LOWER SILURIAN CONODONTS FROM THE SHINE JINST REGION, SOUTHWESTERN MONGOLIA

Lower Silurian conodonts were recovered from carbonate beds in the upper Zalaa and lower Sharchuluut formations at Yamaan Us in the Shine Jinst region, Gobi-Altai Zone, of southwestern Mongolia. Conodonts are described from the Zalaa Formation for the first time; key taxa recovered include Distomodus kentuckyensis, Ozarkodina hassi, Pranognathus siluricus, and Pseudolonchodina expansa. These species constrain the upper Zalaa Formation and lower most Sharchuluut Formation to the expansa Zone, which spans the upper Rhuddanian to lower Aeronian. The presence of a cosmopolitan conodont fauna places these strata from the Gobi-Altai Zone in a basin-shelf marine setting with connection and circulation to the open ocean during the Llandovery.