Paleoenvironmental Interpretations Research Articles

Relative abundance of grazing and browsing herbivores is not a direct reflection of vegetation structure: Implications for hominin paleoenvironmental reconstruction.

The diet of fossil herbivores inferred from enamel stable carbon isotopes is often used to make paleoenvironmental reconstructions. While many studies have focused on using environmental indicator taxa to make paleoenvironmental reconstructions, community-based approaches are considered to provide a more complete picture of paleolandscapes. These studies assume that the diet and relative abundance of herbivores are related to the areal extent of different vegetation types on the landscape. Here, we quantitatively test this assumption in 16 modern ecosystems in eastern and southern Africa with a wide range of woody vegetation cover. We conducted a landscape-level spatial analysis of vegetation patterns using a published land cover data set and computed landscape metrics. We compiled data on relative abundance and diet of herbivores inferred from carbon isotope studies for all large herbivores in these ecosystems. We found that despite differences in the total areal extent of different vegetation types, numerous sizable patches of each vegetation type are available in most ecosystems. However, despite variation across the ecosystems examined, grazers are typically the most abundant herbivores even in sites that have a higher proportion of forest and shrub cover. This indicates that the diet and relative abundance of herbivores is not a simple reflection of the total areal extent of vegetation types available on the landscape. The higher proportion of grazers observed in these ecosystems is a result of multiple factors including habitat heterogeneity, differences in biomass turnover rate between grasses and woody vegetation, resource partitioning, and the advantages of group living in open environments. Comparison of diet and relative abundance of herbivores in modern ecosystems to fossil herbivore assemblages shows that very different vegetation regimes can support similar herbivore assemblages. This study has significant implications for paleolandscape reconstructions and cautions against a simplistic wooded vs. grassland paleoenvironmental interpretations based on fossil herbivore assemblages.

Implication of size fraction on benthic foraminiferal-based paleo-reconstructions: A case study from the Bay of Biscay (NE Atlantic)

Many paleoenvironmental studies based on benthic foraminiferal assemblages use different protocols for sample analysis. A standardized protocol has been recently established for biomonitoring applications, but for paleostudies, the influence of size fraction on benthic foraminiferal composition and biodiversity is poorly documented. We studied fossil foraminiferal assemblages along two paleorecords (BOBGEO-CS05 and SU81–44) from the Bay of Biscay covering the last ∼35 ka cal BP. We investigated diversity and community composition to compare the impact of each size fraction (63-150 μm, >150 μm, >63 μm) on environmental interpretations. Foraminiferal diversity was affected by the accumulation of small opportunistic species. In terms of faunal composition, both paleorecords displayed a different pattern depending on the size fraction selected. While in both cores, the 63-150 μm fraction blurred the signal of some rare indicator species, our results show that i) in BOBGEO-CS05, it yielded no extra ecological information compared to the large fraction whereas ii) in SU81–44, it contained small opportunistic species that were not present in the >150 μm, impacting therefore paleoenvironmental interpretations. According to these findings, we recommend: i) to focus on the large fraction for a thorough taxonomic determination and a detailed analysis of benthic assemblages, and ii) to analyse the small fraction separately after a taxonomical identification of major species and strategic selection of studied samples. Although the 125 μm size limit was not tackled in this study, we recommend to use it for the limit between the small and large fractions instead of 150 μm for harmonization with the previously published standardized protocol for living faunas.

Paleoenvironmental significance of benthic foraminiferal associations of the Hauterivian to Barremian marine beds of the Neuquén Basin, Patagonia, Argentina

