塔里木盆地台盆区三叠纪大型挤压坳陷湖盆层序地层及构造响应

三叠纪是塔里木盆地区域应力场由伸展至挤压的重大转折期,台盆区发育大型挤压坳陷盆地.经过地震层序解释,将台盆区三叠系划分为4个三级层序,其顶、底界面均为区域性削截不整合面;内部除了少量削截、上超和下切谷之外,顶超是最为普遍的层序界面标志.进一步的钻井层序对比表明,层序内幕沉积演化独特,湖扩体系域普遍发育大型辫状河三角洲,其沉积物粒度粗,砂体厚;相反,高位体系域三角洲规模小,沉积物粒度细.结合区域构造背景分析认为,挤压坳陷盆地的层序发育受控于逐渐增强—减弱的幕式挤压作用,湖扩体系域对应于挤压增强时期:一方面,基底挠曲沉降加剧,湖盆范围迅速扩张;另一方面,前隆和周围山系快速隆升,沉积物供给大大增加,甚至超过了可容纳空间的增加速率,导致大型辫状河三角洲的广泛发育.

Tectonic Responses of Triassic Sequence Stratigraphy in the Large-Scale Compressional Down-Warped Lacustrine Basin of Inner Tarim Basin

As the regional stress field transferred from extension to compression in the Triassic, a large-scale down-warped lacustrine basin developed in the interior Tarim basin. According to seismic sequence interpretation, four third-order sequences were identified in the Triassic. Both top and bottom surfaces of the Triassic were regional truncation unconformities. Besides a few terminal types of truncate, up-lap and incised valley, top-lap was the widespread mark of sequence boundary. Furthermore, sequences correlations among wells reveals that sequences were very special in depositional evolutions as follows: in their lake-expanding systems tracts, large-scale braided river deltas had usually developed with coarse sediment and thick sandbodies; contrarily, in their high-stand systems tracts, the deltas were small with much finer sediments. Presumedly, stratigraphic sequences were dominated by episodic compressive tectonism, which gradually intensified and then weakened. Responding to violently compressive action in lake-expanding systems tracts, the lithosphere had flexed and as a result the basin rapidly expanded; on the other hand, the surrounding forebulges and orogenic belts had intensely uplifted, and the sediment supplies had been largely accelerated so that it exceeded the accommodation increment which caused that the braided river deltas had extensively developed.