The study fo cuses on Up per Cre ta ceous-Paleocene de pos its from the Beskid Śląski moun tain range in south ern Po land con sti tut ing the Istebna Beds. The Istebna Beds, also re ferred to as the Istebna For ma tion, are part of the Silesian tec tonic unit, which forms the Outer Carpathian fold-and-thrust belt (part of the Al pine-Carpathian sys tem). The re sults of qual i ta tive and quan ti ta tive lithological-sedimentological stud ies were the ba sis for the in ter pre ta tion of lithofacies types, sed i men tary pro cesses and palaeoenvironment as well as for the re con struc tion of the ar chi tec ture of the depositional sys tem. The anal ysis con ducted on the ba sis of field de scrip tion of the de pos its shows the prev a lence (nearly 70%) of siliciclastic strata rep resent ing a sand stone-con glom er ate as so ci a tion (S-C), which is the main sub ject of this work. The S-C lithofacies: sand stones, grav elly sand stones, sandy con glom er ates and con glom er ates con sti tute the de pos its formed mostly by mass grav ity-flows such as sandy-to-grav elly de bris flows. The dis tri bu tion of the coarse-clastic ma te rial in di cates a sed i ment supply from south erly di rec tions and im plies the pres ence of an ac tive source area in the rear part of the Silesian Ba sin. A succes sion of the sand stone-to-con glom er ate de pos its with the sec ond ary par tic i pa tion of other lithofacies, with a thick ness of ap prox i mately two thou sand metres, in di cates tem po rary in creased di a strophic ac tiv ity in the Silesian Ridge (source area) and the in tense de nu da tion of this area. The up lift of the alimentation area and its de struc tion co in cid ing with en forced rel ative re gres sion and the un cov er ing of the prox i mal depositional zone of the ba sin led to resedimentation of the older intrabasinal ma te rial and re peated mass de po si tion to gether with de liv ery of extraclasts of pre-ex ist ing rocks and min er als. The lithofacies de vel op ment of the sand stone-to-con glom er ate debrites and the re lated sed i men tary palaeotransport di rections sug gest an ac cu mu la tion do main in the form of a lin ear apron depositional sys tem de vel oped in a deep-wa ter set ting. Ex per i men tal mod el ling of sub aque ous sandy flows has con trib uted to a better un der stand ing of the com plex gen e sis of deep-wa ter sed i ment grav ity flows de vel op ing in depositional sys tems rich in sand ma te rial.