摘要
上扬子区早三叠世印度期的地层,从西向东由滨岸相砂泥岩(飞仙关组)到台地碳酸盐岩(大冶组),代表了一个二叠纪与三叠纪之交的大规模碳酸盐台地淹没事件之后、三叠纪早期缓坡型台地的生长发育过程。受制于三叠纪早期的两个海侵—海退旋回,早三叠世印度期大冶组中的鲕粒滩相灰岩经历了自西向东的进积作用。上述沉积作用过程的结果,在湖北利川的三叠系大冶组顶部发育厚层块状鲕粒滩相灰岩;该鲕粒灰岩,较大的粒径以及多样的宏观形态,成为一个窥视鲕粒成因的典型地点。这些主要由碳酸盐泥晶粘聚而成的粒径多超过2 mm的鲕粒,包括同心鲕粒、椭圆鲕粒、复合鲕粒、不规则鲕粒、核心不太清楚的鲕粒等多种类型。这些粒径超过2 mm的巨鲕,不但代表了显生宙较为罕见的沉积学现象,而且有可能代表了二叠纪末期生物大灭绝之后荒凉海底环境的沉积响应,为进一步了解成因还未完全明了的鲕粒所代表的碳酸盐世界提供了一个有意义的实例。
Strata of the Triassic Induan in the Upper-Yangtze region, i. e. the littoral-facies sandstones and mudstones of the Feixianguan Formation in the western part and the ramp carbonates of the Daye Formation in the eastern part, represent a developing process of a ramp carbonate platform. Controlled by the two transgressive-regressive processes in the Induan age of the Early Triassic, the oolitic-bank limestones within the Daye Formation in the Upper-Yangtze region have been undergone the obvious progradation from the west to the east. Resulting from this sedimentary process, a set of oolitic-bank limestones with the thickness of more than 40 meters is developed in the top part of the Triassic Daye Formation at the Lichuan section. For this set of oolitic-bank limestones, the larger grain size and the diversity of morphology make it become a useful example to understand the origin of oolites. Further, the diverse configurations including the circular, the sub-circular, the irregular and the composite shapes of oolites in the top part of the Triassic Daye Formation at the Liehuan section, especially for the development of the giant oolites that are unusual in the Phanerozoic, provide an important clue for the understanding of both the sedimentary response to the mass extinction at the turn from the Permian to the Triassic and the evolving carbonate world that is reflected by the oolite whose origin remains uncertain.
出处
《现代地质》
CAS
CSCD
北大核心
2008年第5期683-698,共16页
Geoscience
基金
国家自然科学基金项目(49802012
40472065)
关键词
巨鲕
鲕粒多样性
大冶组
三叠系
湖北利川
giant oolite
oolitic diversity
Daye Formation
Triassic
Lichuan section in Hubei Province
作者简介
梅冥相，男，教授，博士生导师，1965年出生，沉积学与地层学专业，主要从事沉积学与地层研究工作。Email：meimingxiang@263．com。
