The ∼270 Ma palaeolatitude of Baltica and its significance for Pangea models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86901/1/j.1365-246X.2011.05061.x.pd

New Late Permian paleomagnetic data from Argentina: Refinement of the apparent polar wander path of Gondwana

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95004/1/ggge1994.pd

Le recours aux urgences de l'ESP St Philibert

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Tuning apico-basal polarity and junctional recycling in the hemogenic endothelium orchestrates pre-hematopoietic stem cell emergence complexity

International audienceAbstract Hematopoietic stem cells emerge in the embryo from an aortic-derived tissue called the hemogenic endothelium (HE). The HE appears to give birth to cells of different nature and fate but the molecular principles underlying this complexity are largely unknown. Here we show, in the zebrafish embryo, that two cell types emerge from the aortic floor with radically different morphodynamics. With the support of live imaging, we bring evidence suggesting that the mechanics underlying the two emergence types rely, or not, on apicobasal polarity establishment. While the first type is characterized by reinforcement of apicobasal polarity and maintenance of the apical/luminal membrane until release, the second type emerges via a dynamic process reminiscent of trans-endothelial migration. Interfering with Runx1 function suggests that the balance between the two emergence types depends on tuning apicobasal polarity at the level of the HE. In addition, using new transgenic fish lines that express Junctional Adhesion Molecules and functional interference, we bring evidence for the essential role of ArhGEF11/PDZ-RhoGEF in controlling the HE-endothelial cell dynamic interface, including cell-cell intercalation, which is ultimately required for emergence completion. Overall, we highlight critical cellular and dynamic events of the endothelial-to-hematopoietic transition that support emergence complexity, with a potential impact on cell fate. Major subject areas Developmental Biology and Stem cells, Cell Biology

Tuning apico-basal polarity and junctional recycling in the hemogenic endothelium orchestrates pre-hematopoietic stem cell emergence complexity

Hematopoietic stem cells emerge in the embryo from an aortic-derived tissue called the hemogenic endothelium (HE). The HE appears to give birth to cells of different nature and fate but the molecular principles underlying this complexity are largely unknown. Here we show, in the zebrafish embryo, that two cell types emerge from the aortic floor with radically different morphodynamics. With the support of live imaging, we bring evidence suggesting that the mechanics underlying the two emergence types rely, or not, on apicobasal polarity establishment. While the first type is characterized by reinforcement of apicobasal polarity and maintenance of the apical/luminal membrane until release, the second type emerges via a dynamic process reminiscent of trans-endothelial migration. Interfering with Runx1 function suggests that the balance between the two emergence types depends on tuning apicobasal polarity at the level of the HE. In addition, using new transgenic fish lines that express Junctional Adhesion Molecules and functional interference, we bring evidence for the essential role of ArhGEF11/PDZ-RhoGEF in controlling the HE-endothelial cell dynamic interface, including cell-cell intercalation, which is ultimately required for emergence completion. Overall, we highlight critical cellular and dynamic events of the endothelial-to-hematopoietic transition that support emergence complexity, with a potential impact on cell fate. Developmental Biology and Stem cells, Cell Biology

Late Permian to Late Triassic palaeomagnetic data from Iran: constraints on the migration of the Iranian block through the Tethyan Ocean and initial destruction of Pangaea

International audienceA palaeomagnetic study of Late Permian to early Jurassic rocks from the Alborz and Sanandaj–Sirjan zones in Iran and a compilation of selected palaeopoles from the Carboniferous to the present provide an updated history of the motion of the Iranian block within the Tethys Ocean. The Iran assemblage, part of Gondwana during the Palaeozoic, rifted away by the end of the Permian. We ascertain the southern-hemisphere palaeoposition of Iran at that time using magnetostratigraphy and show that it was situated close to Arabia, near to its relative position today. A northward transit of this block during the Triassic is shown, with an estimated expansion rate of the Neotethyan ridge of 100–140 km Myr−1. The northward convergence with respect to Eurasia ended during the Ladinian (Middle Triassic), and is marked by a collision in the northern hemisphere with the Turan platform, which was the southern margin of the Eurasian continent at that time. No north–south component of shortening is evidenced north of Iran afterwards. An analysis of the declinations from the Late Permian to the present shows different, large rotations, emphasizing the important tectonic phases suffered since the Triassic. Finally, we propose palaeomagnetic reconstructions of the Tethys area during the Late Permian and the Late Triassic, showing that the Palaeotethys Ocean was narrower than previously thought, and did not widen its gate to the Panthalassa before the Triassic period

