Abstract: Progradating deposits,a result of the progressive accumulation and superimposition of sediments transported from provenance to unloading areas,is a normal sedimentary configuration in petro-exploration, dipping to the unloading areas.The interior MKT Formation mudstone of the middle block at the southeast margin of Pre-Caspian Basin is composed of a series of “reverse prograding deposits” dipping west (i.e.towards the early uplifted provenances).As the origin of the sedimentary configuration has triggered many controversies,there is no consensus as to the sedimentation and evolution of the Carboniferous,which has constrained follow-up exploration.Through the analysis of regional setting,dril-ling and seismic data,we made a comparative analysis of such elements as depositional mode,lithology,paleo-geographic location,geometry and scale,discussed the genetic mechanism of the “reverse prograding deposits”,and proposed that the MKT Formation is deep water tractive current deposits,instead of a retrogradation wedge of transgression origin.Therefore,the “reverse prograding deposits” is a peculiar sedimentary configuration resulted from landward migration of sediments along with the deep water tractive current.In the end,we analyzed the evolution of the MKT Formation and divided it into four stages,namely initiation,peak,recession and late adjustment.The discovery of deep water tractive current deposits not only improves our understanding of the sedimentary evolution rules at the southeast margin of the Carboniferous Pre-Caspian Basin,paves the way for further exploration,and enriches the category of basin sedimentation,but also provides a precious case for global research on the Paleozoic deep water tractive current.

Key words: reverse progradation, deep water tractive current deposit, landward migration, retrograding, sedimentary evolution, Carboniferous, Pre-Caspian Basin