Options
Palaeomagnetism of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica
Author(s)
THE ANDRIL-SMS Science Team
Language
English
Obiettivo Specifico
2.2. Laboratorio di paleomagnetismo
Status
Published
JCR Journal
N/A or not JCR
Peer review journal
Yes
Title of the book
Issue/vol(year)
/15 (2009)
Publisher
Terra Antartica
Pages (printed)
193-210
Issued date
2009
Abstract
We conducted initial palaeomagnetic studies on cores from site AND-2A (77°45.488’S,
165°16.605’E, ~383.57 metres water depth). A total of 813 samples were collected that span from the
top of the section down to the base at 1138.54 metres below sea floor (mbsf). Samples were collected
every one or two metres down the core, with paired (pilot) samples being collected about every ten to
twenty metres to allow us to assess the demagnetisation behaviour of the samples using either alternating
field (AF) or thermal demagnetisation. With the exception of only a few intervals, AF demagnetisation
was observed to resolve a characteristic remanent magnetisation (ChRM) as well or better than thermal
demagnetisation. Thermal demagnetisation was particularly ineffective in many intervals owing to thermal
alteration that was common above 500°C and was evident in some samples even at low temperatures.
Above Lithostratigraphic Unit (LSU) 8 (436.18 mbsf), where lithologies are generally more coarse grained
than lower in the section, resolving a ChRM is difficult and recent overprints or a drilling overprint are a
concern. Within LSU 8 and below, most samples have a ChRM that can be resolved. The ChRM is most
likely an original depositional magnetisation throughout most of this lower section, although orthogonal
demagnetisation diagrams contain evidence that normal polarity overprinting affects some intervals. Based on
40Ar/39Ar dates and diatom datums, the magnetozones identified from the base of the hole up to ~266mbsf
are consistent with spanning from either Chron C6n (18.748-19.772 Ma) or C6An.1n (20.040-20.213 Ma)
up through Chron C5Br (15.160-15.974 Ma). Above this, intervals of constant polarity are isolated within
longer stratigraphic intervals of uncertain polarity, making their correlation with the geomagnetic polarity
timescale (GPTS) speculative and highly dependent on ages obtained from other dating methods. One
exception is a reversed-to-normal polarity transition that occurs at ~31 mbsf and is interpreted to most
likely be the Brunhes/Matuyama boundary. The spacing of polarity reversals below 266 mbsf and their
correlation with the GPTS indicates that this part of the stratigraphic section was deposited between 15
to 20 Ma at a mean sedimentation rate of about 18 centimetres (cm)/ thousand year (k.y.).
165°16.605’E, ~383.57 metres water depth). A total of 813 samples were collected that span from the
top of the section down to the base at 1138.54 metres below sea floor (mbsf). Samples were collected
every one or two metres down the core, with paired (pilot) samples being collected about every ten to
twenty metres to allow us to assess the demagnetisation behaviour of the samples using either alternating
field (AF) or thermal demagnetisation. With the exception of only a few intervals, AF demagnetisation
was observed to resolve a characteristic remanent magnetisation (ChRM) as well or better than thermal
demagnetisation. Thermal demagnetisation was particularly ineffective in many intervals owing to thermal
alteration that was common above 500°C and was evident in some samples even at low temperatures.
Above Lithostratigraphic Unit (LSU) 8 (436.18 mbsf), where lithologies are generally more coarse grained
than lower in the section, resolving a ChRM is difficult and recent overprints or a drilling overprint are a
concern. Within LSU 8 and below, most samples have a ChRM that can be resolved. The ChRM is most
likely an original depositional magnetisation throughout most of this lower section, although orthogonal
demagnetisation diagrams contain evidence that normal polarity overprinting affects some intervals. Based on
40Ar/39Ar dates and diatom datums, the magnetozones identified from the base of the hole up to ~266mbsf
are consistent with spanning from either Chron C6n (18.748-19.772 Ma) or C6An.1n (20.040-20.213 Ma)
up through Chron C5Br (15.160-15.974 Ma). Above this, intervals of constant polarity are isolated within
longer stratigraphic intervals of uncertain polarity, making their correlation with the geomagnetic polarity
timescale (GPTS) speculative and highly dependent on ages obtained from other dating methods. One
exception is a reversed-to-normal polarity transition that occurs at ~31 mbsf and is interpreted to most
likely be the Brunhes/Matuyama boundary. The spacing of polarity reversals below 266 mbsf and their
correlation with the GPTS indicates that this part of the stratigraphic section was deposited between 15
to 20 Ma at a mean sedimentation rate of about 18 centimetres (cm)/ thousand year (k.y.).
References
Acton, G., Crampton, J., Di Vincenzo, G., Fielding, C.R., Florindo,
F., Hannah, M., Harwood, D., Ishman, S., Johnson, K., Jovane,
L., Levy, R., Lum, B., Marcano, C., Mukasa, S., Ohneiser, C.,
Olney, M., Riesselman, C., Sagnotti, L., Stefano, C., Strada, E.,
Taviani, M., Tuzzi, E., Verosub, K.L., Wilson, G.S., Zattin, M.,
and The ANDRILL-SMS Science Team, 2008-2009. Preliminary
integrated chronostratigraphy of the AND-2A Core, ANDRILL
Southern McMurdo Sound Project, Antarctica, Terra Antartica,
15, this volume, 211-220.
Cande S.C. & Kent D.V., 1995. Revised calibration of the geomagnetic
polarity timescale for the Late Cretaceous and Cenozoic. J.
Geophys. Res., 100, 6093-6095.
