The pre-rift basement rocks of the Golfo San Jorge basin can be divided from their nature and seismic signature: 1) igneous-metamorphic rocks (non-stratified basement) and 2) neopaleozoic and liassic sedimentary rocks (stratified basement). On the other hand, the Chubut Group (Cretaceous) is characterized by a main volcaniclastic input from the Andes during cretaceous times. However, when the Chubut Group was deposited over or nearly paleo-highs constituted by igneous-metamorphic basement rocks, their lithological composition was modified. These changes have prospective interest because the reservoir rocks deposited in this geological context have significantly better petrophysic characteristics.The paleo-high of basement rocks located in the northwest portion of the Northern Flank (Río Chico High) was studied from seimic sections and cutting record. Seismic lines display a 50 km wide (W-E) high non-stratified basement paleo-high. Some studied wells reached the non-stratified basement showing both metamorphic and igneous rocks. The sedimentary units lied over the igneous-metamorphic basement contains variable amounts of quartz and muscovite grains, including the liassic stratified basement, the Volcanosedimentario Complex (CVS) (Jurassic) and the Chubut Group (Cretaceous). This data allows us to infer that the igneous-metamorphic basement remained as a positive relief supplying quartz and muscovite during many millions of years. In addition, the northern portion of the offshore of the CGSJ was studied from the same methodology. Seismic information allows us to recognize a paleo-high of non-stratified basement in this sector. There, the stratigraphic record from de CVS up to cenozoic rocks contains abundance of quartz and muscovite. So, we interpreted that the non-stratified basement in the northeast sector of the offshore is constituted either by igneous-metamorphic rocks. In this case, the basement signal seems to be magnified by the little volcaniclastic input and the lack of neopaleozoic and liassic units covering the basement.In summary, we considered that the influence of the igneous-metamorphic basement in the northern region of the basin (onshore and offshore) represents a main control in the composition of the sedimentary record deposited over or nearly paleo-highs. The scopes of this work are both methodological as prospective. On the one hand, the basement signal can be recognized from a detailed description of cutting samples. On the other hand, the identification of a sediment supply signal that improve the quality of reservoir rocks in the CGSJ is considered a valuable contribution to understand the oildfields (onshore) and to prospect new exploratory targets (onshore and offshore).