山东东部日青威盆地晚中生代沉积岩元素地球化学特征及沉积环境

发育在苏鲁造山带上的山东东部日青威盆地是晚中生代以来形成的规模较大的裂陷盆地，其独特的沉积特征有别于周缘其他同期陆相断陷盆地，备受沉积学界的广泛关注。为了解日青威盆地沉积期（包括莱阳期和青山期）古盐度、古气候和氧化还原条件等沉积环境特征，对盆地灵山岛、崂山、诸城桃林、海阳丁字湾和即墨周戈庄5个典型剖面沉积岩样品开展主量、微量和稀土元素地球化学分析。5个典型剖面的沉积岩SiO2和Al2O3含量较低，平均值分别为52.13%和13.06%，而Fe2O3含量较高，平均值为6.14%；ΣREE平均值为199.15×10?6，稍高于澳大利亚后太古宙页岩（PAAS），富集轻稀土元素，相对亏损重稀土元素，具有弱铕（Eu）正异常；相对于上地壳（UCC），样品富集大离子亲石元素，亏损过渡族元素。Sr/Ba和Mg/Ca值表明，自莱阳期至青山期，沉积水体趋向于由咸水/半咸水向微咸水环境的变化；Sr/Cu值、∑(Fe+Mn+Cr+V+Ni+Co) / ∑(Ca+Mg+K+Na+Sr+Ba)值和SiO2-(Al2O3+K2O+Na2O)双变量图解表明，莱阳期和青山期均为干燥气候；V/(V+Ni)和Ce异常表明，莱阳期和青山期沉积水体环境以分层不明显的还原环境为主。综合以上研究表明：日青威盆地莱阳期—青山期古盐度的转变以及干燥气候和还原环境对于揭示盆地的沉积演化过程有着重要的地质意义。

Geochemical constraints on depositional environment of Late Mesozoic sedimentary rocks from the Ri-Qing-Wei Basin in the East Shandong

Ri-Qing-Wei (Rizhao-Qingdao-Weihai) Basin in the eastern Shandong Peninsula, which was developed in the Sulu Orogen, is a large-scale rift basin formed since Late Mesozoic. The unique sedimentary features in the basin are different from adjacent terrestrial rift basins in the same period, which have received great attention from sedimentologists recently. To study the paleosalinity, paleoclimate, and redox conditions in the deposition period (the Laiyang and Qingshan Period) in the Ri-Qing-Wei Basin, the geochemical (major, trace and rare earth elements (REEs)) characteristics of sedimentary rocks samples from five field typical profiles situated in the Lingshan Island, Laoshan, Taolin, Dingzi Bay, and Zhougezhuang areas, respectively, were analyzed. The samples are characterized by relatively low content of SiO2 and Al2O3 (avg. 52.13% and 13.06%, respectively) and high contents of Fe2O3 (avg. 6.14%). ΣREE contents of the samples (avg. 199.15×10?6) are higher than those of UCC. The patterns of REE are characterized by LREE enrichment, HREE depletion, and weakly positive Eu abnormity. Compared with UCC, the samples are enriched in LILEs and depleted in transitional elements. The values of Sr/Ba and Mg/Ca indicate that the water body of deposition during the Laiyang-Qingshan period was from saline/semi-saline to weakly saline water. The value of Sr/Cu, ∑(Fe+Mn+Cr+V+Ni+Co)/∑(Ca+Mg+K+Na+Sr+Ba), and bivariate SiO2-(Al2O3+K2O+Na2O) diagram show that the deposition period was in a dry climate environment, and V/(V+Ni) and Ce abnormity indicate that the deposition period was dominated by a reducing condition. The above comprehensive studies show that the transformation of palesalinity, dry climate and eductive environment of the basin have important geological significance for revealing the process of sedimentary evolution in this area.