Pub Date : 2020-07-15DOI: 10.14379/iodp.proc.361.202.2020
J. Just
The paleomagnetic shipboard data of International Ocean Discovery Program Site U1475, with a record reaching back to approximately 7 Ma, allowed for the identification of major magnetic polarity chrons and subchrons back to ~3.5 Ma. However, the natural remanent magnetization (NRM) was very weak, and transitional intervals with unclear polarity were as thick as several meters. The midpoints of these transitional intervals were reported in the shipboard results without decimal places because of the poor data quality. To evaluate and possibly refine the shipboard magnetostratigraphy, subsampling was performed across the polarity transitions. Detailed alternating field (AF) demagnetization experiments were conducted on these discrete samples and were complemented by anhysteretic remanent magnetization acquisition measurements and subsequent demagnetization. AF demagnetization data of NRM were analyzed using anchored principal component analysis (PCA) to obtain the characteristic remanent magnetization. These PCA results generally confirm the smoothed signal across polarity transitions at Site U1475. However, the midpoint depths of the top of the Keana Subchron, the Gauss-Matuyama and Matuyama-Brunhes boundaries, and the base of the Olduvai Subchron were adjusted.
{"title":"Data report: evaluation of shipboard magnetostratigraphy by alternating field demagnetization of discrete samples, Expedition 361, Site U1475","authors":"J. Just","doi":"10.14379/iodp.proc.361.202.2020","DOIUrl":"https://doi.org/10.14379/iodp.proc.361.202.2020","url":null,"abstract":"The paleomagnetic shipboard data of International Ocean Discovery Program Site U1475, with a record reaching back to approximately 7 Ma, allowed for the identification of major magnetic polarity chrons and subchrons back to ~3.5 Ma. However, the natural remanent magnetization (NRM) was very weak, and transitional intervals with unclear polarity were as thick as several meters. The midpoints of these transitional intervals were reported in the shipboard results without decimal places because of the poor data quality. To evaluate and possibly refine the shipboard magnetostratigraphy, subsampling was performed across the polarity transitions. Detailed alternating field (AF) demagnetization experiments were conducted on these discrete samples and were complemented by anhysteretic remanent magnetization acquisition measurements and subsequent demagnetization. AF demagnetization data of NRM were analyzed using anchored principal component analysis (PCA) to obtain the characteristic remanent magnetization. These PCA results generally confirm the smoothed signal across polarity transitions at Site U1475. However, the midpoint depths of the top of the Keana Subchron, the Gauss-Matuyama and Matuyama-Brunhes boundaries, and the base of the Olduvai Subchron were adjusted.","PeriodicalId":258552,"journal":{"name":"South African Climates (Agulhas LGM Density Profile)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128239145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-05DOI: 10.14379/iodp.proc.361.201.2020
D. P. Babin, A. Franzese, S. Hemming, I. Hall, L. Levay, S. Barker, L. Tejeda, M. Simon
X-ray fluorescence (XRF) core scanning was conducted on core sections from International Ocean Discovery Program Site U1474, located in the Natal Valley off the coast of South Africa. The data were collected at 2 mm resolution along the 255 m length of the splice, but this setting resulted in noisy data. This problem was addressed by applying a 10 point running sum on the XRF data prior to converting peak area to element intensities. This effectively integrates 10 measurements into 1, representing an average over 2 cm resolution, and significantly improves noise in the data. With 25 calibration samples, whose element concentrations were derived using inductively coupled plasma–optical emission spectrometry, the XRF measurements were converted to concentrations using a uni-variate log-ratio calibration method. The resulting concentrations of terrigenously derived major elements (Al, Si, K, Ti, and Fe) are anticorrelated with Ca concentrations, indicating the main control on sediment chemistry is the variable proportion of terrigenous to in situ produced carbonate material.
{"title":"Data report: X-ray fluorescence core scanning of IODP Site U1474 sediments, Natal Valley, Southwest Indian Ocean, Expedition 361","authors":"D. P. Babin, A. Franzese, S. Hemming, I. Hall, L. Levay, S. Barker, L. Tejeda, M. Simon","doi":"10.14379/iodp.proc.361.201.2020","DOIUrl":"https://doi.org/10.14379/iodp.proc.361.201.2020","url":null,"abstract":"X-ray fluorescence (XRF) core scanning was conducted on core sections from International Ocean Discovery Program Site U1474, located in the Natal Valley off the coast of South Africa. The data were collected at 2 mm resolution along the 255 m length of the splice, but this setting resulted in noisy data. This problem was addressed by applying a 10 point running sum on the XRF data prior to converting peak area to element intensities. This effectively integrates 10 measurements into 1, representing an average over 2 cm resolution, and significantly improves noise in the data. With 25 calibration samples, whose element concentrations were derived using inductively coupled plasma–optical emission spectrometry, the XRF measurements were converted to concentrations using a uni-variate log-ratio calibration method. The resulting concentrations of terrigenously derived major elements (Al, Si, K, Ti, and Fe) are anticorrelated with Ca concentrations, indicating the main control on sediment chemistry is the variable proportion of terrigenous to in situ produced carbonate material.","PeriodicalId":258552,"journal":{"name":"South African Climates (Agulhas LGM Density Profile)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114675360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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