ANALYSIS ON THE GEOCHEMICAL CHARACTERISTICS AND SEDIMENTARY ENVIRONMENT OF THE LOWER CRETACEOUS LIMESTONE IN JIMO AREA, SHANDONG PROVINCE

In order to study the geochemical characteristics and sedimentary environment of the Lower Cretaceous limestone at Zhougezhuang section in Jimo, Shandong, the authors carry out systematic sedimentological and elemental geochemical tests on the limestone. The results show that the contents of SiO₂ and CaO in the limestone samples are high, with average contents of 16.83% and 39.34%, respectively, and the values of SiO₂ and Al₂O₃ are negatively correlated with that of CaO, suggesting that the sedimentation of limestone be notably influenced by terrigenous sources. Among the trace elements, the Zr content is low, while the Ti content is much greater than the average in carbonate rock, indicating that the sedimentation is mainly terrigenous matters. The total amount of rare earth elements is rich, with enriched HREE, slightly positive anomalies of Gd and Eu, and less negative anomaly of Ce. The ratio of Ce/Ce^* is significantly correlated with Eu/Eu^* and ΣREE. The MgO/Al₂O₃ values range from 0.33 to 0.74, with Sr/Ba of 0.10-0.94, which reflects the continental depositional environment. The V/Cr value of 1.64-1.92, Ni/Co value of 1.83-2.45 and U/Th value of 0.48-0.84 represent the characteristics of oxidation deposition. The MgO/CaO value of 0.03-0.14 and Sr/Cu value of 16.46-20.45 indicate an arid and hot climatic condition. Therefore, the limestone of Zhougezhuang section shows a hot and dry oxidized continental facies sedimentary environment, which can be used to reconstruct and restore the paleoclimate.