New data on seismostratigraphy and sedimentation on the western slope of the middle Caspian

Abstract

The sedimentary sequence of the Caspian Sea is generally well studied by geological and geophysical methods [1], particularly multichannel seismic profiling, which was mainly aimed at study of the deep structure of the sedimentary cover with perspectives for the discovery of hydrocarbon traps (see, e.g., [2]). However, data available for the upper part of the Pliocene‐ Quaternary sedimentary sequence are insufficiently detailed, because the majority of regional continuous seismic profiling (CSP) works were carried out in the 1970s‐1980s using low-resolution equipment [3]. New detailed data on the structure of these sediments in the Middle Caspian area near the Dagestan coast from the upper part of the western slope to the adjacent deep part of the Derbent basin were obtained by a team of scientists from the Institute of Oceanology and Moscow State University during Cruise 19 of the R/V Rift in autumn 2004‐winter 2005 (Fig. 1). The expedition was conducted in the framework of the Federal Targeted Program “The World Ocean” (Subprogram 8 “Complex Study of Processes, Characteristics, and Resources of the Caspian Sea”) simultaneously with engineeringgeological prospecting of the Yalama‐Samur structure for the Lukoil Company. A Geont-shelf high-resolution single-channel seismoacoustic profiler equipped with a spark transmitter (sparker with capacity of 600 J), which provided vertical resolution up to 2 m at a depth of 300‐400 mbsf, was used to study the fine structure of the upper sedimentary sequence. Geological works in the cruise included sampling of sediments with gravity piston corers and study of their physicochemical properties at the Yalama‐Samur test site (Figs. 1, 2). The study area is located in the steepest area of the western slope of the Derbent basin characterized by the highest dip angles and maximal relief differentiation in the entire Middle Caspian [4]. The CSP data show that the slope is composed of two distinct sedimentary complexes with different seismic record patterns. They are separated by a near-horizontal intense reflector (R-2), which extends in the eastern part at a depth of approximately 400 m and gently rises toward the coast (Fig. 2). Comparison with previous materials, including drilling