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Radiometric Ages (radiometric + age)
Selected AbstractsBronze Age paleohydrography of the southern Venetian PlainGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2010Silvia Piovan The Bronze Age paleohydrography of the distal Adige and Po alluvial plain (northeastern Italy) is notable for its relations with protohistoric human activities in this area. This paper regards the stratigraphy and petrography of the Saline,Cona alluvial ridge, upon which the Saline, Sarzano, and Cantarana Bronze Age sites lie, and the petrography of Fratta alluvial ridge, upon which the Frattesina complex (Bronze,Iron Age) lies. Sand analyses indicate the Po River as the source for sediments underlying the alluvial ridge that runs through Fratta Polesine, Rovigo, Sarzano, and Cona. Radiometric ages indicate that the branch of the Saline,Cona ridge was formed by the Po River between the second half of the 3rd millennium B.C. and the end of 2nd millennium B.C. This ridge represents the maximum northward expansion of the Po alluvial system, through the same area of coastal plain crossed by the Adige and Brenta paleochannels. This paleohydrographic setting implies that fluvial connections between the Central Po Plain settlements, the Venetian Plain and Alps were relatively less complex in the Early and Middle Bronze Age than in the Late Bronze Age, when the terminal reach of the Po River was separated by the Adige River by hundreds of km2 of swampy terrain. © 2009 Wiley Periodicals, Inc. [source] Quaternary paleoenvironments and potential for human exploitation of the Jordan plateau desert interiorGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2005Caroline P. Davies The physical, chemical, numerical, and radiometric analyses of a 31-m sediment core from the Qa'el-Jafr basin provide an important record of Quaternary paleoenvironments for the Jordan Plateau and evidence for several significant changes in climate regime. Cluster and PCA analyses of the geochemical data support the designation of major sedimentation regimes identified by stratigraphic and sediment analyses. Multiple cycles of alluvial deposition, lacustrine units, and erosional unconformities characterize the deepest sediments, followed by a period(s) of intense evaporation. Radiocarbon ages of charcoal in the uppermost 7 m place the aeolian/alluvial phase between 16,030 ± 140 yr B.P. and 24,470 ± 240 yr B.P. Deflation processes may explain the lack of a Holocene sequence. Despite lacking radiometric ages for the lower sediments, the thickness and degree of calcium-carbonate cementation suggest considerable age for the basal sediments, which suggests that a very long terrestrial record of Quaternary climate changes has been preserved in the Jafr basin. This new record of paleoenvironments provides important context to the archaeological record of the Jordan Plateau during the Quaternary. Several archaeological surveys demonstrate extensive human exploitation of lakes and springs of the major wadis along the western margin of the Rift Valley. However, little is known of human exploitation of the desert interiors. Qa'el-Jafr sediments demonstrate significant lacustrine and high moisture phases sufficient for human exploitation of the eastern desert during the Pleistocene. © 2005 Wiley Periodicals, Inc. [source] Zircon sensitive high mass-resolution ion microprobe U,Pb and fission-track ages for gabbros and sheeted dykes of the Taitao ophiolite, Southern Chile, and their tectonic implicationsISLAND ARC, Issue 1 2006Ryo Anma Abstract The Late Miocene,Pliocene Taitao ophiolite is composed of a complete sequence of classic oceanic lithosphere and is exposed approximately 50 km southeast of the Chile triple junction, where the Chile Ridge subducts beneath the South American Plate. Gabbros and ultramafic rocks are folded into a complex pattern, but only evidence for block rotation has been reported in the overriding sheeted dyke complex. In the present study, sensitive high mass-resolution ion microprobe U,Pb and fission-track dating methods were applied to zircon crystals separated from gabbros and sheeted dykes. Two sets of radiometric ages of gabbros range between 5.9 ± 0.4 and 5.6 ± 0.1 Ma. These ages coincide within their error ranges and imply rapid intrusion and cooling of gabbros. The U,Pb age of a dacite dyke intruded into the sheeted dyke complex was determined to be 5.2 ± 0.2 Ma. These data indicate that the magmas of the Taitao ophiolite were formed during the 6 Ma Chile Ridge collision event and emplaced in a shorter period than previously thought. A short segment of the Chile Mid-oceanic Ridge must have been emplaced during the 6 Ma event. [source] Hunter-gatherer response to late Holocene climatic variability in northern and central AustraliaJOURNAL OF QUATERNARY SCIENCE, Issue 6 2010Alan N. Williams Abstract Sum probability analysis of 1275 radiometric ages from 608 archaeological sites across northern and central Australia demonstrates a changing archaeological signature that can be closely correlated with climate variability over the last 2 ka. Results reveal a marked increase in archaeological records across northern and central Australia over the last 2 ka, with notable declines in western and northern Australia between ca. AD 700 and 1000 and post-AD 1500 , two periods broadly coeval with the Medieval Climatic Anomaly and the Little Ice Age as they have been documented in the Asia,Pacific region. Latitudinal and longitudinal analysis of the dataset suggests the increase in archaeological footprint was continent wide, while the declines were greatest from 9 to 20° S, 110 to 135° E and 143 to 150° E. The change in the archaeological data suggests that, combined with an increase in population over the late Holocene, a disruption or reorganisation of pre-European resource systems occurred across Australia between ca. AD 700 and 1000 and post-AD 1500. These archaeological responses can be broadly correlated with transitions of the El Niño,Southern Oscillation (ENSO) mean state on a multi-decadal to centennial timescale. The latter involve a shift towards the La Niña-like mean state with wetter conditions in the Australian region between AD 700 and 1150. A transition period in ENSO mean state occurred across Australia during AD 1150,1300, with persistent El Niño-like and drier conditions to ca. AD 1500, and increasing ENSO variability post-AD 1500 to the present. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||