The upper Hauterivian-lower Barremian sedimentary sequences of the Agua de la Mula Member of the Agrio Formation (Neuquén Basin, Argentina) represent shallow marine environments characterized by mixed siliciclastic‑carbonate deposition. Ten benthic foraminiferal associations based on species composition were defined and evaluated in relation to explanatory variables such as facies, sequence stratigraphy, location and age. Variations in sedimentation rates, food and oxygen availability related to relative sea-level changes largely control distribution of the benthic foraminiferal associations. Four associations (Guttulina sp., Polymorphinids, Spiroplectammina sp.2-Haplophragmoides sp.1, and Planularia madagascariensis) are mostly composed by shallow infaunal, bacterial and detritivorous foraminiferal scavengers that largely occur in sandy facies within 3rd-order regressive systems tracts. These associations are thought to be indicative of well oxygenated and organic matter-rich sediments below the sediment-water interface. The remaining six associations consist of epifaunal, mainly opportunistic foraminifera with active herbivorous and detritivorous trophic strategies. Among them, Epistomina hechti - Epistomina australis and Reinholdella hofkeri associations occur in fine-grained, dark shales throughout 3rd-order transgressive systems tracts, and are considered related to oxygen and food stressed environment. An integrated approach, using benthic foraminifera (alpha diversity analysis, epifaunal/infaunal ratio) and multivariate statistical methods (cluster analysis, RDA, partial-RDA, PERMANOVA, PCoA), allowed to evaluate the paleosynecological significance of benthic associations, and to relate certain paleoenvironmental settings to relative sea-level changes recorded in the Agua de la Mula Member. The application of foraminiferal associations analysis in the paleoenvironmental interpretations led to recognize the influence of major relative sea-level changes in shaping higher-frequency sequences for this sector of the Neuquén Basin. Such approach can also be applied to other sectors of the basin and to high-frequency sedimentary sequences of comparable shallow marine settings.

Ichnological evidence of marine incursions in the lacustrine–palustrine Bembridge Limestone Formation (Eocene), Isle of Wight, southern England

Trace fossils are described from the Eocene Bembridge Limestone Formation from the Isle of Wight and used to constrain the paleoenvironmental interpretation. The lacustrine–palustrine succession contains three limestone beds, which are separated by clay and marl. The middle and upper limestone beds reveal complex burrow systems developed at their top. Based on their characteristics, these burrow systems are assigned to the ichnotaxon Balanoglossites triadicus Mägdefrau, which is associated with the shallow superficial grooves Sulcolithos variabilis Knaust. B. triadicus is a common marine trace fossil mainly known from shallow-marine carbonate successions throughout the Phanerozoic. It is accompanied by other marine ichnotaxa such as Arachnostega gastrochaenae Bertling, Gastrochaenolites isp. aff. G. ornatus Kelly and Bromley, Spongeliomorpha iberica Saporta and Thalassinoides suevicus (Rieth). This ichnological evidence confirms the occurrence of short-term marginal-marine incursions in a predominantly lacustrine to palustrine environment.

An approach to using foraminifera in sequence stratigraphic analysis of Wadi Qena, Central Eastern Desert, Egypt

In Egypt, Wadi Qena Middle Eastern Desert, Paleogene successions exposed at Hawashiya and Abu Had sections from north to south were measured and comprehensively investigated for their foraminiferal content. The Dakhla, Tarawan, and Esna formations make up the investigated sections. The studied successions are subdivided into six biozones; they are five zones of the Late Paleocene (Igorina albeari subzone (P3b), G. Globanomalina pseudomenardii/P. Parasubbotina variospira subzone (P4a), Acarinina subsphaerica subzone (P4b), A. soldadoensis/G. pseudomenardii subzone (P4c), Morozovella velascoensis zone (P5), and one zone of the Early Eocene (P. Pseudohastigerina wilcoxensis/M. velascoensis zone (E2). The paleoenvironmental interpretations and interpretation of sea level changes over the study area during the Paleocene-Eocene time interval have been carried out based on the lithostratigraphy, biostratigraphy, paleoecologic parameters (total foraminiferal number (TFN), diversity indices of foraminifera, life strategies of planktonic foraminifera, planktonic/benthonic (P/B) foraminiferal ratio, agglutinated/calcareous benthonic foraminiferal ratios, benthonic foraminiferal biofacies and total organic carbon (TOC), and calcium carbonate CaCo3%). Five sequences are identified in the studied Lower Paleogene successions in the Wadi Qena area. Four depositional sequences are determined in the Paleocene, and one in the Lower Eocene. A comprehensive description of these depositional sequences and their boundaries is provided. The findings of the current study are calibrated with sequence stratigraphy of the world sea-level variations.

