The Pozo D-129 Formation is linked to the sedimentary filling of a big lake during the basal Chubut Group (Barremian?-Aptian) in the Golfo San Jorge Basin. This unit includes the main source rock of the basin as well as reservoirs rocks associated with litoral lobes (deltas) and deep lobes (deep fans). The outcrops of these units are few and restricted to the San Bernardo Fold Belt. New observations over the Cerro Kepi anticline expose deltaic front and channel/bar complex lithofacies associations. The stratigraphic study accomplished there include in situ air-permeability (Kair), Schmidt Hammer rebound index (R) and X Ray portable fluorescence measurements. Petrophysical and geomechanical parameters statistics are: I) Kair (n: 97), Mean: 24.9 mD (Std: 48.7), Q1: 3.4 mD, Q3: 26 mD, and II) R (n: 101), Mean: 47.4 (Std: 8.1), Q1: 43, Q3: 52. Vertical and lateral trends define an increase of hardness and a decrease of permeability when tuffaceous proportion increase. Geochemical results show that concentration of K is similar in tuffaceous sandstones and siltstones, while Fe has values in 75% interquartile bigger for sandstones. The Ca has an interquartile range bigger for sandstones than for tuffaceous siltstones. At the same time, the Q3 in Fe is higher in sandstones. The distribution of Fe and Ca is associated to alteration and cementation favored by coarse-granulometries permeabilities. The quantitative results shows the limited applicability of classic subsurface electrofacies models under volcaniclastic stressed paleoenvironments. Traditional surface sedimentary-logs combined with last-generation equipment allow the calibration and evaluation of an excellent outcrop analogue of deltaic reservoirs from the top of Pozo D-129 Formation Revalidation of an extensional-thermal tectonoestratigraphic context for the base of the Chubut Group is essential to define strategies for the production and exploration of nontraditional stratigraphic levels.