Asymmetric continental deformation during South Atlantic rifting along southern Brazil and Namibia

Plate restoration of South America and Africa to their pre-breakup position faces the problem of gaps and overlaps between the continents, an issue commonly solved with implementing intra-plate deformation zones within South America. One of these zones is often positioned at the latitude of SE/S Brazil. However, geological evidence for the existence of a distinct zone in this region is lacking, which is why it remains controversial and is not included in all modeling studies. In order to solve this problem we present a study of multiple geological aspects of both parts of the margin, SE/S Brazil and its conjugate part NW Namibia at the time of continental breakup. Our study highlights pronounced differences between these regions with respect to Paraná-Etendeka lava distribution, magmatic dyke emplacement, basement reactivation, and fault patterns. In Namibia, faults and dykes reactivated the rift-parallel Neoproterozoic basement structure, whereas such reactivation was scarce in SE/S Brazil. Instead, most dykes, accompanied by small-scale grabens, are oriented margin-perpendicular along the margin from northern Uruguay to São Paulo. We propose that these differences are rooted in large-scale plate movement and suggest a clockwise rotation of southern South America away from a stable northern South America and Africa, in a similar way as proposed by others for a Patagonian continental section just prior to South Atlantic rifting. This rotation would produce margin-parallel extension in SE/S Brazil forming margin-perpendicular pathways for lava extrusion and leading to the asymmetric distribution of the Paraná-Etendeka lavas. NW Namibia instead remained relatively stable and was only influenced by extension due to rifting, hot spot activity, and mantle upwelling. Our study argues for significant margin-parallel extension in SE/S Brazil, however not confined to a single distinct deformation zone, but distributed across ~ 1000 km along the margin

Contrasting stress fields on correlating margins of the South Atlantic

The “passiveness” of passive continental margins across the globe is currently under debate since several studies have shown that these margins may experience a variety of stress states and undergo significant vertical movement post-breakup. Of special interest is the South Atlantic, because the bounding continents have very different recent geological histories, with Africa experiencing continental rifting whereas South America is influenced by subduction on the Pacific side. It is not clear to what extent the Atlantic continental margins are subject to the same stresses and vertical motions as the main continents. To address this problem, we performed a paleostress analysis of two originally adjacent areas, i.e. NW Namibia and SE/S Brazil. Both areas are covered by the ~ 133-Ma-old Paraná-Etendeka extrusives that were emplaced shortly before or during the onset of the Atlantic rifting. Thus, the volcanics serve as a time marker for syn- or post-rift deformation. Collected fault slip data in the volcanics reveal remarkable differences between the two correlating areas. NW Namibia was dominated by extension in ENE-WSW and SW-NE directions, and by minor strike-slip movement with NW-SE directed compression. SE/S Brazil was mostly affected by strike-slip faulting, with compression oriented E-W and SW-NE. Similar fault systems appear widespread across SE Brazil and may be the combined result of flexural margin bending and the Nazca plate subduction. The results of NW Namibia differ from known compressional stress tensors in western South Africa, post-dating 90 Ma. The south-western African continental margin may thus have experienced a spatially variable stress history. Our results show that the tectonic evolution of the continental margins of the South Atlantic is not passive and that both margins vary significantly in structural style and stress fields, indicating that variable plate boundary forces play a major role in margin evolution

Deformation and fluid flow in the Huab Basin and Etendeka Plateau, NW Namibia

The Lower Cretaceous Twyfelfontein sandstone formation in the Huab Basin in NW Namibia shows the effects of volcanic activity on a potential reservoir rock. The formation was covered by the Paraná-Etendeka Large Igneous Province shortly before or during the onset of South-Atlantic rifting. Deformation bands found in the sandstone trend mostly parallel to the continental passive margin and must have formed during the extrusion of the overlying volcanic rocks, indicating that their formation is related to South-Atlantic rifting. 2D-image porosity analysis of deformation bands reveals significant porosity reduction from host rock to band of up to 70 %. Cementation of the sandstone, linked to advective hydrothermal flow during volcanic activity, contributes an equal amount to porosity reduction from host rock to band when compared to initial grain crushing. Veins within the basaltic cover provide evidence for hot fluid percolation, indicated by spallation of wall rock and colloform quartz growth, and for a later low-temperature fluid circulation at low pressures indicated by stilbite growth sealing cavities. Sandstone samples and veins in the overlying volcanic rocks show that diagenesis of the Twyfelfontein sandstone is linked to Atlantic rifting and was affected by both hydrothermal and low-thermal fluid circulation

An Unusual Case of Chronic Superior Mesenteric Vein Thrombosis

Introduction:Intestinal ischemia can be caused by any process that reduces intestinal blood flow. Mesenteric venous thrombosis (MVT) describes thrombosis of the superior or inferior mesenteric vein, and represents approximately 10 percent of all cases of acute mesenteric ischemia. The incidence of MVT has increased over the past 40 years, likely as a result of greater use of abdominal CT, and may present with acute abdominal pain or as an asymptomatic incidental finding on abdominal imaging. We present a rare and unusual case of MVT. Case presentation: A 42 year old female with decompensated alcoholic liver cirrhosis presented to the ED with severe RLQ pain associated with nausea and nonbloody emesis. She had a pulse of 130, BP of 102/47 and temperature of 102.5. Physical exam demonstrated a mildly distended abdomen with tenderness to palpation of the right upper and lower quadrants, and a negative fluid wave shift. Lactic acid on admission was 3.9. She was resuscitated with IV fluids and started on broad spectrum antibiotics. Blood cultures on admission grew E. coli. Lactic acid continued to rise despite fluid replacement and antibiotics, and her pain did not subside. A CT abdomen & pelvis with contrast was ordered for concern of acute appendicitis, and was notable for thickening of the terminal ileum with a normal caliber appendix. Her lactic acid peaked at 6.7, and concern arose for mesenteric ischemia. A CT angiography abdomen & pelvis was done revealing a chronic occlusion of the central superior mesenteric vein, with cavernous transformation. The patient’s lactic acid improved, and she remained hemodynamically well compensated despite no intervention pursued for her MVT after involving GI and IR. She was eventually discharged in stable condition. Discussion: Two large series demonstrated that chronic MVT accounts for 24% to 40% of total cases of MVT. Our patient had the rarer chronic MVT in the setting of suspected mesenteric ischemia, however, this was likely an incidental finding and was not the source of her pain. Our case highlights the importance of acknowledging the different presentations of MVT such that investigation and management is not confounded by the rarity of the pathology

