Marine Paleoenvironments Research Articles

Sedimentary molybdenum and uranium cycling under seasonally contrasting redox conditions on the Namibian Shelf

Sedimentary molybdenum (Mo) and uranium (U) enrichments have been widely used as a proxy for redox conditions in oxygen-depleted marine paleo-environments. However, in a dynamic upwelling system the seasonal fluctuations from oxic to completely anoxic-sulfidic bottom waters and lateral sediment transport can modify the primary Mo and U signal of the sediment, which in turn may impact paleo-redox interpretations. In this study we present pore water and solid phase data collected at two cross shelf transects during the ‘more oxygenated’ austral winter and ‘anoxic’ austral summer to study the influence of spatially and seasonally contrasting redox conditions on the formation of authigenic Mo and U enrichments in organic carbon (TOC) rich mud belt sediments on the Namibian shelf. A mass balance was established for each element based on diffusive fluxes and element mass accumulation rates to evaluate the respective mechanisms of trace metal delivery, accumulation and recycling.Mo is delivered to the sediment in its dissolved form via diffusion across the sediment–water interface, especially during austral summer when bottom waters are anoxic and surface sediments are highly sulfidic. In the center of the inner shelf mud belt, the benthic Mo fluxes of up to 37 nmol cm−2 yr−1 into sulfidic surface sediments are the highest ever reported for reducing sulfidic systems and agree with the rate of Mo accumulation in the solid phase. Concurrently, high sedimentation rates and low terrigenous input limit solid phase Mo accumulation on the Namibian shelf. In ancient marine sediments, this mode of Mo cycling can be identified by low Mo/TOC ratios of ∼2 similar to those found in sediments deposited below the perennial oxygen minimum zone on the Peruvian shelf and to those found in deposits of the Cretaceous Oceanic Anoxic Event 2. Diffusive U fluxes into the sediment are generally too low to account for the sedimentary enrichment leading to the conclusion that U is delivered mainly in particulate form. In areas with anoxic bottom water, shallow dissolved U maxima directly below the sediment water interface and rather low sedimentary U content indicate that particulate U is recycled and largely released back into the bottom water. At sites where bottom water oxygen concentrations vary from anoxic to completely oxic on seasonal timescales, the depth at which Mo and U are removed from pore waters moves vertically within the sediment column thus defining a layer between the sediment surface and ∼20 cm depth, in which Mo and U accumulate in the solid phase. Our results emphasize the importance of short-term redox fluctuations in the bottom waters and underlying sediments, as well as lateral sediment transport for the authigenic enrichment of redox-sensitive trace metals in reducing shelf sediments. The relative enrichment patterns identified might be useful for the reconstruction of open marine anoxia in the geological past.

SIMPLE STRUCTURES AND COMPLEX STORIES: POTENTIAL MICROBIALLY INDUCED SEDIMENTARY STRUCTURES IN THE EDIACARAN SERRA DE SANTA HELENA FORMATION, BAMBUÍ GROUP, EASTERN BRAZIL

ABSTRACT Microbially induced sedimentary structures (MISS) are abundant in Ediacaran and lower Cambrian successions. However, the relationship between MISS distribution and facies has not been thoroughly explored in Ediacaran–Cambrian successions in South America. This study documents the occurrence of MISS and other potential biogenic structures from the late Ediacaran Serra de Santa Helena Formation in the Bambuí Group of eastern Brazil. This unit overlies the Cloudina-bearing Sete Lagoas Formation and is a mixed carbonate-siliciclastic succession devoid of macroscopic body fossils. Potential microbial structures include wrinkled structures such as “elephant-skin” and Kinneyia-like textures, as well as pustular structures and abundant positive epirelief discoidal structures. Another putative biogenic structure is a mm-wide meandering groove resembling a simple locomotion trail of a small vagile benthic metazoan. Microbial surface textures (i.e., “elephant skin” and Kinneyia-type wrinkles) were mainly observed in heterolithic deposits, usually at the interface between sandstone and siltstone/shale. On the other hand, discs show a facies-independent distribution, observed in heterolithic as well as carbonate and marl deposits. Petrographic analyses of these discs suggest that they have complex origins and some of them may be diagenetic structures. Thus, while facies may have strongly controlled the preservation of MISS-related structures and textures in the Serra de Santa Helena Formation, their abundance and diversity in tidal flat deposits indicate the wide distribution of matgrounds in these shallow marine paleoenvironments. Also, we demonstrate how detailed description and classification of simple features, such as discoidal structures, is an important task for paleoenvironmental reconstruction of marine ecosystems at the Ediacaran–Cambrian transition when the microbially bounded substrates played important roles in the dynamics of coastal environments.

