Tethys-wide mid-Carnian (Late Triassic) carbonate productivity gap:
Evidence from Spiti (Indian Himalaya)



Rapid mid-Carnian (Julian 1/Julian 2) lithological change from carbonates to terrigenous sediments is described from the Southern Tethyan margin. It is inferred to be equivalent to a carbonate production gap recognized in many basinal successions along the northwestern Tethys (Dinarids, Southern and Northern Alps, Western Carpathians) related to a supra-regional depositional turnover.
The Guling and Lalung section in the Spiti region record a sudden increase of terrigenous influx within the Trachyceras aonoides ammonite subzone (Julian 1/II), recognisable all over the Himalaya. During this time-interval, the depositional setting shallowed rapidly from deep slope to proximal slope-facies. These observations are here explained by a change in Tethyan plate dynamics, resulting in extensional movements in the deep-shelf-environment and increased monsoonal activity during the Late Triassic. This resulted in increased weathering of continents and enhanced terrigenous influx. Laminated shales in the lower Rama Formation of Lalung record an anoxic event comparable to black shales in the Austroalpine domain. That these anoxic events in both regions were of local character, is interpreted due to the absence of significant 13C-shifts across the lithologic boundaries: the main sea water chemistry of the Tethys must have been remained unaffected during the described event.


published in: Int. Journal of Asian Earth Sciences, 30: 285-292, London