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Based on the concentrations of the trace elements, rare earth elements (REE), and Sr isotopic compositions in reef carbonates from the well ‘Xike-1’ reef core of the Xisha Islands, the constraints on sediment provenance and paleoenvironment were defined. Variations of the terrigenous input into the paleoseawater were traced in detail and the paleoenvironment and sediment provenance were further investigated. The results show that the HREE/LREE values in the reef carbonates are negatively associated with their Th and Al concentrations; however, their Al and Th concentrations show positive correlation. The lowest 87Sr/86Sr values in the reef carbonates generally coincide with the lowest values of Al, Th concentrations and the highest values of HREE/LREE. These data indicate that the HREE/LREE, Al concentrations, and Th concentrations of the reef carbonates are useful indexes for evaluating the influence of the terrigenous inputs on the seawater composition in the study area. From top to bottom, the changing process of the HREE/LREE values and Al, Th concentrations can be divided into 6 intervals; they are H1 (0–89.30 m, about 0–0.11 Myr), L1 (89.30–198.30 m, about 0.11–2.2Myr), H2 (198.30–374.95 m, about 2.2–5.3Myr), D (374.95–758.40 m, about 5.3–13.6 Myr), L2 (758.40–976.86m, about 13.6–15.5Myr), and H3 (976.86–1200.00m, about 15.5–21.5Myr). Moreover, the changing trend of the HREE/LREE values coincides with that of the seawater δ13C values recorded by benthonic foraminiferal skeletons from the drill core of ODP site 1148 in the South China Sea (SCS), but not with that of the seawater δ18O values. The high uplifting rates of the Qinghai-Tibet Plateau coincide with the high Th and Al concentrations and the low HREE/LREE values in the reef carbonates. These data indicate that the main factors controlling the changes of terrigenous flux in the SCS are the tectonic activities associated with Qinghai-Tibet Plateau uplifting and the variations of uplifting rates rather than paleoclimatic changes.

Endoscopic imaging is the main method for detecting gastrointestinal diseases, which adversely affect human health. White light endoscopy (WLE) was the first method used for endoscopic examination and is still the preliminary step in the detection of gastrointestinal diseases during clinical examination. However, it cannot accurately diagnose gastrointestinal diseases owing to its poor correlation with histopathological diagnosis. In recent years, many advanced endoscopic methods have emerged to improve the detection accuracy by endoscopy. Chromoendoscopy (CE) enhances the contrast between normal and diseased tissues using biocompatible dye agents. Narrow band imaging (NBI) can improve the contrast between capillaries and submucosal vessels by changing the light source acting on the tissue using special filters to realize the visualization of the vascular structure. Flexible spectral imaging color enhancement (FICE) technique uses the reflectance spectrum estimation technique to obtain individual spectral images and reconstructs an enhanced image of the mucosal surface using three selected spectral images. The i-Scan technology takes advantage of the different reflective properties of normal and diseased tissues to obtain images, and enhances image contrast through post-processing algorithms. These abovementioned methods can be used to detect gastrointestinal diseases by observing the macroscopic structure of the digestive tract mucosa, but the ability of early cancer detection is limited with low resolution. However, based on the principle of confocal imaging, probe-based confocal laser endomicroscopy (pCLE) can enable cellular visualization with high-performance probes, which can present cellular morphology that is highly consistent with that shown by biopsy to provide the possibility of early detection of cancer. Other endoscopic imaging techniques including endoscopic optical coherence tomography (EOCT) and photoacoustic endoscopy (PAE), are also promising for diagnosing gastrointestinal diseases. This review focuses on these technologies and aims to provide an overview of different technologies and their clinical applicability.

The “dolomite problem” is a key issue in research on carbonate diagenesis, and it is still a controversial scientific problem. The origin of the Neogene dolostones in the Xisha Islands has remained disputed until now. However, the geochemical characteristics of dolomite-hosted fluid inclusions can potentially provide a relatively direct record of the origin and evolution of their dolomitizing fluid. In this article, based on the samples selected from the well “Xike-1” (also known as “ZK-1” and “XK-1”) reef core of the Xisha Islands, the hydrogen isotopic compositions and gas and liquid compositions of the fluid inclusions hosted in calcite and dolomite were analyzed. Meanwhile, the isotopic compositions of carbon and oxygen in the calcite and dolomite minerals were also tested. The origin of the dolomitizing fluid was traced in detail, which provided important evidence for establishing the dolomitization model of the primary dolomites in the study area. The main gas compositions of the dolomite-hosted fluid inclusions are CO2, H2O, N2, and O2, which are similar to those of the atmosphere, indicating that the dolomites in this area experienced a partly oxygenated diagenetic environment. From high to low, the cation concentrations of the liquid component in the dolomite-hosted fluid inclusions are Mg2+, Ca2+, Na+, and K+, whereas their main anion compositions are SO42−, Cl−, and F−, which are characterized by high SO42− concentrations and low Cl/Br ratios. The δ13C values (PDB) of the dolomites range from 1.9‰ to 3.0‰, and their δ18O values (PDB) range from 2.1‰ to 4.7‰. The calculated Z values (which can be used to trace the salinity of diagenetic fluid) based on the δ13C and δ18O values of the dolomites range from 133.0 to 135.8, which are higher than that of modern seawater (approximately 120). These data indicate that the dolomitizing fluid of the primary dolomites in the Xisha Islands is the high-salinity concentrated seawater derived from a surface environment. In addition, the model of seepage-reflux dolomitization can better interpret the dolomitizing process of the primary dolomites in the Xisha Islands.