|
|
Previous analysis of 87Sr/86Sr ratios shows that 10th through 12th century Chaco Canyon was provisioned with plant materials that came from more than 75 km away. This includes (1) corn (Zea mays) grown on the eastern flanks of the Chuska Mountains and floodplain of the San Juan River to the west and north, and (2) spruce (Picea sp.) and fir (Abies sp.) beams from the crest of the Chuska and San Mateo Mountains to the west and south. Here, we extend 87Sr/86Sr analysis to ponderosa pine (Pinus ponderosa) prevalent in the architectural timber at three of the Chacoan great houses (Pueblo Bonito, Chetro Ketl, Pueblo del Arroyo). Like the architectural spruce and fir, much of the ponderosa matches the 87Sr/86Sr ratios...
|
Using isotopic ratios of Sr, C and O, we trace calcium carbonate through surface systems across a wide region of semi-arid terrain in Arizona, southwestern USA, in order to evaluate the contribution of cations from silicate weathering to soil carbonate. We present 87Sr/86Sr ratios of soil carbonate, parent rock, dry river course silts, floodplain, playa, dust and rain samples, as well as ?18O and ?13C values of selected samples. Results show that both parent rock and dust are important sources of cations for soil carbonate in this inland setting where bedrock is dominated by silicate lithologies. Dust in southeast Arizona has higher 87Sr/86Sr ratios (0.7100?0.7123) than Phanerozoic sea water (0.7070?0.7096). These...
|
Aim To document the impact of late Quaternary pluvial events on plant movements between the coast and the Andes across the Atacama Desert, northern Chile.Location Sites are located along the lower and upper fringes of absolute desert (1100–2800 m a.s.l.), between the western slope of the Andes and the Coastal Ranges of northern Chile (24–26° S).Methods We collected and individually radiocarbon dated 21 rodent middens. Plant macrofossils (fruits, seeds, flowers and leaves) were identified and pollen content analysed. Midden assemblages afford brief snapshots of local plant communities that existed within the rodents’ limited foraging range during the several years to decades that it took the midden to accumulate....
|
Over the last eight years, we have developed several paleoenvironmental records from a broad geographic region spanning the Altiplano in Bolivia (18uS–22uS) and continuing south along the western Andean flank to ca. 26uS. These records include: cosmogenic nuclide concentrations in surface deposits, dated nitrate paleosoils, lake levels, groundwater levels from wetland deposits, and plant macrofossils from urine-encrusted rodent middens. Arid environments are often uniquely sensitive to climate perturbations, and there is evidence of significant changes in precipitation on the western flank of the central Andes and the adjacent Altiplano. In contrast, the Atacama Desert of northern Chile is hyperarid over many millions...
|
We evaluate the impact of exceptionally sparse plant cover (0–20%) and rainfall (2–114 mm/yr) on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet, the Atacama Desert in northern Chile. δ13C and δ18O values of carbonates from the Atacama are the highest of any desert in the world. δ13C (VPDB) values from soil carbonate range from −8.2‰ at the wettest sites to +7.9‰ at the driest. We measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of [Cerling (1984) Earth Planet. Sci. Lett. 71, 229–240], in which we assumed an exponential...
|
View more...
|