Mechanical properties of sediments issued from giant submarine landslides in the shallow subsurface of the Amazon fan

International audienceThe equatorial Atlantic margin to the north of the Amazon is strongly affected by gravi- tational processes presenting all forms of rupture of submarine slopes, representing a major geological hazard. The potential causal factors of these underwater landslides were studied from the integration of marine geophysical data (sediment sounder) and physical properties of sediment collected during the AMAGAS campaign (French Guiana-Brasil, 2023). The main geomechanical properties studied were density, compressive strength (Cu), P-wave ve- locities (Vp) and undrained shear strength (Su). These parameters represent good proxies of the mechanical state of slope sediments, such as overall erosion and level of consolidation. Acoustic anomalies observed in sub-bottom (chirp) profiles such as chaotic facies or acoustic wipe-outs indicated the presence of significant free gas content in the investigated sediments. Partial and total losses of Vp measurements were also consistent with the presence of gas or possibly gas hydrates.We measured unexpectedly low values of density and resistance, leading us to infer that the presence of free gas has a negative effect on density and resistance. A few preliminary studies comparing the high resolution seismic chirp data of the logged coring sites to the Cu measures and density measures have shown good correlations. They could lead to different comprehension and interpretation of Chirp data. Many other studies such as oedometric, triaxial and in vane tests are programmed as soon as the cores will probably confirm our hypothesis.On the basis of onboard data, we propose that slope failures observed along the studied area are likely controlled by reduced sediment strengths due to low effective stresses driven by the presence of free gas. The campaign has revealed numerous fluid escape features that raise the question of broad and massive slope failures in the Amazon fan

Age dating and triggering mechanisms of recent submarine landslides in the Alboran Sea

International audienceIn the southern margin of the Alboran Sea, the sedimentary succession over the past 1 Myr contains several submarine landslides. We observe that their geographical distribution does not appear to be related to the active Al Idrissi fault system (AIFS) responsible of the recent earthquakes (i.e. they are located more than 10 km away). The head scarps of landslides west of AIFS coincide with the edges of the thickest parts of the contourite drifts dominating this margin. This evidence potentially supports the idea that landslide initiation is related to locally higher sedimentation rates in the edges of contourites, which drive upward fluid flow. Additionally, contourite edges overlying active blind thrusts, initiated during the Tortonian due to the Euro-African convergence, suggest that fluid flow could also result from tectonic activity. These two hypothesis converge on the following idea: local upward fluid flow reduces the effective stresses of contourite edges, thus preconditioning their stability and bringing the slopes to a sort of metastable state. While the distances between the investigated landslides and the AIFS cannot be used as evidence for earthquakes as potential triggers, the discussion of the far-reaching effects of earthquakes on metastable slopes remains open. During the Albacore cruise (NO Pourquoi Pas?, 2021) several calypso cores were collected at three sites west of the AIFS, both inside and outside landslides with a seafloor expression. The objective is to better understand the role of sedimentation rates in fluid flow generation and the potential effects of seismic loading on landslide triggering. Correlations between continuous density and magnetic susceptibility measurements of whole round cores and in- situ geotechnical measurements provide information about the presence of a sediment drape overlying landslide deposits. Isotopic δ18O analysis of planktonic foraminifera from sediment cores, correlated with paleoceanographic records in the Alboran sea, suggests an age of 12-13 ka for the base of the sediment drape in all three sites, indicating a synchronous triggering mechanism