Northern limits of the eastern Gondwana: palaeobotanical evidence

Abstract

The northern margin of the Gondwanaland along the Indian block has been debated for some time now. According to the earlier view the northern margin ran along the Indus-Yarlung-Zangbo Suture. Newly acquired data has been interpreted to show that eastern Gondwana was much bigger than generally believed.

In the present work we analyze the floras that grew around the northern margin of the eastern Gondwana assembly to see if the distribution of plant fossils also provides supporting evidence for a ‘greater’ India. The floras that have been examined in the present synthesis originate in the Permian of New Guinea, Sumatra (Indonesia), Malaysia, Thailand, Tibet, Northern China, Kashmir (India), Saudi Arabia, Iran, Iraq and Turkey and Mesozoic of Ladakh (India), Bhutan and Nepal.

The analysis shows that though some of the floral assemblages contain certain elements that could be of Gondwana affinity yet the overall composition of almost all the floral assemblages, except the one from Kashmir, is basically Cathaysian. Whether these Cathaysian type floral assemblages occupied the northern margin of the eastern Gondwana or they flourished on the southern margin of Laurasia, or they grew all along the shores of the Tethys, has to be examined.

The latitudinal variation in vegetation, however, does not seem to explain the intermixing of elements of different floral provinces in the coastal vegetation on the two shores of a fairly wide, though shallow, Tethys as in Kashmir and in southern Tibet. Even if both these regions were on the same side of Tethys, intermixing of Gondwana and Cathaysia floras is not explained as no direct migratory routes from Laurasia are available in Gondwana assemblies.

This coupled with the occurrence of northern Mesozoic flora at Fukche, Ladakh, and near Lhasa indicates that the Indian Gondwana did not extend north of the Indus-Yarlung-Zangbo Suture Zone.