Large scale magnetotelluric sounding at the periphery of the Songliao Basin, NE China

Abstract

Recently, China Geological Survey (CGS) has launched 3D geological mapping programs from regional to local scales. The project Deep geological survey at the periphery of the Songliao Basin funded by CGS was implemented from 2012 to 2014. Its main goals are to reveal the tectonic framework of the Jarud Basin (JB) as well as to identify the strata distribution of Permian Linxi Formation by integrating new electromagnetic data with existing geophysical and geological data since black mudstones in the Linxi Formation have shown the potential of shale gas. The study area is situated in Jarud Banner and Ar Horqin Banner, Inner Mongolia, China. It is covered dominantly with Cretaceous-Jurassic igneous rocks with exception of the small southeastern part. It is tectonically located in the southern Great Khingan Range, western margin of the Songliao Basin, north of Xar Moron Fault. Over years of 2012 to 2014, a magnetotelluric survey was carried out at the west of the Songliao Basin. A total of 1559 stations including existing MT data on eight NW and five NE profiles were obtained, covering area that exceeds 10,000 km2. After dimensionality analysis and static shift removal, the nonlinear conjugate algorithm was used to conduct 2D inversion for TM and TE modes. Inversion results revealed numerous large faults, some of which constitute the boundaries of the Jarud Basin, and modified the tectonic framework. Integrated with well logging and geological data, two Paleozoic fault depressions (Gadasu and Hunnitu) and one Mesozoic depression was discovered. Two Paleozoic sag were inferred to be presence of Linxi Fms. One Mesozoic sag was inferred to be hydrocarbon potential. Attention should be paid to Gadasu sag with area of around 500 km2 since it contains reasonably thick conductive sediments exceeding 4 km in depth which might be black mudstones pertaining to shale gas.