Neutrino Mass and μ→e+γ\mu \rightarrow e + \gamma from a Mini-Seesaw

The recently proposed "mini-seesaw mechanism" combines naturally suppressed Dirac and Majorana masses to achieve light Standard Model neutrinos via a low-scale seesaw. A key feature of this approach is the presence of multiple light (order GeV) sterile-neutrinos that mix with the Standard Model. In this work we study the bounds on these light sterile-neutrinos from processes like \mu ---> e + \gamma, invisible Z-decays, and neutrinoless double beta-decay. We show that viable parameter space exists and that, interestingly, key observables can lie just below current experimental sensitivities. In particular, a motivated region of parameter space predicts a value of BR(\mu ---> e + \gamma) within the range to be probed by MEG.Comment: 1+26 pages, 7 figures. v2 JHEP version (typo's fixed, minor change to presentation, results unchanged

The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls

Cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences, provided that an imprint of insolation variations caused by Earth’s orbital eccentricity, obliquity and/or precession is preserved (Milankovitch forcing). Numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy, but the robustness of the methodology and its dependence on the investigator have not been systematically evaluated. We developed the Cyclostratigraphy Intercomparison Project (CIP) to assess the robustness of cyclostratigraphic methods using an experimental design of three artificial cyclostratigraphic case studies with known input parameters. Each case study is designed to address specific challenges that are relevant to cyclostratigraphy. Case 1 represents an offshore research vessel environment, as only a drill-core photo and the approximate position of a late Miocene stage boundary are available for analysis. In Case 2, the Pleistocene proxy record displays clear nonlinear cyclical patterns and the interpretation is complicated by the presence of a hiatus. Case 3 represents a Late Devonian proxy record with a low signal-to-noise ratio with no specific theoretical astronomical solution available for this age. Each case was analyzed by a test group of 17-20 participants, with varying experience levels, methodological preferences and dedicated analysis time. During the CIP 2018 meeting in Brussels, Belgium, the ensuing analyses and discussion demonstrated that most participants did not arrive at a perfect solution, which may be partly explained by the limited amount of time spent on the exercises (∼4.5 hours per case). However, in all three cases, the median solution of all submitted analyses accurately approached the correct result and several participants obtained the exact correct answers. Interestingly, systematically better performances were obtained for cases that represented the data type and stratigraphic age that were closest to the individual participants’ experience. This experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions and, importantly, that it is a trainable skill. Finally, we emphasize the importance of an integrated stratigraphic approach and provide flexible guidelines on what good practices in cyclostratigraphy should include. Our case studies provide valuable insight into current common practices in cyclostratigraphy, their potential merits and pitfalls. Our work does not provide a quantitative measure of reliability and uncertainty of cyclostratigraphy, but rather constitutes a starting point for further discussions on how to move the maturing field of cyclostratigraphy forward

Sedimentary development and correlation of long-term off-reef to shallow-water Devonian carbonate records in Europe

The Devonian Period was characterized by extensive shallow-marine regions, with the largest carbonate platform development of the Phanerozoic Eon. The research carried out in this thesis integrates field work, petrographic analysis, conodont biostratigraphy, elemental and carbon isotope geochemistry, magnetic susceptibility and magnetic hysteresis measurement. The aim, to better understand and characterize the environmental conditions that led to the development of three of the largest European Devonian carbonate platforms. This multi-disciplinary study also proposes to validate the use of magnetic susceptibility as a reliable tool for palaeoenvironmental reconstruction and long-distance correlation in marine carbonate. Fieldwork was conducted on four key sections of the European Pre-Mesozoic massifs: the Ardennes (La Thure and Fromelennes-Flohimont), the Rheinisches Schiefergebirge (Burgberg) and the Carnic Alps (Freikofel). The large quantity and in-depth analysis of rock samples and thin-sections has demonstrated the fascinating environmental diversity that shaped the carbonate platforms in the Rhenohecynian and Paleotethys oceans towards the mid-late Devonian times. The aforementioned analysis has enabled the development of reconstructed sedimentary models and large-scale shallowing-deepening histories for each section. New and published biostratigraphic data provided reliable age constraints for the foremost environmental changes evident in each of the sections. δ13C results from the Frasnian – Famennian boundary in the Burgberg and Freikofel sections have revealed Kellwasser events in limestone lithologies. Based on the analysis of ±1800 samples, a high-resolution magnetic susceptibility (MS) curve for each section has been developed, highlighting the strong link between the MS signatures and the syn-sedimentary parameters, such as carbonate productivity/sedimentation rate, water agitation and siliciclastic input. The comparison between MS and elemental geochemistry datasets has demonstrated the inherent-parallel link existing between the siliciclastic input proxies and the variation in MS signature in each of the sections. Magnetic hysteresis measurements have shown that ferromagnetic minerals such as magnetite control the MS signal. By comparing our data sets with published data we could confirm that our MS signal is remagnetized. However links between siliciclastic input proxies and MS, and between MS and environmental parameters have proven a relatively good preservation of the primary depositionally-induced MS signal. Finally, by integrating complete data and establishing a correlation chart including the four long-term MS curves, it is apparent that on a regional scale long-term MS trends can be correlated, as long as the evolution of the main depositional setting in the sections studied remains comparable. The significant impact of syn-sedimentary parameters on the final MS signature seems to obscure the imprint of parameters driving variations in continental erosion (e.g., climate, sea-level and tectonic variations) and therefore limiting the inter-regional correlations. This collaborative project on time-series analysis of long-term high-resolution MS records in the Dinant Syncline has revealed the imprint of astronomical parameters, giving rise to a more accurate estimate of the Givetian Stage’s duration

