The Qiman Tagh and the Qaidam Basin within the northern Tibetan Plateau are contrasting in geomorphological, geological, and geophysical features. The Yingxiong Range is the largest anticlinal belt in the SW Qaidam Basin and holds a key in understanding the relationship between the above two tectonic units. Herein, we investigated the geometry, shortening, timing and mechanism of the structural deformation across the Yingxiong Range by integrating field mapping, interpretation of 3-D/2-D seismic reflection data and analogue modeling. The structural interpretation demonstrates that the Yingxiong Range is primarily controlled by NE-directed basement-involved reverse faults. These faults likely sole into a décollement layer at depth of~15 km through the excess area-depth analysis. This pattern is complicated by the development of a local salt layer that decouples the deformation of underlying and overlying strata, as indicated by analogue modeling. Deformation initially occurred at~8.1 Ma but strengthened at~2.5 Ma, with total shortening up to~5 km in the NW part but decreasing to <2 km to the SE. Together with published results, our findings revealed an NE-directed thrust system involving the Qiman Tagh and the SW Qaidam Basin, with the Yingxiong Range as the front of this system. We further inferred that this NE-directed thrust system in the upper crust, together with the previously identified SW-directed deep reverse fault offsetting the Moho, may form a southwestward tapering tectonic wedge, which likely results from the heterogeneity of lithospheric mantle between the Qaidam Basin and the Qiman Tagh-East Kunlun Shan.
The biogas lithologic reservoirs in Sanhu Area of the Qaidam Basin has a broad exploration prospect, however, the demands of structural implementation and reservoir prediction can hardly be met with the existing P-wave seismic data due to the thin thickness of single sandstone layers, the rapid lateral changes and the low prediction accuracy of lithologic reservoirs. The SH-wave data has a higher resolution ability in lithology prediction. I can better reflect the lateral change features of formations. Because few SH-wave logging data are available and they are in accurate in the current study area, the SH-wave velocity is estimated through petrophysical modeling and the calibration and horizon interpretation of the SH-wave data are realized combined with the P- and SH-wave matching technology. Through the inversion of S-wave data,the lithological distribution of formations are predicted in combination with the comrehensive analysis of P-wave data, which provides a favorable basis for the survey of lithologic gas reservoir in the research area and achieves a good good result. In this way,a set of reservoir prediction methods and processes suitable for the shallow biogas lithological exploration in the Sanhu Area have formed initially.
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