Since the Neogene, the ancient Songhua-Liao River system have undergone several changes with the alternation of fluvial and lacustrineformation on a large scale.
The middle Jurassic series Yanan Formation of in Lingwu coalfield is a lacustrine deltaic deposit.
灵武煤田的中侏罗统延安组含煤岩系为一湖泊三角洲沉积。
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Major sedimentary facies in the Huanhe-Huachi Formation include lacustrine facies, delta facies, meandering fluvial facies, and interbedded eolian sandstone facies.