Exploration for oil and gas in the marine strata of the Micang-Daba piedmont and its adjacent area turned out to be not so encouraging due to poor preservation conditions caused by multiple tectonic deformations.By characterizing carbon and oxygen isotopes and fluid inclusions in calcite veins in tectoclases

we tried to evaluate conditions for hydrocarbon preservation in these strata based on analyses of paleo-fluid

including origin

phases of activity and mixing of meteoric water.Results show that meteoric water infiltration increased progressively from the center to the edge of the basin and the infiltrating depth of the water was mostly between 1 200 and 3 000 meters in the piedmont.The homogenization temperature and salinity measurements of fluid inclusions indicate two phases of paleofluid activity corresponding respectively to the Yanshanian and Himalayan tectonic movements.During the Yanshanian movement

the meteoric water infiltration was weak and the marine strata in the study area had favorable preservation conditions for hydrocarbons.While during the Himalayan movement

the meteoric water infiltration was intensive.Together with a strong tectonic uplift and erosion

the infiltration made preservation conditions for hydrocarbon worse.