PRELIMINARY NOTE ON THE PALEOMAGNETIC|
REVERSAL RECORD OBTAINED FROM TWO MALLORCAN CAVES
by J. S. Kopper
Muestras de sedimentos obtenidas en dos cuevas mallorquinas con la ayuda del Speleo Club Mallorca, ponen
de manifiesto una inversión del campo magnético terrestre en puntos sincrónicos de ambos depósitos (alrededor de
un metro de profundidad). Esta inversión es la primera que ha sido observada en sedimentos de cueva, pareciendo
corresponder al período "Mungo" que finalizó hace unos 32.000 años. Previamente, el "Mungo" solamente había
sido identificado en sedimentos lacustres de Australia y en sedimentos marinos profundos del Golfo de Méjico.
Sediment samples obtained from two Mallorcan caves with the help of the Speleo Club Mallorca show a rever-
sal of the earth's magnetic field at synchronous points in the two deposits, circa 1 m (Fig. 1). This reversal is the
first ever observed in cave sediments and is thought to be the Mungo event which ended about 32.000 B.P. Pre-
viously, the Mungo event had only identified in lake sediments from Australia and deepsea sediments from the Gulf
of México (Freed and Healy 1974).
Continuous sediment samples were taken from the surface to a depth of 2,7 m at Co ya de Sa Campana (Sa
Calobra, Mallorca), and from the surface to 1,8 m at the Co ya de Canet (Esporles, Mallorca). The records of
paleomagnetic declination, inclination and intensity were then obtained for both caves at the University of Edin-
burgh, United Kingdom, with a Digico fluxgate magnetometer. The curves of declination and intensity together with
the stratigraphic sections of the caves are shown in Figure 1. It can be seen that the reversal begins in both caves
at close to 1 m and continues through to the bottom of the section at Canet (1,8 mY and to about 2 m at Campana.
A sample of travertine from Canet is now being dated isotopically (230Th/234U) to test our interpretation of the
age of the reversal.
While the paleomagnetic testing of these two caves was done primarily to help reconstruct the behavior of the
earth's magnetic field in the past, the results obtained should be very useful in dating other Mallorcan caves as well
as caves in other parts of Europe. When the age of the reversal is exactly known the points at the begining and
ending of the reversal can be used to date other cave sediments which contain similar evidence in their paleomag-
netic logs. Paleomagnetic dating of cave sediments is much less expensive, faster and more convenient than most
other methods, such as radiocarbon. It can sometimes be used in cave sediments that contain no record of a re-
versal by matching the curves of inclination and declination with a reference curve (Creer and Kopper 1974). The re-
cord of geomagnetic reversals for the past 2 million years is shown in Figure 2.
CREER K. M., and KOPPER J. S. (1974): "Paleomagnetic dating of cave paintings in Tito Bustillo Cave, Asturias,
Spain". Science 186: 348-350
FREED W. K. and HEALY N. (1974): "Excursions of the Pleistocene geomagnetic field recovered in Gulf of México
sediments" . Earth and Planetary Science Letters. 24: 99-104
COVA DE SA CAMPANA
earth's magnetic field history=
i ÍIIIlii REVERSED