CONICET | Buscador de Institutos y Recursos Humanos

Sediment dynamics in Bahía Blanca estuary (Argentina) permits the formation of longitudinal banks, one of which is La Lista Bank, located at the mouth of a homonymous tidal channel. The purposes of the present research were to study the processes and mechanisms involved in the formation and maintenance of this bank, and to identify seismic sequences which could be indicative of its origin and current morphoevolutive trend. To this end, different methods and techniques, such as side scan sonar, 3.5 kHz profiler and bottom sediment sampling were followed. Our analysis of seismic-acoustic records revealed bottom morphological features (sand dunes, sand ribbons, comet marks, an escarpment) which, based on our analysis of current measurements and our estimations of transport as bedload, have contributed to tracing a sediment circulation pattern in the study area. Taken together, our findings allowed us to identify the areas dominated by erosion, sediment transport or depositional processes. Bedload material was found to be exported to the outer sector and held on the flanks of the bank, particularly, in its southern part. Inference on the morphoevolutive trend in the study area was based on evidence related to migration patterns and changes observed in the flanks and inner structure of the bank. The morphological evolution of La Lista bank is associated to a residual sediment transport model with trajectories opposite to its two flanks, which results from the action of ebb tides in the N flank and flood tides on the S flank. This process induces a gradual increase in the bank height and longitudinal growth. La Lista bank evolution agrees with the motion sequence and development pattern proposed by Caston (1972) for a linear bank except that this model is repeated as the bank grows. Taken together, 49 the seismostratigraphic data collected in our research indicates that the origin of this bank is associated to the Holocene marine regression process. Caston, V.N.D., 1972. Linear sand banks in the Southern North Sea. Sedimentology 18, 63-78.