元古界（the Proterozoic Erathem）是指元古代形成的地层，属年代地层单位，符号Pt。
n. Proterozoic ; Algonkian
详细的研究表明了早元古界桐柏山群不能成为老湾花岗岩的源岩。
Early Proterozoic Tongbaishan group cannot be the source rock of the granite by study in detail.
下元古界秦岭群是成矿有利环境，韧性剪切带是控岩控矿的主要构造。
The Qinling Group of Lower Proterozoic is an advantageous environment for metallogenesis and the ductile shear zone is a major structure to control rocks and ores.
本文进一步提出了蓟县地区中元古界雾迷山组中存在着风暴沉积的证据。
This paper, however, presents evidence of the presence of storm deposits in the middle Proterozoic Wumishan Formation in the Jixian area.
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