Mono Lake excursion

from Wikipedia, the free encyclopedia

The Mono Lake Excursion ( English Mono Lake Excursion , abbreviated to MLE ) was a polarity excursion within the Brunhes polarity zone , i.e. the attempt to reverse the polarity of the earth's magnetic field . The event took place around 34,000 years ago in the Vistula High Glacial .

Type locality and designation

View from Mount Dana to Mono Lake

The Mono Lake excursion was named after its type locality , the Mono Basin on Mono Lake in California . It was discovered in 1971 by Denham and Cox in lake sediments of the basin .

The Mono Lake excursion is in Australia as Mungo Lake Excursion and in Norway as Valderhaug excursion known.

Geographical distribution

In addition to the type locality, the Mono Lake excursion is often found in the Basin and Range Province , in loess areas in China (but also in Lower Austria ) and in cave sediments in Norway . In the marine area, it can be detected in drill cores , for example off Greenland in the Irminger Basin of the North Atlantic .

stratigraphy

The Mono Lake excursion took place in the Denekamp Interstadial and correlates with the Greenland Stadium GST7 ; it falls between the two Dansgaard-Oeschger events DO7 and DO6 . It was preceded by the Laschamp event , centered around 41,000 years BP (39,000 BC ) , a very brief reversal of the polarity of the earth's magnetic field.

Dating

Based on the GRIP time scale , the Mono Lake excursion can be assigned an age of 31,500 years BP, according to the GISP2 - oxygen isotope curve, however, 34,000 years BP (32,000 BC).

The excursion can be dated absolutely on the basis of a volcanic ash layer occurring in the mono-basin . This ash layer # 15 was deposited in the middle of the field change and could be determined in the Pyramid Lake basin by Benson et al. (2003) with 28,620 ± 300 radiocarbon years . On the GISP2 time scale, this corresponds to 32,400 years BP (or calibrated with CalPal 33,077 ± 472 years BP). Assuming that the total duration of the anomaly was about 2000 years, the time span is 33,300 to 31,500 years BP (or 34,000 to 32,000 years BP according to CalPal). Channell 2006 was also able to establish a time span of 34,000 to 32,000 years BP in the Irminger Basin.

characterization

The Mono Lake excursion made itself felt by a clear drop in the field strength of the earth's magnetic field , which, however, remained far behind the Laschamp event. For example, the paleointensities in the GLOPIS curve show a decrease of around 50%. Due to the field strength loss, there was an increase in cosmic radiation , which extends in an increased number of radionuclides 10 Be and 36 was to identify Cl and also in GRIP - ice core could be detected.

Starting from + 60 ° (60 ° N), the magnetic inclination reached approximately -30 ° (30 ° S) during the field excursion, only to return to + 80 ° (80 ° N) afterwards. The development of the declination took place in two steps: below the ash layer it migrated from north (020 °) to northwest (300 °), and then returned to its original position. Above the ash layer, there was then a striking eastward drift (114.5 °) with a subsequent return to the north. The virtual geomagnetic pole (engl. Virtual Geomagnetic poles or abbreviated VGP ) passed through a large loop in the clockwise direction, the touched 35 ° northern latitude and was centered at 35 ° east longitude. The latter was followed in a counterclockwise direction by a smaller loop that circled 70 ° north latitude and 270 ° longitude.

parameter

The dipole moment decreased in the course of the Mono Lake excursion from 8 to 4 * 10 22 Am 2 and then increased again to around 10 * 10 22 Am 2 . The flow of the chlorine radionuclide resulted in an average increase of 50% to 1200 atoms / cm 2 year, with peak values ​​at around 1500 atoms / cm 2 year. The formation rate of beryllium-10 lifted with 0.5 atoms / cm 2 year, only little from the usual values (0.3 to 0.4 atoms / cm 2 year) from.

Individual evidence

  1. ^ CR Denham, A. Cox: Evidence that the Laschamp polarity event did not occur 13 300–30 400 years ago . In: Earth Planet. Sci. Lett. tape 13 , 1971, p. 181-190 .
  2. M. Barbetti, M. McElhinny: The Lake Mungo geomagnetic excursion . In: Philosophical Transactions of the Royal Society of London . A 281, 1976, p. 515-542 .
  3. Jan Mangerud, inter alia: Paleomagnetic correlations between scandinavian ice-sheet fluctuations and greenland dansgaard – oeschger events, 45,000–25,000 yr BP In: Research . tape 56 , 2001, p. 299-307 .
  4. ^ A b G. Wagner, inter alia: Chlorine-36 evidence for the Mono Lake event in the Summit GRIP ice core . In: Earth and Planetary Science Letters . tape 181 , 2000, pp. 1-6 .
  5. M. Stuiver, P. Grootes: GISP2 oxygen isotope ratios . In: Quaternary Research . tape 53 , 2000, pp. 277-284 .
  6. L. Benson, et al: Age of the Mono Lake excursion and associated tephra . In: Quaternary Science Reviews . tape 22 , no. 2–4 , 2003, pp. 135-140 .
  7. JET Channell: Late Brunhes polarity excursions (Mono Lake, Laschamp, Iceland Basin and Pringle Falls) recorded at ODP Site 919 (Irminger Basin) . In: Earth and Planetary Science Letters . tape 244 , 2006, pp. 378-393 .
  8. C. Laj, C. Kissel, J. Beer: High resolution global paleointensity stack since 75 kyr (GLOPIS-75) calibrated to absolute values . In: JET Channell, et al. (Ed.): Timescales of the Paleomagnetic Field (=  Geophysical Monograph . Volume 145 ). American Geophysical Union, 2004, p. 255-265 .
  9. JC Liddicoat, RS Coe: Mono Lake Excursion Reviewed . In: American Geophysical Union, Spring Meeting . 2007, bibcode : 2007AGUSMGP51A..04L .
  10. JC Liddicoat, RS Coe: Mono Lake Geomagnetic excursion . In: Journal of Geophysical Research . tape 84 , No. B1, 1979, pp. 261-271 .
  11. ^ R. Muscheler, among others: Changes in the carbon cycle during the last deglaciation as indicated by the comparison of 10Be and 14C records . In: Earth Planet. Sci. Lett. tape 219 , 2004, pp. 325-340 .