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High resolution full vector record of four consecutive Mid Miocene geomagnetic reversals

Linder, Julia, and Roman Leonhardt (2009), High resolution full vector record of four consecutive Mid Miocene geomagnetic reversals, PEPI, 177, 88-101, doi:doi:10.1016/j.pepi.2009.07.013.

Seventy Mid Miocene lava flows from flood basalt piles near Neskaupstadur (East Iceland)
were sampled, which provide a quasi-continuous record of geomagnetic field variations.
Samples were collected along the Profile B of Watkins and Walker (1977), which was
extended about 250 m farther down in a neighboring stream bed. Published radiometric
age determinations range from 12.2 to 12.8 Ma for the sampled sequence. Four reversals
were recorded in this profile, with 18 transitional lavas found within or between 17 normal
and 30 reversed polarity flows. The large amount of transitional lavas and the large virtual
geomagnetic pole dispersion for stable field directions are noteworthy as such features are
commonly observed in Icelandic lavas and manifest in a far-sidedness of the average
VGP. The reason for this characteristic, which could be related to an anomaly beneath
Iceland, a global field phenomenon, local tectonics, and/or non-horizontal flow
emplacement, is scrutinized. Non-horizontal flow emplacement is likely in volcanic
environments particularly if the sampled lavas are located on the paleoslopes of a central
volcano. From the difference of the observed paleomagnetic mean directions to the
expected directions assuming a geocentric axial dipole (GAD), a paleoslope which would
explain the observed difference was calculated numerically. The obtained dip and dip
direction point consistently to a possible volcanic extrusion center of the lavas. The
determined paleodip, however, proved to be significantly too high compared to the usual
slope of a central volcano, suggesting further reasons for deviations from the GAD. Other
datasets of this age from Europe also show enhanced VGP dispersion, suggesting further
contributions of geomagnetic origin for this observation. Basically all reversal paths move
across the Pacific. Transitions were identified as belonging to C5An.1r - C5Ar.3r based on
the Astronomically Tuned Neogene Timescale (Lourens et al., 2004). We selected 122
samples for paleointensity measurements using a modified Thellier method including tests
for alteration and multidomain bias. 85 of the measured samples yielded data of sufficient
quality to calculate paleointensities for 26 lava flows. The average paleointensity for stable
field directions was 23.3 μT, whereas the intensity drops to a minimum of 5.8 μT during
field transitions. The stable field intensities represent only about half of the present day
field. The sawtooth pattern of intensities, which is characterized by a sharp increase of
intensity directly after a reversal and then followed by a gradual decrease towards the next
reversal, was not found in this study.
Further information
  author = {Julia Linder and Roman Leonhardt},
  journal = {PEPI},
  pages = {88-101},
  title = {{High resolution full vector record of four consecutive Mid Miocene geomagnetic reversals}},
  volume = {177},
  year = {2009},
  url = {http://www.sciencedirect.com/science?{\_}ob=MImg{\&}{\_}imagekey=B6V6S-4WW2SMV-1-1{\&}{\_}cdi=5822{\&}{\_}user=616146{\&}{\_}orig=browse{\&}{\_}coverDate=07%2F28%2F2009{\&}{\_}sk=999999999{\&}view=c{\&}wchp=dGLbVzb-zSkzV{\&}md5=f6c3e7bfe7534963565c8b6bab1e7ee4{\&}ie=/sdarticle.pdf},
  doi = {doi:10.1016/j.pepi.2009.07.013},
%0 Journal Article
%A Linder, Julia
%A Leonhardt, Roman
%D 2009
%V 177
%P 88-101
%T High resolution full vector record of four consecutive Mid Miocene geomagnetic reversals
%U http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V6S-4WW2SMV-1-1&_cdi=5822&_user=616146&_orig=browse&_coverDate=07%2F28%2F2009&_sk=999999999&view=c&wchp=dGLbVzb-zSkzV&md5=f6c3e7bfe7534963565c8b6bab1e7ee4&ie=/sdarticle.pdf
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