Overprinting of δ13Corg signatures in the sedimentary record linked to hydrocarbon migration: Evidence from Paleozoic drill cores from the Ordos Basin, China

Carbon isotopic compositions of organic matter (δ13Corg) provide critical information about changes in the global carbon cycle through Earth's history. However, several biotic and abiotic processes occurring after sediment deposition may overprint the original geochemical signals, complicating their paleoenvironmental interpretation. Here, we report multiple large and rapid δ13Corg swings (ranging from −30.8‰ to −23.3‰) from three Paleozoic drill cores in the Ordos Basin, Northwest China, which may reflect different organic contributions related to lithology. As a potentially important organic matter source, migrated hydrocarbons may substantially alter the original δ13Corg and total organic carbon contents (TOC), and their oxidation may contribute to forming 13C- and 18O-depelted carbonate cements in siliciclastic-dominated strata at depth. Cross-plots of δ13Corg and TOC from samples of the three drill cores all show similar hyperbolic trends that are well simulated using Rayleigh fractionation and a two-component mixing model, thus providing potential criteria for identifying the reservoir and the related hydrocarbon source in oil exploration. Our data call for a critical reassessment of the δ13Corg records of sedimentary rocks if hydrocarbon redistribution or mixing of organic sources is suspected to have occurred during the burial history.

Effects of minerals (phyllosilicates and iron oxides) on the responses of aliphatic hydrocarbon containing kerogens (Type I and Type II) to analytical pyrolysis

Organic matter in sediments is dominated by kerogen, a high molecular weight geomacromolecule. Kerogen can be subdivided into Types I to IV that provide paleoenvironmental and petroleum potential information. Kerogen typing can be performed by several chemical methods including elemental analysis (H/C and O/C), FTIR and pyrolysis-gas chromatography techniques. However, kerogens occur naturally within mineral matrices and these can influence the chemical responses. We have examined the effects of a range of minerals (namely kaolinite, lizardite, ripidolite, illite, montmorillonite, haematite, goethite, limonite and magnetite) on the responses of kerogen to pyrolysis-gas chromatography-mass spectrometry. We used aliphatic hydrocarbon containing kerogen Types I and II from Carboniferous Midland Valley shales of Scotland and the Jurassic Oxford Clay of southern England, respectively, as well as a pure synthetic aliphatic polymer, polyethylene. We find that the aliphatic organic matter in Type I kerogens is transformed by interaction with minerals during pyrolysis to give a signal incorrectly suggesting more contributions from land plant-containing kerogens, such as a large number of aromatic molecules. Pyrolysis with goethite, limonite and magnetite leads to almost complete destruction of the organic matter. Hence, the mineral composition of sedimentary rocks during pyrolysis should be considered when assigning kerogen types. Failure to consider the effects of minerals can lead to incorrect assignment of kerogen type and, therefore, erroneous interpretations of paleoenvironments and petroleum potential.

The influence of submarine canyons-related processes on recent benthic foraminiferal distribution, Espírito Santo Basin, Southeastern Brazil

The complex topography of submarine canyons may result in different composition of benthic foraminifera assemblages. To understand how trophic, hydrological and sedimentological conditions in submarine canyons can influence the distribution of benthic foraminifera, and to use this information to corroborate paleoenvironmental interpretations for the Holocene, we investigated recent benthic foraminiferal assemblages (total fauna >63 μm) and sedimentological data in two canyons (CANWN and CAND) in the Espírito Santo Basin (ESB) between 18°20′ and 21°20′ S. Surface sediment samples (0–2 cm) were collected inside the canyons (150 to 1300 m water depth) and in shelf-slope adjacent transects (50 to 1300 m water depth). The density, taxonomic diversity, and assemblage composition of benthic foraminifera change with depth and location. The distinct ecological preferences of the most abundant taxa allowed us to recognize five benthic foraminiferal groups. Three groups (V, III, and I) are present in different bathymetric sectors; Group V: outer shelf (50 m), Group III: upper, and middle – lower slope (150 to 400 m), and Group I: middle – lower slope (1000 to 1300 m). Groups II and IV show no characteristic bathymetric distribution and are present only in CAND and in CANWN, respectively. Group V consists of Hanzawaia boueana, Peneroplis planatus, and Quinqueloculina lamarckiana; Group III is dominated by Globocassidulina rossensis and Trifarina spp.; Group I consists of Globocassidulina crassa, Bolivina lowmani, Gavelinopsis versiformis, Alabaminella weddellensis, and Epistominella exigua. The main species in Group II (CAND, 150, 1000 to 1300 m) are Trifarina angulosa, Globocassidulina subglobosa, and Discorbis vilardeboanus. Group IV (middle – lower CANWN, 1000 to 1300 m), consists mainly of agglutinated species Glomospira charoides, Rhabdammina abyssorum, and Psammosphaera fusca. Our data suggest that the quantity (and quality) of food supply, hydrodynamic conditions and sediment properties are the main drivers controlling the bathymetric distribution of benthic foraminiferal assemblages in both canyons. The middle – lower CANNW revealed unstable trophic conditions, related to terrigenous sediment input due to turbidity currents. In CAND, the foraminiferal assemblages ecology indicated sufficient organic matter supply that favors species establishment and diversity, indicating a more productive and less unstable environment than in CANWN.

