Abstract
The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance.
Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms.
The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls.
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References
Ameghino, F.: Las formaciones sedimentarias de la región litoral de Mar del Plata y Chapalmalán. An. Mus. Nac. Buenos Aires 3, 343–428 (1908)
Andreis, R.: Petrologia y paleocorrientes de la Formacion Rio Negro (tramo Gral Coneca-Boca del rio Negro) 1965. Rev. Museo de la Plata. Nueva Serie Tomo V Geol., 36, La Plata, 245–310 (1965)
Blasi, A. M.: Sedimentologia del rio Colorado. 1986 PhD Thesis FONM University of La Plata (unpubl.) 1986. 238 p.
Blasi, A. M.; Manassero, M.: The Colorado river of Argentine: source, climate and transport as controlling factors in plate tectonic sand compositions. (1990) Journal of South American Earth Science 3 (1): 65–70
Fidalgo, F.; Tonni, E. P.: Sedimentos eólicos del Pleistoceno tardio y reciente en el área interserrana bonaerense. VIII Congreso Geológico Argentino, ACTAS III: 33–39 (1981)
Figini, A. J.; Carbonari, J. E.; Gómez, G. J.; Tonni, E. P.; Fidalgo, F.: Datación de restos óseos de la Formación La Postrera en el partido de Loberia, provincia de Buenos Aires, Argentina X Congreso Geológico Argentino, Tucumán, ACTAS: 185–188 (1987)
Fisher, R. V.; Proposed classification of volcaniclastic sediments and rocks. Geol. Soc. Bull. 72, 1407–1414 (1961)
Flegenheimer, N.; Zárate, M: Sitios arquelℷicos y geocronologia de los ultimos 10000 años en las sierras de Tandil. (1989) Simposio Internacional sobre el Holoceno de América del Sur, noviembre, Paraná, Argentina, ACTAS (1986): 171–174
Folk, R.: The distinction between grain size and mineral composition in sedimentary rock nomenclature. Jour. Sed. Petrol. 62, 344–359 (1954)
Folk, R.; Ward, W. C.: The Brazos river bar: a study on the significance of grain-size parameters. Jour. Sed. Petrol. 27, 1, 3–27 (1957)
Frenguelli, J.: Observaciones geológicas en la región constanera sur de la provincia de Buenos Aires. Univ. Nac. Lit. Fac. Cienc. Educ., Anales Paraná, II 1–145 (1928)
Frenguelli, J.; Loess y limos pampeanos. 1955. Serie Técnica y Didáctica. n° 7 Facultad de Cien. Nat. y Museo. UNLP. Min. Educ. de la Nación, pp. 88 (1955)
Frenguelli, J.; Neozoico: En Geografia de la República Argentina. Soc. Arg. de Est. Geograf., GAEA, II, 1–212 (1957)
Heusser, J. C.; Claraz, G.: Essai pour servir a une description physique et geognostique de la province argentine de Buenos Ayres. Mém. Soc. Helvetique Sci. Natur, 21, 139 (1866)
Kraglievich, J. L.: El perfil geológico de Chapadmalal y Miramar, provincia de Buenos Aires. Rev. del Museo de Mar del Plata 1, 8–37 (1952)
Pye, K.: Aeolian dust and dust deposits. Academic Press, pp. 334 1987
Rabassa, J.; Brandani, A.; Politis, G.; Salemme, M.: La “pequeña Edad de Hielo” (Siglos XVI a XIX) y su posible influencia en la aridización de áreas marginales de la Pampa húmeda (provincia de Buenos Aires). Iras. Jorn. Geol. Bonae., Tandil (11–15 noviembre 1985) Resúmenes: 15–16 CIC, La Plata (1985)
Tapia, A.: Las cavernas de Ojo de Agua y Las Hachas. Historia geológica de la región de la Brava en relación con la existencia del hombre prehistórico. Bol. Direcc. Gen. Industria Minera, 43, 1–126 (1937)
Teruggi, M. E.: The nature and origin of Argentine loess. Jour. Sed. Petrol. 27, 322–332 (1957)
Tricart, J. L. F.: Geomorfologiá de la Pampa Deprimida. INTA Colección Cient. Buenos Aires, 12, pp 202 (1973)
Visher, G. S.: Grain size distributions and depositional processes. Jour. Sed. Petrol. 39, 1074–1106 (1960)
Zárate, M.; Fasano, J. L.: The Pilio-Pleistocene record of the Central Eastern Pampas, Buenos Aires Province, Argentina: The Chapadmalal case study. Paleogeography, Paleoclimatology, Palaeoecology 72, 27–52 (1989)
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Zarate, M., Blasi, A. Late pleistocene and holocene loess deposits of the Southeastern Buenos Aires province, Argentina. GeoJournal 24, 211–220 (1991). https://doi.org/10.1007/BF00186018
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DOI: https://doi.org/10.1007/BF00186018