Late Devonian carbonate magnetostratigraphy from the Oscar and Horse Spring Ranges, Lennard Shelf, Canning Basin, Western Australia

Does the planetary dynamo go cycling on? Re-examining the evidence for cycles in magnetic reversal rate

“…Magnetostratigraphic data from the latest geologic timescale (2012) was examined and a polarity and time sequence was collected from the entire Phanerozoic eon ( Supplementary Table 1; Figures 1a and 1b). New results from the Devonian (Hansma et al, 2015) were utilized as no reliable data were available from the 2012 timescale. Values assigned to a polarity interval are either 0 (reverse polarity) or 1 (normal polarity).…”

Upper Kellwasser carbon isotope excursion pre-dates the F–F boundary in the Upper Devonian Lennard Shelf carbonate system, Canning Basin, Western Australia

“…Magnetostratigraphic correlation of WV with previously examined records from VHS and SO (Hansma et al, 2015) revealed seven major magnetozones for the interval of time studied (Figure 2; Frasnian conodont Zone 11 to Famennian crepida Zone). Four periods of mixed, dominantly reversed polarity and three periods of normal polarity have been recognized, and the F-F boundary has been identified within the N7 normal chron.…”

“…In three of our measured sections the isotopic expression of the Upper Kellwasser was observed in continuous succession in grainstone, breccia, and massive boundstone from middle-and upper-slope settings where depositional dips were relatively steep (up to 30˚) and sedimentation rates presumably greater (Playton, 2008;Hansma et al, 2015). A combination of expanded stratigraphy and high-density sampling demonstrates that the timing of maximum values associated with the Upper Kellwasser excursion is different than previously documented (Figures 2 and 3).…”

“…Paleomagnetic data for CL were not incorporated into this study--due to the relatively condensed nature of this section, magnetostratigraphic correlations were ambiguous. Samples obtained for conodont analysis were collected from all sections but were only age diagnostic for the SO, VHS, and CL sections (Hansma et al, 2015;Roelofs et al, 2015). For additional constraint, an independent conodont study (Klapper, 2007) conducted at the VHS site was incorporated into our work.…”

“…The paleomagnetic reversal records were derived from previously published datasets analyzed at the University of Western Australia; data for VHS and SO were reported by Hansma et al (2015) and WV was evaluated by Tohver et al (in prep.). Paleomagnetic data for CL were not incorporated into this study--due to the relatively condensed nature of this section, magnetostratigraphic correlations were ambiguous.…”