藏北多格错仁红层及孢粉组合特征

青藏高原北部羌塘地块广泛出露第三纪陆相红层 ,确定这些红层及其变形的时代对认识青藏高原的形成演化过程具有非常重要的意义。 1998～ 1999年 ,INDEPTH III项目地质课题组人员 2次深入西藏可可西里地区进行科学考察 ,新发现藏北多格错仁红层 ,并在其中发现较多种属的孢粉化石。该孢粉组合反映以温带旱生草原为主体的古植被面貌。通过对青藏高原北部及邻区主要新生代盆地孢粉组合与古环境演化的对比分析 ,结合多格错仁红层上覆弱变形玄武岩 2 5～ 3 2Ma的40 Ar- 3 9Ar高精度测年资料 ,推断多格错仁红层的形成时代为晚中新世 ,多格错仁红层挤压变形所致的约 5 0 %的地壳缩短量发生在中新世末—上新世初。这些资料为建立青藏高原动力学模式提供了新的年代依据

STRATA AND SPORES ASSOCIATION OF DOGAI CORING REDBEDS OF NORTH TIBETAN PLATEAU

Widespread fluvial redbeds are exposed widely in Qiangtang block of North Tibetan Plateau. Dating these redbeds can provide very important data for understanding the geological and deformational history of North Tibetan Plateau.The geological group of INDEPTH III studied the stratigraphy and deformation of Dogai Coring redbeds in North Tibetan Plateau, and discovered varieties of spores for time determination. The spores association corresponds to the vegetation dominated by arid grassland and in Late Miocence Pliocene period. The latest 40 Ar- 39 Ar dating of the basalt overlying Dogai Coring redbeds gives ages ranging from 2 5Ma to 3 2Ma, which provides upper limit age for strata and deformation of Dogai Coring redbeds. It is inferred that the Dogai Coring redbeds formed in Late Miocene, and the crustal shortening of Dogai Coring redbed basin, circa 50%, occurred at the end of Miocene Early Pliocene.The time of strata and deformation of Dogai Coring redbeds sets a new constrain for understanding the geodynamic process of the Tibetan Plateau.