科研之友
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摘要
This study presents high-resolution oxygen and carbon isotopic records of paleosol carbonates from fluvial sediments and lacustrine carbonates, sampled from the Jingou He and Kuitun He stratigraphic sections, located in the northern Tianshan piedmont. These sections expose remarkable outcrops of Junggar foreland basin sediments that have been previously dated by high-resolution magnetostratigraphy to between similar to 23.6 and similar to 1 Ma, and similar to 10.5 and similar to 3.1 Ma. A total of 216 samples of fluvio-lacustrine sediments were collected from which isotopic analyses yield delta O-18 (SMOW) values that range from 13.7 parts per thousand to 29.9 parts per thousand in the Jingou He section, and 16.3 parts per thousand to 21.0 parts per thousand in the Kuitun He section. delta C-13 (PDB) values range from -12.9 parts per thousand to 3.0 parts per thousand in the Jingou He section and from -7.8 parts per thousand to -4.0 parts per thousand in the Kuitun He section. delta O-18 values decrease between similar to 25 and 23 Ma, and then remain relatively steady, with the exception of one period that contains samples with higher oxygen isotope values at similar to 16 Ma. During the periods when there are samples that overlap in time from the Kuitun He and Jingou He sections, we observe a difference of similar to 1.7% between values from the two locales. The delta C-13 values also decrease between similar to 25 and 23 Ma, and then remain relatively steady until similar to 10 Ma with, again, one short period of higher values at similar to 16 Ma. Then, between similar to 10 and 3.1 Ma, carbon isotope values progressively increase. We interpret that delta O-18 and delta C-13 isotopic values during lacustrine periods (similar to 25-23 Ma and similar to 16 Ma) as largely controlled by evaporation and opening/closing of the lake to external inputs. We interpret the delta O-18 values of paleosol carbonate in the Junggar Basin to be influenced by the hypsometry of the high Tianshan range while the delta C-18 values may record the uplift history of the depositional area in the foreland basin itself as well as the isotopic composition of plants. Consequently, we conclude that the Jingou He and Kuitun He drainage basins in the Central Tianshan have remained at relatively unchanged elevations for the past similar to 20 Ma. We also suggest that the elevation of the southern part of the foreland basin increased between similar to 10 and similar to 3.1 Ma, probably as a result of tectonic deformation in the piedmont and sedimentary filling of the sedimentary basin. The carbon isotope record remains relatively stable through time, and isotopic values suggest that there was little or no expansion of C4 plants in this region in the late Miocene.
- 出版日期2012-8
- 单位南阳理工学院