Late Miocene biostratigraphy and paleoenvironment of the Sais Basin (southern Rifian Corridor, Morocco): New insights from the Moulay Yakoub area

During the Late Miocene, the Rifian Corridor was one of the two main corridors allowing exchanges between the Atlantic and the Mediterranean Seas. Sedimentary records accumulated along this corridor and specifically, in the Sais Basin, constitute case-study material for understanding the impact of the South Rifian Corridor on the evolution of the fauna, phytoplankton and environment during the Late Miocene. In order to reconstruct the evolution of marine paleoenvironments in the Moulay Yakoub region and to compare this evolution with other areas of the Sais basin, we conducted an integrated biostratigraphic and palynological study of the Upper Miocene of borehole KA 102. High-resolution biostratigraphy based on planktonic foraminifera revised and defined the chronostratigraphic framework of the Upper Miocene sedimentary series of the Moulay Yakoub region providing an age of 7.8 Ma to 6.52 Ma (Late Tortonian to Early Messinian). In the Late Tortonian, the planktonic foraminiferal assemblages suggest an open and relatively deep marine environment. At the Tortonian/Messinian boundary, planktonic foraminiferal and dinoflagellate associations, as well as distal indices, suggest a relatively deep and neritic distal marine environment with a decrease in diversity and an increase in reworked taxa. Surface waters are warm with a minor cooling trend observed just below this boundary. In comparison to previously studied sections in the Sais Basin, the Lower Messinian is characterized by a deeper and more distal marine environment. However, proximal trends and warm surface water conditions persisted in all studied areas from the basin during this period.

A new pelican (Aves: Pelecanidae) from the Upper Miocene of Argentina: new clues about the origin of the New World lineages

ABSTRACT Pelecanus paranensis sp. nov., a new pelican (Aves, Pelecanidae) from the marine Upper Miocene Paraná Formation, which crops out in the Province of Entre Ríos, Argentina, is described. This record constitutes the first report of a fossil pelican from Argentina and the southernmost from South America. The holotypical specimen consists of a very large and nearly complete pelvis, which is characterized by having the cristae iliacae dorsales continuous throughout its entire length and a large foramen acetabuli. The U-shaped morphology of the postacetabular section of the pelvis of the new species as well as the wide incisura sutura iliosynsacralis, allow to infer its phylogenetic position within the New World pelican species clade, showing a close relationship with the clade (P. occidentalis + P. thagus). A probable trans-Atlantic dispersal route for the ancestor of the New World pelicans is thus inferred. The inland Paranaense Sea, which flooded the South American Chaco-Paraná basin during the mid-Neogene, is proposed as a south-north pathway for ancestral forms of the clade (P. occidentalis + P. thagus). These regressive marine paleoenvironments of the Late Miocene may have acted as the evolutionary driver for the transition of pelican species from brackish or freshwater habitats to those inhabiting strictly marine coastlines.

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.

Marine mammals fossil remains and synthesis of the sedimentary and paleontological record of the Furninha Cave Pleistocene (Peniche, Portugal)

The Gruta da Furninha is a cave-site in Lower Jurassic limestones, of mainly marine genesis located at ~850 m SE of the Carvoeiro Cape, on the southern coast of the Peniche peninsula (central western mainland Portugal). The entrance gallery, situated in the middle of the cliff, is at ~15 m of altitude. This cave contained a rich and diverse fossiliferous set of Late Pleistocene vertebrates, distributed in several stratigraphic levels, currently housed at the Geological Museum of LNEG (Lisbon). The cave had a record of primitive human occupations documented by 106 Middle to Late Paleolithic artefacts, found in the lower lithostratigraphic unit (Pleistocene). It had also another human occupation in an upper unit (Neolithic, Holocene), where were found human skeleton elements and artefacts. This study focuses on two teeth previously identified as crocodile, housed in collections of the Geological Museum in the assemblages of the Furninha Cave and on a set of five bones, housed at Centro Português de Geo-História e Pré-História (CPGP) collected in a marine terrace in the Furninha cliff. The occurrence of crocodile remains in the Upper Pleistocene of Portugal is not consistent with the fossil record of this period or with the environmental conditions associated with the fully marine paleoenvironments around Furninha Cave. A more detailed analysis of these teeth and their stratigraphic location, now supports that they are cetacean teeth with ~80 ka, which is consistent with the fossil association, depositional environments and climate conditions of the Late Pleistocene in mainland Portugal. To add to these two teeth, in 2017 in sedimentary field work in the marine terraces on the cliffs of the Gruta da Furninha, at the level of 4 to 7 m, found five bones remains, which could be carpal bones of marine mammals.

