Early Devonian ammonoid faunas in the Zeravshan Mountains (Uzbekistan and Tadjikistan) and the transition from a carbonate platform setting to pelagic sedimentation

Abstract

Thick Early Devonian carbonatic sedimentary successions, exposed in the Zeravshan Mountains of Uzbekistan, display a transition from a reefal to a pelagic facies. This allows us to document and analyze the history of sedimentation and changes in marine faunas of this region. The late Pragian succession of Bursykhirman Mountain is documented with the transition from platform carbonates to pelagic sediments. Lithology and microfacies through the early Emsian sedimentary sequence of two ammonoid-bearing sections were investigated with a focus on the Dzhaus Beds. In addition to this sedimentological analysis, we discuss the palaeobiogeographically peculiar situation of Uzbekistan (palaeocontinent Kazakhstania). Many species found in the Kitab State Geological Reserve are endemic and at least restricted to the South Tien Shan. We suggest a moderately close relationship to southern Chinese and Vietnamese faunas, even though more palaeontological data from the latter two regions is needed for a test. We also revise the cephalopod fauna from the Kitab Reserve and introduce the following new taxa: Beckeroceras gen. nov., Uzbekisphinctes gen. nov., Ivoites meshchankinae sp. nov., Kitabobactrites salimovae gen. et sp. nov., and Metabactrites rakhmonovi sp. nov. • Key words: Pragian, Emsian, carbonate microfacies, endemism, Ammonoidea, palaeogeography