REE Compositions of Sedimentary Strata of Guichi Stratigraphic Region，Northern Margin of Yangtze Block，and Its Geologic Significance

A study of REE compositions of Sinian to Triassic sedimentary strata from Guichi stratigraphic region located in northern margin of the Yangtze block indicates that average total REE concentration is 127μg/g which is lower than that of sedimentary rocks from the whole world(230 μg/g) and approximately resembles to that of sedimentary rocks from the platforms(129 μg/g). Among different lithologies, average total REE concentration of shales is the highest(230 μg/g), that of limestones is the lowest(18 μg/g) and that of sandstones and siltstones is in between(213 μg/g) .REE concentrations of strata of different geologic ages are controlled by lithology.REE concentrations of Ordovician and Triasaic strata consisting mostly of carbonate rocks are the lowest(40 and 44 μg/g, respectively), and those of Silulian and Devonian strata consisting mainly of terrestrial detrital rocks are the highest (231 and 248 μg/g, respectively). Sedimentary rocks studied show very similar REE patterns with LREE enrichment and negative Eu anomaly regardless of lithology and stratigraphic age. Samples are plotted in a confined area in Σ(La～Nd)-Σ(Sm～Ho)-Σ(Er～Lu) ternary plot, suggesting homogeneity of REE composition and a stable environment for the studied region. Similarity between REE compositions of sedimentary rocks from the studied region and that from typical platforms of the world suggests the platform character of the studied region during Sinica to Triassic. Results of this study suggests that the provenance of the studied sedimentary rocks is not the Jiangnanian old land mass, but the old continent(s) from the north.

Characteristics analysis and model prediction of sea-salt water intrusion in lower reaches of the Weihe River,Shandong Province,China

Marine sedimentary strata are widely distributed in the coastal zone of the study area, and are rich in brine resources. The exploitation of underground water resources often first caused the intrusion of salt water in the marine strata. Based on the analysis of sea-salt water intrusion feature, the sea-salt water intrusion is divided into four stages: The occurrence and development stage(1976–1985), the rapid development stage(1986–1990), the slow development stage(1990–2000) and the stable development stage(2000–2015). Based on the comparative analysis of the relationship between seawater intrusion and influencing factors, this paper presents that the groundwater exploitation and the brine resources mining are the main control factors of sea-salt water intrusion. On this basis, we have established a numerical model of the sea-salt water intrusion. Using this model, we predicted the development trend of the sea-salt water intrusion. The results show that if the current development of groundwater and brine is maintained, the sea-salt water intrusion will gradually withdraw; once development of brine stops, sea-salt water will invade again. This provides the scientific basis for the rational exploitation of groundwater and the prevention of sea-salt water intrusion.