind erosion, which may affect the reliability of phytolith‐based paleoenvironmental reconstructions. Moreover, there is a lack of quantitative studies of the dispersion and deposition of phytoliths by wind erosion. Here we apply Sutton's equation and theoretical models from the field of blown sand physics and engineering to quantify the lateral migration of various phytolith morphotypes in the surface soil of sand dunes in the Horqin Sandy Land in China. Phytolith morphotypes and concentrations were determined in addition to sedimentary organic matter content and grain size. Combined with the analysis of plant communities, these measurements were used to quantify the lateral migration of phytolith morphotypes, and the results were compared with theoretical models. We found that phytolith concentrations decreased exponentially under an annual average wind speed with distance from the surface source; specifically, a large proportion of lateral phytolith migration occurred within the distance of ~3–5 m. There were significant linear correlations between the phytolith concentration and other environmental factors. A comprehensive form of Sutton's equation was used to estimate that a relatively large proportion (8.35%) of short‐cell phytoliths may migrate laterally on dunes that are vulnerable to wind erosion. However, large phytoliths are deposited almost in situ, and relatively limited lateral migration of wind‐transported phytoliths occurs in the Horqin Sandy Land overall. Our results provide a theoretical model and practice template for the application of phytolith analysis to soil and sediments, especially as a proxy of past vegetation and ecological change in the Horqin Sandy Land, and other areas affected by wind erosion. Additionally, short‐cell phytoliths in palaeoenvironmental contexts satisfy the criteria necessary to investigate the extent with frequent aeolian activity.

The Origin and Nature of Magnetic Particles From Soils and Sediments Constrained by Hydrodynamics and Geochemistry Around a Tropical Lagoon System

AbstractMagnetic iron oxides are commonly enriched in soils and sediments on Earth's surface. Magnetic properties are widely employed in soil taxonomy, sediment tracing and paleoclimate reconstruction as indicators of associated pedogenic and depositional processes. However, in coastal regions, frequent shifts in pedogenesis and diagenesis accompanied by changes in hydrodynamic and geochemical conditions from land to sea can influence the formation and preservation of magnetic particles in sediment sequences. To discern the origin and nature of magnetic particles driven by these processes, we systematically examined soils and sediments around a tropical lagoon that has been closing for two hundred years. We found that the finest superparamagnetic particles are enriched along with hematite from inland soils with high‐Fe and high‐Al backgrounds, which was driven by pedogenesis. Single‐domain ferrimagnetic particles are enriched along with amorphous iron oxides in the lagoon with high‐Mg and high‐Mn backgrounds, which was driven by early diagenesis in quiet and reducing depositional environments. Coarse titanomagnetite particles are strongly enriched in inshore sediments with high‐Si and high‐Ti backgrounds, which was driven by seawater elutriation. However, magnetic particles in barrier bar soils have mixed features depending on the neighboring environment. Identifying magnetic particles derived from different soils and sediments in tropical coastal regions can assist in tropical coastal paleoclimate and paleoenvironment reconstruction on the basis of magnetic properties along coastal sediment sequences.

Kinetics of hydrogen isotope exchange in kaolinite and the prediction of δD signature retention over geological time

Retention of the pristine hydrogen isotope composition (expressed as δD) formed during mineral formation in equilibrium with water is the basis for any paleoenvironmental reconstructions and for tracing mineral reactions using hydrogen (or H and O) isotope composition in kaolinite. Not only do post-formation reactions cause partial equilibration with ambient water, altering the pristine signature, but also result in the decoupling of H and O diffusion.In this study, kaolinite samples of different structural order (expressed, for example, as the Hinckley Index) were tested for their susceptibility to H isotope exchange under D2O vapor in an open system. The H isotope exchange was detected by recording the kaolinite’s structural OH and OD stretching mode using infrared spectroscopy. A number of different in-situ and ex-situ testing protocols under diverse temperature ranges (90 °C, 125–275 °C, 300–700 °C), show consistent kinetics and mechanism. In each kaolinite sample, the H isotope exchange rate increases with temperature; however, the major control on the reaction rate is the kaolinite crystallite’s structural order, not the particle (agglomerated crystallites) size. The hydrogen isotope composition in kaolinite can be altered independently of oxygen atoms, likely via proton hopping mechanism through structural defects. The H isotope exchange reaction under vapour shows a two-mode kinetics: the time-to-the-quarter (TTTQ; t1/4) dependence dominates in the first part of the reaction or in low-temperature reactions, transitioning to the log10t (Elovich) relationship and with lower activation energy, in advanced stages and in higher temperatures. Extrapolating the TTTQ model to temperatures < 90 °C allows estimating the rate of H isotope exchange between water vapor and kaolinite. The paper presents the prediction of preservation of pristine δD signature and thus reliability of using isotope data in kaolinites of different origins and structural order when exposed to pore water / water vapor over geological timescales.

