Modelo de sedimentación fluvial y paleohidráulica en una cuenca tectónicamente activalos depósitos fluviales Plio-Pleistocenos del Río Grande, Nuevo Méjico, USA

Resumo

Plio-Pleistocene sediments of the ancestral Rio Grande (Camp Rice Formation) are preserved and exposed in the uplifted southern portion of the Robledo Mountains horst of the southern Rio Grande rift. Numerous river channel and floodplain lithofacies are indicative of varied deposition in channel bar com plexes of low-sinuousity, pebbly sandbed channels that traversed generally dryland floodplains and shifted in and out o f the study area five times over the 1my orso recorded by the succession. Camp Rice's braided deposits show common low angle bedsetsascribed to deposition over low-angle dunes in active channels. M ost relevant points concerningthis study are: I) An avulsion node was located at the stationary southern tip to the East Robledofault during Gauss times, with channels to the north flowing close to the fault and preventingfan progradation. 2) Complexes o f initial avulsion breakout channels show at the base o f majorsandstone storeys. 3) Flow concentration, coarse bedload input and seasonal discharge conditionsgave way to a reduction in channel number and the development o f a braided river. 4)Subsequent Matuyama growth o f the fault caused deposition to cease as the whole successionwas uplifted in its footwall, and a thick petrocalcic horizon developed. Finally fan progradationinto the Mesilla basin ocurred. 5) Estimated mean aggradation rate is 0.05mm a 1; majoravulsion rate 200 k a ’ and apparent channel belt recurrence interval within sandbodies o f order100 ka.