'Palaeoshellomics' reveals the use of freshwater mother-of-pearl in prehistory

The extensive use of mollusc shell as a versatile raw material is testament to its importance in prehistoric times. The consistent choice of certain species for different purposes, including the making of ornaments, is a direct representation of how humans viewed and exploited their environment. The necessary taxonomic information, however, is often impossible to obtain from objects that are small, heavily worked or degraded. Here we propose a novel biogeochemical approach to track the biological origin of prehistoric mollusc shell. We conducted an in-depth study of archaeological ornaments using microstructural, geochemical and biomolecular analyses, including 'palaeoshellomics', the first application of palaeoproteomics to mollusc shells (and indeed to any invertebrate calcified tissue). We reveal the consistent use of locally-sourced freshwater mother-of-pearl for the standardized manufacture of 'double-buttons'. This craft is found throughout Europe between 4200-3800 BCE, highlighting the ornament-makers' profound knowledge of the biogeosphere and the existence of cross-cultural traditions

In Situ carbon and oxygen isotopes measurements in carbonates using laser-induced calcination: A step forward field isotopic characterization

International audienc

Influencias diagenéticas y detríticas en la mineralogía de las arcillas y en la geoquímica de los isótopos de carbono de los sedimentos del Campaniano-Maastrichtiano de la cuenca de Tremp-Graus (sur de los Pirineos, España).

15 pagesInternational audienceA 1000 m-thick sequence of Upper Cretaceous sediments outcropping in the Isabena Valley (Tremp-Graus Basin, Spain) has been studied to explore the evolution of environmental conditions that prevailed in this basin. A biostratigraphic study based on calcareous nannofossils was carried out to better constraint the age of the deposits, supplemented by carbon isotope stratigraphy on bulk carbonates. Clay mineral assemblages were identified by X-Ray diffraction combined with organic matter (OM) characterisation by Rock–Eval pyrolysis. The Late Campanian Event and Campanian Maastrichtian Boundary Event are clearly identified from the new δ13Ccarb dataset. The clay assemblage is composed of a complex mixture of chlorite, illite, kaolinite and mixed-layers including illite–smectite and chlorite–smectite. A progressive illitisation of smectite is recorded from the top to the base of the section due to the increasing burial depth. This evolution is consistent with increasing Tmax values of OM evolving from 425 (immature OM) to 449 °C (mature OM) from the top to the base of the section. Thus, detrital minerals are preserved only in the upper part of the section. The clay sedimentation is dominated by smectites likely originating from the Ebro massif, while increasing proportions of kaolinite are recorded from the uppermost Campanian and during the Maastrichtian. This evolution of the clay mineral assemblage is interpreted as a result from a change of source from south to northeast, with contributions from kaolinite-rich weathering profiles (including bauxites) to the northeast of the study area, reflecting a more hydrolysing climate.Una secuencia de 1.000 m de espesor de sedimentos del Cretácico Superior aflorantes en el Valle del Isábena (Cuenca de Tremp-Graus, España) se fue estudiado para explorar la evolución de las condiciones ambientales que prevalecieron en esta cuenca. Un estudio bioestratigráfico basado en nanofósiles calcáreos para restringir mejor la edad de los depósitos se ha realizado, complementado con una estratigrafía isotópica del carbono en los carbonatos masivos. Los conjuntos de minerales de arcilla se identificaron a través de la difracción de rayos X combinada con la caracterización de la materia orgánica (MO) utilizando pirólisis Rock-Eval. El Evento Campaniano Tardío y el Evento Limítrofe Campaniano Maastrichtiano se identifican claramente a partir del nuevo conjunto de datos δ13C. El conjunto de arcillas está compuesto por una compleja mezcla de clorita, illita, caolinita y capas mixtas que incluyen illita-esmectita y clorita-esmectita. Se registra una progresiva ilitización de la esmectita desde la parte superior hasta la base de la sección debido al aumento de la profundidad de enterramiento. Esta evolución es coherente con el aumento de los valores de Tmáx de la MO que evolucionan de 425 (MO inmadura) a 449 °C (MO madura) desde la parte superior hasta la base de la sección. Así, los minerales detríticos se conservan sólo en la parte superior de la sección. La sedimentación de arcilla está dominada por esmectitas probablemente originadas en el macizo del Ebro, mientras que se registran proporciones crecientes de caolinita desde el Campaniense superior y durante el Maastrichtiano. Esta evolución conjunto de minerales arcillosos se interpreta como el resultado de un cambio de fuente del sur al noreste, con contribuciones de perfiles de meteorización ricos en caolinita (incluyendo bauxitas) al noreste del área de estudio, reflejando un clima más hidrolizado

Geochemical processes leading to the precipitation of subglacial carbonate crusts at Bossons glacier, Mont Blanc Massif (French Alps).

