Geophysical and drilling data-proved that Upper Paleozoic sediments of several thou-sand meters thick are preserved in east part of Bayanhot Basin

of which the Ordovician Tremadocian-Arenigian and Llanvirnian-Llandeilian are respectively typical platform de-posits and Helan aulacoge deposits;Carboniferous Tournaisian-Visean and Namurian-Westfalian are respectively steady transgressional deposits and Helan collisional valley de-posits.The discovery shows that the study region had not uplifted all the time.