Calcareous Nannofossil variability controlled by Milankovitch and sub-Milankovitch periodicity in the Monte San Nicola section (Gelasian GSSP / MIS 100–104)

The Quaternary marks the beginning of the ice ages, with the establishment of a stable Northern Hemisphere ice sheet. The Monte San Nicola section, southern Sicily (Italy) is the Global Boundary Stratotype Section and Point of the Gelasian Stage of the Lower Quaternary Subseries and is attracting new attention for providing valuable information on paleoclimate evolution.Here we present a paleoenvironmental reconstruction based on new data from calcareous nannoplankton, the phytoplankton organisms that are sensitive to sea surface changes and water column dynamics. We adopt statistical and signal analysis to support our paleoenvironmental model. The most evident paleoenvironmental signal throughout the investigated interval is the contrast between the abundance patterns of placoliths and Florisphaera profunda, the former pointing to surface productivity (water column mixing, shallow nutricline), the latter to the establishment of a deep nutricline. The observed nutricline depth shift occurred with a regular precessional pace, following Northern Hemisphere summer insolation and, likely, North African monsoon activity. A significant periodicity of 8 kyr, in tune with late Quaternary Heinrich events, is also observed in nannoplankton taxa, supporting previous findings on the existence of suborbital climatic variability even at the Pliocene-Pleistocene transition.

Signals of soil formation during pre-glacial maximum on the byers peninsula (maritime antarctica)

The Maritime Antarctic is one of the most sensitive regions on Earth to warming, recording permafrost degradation and glacial retreat in the last 10 kyr. The timing of deglaciation and the pedological implications are still poorly elucidated in many ice-free areas of the Antarctic. The severity of the Last Glacial Maximum (LGM) across the Maritime Antarctic has limited paleoenvironmental records of pre-LGM terrestrial signals, constraining knowledge of climate trends in the Late Pleistocene. Byers Peninsula is one of the most extensive ice-free areas in the Maritime Antarctic. So, we hypothesized that soils in Byers Peninsula host Pleistocene sedimentological and pedological evidence of landscape evolution. This study investigated soil genesis in Byers Peninsula. Radiocarbon and OSL dates provided a chronology of nine soil profiles. Morphological, physical, and chemical analysis characterized soil formation. Isotopic composition of organic matter tracked the main photosynthetic processes. Endolithic soil organic matter in a pre-LGM soil indicates soil genesis at 31,690 cal yr BP, much earlier than the common age models of approximately 10,000 cal yr BP in previous studies. Burial and 14C ages in Cryosols formed on beach sediments above 70 m and on cliffs suggest marine terrace uplift and soil genesis in cliffs during the Late Pleistocene-Early Holocene. Younger Cryosols and Leptosols soils formed on raised beaches in Late Holocene. These findings suggest an older glacial retreat in the Maritime Antarctic. Soil proxies in potential pre-LGM ice-free areas are promising tools for paleoenvironmental reconstructions of the Maritime Antarctic.

Vertebrate taphonomy and taphofacies of the Capianga Member, Aliança Formation (Jurassic), Jatobá Basin, Brazil

In addition to the study of sedimentary facies, the reconstruction of paleoenvironments depends on a detailed understanding of the taphonomy of a fossil accumulation. The Capianga Member of the Aliança Formation (Middle to Late Jurassic of the Jatobá Basin, northeastern Brazil) reveals vertebrate fossil accumulations composed predominantly of disarticulated bone and osteoderms, scales, spines and isolated teeth from a lacustrine paleoenvironment. However, the taphonomic history of the accumulation has not yet been studied extensively. The present work aims to interpret taphonomic facies based on lithological data and the systematic collection of fossils from the Capianga Member of the Aliança Formation, located in the northeastern portion of the Jatobá Basin, mainly in the municipality of Ibimirim. Six lithofacies were identified: Fm – massive claystones, Fl – Shale laminated Lt – calcilutites, Lc – calcarenites, Gf – fibrous gypsum and Scl – calciferous sandstones. Two primary taphonomic classes were recognized, consisting essentially of disarticulated elements, including (1) incomplete, semi-complete, or rarely complete bioclasts (such as osteoderms and fish scales) and (2) small-sized, occasionally complete bioclasts (osteoderms and scales) that sometimes compose bonebeds. According to the vertebrate taphonomy characteristics, three taphofacies were identified, with the Taphofacies A and B occurring in calcarenites and the Taphofacies C in calcilutites. The interpretation of these taphofacies reveals a multi-episodic history of the lacustrine environment. The integrated model suggests that the genesis of the identified taphofacies is linked to the action of lowering the water level of the paleolake, as well as the agents responsible for transport and disarticulation. These agents are related to pre-burial sub-aerial exposure, the action of unidirectional turbidity currents in shallow waters, and the likely influence of storms.