Preservation and Taphonomy of Fossil Insects from the Earliest Eocene of Denmark.

Simple SummaryInsect fossils dating 55 million-years-old from the Stolleklint Clay and Fur Formation of Denmark are known to preserve both fine morphological details and color patterns. To enhance our understanding on how such fragile animals are retained in the fossil record, we examined a pair of beetle elytra, a wasp and a damselfly using sensitive analytical techniques. In our paper, we demonstrate that all three insect fossils are composed of cuticular remains (that is, traces of the exoskeleton) that, in turn, are dominated by the natural pigment eumelanin. In addition, the beetle elytra show evidence of a delicate lamellar structure comparable to multilayered reflectors that produce metallic hues in modern insects. Our results contribute to improved knowledge on the process of fossilization of insect body fossils in marine environments.Marine sediments of the lowermost Eocene Stolleklint Clay and Fur Formation of north-western Denmark have yielded abundant well-preserved insects. However, despite a long history of research, in-depth information pertaining to preservational modes and taphonomic pathways of these exceptional animal fossils remains scarce. In this paper, we use a combination of scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to assess the ultrastructural and molecular composition of three insect fossils: a wasp (Hymenoptera), a damselfly (Odonata) and a pair of beetle elytra (Coleoptera). Our analyses show that all specimens are preserved as organic remnants that originate from the exoskeleton, with the elytra displaying a greater level of morphological fidelity than the other fossils. TEM analysis of the elytra revealed minute features, including a multilayered epicuticle comparable to those nanostructures that generate metallic colors in modern insects. Additionally, ToF-SIMS analyses provided spectral evidence for chemical residues of the pigment eumelanin as part of the cuticular remains. To the best of our knowledge, this is the first occasion where both structural colors and chemical traces of an endogenous pigment have been documented in a single fossil specimen. Overall, our results provide novel insights into the nature of insect body fossils and additionally shed light on exceptionally preserved terrestrial insect faunas found in marine paleoenvironments.

Graphic correlation and paleoenvironmental investigation of the upper Eocene–lower Oligocene sediments in the Dahomey Basin, southwestern Nigeria: insights from palynomorphs

This study presents the results of a comprehensive qualitative and quantitative palynological analysis of four shallow boreholes (Epe-1, Olokonla-1, Ikoyi-1 and Badore-1) in the lower Eocene–upper Oligocene periods of the Dahomey Basin, southwestern Nigeria. The lithostratigraphic analysis revealed three lithologies (sandy-shales, shaly-sands and sandstones). Two most important palynological zones, the Verrucatosporites usmensis, as well as the Magnastriatites howardi Pan-tropical zones, are delineated. First Appearance Datum (FAD) of Achomosphaera alcicornu marked the late Eocene–early Oligocene boundaries (E/O) within the four boreholes, while FAD of Adnatosphaeridium multispinosum defined the late Eocene–early Oligocene boundary (E/O) in Ikoy-1. Two informal palynological assemblage zones were revealed in the four boreholes. Common occurrences of palms, mangrove, fresh water and brackish water pollen, and pteridophyte spores with spots records of marine elements and algae species during marine invasion suggested fluctuation from fluvio-deltaic/nearshore to marginal marine paleoenvironments. Graphic correlation discloses that for every meter of sedimentary rock accretion within Epe-1, equally amounted to merely 0.31 m, 0.56 m, as well as 0.47 m of sediments, which were put down in Olokonla-1, Ikoyi-1, as well as Badore-1, respectively. These comparative rates of sedimentary rock accretion show with the purpose of either there is fewer attrition occurrence and/or extra accommodation gap within Epe-1 than Olokonla-1, Ikoyi-1, as well as Badore-1. The assessment of the slopes, intercept and correlation equations through graphic correlation procedures enable the identification of four biostratigraphic events in Epe-1, Olokonla-1, Ikoyi-1, as well as Badore-1. The findings in this investigation are necessary for depositional succession and paleoenvironmental understandings, as well as basin investigation, and above all, to show a relationship of broadly separated boreholes.

