An official website of the United States government
South America, from southernmost Bolivia through central Argentina, contains a useful Late Miocene to Holocene record of eolian sedimentation that can be used to advance our understanding of atmospheric circulation and dust production pathways over that interval. Our research indicates that loess provinces in the eastern Andes, Chaco Plains, and Pampean Plains had quasi-independent dust production pathways. A summary of our findings is as follows. 1) Detrital zircon crystals in the high-elevation upper Pleistocene loess deposits in the eastern Andes area of Tafí del Valle were primarily derived from the Puna Plateau to the west. At a latitude of ~27° S, this necessitates a several-degree equatorward shift in the upper- and lower-level westerlies during intervals with high dust accumulation in Tafí del Valle. 2) Upper Pleistocene to Holocene eolian sand deposits of the Pampean Sand Sea and loessic strata in the central and eastern Pampas contain detrital zircon U-Pb age spectra indicating derivation from the Río Desaguadero, Río Colorado, and Río Negro which drain the central Andes. Although the present-day Puna-Altiplano Plateau is hyperarid, the presence of major Argentine river systems in the dust production pathways of the Pampas is important for identifying the relative importance of precipitation and river courses on dust production, which parallels the relationship between the Yellow River and Chinese Loess Plateau in East Asia. 3) Upper Miocene strata of the Cerro Azul Formation, deposited between ~8.9 and ~5.5 Ma, include loess and aggradational paleosols. These eolian strata yield detrital zircon U-Pb age spectra that are consistent with the present-day Río Colorado and Río Negro, and similar to the Upper Pleistocene to Holocene deposits of the Pampas. This suggests a Late Miocene establishment of the Pampean eolian system. Interestingly, the Pampean eolian system and Chinese Loess Plateau both cover the same latitudes (~33°-39°) but in different hemispheres, and both were established at roughly the same time during the Late Miocene. These observations point to bihemispheric intensification of Hadley circulation in forcing the establishment of these two large eolian provinces.
more »
« less
This content will become publicly available on December 1, 2025
Early human foraging paleoecology in the highlands of Potosí, Bolivia
For centuries the Cerro Rico of Potosí in the South American Andes has been known as the richest silver mine in the world but also as a notoriously challenging place for human habitation due to its extreme elevation. Nevertheless, little is known about the temporal depth and socioecological dynamics associated with the initial occupation of this region. In this paper, we present an archaeological and paleoecological assessment of the earliest human peopling of Potosí and the eastern south-central Andes. Systematic surveys in two neighboring regions complemented by test excavations, artifact analysis, and radiocarbon dating revealed evidence of foraging occupations dating to the Early Holocene as well as by agropastoralist communities during the Late Holocene. Local paleoenvironmental records suggest that periods of increased humidity might have fostered ecological productivity that incentivized settlement in this high elevation setting. The nature of the occupations and associated technological organization is consistent with findings from sites elsewhere in the arid Andes.
more »
« less
- PAR ID:
- 10617538
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Quaternary Environments and Humans
- Volume:
- 2
- Issue:
- 6
- ISSN:
- 2950-2365
- Page Range / eLocation ID:
- 100046
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Abstract Waterfall Bluff is a rock shelter in eastern Pondoland, South Africa, adjacent to a narrow continental shelf that limited coastline movements across glacial/interglacial cycles. The archaeological deposits are characterized by well-preserved stratigraphy, faunal, and botanical remains alongside abundant stone artifacts and other materials. A comprehensive dating protocol consisting of 5 optically stimulated luminescence ages and 51 accelerator mass spectrometry 14 C ages shows that the record of hunter-gatherer occupations at Waterfall Bluff persisted from the late Pleistocene to the Holocene, spanning the last glacial maximum and the transition from the Pleistocene to the Holocene. Here, we provide detailed descriptions about the sedimentary sequence, chronology, and characteristics of the archaeological deposits at Waterfall Bluff. Remains of marine mollusks and marine fish also show, for the first time, that coastal foraging was a component of some hunter-gatherer groups’ subsistence practices during glacial phases in the late Pleistocene. The presence of marine fish and shellfish further demonstrates that hunter-gatherers selectively targeted coastal resources from intertidal and estuarine habitats. Our results therefore underscore the idea that Pondoland's coastline remained a stable and predictable point on the landscape over the last glacial/interglacial transition being well positioned for hunter-gatherers to access resources from the nearby coastline, narrow continental shelf, and inland areas.more » « less
-
Quaternary dust production in southern South America is of particular interest because of its impacts on the global radiative forcing budget and on ocean chemistry. Characterizing dust production and delivery pathways is fundamental for understanding how dust-climate feedbacks in this region operate. A Holocene centered view of South American dust production emphases hyper arid basins on the Puna-Altiplano Plateau and the glaciated terrains of Patagonia as primary dust sources. Applying this Holocene-centric view to Pleistocene glacial-stadial period dust production is problematic as it largely ignores how glacial-inter-glacial variability impacts surficial processes and regional humidity, and thus dust production and transport. We sampled fluvial, loess and eolian dune deposits from central Argentina for U-Pb detrital zircon analysis in order better understand Pleistocene-Holocene dust production pathways and assess the relative importance of Andean rivers and dunes fields of the Pampa Plains as dust sources. Our data indicate that rivers draining the Andes south of the Pampa Plains and large vegetation-stabilized dune fields could have played a fundamental role in late Pleistocene glacial and stadial period dust production. If valid, dust production in this manner is at odds with the Holocene-centric view of South American dust production.more » « less
-
The biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Ni~no events. Over the coming decades these events are projected to double under the 1.5 C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Ni~no-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Ni~no reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization e such as Alnus acuminata e covary with El Ni~no-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Ni~no, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.more » « less
-
Global warming during the Last Glacial Termination was interrupted by millennial-scale cool intervals such as the Younger Dryas and the Antarctic Cold Reversal (ACR). Although these events are well characterized at high latitudes, their impacts at low latitudes are less well known. We present high-resolution temperature and hydroclimate records from the tropical Andes spanning the past ~16,800 y using organic geochemical proxies applied to a sediment core from Laguna Llaviucu, Ecuador. Our hydroclimate record aligns with records from the western Amazon and eastern and central Andes and indicates a dominant long-term influence of changing austral summer insolation on the intensity of the South American Summer Monsoon. Our temperature record indicates a ~4 °C warming during the glacial termination, stable temperatures in the early to mid-Holocene, and slight, gradual warming since ~6,000 y ago. Importantly, we observe a ~1.5 °C cold reversal coincident with the ACR. These data document a temperature change pattern during the deglaciation in the tropical Andes that resembles temperatures at high southern latitudes, which are thought to be controlled by radiative forcing from atmospheric greenhouse gases and changes in ocean heat transport by the Atlantic meridional overturning circulation.more » « less