Variations of organic matter content and type within the sequence stratigraphic framework of the lacustrine deep-water Dongyuemiao formation, Sichuan Basin, Western China

The organic matter (OM) enrichment patterns and mechanisms in lacustrine deep-water shale successions were controlled by complex geological and biological processes, rather than any single factor. The integration of sedimentology, petrography, geochemistry, and sequence stratigraphy in the study of shale successions is vital to the development of robust paleoenvironmental interpretations and OM enrichment model. Based on a systematic sedimentological, petrographic, and geochemical analysis of three continuous cored wells of the Lower Jurassic Dongyuemiao Formation, Sichuan Basin, within a sequence stratigraphic framework, this study reports the complex geological responses in detrital input, sedimentation rate, benthic redox conditions, primary water column productivity, and OM enrichment pattern that caused by lake-level fluctuation. The results indicate that none of the proxies for detrital input, redox conditions, or productivity exhibit a significant correlation with total organic carbon (TOC) content in sediments. The OM enrichment was regulated by a complex interplay of these three factors, which is a function of relative lake-level fluctuation. In general, detrital input was decreased during lake-level transgression; whereas increased during lake-level regression. Reducing conditions and primary productivity were generally enhanced during lake-level transgression; whereas diminished during lake-level regression. Coupled relationships between lake-level fluctuation, bulk TOC content, and OM types were observed. The bulk TOC content and liptinite proportion in sediments increased gradually during the lake-level transgression. In contrast, the bulk TOC content and liptinite proportion in sediments gradually decreased during the lake-level regression. This general principle applies to both second-order and third-order lake-level fluctuation. Our study demonstrates that the development of a reliable OM enrichment model in lacustrine shale successions requires a comprehensive sequence stratigraphic framework.

Morphosedimentary and geoarchaeological records during the last 1400 years in the Ebro depression (NE Spain) and their paleoenvironmental interpretation

Most studies on the geomorphological evolution of the Holocene from the Ebro depression (NE Spain) are focused on the period up to the Roman Epoch (218 BC–476 AD) while some references to medieval (476 AD–15th century) deposits are also occasionally dated. This paper focuses on the establishment of aggradation units on the valley bottoms and slopes of the Ebro depression after 1400 BP, their origin, comparison with other areas, and relationship with global paleoenvironmental changes. These units were produced after the incision phase that marked the end of the large Holocene accumulation (unit H1) around 1400 BP (at the end of the Late Roman Epoch). Morphosedimentary records enable us to establish three aggradation units during the last 1400 years: unit H2 ( ca. 1400–650 cal BP); unit H3 – with two H3A subunits ( ca. 650–500 cal BP) and H3B ( ca. 500–320 cal BP); and the H4 unit (after 320 cal BP). These units are organized following five types of aggradation/incision arrangements with differing complexities. There are also connections among these units and two slope stages in the region. Finally, the genetic relationships between these units and global paleoenvironmental changes are shown (LALIA, MCA, and LIA) and related to anthropic activity. This contribution is the first detailed and systematic approach to the study of morphosedimentary units and sedimentary arrangements during the Recent Holocene in the Mediterranean area.