Picking out the warp and weft of the Ediacaran seafloor: Paleoenvironment and paleoecology of an Ediacara textured organic surface

The Ediacara Biota, Earth’s earliest ecosystems of complex, macroscopic, multicellular organisms, is preserved in terminal Ediacaran strata worldwide. In the Ediacara Member of South Australia, Ediacara fossil assemblages occur in intimate association with macroscopic, iterative organosedimentary structures, known as “textured organic surfaces” (TOS). These widespread surfaces encompass considerable variability in size and complexity and likely included densely aggregated eukaryotic macroorganisms as well as microbial consortia. The presence of a heterogeneous organic substrate appears to have strongly influenced the ecology of Ediacara benthic ecosystems, and to have fostered the emergence of complex animal-style ecological strategies. Organic substrates may have additionally played an important role in the fossilization of these communities. Systematic sedimentary and paleoecological analysis of approximately 300 square meters of reconstructed fossiliferous bedding planes at Nilpena Ediacara National Park indicates that the distribution of both particular macrofossil taxa and particular TOS appears to be facies-specific. The TOS “weave” exemplifies this facies specificity, and occurs only along rippled sandstone event beds in the Oscillation-Rippled Sandstone Facies. Detailed characterization of the morphology, spatial distribution and sedimentology of weave, as well as distinctive associations with body and trace fossil assemblages, suggest that this TOS is strongly linked to hydrodynamic disturbance. Weave assemblages may therefore provide unique insights into not only Ediacara matground communities but also the local environmental conditions that shaped the ecology and fossilization of Ediacara assemblages. More broadly, the abundance, diversity and facies specificity of TOS suggest that these structures can be used to gauge whether paleoenvironmental and taphonomic conditions favorable for colonization by and preservation of Ediacara macroorganisms were present across a wide range of shallow marine paleoenvironments. TOS may therefore provide a means of constraining whether the absence of Ediacara-type taxa from either older or younger strata is evolutionarily meaningful, and for reconstructing the evolutionary ecology of the Ediacaran-Cambrian transition.

The trace fossil gyrochorte: ethology and paleoecology

Specimens of the trace fossil Gyrochorte from the Ordovician, Jurassic and Cretaceous of Utah, and the Pliocene of Spain are described. These occurrences expand the stratigraphic range of the ichnogenus, and allow for a re­examination of this paleoenvironmentally sensitive and puzzling trace fossil. The recognition of the penetrative characteristic of the trace is essential for a correct identification, as some trace fossils have been erroneously ascribed to Gyrochorte in the past. The producer must have been a detritus-feeding worm-like animal, probably an annelid, that created a bilobed, vertically penetrating and sometimes plaited meandering trace. Gyrochorte typically occurs in sandy facies in moderately energetic nearshore and shallow marine paleoenvironments in association with other trace fossils, usually pascichnia and fodinichnia

Sedimentology and Calcareous Nannofossil Biostratigraphy of Alaka Well, Niger Delta, Nigeria

Calcareous nannofossil biostratigraphy of Alaka well was carried out to identify the biohorizons that exist, ultimately for biozonation, chronostratigraphy and geologic age calibration of the studied interval. The study involved sedimentology analysis, gamma ray description and preparation of two hundred and twelve (212) ditch cuttings, sampled at 9.144m intervals for the study of calcareous nannofossils on smear slides. Sedimentology and gamma ray analyse showed deposition within shallow marine paleoenvironments with alternating minor transgressions in a generally progradational delta setting, accounting for the low calcareous nannofossil occurrences. The calcareous nannofossil assemblages recovered from the slide preparations consist of fourteen (14) species, comprising nine (9) long ranged, non-stratigraphic significant forms and five (5) short ranged stratigraphic significant forms. The biohorizons identified included Base (B) occurrence of Catinaster coalitus at 3578m; Discoaster hamatus at 2874m; Top (T) occurrence of Discoaster hamatus at 2518m and Base absence (Ba) of Reticulofenestra pseudoumbilicus at 2280m. Other biohorizons included Top occurrence (T) of Discoaster bollii at 2435m and Discoaster deflandrei at 3578m respectively. The biohorizons defined boundaries between biozones and showed that the studied interval penetrated four biozones from CNM11 to CNM14 of Backman et al. (2012), NN7 to NN10 of Martini (1971) and CN5b to CN8a of Okada and Bukry (1980). The geologic age of the studied interval ranged between about 11.60 Ma within CNM11/NN7/CN5b zone to about 8.80 Ma within CNM14/NN10/CN8a zone, the standard chronostratigraphy lies within Tortonian stage. Two chronostratigraphic surfaces were mapped in the studied section and comprised one global maximum transgression at 3514m corresponding to 10.5 Ma maximum flooding event, and one localized maximum transgression at 2847m corresponding to 9.5 Ma maximum flooding surface, separated by sea-level lowstand mapped at 3331m and corresponding to 10.35 Ma.