Das Laufen und die Vereinigung der Eichkopplungen des Standardmodells zur Drei-Schleifen-Ordnung

Im Rahmen dieser Dissertation werden alle wichtigen Drei-Schleifen-Korrekturen zu den Eichkopplungs-Beta-Funktionen des Standardmodells der Teilchenphysik vorgestellt. Außerdem wird die Eichkopplungsvereinigung im Rahmen des Minimalen Supersymmetrischen Standardmodells auf höchster Präzision untersucht. Beide Analysen wurden computergestützt durchgeführt, für diese Analysen neu entwickelte Programme sind dokumentiert

Microstructure and fluid flow in the vicinity of basin bounding faults in rifts – The Dombjerg Fault, NE Greenland rift system

Faults commonly form loci for high fluid flux in sedimentary basins, where fluids, rocks and deformation processes frequently interact. Here, we elucidate the interaction of fluid flow, diagenesis and deformation near basin-bounding faults in sedimentary basins through a study in the vicinity (0–3.5 km) of the Dombjerg Fault in the NE Greenland rift system. Due to fault-controlled fluid circulation, fault-proximal syn-rift clastics underwent pervasive calcite cementation, whereas uncemented clastics at some distance from the fault remained highly porous and friable. Correspondingly, two distinct deformation regimes developed to accommodate continued deformation: discrete brittle fractures formed in calcite cemented rocks, whereas cataclastic deformation bands formed in uncemented deposits. We show that low-permeable deformation bands forming in highly porous rocks were associated with localized host rock alteration, and chemical reduction of porosity along bands. In rocks with cementation-induced low porosity, brittle fractures created new pathways for fluids, but were subsequently filled with calcite. Occasionally, veins comprise multiple generations of microcrystalline calcite, likely precipitated from rapidly super-saturated fluids injected into the fractures. This suggests cemented deposits sealed uncemented compartments, where fluid overpressure developed. We conclude that compartmentalized flow regimes may form in fault-bounded basins, which has wide implications for assessments of potential carbon storage, hydrocarbon, groundwater, and geothermal site

The Correlation Problem in Operational Risk

This paper demonstrates that aggregate losses are necessarily low as long as we remain under the standard assumptions of LDA models. Moreover empirical findings show that the correlation between two aggregate losses is typically below 5%, which opens a wide scope for large diversification effects, much larger than those the Basel Committee seems to have in mind. In other words, summing up capital charges is in substantial contradiction with the type of correlation consistent with the standard LDA model

The "Studies in Ethnomethodology" Are a Way of Understanding and Handling Empirical Materials and Thoughts. Eric Laurier in Conversation With Hannes Krämer, Dominik Gerst & René Salomon

In the following conversation Eric LAURIER talks about the role of ethnomethodology's foundational account—the "Studies in Ethnomethodology" (GARFINKEL, 1967)—within the UK and the influence of the book on his own research as well as on human geography, mobility studies, actor-network-theory, and a general social science methodology. He therefore underlines the peculiar focus of GARFINKEL on the everyday, his non-ironic position towards member's practices, and the plurivocality of the book. Giving an elaborated account on the methodological challenges with an ethnomethodological approach including video recordings he differentiates between the video as a research tool and video usage as a member's practice. LAURIER demonstrates the inspiring and initiating content of the studies as well as its limits. By doing so he can show the prolific quality for current research fields like the study of mobility and movement, the question of space and place, and the role of the "Studies in Ethnomethodology" as a political text

A geological collection and methodology for tracing the provenance of Palaeolithic colouring materials

Although prehistoric sites frequently contain numerous fragments and traces of many different kinds of colouring matter, intensive study of this type of archaeological remains began only recently. Such studies, aimed at determining how raw materials formed and changed over time, and how they were transported by the groups of humans who used them, are extremely valuable as they reveal shared strategies, that is, cultural traditions and the spaces in which they developed. The scope of this paper focusses on the description of the main geological contexts in which ferruginous colouring materials form and are found. In the framework of a collective research program called Pigmentothèque (iron- and manganese-rich rocks and minerals library), geological surveys are conducted taking into consideration the geological settings in which colouring materials are present and using a common record and sampling methodology which is followed by petrophysical, mineralogical and chemical analyses based on a shared procedure and vocabulary. In order to go beyond descriptions based solely on colour and chemical composition, we describe the great variety of iron-rich materials that can be used to obtain colouring matter. This diversity in the formation and evolution of iron-rich materials must be taken into account when trying to understand past humans’ choices of raw materials, their provenance and the anthropogenic and natural modifications they have undergone. We also describe criteria for recognising cohesive remains of colouring matter during archaeological excavations, so these artefacts can take their place alongside other mineral resources in helping improve our understanding of past societies