200 research outputs found
Evolution of carbonated lacustrine environment with stromatolites : a paleoecological approach (quarry of Montaigu-le-Blin, Limagne graben, Allier, France)
La carriĂšre de Montaigu-le-Blin, situĂ©e en Limagne bourbonnaise permet dâanalyser en dĂ©tail la sĂ©dimentation
lacustre aquitanienne et de reconstituer les environnements de dépÎt. Les sédiments marneux et calcaires renferment
une faune dâeau douce et une flore particuliĂšrement dĂ©veloppĂ©es. Les dĂ©pĂŽts sĂ©dimentaires traduisent des
variations pĂ©riodiques du niveau de la tranche dâeau qui provoquent aussi des variations pĂ©riodiques des conditions chimiques
au sein du lac. Ils sont représentatifs de milieux alternativement anoxiques et oxygénés. Ces variations sont le
rĂ©sultat dâalternances de pĂ©riodes dâhumiditĂ© variable, et seraient donc dâorigine climatique. Ces alternances ont provoquĂ©
des variations pĂ©riodiques des assemblages floro-fauniques : des thanatocĆnoses surviennent durant les pĂ©riodes
anoxiques, alors que le développement majeur des algues encroûtantes responsables de la formation de concrétions algaires,
apparaĂźt lors des pĂ©riodes oxygĂ©nĂ©es. Ces pĂ©riodes sont Ă©galement marquĂ©es par une augmentation de lâhydrodynamisme,
associée à des apports détritiques du bassin versant. Les stromatolithes présents dans le milieu montrent des
morphologies trÚs variées, tributaires des associations de flore et de faune (algues, bactéries, fourreaux de larves de TrichoptÚres)
qui les composent, ainsi que de leur milieu de croissance. Les associations de stromatolithes forment des
complexes plurimĂ©triques que lâon propose de situer par rapport Ă un palĂ©orivage
New bryozoans from the Upper Ordovician of Morocco and their place in the temperate-to-cool water Mediterranean Province
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 sâintĂ©resse aux principaux facteurs clĂ©s de cette derniĂšre et associe les effets dâune glaciation continentale Ă une pĂ©riode
de bas niveau du CO2 atmosphĂ©rique. Lâaccumulation dâun important volume de carbonates au cours de lâOrdovicien
terminal prĂ©-Hirnantien dans des rĂ©gions oĂč ces derniers Ă©taient antĂ©rieurement absents est considĂ©rĂ©e comme un
important puits de CO2 atmosphĂ©rique. Cette accumulation pourrait ĂȘtre la cause dâune baisse importante de la tempĂ©rature
moyenne au dĂ©but de lâHirnantien Ă laquelle sâajoute un autre processus de rĂ©troaction tel que la mĂ©tĂ©orisation des
carbonates. Une augmentation du flux de CO2 de lâatmosphĂšre vers les ocĂ©ans par dissolution devrait avoir Ă©tĂ© favorisĂ©e
par la prĂ©cipitation de carbonates. Lâimportante inondation du continent Laurentia, situĂ© Ă basse latitude au cours du
Cincinnatien, et lâimplantation dâune sĂ©dimentation carbonatĂ©e tempĂ©rĂ©e sur la marge nord-gondwanienne au cours de
lâAshgill (pre-Hirnantien), ont favorisĂ© lâenfouissement de plus de 840 Ă 1015 kg (1,9 Ă 1019 mol) de CO2 dissous. Cette
masse représente environ 350 fois la valeur actuelle du CO2 atmosphérique. Cette précipitation devrait avoir altéré fortement
lâĂ©quilibre entre le CO2 dissous dans les ocĂ©ans et la pression partielle de CO2 dans lâair, entraĂźnant Ă©ventuellement
une rĂ©duction de cette derniĂšre. Lâapproche dĂ©veloppĂ©e 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 ocĂ©ans sur les plates-formes, devrait avoir provoquĂ© lâarrĂȘt de la production de sĂ©diments carbonatĂ©s et de
lâabsorption de CO2. Le niveau de CO2 prĂ©glaciaire devrait dĂšs lors se rĂ©tablir Ă la faveur du dĂ©gazage de CO2 par volcanisme.
Toutefois, aprĂšs la fonte des glaces, les circulations ocĂ©aniques ne reprennent pas et lâabsence des courants instaurĂ©s
lors de lâAshgill (prĂ©-Hirnantien) par une importante stratification des eaux ocĂ©aniques empĂȘche la reprise dâune
importante sĂ©dimentation carbonatĂ©e. Les pics positifs bien connus du ÎŽ13C Ă la base de lâHirnantien sont attribuĂ©s au
lessivage et Ă la dissolution des carbonates enrichis en 13C lors de lâimportante Ă©mersion des plate-formes
Discontinuidades sedimentarias en la transiciĂłn CĂĄmbrico Inferior-Medio del manto del Esla, Zona CantĂĄbrica
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 (75â620 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
CambrianâOrdovician extension, the OrdovicianâSilurian glacial rebound,
the SilurianâDevonian 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
CambrianâOrdovicianâSilurian period. These structures may have been
inverted or reactivated during the Devonian (i.e., Caledonian, MidâLate
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 archesâbasins 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
900â520 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 Earthâs
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 ÎŽ34S values1. Considering
the sulfate-sulfur isotopic compositions associated with both environments, micropyrites display a remarkably narrow range
of Îpyr (i.e. Îpyr ⥠Ύ34SSO4 â ÎŽ34Spyr) between 56 and 62â°. These measured Îpyr 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/ ÎČ-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
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