Genetic characteristics of hydrothermal sedimentary siliceous dolomitic micrite mounds in the Dalong Formation of the northern Longmenshan Fault 1

Abstract The origins of deep-water micrite mounds remain controversial. The present study investigates siliceous dolomitic micrite mounds produced as interlayers in a large set of siliceous rocks in the Upper Permian Dalong Formation on the west side of the northern member of the Longmenshan Fault, China. Their geological occurrence, rock structure, material composition, sedimentary facies, trace elements, stable isotopes (carbon, oxygen, strontium) and rare earth elements are comprehensively analysed. It is proposed that micrite mounds are the composite sedimentary product of submarine hydrothermal exhalation-sedimentation and biological activity. The discovery and significance of the Dalong Formation siliceous dolomitic micrite mounds (DSDMMs) can be summarized as follows: 1) This is a new type of micrite mound, thereby increasing knowledge of the origins of such mounds. 2) The origin of these mounds is dominated by submarine hydrothermal exhalation-sedimentation, supplemented by biological activity. 3) Primary dolomite is deposited by hot water from a submarine (or lake bottom) exhalation-sedimentation system. 4) In submarine hydrothermal systems, the prosperity of hydrothermal biological communities and the high-speed burial of their organic carbon are important issues worthy of further study.