东非鲁武马盆地海底旋回坎沉积演化及控制因素

Sedimentary Evolution and Control Factors of Submarine Cyclic Steps in the Rovuma Basin,East Africa

鲁武马盆地海底水道—朵体过渡带具有高波脊和深刻槽相间的旋回坎地貌。利用高品质的三维地震资料,借助多种地震解释技术,对水道—朵体过渡带内不同期次旋回坎的形态、尺度、移动方式开展细致描述,分析多期旋回坎演化规律。研究结果表明,鲁武马盆地海底水道—朵体过渡带内主要发育三期旋回坎,同一期次旋回坎内部地震反射连续性较差,同相轴以叠瓦状方式向迎流面倾斜。不同期次旋回坎的反射同相轴之间呈角度接触。北部中期旋回坎相对早期向陆迁移,晚期旋回坎沉积于南部,形成南、北迥异的地貌形态。水道—朵体过渡带的北部平均波长低于南部,平均波高北部比南部大得多,反映了多期迁移叠置旋回坎的演化。

The submarine channel-lobe transition zone in the Rovuma Basin(located on the border between Tanzania and Mozambique,east Africa)is characterized by a bed profile with high ridges and deep scours.High-resolution 3 D seismic data and various seismic interpretation techniques were used in this study.The morphology,scale and movement of cyclic steps at different stages in the transition zone are described in detail,and analysis of the cyclic pattern showed that the cyclic steps occurred mainly in three stages.Seismic reflections had poor continuity at identical stages of the cycles,tending towards imbricate reflections of the up-flow surfaces.There is angular contact between the reflections of different stages in the channel-lobe transitional zones.Unlike the early cyclic steps,the up-current middle cyclic steps migrated from basin to land in the north,and the late cyclic steps were deposited only in the south.The multi-stage migration and overlap of cyclic steps has resulted in the evolution of different northern and southern geomorphological forms,with lower average wavelength and much larger average amplitude in the north.The later deposits cover the upstream surface of the previous deposits,with eroded backstream surfaces being seen on each deposit.The wave heights of the deposits at different stages were significantly increased by overlapping.The location of the backflow and upflow zones of the waves also changes.Affected by the southward migration of the channel,the geomorphological form of the mid-stage cyclic steps and the southward dip of the underlying strata resulted in a new,unchanged cyclic step in the south of the channel-lobe transitional zone,and the form of the antidune bed is well preserved.