基于物源分析研究流域盆地范围和岩性组合对陆架边缘三角洲的控制作用：以墨西哥湾Guadalupe古近系源-汇系统为例

Sediment routing and supply reflect the interactions of tectonic activities, climate, lithology, relief, and other factors within the drainage basin and have important controls on stratigraphic architecture and sandbodies size in the sedimentary basin. Therefore, it serves as an important bridge connecting the source area to the basinal sink. The Guadalupe source-to-sink system in the northwestern Gulf of Mexico has experienced big changes of sediment volume and shelf-margin delta progradation rate in the Paleocene-Early Eocene. Currently, the fluctuations of sea level cannot fully explain this change, and thus, the sediment supply rate from upstream should be considered to help decipher such phenomena. In order to solve the abovementioned problem, this work will first identify the major sediment source areas and recover the paleo-drainage system, by using petrographic analysis and detrital zircon U-Pb and (U-Th)/He double dating. Then the drainage area and source lithology features can be reconstructed based on the provenance analysis. Given the relief in the potential source was relatively stable and the paleo-temperature has been well constrained by previous studies, this work focuses on the influences of drainage area and source lithology on the sediment supply rate. Finally, this work will integrate the sediment supply rate and sea level changes to explain the variation of sediment volume and shelf-margin delta progradation rate. This work also provides references for similar source-to-sink studies in China.

沉积物搬运路径和供应量是流域盆地内构造活动、地貌、气候和岩性等要素综合作用的结果，同时对盆地边缘的地层结构和砂体的展布及规模具有重要的控制作用,是源-汇系统上下游重要的沟通桥梁。美国墨西哥湾西北部Guadalupe源-汇系统在古新世-早始新世存在陆架边缘三角洲进积速率和盆地内砂体规模发生显著变化的特征，目前从海平面升降的角度尚无法很好解释这种变化，因此需要结合源区的沉积物供应量来综合分析。本次研究针对Guadalupe源-汇系统存在的问题，以岩石学、碎屑锆石U-Pb和（U-Th）/He双重测年为分析手段，识别主要的沉积物源区，重建沉积物搬运路径。在物源体系厘定基础之上，圈定流域盆地范围和恢复供源区的岩性组合特征。在潜在源区古高程未有明显变化和古气温相对确定的条件下，重点分析流域盆地范围和岩性组合变化对沉积物供应量的控制，进而结合海平面升降探讨其与沉积区陆架边缘三角洲进积速率和砂体规模变化的

对于大型源汇系统而言，其往往具有着很大规模的沉积物供应量，因此其三角洲的生长速率（如进积和加积速率）不仅仅取决了海平面的变化，而在很大程度上也受到了沉积物供应量的影响。而沉积物的供应量受到源区的母岩性质及组成的影响，源区的岩性剥蚀序列扮演着重要的角色，而这一点往往被研究者所忽视。本文选取美国墨西哥湾西北部Guadalupe三角洲源-汇系统开展物源区母岩性质及组合变化对沉积物供应量及三角洲生长的控制作用研究。本次研究系统的恢复了美国墨西哥湾西北部Guadalupe三角洲从古新世-中中新世的物源区及范围。同时揭示了在物源区范围变化幅度不大的情况，源区的剥蚀序列导致的岩性差异是影响沉积区碎屑锆石年龄组成及沉积物供应量变化的重要控制因素。这种母岩岩性的差异演化也很大程度上影响了沉积区陆架边缘三角洲的生长速率，而海平面的变化在其中并不是主控因素。本研究工作可以对国内外沉积盆地的源汇系统研究具有指示意义。