Paleoclimatic Information of O₂m⁶₅ Deposition Stage in Northern Shaanxi Salt Basin: Evidence from fluid inclusion in halite

Key words: 
• fluid inclusions in halite /
• homogenization temperature /
• cooling nucleation method /
• halite of northern Shaanxi Basin in Ordovician /
• paleoclimate

Abstract: The homogenization temperature of fluid inclusions reflects the temperatures of the brines from which halite crystals grew. Therefore, it is a powerful tool to reveal the paleoclimate. Northern Shaanxi Salt Basin is located in the central and eastern of Ordos Basin. There is thick-bedded salt in Ordovician Majiagou Formation.  Petrographical research and the homogenization temperature measurement of  the samples which come from Zhenjia-1 core have been studied in detail. The results of petrographic research show that there are three types of fluid inclusions which are square, round and irregular. They contain  liquid inclusion,  liquid-gas inclusion and  liquid-gas -crystal inclusion.  The homogenization temperatures of fluid inclusions  have been measured by cooling nucleation method. It shows that the homogenization temperatures of fluid inclusions of sample zjy-1(2 738 m deep) range 18.5℃ to 27℃, sample zjy-2(2 740 m deep) range 14.9℃ to 29.9℃, sample zjy-3(2 744 m deep) range 24℃ to 39.6℃, and sample zjy-4(2 812.8 m deep) range 14.7℃ to 31℃. Comparing with previous paleotemperature, the records are basically coincident. The homogenization temperatures reflect the paleotemperature of Northern Shaanxi Salt Basin in the O₂m⁶₅ stage of Ordovician period is about 27℃~36.9℃,    the paleoclimate is arid and hot in low-latitude arid zone of the southern hemisphere.