The is a geological formation in the Gansu province of China that spans up to 100 m thick and is widely distributed within the , with a paleomagnetic age of between 11 and 6.4 Mya (Upper/Late Miocene). The formation is divided into three parts which represent three different ages, generally referred to as the "upper part" (youngest, at 6-7 mya), the "middle part" (intermediate, at 9 to 7.6 mya. Also known as the Dashengou fauna, and the "lower part" (oldest).