Taphonomic feedback, paleoecology, and ostracod biostratigraphy of the Oligocene-Miocene carbonate deposits in the onshore Pará-Maranhão Basin, Northern Brazil

The Oligocene-Miocene carbonates of the Bragantina Platform are represented by densely fossiliferous rocks, which overlay the basement of the Northern Brazilian coast. Outcrop-based stratigraphy analysis combined with petrography, taphonomy, paleoecology, and ostracod biostratigraphy was carried out in the eight (8) m-thick of the Neogene mixed carbonate-siliciclastic succession exposed mainly in the Atalaia Beach. This outcrop is the classical exposure of the Pirabas Formation, generally overlaid by the siliciclastic deposits of the middle Miocene Barreiras Formation. The taphonomic signature in the last carbonate beds of this sedimentary succession indicates intense storms as autogenic processes succeeded by rapid allogenic burial by Barreiras’ deposits. These processes caused death, disarticulation, and accumulation of the benthic communities in the shallow platform, forming a coquina substrate (Taphofacies 1). During a low-energy period, shell-gravel-dwelling individuals represented mainly by Turbinella tuberculata and Mercenaria prototypa colonized this carbonate hardground (Taphofacies 2). Forced regression of Barreiras’ siliciclastics caused a fast shift of continental facies over coastal carbonate zones. The rapid burial culminated in the death of benthic communities creating a geochemical environment propitious for the pyritization of shells, leaves, and trunks (Taphofacies 3). The ostracod biozonation formed by the Cytherella stainforthi biozone and by the Quadracythere brachypygaia, Jugosocythereis pannosa, and Neocaudites macertus sub-biozones support the paleoenvironmental interpretation, chronocorrelation with the Caribbean units and confirm the Miocene age for this carbonate succession. Although taphonomic, paleoecologic, and biostratigraphic studies were carried out in a unique occurrence of the Pirabas Formation. These high-resolution stratigraphy analysis allowed the discovery of the details of this burial event that led to the shutdown of carbonate fabric on the Eastern Amazon Coast.

Pollen and spores morphology from the Holocene of the Iberá Wetlands in northeastern Argentina

Background and aims: Taxonomic works of the modern pollen grains from the vegetation of the Iberá Wetlands from northeastern Argentina, and other areas of the Corrientes province, have mostly been carried out in last decade. However, very few of these taxonomic works include illustration of palynomorphs. The objective of this contribution is to provide the first morphological records of palynomorphs of angiosperms, ferns, lycophytes and bryophytes from sediments from the Holocene of the Iberá Wetlands. M&M: Core samples obtained by mean of a Livingston-type sampler from six lakes in their central and deepest parts on the western margin of the Iberá Wetlands were analyzed. Results: Fifty-five types of palynomorphs are described and illustrated: 46 pollen types correspond to 27 families of angiosperms and nine trilete spore-types to ferns, lycophytes and bryophytes. Information to differentiate local (species that form part of the natural vegetation of the Iberá Wetlands) and extra-local taxa (those that do not belong to the Iberá), that achieved to depocenters mostly by means of wind currents coming from farther regional vegetation, was included. Conclusions: Pollen grains and spores identifications up to species level enhances paleoenvironmental reconstructions based on more accurate ecologic information and geographical distribution. This work broadens the knowledge of the palynological flora of northeastern Argentina and it will contribute to differentiate the local vegetation from the extra-local in future paleocological and paleoenvironmental interpretations.

Stratigraphic and paleoenvironmental interpretation of the larger benthic foraminifera assemblages and stable isotope analysis from the middle Eocene of Cappadocia, Turkey

This study investigates the changes in paleoenvironmental conditions in the northern branches of the Neo-Tethys by employing geochemical proxies and shell data of larger benthic foraminifera (LBF) located in central Cappadocia. Three measured stratigraphic sections are studied from the Altipinar Formation (Boztepe Member), which is dated as middle Eocene. Three genera and five species were recorded as a result of the paleontological analyses, namely, Alveolina sp., Assilina exponens, Nummulites aturicus, Nummulites maximus and Nummulites perforatus. Composed of clayey sandy limestones, the Boztepe Member is represented by SBZ (Shallow Benthic Zones) 16-17 (late Lutetian/early Bartonian). In the Cappadocia region, a warming event was characterized by a temperature increase of 3 degrees C to 4.5 degrees C, and the warming started after 41.0 Ma (younger than the Lutetian /Bartonian boundary). The peak warming occurred around 40.0 Ma (early Bartonian). This period corresponds to the Middle Eocene Climatic Optimum (MECO), which was a significant global warming event. The findings of this study are confirmed by numerous studies that the global warming event occurred in the middle Eocene (between 41.8 and 39.7 Ma.). Additionally, while paleoenvironmental changes had no effect on the shell shape of Assilina exponens, they had a significant effect on the shell shape of Nummulites perforatus. The diameter/thickness ratio of benthic foraminifera tends to be smaller in shallow conditions than in deep conditions. This was observed as their shell shapes became more spherical.

