Based on drilling, logging and various test data, this paper studied the origin of deep-semi deep lacustrine dolostones of the Lower Cretaceous Tenggeer Formation in Baiyinchagan sag of Erlian Basin, Inner Mongolia.Core observation and thin section analysis data in combination with electron probe, energy spectrum, trace element and X-ray diffraction were used to analyze mineral composition and texture, structure of the rock.On this basis, we identified the origin of the dolostones.The results show that the dolostones(zeolitic dolostones and zeolite with single layer thickness of 0.2-1.5 m)in the study area are composed of ankerite(proportion of Fe is 0.5%-5%), natrolite, analcite, sjogrenite, barite and pyrite.The dolomite crystals feature in size of 10-200 μm, wavy extinction, saddle morphology and development of fissures.These dolostones have muddy-micritic or intraclast(mainly from dolomites and zeolites)structures.Laminated, contemporaneous deformation, net-veined, and brecciated structures are common.GR is 700-1 100 API, which is 2-4 times as large as that of normal mudstones.U and Th content is up to 40-60 ppm and 60-100 ppm respectively.Trace elements, including Cu, Ni, Co, Fe and Mn, have a similar composition and distribution with the modern hydrothermal sediments on the Red Sea floor.The dolostones are distributed along the basement faults laterally.It is concluded that this is a set of 'white smoke chimney' hydrothermal dolostones.However, these sediments are rarely reported.The study of the chemical and thermodynamics process is deficient, and the deposition mechanism is not very clear.This research will be helpful for enriching the theory of sedimentology and discovering more mineral resources associated with hydrothermal sediments.
