Abstract <p>Modeling of X-ray diffraction patterns was used to study clay minerals from Upper Pleistocene sediments of Hole ODP 1036A, which was drilled to a depth of 38.50 m, 9 m from a hydrothermal vent with a temperature of 268°C in the Dead Dog hydrothermal field (northern part of the Middle Valley of the Juan de Fuca Ridge). In the sediment section of Hole ODP 1036A, terrigenous clay minerals were preserved in the depth range from 6.10 to 10.04 m under low temperature conditions of ∼17°C. They consist of dioctahedral smectite, mixed-layer smectite–illite, illite, and trioctahedral chlorite. In the depth range from 10.04 to ∼20 m at temperatures from ∼112 to 200°C, trioctahedral mixed-layer chlorite–smectite formed instead of terrigenous clay minerals. In the lower half of the sediment section from Hole ODP 1036A, in the depth range of 20–38.50 m at temperatures from 200 to 330°C, trioctahedral chlorite–corrensite formed, and chlorite formed at the very bottom of the section.</p>