The upper Hauterivian–Barremian (Lower Cretaceous) Arrifes section (Algarve Basin, Southern Portugal): A palynostratigraphic and palaeoenvironmental approach

Integrated sedimentological, palynological, and palynofacies analyses of the Arrifes section in the central Algarve Basin (southern Portugal) provided new information on the age and environments of this Lower Cretaceous sequence. The sedimentary succession at the Arrifes section consists of fossiliferous interbedded limestones, marly limestones, and marls, dated as latest Hauterivian to late Barremian age (Lower Cretaceous) based on key dinoflagellate taxa. During this interval, the Arrifes area records climatic shifts and, multiple sea-level fluctuations; overall deposition was in shallow subtidal to intertidal settings, with deposition of carbonate and marly sediments. During the latest Hauterivian to earliest Barremian interval, an evident sea-level fall culminated in the subaerial exposure of the local carbonate ramp with increased influx of clastic sediments. However, during the Barremian, both sedimentological and palynological analyses suggest an overall deepening of the water depth towards the top of the section. These overall increase in the water column are confirmed by oscillation of terrestrial/marine palynomorph groups and supported by dinosaur track levels at the top of the succession; the latter indicate that sedimentation occurred in intertidal to subtidal environments. Finally, an attempt was made to correlate the Arrifes section with other sections from the Algarve Basin, as well as with broader region. These new data suggest a setting in the Tethyan basin influenced during the latest Hauterivian to the end of the Barremian. These new data allow local correlations and new palynological ages and paleoenvironmental interpretations for the Lower Cretaceous succession of the Algarve Basin.

Source-rock potential and paleoenvironment of the Coniacian Numanha Formation, northeastern Nigeria: An integrated palynofacies and geochemical approach

A study of source-rock characterization and paleoenvironmental interpretation has been carried out on a relatively thick Coniacian sedimentary succession from the Numanha Formation in the Guyuk area of the Yola arm in the Northern Benue Trough, northeastern Nigeria. The aim is to provide organic facies data for the assessment of its hydrocarbon generating potential owing to the high prospects of its lateral equivalent Fika Shale in the Gongola arm of the Northern Benue Trough. The investigation of 98 samples from three outcrop sections [09° 50′ N, 11° 51′ E; 09° 54′ N, 11° 50′ E; 09° 54′ N, 11° 49′ E] which includes palynofacies analysis, spore/pollen coloration, and geochemical analyses enabled an evaluation of organic matter richness and quality. Measured TOC ranges between 0.01 and 7.4% which reflects poor to good organic richness, while visual kerogen characterization shows thermally mature Type II-III kerogen indicative of oil and gas prone materials. Recovered palynomorphs comprised both marine (dinoflagellate cysts, microforaminiferal test linings) and terrestrial (spores, pollen, freshwater alga Pediastrum) taxa. These palynomorphs vary in proportion at different horizons of the sections indicating shoreline fluctuations. Except for the Kurnyi section, amorphous organic matter occurs in minor percentages, indicating low preservation potential during deposition. All data indicate that the Numanha Formation was deposited in a highly proximal to mud-dominated oxic shelf environment.

