CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Sedimentologycal development of cheniers. An Holocene example from the Bahía Samborombón, Argentina.
Autor/es:
SEBASTIÁN RICHIANO, AUGUSTO N. VARELA, LEANDRO D'ELIA, ANDRÉS BILMES Y MARINA AGUIRRE
Lugar:
Mendoza
Reunión:
Congreso; 18Th International Sedimentological Congress; 2010
Institución organizadora:
International Association of Sedimentologists
Resumen:
In the Argentinean littoral zone several transgressive - regressive events occurred during the Quaternary. Excellent examples of these events are very well exposed along the Bahía Samborombón locality (S 35º 58’ 24’’; W 57º 27’ 00’) in the Buenos Aires province coastal area. Following the stratigraphic scheme of Fidalgo (1979) modified by Fucks et al. (in press.) the studied deposits are included in the Las Escobas Formation. This unit is divided into 3 members, Destacamento Río Salado Mb. (tidal flat, 5.8-7 ka B.P.), Cerro de la Gloria Mb. (beach ridge, ca. 3-8 ka B.P.) and Canal 18 Mb. (coastal lagoon, 6-7 ka B.P). Stratigraphic sections were measured and described in detail for each unit The Destacamento Río Salado Mb is about 0.5 m thick and is composed of silty to very fine-grained sands with wavy stratification. The Cerro de la Gloria Mb in the study area is a bioclastic ridge 200 m wide and 5 m thick oriented subparallel to the modern coastline. The main lithologic components are molluscan shells (+ 70 %) with low proportion of coarse- to medium-grained sand. In cross-section perpendicular to the coastline, the ridge shows lenticular, trough and sigmoidal geometry, eventually there are planar beds. Cross bedding, hummocky cross stratification and parallel stratification are the most common sedimentary structures. The Canal 18 Mb is 3 m thick and is composed of fine-grained sands and silts, usually containing both articulated bivalve shells in life position and tabular levels of disarticulated shells with no preferential orientation. The sea-level rise generated a transgressive surface that marks the beginning of the Destacamento Río Salado Mb in the study area. During this stage the sediment flux from the continent was reduced. This event promoted that in several storm episodes mollusc valves were accumulated generating the chenier, while the finer-grained sediments were washed by tides. When the chenier was completely formed a lagoonal environment was developed toward the continent (canal 18 Mb). Our results show that during the Holocene, Bahía Samborombón was under a period of sediment starvation which generated the landward progradation of a bioclastic bar above the tidal flat deposits. This study provides an opportunity to show the interplay between sea level, sediment input and climate in littoral environments during the mid-Holocene climatic optimum.