Palinostratigraphy and Paleoenvironments in the Gorodishchi Section (Middle Volga River Region, Kimmeridgian–Hauterivian)

Abstract —Eight dinocyst-based and three spore- and pollen-based biostratigraphic units are defined in the Kimmeridgian, Volgian, and Hauterivian of the Gorodishchi section, based on a biostratigraphic analysis of the successions of marine and terrestrial palynomorphs. Algological assemblages are described in more detail, and additional criteria for the definition of dinocyst zones established by previous researches are given. A more detailed biostratigraphic subdivision of the middle part of the Volgian is proposed. A local dinocyst zone in the Hauterivian and a biostratigraphic succession of spore–pollen units in the entire section are described for the first time. The research results demonstrate that the boundaries of many palynostratigraphic units exhibit a considerable correlation potential. Based on a biofacies analysis of the microphytoplankton, the dynamics of transgressive–regressive events is studied in relation to the accompanying oxygen and trophic conditions. Possible relationships between marine paleoenvironments and climatic changes reconstructed on the basis of spore–pol­len data are discussed.

Intratest Variations in Trace Element Composition of Amphistegina lessonii Using Femtosecond‐Laser Ablation‐ICP‐Mass Spectrometry: A Field Study From Akajima, Okinawa Prefecture, Japan

AbstractAmphistegina are common larger benthic foraminifer in coral reefs, with a nearly circumtropical distribution, and are major contributors to the CaCO3 budget of shallow marine environments. The family Amphisteginidae is dominant in Cenozoic carbonates. However, its potential as a proxy for paleoclimate reconstruction has not been completely explored. The intratest variability in trace elements of Amphistegina lessonii has been investigated using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry (fs‐LA‐ICP‐MS). We collected and analyzed adult specimens of A. lessonii in September 2003, November 2003, January 2004, and March 2004, from ∼2 m water depth in the coral reefs of Akajima, Okinawa, Japan. Tests of A. lessonii from these four collections were analyzed for Mg/Ca of the septa to observe Test Size‐Lifespan relationships. The lifespan of a specimen of A. lessonii of 1,200 µm in diameter is estimated at ∼3 and ∼2 months for specimens 900 µm in size. Over the estimated lifespans, Mg/Ca of individual specimens of A. lessonii is highly variable and displays co‐variation with temperature and tidal heights. Future projects may apply and further test this approach for the reconstruction of the tropical shallow marine paleoenvironments.

Mineralogy and geochemistry of deeply-buried marine sediments of the Vaca Muerta-Quintuco system in the Neuquén Basin (Chacay Melehue section), Argentina: Paleoclimatic and paleoenvironmental implications for the global Tithonian-Valanginian reconstructions

The Vaca Muerta-Quintuco (VM-Q) system of Tithonian-early Valanginian age was studied in the Chacay Melehue section of the Neuquén Basin (western Argentina) by means of sedimentological, mineralogical and geochemical analyses in order to determine the main driving factors that triggered the paleoenvironmental change from a carbonate ramp (Vaca Muerta Formation, VMFm) to a mixed siliciclastic/carbonatic marine environment (Quintuco Formation, QFm). The VMFm was divided into two stratigraphic intervals: Lower VMFm (LVMFm) and Upper VMFm (UVMFm), whereas the QFm is subdivided into the Puesto Barros Member (PBMb) and the Cerro La Visera Member (CVMb), which can be correlated to other sections in the basin (e.g., Puerta Curaco). Isolated, turbiditic sandstone beds, correlated to the Huncal Member, are included in the QFm.The LVMFm (Tithonian) and the UVMFm (Berriasian) are constituted by dark, well-laminated marls, mudstones, calcite concretions and tuffs. The PBMb (earlier early Valanginian) is constituted by marls and sandstones, whereas the CVMb (later early Valanginian) is constituted by marls, mudstones, siltstones, sandstones and coquinas. The LVMFm (Total organic carbon, TOC ~ 1–4 wt%) is characterized by the enrichment of redox sensitive trace elements (RSTE), where the enrichment of Ni and Cu suggest high productivity in the water column, and the enrichment of Mo, U, V points to sea bottom anoxia, with periods of increased oxygenation as deduced from higher P concentrations in marls and mudstones. The clay mineral association is constituted by mixed-layer illite/smectite formed by the transformation of smectitic layers. The predominance of smectite in coeval sucessions, less overprinted by burial diagenesis, suggests a temperate and semi-arid climate in the adjacent continent. The UVMFm (TOC ~ >1 wt%) is characterized by a gradual decrease of the RSTE pointing to a decrease in productivity and a slight increase in the oxygenation of the sea bottom. In addition, a change towards more humid conditions in the continent is inferred by both the increase in the Chemical Index of Alteration and the Al2O3/TiO2 ratio. The PBMb (TOC ~1 wt%) has even lower content of RSTE indicating diminished sea water productivity and a gradual rise of the oxygenation of the sea bottom. In this interval, increased illite contents suggest periods of enhanced physical weathering, probably related to the tectonic uplift of the Huincul Ridge. The RSTE in the CVMb (TOC <1 wt%) documents a fully oxygenated sea bottom, where the productivity of the water column was negligible. The presence of kaolinite and the increment of the detrital sedimentation in the CVMb indicate a change towards more humid conditions in the hinterlands. The enhanced runoff caused by this paleoclimatic change towards more humid conditions that started in the early Berriasian and increased during the later early Valanginian triggered the change from carbonate ramp to mixed siliciclastic/carbonatic to siliciclastic marine paleoenvironments. The organic carbon isotope composition (δ13Corg vs. VPDB) of the VMFm ranges between −30.0 and −23.4‰, whereas in the QFm values range between −29.0 and −23.9‰. Two positive carbon isotope excursions (PCIE) are recorded in the system: PCIE-A in the lower part of the VMFm (early Tithonian) with δ13Corg values ~ −25‰, and PCIE-B in the upper part of the QFm (later early Valanginian) with δ13Corg values ~ −24.5‰. The shift in δ13Corg at PCIE-B is up to +4.2‰ and marks the onset of the Weissert Event. This is the first time that the onset of this event is recorded in the Neuquén Basin, within the Lissonia riveroi ammonite zone. The results of our study confirm that clay mineralogy, trace elements and stable isotopes are valuable proxies of past ocean-climate variability even in sediment deposits that underwent near-surface and deep burial diagenesis.