16 pagesInternational audienceCold climate carbonates can be used as paleoclimatic proxies. The mineralogy and isotopic composition of subglacially precipitated carbonate crusts (SPCCs) provide insights into the subglacial conditions and processes occurring at the meltwater-basement rock interface of glaciers. This study documents such crusts discovered on the lee side of a gneissic roche moutonnée at the terminus of the Bossons glacier in the Mont Blanc Massif area (France). The geological context and mineralogical investigations suggest that the Ca used for the precipitation of large crystals of radial fibrous sparite observed in these crusts originated from subglacial chemical weathering of Ca-bearing minerals of the local bedrock (plagioclase and amphibole). Measurements of the carbon and oxygen isotope compositions in the crusts indicate precipitation at, or near to, equilibrium with the basal meltwater under open system conditions during refreezing processes. The homogeneous and low carbonate δ13C values (ca. −11.3‰) imply a large contribution of soil organic carbon to the Bossons subglacial meltwater carbon reservoir at the time of deposition. In addition, organic remains trapped within the SPCCs give an age of deposition around 6,500 years cal BP suggesting that the Mid-Holocene climatic and pedological optima are archived in the Bossons glacier carbonate crusts

Diagenetic and environmental control of the clay mineralogy, organic matter and stable isotopes (C, O) of Jurassic (Pliensbachian-lowermost Toarcian) sediments of the Rodiles section (Asturian Basin, Northern Spain)

Clay mineralogical and geochemical analyses (δ18Ocarb, and paired carbonate and organic matter carbon isotope), completed by the characterization of organic matter, have been performed on the Pliensbachian sediments exposed on the Rodiles section (Asturian Basin, Northern Spain). The objectives were to precise the Pliensbachian climate evolution at a relatively low paleolatitude of the Tethyan domain by comparison with previously published high-resolution clay mineralogical and geochemical data from the NW Tethyan domain (e.g. Paris Basin and Cardigan Bay Basin, West Wales). The clay mineral assemblages are dominantly composed of illite and illite-smectite mixed-layers (I–S) associated with minor proportions of chlorite and kaolinite. Smectites are not identified what may result either to their absence at the time of sedimentation or to their progressive illitization due to the burial diagenesis. Rock-Eval data show that organic matter reaching more than 5% in black-shale horizons is thermally mature with Tmax comprised between 444 and 454 °C indicating that the section is in the oil window and that the burial temperature reached or exceeded 80–90 °C. The low δ18Obulk values comprised between −3 and −6‰ clearly results from a diagenetic influence (thermal effect due to burial) but their fluctuations compared with δ18O measured on well-preserved belemnites guards show that the overall trend is however preserved. By comparison with higher latitude sedimentary basins, the most striking feature is the very small proportions of kaolinite (generally less than 5% while the proportions of this mineral reach 40% at higher paleolatitudes), except at the Pliensbachian/Toarcian transition, where the proportion of kaolinite increases significantly. Clay minerals likely originated from the erosion of the Iberian Massif located to the South of the Asturian Basin in a semi-arid climatic belt. This may explain the scarcity of kaolinite by comparison with sedimentary basins located at higher latitude influenced by more humid climate. The increasing proportions of kaolinite by the end of the Pliensbachian suggest southward expansion of the humid belt as a consequence of cooler temperatures and the establishment of steeper latitudinal gradients of temperature likely resulting from the formation of restricted polar ice cap. The main δ13C (on both 13Cinorg and 13Corg) Pliensbachian excursions including the negative excursion of the Sinemurian/Pliensbachian Boundary Event (SPBE) and the Late Pliensbachian positive excursion are well recognized

Clay mineralogical and geochemical expressions of the “Late Campanian Event” in the Aquitaine and Paris basins (France): palaeoenvironmental implications.

11 pagesInternational audienceCampanian sediments from two French sedimentary basins were studied, using clay mineralogy and stable isotope (δ13C and δ18O) geochemistry, in order to investigate the Late Campanian Event. The clay fraction of the Campanian sediments from the Tercis-les-Bains section (Aquitaine Basin) and from the Poigny borehole (Paris Basin) is mainly composed of smectite. This background sedimentation was, however, interrupted during the Upper Campanian in the two basins by a substantial increase in detrital inputs, including illite, kaolinite, and chlorite at Tercis-les-Bains, and illite at Poigny. This detrital event, resulting from the enhanced erosion of nearby continental areas triggered by increasing runoff, has also been recognized in the Tethys and South Atlantic oceans. It coincided with a global negative carbon isotope excursion, the Late Campanian Event (LCE). Carbon isotope stratigraphy was used to correlate the two basins with previously studied sections from distant areas. Spectral analysis of the bulk δ13C from Tercis-les-Bains suggests a duration of ca. 400 kyr for a pre-LCE negative excursion and ca. 800–900 kyr for the LCE sensu stricto. The detrital event, as characterized by clay mineralogy, spans the interval that comprises the pre-LCE and the LCE, with a duration of 1.3 Myr. Intensification of continental erosion during the LCE may have resulted either from the Late Campanian polyplocum regression and/or from a regional tectonic pulse that triggered the emersion of previous submerged shelf areas and the increase of silicate erosion. As the LCE seems to be recorded at a large geographic scale, it is proposed here that enhanced chemical weathering and an associated decrease in atmospheric pCO2 levels could have contributed to the long-term Late Cretaceous cooling trend

