Palaeosecular Variation from a Vancouver Island Stalagmite and Comparison with Contemporary North American Records.

Abstract

A record of palaeosecular variation has been obtained from a stalagmite from Vancouver Island, Canada, spanning the period 16.9 ± 6.0 to 13.3 ± 2.3 ka. Dating control was provided using the uranium-thorium disequilibrium method. The main magnetic remanence carrier in the speleothem is a fine-grained magnetite which is thought to be of detrital, rather than chemical, origin. The record is apparently free from any depositional inclination errors and compares well with a contemporaneous speleothem record obtained from the same cave (Latham et al., 1987). Good correlation also exists with several North American lacustrine records. The record provides evidence of clockwise looping of the position of the virtual geomagnetic pole over western Canada from about 14.9 to 13.6 ka, and in the interval from 16.9 to 15.2 ka the data can be modelled by a stationary, oscillating, inward-pointing source to the north-west of the sampling site.

Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia.

“…comm.). In contrast, regularly flooded and consequently dirty speleothems are likely to be dominated by a depositional remanent magnetisation (DRM) which arises from the deposition of magnetic grains on the speleothem surface either from floodwaters or dripwaters (Latham and Ford, 1993;Lean et al, 1995). In the majority of cases speleothem remanences dominated by a DRM are easily measured on a cryogenic magnetometer.…”

“…3.1 Acquisition of remanence Several speleothem studies have suggested how a speleothem acquires its remanence (for example Latham et al, 1982;Morinaga et al, 1987;Latham and Ford, 1993;Perkins and Maher, 1993;Lean et al, 1995). In essence, these studies have suggested that in clean, unflooded speleothems the dominant mechanism of remanence acquisition is a form of chemical remanent magnetisation (CRM) whereby magnetite is co-precipitated during calcite precipitation after iron complexed with organics is liberated in reduced form (Latham et al, 1982;Latham and Ford, 1993;Perkins and Maher, 1993).…”

“…Tests for depositional inclination errors in these speleothems were made by comparing directions from lateral sub-samples with time equivalent (coeval) central sub-samples (Latham and Ford, 1993;Lean et al, 1995). Thus, any inclination error would likely manifest itself differently Table 1.…”

“…The main attractions of speleothems as recorders of PSV are that they grow continuously (with some exceptions), can be oriented prior to removal and do not appear to contain inclination errors Perkins and Maher, 1993;Lean, 1995;Lean et al, 1995). They also appear to record the ambient field instantaneously during crystallisation (Latham et al, 1986).…”

“…The fact that calcium-carbonate speleothems record palaeosecular variation reliably has been demonstrated in several studies (Latham et al, 1982(Latham et al, , 1986(Latham et al, , 1987Latham and Ford, 1993;Morinaga et al, 1989;Perkins and Maher, 1993;Lean et al, 1995). Currently, the main aims in speleothem palaeomagnetic research are to acquire and compare speleothem records from similar locations in order to ensure repeatability and to expand the global coverage and time-span of such sets of records.…”