Paleoenvironmental interpretation of the Late Triassic Norian – Rhaetian boundary interval in the Whitehorse Trough (Stikine Terrane, northern Canadian Cordillera)

The Norian – Rhaetian boundary (NRB) is associated with significant faunal turnover in a wide variety of groups. Following the relative stability of the Norian Stage, this boundary potentially marks the beginning of a protracted and continuous episode of elevated extinction rates, which culminated with the end-Triassic mass extinction. Despite the importance of the NRB to paleontological trends in the Late Triassic, much about this event remains enigmatic, including potential causal mechanisms as well as the characteristics of the resulting paleoenvironmental changes. Fossiliferous limestone of the Sinwa Formation occurs in extensive outcrops throughout northwestern British Columbia and provides an exceptional record of Upper Triassic stratigraphy that represents a paleogeographic region largely uninvestigated prior. The present study integrates lithostratigraphic, paleontological, and geochemical data to reconstruct the shallow marine paleoenvironments recorded by the Sinwa Formation in two sections on Mount Sinwa, south of Atlin, within the Stikine Terrane. The progression of lithological facies observed in these sections suggests a gradual base level rise throughout the late Norian. Following this steady facies progression is a prominent shift from coral reef boundstone to shale near the top of both sections. This facies change approximately coincides with the NRB interval as evidenced by the first occurrence of the latest Norian – Rhaetian conodont species Mockina mosheri morphotype B, as well as by Re – Os isochron ages of organic-rich limestone. Although the base level rise observed at the NRB interval could be due to regional tectonics, it could also potentially be recording eustatic sea level rise given the lack of consensus around sea level change at the NRB. Measurements of late Norian 87Sr/86Sr ratios on Mount Sinwa are consistent with those recorded in Tethyan studies, but the Panthalassan record overall does not replicate the same drop across the NRB observed in the Tethys. The lithological facies shift is also immediately preceded by a negative excursion in the δ13C values of carbonate, indicating that the NRB interval on Mount Sinwa is associated with coral reef collapse as well as the globally observed disruption of carbon cycling.

Biostratigraphy and paleoenvironment correlation based on benthic foraminifera from the cenozoic Marajó and Pirabas formations, Eastern Amazon Coast, Brazil

The Oligocene-Miocene foraminifera biostratigraphy correlation has been applied successfully as a geological tool for establishing the paleoenvironmental conditions during the deposition of siliciclastic and carbonate strata in the Eastern Amazon coastal basins. In this region, previously interpreted tectonic compartments represented by the Marajó Basin and Bragantina Platform were the main sites of siliciclastic and carbonate sedimentation influenced by Late Paleogene-Neogene transgressive–regressive events. In the subsident Marajó basin, a siliciclastic estuary was developed, supplied by the Cratonic Amazon River. The transcontinental river did not influence the Bragantina region to the East, allowing the implantation of a shallow carbonate platform. These Neogene segments require further sedimentological, stratigraphic, and paleontological studies to define these limits. The use of foraminifera content has been considered an important tool to assist in this differentiation, providing a paleoenvironmental and paleoecological reconstruction model. This work used qualitative and quantitative analyses integrating several diversity indices, complementing the R-mode cluster and the correlation of planktonic and benthic (P/B) ratios. The similarity in faunal diversity indicated that these siliciclastic and carbonate units represented by the Marajó and Pirabas formations are chronocorrelated. Marajó Formation is interpreted as a restricted, suboxic, marginal marine environment (lagoons/mangroves) with variable salinity and abundance of the species as Cribroelphidium williamsoni, Ammonia tepida, and A. beccari. In contrast, the Pirabas Formation was deposited in a brackish, oxic, and carbonate platform characterized by Cibicidoides subhaidingerii, Cibicides pachyderma A. beccarii, and Cassidulina laevigata species. These foraminifera assemblages confirm the previous stratigraphic and paleoenvironmental interpretations providing new insights into understanding the Late Paleogene-Neogene evolution of the Eastern Amazonia Coast.

Multiple sulfur isotope systematics of pyrite for tracing sulfate-driven anaerobic oxidation of methane

