Review of lake sediment palaeomagnetic data

Abstract

Abstract. This first part of a two part review is essentially descriptive: palaeomagnetic data sets used to compile the publisheffreference curves of geomagnetic secular variations (SV) through Holocene time are critically examined, particularly with respect to coring techniques used for sampling, reliability of the measured directions of remanent magnetization and transformation to timescales. Also, progress made in extending SV records into Late Glacial time is reviewed. SV curves have been constructed for W. Europe and N. America going back respectively to 22000 and 31000 yr before the present (bp). The best quality SV records have invariably been obtained from homogeneous muds and clays which typically smooth the geomagnetic signal over intervals of a few hundred years. They show irregular oscillatory patterns in contrast with certain records obtained from some inhomogeneous sections which Show sequences of strongly aberrant palaeomagnetic directions. The latter have been interpreted by some authors as evidence of abnormal geomagnetic field behaviour but such evidence is, on the whole, found to be unconvincing. If geomagnetic excursions or aborted attempts at polarity reversal have occurred, they must have been so rapid as to have been smoothed out in the quasi-continuous records obtained from homogeneous muds. The second part of the review, to be published shortly in this journal, will deal with analyses and interpretations of the data presented here.

A Late Devensian Lateglacial palaeomagnetic record from Llyn Gwernan, North Wales: comparison with other NW European records

“…The greater amplitude of the Llyn Gwernan features may be attributable to the high sedimentation rates at this site, yielding a higher resolution record. Inclination feature I1 occurs near the base of the Flandrian and appears to be comparable to feature zr of the European records (Creer et al 1980;Creer 1985) (feature a of the Swedish records : Sandgren 1986;Bjorck & Sandgren 1985). Inclination features 12 and 13 are thought to probably correspond to secondary fluctuations in inclination occurring within the large inclination swing between the features v and 5.…”

“…Declination feature 0 3 occurs in the upper part of the Lateglacial Interstadial. This is compared with feature 0 of the European records (Creer 1985). However, this feature is observed to be up to 1600 yr younger in the European sites.…”

“…1980;Creer 1985;Sandgren 1986) for direct comparison of the features of the directional logs (Fig. 7).…”

“…1980;Bonifay et al 1985;Creer 1985;Bjorck & Sandgren 1985;Smith 1985;Creer et al 1986;Sandgren 1986.…”

Variations of the relative palaeointensity of the geomagnetic field in western Europe in the interval 25-10 kyr BP as deduced from analyses of lake sediments

“…These records can be correlated with those of contemporaneous sedimentary sequences studied in other areas (Thouveny et al 1985;Creer 1985) although the Holocene record does not provide highly satisfying results. Some palaeointensity evaluations using the ARM method on these sediments have already been presented and discussed in Thouveny (1983) and Smith (1985).…”