Pongolum

As part of the redefinition of the Precambrian is Pongolum the second and final period in the era of Mesoarchaikums . It took 240 million years, from 3020 to 2780 million years BP .

designation

The Pongolum, English Pongolan , was named after the Pongola Supergroup in South Africa and Swaziland . The Pongola Supergroup got its name from its type locality along the Pongola .

Redefinition of the Precambrian Periods

In the course of moving away from period boundaries determined purely by radiometry, the GSSP principle should now be applied as far as possible in the Precambrian, according to Gradstein et al. (2012) . The periods are thus defined on the basis of significant geological events and no longer on arbitrary, radiometric ages.

Definition of the pongolum

The lower limit of the Pongolum for the first Mesoarchean period, the Vaalbarum , is determined by a GSSP at the concordant contact between the basal conglomerate and the quartz-rich sandstone of the Gorge Creek Group ( De Gray Supergroup ) in Western Australia . It can be assigned an age of 3,020 million years BP. The upper limit of the Pongolum to the Neoarchean (and thus to the Methanian period ) is also defined by a GSSP, which comes to lie at the base of the Mount Roe Basalt in Western Australia. Mount Roe Basalt, deposited from 2,780 million years ago BP, belongs to the Fortescue Group and thus to the Mount Bruce Supergroup .

meaning

The Pongolum is characterized by the first appearance of terrestrial sedimentary basins that could form on stabilized continents . In mighty, undisturbed sequences on shelf platforms , the colonization of flat, sandy facies areas by microbes can now be demonstrated. Microbial communities can be found in the supergroups on the Kaapvaal craton of South Africa and the Pilbara craton of western Australia. For example, microbial communities are very well preserved in the Pongola Supergroup , which is more than 9,000 meters thick .

icing

The oldest glaciation in the history of the earth, which occurred around 2900 million years BP, can be verified by two diamictite horizons in the Mozaan Group of the Pongola Supergroup ( Delfkom formation ).

stratigraphy

North-south profile by the Witwatersrand Supergroup, South Africa

Significant geological formations

• Pilbara Kraton in Western Australia:
  • De Gray Superbasin with the De Gray Supergroup - 3050 to 2930 million years BP:
    • Gorge Creek Group - 3050 to 3020 million years old BP
    • Whim Creek Group - 3010 to 2990 million years old BP
    • Mallina Basin - 2970 to 2940 million years old BP
    • Croydon Group - 2970 to 2940 million years BP
    • Nullagine Group - 2930 to 2910 million years old BP
• Kaapvaal Kraton in South Africa:
  • Pongola Supergroup in South Africa and Swaziland - 3000 to 2870 million years BP
    • Nsuze Group - 2980 to 2960 million years BP
    • Mozaan Group - around 2950 to 2837 (?) Million years BP
  • Witwatersrand Supergroup in South Africa - 2985 to 2780 million years BP
    • West Rand Group - 2985 to 2914 million years old BP
    • Central Rand Group - 2872 to 2780 million years BP
• North China Kraton - 3100 to 2900 million years BP:
  • Quishui Group in eastern Shandong
  • Longgang Group in southern Jilin
  • Lower Anshan Group in northern Liaoning
  • Qianan Supracrustals in eastern Hebei
  • Chentaigou Supracrustals in Anshan
• Dharwar Kraton in southern India :
  • Sargur Group - 3100 to 2900 million years old BP
  • Dharwar supergroup
    • Bababundan Group - 2900 to 2600 million years BP
      • Kalasapura Formation - around 2910 million years ago BP
      • Santaveri Formation and Allampur Formation - 2848 to 2747 million years BP
• Singhbhum Kraton in Northeast India:
  • Iron Ore Group - 3100 to 2900 million years BP

Deposits

• Gold :
  • Red Lake greenstone belt of the Superior Craton with the Campbell-Red Lake orogenic gold deposit - 2990 to 2890 million years BP
• Gold and uranium :
  • The Witwatersrand Supergroup in South Africa is home to the largest gold deposits in the world.
• Chromium ( Chromite ):
  • Nuggihalli Schist Belt , Sargur Group, South India

Geodynamics

Orogenesis

• North Pilbara Orogeny - 2950 to 2910 million years BP. The Kurrana Terran is secreted in the southeast of the East Pilbara Block. The outcrop of postectonic granites between 2890 and 2830 million years BP leads to final cratonization.

Individual evidence

1. ↑ gold, DJC: The Pongola Supergroup . In: MR Johnson, et al. (Ed.): The Geology of Africa . Geological Society of South Africa & Council for Geoscience, Johannesburg / Pretoria 2006, p. 135-148 .
2. ^ Felix M. Gradstein, among others: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45 , no. 2 , 2012, p. 171-188 .
3. ^ N. Noffke: Turbulent lifestyle: Microbial mats on Earth's sandy beaches - Today and 3 billion years ago . In: GSA Today . tape 18 , 2008, p. 4-9 .
4. ↑ A. Mund, RJ Walker, JR Reimink, RL Rudnick, RM Gaschnig: Tungsten-182 in the upper continental crust: Evidence from glacial diamictites . (PDF) In: Chemical Geology . 494, September 2018, pp. 144–152. doi : 10.1016 / j.chemgeo.2018.07.036 .
5. ^ G. Chi, inter alia: Formation of the Campbell-red Lake gold deposit by H ₂ O-poor, CO ₂ -dominated fluids . In: Mineralium deposita . tape 40 , 2006, pp. 726-741 .