Strata of the Late Mesozoic in the North of Qiangtang Basin: A Discovery of the Early Cretaceous Marine Strata 

Key words: 
• Qiangtang basin /
• ShengliheTuonamu region /
• Early Cretaceous /
• stratigraphic correlation /
•  /
•  /
•  /

Abstract: In the Late Jurassic period, Qiangtang basin has experienced an obvious tectonic uplift and turned into a terrestrial basin. Most of the region has undergone erosion in the Cretaceous, which results in the lack of Lower Cretaceous. Therefore, to confirm the existence of the Early Cretaceous marine sediments in the Qiangtang basin, this paper conducted a research on ShengliheTuonamu region preliminarily judged as Late JurassicEarly Cretaceous marine strata era, which is based on the Nadigangri section and combined with the Shenglihe, Tuonamu, Changsheshan sections which are preliminary judged on the Early Cretaceous era oil shale formation on the auxiliary sections, with the adoption of paleontological fossils and isotopic chronology to judge the era of each formation of the section from the top to the bottom and rejudge the era of the Original Suowa formation. The results show that original Suowa Formation is in the Late JurassicEarly Cretaceous, Suowa formation is in the Late Jurassic, Weimingming formation is in the Early Cretaceous, and Xueshan formation is in the Late Early CretaceousEarly Late Cretaceous. The formation comparison show that the era which was initially judged as Late JurassicEarly Cretaceous shale limestonegypsum marine strata should be Early Cretaceous. In the Early Cretaceous period, Early Cretaceous marine strata are widely distributed in ShengliheTuonamu region, lithology formations of which are different in different regions. This stratum is oil shale and the thickest in ShengliheChangsheshan region, which gradually becomes thinner along the east and transits into shale sediment, and into limestone sediment in the west. Regionally, the existence of the Early Cretaceous strata is important to the conditions of the underlying oil and gas storage.