Fielding C.R., Atkins C.B., Bassett K.N., Browne G.H., Dunbar G.B.,
Field B.D., Frank T.D., Krissek L.A., Panter K.S., Passchier S.,
Pekar S.F., Sandroni S., Talarico F., & the ANDRILL-SMS Science
Team, 2008. Sedimentology and Stratigraphy of the AND-2A
Core. ANDRILL Southern McMurdo Sound Project, Antarctica.
Terra Antartica, 15, this volume, 77-112.
Fisher R.A., 1953. Dispersion on a sphere. Proc. R. Soc. London
A, 217, 295-305.
Gradstein F.M., Ogg J.G., & Smith A.G, 2004. A Geologic Time
Scale 2004. Cambridge University Press, Cambridge, United
Kingdom, 610 pp.
Kirschvink J.L., 1980. The least-squares line and plane and the
analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc.,
62, 699-718.
Kretz R., 1983. Symbols for rock forming minerals. American
Mineralogist, 68, 277-279.
Panter K.S., Talarico F., Bassett K., Del Carlo P., Field B., Frank
T., Hoffman S., Kuhn G., Reichelt L., Sandroni S., Taviani M.,
Bracciali L., Cornamusini G., von Eynatten, H., Rocchi S., &
the ANDRILL-SMS Science Team, 2008-2009. Petrologic and
geochemical composition of the AND-2A Core, ANDRILL,
Southern McMurdo Sound Project, Antarctica. Terra Antartica,
15, this volume, 147-192.
Turner G.M., 2001. Toward an understanding of the mulicomponent
magnetization of uplifted Neogene marine sediments in New
Zealand, J. Geophys. Res., 106, 6385-6397.
Wessel P., & Smith W.H.F., 1998. New, improved version of the
Generic Mapping Tools released. Eos Trans. AGU, 79, 579.
Wilson G.S., Florindo F., Sagnotti L., Ohneiser C., & the ANDRILLMIS
Science Team, 2007. Palaeomagnetism of the AND-1B
Core, ANDRILL McMurdo Ice Shelf Project, Antarctica. Terra
Antartica, 14, 289-296.
Worm H.-U., 1998. On the superparamagnetic-stable single
domain transition for magnetite, and frequency dependence
of susceptibility. Geophys. J. Int., 133, 201-206.
F., Hannah, M., Harwood, D., Ishman, S., Johnson, K., Jovane,
L., Levy, R., Lum, B., Marcano, C., Mukasa, S., Ohneiser, C.,
Olney, M., Riesselman, C., Sagnotti, L., Stefano, C., Strada, E.,
Taviani, M., Tuzzi, E., Verosub, K.L., Wilson, G.S., Zattin, M.,
and The ANDRILL-SMS Science Team, 2008-2009. Preliminary
integrated chronostratigraphy of the AND-2A Core, ANDRILL
Southern McMurdo Sound Project, Antarctica, Terra Antartica,
15, this volume, 211-220.
Cande S.C. & Kent D.V., 1995. Revised calibration of the geomagnetic
polarity timescale for the Late Cretaceous and Cenozoic. J.
Geophys. Res., 100, 6093-6095.
Fielding C.R., Atkins C.B., Bassett K.N., Browne G.H., Dunbar G.B.,
Field B.D., Frank T.D., Krissek L.A., Panter K.S., Passchier S.,
Pekar S.F., Sandroni S., Talarico F., & the ANDRILL-SMS Science
Team, 2008. Sedimentology and Stratigraphy of the AND-2A
Core. ANDRILL Southern McMurdo Sound Project, Antarctica.
Terra Antartica, 15, this volume, 77-112.
Fisher R.A., 1953. Dispersion on a sphere. Proc. R. Soc. London
A, 217, 295-305.
Gradstein F.M., Ogg J.G., & Smith A.G, 2004. A Geologic Time
Scale 2004. Cambridge University Press, Cambridge, United
Kingdom, 610 pp.
Kirschvink J.L., 1980. The least-squares line and plane and the
analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc.,
62, 699-718.
Kretz R., 1983. Symbols for rock forming minerals. American
Mineralogist, 68, 277-279.
Panter K.S., Talarico F., Bassett K., Del Carlo P., Field B., Frank
T., Hoffman S., Kuhn G., Reichelt L., Sandroni S., Taviani M.,
Bracciali L., Cornamusini G., von Eynatten, H., Rocchi S., &
the ANDRILL-SMS Science Team, 2008-2009. Petrologic and
geochemical composition of the AND-2A Core, ANDRILL,
Southern McMurdo Sound Project, Antarctica. Terra Antartica,
15, this volume, 147-192.
Turner G.M., 2001. Toward an understanding of the mulicomponent
magnetization of uplifted Neogene marine sediments in New
Zealand, J. Geophys. Res., 106, 6385-6397.
Wessel P., & Smith W.H.F., 1998. New, improved version of the
Generic Mapping Tools released. Eos Trans. AGU, 79, 579.
Wilson G.S., Florindo F., Sagnotti L., Ohneiser C., & the ANDRILLMIS
Science Team, 2007. Palaeomagnetism of the AND-1B
Core, ANDRILL McMurdo Ice Shelf Project, Antarctica. Terra
Antartica, 14, 289-296.
Worm H.-U., 1998. On the superparamagnetic-stable single
domain transition for magnetite, and frequency dependence
of susceptibility. Geophys. J. Int., 133, 201-206.
Type
article
File(s)
No Thumbnail Available
Name
ARTICLE.pdf
Size
2.71 MB
Format
Adobe PDF
Checksum (MD5)
9b163776705f261d20e1693dd8cae8cb