Multi-pulsed turbidity current dynamics and geological implications

Deposits of turbidity currents - turbidites - commonly exhibit upward-fining grainsize profiles, reflecting deposition from flows with simple rapidly-waxing then progressively-waning velocity structures. However, turbidites with patterns of multiple cycles of inverse-to-normal grading are not uncommon. Such deposits are interpreted as being deposited under the influence of repeated waxing-waning velocity cycles within multi-pulsed turbidity currents and are termed "multi-pulsed turbidites". Multi-pulsed flow can be initiated by sequences of retrogressive submarine failures in which each slumping episode can form a pulse in the velocity structure, or may arise due to the combination of multiple flows at downstream confluences; separate flows may even run into each other over long distances. In the first case, it has been inferred that multi-pulsed deposits might carry signals of flow initiation, with each slump linked to a seismic impulse, and further, that such signals can be recognised in the vertical grading structures of distal turbidites. The focus of this research has been to establish i) how multi-pulsed flow dynamics and associated deposits vary along flow pathways and ii) the degree to which grading structures in turbidites deposited by multi-pulsed flows permit inference of flow initiation mechanisms. Initial experiment modelling of single- and multi-pulsed solute-driven gravity flows shows that internal pulses are necessarily advected forward, eventually merging with the flow head such that multi-pulsed flows transition from being cyclically waxing-waning to waxing on arrival then monotonically waning. This finding implies that initiation signals should be distorted then lost in any deposits along the flow pathway. Accordingly, an interpretational template for the spatial variation in turbidite character along flow pathways was developed, accounting for both pulse merging and flow combination at confluences. Further experiments were conducted to support a scaling analysis to estimate merging lengths; these lengths are shorter than those documented from prototype settings, and may reflect a limitation in the scope of application, arising from experimental constraints. Experiment modelling of single- and multi-pulsed sediment-driven gravity flows confirms the occurrence of the pulse merging phenomenon in turbidity currents. Analysis of associated deposits confirms the downstream spatial transition from multi- to uni-pulsed turbidites, albeit with the point of transition being more proximal in the laboratory deposit than the point of pulse merging. However, the spatial persistence of the complex velocity structure up to the point of merging need not be reflected in the associated deposit. Beyond the merging point, single-pulsed turbidites must always be deposited. Such deposits cannot be used to infer flow initiation mechanisms

Dynamics and deposition of sediment-bearing multi-pulsed flows and geological implication

Previous studies on dilute, multi-pulsed, subaqueous saline flows have demonstrated that pulses will inevitably advect forwards to merge with the flow front. On the assumption that pulse merging occurs in natural-scale turbidity currents, it was suggested that multi-pulsed turbidites that display vertical cycles of coarsening and fining would transition laterally to single-pulsed, normally graded turbidites beyond the point of pulse merging. In this study, experiments of dilute, single- and multi-pulsed sediment-bearing flows (turbidity currents) are conducted to test the linkages between downstream flow evolution and associated deposit structure. Experimental data confirm that pulse merging occurs in laboratory-scale turbidity currents. However, only a weak correspondence was seen between longitudinal variations in the internal flow dynamics and the vertical structure of deposits; multi-pulsed deposits were documented, but transitioned to single-pulsed deposits before the pulse merging point. This early transition is attributed to rapid sedimentation-related depletion of the coarser-grained suspended fraction in the laboratory setting, whose absence may have prevented the distal development of multi-pulsed deposits; this factor complicates estimation of the transition point in natural-scale turbidite systems

Dynamics and Deposition of Sediment-Bearing Multi- Pulsed Flows and Geological Implication

Copyright © 2019, SEPM (Society for Sedimentary Geology) Previous studies on dilute, multi-pulsed, subaqueous saline flows have demonstrated that pulses will inevitably advect forwards to merge with the flow front. On the assumption that pulse merging occurs in natural-scale turbidity currents, it was suggested that multi-pulsed turbidites that display vertical cycles of coarsening and fining would transition laterally to single-pulsed, normally graded turbidites beyond the point of pulse merging. In this study, experiments of dilute, single- and multi-pulsed sediment-bearing flows (turbidity currents) are conducted to test the linkages between downstream flow evolution and associated deposit structure. Experimental data confirm that pulse merging occurs in laboratory-scale turbidity currents. However, only a weak correspondence was seen between longitudinal variations in the internal flow dynamics and the vertical structure of deposits; multi-pulsed deposits were documented, but transitioned to single-pulsed deposits before the pulse merging point. This early transition is attributed to rapid sedimentation-related depletion of the coarser-grained suspended fraction in the laboratory setting, whose absence may have prevented the distal development of multi-pulsed deposits; this factor complicates estimation of the transition point in natural-scale turbidite systems

