Slump structures in quaternary slope sediments of the northern Derbent Basin (Caspian Sea)

During Cruise 20–3 of the R/V Rift (April, 2006), the area that includes the shelf and slope of the Derbent Basin in the northern Middle Caspian was studied using the continuous seismoacoustic profiling method. In accordance with the previous standpoint, two Pleistocene deltaic complexes formed in the Enotaevian and Mangyshlakian time are defined in this area. The seismoacoustic records obtained for the northern slope of the Derbent Basin demonstrate the development of specific rootless exogenic-gravitational fold structures in the upper (∼150–200 m) Quaternary part of the sedimentary sequence. The Quaternary section encloses angular unconformities indicating the pulsating mode of gravitational processes in the northern slope of the basin. South-dipping gravitational normal faults (and/or normal fault-related flexures) displacing the bottom surface and uppermost sedimentary layers (with vertical amplitudes up to 5–6 m) were defined in the southern part of the study area. Several impulses of the submarine slump structures predated and accompanied the deposition of the upper deltaic sequence (Mangyshlakian), although their most intense formation took place later during the Novocaspian (Holocene) time. Thus, the structural analysis of the seismoacoustic data revealed intense development of different-origin and different-age gravitational structures within the Quaternary sediments in the northern slope of the Derbent Basin. These results should be taken into consideration when designing, building, and operating submarine constructions in order to prevent potential natural hazards and reduce their consequences.