Lower Palaeozoic and Devonian carbonate facies in Nepal

Nepal is localized in the central part of the Himalayan arc. In uplift since the Cenozoic time, the Himalaya is traditionally divided into six lithotectonic zones extending in parallel belts. From north to south there are respectively: (1) the Trans-Himalayan batholith; (2) the Indus-Tsangpo suture zone; (3) the Tethyan (Tibetan) Himalaya; (4) the Higher (Greater) Himalaya; (5) the Lesser Himalaya; and (6) the Sub-Himalaya. This PhD thesis is focused on the Tethyan sedimentary rocks exposed in the Nepal Tethyan Himalaya belt and in the thrusting nappes belonging to the Lesser Himalaya. These nappes contain unmetamorphosed sedimentary rocks which might belong to the Tethyan sedimentary succession. The Tethyan Himalaya has preserved highly fossiliferous marine rocks deposited on the shelf and slope of the Indian continental margin from Late Proterozoic-Cambrian through early Eocene times. The main objective of this PhD thesis is to build a first sedimentological canvas for the Lower Paleozoic and Devonian carbonated rocks of Nepal which could be compared with the Belgian facies. This long distance comparison between the Belgian and the Nepalese basins will allow to have a better understanding of the phenomena that run the global carbonate sedimentation. The methods that will be used to achieve this work are: (1) bed by bed sampling; (2) petrographic analysis and facies modelling; (3) magnetic susceptibility analysis for correlations and eustatism and (4) paleontological datation. A first sedimentological campaign took place during the months of March and April 2009. It allowed to study three sections around Katmandu valley and two sections in the Annapurna range (Manang area). The sections studied around Katmandu (Pulchauki and Chandragiri Hill) belonged to the Formation of Chandragiri (Ordovician) and Godavari (Devonian) which are mainly constituted by carbonate rocks. The sections described in Manang area are mainly made-up by the terrigeneous rocks of the Dark Band, Tilicho Pass and Tilicho Lake Formation (Silurian to Lower Carboniferous). The diversity of facies observed in these five sections will be exposed

Magnetic susceptibility records for global stratigraphic correlations? New constraint in the context of carbonate platform reconstruction (Middle Devonian, Ardennes)

peer reviewedThis study undertakes a multi-disciplinary approach (sedimentology, magnetic susceptibility, geochemistry and hysteresis magnetic measurement) to increase our understanding of the Ardennes Givetian platform (Belgium and France) and to address a major question on the reliability of the magnetic susceptibility (MS) records for global correlations of marine carbonate records. Sedimentological analyses on two successions lasting millions of years, reveal an extended diversity of shallow- to off-reef palaeoenvironmental settings across the platform and allow to constrain the main sea-level fluctuations and associated environmental changes throughout the Givetian in Ardennes. The comparison of the two MS profiles allows to provide correlations, despite the long distance between the sections and their different sedimentological background. However, the comparison of the MS profiles from the Ardennes with contemporaneous data from the Rhenische Schiefergebirge (Germany) does not show any evidences of correlation, challenging studies that present the MS signal as a global correlation tool. These outcomes are crucial because they have repercussions on future global and regional stratigraphic issues as well as for paleoclimatic reconstructions. Here, we provide new evidences outlining that autogenic processes, which operate at long time scale, modulate the MS signal and have a strong influence over the magnetic susceptibility records that can leads to the absence of correlation within long-term MS trends

