西藏沙丁、荣布地区三叠系—老第三系沉积地质特征

Sedimentary geology of the Triassic-Paleogene strata in the Shading and Rongbo regions, Xizang

关键词:  西藏沙丁荣布地区  三叠纪-老第三纪  沉积地质

Key words:  Shading and Rongbo regions in Xizang  Triassic-Paleogene  sedimentary geology

摘要:

研究区从三叠纪到老第三纪,发育的岩石地层主要有确哈拉群（T₃）、希湖群(J_1-2)、拉贡塘组(J_2-3)、多尼组（K₁）、竟柱山组（K₂）和牛堡组(E_2-3)。在沉积相上,经历了从深水沉积到浅水直至陆相沉积的演变,发育有冲积扇、河流、湖泊、三角洲（潮汐）、障壁海岸、浅海、深海和火山碎屑流沉积。古地理分析表明,研究区晚三叠世古地理轮廓是一个从东南向西北和东北方向由浅水碳酸盐台地及深水陆层海底扇沉积共同发育的沉积盆地;早中侏罗世,演变成为一个由深水砂质浊积岩和细屑浊积岩组成的水下席状体沉积;进入中晚侏罗世,其古地理表现为一个陆屑浅海有障壁海岸;到了晚白垩世,研究区表现为以含煤沉积为特征的三角洲相沉积。

Abstract:

The Triassic-Paleogene lithostratigraphic units in the Shading and Rongbo regions, Xizang mainly consist of the Quehala Group (T₃), Xihu Group (J_1-2), Lhagongtang Formation (J_2-3), Duoni Formation (K₁), Jingzhushan Formation" (K₂) and Niubao Formation (F_2-3). The sedimentary facies show a depositional evolution from the deep-water sediments through shallow-water sediments to the continental sediments, including alluvial fan, river, lake, delta (tide-dominated), barrier coast, shallow sea, deep sea and volcanic debris flow deposits. The palaeogeographic research indicate that the palaeogeographic outline of the study area recorded the evolution from a sedimentary basin in which the shallow-water carbonate platform sediments and deep-water terrigenous elastic submarine fan developed from southeast to northwest and northeast during the Late Triassic through a submarine sheet-like model composed of deep-water sandy turbidite and fine-gained turbidite during the Early Jurassic to a terrigenous elastic barrier coast during the Middle and Late Jurassic and finally to the coal-bearing delta sediments during the Late Cretaceous.