摘要:
石炭纪内蒙古西南部广泛发育砂坝─泻湖沉积体系,该体系不同时期形成的泻湖沉积物相互叠置?沉积厚度大?沉积层序多样,这在全新世泻湖中难以形成和观察到?依据沉积特征?沉积层序,识别出与现代同类沉积体系相似的四种基本类型:海侵型?海退型?稳定型和局部海侵型?这表明研究全新世砂坝─泻湖体系得出的地层模式有助于识别地质时期的同类沉积体系?由于研究地区石炭纪砂坝─泻湖体系发育于广阔的空间和较长的时间内,它们常成复合类型,如海侵型─局部海侵型?稳定型─局部海侵型?此外,全新世稳定型砂坝─泻湖体系的上覆和下优层皆为陆相,但是石炭系同类沉积体系在同一地区连续叠置,这是长时期构造持续下陷和岸线相对稳定的反映?海侵型砂坝─泻湖体系形成于海侵层序中,泻湖沉积物的厚度大于砂坝沉积物的厚度,据此,建立了不同于现代同类沉积体系的地层模式?
Abstract:
The barrier-lagoon systems(BLS)are widely distributed in the southwesten Inner Mongolia Autonomous Region during Carboniferous Period. The lagoon deposits of different stages in the systems are superimposed mutually,forming various sequences,with a great thickness. This is hard to be formed and preserved in the Holocene. According to sedimentological characteristics and depositional sequence,the transgressive,regressive,stationary and locally transgressive barrier lagoon systems in the carboniferous deposits of the studied area have been recognized, which are similar to the types in Holocene. It confirms that the stratigraphic models of barrier-lagoon systems summarized in the study of Holocene are helpful for recognition and study of the analogies in the geological time. However,the barrier-lagoon systems of the Carboniferous Period in the studied area have been formed in broad space for a long time,they are usually compound,such as transgressive-locally transgressive,stationary-locally transgressive BLS. In addition,the stationary BLS is characterized by both underlying and overlying strata to be terrestrial in Holocene,but the counterparts in the carboniferous deposits of the studied area are characterized by superimposition of more than ten barrier-lagoon sequences almost in the same area for a long time under conditions of continuous tectonic subsidence and stabilization of coastline. The transgressive barrier-lagoon systems occur in transgressive sequence and have lagoon deposits exceeding the coincident barrier sands in thickness. The formation model for BLS has been established.
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