FOSSIL CONSTRAINTS IN RECONSTRUCTING INDIAN EQUATORIAL PERI-GONDWANALAND DURING THE CAMBRIAN

Faunal data provide constraints upon tectonic models, particularly in such areas of extreme structural complexity such as the Himalaya. Although Cambrian fossils from the Himalaya have been described sporadically for over 130 years, only recently have attempts been made to integrate these data into a regional biostratigraphic framework. This has required taxonomic revision of finds previously made from the Himalaya, supplemented by the recovery of additional material. Within the Himalayan margin, fossil evidence is consistent with other types of stratigraphic data and suggests that all portions of the Himalayan margin were part of a passive margin sequence during the Cambrian. Both biostratigraphic and biogeographic evidence from trilobites is critical to demolishing recent claims that the Himalayan margin is an amalgam of Indian shield and exotic material. Himalayan faunas apparently show little endemism and are consistent with those of the equatorial peri-Gondwanan region. This, coupled with the limited development of Upper Cambrian deposits on the Himalayan margin, hinders assessment of the detailed relationships of the Himalayan margin to "outboard" blocks, such as portions of Tibet, Sibumasu, Qamdo-Simao, and the Yangtze Platform. There is no direct evidence for the existence of Cimmeria during the Cambrian Period. Fieldwork in rocks that are apparently of Late Cambrian age in Bhutan may help resolve these issues.