The fossil bivalve Angulus benedeni benedeni: A potential seasonally resolved stable-isotope-based climate archive to investigate Pliocene temperatures in the southern North Sea basin

Bivalves record seasonal environmental changes in their shells, making them excellent climate archives. However, not every bivalve can be used for this end. The shells have to grow fast enough so that micrometre- to millimetre-sampling can resolve sub-annual changes. Here, we investigate whether the bivalve Angulus benedeni benedeni is suitable as a climate archive. For this, we use ca. 3-million-year-old specimens from the Piacenzian collected from a temporary outcrop in the Port of Antwerp area (Belgium). The subspecies is common in Pliocene North Sea basin deposits, but its lineage dates back to the late Oligocene and has therefore great potential as a high-resolution archive. A detailed assessment of the preservation of the shell material by micro-X-ray fluorescence, X-ray diffraction, and electron backscatter diffraction reveals that it is pristine and not affected by diagenetic processes. Oxygen isotope analysis and microscopy indicate that the species had a longevity of up to a decade or more and, importantly, that it grew fast and large enough so that seasonally resolved records across multiple years were obtainable from it. Clumped isotope analysis revealed a mean annual temperature of 13.5±3.8°C. The subspecies likely experienced slower growth during winter and thus may not have recorded temperatures year-round. This reconstructed mean annual temperature is 3.5°C warmer than the pre-industrial North Sea and in line with proxy and modelling data for this stratigraphic interval, further solidifying A. benedeni benedeni's use as a climate recorder. Our exploratory study thus reveals that Angulus benedeni benedeni fossils are indeed excellent climate archives, holding the potential to provide insight into the seasonality of several major climate events of the past ∼25 million years in northwestern Europe

Stable isotope record of Triceratops from a mass accumulation (Lance Formation, Wyoming, USA) provides insights into Triceratops behaviour and ecology

Our understanding of Late Cretaceous dinosaur ecosystems from North America has considerably improved through stable isotope analyses on fossil bones and teeth. Oxygen and carbon stable isotopic compositions of structurally-bound carbonate in these fossil apatites are commonly used to infer variations of ingested water and food sources, which are in turn related to environmental and climatic conditions. Incremental isotopic records potentially provide insights into seasonality and migratory behaviour. So far, these reconstructions are based on vertebrate remains from spatiotemporally diverse datasets. Here, we present oxygen (δ18O) and carbon (δ13C) isotopic records from a large, spatially and temporally well-constrained, Triceratops bonebed from the Upper Maastrichtian Lance Formation (eastern Wyoming. USA). These isotopic compositions allow to elucidate the palaeoecology of these large herbivores and their ecosystem in detail, as well as their habitat use, diet and possible migration. The δ18O signature from incrementally sampled Triceratops teeth reveal relatively low intra-tooth variation (average 1.3 ‰), comparable to contemporaneous dinosaur species as well as modern herbivorous mammals. Average δ13C values (−5.4 ‰) are somewhat higher than for modern C3 plant grazers, and hint towards complex interactions during carbon uptake by non-avian herbivorous dinosaurs. Calculated δ18O of drinking water (−14.8 ‰) combined with the local sedimentology of fine-grained siliciclastic deposits with high total organic and low carbonate contents strongly suggest a freshwater environment. Additionally, the combined average δ18O and δ13C Triceratops isotope signatures indicate a living environment intermediate between inland forests and coastal floodplains, expanding on earlier theories of ornithischian niche partitioning. Our robust dataset provides meaningful tests of habitat and palaeoecological hypotheses for Triceratops, and highlights the application of spatiotemporally well-constrained fossil remains

Globally distributed iridium layer preserved within the Chicxulub impact structure

