摘要
晚三叠世延长组长7、长6油层组沉积期，鄂尔多斯盆地三角洲与重力流复合控砂形成了湖盆中部地区大面积发育的厚层深水砂岩。采用锆石原位U—Pb年龄分析技术获得长7底部和中上部凝灰岩年龄分别为228．2±2．0Ma和221．8＋2．0Ma，在此基础上推算长。中上部和长6中下部重力流的形成时间为距今215～224Ma。凝灰岩和重力流沉积的时间段与秦岭地区构造活动相对最活跃的时期（印支中期）基本一致。因此长。底部分布稳定的凝灰岩薄层和湖退早期大面积分布的重力流沉积砂体为构造作用控制下的事件沉积。在印支中期事件影响下，长，底部凝灰岩事件层广泛发育，事件层上下地层碎屑组分差异较大，构造事件控制了大面积深水坳陷的形成、沉积体系的变化、盆地沉积中心的迁移及重力流沉积事件的发生。
A large area of deep-water sandstone was formed under the combined action of delta and gravity flow in the central Ordos Basin during the depositional period of the Ch6 and Ch7 oil-bearing formations of the Upper Triassic Yanchang Formation. According to U-Pb dating of zircons by the method of LA-ICP-MS, the ages of the tuff layers at the bottom and upper parts of Ch7 oil-bearing formation are 228.2±2.0 Ma and 221.8±2.0 Ma, respectively. Based on the ages of the tuff layers, it is suggested that the gravity flow complexes at middle-upper Ch7 and lower-middle Ch6 oil-bearing formations were formed during 215-224 Ma. The depositional time of tuff and gravity flow is roughly the same as the time when tectonics are most active in the Qinling area, i.e. middle Indosinian period. The steadily widespread tuff at the bottom of the Ch7 oil-bearing formation and the extensive gravity flow sediments formed at early lake regression period are the direct outcomes of the tectonic event. Tuff layers are widely deposited at the bottom of Ch7 oil-bearing formation under the influence of the middle Indosinian tectonic events. Divided by the tuff layers, there is obvious difference in clastic composition between the lower and upper strata. The events control formation of large-area deep-water depressions, change of depositional system, migration of depositional center, and occurrence of gravity flow.
出处
《石油勘探与开发》
SCIE
EI
CAS
CSCD
北大核心
2013年第5期513-520,共8页
Petroleum Exploration and Development
基金
国家科技重大专项"大型油气田及煤层气开发"(2011ZX05044
2011ZX05001-004)