Niche expansion for phototrophic sulfur bacteria at the Proterozoic–Phanerozoic transition

Fossilized carotenoid hydrocarbons provide a window into the physiology and biochemistry of ancient microbial phototrophic communities for which only a sparse and incomplete fossil record exists. However, accurate interpretation of carotenoid-derived biomarkers requires detailed knowledge of the carotenoid inventories of contemporary phototrophs and their physiologies. Here we report two distinct patterns of fossilized C40 diaromatic carotenoids. Phanerozoic marine settings show distributions of diaromatic hydrocarbons dominated by isorenieratane, a biomarker derived from low-light-adapted phototrophic green sulfur bacteria. In contrast, isorenieratane is only a minor constituent within Neoproterozoic marine sediments and Phanerozoic lacustrine paleoenvironments, for which the major compounds detected are renierapurpurane and renieratane, together with some novel C39 and C38 carotenoid degradation products. This latter pattern can be traced to cyanobacteria as shown by analyses of cultured taxa and laboratory simulations of sedimentary diagenesis. The cyanobacterial carotenoid synechoxanthin, and its immediate biosynthetic precursors, contain thermally labile, aromatic carboxylic-acid functional groups, which upon hydrogenation and mild heating yield mixtures of products that closely resemble those found in the Proterozoic fossil record. The Neoproterozoic-Phanerozoic transition in fossil carotenoid patterns likely reflects a step change in the surface sulfur inventory that afforded opportunities for the expansion of phototropic sulfur bacteria in marine ecosystems. Furthermore, this expansion might have also coincided with a major change in physiology. One possibility is that the green sulfur bacteria developed the capacity to oxidize sulfide fully to sulfate, an innovation which would have significantly increased their capacity for photosynthetic carbon fixation.

A unique bacteriohopanetetrol stereoisomer of marine anammox

Anaerobic ammonium oxidation (anammox) is a major process of bioavailable nitrogen removal from marine systems. Previously, a bacteriohopanetetrol (BHT) isomer, with unknown stereochemistry, eluting later than BHT when examined by high performance liquid chromatography (HPLC), was detected in ‘Ca. Scalindua profunda’ and proposed as a biomarker for anammox in marine paleo-environments. However, the utility of this BHT isomer as an anammox biomarker is hindered by the fact that four other, non-anammox, bacteria are also known to produce a late-eluting BHT stereoisomer. The stereochemistry in Acetobacter pasteurianus, Komagataeibacter xylinus and Frankia sp. was known to be 17β, 21β(H), 22R, 32R, 33R, 34R (BHT-34R). The stereochemistry of the late-eluting BHT in Methylocella palustris was unknown. To determine if marine anammox bacteria produce a unique BHT isomer, we studied the BHT distributions and stereochemistry of known BHT isomer producers and of previously unscreened marine (‘Ca. Scalindua brodeae’) and freshwater (‘Ca. Brocadia spp.’) anammox bacteria, using HPLC and gas chromatographiy (GC) analysis of acetylated BHTs and ultra high performance liquid chromatography (UHPLC)-high resolution mass spectrometry (HRMS) analysis of non-acetylated BHTs. The 34R stereochemistry was confirmed for the BHT isomers in Ca. Brocadia sp. and Methylocella palustris. However, ‘Ca. Scalindua spp.’ synthesises a stereochemically distinct BHT isomer, with still unconfirmed stereochemistry (BHT-x). Only GC analysis of acetylated BHT and UHPLC analysis of non-acetylated BHT distinguished between late-eluting BHT isomers. Acetylated BHT-x and BHT-34R co-elute when examined by HPLC. As BHT-x is currently only known to be produced by ‘Ca. Scalindua spp.’, it may be a biomarker for marine anammox.

