Architecture of Shelly beach ridges in a sheltered beach environment in Punta Perdices beach, San Antonio bay, Argentina

Abstract

On the northern coast of the San Matías Gulf, Argentina, San Antonio Bay is developed, with an approximate area of 160 km2. The region has a diversity of depositional systems, both inside and outside the bay, which are morphologically characterized by the deposits of plains and tidal channels, beach ridges, beaches and dunes. In this environment relatively protected by the Villarino Peninsula, against the high energy of waves coming from the gulf, the circulation of water is governed by a regime of semidiurnal macro-tides with syzygy amplitudes of up to 9 m, which enter through the single channel, communicating the bay to the ocean. The edges of the Villarino Peninsula have a large number of beach ridges, in the form of extensive modern bioclastic deposits, where bivalves with whole, fragmented, and gastropod valves predominate. The objective of this work is the development of models of depositional architecture of the coquinas of the Villarino Peninsula, through terrain mapping (DGPS) and acquisition of lines by ground penetration radar (GPR), in addition to understanding the Holocene-modern sedimentary dynamics of this region. Surveys with GPR were carried out in the sector of Punta Perdices Beach in the Peninsula Villarino sectors of bioclastic deposits, in a total of 23 GP R lines, where there are several sets of beach ridges (Holocene) with an average width of 100 m, which extend for more than 1 km, located in the sheltered area of the bay. The processed and interpreted GPR data were used to investigate the lateral and vertical relationships of the facies, the depositional geometries and geophysical signatures, developed by progradation mechanisms induced by the hydrodynamics of waves and tides. The genesis of these a lot of bioclasts deposits are discussed, mainly due to the macro tide regime of the region and the littoral drift of the semicircular bay, where the geomorphological features of an actual coastal terrace were described. Depositional models of coquinas in Pleistocene, Holocene, and actual beach environments are scarce in the literature. The obtained results can be analyzed and compared to analogues of hydrocarbon deposits.