Assessing the potential of n-alkyl amides and n-alkyl nitriles in the arid sedimentary strata of northwestern China as environmental indicators

Recent advancements in the application of lipid biomarkers as paleoenvironmental indicators have provided invaluable insights into the dynamics of climatic variations, vegetative histories, and anthropogenic impacts. However, our current understanding of nitrogen-containing lipid biomarkers (NCLBs) in sedimentary deposits remains limited, notwithstanding their potential significance in global nitrogen cycling. To bridge this research gap, a comprehensive study was conducted to characterize the distribution patterns of n-alkyl amides (NAAs) and n-alkyl nitriles (NANs) in representative paleo-lake and loess sedimentary profiles from the arid region of northwestern China (NWC). The widespread occurrence of these NCLBs across late Quaternary strata, with distinct distribution patterns observed in various settings, suggests their formation under diverse environmental conditions. The prevalence of NAAs in arid sedimentary deposits can primarily be attributed to the diverse array of local biota, including vascular plants, algae, and fungi, rather than being solely associated with biomass burning, as commonly assumed. Furthermore, the distribution patterns of NANs closely align with those of NAAs, indicating their formation through thermally induced dehydration of precursor NAAs. Both groups of NCLBs exhibit significant preservation potential in sediments within NWC, which is believed to be intimately linked to the region's arid and cold climate as well as its neutral or weakly alkaline depositional setting. These findings underscore the prospective use of NAAs as indicators of environmental changes and NANs as potential markers of past fire-related activities, making them valuable tools for paleoenvironmental reconstructions of late Quaternary strata, especially in arid, cold, and weakly alkaline regions.

Mandibular ecomorphology in the genus ursus (Ursidae, Carnivora): relevance for the palaeoecological adaptations of cave bears (U. spelaeus) from Scladina cave

ABSTRACT Considerable morphological and ecological diversity has been found in extinct and extant members of the bear genus, Ursus, and appears to be key in explaining how they have thrived across vast ecological gradients. One example is the cave bear Ursus spelaeus. We applied 2D geometric morphometric techniques to describe morphological changes in the mandibles of extant Ursus species to further interpret the palaeoecology of U. spelaeus. Ursus species were discriminated using their mandibular morphology, which showed intra and interspecific shape variation that was indirectly linked to climatic adaptations through dietary variation. Mandibles of bears that inhabit colder, drier and more seasonal environments were generally slender with large diastema and a dorsoventrally smaller ramus. In contrast, species from warmer environments with higher levels of precipitation were found to have a dorsoventrally taller ramus (relative to the corpus). Discriminant function analyses of the morphology of U. spelaeus suggested adaptations to a series of fluctuating environments through time, helping to assess previously proposed Marine Isotope Stages for sedimentary deposits in Scladina Cave. Our geometric morphometrics analyses of bear mandibular ecomorphology demonstrates how geometric morphometrics provides a valuable tool to enhance paleoenvironmental reconstructions within deposits of the same fossil site.

Paleoenvironmental reconstruction of a Neogene diatomite deposit from La Pampa Province (Argentina)

Diatomite deposits constitute siliceous biogenic sedimentary rocks primarily composed of diatoms. In Argentina, there is a scarcity of paleoenvironmental reconstructions for these deposits. This study focuses on the analysis of the diatom content in a Plio-Pleistocene diatomite from La Pampa Province. The aim is to identify diatom diversity and reconstruct the evolution of paleoenvironments. The studied section of 4.40 m is located at the CP site (38°08′40.5′’S; 67°09′23.2′’W, El Sauzal Formation). The profile is a laminated white diatomite with three levels of volcanic ash. Seven samples 50 cm-equidistant were extracted and oxidized with H2O2 for diatom analysis. 500 valves/slide were counted in order to calculate relative abundances. Diatom zones were defined using CONISS. The analysis revealed 72 morphospecies, with 28 of them exhibiting abundances > 4%. The diatom flora is predominantly composed of small fragilarioid diatoms accompanied by Discostella, Aulacoseira, Epithemia, Rhopalodia, and Cymbella species, indicating a lacustrine origin. At the base, a paleolake with a relatively alkaline pH, low nitrogen concentrations and high phosphates (volcanic ash) favored the growth of a diverse diatom community. Towards the top, the dominance of fragilarioids, the decrease in freshwater planktonic taxa and the presence of gypsum suggest a shallower environment with increased salinity during the drier periods of the Plio-Pleistocene.

Facies Analysis and Paleoenvironmental Reconstruction of Ghar Formation in Al-Muthanna Governorate, Southern Iraq

The Oligocene-Miocene succession in Al-Muthanna Governorate of southern Iraq shows significant mixed siliciclastic-carbonate formation. Fourteen samples are collected from two wells and four outcrops in Al-Muthanna area for studying the facies and paleoenvironments of the Ghar Formation. It is mainly composed of sandstone, calcareous sandstone, and carbonate rocks. Six facies associations are identified in the mixed siliciclastic-carbonate deposit: the carbonate type, including sabkha, lagoon, intertidal-subtidal, and lacustrine; the mixed type, including shoreface; and the siliciclastic type, including distributary channels. The major minerals in this formation are quartz, calcite, and dolomite, whereas feldspar and gypsum are the minor minerals. Clay minerals such as Palygorskite and Montmorillonite were also identified. The carbonate rocks of the Ghar Formation reflected deposition in the evaporitic platform (Sabkha), shallow restricted (lagoon), tidal and lacustrine environments. Ghar formation is considered transitional in conditions between a very restricted shallow marine and near-shore environment, whereas the clastic facies in Ghar Formation indicated deposition in the delta front channel.