Lithological markers of protobazhenit mats splitting on sedimentary slope

Abstract

Bazhenov abnormal sequences (BAS) are treated as result of protobazhenit plastic deformation by neocomian submarine slump on sedimentary slope. Protobazhenit mats had low bulk density (1.1-1.5 g/sm3) and positive buoyancy in silty-sandy mud of unconsolidated deposits (bulk density 1.7-1.8 g/sm3). Conceptual geomechanical model of BAS generation includes 6 studies: 1 - bedding (slipping) slide, breakage of under-achimovsky clay and protobazhenit, 2 - out-flow achimovsky sandy slump, 3 - slump pulp spreading under protobazhenit layer with its deformation and cracking, 4 - protobazhenit layer cracking due to local loading of growing sedimentary slope, 5 - secondary heaving sand injection through lateral protobazhenit brake side, 6 - burial stage. Up-floating of protobazhenit mats on semiliquid sedimentary slope occurred discretely with numerous subsidings, splittings and jumpings events. During sedimentary slope progradation mats had lack of Archimedes stability due to rising of sedimentary level, led to increment of hydraulic pressure on their side surfaces. The hydraulic fracturing conditions appeared when this pressure exceeded protobazhenit shear strength. Fracturing event was provoked by microseism or by hydraulic shock of gravity mass movement. Mat usually had splitted on two parts: lower part was fixed within sediments, upper one lifted to Archimedes equilibrium level. Splitting and up-lifting of mat produced debris flows, those were spreading on slope and enriched by protobazhenit’sinclasts. These outstanding debrit layers with bazhenitinclasts may be used as lithological markers of mats splitting events for achimovsky sequences. Theoretical model is illustrated by seismostratigraphic interpretation of achimovsky beds of Imilorskoe field of West Siberia. Two types of debrit layers with bazhenitinclasts was detected in well core. First type is generated byptotobazhenit layer’s breakage by non-uniform load of sedimentary slope (fixed in one well). The second type is associated with on-slope splitting and up-lifting of protobazhenit mats (traced in core of three wells).

Keywords

• баженовская свита
• аномальный разрез
• подводный оползень
• дебрит
• инкласт
• bazhenov abnormal sequences
• geomechanical model
• submarine slump
• debrit
• inclast