Formas mareales de la Ría del Deseado, Santa Cruz

patagonian rivers flow across desert lands and between two plateaux of mesozoic, tertiary and quaternary rocks. the original wide valleys were reduced by the deposition of terminal moraines which blocked some atlantic watersheds at the headlands and were responsible for the changes in the outflow of the rivers. strong westerly winds increase the evaporation. those rivers that arrived to the atlantic coast are subject to the action of large tidal ranges that contribute to change their inlets twice a day moving towards the headlands along manykilometers. these estuaries are called "rías" in the partial sense, and worlwide used, equivalent to "drowned river valleys" from von richtoffen, but where a structural control should not be discarded, as stated originaly for the "rías baixas" of galicia. patagonian rías have particular characteristics: river outflows and valley capacities diminished, and a holocene sea-level fluctuation that affected the morphosedimentary evolution of the estuaries. the deseado river estuary has a funnel shape oriented towards the northeast and changing to an eastward direction at the inlet. the river has excavated this inlet into piroclastic rocks of jurassic age. gorges and small canyons are indicating erosion features that cannot be justified by present-day processes. a sediment sampling was carried out at this estuary in order to recognize present sediment dynamics previous to any alteration induced by mariculture activity or harbour enviroments. at the inner estuary, extended tidal flats, marshes and tidal channels were recognized. tidal-sand banks conforming a flood delta and elevated beaches (with shell middens on top) characterize the middle portion of the estuary. salinity measurements and morphologic analysis indicate that the tidal excursion extends about 40 km. into the estuary. non-operating tidal flats were recognized at the bottom of some canyons. the ca？adón del puerto is a relict tidal flat originated by changes in the river dyn