Influence of the local controling factors over the Early Triassic paired carbon isotopoes fluctuations

International audienceImportant and recurrent perturbations of the carbon isotope signals are recorded during the Early Triassic, in the aftermath of the end-Permian mass extinction (~252 Ma). These perturbations, among the largest observed throughout the Phanerozoic, are most notably represented by a globally recognized couplet of a negative and a positive excursions, before and across the Smithian/Spathian boundary (SSB, ~1.5 Myr after the Permian/Triassic boundary), imprinted in both the carbonate and organic matter reservoirs. These fluctuations are generally assumed to be linked to environmental perturbations related to a late degassing of the Siberian Traps. Recent works on the Early Triassic Sonoma Foreland Basin (western USA) have shown that local secondary processes can have a strong influenceon the carbon isotope record, preventing its usual use for long-distance correlations and global climatic interpretations. Here, new measurements of paired carbon isotopes (carbonate and organic matter fractions) from the Griesbachian-Dienerian up to the lower Spathian have been performed on a section of the Sonoma Foreland Basin, at Hot Springs (SE Idaho). We show that both carbonate and organic matter δ13C signals mirror the signal recognized at the global-scale, particularly for the SSB event, and that this signal is not due to secondary diagenetic processes. However, if SSB excursions are observed in both signals, dampened variations in the organic reservoir are observed. These variations in the net isotopic effect (i.e., δ13C) reflect a complex set of locally controlled forcing parameters (including, but not restricted to, e.g. mixing of terrestrial and marine organic matters in relation to variation in sedimentary depositional setting), rather than suggested CO2-driven temperature variations. We argue that even if the globally recognized variations of the carbon isotope record are observed, the Hot Springs isotope signal most probably reflects primarily the local geological context rather than diagenetic or exogenic carbon cycle processes. We therefore question the validity of high-resolution carbon signals for long-distance correlations during the Early Triassic. Rather, we suggest to use the carbon signal to characterize fluctuating local conditions during deposition

Influence of the local controling factors over the Early Triassic paired carbon isotopoes fluctuations

International audienceImportant and recurrent perturbations of the carbon isotope signals are recorded during the Early Triassic, in the aftermath of the end-Permian mass extinction (~252 Ma). These perturbations, among the largest observed throughout the Phanerozoic, are most notably represented by a globally recognized couplet of a negative and a positive excursions, before and across the Smithian/Spathian boundary (SSB, ~1.5 Myr after the Permian/Triassic boundary), imprinted in both the carbonate and organic matter reservoirs. These fluctuations are generally assumed to be linked to environmental perturbations related to a late degassing of the Siberian Traps. Recent works on the Early Triassic Sonoma Foreland Basin (western USA) have shown that local secondary processes can have a strong influenceon the carbon isotope record, preventing its usual use for long-distance correlations and global climatic interpretations. Here, new measurements of paired carbon isotopes (carbonate and organic matter fractions) from the Griesbachian-Dienerian up to the lower Spathian have been performed on a section of the Sonoma Foreland Basin, at Hot Springs (SE Idaho). We show that both carbonate and organic matter δ13C signals mirror the signal recognized at the global-scale, particularly for the SSB event, and that this signal is not due to secondary diagenetic processes. However, if SSB excursions are observed in both signals, dampened variations in the organic reservoir are observed. These variations in the net isotopic effect (i.e., δ13C) reflect a complex set of locally controlled forcing parameters (including, but not restricted to, e.g. mixing of terrestrial and marine organic matters in relation to variation in sedimentary depositional setting), rather than suggested CO2-driven temperature variations. We argue that even if the globally recognized variations of the carbon isotope record are observed, the Hot Springs isotope signal most probably reflects primarily the local geological context rather than diagenetic or exogenic carbon cycle processes. We therefore question the validity of high-resolution carbon signals for long-distance correlations during the Early Triassic. Rather, we suggest to use the carbon signal to characterize fluctuating local conditions during deposition