Greinar (Vísindafélag Íslendinga) - 01.01.1977, Síða 12

10
spondingly to rise if the temperature is increased by the de-
position of a thiek organic layer of low heat conductivity.
Such sedimentation took place in the Eocene and the Lower
Oligocene. Together with the Oligocene uplift of the Icelandic
Plateau Basalts, a global zigzag zone, coaxial with the present
mid-ocean ridges, and 150—200 km broad became emergent.
The sediments were then wiped out in this now submarine
zone. It was probably the 300—400 m thick organic global
layer of sediments which in the end caused the great Oligo-
cene transgression. The great regression which followed was
due to a rise of the Moho and the consequent formation of
deep ocean basins. The sea-level dropped by 200 m, but the
ocean floor dropped generally more, as the return of the waters
from the epicontinental seas demand. Therefore, the formerly
emergent “proto-ridge” was submerged by the beginning of
the Miocene. The rugged present forms of the mid-ocean ridges
are probably largely due to intense global stress fields during
the severe climatic spells of the Pleistocene.
Elongated troughs, filled with sediments, are a natural
coastal phenomenon where drainage provides enough detrital
material from a large land area. At a certain stage, shear leads
to the formation of dense polymorphs in the depths and a
continued deepening of the trough without any violence of
isostasy. At any stage of such a trough, and at any depth,
the external pressure is automatically greater than the inter-
nal pressure. This state leads to the known further orogenic
development. Colliding continents are an unnecessary and anti-
quated concept. For the closely similar Hercynian to Alpinine
trends from Burma to New Zealand and Australia, we must
demand a guiding coast of a land which provided the sedi-
ments for the respective troughs. The Indian subcontinent at
one end and Australia and New Zealand at the other, fit very
well as remnants of such a land, now largely submerged. The
rhyming of the Hercynian trend from Burma to Australia ex-
cludes drift of Australia and India.