Study on sedimentary characteristics of Middle Ordovician Keliomori Formation in western Ordos Basin

The Lower Paleozoic Ordovician system in the western Ordos Basin has attracted much attention because of its great potential for oil and gas exploration, and the carbonate rock developed in the Middle Ordovician Keliomori Formation is expected to be the next exploration target layer, so study on its sedimentary characteristics can provide geological basis for the exploration of Ordovician gas in the west margin. By means of outcrops investigation, core observation and thin section identification, the characteristics of petrology, sedimentary facies types and spatial distribution of the Keliomori Formation are studied. It is shown that the Keliomori Formation is mainly composed of thin layer micrite, calcirudyte, calcarenite, calcisiltite, bioclastic limestone and black shale. They have micrite structure, granular structure, and thin layer, lamellar, nodular, brecciform structure, slump and Bauma sequence can be seen. The sedimentary facies platform front slope and deep water slop-trough, which are distributed in a narrow strip along the north-south direction. From east to west, the platform front slope facies develops in the open sea platform close to the Ordos base, and rapidly changes into deep water slop-trough facies westward, and the sea water has a gradual deepening trend.