摘要:
天津蓟县中元古界雾迷山组为一套厚3000余米的碳酸盐岩地层,叠层石生物层和凝块石生物丘特别发育。它们与潮坪相泥晶白云岩和泥质白云岩构成具对称相序组构的环潮坪型碳酸盐米级旋回层序。米级旋回层序之顶覆以厚度不等的潟湖相白云质泥页岩。常常3～5个米级旋回层序呈有序叠加构成五级准层序组,少数米级旋回层序还可识别出5个七级韵律层而呈现出1:5的叠加关系。因此,七级韵律层、米级旋回层和五级准层序组分别与岁差旋回、短偏心率旋回、长偏心率旋回间存在有成因联系。根据米级旋回层序在长周期层序中的有序垂直叠加形式,在雾迷山组中可识别出26个三级层序,进一步归为6个二级层序。
Abstract:
The Mesoproterozoic Wumishan Formation in Jixian,Tianjin represents a succession of 300-m thick carbonate strata,in which stromatolite biostromes and clotted bioherms are best developed.These biostromes and bioherms,together with tidal-flat dolomicrite and muddy dolostone,form circum-tidal flat meter-scale carbonate cyclic sequences with symmetrical facies sequences and fabrics.These cyclic sequences are overlain by the lagoon dolomitic mudstones and shales.Generally speaking,three to five orderly stacked meter-scale cyclic sequences may form one fifth-order parasequence set.Occasionally,five seventh-order rhythmites are also recognized in some of the meter-scale cyclic sequences.Therefore,the seventh-order rhythmites, meter-scale cyclic sequences and fifth-order parasequence sets are correlative in origin with precession of equinox cycles,short eccentricity cycles and long eccentricity cycles,respectively. Viewed from the ordered stacking patterns of the meter-scale cyclic sequences in the long-period sequences,twenty-six third-order sequences may be identified in the Wumishan Formation. These third-order sequences may also be incorporated into six second-order sequences.
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