MIDDLE JURASSIC (BATHONIAN-CALLOVIAN) AMMONITES FROM THE AMDO AREA, NORTHERN TIBET
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Abstract:
New collections of ammonites have been recently carried out in the Amdo area, northern Tibet. The Bathonian ammonites have been referred to Oxycerites oppeli Elmi,Homoeoplanulites cf. homoeomorphus (Buckman),H. cf. acuticosta (Roemer), Choffatia cf. vicenti Mangold, Siemiradzkia cf. matisconensis (Lissajous), Procerites sp., Neuqueniceras cf. yokoyamai Kobayashi and Fukada, and Indosphinctes sp. The Callovian ammonites include Oxycerites cf. subcotarius (Oppel),Macrocephalites? sp., Homoeoplanulites cf. furculus (Neumayr), Indospinctes (Elatmites) cf. reveli Mangold and Reineckeites sp. At generic level Indosphinctes,Indospinctes (Elatmites),Neuqueniceras, Siemiradzkia and Procerites are found in North Tibet for the first time, suggesting an age from middle Bathonian to early Callovian. The Middle Jurassic ammonites in this area exhibit a strong endemicity. Both ORBIS of the Upper Bathonian and KOENIGI zones of the Lower Callovian are significant intervals for faunal dispersal.
