REDEFINITION OF THE EARLY PLEISTOCENE QANGZÊ FORMATION AND SEQUENCE STRATIGRAPHIC DIVISION IN THE ZANDA BASIN, NGARI, TIBET
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摘要: 根据札达盆地香孜组河湖相地层剖面的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将札达盆地下更新统香孜组河湖相地层划分为2个沉积相、3个岩段。香孜组一、二岩段为一套砾岩夹砂岩的粗碎屑岩,属典型的冲(洪)积扇沉积物;第三岩段为砾岩与砂岩互层,属冰水冰缘相沉积。ESR法和古地磁法测年结果表明,札达盆地香孜组河湖相地层的形成时代为早更新世早期(2.68~1.36 Ma).札达盆地为一同生断陷盆地,在后期重新复活的过程中,盆地只经历了冲积体系域和水进体系域。冲积体系域形成于札达盆地早更新世早期重新复活层序发育的早、中期,水进体系域形成于札达盆地早更新世早期重新复活层序发育的晚期。Abstract: Based on the contact relationships,sedimentary cycles,sedimentary systems and lithofacies and lithologic characteristics of the stratigraphic section,the fluvio-lacustrine sediments of the early Pleistocene Qangzê Formation in the Zanda basin are divided into 2 sedimentary facies and 3 lithologic members.The first and second members of the Qangzê Formation consist of a sequence of coarse clastic rocks of conglomerate with sandstone,belonging to typical alluvial(diluvial) fan deposits.The third member consists of alternating beds of sandstone and conglomerate,belonging to glaciofluvial and paraglacial deposits.ESR and paleomagnetic dating indicates that the age of the fluvio-lacustrine sediments of the Qangzê Formation in the Zanda basin is earliest Pleistocene(2.681.36 Ma).The Zanda basin was a syngenetic downfaulted basin,which only experienced the alluvial systems tract and transgressive systems tract in the process of its reactivation in the late stage.The alluvial systems tract was formed in the early and middle stages of development of the reactivated stratigraphic sequence in the early part of the early Pleistocene,while the transgressive systems tract was formed in the late stage of development of the reactivated stratigraphic sequence in the early part of the early Pleistocene.
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Key words:
- early Pleistocene /
- fluvio-lacustrine sediments /
- sequence stratigraphy /
- Zanda basin,Tibet /
- Qangzê Formation /
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