- Email: [email protected]
Questioning the global nature of the Toarcian carbon isotope excursions
Goldschmidt Conference Abstracts 2006
Questioning the global nature of the Toarcian carbon isotope excursions R.J. NEWTON, E. REEVES, N. KAFOUSIA, P.B. WIGNALL, S.H. BOTTRELL School of Earth and Environment, University of Leeds, LS2 9JT, UK ([email protected]) Two new records of seawater sulfate-sulfur isotopes derived from carbonate associated sulfate suggest that other isotopic records found in sediments from the European epicontinental sea (EES) during the Toarcian may represent principally local scale rather than global changes. The first of these, from belemnites from the Yorkshire coast in the UK (within the EES), describe a rapid change from +16.5& to +22.2& d34SVCDT between the semicelatum and exaratum ammonite subzones. Radiometric dating shows that the entire Toarcian represents around 5 myr and individual subzones (if equal in length) can be calculated to be around 400,000 years in duration. Hence, it is conservatively estimated that this 6& isotopic change occurred in 1.5 myr or less. This is considerably shorter than the modern residence time of sulfate in the oceans (20 myr) and requires either; that the concentration of oceanic sulfate in the Toarcian was much lower than its modern value, or; that the European epicontinental sea became isolated from the worlds oceans at this time. A second record from southern Tibet from sediments deposited on the margin of Tethys, whilst having less exact dating and a degree of scatter, shows no such consistent change and records an average value of around +18& d34SVCDT. The Tibetan data therefore favours the hypothesis that the EES developed a chemistry significantly different from that of the worlds oceans during the Toarcian. If correct, this suggests that carbon (and other) isotope data from Toarcian sediments from the EES only records regional variation and calls into question previous models of extensive synchronous global carbon burial, as well as the need for large scale methane release at this time. doi:10.1016/j.gca.2006.06.890
A443
Using statistical method and geochemical mapping techniques in exploration of gold and base metals in Khuni area, Anarak, Iran MOHAMMAD HADI NEZAMPOUR1, HAMID MOSAZADEH2 1
Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran (hadi.nezampour@ gmail.com) 2 Department of Exploration, Kan Azin Consuming and Research Company, Tehran, Iran ([email protected]) This paper concern the application of statistical and geochemical distribution and anomaly mapping based on the results of stream sedimentary exploration data in Khuni area, central of Iran. Samples were collected from 262 stream drainage site during the Khuni stream sediment sampling program. All samples were analyzed for 22 trace elements; results for 11 of these are used in this paper. Then; the different statistical techniques were used and compared for determination of statistical central parameter on the primary or normal data, and we propose a new method based on Lepletie–Winsorian method, for determination of average data without deleting outlier and normalization data. Replacement of censored data, determination of analysis precision, coefficient variable, and cluster analysis are another sections of application statistical techniques in the Khuni area. Monoelement maps provided for visualization of general distribution of element values, without normalization data. Several geochemical mapping technique on the base of their effectiveness in detecting of gold and base metals geochemical anomalous were used. These methods are applied to determine anomalous area, by: (1) calculation of threshold values, using mean and standard division of normal data, (2) factor anomaly maps, based on factor analysis for assemblage of elements, (3) gap statistical method to avoid personal error, and (4) P · N method that classified anomalous area. Analyzing and processing of data in the stream sedimentary samples indicate to presence of three new mineralization anomalies; located in the south-east, north-east, and in the south-west of the area. The south-east and north-east anomalies contain high grade of gold (up to 5000 ppb) and south-west anomaly is enriched in base metals (up to 2 wt%).
References Zhang, C., Selinus, O., 1998. Statistics and GIS in environmental geochemistry–some problems and solutions. J. Geochem. Explor. 64, 339–354. doi:10.1016/j.gca.2006.06.891
Questioning the global nature of the Toarcian carbon isotope excursions R.J. NEWTON, E. REEVES, N. KAFOUSIA, P.B. WIGNALL, S.H. BOTTRELL School of Earth and Environment, University of Leeds, LS2 9JT, UK ([email protected]) Two new records of seawater sulfate-sulfur isotopes derived from carbonate associated sulfate suggest that other isotopic records found in sediments from the European epicontinental sea (EES) during the Toarcian may represent principally local scale rather than global changes. The first of these, from belemnites from the Yorkshire coast in the UK (within the EES), describe a rapid change from +16.5& to +22.2& d34SVCDT between the semicelatum and exaratum ammonite subzones. Radiometric dating shows that the entire Toarcian represents around 5 myr and individual subzones (if equal in length) can be calculated to be around 400,000 years in duration. Hence, it is conservatively estimated that this 6& isotopic change occurred in 1.5 myr or less. This is considerably shorter than the modern residence time of sulfate in the oceans (20 myr) and requires either; that the concentration of oceanic sulfate in the Toarcian was much lower than its modern value, or; that the European epicontinental sea became isolated from the worlds oceans at this time. A second record from southern Tibet from sediments deposited on the margin of Tethys, whilst having less exact dating and a degree of scatter, shows no such consistent change and records an average value of around +18& d34SVCDT. The Tibetan data therefore favours the hypothesis that the EES developed a chemistry significantly different from that of the worlds oceans during the Toarcian. If correct, this suggests that carbon (and other) isotope data from Toarcian sediments from the EES only records regional variation and calls into question previous models of extensive synchronous global carbon burial, as well as the need for large scale methane release at this time. doi:10.1016/j.gca.2006.06.890
A443
Using statistical method and geochemical mapping techniques in exploration of gold and base metals in Khuni area, Anarak, Iran MOHAMMAD HADI NEZAMPOUR1, HAMID MOSAZADEH2 1
Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran (hadi.nezampour@ gmail.com) 2 Department of Exploration, Kan Azin Consuming and Research Company, Tehran, Iran ([email protected]) This paper concern the application of statistical and geochemical distribution and anomaly mapping based on the results of stream sedimentary exploration data in Khuni area, central of Iran. Samples were collected from 262 stream drainage site during the Khuni stream sediment sampling program. All samples were analyzed for 22 trace elements; results for 11 of these are used in this paper. Then; the different statistical techniques were used and compared for determination of statistical central parameter on the primary or normal data, and we propose a new method based on Lepletie–Winsorian method, for determination of average data without deleting outlier and normalization data. Replacement of censored data, determination of analysis precision, coefficient variable, and cluster analysis are another sections of application statistical techniques in the Khuni area. Monoelement maps provided for visualization of general distribution of element values, without normalization data. Several geochemical mapping technique on the base of their effectiveness in detecting of gold and base metals geochemical anomalous were used. These methods are applied to determine anomalous area, by: (1) calculation of threshold values, using mean and standard division of normal data, (2) factor anomaly maps, based on factor analysis for assemblage of elements, (3) gap statistical method to avoid personal error, and (4) P · N method that classified anomalous area. Analyzing and processing of data in the stream sedimentary samples indicate to presence of three new mineralization anomalies; located in the south-east, north-east, and in the south-west of the area. The south-east and north-east anomalies contain high grade of gold (up to 5000 ppb) and south-west anomaly is enriched in base metals (up to 2 wt%).
References Zhang, C., Selinus, O., 1998. Statistics and GIS in environmental geochemistry–some problems and solutions. J. Geochem. Explor. 64, 339–354. doi:10.1016/j.gca.2006.06.891