Expression of Early Cretaceous global anoxic events in Northeastern Brazilian basins

In different basins around the world, organic-rich layers from the Cretaceous are being associated with perturbations in the global carbon cycle that reflect abrupt climatic and oceanic changes responsible for increased anoxia. In the northeastern part of Brazil, organic-rich rocks from the Parnaíba and São Luís basins—deposited during the late Aptian-early Albian and associated with the Codó Formation—offer an interesting stratigraphic record to evaluate the influence of oceanic anoxic events on restricted marine paleoenvironments. Therefore, an integrated study using different geochemical proxies (total organic carbon (TOC), Rock-Eval pyrolysis, δ13Corg, δ15Ntotal, and biomarkers) was conducted on sedimentary sections of the São Luís and Parnaíba basins (Codó Formation), which are assigned to the upper Aptian-lower Albian. The δ13Corg data obtained were compared with the isotopic δ13Corg profile from the section of the Santa Rosa Canyon (Mexico) where the record of the anoxic Aptian-Albian event (oceanic anoxic event 1b) was characterized. The stratigraphic record of the Codó Formation in both the basins presented the C11–C12 Cretaceous isotopic segments with clear 13Corg depletion associated with a spike in TOC that reached 10% at Parnaíba Basin and 15% at São Luís Basin. At Parnaíba Basin, biomarker results showed a high abundance of the terpane gammacerane, suggesting conditions of water-mass stratification and hypersalinity, setting that took place in the southern hemisphere during OAE 1b and enhanced preservation of organic matter in different basins. Also, marine sources were evidenced by the predominance of the C27 ααα(R) sterane and by the identification of the C30 ααα(R) sterane. In addition, the presence of the biomarkers C27 trisnorhopane 17β, C29αβ and C29 ααα (R) sterane reflect the contribution of terrigenous material to organic matter, which is commonly observed during anoxic events due to the acceleration of the hydrological cycle. Nitrogen isotopes revealed a relatively positive value (greater than 3%) which suggests anaerobic reduction of NO3- to N2 under suboxic to anoxic conditions (denitrification). Otherwise, a negative δ15N trend was observed in samples from the negative δ13Corg trend which represented a high organic carbon content. This δ15N signature suggests a decrease in the available NO3- (beginning of exhaustion) and an enhanced level of nitrogen fixation by microbial organisms during the anoxic event, which is also supported by a higher abundance of prokaryotic biomarkers (hopanes) in the organic matter.

A Bird's Eye View: Hesperornithiforms as Environmental Indicators in the Late Cretaceous Western Interior Seaway

Seabirds are considered indicators of ecological hotspots in modern ecosystems because their biogeographic distribution is correlated with physical, chemical, and biological oceanographic factors. Pursuit diving seabirds – those that actively pursue prey underwater – are generally more limited in distribution and more closely tied to oceanographic factors, as diving ability is often gained at the expense of flight capabilities. Today, wing propelled pursuit diving seabirds are restricted to colder waters; foot propelled divers have a broader latitudinal distribution, but do not forage far from shore in marine environments. In comparison, Late Cretaceous Northern Hemisphere seas were host to foot propelled pursuit diving seabirds called hesperornithiforms. Their Western Interior Seaway fossil record, in particular, reflects the broad latitudinal distribution of modern foot propelled divers, but with occurrences of offshore foraging more typical of modern wing propelled divers. The presence of hesperornithiforms in such a wide variety of environments (Boreal, Tethyan, coastal, nearshore, and offshore) suggests different ecological and oceanographic conditions affected biogeographic patterns of Late Cretaceous divers. The purpose of this study is to explore Late Cretaceous hesperornithiform paleobiogeography in light of what is known about how biotic and environmental factors affect modern pursuit diving seabirds to better understand WIS paleoecology.The Late Cretaceous was characterized by greenhouse climate, high sea levels, and epicontinental seas that provided marine paleoenvironments with no modern analogs. Two notable ecological differences between the Late Cretaceous and today are the presence of marine reptiles (and absence of marine mammals) as apex predators and the lack of acanthomorph fish diversity. Spatio-temporal overlap among hesperornithiforms, marine reptiles, and large predatory fishes implies different competition and predator-prey relationships among marine carnivores than today. Differences in swimming capabilities between marine reptiles and marine mammals may partially account for the presence of hesperornithiforms in warm, offshore waters. Additionally, environmental factors relating to the unique paleoceanography of the WIS would have also influenced hesperornithiform populations. Ample shoreline, abundant shallow water habitats, and high primary production made epicontinental seas hotspots for pursuit diving seabirds, despite warmer temperatures. Together, ecosystem structure and the unique oceanographic factors characterizing epicontinental seas both contribute to differences in seabird biogeography between the Late Cretaceous and today.

