Friday, February 20, 2009

Primarrumpf Means Primary Peneplain

No one took the bait so here' s the answer.

The term is German, I guess at least that much was obvious and means the primary or oldest peneplain on the continent. This becomes then the reference surface for evaluating subsequent cycles of denudation and planation the continent or region may experience.

In an Indian context, the primary peneplain is the one which formed when India was part of Gondwanaland. Through the late Paleozoic and the Mesozoic there was tectonic stability in the Indian shield region and vast portions of the cratonic shield areas were beveled into a low relief plain. In the late Mesozoic, rifting of India from Antarctica and then Madagascar and Seychelles formed the east coast and west coast margins respectively. The shield area which made up the hinterlands of these margins was rejuvenated and experienced substantial amounts of epeirogenic uplift - mostly thought to be a flexural response to denudational unloading - through the late Cretaceous to mid Cenozoic.

These denudational cycles have destroyed this planation surface over most of its former extent. But remnants of this primary peneplain is now found at about 2400 m MSL in parts of south India. This peneplain is the plateau areas of Bison Swamps, Sispara Pass and Mukurti Lake in the Nilgiri hills and the Vandaravu and Anaimundi flats of the Palni hills. In figure below the surface S0 is the primarrumpf or primary peneplain.

It is preserved here most likely because it mantles charnokites (hypersthene bearing granulite) which are very resistant rocks, compared with the granitic gneisses and other PreCambrian greenstone facies metamorphics that make up much of the Indian shield area. Great charnokite domes rise above this ancient surface reaching altitudes of about 2600 m MSL at Palni and Anamalai and Nilgiri (the figure misrepresents the altitudes. Anamalai or Anamudi peak is 2695 m MSL). These are just about the highest elevations found anywhere in ancient shield regions around the world.

You can get a glimpse of Mesozoic topography of the Indian shield area at these altitudes. A gently undulating plain interspersed with domes of resistant rocks like charnokites.

Surfaces S1 and S2 and S3 have their own stories and I'll be posting on them in the next few days, especially on how they control the local economies of the region.


  1. I did take the bait. ;-) I recognised the German words, and “primär” was no problem. However, I wasn't sure about “Rumpf” (basically meaning body or torso). Then, I was too curious to wait for the solution and looked it up. So an answer by me wouldn't have been fair…

    Still, thanks a lot for the nice example for a Primärrumpf!

  2. ya, its a tricky word and even if you know German the meaning is not apparent :-)