Acastum

In the course of the redefinition of the Precambrian, the Acastum becomes the first period within the era of the Paleoarchean . It took 220 million years, from 4030 to 3810 million years BP .

etymology

The name Acastum, engl. Acastan or Acastan period goes back to the Acasta gneiss of the slave kraton in northwestern Canada . The Acasta gneiss was named after the Acasta River .

Redefinition of the Precambrian Periods

Due to the moving away from period boundaries determined purely by radiometry, Gradstein et al. (2012) should now apply the GSSP principle as far as possible in the Precambrian as well . The periods are thus defined on the basis of significant geological events and no longer on arbitrary, radiometric ages. In the absence of supracrustal rock series, the lower and upper limits of the acastum must necessarily be determined chronometrically.

Definition of the acastum

Handpiece of the tonalitic Acasta gneiss, the oldest known rock on earth

The Acastum is the first period of the Archean and therefore also of the Paleo-Archean . Its lower limit to the previous Hadean and its second era, the Jack Hillsium or the Zirconium , is chronometrically set at 4030 million years BP. The upper limit to the following isuum is also defined chronometrically and is 3810 million years BP.

meaning

With the Acastum, rocks are preserved for the first time in the history of the earth . The oldest known crustal rock is the acasta gneiss of the slave kraton, after which the period was named. Earthly stratigraphy begins with its formation . The Acasta gneiss was formed in the time interval 4030 to 3940 million years BP. From the first 500 million years of the earth's history, no reliably dated crustal rocks have become known. Rocks of the Nuvvuagittuq greenstone belt may be older than that, but this is still controversial.

Individual evidence

^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .
↑ Iizuka, T. et al .: Geology and zircon geochronology of the Acasta Gneiss Complex, northwestern Canada: new constraints on its tectonothermal history . In: Precambrian Research . tape 153 , 2007, p. 179-208 .

[1] Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .

[2] Iizuka, T. et al .: Geology and zircon geochronology of the Acasta Gneiss Complex, northwestern Canada: new constraints on its tectonothermal history . In: Precambrian Research . tape 153 , 2007, p. 179-208 .