Internal architecture of beachface deposits and berms in hypertidal El Páramo spit (Tierra del Fuego, Argentina) revealed by GPR
Résumé
Coastal barriers such as beach ridges and spits are sedimentary features primarily shaped by wave action. However, in high tidal range environments, these landforms are subject to large water level fluctuations, strong currents, and specific coastline morphologies. The influence of the tidal context on the dynamics and internal architecture of such coastal barriers has not been studied in depth. Here, we present preliminary results from a GPR survey on the terminus of El Páramo spit in Tierra del Fuego (Argentina), supported by geomorphological observations, satellite imagery, and regional metocean data. This ∼ 18 km gravel spit, subject to a 10.5 m tidal range, partially encloses the San Sebastián Bay (Bujalesky et al. 2015). This singular setting results in complex dynamics, with waves coming from the Atlantic Ocean and waves propagating from the bay driven by dominant westerly winds, in addition to tidal circulation into the bay. El Páramo spit terminus is composed of two main sets of ridges, which show contrasting directions of progradation. Set A is the largest and consists of ridges formed on the Atlantic side; set B is intertwined with set A along a central suture and is formed on the bay side. GPR data reveal contrasting internal architecture in the two sets. Set A shows beachface reflections dipping seaward and abundant berm-like reflectors at different altitudes above mean high water and high spring tide level, likely influenced by the hypertidal conditions. Set B contains steeper beachface deposits dipping bayward, which may reflect a stronger longshore drift in contrast to the ocean side (Pancrazzi et al., 2024). Berm-like reflectors are present but at a lower altitude compared with those of set A, and mainly around mean high water level. Further GPR, climatic, and tidal analyses are required to clarify architectural differences and the roles of tidal currents, tidal level fluctuations, wind, and seasonal wave variability. This study is part of a broader project along the macro- to hypertidal coasts of southern Argentinian Patagonia investigating how tidal range affects coarse-grained barrier morphodynamics.
