Las sucesiones sedimentarias continentales expuestas en Centinela del Mar, provincia de Buenos Aires, Argentina (Pleistoceno Inferior-Holoceno)

Abstract

RESUMENSon descriptas e interpretadas las características geomorfológicas y sedimentarias de las sucesiones continentales expuestas en los acantilados litorales y sectores aledaños de la localidad Centinela del Mar. Se definen catorce litofacies, cuyas relaciones, geometría y estructuras son representadas mediante perfiles transversales y longitudinales de detalle. En el sector basal y medio del perfil fueron reconocidas facies de distinto grado de transporte y retrabajo ácueo, en tanto, en el sector superior fue identificada una secuencia de facies marinas y perilitorales correspondientes a la transgresión «Belgranense» (=Fm. Pascua), culminando la sucesión facies eólicas relictuales. Las diferentes interpretaciones históricas son ampliamente discutidas, homologándose las unidades referidas previamente con las propuestas en este trabajo. Dichas unidades se correlacionan con aquellas definidas en el esquema aloestratigráfico propuesto para el área comprendida entre Playa San Carlos y Arroyo Chapadmalal. Esto permitió reconocer para el área bajo estudio la presencia de las Aloformaciones Punta San Andrés y Arroyo Lobería (sector basal-medio y cuspidal, respectivamente). Entre estas dos entidades, se intercala una asociación de facies marinas progradantes hacia ambientes perilitorales definidas y nominadas aquí como Aloformación Centinela del Mar. Finalmente, la información aquí reunida (magnetoestratigrafía, dataciones radiométri-cas, correlaciones estratigráficas, etc.) permite indicar, al menos preliminarmente, que la sucesión de Centinela del Mar corresponde al intervalo Ensenadense-Lujanense (Pleistoceno Inferior-Holoceno).Palabras clave: Litofacies, Estratigrafía, Geomorfología, Pleistoceno, Centinela del Mar, Buenos Aires, Argentina. ABSTRACTIn the present paper, the geomorphological and sedimentary characteristics of the continental sequences exposed on the coastal cliffs and surrounding areas of the Centinela del Mar locality are described and interpreted. Fourteen lithofacies are defined, their relation, geometry and structure are represented using transversal and longitudinal detailed profiles. In the basal and medium sector of the profile, facies of different degrees of transport and aqueous rework were recognized. In the superior sector, a succession of marine peri-coastal facies corresponding to the «Belgranense» transgression (=Fm. Pascua) were identified, ending the secuence with relictual eolic facies. The different historical interpretations are discussed, homologating the units referred previously with the ones proposed on this paper. These units are correlated with those defined in the allostratigrapic scheme proposed by other authors for the area covered between Playa San Carlos and Arroyo Chapadmalal. This allowed recognize for the area under study the presence of the Punta San Andrés and Arroyo Lobería Alloformations (basal-medium and superior sector, respectively). Between these two entities, a association of well defined progradant marine facies are found and named on this paper as Centine...

A Pleistocene freshwater ichthyofaunal assemblage from central Argentina: What kind of fishes lived in the Pampean lagoons before the extinction of the megafauna?

“…The sedimentary succession exposed in the area was described and analysed in detail by Cenizo [36], who established a stratigraphic section composed of 14 lithofacies grouped into four facies associations that correspond to three alloformations.…”

“…The fish remains found in Centinela del Mar come from the Lithofacies G, I and K (Figs 1 and 2; hereafter Lf G, Lf I and Lf K [32,33,34,35], which were referred to as units E, G and I, respectively, in [37,38]. These stratigraphically contiguous units are located in the upper-mid section of the local section and correspond to a prograding system of fluvio-lacustrine to estuarine-marine environments [31,36]. The Lf I, located between Lf G and K, yielded the most important ichthyofaunal assemblage in terms of abundance and diversity, and this contribution is mainly focused on interpreting the fish assemblage recovered from this unit.…”

“…Both Lf G and Lf I are grouped into the Facies Association 2 (FA2, [36]). It was tentatively correlated with the unit Upper Allomember of the Punta San Andrés Alloformation [36], located about 50 km NE of the Centinela del Mar [39,40].…”

“…Both Lf G and Lf I are grouped into the Facies Association 2 (FA2, [36]). It was tentatively correlated with the unit Upper Allomember of the Punta San Andrés Alloformation [36], located about 50 km NE of the Centinela del Mar [39,40]. These units are well exposed and extend all over the cliff surface of Centinela del Mar to the NE and SW [36,40].…”

“…The Lf G is represented by 2 m of light brown sandy loessoid silts, generally with cross-bedding stratification. This body has mantle-like sedimentary geometry, showing a transitional basal contact with the underlying Lf F. The latter is represented by flow deposits with abundant carbonate clasts, extending throughout the regional outcrop [36]. The Lf G has meteorite impact-derived glasses (locally known as "escorias"), radiometrically dated (40Ar/39Ar) at 230 ±30 ka [41].…”