Morphological, molecular and MALDI-TOF MS identification of ticks and tick-associated pathogens in Vietnam

International audienceMatrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a promising and reliable tool for arthropod identification, including the identification of alcohol-preserved ticks based on extracted leg protein spectra. In this study, the legs of 361 ticks collected in Vietnam, including 251 Rhiphicephalus sanguineus s.l, 99 Rhipicephalus ( Boophilus ) microplus , two Amblyomma varanensis , seven Dermacentor auratus , one Dermacentor compactus and one Amblyomma sp. were submitted for MALDI-TOF MS analyses. Spectral analysis showed intra-species reproducibility and inter-species specificity and the spectra of 329 (91%) specimens were of excellent quality. The blind test of 310 spectra remaining after updating the database with 19 spectra revealed that all were correctly identified with log score values (LSV) ranging from 1.7 to 2.396 with a mean of 1.982 ± 0.142 and a median of 1.971. The DNA of several microorganisms including Anaplasma platys , Anaplasma phagocytophilum , Anaplasma marginale , Ehrlichia rustica , Babesia vogeli , Theileria sinensis , and Theileria orientalis were detected in 25 ticks. Co-infection by A . phagocytophilum and T . sinensis was found in one Rh . ( B ) microplus

Catheter-directed intra-arterial thrombolysis in the treatment of acute thrombosis of below-the-knee arteries

Selecting treatment options in acute arterial thrombosis of the lower extremity, which threatens limb viability, is still a challenge for vascular surgeons. Early restoration of blood flow is crucial and is conducted by surgical thrombectomies or endovascular procedures, depending on patient condition. Catheter-directed thrombolysis with or without percutaneous mechanical thrombectomy for acute limb ischemia has been widely implemented from the early 1990s. Here, we present 2 cases of acute thrombosis of below-the-knee arteries, where we successfully saved the involved limbs using catheter-directed thrombolysis and thrombus aspiration

Optimizing Active Tuberculosis Case Finding: Evaluating the Impact of Community Referral for Chest X-ray Screening and Xpert Testing on Case Notifications in Two Cities in Viet Nam

To accelerate the reduction in tuberculosis (TB) incidence, it is necessary to optimize the use of innovative tools and approaches available within a local context. This study evaluated the use of an existing network of community health workers (CHW) for active case finding, in combination with mobile chest X-ray (CXR) screening events and the expansion of Xpert MTB/RIF testing eligibility, in order to reach people with TB who had been missed by the current system. A controlled intervention study was conducted from January 2018 to March 2019 in five intervention and four control districts of two low to medium TB burden cities in Viet Nam. CHWs screened and referred eligible persons for CXR to TB care facilities or mobile screening events in the community. The initial diagnostic test was Xpert MTB/RIF for persons with parenchymal abnormalities suggestive of TB on CXR or otherwise on smear microscopy. We analyzed the TB care cascade by calculating the yield and number needed to screen (NNS), estimated the impact on TB notifications and conducted a pre-/postintervention comparison of TB notification rates using controlled, interrupted time series (ITS) analyses. We screened 30,336 individuals in both cities to detect and treat 243 individuals with TB, 88.9% of whom completed treatment successfully. All forms of TB notifications rose by +18.3% (95% CI: +15.8%, +20.8%). The ITS detected a significant postintervention step-increase in the intervention area for all-form TB notification rates (IRR(β6) = 1.221 (95% CI: 1.011, 1.475); p = 0.038). The combined use of CHWs for active case findings and mobile CXR screening expanded the access to and uptake of Xpert MTB/RIF testing and resulted in a significant increase in TB notifications. This model could serve as a blueprint for expansion throughout Vietnam. Moreover, the results demonstrate the need to optimize the use of the best available tools and approaches in order to end TB