Sea-Level Changes and Formation of Cyclic-Sequence of Cambrian-Ordovician in Akesu-Bachu Area,Xinjiang
-
摘要: 通过研究新疆阿克苏 巴楚地区寒武 奥陶系沉积特征、层序地层序列及其海平面变化规律,首次识别出2个二级旋回层序、4个三级旋回层序和9个四级旋回层序。重点对三级旋回层序的层序界面性质及其体系域特点进行了深入、细致的分析。研究表明,每一旋回层序的形成,理论上均由海平面相对快速上升、缓慢上升、静止、缓慢下降和快速下降所引起,但实际情况较之复杂。海平面上升的最大幅度发生在丘里塔格晚期—吐木休克早期,之后由于构造运动和全球海平面下降,该区海平面亦快速下降,海水迅速退出本区,致使该区普遍缺失上奥陶统。Abstract: The Cambrian-Ordovician sequences are the most widespread ones in Tarim basin.More and more results of explorations and exploitations indicate that they are most important source and reservoir rocks in the basin. It is a set of shallow-bathyal deposits of carbonate and clastic rocks. The sedimentary facies of the study area were a kind of local platform in Cambrian,and platform-open sea shelf in Early-Middle Ordovician,at the same period,it was shelf facies in Keping area and open platform facies in Bachu area.In late Ordovician,the bulk areas were rapidly uplifted and changed into land by the influences of Caledonian orogeny. So the Upper Ordovician was hiatus or truncation in most areas of the basin. The variations of sea level had varying scales or orders during the long geological history and it led to formation of various sedimemtary characteristics in which it were objectively recorded in sedimentary rocks and sequences.For this reason,by means of studying the sedimentary features,sequences and boundary characters in the rocks and strata,it is able to estimate the laws of sea level changes during the period of sedimentation,analyse the conditions of paleogeography and paleoclimatology,and provide some scientific basis for exploration of oil and gas.Through study on the deposition characteristics,sequence stratigraphic framework and sea level changes,two second-order cyclic sequences,four third-order cyclic sequeces and nine fouth-order cyclic sequences have been recognized.Detailed analysis has focussed on the third-order cyclic sequences. The study shows that the formation of every cyclic sequence is caused by the relatively rapid rise,slowly rise,stagnant,slowly fall and rapid fall of the sea-level,in which the maximun sea-level rise occured during late Qioulitage period-early Tumuxiouke Period and,thereafter,for the sake of tectonic activity and global sea-level fall,the sea water withdrawed rapidly from the study area,resulting in the loss of the Upper Ordovician deposition. In brief,according to the evolutionary history of sea level changes and cyclic-sequence,there were two times large scale transgression-regression during the period,and it was the Early-Middle Cambrian and Late Cambrian-Orovician,in which the period of maximum transgression was the Middle Ordovician in the Tarim basin.In the long period(Ⅲ-order) of sea level changes,it contained many high-frequency short-period variations of sea level that it was named composite sea level change.
-
Key words:
- cyclic-sequence /
- system /
- tract /
- sea-level /
- changes
-
[1] 梅冥相.碳酸盐旋回与层序[M] .贵阳:贵州科技出版社,1995.90~91 [2] 顾家裕等著.沉积相与油气[M] .北京:石油工业出版社,1994.75~76 [3] 周志毅,陈丕基主编.塔里木生物地层和地层演化[M] .北京:科学出版社,1990.47~49 [4] Chow N,James N P.Cambrian Grand Cycles:a northern Appalachian Perspctive[J] .Geol.Soc.Am.Bull.,1987,98:418~429 [5] 马宝林,温常庆主编.塔里木沉积岩形成演化与油气[M] .北京:科学出版社,1991.87~93 [6] 梅冥相,梅仕龙.华北中寒武世张夏组复合海平面变化旋回层序[J] .沉积学报.1997,15(4):5~9
计量
- 文章访问数: 643
- HTML全文浏览量: 21
- PDF下载量: 467
- 被引次数: 0