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- Yang, H., et al.
(författare)
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Preliminary Characterization of Submarine Basalt Magnetic Mineralogy Using Amplitude-Dependence of Magnetic Susceptibility
- 2024
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Ingår i: Geochemistry, Geophysics, Geosystems. - 1525-2027. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- The past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non-destructive method that utilizes the amplitude-dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock-magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude-dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude-dependence should ideally be demagnetized either using alternating fields or via finely-spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples.
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- Thoram, S., et al.
(författare)
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Nature and Origin of Magnetic Lineations Within Valdivia Bank : Ocean Plateau Formation by Complex Seafloor Spreading
- 2023
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 50:13
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Tidskriftsartikel (refereegranskat)abstract
- Valdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan-Gough hotspot at the Mid-Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi-linear polarity zones crossing the plateau and following expected MAR paleo-locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n-C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading-type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.
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- Glasbey, James, et al.
(författare)
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The impact of conversion on the risk of major complication following laparoscopic colonic surgery : an international, multicentre prospective audit
- 2018
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Ingår i: Colorectal Disease. - : Wiley. - 1462-8910. ; 2020 Suppl 6, s. 69-89
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Laparoscopy has now been implemented as a standard of care for elective colonic resection around the world. During the adoption period, studies showed that conversion may be detrimental to patients, with poorer outcomes than both laparoscopic completed or planned open surgery. The primary aim of this study was to determine whether laparoscopic conversion was associated with a higher major complication rate than planned open surgery in contemporary, international practice.METHODS: Combined analysis of the European Society of Coloproctology 2017 and 2015 audits. Patients were included if they underwent elective resection of a colonic segment from the caecum to the rectosigmoid junction with primary anastomosis. The primary outcome measure was the 30-day major complication rate, defined as Clavien-Dindo grade III-V.RESULTS: Of 3980 patients, 64% (2561/3980) underwent laparoscopic surgery and a laparoscopic conversion rate of 14% (359/2561). The major complication rate was highest after open surgery (laparoscopic 7.4%, converted 9.7%, open 11.6%, P < 0.001). After case mix adjustment in a multilevel model, only planned open (and not laparoscopic converted) surgery was associated with increased major complications in comparison to laparoscopic surgery (OR 1.64, 1.27-2.11, P < 0.001).CONCLUSIONS: Appropriate laparoscopic conversion should not be considered a treatment failure in modern practice. Conversion does not appear to place patients at increased risk of complications vs planned open surgery, supporting broadening of selection criteria for attempted laparoscopy in elective colonic resection.
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