Other
Scientific paper
Mar 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998e%26psl.156..209m&link_type=abstract
Earth and Planetary Science Letters, Volume 156, Issue 3-4, p. 209-224.
Other
4
Scientific paper
Magnetostratigraphic data are reported from the Coniacian to early Late Campanian chalk sequences at Culver Cliff and Scratchell's Bay on the Isle of Wight and Seaford Head in East Sussex, UK. Mean natural remanent magnetisation (NRM) intensity values for individual sample sites range from 0.0013 to 1.6008 mA/m, with an overall mean of 0.0165 mA/m. Reliable determination of the remanence of the very weakly magnetic units was achieved by carrying out replicate palaeomagnetic measurements on large volume samples, using a 2-G `wholecore' cryogenic magnetometer. Palaeomagnetic measurements on other, standard-sized samples were made with a CCL `discrete sample' cryogenic magnetometer. Incremental thermal and AF demagnetisation treatment was used to remove magnetic overprints and to isolate the characteristic remanent magnetisation (ChRM). A reliability classification scheme has been developed and applied in this study, to provide an objective assessment of the quality of the palaeomagnetic results. IRM acquisition experiments suggest that the dominant magnetic mineral in these sediments is magnetite, but mixtures of hematite and magnetite occur also. SEM and TEM studies of magnetic mineral extracts indicate the presence of magnetite and hematite, preserved as inclusions within silicate grains, together with abundant bacterial magnetite preserved as individual grains and chains in some samples. Samples containing the greatest proportions of bacterial magnetite generally have the highest NRM intensity. The composite magnetic polarity sequence, derived by combining the data from all three sections, is characterised by three principal magnetic polarity zones which can be correlated with geomagnetic Chrons C34n, C33r and C33n, respectively. The positions of the chron boundaries have been tied to macrofossil and nannofossil biostratigraphic zones in these sections. A series of previously undocumented short magnetic polarity sub-chrons has been identified within the longer magnetochrons. These have potential value for high-resolution stratigraphic correlations and significance for theories of geodynamo behaviour.
Burnett Jackie A.
Gale Andy S.
Hailwood Ernie A.
Montgomery Paul
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