Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Linking the karst record to atmospheric, precipitation, and vegetation dynamics in PortugalPublication . Thatcher, Diana L.; Wanamaker, Alan D.; Denniston, Rhawn F.; Ummenhofer, Caroline C.; Regala, Frederico T.; Jorge, Nuno; Haws, Jonathan; Chormann, Alaina; Gillikin, David P.Cave deposits can be valuable sources of paleoclimate data, especially when atmospheric circulation patterns, precipitation variability, vegetation changes, and the chemical evolution of waters moving through the karst environment can be mechanistically linked to speleothem proxies. In particular, an evaluation of the factors that control the isotopic composition of precipitation and the evolution of rainwater during migration from the land surface to the cave are needed to robustly develop speleothems as hydroclimate-sensitive proxies. One area in which precipitation and atmospheric variability are closely linked is western Iberia, where rainfall is strongly influenced by the Azores High, part of the North Atlantic Oscillation (NAO) dipole. Therefore, in order to better characterize the factors that influence the isotopic composition of precipitation in Portugal and to evaluate the potential of using stalagmites from this region as hydroclimate (and NAO-sensitive) proxies, we investigated Global Network of Isotopes in Precipitation (GNIP) data from ten mainland Portugal sites spanning multiple decades. In addition, we use more than one hydrologic year of precipitation amount and isotope data from Buraca Gloriosa (BG), a cave in western Portugal, the site of on-going speleothem analyses, as well as six years of environmental monitoring from BG. We present an integrated analysis of rainfall and vegetation through the normalized difference vegetation index (NDVI) following extremely wet and dry winters. Summer vegetation density, related to the amount of precipitation in the preceding winter wet season, as well as prior calcite precipitation (PCP), would largely control the stable carbon isotopic signature (delta C-13) in stalagmites at BG. Cool season recharge is likely the dominant factor for the oxygen isotopic composition (delta O-18) of water percolating through the cave system, while amount effects exert the primary control on precipitation delta O-18 values. Based on HYSPLIT modeling, moisture sources overwhelmingly originate from the Atlantic Ocean as opposed to the Mediterranean or elsewhere
- The Gravettian-Solutrean transition in westernmost Iberia: new data from the sites of Vale Boi and Lapa do PicareiroPublication . Belmiro, Joana; Bicho, Nuno; Haws, Jonathan; Cascalheira, JoãoThis study presents the analysis of the lithic assemblages from Layers 5 and 4E (Terrace) of the site of Vale Boi (southern Portugal) and Levels U and T from Lapa do Picareiro (central Portugal). We aimed to understand the technological patterns and raw material exploitation during the Gravettian-Solutrean transition in westernmost Iberia and test the traditional models with assemblages from recently excavated sites, while expanding the geographic range. Results show the existence of two discrete phases in each site. The first, with high frequency of quartz use for bladelet production, seems to reflect the presence of a Terminal Gravettian horizon, as defined by Almeida (2000). The second, with some significant differences between sites, attests the presence of Vale Comprido technology and lower quartz frequencies at Vale Boi, representing a Proto-Solutrean occupation; and the presence of a blade component in Lapa do Picareiro that, together with the respective absolute chronology, may be attributed to a Proto-Solutrean or an Early Solutrean horizon. In general terms, this study allowed to confirm that the Terminal Gravettian and the Proto-Solutrean are discrete phases across the transition, in agreement with the Three-Phase model presented by Zilh˜ao (1997). It further consolidates the expansion of similar techno-cultural patterns to southern Portugal, which may be explained by the significant changes in the dynamic of social networks (Cascalheira and Bicho, 2013).