Trilobites and Sedimentary Settings from the Lower Ordovician (Tremadocian; Bienvillia tetragonalis Biozone) of Iturbe, Jujuy Province, Argentina

In the Argentinian Cordillera Oriental, the Iturbe River area represents an intermediate territory between Sierra de Santa Victoria to the north and the Quebrada de Humahuaca to the south. Lower Ordovician outcrops of this region were cited in the literature as highly fossiliferous, although they are still imperfectly known. A Tremadocian succession of the Santa Rosita Formation near the village of Iturbe, Jujuy Province, is described herein. It displays different marine paleoenvironments and a relatively high-diversity trilobite assemblage. The sedimentary features of the lower and middle parts of the succession denote deposition in upper offshore and offshore transition environments, whereas those of the upper part are characteristic of a deeper, lower offshore setting. Taxa recognized include Gymnagnostus sp., Micragnostus iturbensis sp. nov., Geragnostus callaveiformis Harrington and Leanza, Geragnostus sp., Conophrys cf. salopiensis (Callaway), Leptoplastides granulosus (Harrington), Bienvillia tetragonalis (Harrington), B. rectifrons (Harrington), Parabolinella boliviana Juarez Huarachi, Asaphellus stenorhachis (Harrington), Apatokephalus tibicen P?ibyl and Van?k, and Pyrimetopus sp. This association indicates correspondence with the Bienvillia tetragonalis Zone (lower upper Tremadocian); a unit that to date is recorded with confidence only in a few localities of the Cordillera Oriental, in diverse facies. This study provides information on the morphology of several key taxa of the biozone, as well as new evidence in favour of a correlation with the Conophrys salopiensis Zone of England. The assemblage studied is assignable to the middle Tremadocian Olenid-Asaphellus biofacies, which occurs typically in upper offshore to offshore transition deposits.

A novel multiproxy approach to reconstruct the paleoecology of extinct cephalopods

Reconstructing marine paleoenvironments from the skeletal hardparts of nektic organisms is often hampered by their unknown migrational pathways involving different water masses and their corresponding physico-chemical parameters. Despite significant progress over the last years, the reconstruction of migration patterns of extinct ammonoids is difficult because both, vertical and horizontal ones lead to an intricate combination of reconstructed seawater temperatures. Paleonvironmental data retrieved from exceptionally well-preserved lower Albian (Douvilleiceras mammillatum ammonite zone, uppermost CC8a nannofossil zone, 110.5–111.0 Ma) cephalopod shells from Madagascar (Mahajanga Basin, 40–42° southern latitude) are reconstructed based on a novel multi-proxy approach. Here we combine and contrast: (i) nacre tablet-paleobathymetry, (ii) Westermann Morphospace, and (iii) shell isotope geochemistry analysis. Results obtained allow for a robust reconstruction of habitat depth, paleo-seawater temperatures, and paleoecology of extinct cephalopod taxa. The discocone nautiloid Cymatoceras is regarded as vertical migrant with a maximum habitat depth of 250 m and a mean habitat water temperature of 20–21 °C. All three ammonoid taxa (Cleoniceras, Desmoceras, and Eogaudryceras) share a platycone to planorbicone shell shape suggesting a demersal life habit at maximal water depths of 450–500 m and temperatures of 19–21 °C for Cleoniceras and Desmoceras, and the deepest (525 m) and coolest (14 °C) habitat for Eogaudryceras. Circumstantial evidence from benthic mollusk shells from the same stratigraphic interval as well as sedimentological and paleopathological data provide further support for habitat reconstructions. Reconstructed paleotemperatures shown here provide well-constrained evidence for the thermal structure of past oceanic water masses and have significance for Cretaceous paleoceanography in general.