Cyclostratigraphic calibration of the Late Devonian time scale

The Late Devonian period was affected by major, irreversible changes including two of the most severe biodiversity crises in Earth’s history, the so-called Kellwasser and Hangenberg Events (respectively at the Frasnian – Famennian and the Famennian – Carboniferous boundaries). Currently, hypotheses for the Late Devonian extinctions include sea-level fluctuations and regression, climate cooling, ocean anoxia, massive volcanism and/or bolide impact. Unfortunately, testing these hypotheses is impaired by a lack of sufficient temporal resolution in paleobiological, tectonic and proxy climate records. Recent advances in astronomical dating have improved the accuracy of the Frasnian time scale and part of the Famennian (De Vleeschouwer et al., 2012, 2013). However, the time duration of the Famennian stage remains poorly constrained even though this is the key to understanding cause-and-effect relationships of the Late Devonian greenhouse–icehouse transition and the onset of the end Famennian glaciation that ultimately led to the Hangenberg Event at the Devonian–Carboniferous boundary. During the Late Devonian an epieric sea in mid-continent North America occupied the Illinois Basin onto which a Late Frasnian – Early Carboniferous sequence of deep-shelf deposits was archived. A complete record of this sequence, mainly composed of marl, organic-rich shale, silty-shale and carbonate, is captured in three overlapping cores stored in the Iowa Geological Survey (H-30, Sullivan Slough and H-32). H-30 records the Frasnian-Famennian boundary, the Sullivan Slough covers almost all the Famennian (middle triangularis-upper expansa conodont zones) and H-32 spans the junction between the uppermost Famennian and lowermost Carboniferous. To have the best chance of capturing Milankovitch cycles (long- and short-eccentricity cycles as well as obliquity and precession), 2200 rock samples were collected at 5-cm intervals across the entire sequence. Magnetic susceptibility (MS) was measured on each sample and the preservation of paleoenvironmental/climatic information into the signal was verified through geochemical analyses (Ti, Al, Zr by XRF) and magnetic measurements (low temperature magnetic susceptibility and IRM acquisitions). Correlation and overlap between each core was made using available conodont biostratigraphy and then refined by comparing the trends in the MS and δ13C signals for critical intervals. To estimate the duration of the Famennian stage we applied multiple techniques on the MS signal (multitaper method, evolutive harmonic analysis and adaptive-weighted harmonic F-test). By combining these techniques, we identified highly stable 405-kyr cycles across the Sullivan Slough and the H-32 cores. 405-kyr cycles were not observed in H-30, but 100-kyr cycles were identified. A preliminary estimate of the duration for the Famennian stage using the 405-kyr cycle as chronometer constrains the duration of the Famennian stage to 13 ± 0.4 Myr with an average sedimentation rate of 0.5 cm/kyr across the sequence

CYCLOSTRATIGRAPHIC ANALYSIS OF THE LOWER CRETACEOUS TERRESTRIAL SONGLIAO BASIN, NORTHEAST CHINA

peer reviewedRecent exploration of the Songliao Basin, NE China, which is one of the largest and longlived Cretaceous continental basins in the world with a continuous 10-km-thick sequence of strata, provides new opportunities to study terrestrial climate change and to improve the Early Cretaceous time scale. Understanding the evolution of the basin, including the climatic and environmental changes that affected sediment deposition, is key to identifying the forces that led to enhanced carbon burial and preservation, leading to today’s oil and gas reserves in the basin. In this study, we conduct cyclostratigraphic analysis on natural gamma-ray logs from extended boreholes in the Songliao Basin. The target is the Lower Cretaceous Shahezi Formation (K1S), a 836-m-thick succession with black and dark grey mudstone, siltstone, fine grained sandstone, gravel-bearing sandstone and conglomerate, together with meter-scale black coal units distributed throughout the upper part of the formation. The mudstones have the highest gamma-ray values and the conglomerates the lowest gammaray values. Time series analysis of the gamma-ray logs from selected boreholes reveals power spectra that are consistent with Earth’s astronomical frequencies of precession, obliquity and orbital eccentricity, providing strong evidence for astronomically driven climate change. The results also indicate that black coal coincides with short eccentricity minima that exceed a threshold. We conclude that the age of K1S is from early Valanginian to late Hauterivian with a duration of approximately 11 million years by calculating cycle number and matching with the La2004 theoretical astronomical model. The formation may also reflect the well-known transient cooling Weissert Event in the mid-Valanginian as evidenced by marine glendonites at Svalbard Island. The cyclic evolution of the formation’s lithology indicates a paleo-lake and surrounding environment that expanded and contracted repeatedly. Astronomical forcing influenced paleo-lake level: climate was warm and humid with high orbital eccentricity, and cold and dry with low orbital eccentricity. Sedimentation rates significantly decreased from lower to upper K1 S as the basin evolved from synrift to post-rift conditions

Magnetic susceptibility evolution on Paleozoic sedimentary settings, a clue for past paleoenvironments

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