Evolution of carbonated lacustrine environment with stromatolites : a paleoecological approach (quarry of Montaigu-le-Blin, Limagne graben, Allier, France)

La carrière de Montaigu-le-Blin, située en Limagne bourbonnaise permet d’analyser en détail la sédimentation lacustre aquitanienne et de reconstituer les environnements de dépôt. Les sédiments marneux et calcaires renferment une faune d’eau douce et une flore particulièrement développées. Les dépôts sédimentaires traduisent des variations périodiques du niveau de la tranche d’eau qui provoquent aussi des variations périodiques des conditions chimiques au sein du lac. Ils sont représentatifs de milieux alternativement anoxiques et oxygénés. Ces variations sont le résultat d’alternances de périodes d’humidité variable, et seraient donc d’origine climatique. Ces alternances ont provoqué des variations périodiques des assemblages floro-fauniques : des thanatocœnoses surviennent durant les périodes anoxiques, alors que le développement majeur des algues encroûtantes responsables de la formation de concrétions algaires, apparaît lors des périodes oxygénées. Ces périodes sont également marquées par une augmentation de l’hydrodynamisme, associée à des apports détritiques du bassin versant. Les stromatolithes présents dans le milieu montrent des morphologies très variées, tributaires des associations de flore et de faune (algues, bactéries, fourreaux de larves de Trichoptères) qui les composent, ainsi que de leur milieu de croissance. Les associations de stromatolithes forment des complexes plurimétriques que l’on propose de situer par rapport à un paléorivage

La sédimentation carbonatée ordovicienne : un des principaux facteurs déclencheur de la glaciation hirnantienne

Une nouvelle approche concernant le déroulement de la glaciation hirnantienne est proposée dans ce travail. Elle s’intéresse aux principaux facteurs clés de cette dernière et associe les effets d’une glaciation continentale à une période de bas niveau du CO2 atmosphérique. L’accumulation d’un important volume de carbonates au cours de l’Ordovicien terminal pré-Hirnantien dans des régions où ces derniers étaient antérieurement absents est considérée comme un important puits de CO2 atmosphérique. Cette accumulation pourrait être la cause d’une baisse importante de la température moyenne au début de l’Hirnantien à laquelle s’ajoute un autre processus de rétroaction tel que la météorisation des carbonates. Une augmentation du flux de CO2 de l’atmosphère vers les océans par dissolution devrait avoir été favorisée par la précipitation de carbonates. L’importante inondation du continent Laurentia, situé à basse latitude au cours du Cincinnatien, et l’implantation d’une sédimentation carbonatée tempérée sur la marge nord-gondwanienne au cours de l’Ashgill (pre-Hirnantien), ont favorisé l’enfouissement de plus de 840 × 1015 kg (1,9 × 1019 mol) de CO2 dissous. Cette masse représente environ 350 fois la valeur actuelle du CO2 atmosphérique. Cette précipitation devrait avoir altéré fortement l’équilibre entre le CO2 dissous dans les océans et la pression partielle de CO2 dans l’air, entraînant éventuellement une réduction de cette dernière. L’approche développée dans ce travail offre une explication simple pour la fin accélérée de la glaciation. La baisse du niveau marin relatif, attribuée au glacio-eustatisme associée au recul de la ligne de rivage des océans sur les plates-formes, devrait avoir provoqué l’arrêt de la production de sédiments carbonatés et de l’absorption de CO2. Le niveau de CO2 préglaciaire devrait dès lors se rétablir à la faveur du dégazage de CO2 par volcanisme. Toutefois, après la fonte des glaces, les circulations océaniques ne reprennent pas et l’absence des courants instaurés lors de l’Ashgill (pré-Hirnantien) par une importante stratification des eaux océaniques empêche la reprise d’une importante sédimentation carbonatée. Les pics positifs bien connus du δ13C à la base de l’Hirnantien sont attribués au lessivage et à la dissolution des carbonates enrichis en 13C lors de l’importante émersion des plate-formes

Discontinuidades sedimentarias en la transición Cámbrico Inferior-Medio del manto del Esla, Zona Cantábrica

In the Esla nappe, three major discontinuities have been recognized within the Lancara Formation. Discontinuity D1 is located at the top of the white bedded limestones. It is recognized as an erosive contact and marks a sharp change from a peritidal-dominant, homoclinal ramp to a ramp with oolitic and bioclastic shoals distinguished here as the grey lenticular limestones. Discontinuity D2 is placed at the top of the grey lenticular limestones and is the boundary between the lower and upper Lancara members. A discontinuous ferruginous level or hard ground marks the boundary in the Esla nappe. Discontinuity D3 is placed at the bottom of the griotte tectofacies. It marks a major tectonic pulse and the input of fine-grained siliciclastics. In some areas, it is not sharp but gradual. D3 is a diachronous boundary, dated in some areas of the Cantabrian platform. The D3 surface is easily recognisable in SW Europe as a tectonically induced contact reflecting the diachronous and progressive breakdown of some platforms in SW Europe

Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)

The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620&thinsp;km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary structures and major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound, the Silurian–Devonian Caledonian extension/compression, the late Devonian extension/compression, and the Hercynian compression. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late Devonian) compression and the Carboniferous (i.e., pre-Hercynian to Hercynian). Additionally, basement characterization from geological and geophysics data (aeromagnetic and gravity maps), shows an interesting age-dependent zonation of the terranes which are bounded by mega-shear zones within the arches–basins framework. The old terranes are situated under arches while the young terranes are located under the basins depocenter. This structural framework results from the accretion of Archean and Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny 900–520&thinsp;Ma). Therefore, the sedimentary infilling pattern and the nature of deformation result from the repeated slow Paleozoic reactivation of Precambrian terranes bounded by subvertical lithospheric fault systems. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e., far-field orogenic belt, glaciation).</p

