Environmental history since 11,000 ¹⁴c yr b.p. of the northeastern Pampas, Argentina, from alluvial sequences of the Luján River

Abstract

Sedimentological, malacological, and pollen analyses from 14C-dated alluvial sections from the Luján River provide a detailed record of environmental changes during the Holocene in the northeastern Pampas of Argentina. From 11,200 to 9000 14C yr B.P., both sedimentary and biological components suggest that the depositional environment was eutrophic, alkaline, and freshwater to brackish shallow water bodies without significant water circulation. During this time, bioclastic sedimentation was dominant and the shallow water bodies reached maximum development as the climate became more humid, suggesting an increase in precipitation. Short-term fluctuations in climate during the last stage of this interval may have been sufficient to initiate changes in the water bodies, as reduction of the volume alternated with periods of flooding. The beginning of the evolution of shallow swamps in the wide floodplain or huge wetlands was contemporaneous with a sea level lower than the present one. From 9000 and 7000 14C yr B.P., mesotrophic, alkaline, brackish, probably anoxic swamps existed. Between 7000 and 3000 14C yr B.P., anoxic calcareous swamps were formed, with subaerial exposure and development of the Puesto Berrondo Soil (3500–2900 14C yr B.P.). A trend to a reduction of water bodies is recorded from 9000 to ca. 3000 14C yr B.P., with a significant reduction after ca. 7000 14C yr B.P. A shift to subhumid–dry climate after 7000 14C yr B.P. appears to be the main cause. During this time, an additional external forcing toward higher groundwater levels was caused by Holocene marine transgression causing changes in the water bodies levels. The climate became drier during the late Holocene (ca. 3000 yr B.P.), when clastic sedimentation increased, under subhumid–dry conditions. Flood events increased in frequency during this time. From ca. A.D. 1790 to present, the pollen record reflects widespread disturbance of the vegetation during the European settlement.

Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America

“…In the Holocene, C4 vegetation increased, as did seasonal variation in proportions of C3 versus C4 grasses (43)(44)(45). Overall, the increase in C4 grasses (46) and other vegetational changes (Supporting Information) are consistent with late-Quaternary climatic warming driving a transition to warmer, more humid conditions, as also indicated by sedimentology (47), malacological remains (48), and paleobotanical data (43)(44)(45)49).…”

“…S5), which actually retracted in range across the Pleistocene-Holocene transition (43,48). However, many undated Notiomastodon specimens (52) come from northern Uruguay and southern Brazil (Fig.…”

Geoarchaeological and Paleoenvironmental context of the human settlement in the Eastern Tandilia Range, Argentina

“…The human populations that would have lived in this area c. 11,000-10,000 BP would therefore done so under colder, dry sub-humid conditions (Quattrocchio et al, 2008;Tonni and Cione, 1994;Prieto, 1996;Tonni et al, 1999Tonni et al, , 2003. Between c. 10,500 and 9000 BP a change in these dry conditions towards higher rainfall levels and temperatures has been indicated by numerous proxy records from the Pampas region (Tonni and Fidalgo, 1978;Prado et al, 1987;Alberdi et al, 1989;Tonni y Cione, 1994;Prieto, 1996;Zárate et al, 1995Zárate et al, , 2000Zarate, 1997;Borrero et al, 1998;Bonadonna et al, 1999;Tonni et al, 1999;Martinez, 1999Martinez, , 2001Martinez, , 2007Prieto et al, 2004;Grill et al, 2007;Gutierrez y Martínez, 2008;Gutierrez et al, 2010).…”

Stable isotope composition of freshwater mollusk shells from Central-Western Argentina

“…Prieto et al, 2004;De Francesco et al, 2007;De Francesco & Hassan, 2009). Many of these deposits occur at different hydrological settings along gradients of aridity and altitude, and possess abundant mollusk shells whose stable isotope compositions remain nearly unknown.…”