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キーワード:
leaf wax
n-alkane
deuterium/hydrogen isotopic ratio
inverse altitude
effect
paleoelevation
paleoaltimetry
isotope-based paleoaltimetry
tibetan plateau
d values
paleoelevation
reconstruction
orographic controls
terrestrial plants
organic-matter
aquatic plants
d/h ratios
hydrogen
要旨:
Estimating past elevation not only provides evidence for vertical movements of the Earth's lithosphere, but also increases our understanding of interactions between tectonics, relief and climate in geological history. Development of biomarker hydrogen isotope-based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance. Here we present leaf wax-derived n-alkane delta D (delta D-wax) values along three soil attitudinal transects, at different latitudes, in the Wuyi, Shennongjia and Tianshan Mountains in China, to investigate delta D-wax gradients and the apparent fractionation between leaf wax and precipitation (epsilon(wax-p)). We find that soil delta D-wax track attitudinal variations of precipitation delta D along the three transects that span variable environment conditions and vertical vegetation spectra. An empirical delta D-wax-altitude relation is therefore established in which the average delta D-wax lapse rate of -2.27 +/- 0.38 parts per thousand/100 m is suitable for predicting relative paleoelevation change (relative uplift). The application of this empirical gradient is restricted to phases in the mountain uplift stage when the atmospheric circulation had not distinctly changed and to when the climate was not arid. An empirical delta D-wax-latitude-altitude formula is also calculated: delta D-wax = -0.483LAT -0.0227ALT -261.5, which gives the preliminary spatial distribution pattern of delta D-wax a in modern China. Mean value of epsilon(wax-p) in the extreme humid Wuyi Mountains is quite negative (-154 parts per thousand), compared to the humid Shennongjia (-129%.) and the arid (but with abundant summer precipitation) Tianshan Mountains (-130 parts per thousand), which suggests aridity or water availability in the growing season is the primary factor controlling soil/sediment epsilon(wax-p). Along the Tianshan transects, values of epsilon(wax-p) are speculated to be constant with altitude; while along the Wuyi and Shennongjia transects, epsilon(wax-p) are also constant at the low-mid altitudes, but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation delta D or the vegetation shift to grass/conifer. Additionally, a reversal of altitude effect in the vertical variation of delta D-wax was found in the alpine zone of the Tianshan Mountains, which might be caused by atmospheric circulation change with altitude. This implies that the paleo-circulation pattern and its changes should also be evaluated when stable isotope-based paleoaltimetry is applied. (C) 2010 Elsevier B.V. All rights reserved.