Sulfate-driven anaerobic oxidation of methane (SD-AOM) is ubiquitous in marine sedimentary environments, governing the global methane budget and the redox evolution of Earth's surface. Tracing SD-AOM and organoclastic sulfate reduction (OSR) from the pyrite archive is key to the reconstruction of SD-AOM activity and paleoenvironmental interpretation. However, discriminating the origins of pyrite – basically SD-AOM and OSR – is commonly challenging due to frequent overlap of δ34Spy values. Multiple sulfur isotopes of pyrite are expected to be an effective tool to distinguish between OSR and SD-AOM, yet variable uncertainties and unknowns remain. Here we investigated the δ34S and Δ33S values of pore-water sulfate and authigenic pyrite from a piston core taken on the continental slope of the South China Sea. A positive Δ33S - δ34S correlation of pore-water sulfate is observed in the upper OSR-dominated zone, resulting in Δ33S and δ34S values of sulfate diffusing into the sulfate-methane transition zone (SMTZ) >0.1‰ and >30‰ larger than the corresponding values of seawater sulfate. A negative Δ33S - δ34S trajectory of pore-water sulfate and pyrite is observed for the SMTZ, agreeing with low sulfur isotope fractionation characteristic for SD-AOM and a diagnostic large Δ33S - δ34S field of SD-AOM-derived pyrite. These findings elucidate that the multiple sulfur isotope systematics of pyrite in methane-bearing sediment depends on (1) mass transport effects of dissolved sulfate and sulfide, (2) the relative contribution of OSR and SD-AOM to the pore-water sulfide and pyrite pools, and (3) the sulfur isotope fractionation during microbial sulfate reduction. Our study highlights the importance of mass transport dynamics on the isotopic composition of pyrite, a factor that needs to be considered in any attempt to reconstruct the origin of early diagenetic pyrite and the paleoenvironmental setting with multiple sulfur isotopes.

Comment on Souza and Perez Filho (2019) “Late Holocene coastal dynamics, climate pulses and low terraces in the coast of the state of São Paulo, southeast Brazil”

Souza and Perez Filho (2019) inferred two transgressive events in the Late Holocene record of lower Ribeira de Iguape River and Ilha Comprida barrier, Southeastern Brazil, based on luminescence ages and paleoenvironmental interpretation of four columnar sections. In the present paper, we discuss inconsistencies on the methods applied and sample design adopted by those authors, which lead to an incorrect model of coastline evolution for the region over the time period covered by the dates obtained. The dataset presented by Souza and Perez Filho (2019) allows the reinterpretation of the deposits studied as regressive and fits into previous models of regional coastal evolution.

Genesis and soil environmental implications of intact in-situ rhizoliths in dunes of the Badain Jaran Desert, northwestern China

Desert rhizoliths are generally found as weathered, broken and scattered samples on dune field surface, but rarely in-situ in their initial states buried under the soil of desert in the Badain Jaran Desert, northwest China. This study offers an assessment of the morphological, mineralogical, and chemical properties of intact and in-situ rhizoliths found in soils of swales and depressions among dune chains. The characteristics of these rare and precious objects were assessed using optical polarizing microscopy, cathodoluminescence, scanning electronic microscopy, radiocarbon dating, and stable isotopic analyses, providing the opportunity for discussion of the rhizolith formation mechanisms and associated environmental conditions. Field and laboratory investigations showed that the in-situ intact rhizoliths were formed only in the places where Artemisia shrubs are living, and the remaining root relicts within rhizoliths belong to this species. The spatial distribution of rhizoliths also suggested that low topographic positions on a landscape provided soil moisture, and redox environments favored rhizolith formation. A semi-closed redox environment in the subsoil at swales and depressions, where water is always present, along with the sandy soil texture, facilitated fast water percolation to deeper depths and condensation. Such a soil environment not only provides water for Artemisia growth, but also for the weathering of minerals such as felspars and calcite from primary carbonates, and for the decomposition of root relicts. Furthermore, harsh climatic conditions, such as strong winds and solar radiation, led to water evaporation through dead root channels and triggered the calcification along the root relicts. The entrapped lithogenic carbonates and to a lesser extent the decomposition of Artemisia roots provided the carbon sources for the rhizoliths formation, while the weathering of soil minerals, particularly feldspars and carbonates, was the main source of Ca. Rhizoliths in the Badain Jaran desert formed relatively quickly, probably over a few soil drying episodes. This led to the entrapment of a large quantity of lithogenic carbonates (more than 90% of carbon) within rhizolith cement. The re-dissolution of the entrapped lithogenic carbonates in rhizolith tubes should be taken into account in the paleoenvironmental interpretation of 14C ages, the latter suggesting that rhizoliths formed during the Holocene (~ 2053 years cal BP, based on root organic relicts).