Abstract：A set of marine carbonate rocks interbedded with clastic rock was deposited in the Early Paleozoic in the Ordos area，with huge thickness and various sedimentary types.According to characteristics of sedimentary sequence，petrology，sedimentary structure and palaeontology，four depositional systems can be distinguished in the Lower Paleozoic in the Ordos including coast，carbonate rock platform，platform margin and deepwater slope-trough，which can be subdivided into several subfacies and microfacies.For each facies，its sedimentary characteristics，spatial and temporal distribution were summarized.Based on these studies，the lithofacies palaeogeography maps of the Lower Paleozoic in the Ordos were compiled by each age.The Early Cambrian only formed a set of mud-sand flat and mud-dolostone flat sediments around the southwestern margin of the Ordos land.Followed the marine transgression spread in the Middle Cambrian，the central-eastern part of the Ordos was gradually transformed from sand-mud flat to restricted platform-open platform sediments，and developed platform edge to deepwater trough sediments in the western margin.Since the Late Cambrian marine regression，the central-eastern part of the Ordos was changed to restrictive platform dolostone flat sediments，but the deepwater slope-trough facies was still developed in the western margin.To the Early Ordovician，the main body of the Ordos became a uniform palaeoland with mud-dolostone flat and dolomitic-limestone flat sediments around its southeastern margin.Then a massive transgression in the Middle Ordovician led to an extensive shallow epicontinental deposits in the Ordos.The Northern Shaanxi Depression formed a gypsum salt lake，and developed restrictive platform-open platform sediments outside it.At the late Middle Ordovician，the southwestern margin began to develop platform foreslope-deepwater trough facies sediments.The Late Ordovician Caledonian Movement uplifted the main Ordos as a land，and formed a narrow sea continuing deposit in the southwestern margin of the Ordos.The sedimentary facies was quickly changed from carbonate rock platform to deepwater slope-trough，and developed some reefs in the southern margin of Ordos，indicating the epicontinental marginal rimmed platform deposit.
