羌塘盆地侏罗纪末—早白垩世沉积特征与地层问题

Late Jurassic-Early Cretaceous strata and their sendimentary characteristics in the Qiangtang basin,northern Tibet

羌塘盆地侏罗纪末至早白垩世地层包括扎窝茸组、雪山组、白龙冰河组和索瓦组上段,目前对它们的划分、对比和相互间关系的认识不一。笔者根据各组的含义和时代依据,指出各地层组为岩石地层单元,目前资料尚不足以作进一步年代学划分。通过全面统计各组的分布情况,分析各组的沉积特征,发现白龙冰河组为陆棚相,仅见于盆地北西部;索瓦组上段为海湾泻湖相,见于盆地中部;雪山组和扎窝茸组为河流—三角洲相,见于北东部。为此,认为各地层组是盆地内同期异相沉积,作为上下关系处理是不妥的,据此又提出了新的地层对比方案,认为盆内最高海相层位应该跨入了下白垩统,海水最终是向北西方向逐步退出盆地的。

The Late Jurassic-Early Cretaceous strata mainly include the Zhaworong Formation, Xueshan Formation,Bailongbinghe Formation and upper member of the Suowa Formation in the Qiangtang basin.Up to now there are different views about their division,correlation and mutual relation.This paper summarizes the definition and age evidence of each formation and points out that these formations are lithostratigraphic units.The available data are not enough to make a further chronological division.By the statistics of the distribution of various formations and analysis of the sedimentary characteristics of various formations,it is found that the Bailongbinghe Formation is of continental shelf facies and distributed in the northeastern part.Thus the authors think that these formations are contemporaneous and heteropic deposits,and that it is not advisable to consider their relationships to be overlying and underlying.According to this,the authors proposes a new scheme of stratigraphic correlation and think that the highest marine horizon in the basin should extend to the Lower Cretaceous and that seawaterret reated from the basin gradually from southeast to northwest.