关键词: 地质时代, 古气候, 孢粉组合, 索瓦组上段, 早白垩世, 羌塘盆地

Abstract:

The upper part of the Suowa Formation in the central district of the North Qiangtang depression is the sediment during the latestage evolution of the Qiangtang basin, which deposits in tidal flatlagoonal environment. By strata correlation of the upper part of the Suowa Formation, it is found that its lithology is different in the eastern, western and southern areas, and the places where the oil shale exposed only aligned around the epicontinental restricted gulflagoon areas
e g. Shengli River area, Changshe Mountain area and Tuolamu area in the southern margins of the North Qiangtang basin. The deposition of the oil shale is obviously controlled by differential palaeotopography. Based on the fossil assemblages in the upper part of the Suowa Formation and its underlying strata, and combined with the Re-Os dating of the Shengli River oil shale, the geological age of the upper part of the Suowa Formation is suggested to be Early Cretaceous. The Cretaceous spores and pollen assemblages and silicified wood reveal that the climate during the early period of the upper part of the Suowa Formation was warm and humid, while the climate during the later period was hot and arid. Furthermore, the vertical changed climate may be not restricted to the Shengli River region, but the whole North Qiangtang basin. The discovery of the oil shalegypsum sedimentary associations is of important implications for our knowledge of the hydrocarbon accumulation and preservation of the Qiangtang basin during the late stage evolution.

Key words: geological age, palaeoclimate, palynological assemblage, the upper
part of the Suowa Formation, Early Cretaceous, Qiangtang basin