Early precipitated micropyrite in microbialites: A time capsule of microbial sulfur cycling

Microbialites are organosedimentary rocks that have occurred throughout the Earth’s history. The relationships between diverse microbial metabolic activities and isotopic signatures in biominerals forming within these microbialites are key to understanding modern biogeochemical cycles, but also for accurate interpretation of the geologic record. Here, we performed detailed mineralogical investigations coupled with NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) analyses of pyrite S isotopes in mineralising microbial mats from two different environments, a hypersaline lagoon (Cayo Coco, Cuba) and a volcanic alkaline crater lake (Atexcac, Mexico). Both microbialite samples contain two distinct pyrite morphologies: framboids and euhedral micropyrites, which display distinct ranges of δ34S values1. Considering the sulfate-sulfur isotopic compositions associated with both environments, micropyrites display a remarkably narrow range of Δpyr (i.e. Δpyr ≡ δ34SSO4 − δ34Spyr) between 56 and 62‰. These measured Δpyr values agree with sulfate-sulfide equilibrium fractionation, as observed in natural settings characterised by low microbial sulfate reduction respiration rates. Moreover, the distribution of S isotope compositions recorded in the studied micropyrites suggests that sulfide oxidation also occurred at the microbialite scale. These results highlight the potential of micropyrites to capture signatures of microbial sulfur cycling and show that S isotope composition in pyrites record primarily the local micro-environments induced by the microbialite

Arterial pulse wave modelling and analysis for vascular age studies: a review from VascAgeNet

Arterial pulse waves (PWs) such as blood pressure and photoplethysmogram (PPG) signals contain a wealth of information on the cardiovascular (CV) system that can be exploited to assess vascular age and identify individuals at elevated CV risk. We review the possibilities, limitations, complementarity, and differences of reduced-order, biophysical models of arterial PW propagation, as well as theoretical and empirical methods for analyzing PW signals and extracting clinically relevant information for vascular age assessment. We provide detailed mathematical derivations of these models and theoretical methods, showing how they are related to each other. Finally, we outline directions for future research to realize the potential of modeling and analysis of PW signals for accurate assessment of vascular age in both the clinic and in daily life

SerpinB2 regulates stromal remodelling and local invasion in pancreatic cancer

Pancreatic cancer has a devastating prognosis, with an overall 5-year survival rate of ~8%, restricted treatment options and characteristic molecular heterogeneity. SerpinB2 expression, particularly in the stromal compartment, is associated with reduced metastasis and prolonged survival in pancreatic ductal adenocarcinoma (PDAC) and our genomic analysis revealed that SERPINB2 is frequently deleted in PDAC. We show that SerpinB2 is required by stromal cells for normal collagen remodelling in vitro, regulating fibroblast interaction and engagement with collagen in the contracting matrix. In a pancreatic cancer allograft model, co-injection of PDAC cancer cells and SerpinB2(-/-) mouse embryonic fibroblasts (MEFs) resulted in increased tumour growth, aberrant remodelling of the extracellular matrix (ECM) and increased local invasion from the primary tumour. These tumours also displayed elevated proteolytic activity of the primary biochemical target of SerpinB2-urokinase plasminogen activator (uPA). In a large cohort of patients with resected PDAC, we show that increasing uPA mRNA expression was significantly associated with poorer survival following pancreatectomy. This study establishes a novel role for SerpinB2 in the stromal compartment in PDAC invasion through regulation of stromal remodelling and highlights the SerpinB2/uPA axis for further investigation as a potential therapeutic target in pancreatic cancer

ROR1 and ROR2 expression in pancreatic cancer

Background: The Wnt receptors ROR1 and ROR2 are generating increased interest as cancer therapeutic targets but remain understudied in pancreatic ductal adenocarcinoma (PDAC). Compared to canonical Wnt/ β-catenin signalling, the role of noncanonical Wnt signalling in PDAC remains largely unknown. Only one study has investigated the prognostic significance of the noncanonical Wnt signalling receptor, ROR2 in PDAC. No studies have investigated the prognostic role of ROR1 in PDAC. Methods: Here, we performed analysis of ROR1 and ROR2 mRNA expression in three publicly available datasets ICGC-PACA-AU (n = 81), TCGA-PAAD (n = 150) and CPTAC-PDAC (n = 137). ROR1 and ROR2 protein expression from the CPTAC-PDAC discovery cohort were also analysed. Immunohistochemistry (IHC) using the validated anti ROR1 monoclonal antibody (4A5) was performed on the Australian Pancreatic Cancer Genome Initiative (APGI) cohort of PDAC samples (n = 152). Association between ROR1 cytoplasmic staining intensity and clinicopathological parameters including stage, grade and overall survival (OS) was investigated. Results: High ROR1 mRNA expression levels correlated with a favourable OS outcome in all of the ICGC-PACA-AU, TCGA-PAAD and CPTAC-PDAC cohorts. ROR1 protein expression was not associated with stage, grade or OS in the APGI cohort. Conclusion: ROR1 and ROR2 have potential as prognostic markers when measured at the mRNA level in PDAC. Our IHC cohort did not support ROR1 protein expression in predicting OS, and highlighted the discrepancy of prognostic biomarkers when measured by MS, IHC and RNAseq