- The early Aurignacian dispersal of modern humans into westernmost EurasiaPublication . Haws, Jonathan; Benedetti, Lucilla; Talamo, Sahra; Bicho, Nuno Gonçalo Viana Pereira Ferreira; Cascalheira, João; Ellis, M. Grace; Carvalho, Milena M.; Friedl, Lukas; Pereira, Telmo; Zinsious, Brandon K.Documenting the first appearance of modern humans in a given region is key to understanding the dispersal process and the replacement or assimilation of indigenous human populations such as the Neanderthals. The Iberian Peninsula was the last refuge of Neanderthal populations as modern humans advanced across Eurasia. Here we present evidence of an early Aurignacian occupation at Lapa do Picareiro in central Portugal. Diagnostic artifacts were found in a sealed stratigraphic layer dated 41.1 to 38.1 ka cal BP, documenting a modern human presence on the western margin of Iberia ∼5,000 years earlier than previously known. The data indicate a rapid modern human dispersal across southern Europe, reaching the westernmost edge where Neanderthals were thought to persist. The results support the notion of a mosaic process of modern human dispersal and replacement of indigenous Neanderthal populations.
- Human adaptive responses to climate and environmental change during the Gravettian of Lapa do Picareiro (Portugal)Publication . Haws, Jonathan; Benedetti, Michael; Carvalho, Milena; Ellis, Grace; Pereira, Telmo; Cascalheira, João; Bicho, Nuno; Friedl, LukasOn the Iberian Peninsula, abrupt climate shifts during the Late Pleistocene impacted human and natural systems. Our knowledge of human adaptive responses to these climatic perturbations has improved in recent years with the development of new radiocarbon techniques that have increased the temporal resolution of cultural chronologies. At the same time, new high-resolution paleoclimatic records from Greenland ice cores, deep-sea sediment cores, speleothems, and microfaunal assemblages have permitted detailed paleoenvironmental reconstructions. Combined with the archaeological record of culture change, these data sets allow for a better understanding of the nature of human socio-ecological systems during the Late Pleistocene. Here we present new data on the Gravettian occupations at Lapa do Picareiro, a cave site in Portugal with a long continuous stratigraphic sequence spanning MIS 3 and 2. The ongoing excavation of Lapa do Picareiro has revealed at least three Gravettian levels with very different patterns of raw material use and technological reduction. The Early Gravettian levels contain a quartzite flake assemblage with several refitting clusters and a small chert assemblage with nosed endscrapers and bladelet technology. The Late or Terminal Gravettian level contains carinated endscraper/core-bladelet technology, mainly quartz, with chert blade production, and a few bone tools. The faunal assemblages also have a different character. Both contain a similar range of medium and large ungulates but the earlier Gravettian has a much richer and more diverse assemblage of small animals. These combined archaeological data sets provide a new perspective on Gravettian human adaptations in response to climate shifts, especially Heinrich Event 3 and Greenland Interstadials 4 and 3.
- Late Pleistocene Landscape and Settlement Dynamics of Portuguese EstremaduraPublication . Haws, Jonathan; Benedetti, Michael; Funk, Caroline L.; Bicho, Nuno; Pereira, Telmo; Marreiros, Joao; Daniels, J. Michael; Forman, Steven L.; Minckley, Thomas A.; Denniston, Rhawn F.Here we report the results of an integrated geoarchaeological survey to study Palaeolithic human settlement dynamics in the coastal region of Portuguese Estremadura. The region has been an important focus of human occupation across multiple glacial-interglacial cycles, including periods of well-documented abrupt climate instability during MIS 3 and 2. The pedestrian survey covered a roughly 10 km wide strip of land between Sao Pedro de Muel and Peniche. The survey intensively targeted three landscape settings with Pleistocene-age surfaces and sediments: the coastal bluffs with exposed aeolian, fluvial, and colluvial sands; the Caldas da Rainha diapiric valley and associated fluvial/estuarine fills; and, Cretaceous chert-rich limestone uplands that bound the inland margin of the study area. We discovered dozens of new Palaeolithic sites, analyzed numerous Pleistocene sedimentary sections, and applied widespread OSL-dating to establish age control that allowed us to build a regional geomorphic history to contextualize Late Pleistocene human settlement across the region.