Field of Science

Stratigraphic Correlations of Gondwanan Basins in India and the "Laurasian" Fauna of Northern Gondwana in the Late Triassic

Here is a fairly obscure, but interesting new paper providing updated correlations of strata (including that of Triassic age) in the Gondwanan Basins of India. The final paper could have benefited from some more editing, but overall it provides a decent synthesis and outlines some of the problems of correlations in this are of Gondwana. Most significant is that there are no absolute time constraints available for these strata because of the lack of datable volcanic materials. The overall climate for the entire Triassic for this area is given as arid with a key sea level regression in the Norian. Note, however, that the authors explicitly use the 2004 ISC timescale, and that under currently proposed revisions to this timescale the Carnian is more restricted.

The Triassic vertebrate fauna of India has always struck me as bizarre, mainly because the Early Triassic fauna is extremely similar to that of the Lystrosaurus assemblage zone of South Africa, and does contain several species of Lystrosaurus. Yet the Middle and Late Triassic fauna has much more of a Laurasian feel to it, especially the Late Triassic fauna, which includes basal phytosaurs such as Parasuchus, and more advanced phytosaurs such as a Leptosuchus-like form. Aetosaurs are represented by a paratypothoracisine form, which are only known from North America and Europe. Finally, metoposaurid temnospondyls are also common as in North America and Europe.

This seems very odd to me given that in paleogeographic reconstructions throughout the Triassic, India is firmly nestled on the western edge of modern day Africa, contacting Australia, and Antarctica, and separated from North America by all of northern Africa and from Europe by the Tethys. Unfortunately the Triassic fauna of North Africa is extremely sparse, although the Moroccan fauna is very similar to that of India and Laurasia. Perhaps Northern Africa served as a corridor for the Laurasian-type fauna, whereas there was some restriction from South America and South Africa in the Latest Triassic.  Thus it seems that at this time there are not distinct Laurasian and Gondwanan distributions of tetrapods, but rather separate southern Gondwana and northern Gondwana/Laurasia distributions.

Mukhopadhyay, G., Mukhopadhyay, S. K., Roychowdhury, M., and P. K. Parui. 2010. Stratigraphic Correlation between Different Gondwana Basins of India.
Journal of the Geological Society of India 76:251-266. DOI: 10.1007/s12594-010-0097-6

Abstract - Gondwana Basins of India occur within the suture zones of Precambrian cratonic blocks of Peninsular India along some linear belts. More than 99% of the total coal resource of the country is present within these basins. The basins are demarcated by boundary faults having graben or half-graben geometry. These basins preserve a thick sedimentary pile deposited over nearly 200 million years from latest Carboniferous to Lower Cretaceous. However, due to lack of well-constrained data, age of most of the formations is assigned tentatively. This has resulted in diversified views on both intra- and inter-basinal stratigraphic correlation particularly in case of Upper Gondwana formations. It is well recognised that there are distinct spatial and temporal similarities in lithological, faunal and floral distribution in different Gondwana Basins of southern continents, including India, that were once part of supercontinent Gondwanaland. To address the problems of Indian Gondwana stratigraphy, during the present study, some unique events, also recognised in other parts of Gondwanaland, like marine flooding surfaces, large scale tectonic events or major change in depositional environment have been used as a tool for temporal correlation within the Gondwana Basins of India. Many of these events have been dated from different basins elsewhere. Considering these major events as time planes the total time span of deposition in Gondwana Basins has been classified into seven time slots. Recognition of these time planes helps in interbasinal correlation of different formations in Indian Gondwana basins and assigning the age, wherever available. This approach also helps in better understanding of basinal history. Unless otherwise mentioned, the time scale proposed by International Commission on Stratigraphy (2004) has been followed in this paper.

1 comment:

  1. India is interesting because of the MIX of Laurasian and Gondwanan faunas; it has aetosaurs, metoposaurs, and phytosaurs, but also rhynchosaurs and cynodonts, which are are virtually absent in Laurasia. Unfortunately, the Indian aetosaurs have never been described in detail, although I have seen some interesting and suggestive photos; we need to get over there and describe that shit.

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