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide

Hot carbonates deep within the Chicxulub impact structure

Constraining the thermodynamic conditions within an impact structure during and after hypervelocity impacts is extremely challenging due to the transient thermal regimes. This work uses carbonate clumped-isotope thermometry to reconstruct absolute temperatures of impact lithologies within and close to the ∼66 Myr old Chicxulub crater (Yucatán, México). We present stable oxygen (δ18O), carbon (δ13C), and clumped-isotope (Δ47) data for carbonate-bearing impact breccias, impact melt rock, and target lithologies from four drill cores on a transect through the Chicxulub structure from the northern peak ring to the southern proximal ejecta blanket. Clumped isotope-derived temperatures (T(Δ47)) are consistently higher than maximum Late Cretaceous sea surface temperatures (35.5°C), except in the case of Paleogene limestones and melt-poor impact breccias outside of the crater, confirming the influence of burial diagenesis and a widespread and long-lived hydrothermal system. The melt-poor breccia unit outside the crater is overlain by melt-rich impact breccia yielding a much higher T(Δ47) of 111 ± 10°C (1 standard error [SE]), which likely traces the thermal processing of carbonate material during ejection. Finally, T(Δ47) up to 327 ± 33°C (1 SE) is determined for the lower suevite and impact melt rock intervals within the crater. The highest temperatures are related to distinct petrological features associated with decarbonation and rapid back-reaction, in which highly reactive CaO recombines with impact-released CO2 to form secondary CaCO3 phases. These observations have important climatic implications for the Cretaceous–Paleogene mass extinction event, as current numerical models likely overestimate the release of CO2 from the Chicxulub impact event.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Gold mineralization in the Mesoproterozoic Karagwe-Ankole belt (Byumba, Rwanda) : new insights from petrography and trace element mapping

A recent increase of interest in the various mineral deposits of the Central African Karagwe-Ankole belt (KAB) has led to many new discoveries and exciting research. Gold deposits in the KAB still have many unanswered questions concerning their formation conditions. The aims of this research are to determine the controlling factors on gold distribution at the Byumba deposit (Rwanda) and to resolve the relationship between the different vein generations and the tectonic evolution of the area. To achieve this, drill cores from the Byumba deposit were logged and sampled for further petrographic research and major and trace element mapping. Micro X-ray fluorescence (mu XRF) is used for the identification and distribution of gold and of different types of alteration/mineralization. Five main phases of quartz veining are identified which can be linked to the different phases of deformation that are recognized in the KAB. Important phases of folding and shearing are distinctly present at Byumba and associated with sericitization and chloritization. Sulfides are predominantly present in the form of pyrite, with minor associations of arsenopyrite, chalcopyrite, pyrrhotite and covellite. Primary gold mineralization seems to be correlated to chlorite-rich shear veins. Gold occurs within an early quartz phase and not associated with pyrite

Gold mineralization in the Mesoproterozoic Karagwe-Ankole belt (Byumba, Rwanda): new insights from petrography and trace element mapping

status: publishe

Microstructures and sclerochronology of exquisitely preserved Lower Jurassic lithiotid bivalves: Paleobiological and paleoclimatic significance

Lithiotids are enigmatic, large-sized bivalves that formed an important biotic component of tropical shallow marine environments during the Early Jurassic. Lithiotis problematica and Cochlearites loppianus are the most peculiar lithiotids, characterized by stick-like shells of predominantly aragonite which is generally calcitized or replaced by sparry calcite. Uniquely preserved specimens of these two species from the upper Sinemurian-Pliensbachian (Lower Jurassic) Rotzo Formation (Trento Platform, northern Italy), containing large parts of pristine shell (based on SEM, cathodoluminescence, and μXRF analysis), were selected for a sclerochronological and sclerochemical study, allowing to describe in detail the lithiotid microstructures, to decipher seasonal patterns and to investigate their functional and paleoenvironmental significance. We show that the outer shell layer of lithiotids, rarely preserved, consists of a calcitic simple prismatic microstructure with an asymmetrical thickness between the two valves, whereas the inner layer is aragonitic and is mainly composed of a fibrous irregular spherulitic prismatic fabric, which allowed a very fast shell growth. The latter microstructure is currently unknown in other mollusc shells. We recognized diurnal, fortnightly and annual growth increments, documenting a maximum annual growth of about 25 mm/yr in ventral direction. Stable isotopes show a clear annual periodicity suggesting seasonal changes in the paleoenvironment, which also affected the shell microstructures. During the warm season, first-order prisms are very elongated and show a massive structure without growth breaks, whereas during the cold season prisms are short and with growth cessations. Our results highlight the unique adaptation of lithiotid bivalves that allowed them to dominate the tropical shelf seas during the Early Jurassic

The Maastrichtian Geoheritage Project: an introduction, first results and outlook.

Abstract and presentation at the International Symposium on Chalk & Flint, November 30th 2019, Maastricht, The Netherlandsedition: International Symposium on Chalk & Flint abstract bookstatus: publishe

Late orogenic gold mineralization in the western domain of the Karagwe-Ankole Belt (Central Africa): Auriferous quartz veins from the Byumba deposit (Rwanda)

status: Published onlin